Observation and measurement of forward proton scattering in association with lepton pairs produced via the photon fusion mechanism at ATLAS

Observation and Measurement of Forward Proton Scattering in Association with Lepton Pairs Produced via the Photon Fusion Mechanism at ATLAS G. Aad et al.* (ATLAS Collaboration) (Received 2 October 2020; revised 30 October 2020; accepted 23 November 2020; published 23 December 2020) The observation of forward proton scattering in association with lepton pairs (eþe−þpor μþμ−þp) produced via photon fusion is presented. The scattered proton is detected by the ATLAS Forward Proton spectrometer, while the leptons are reconstructed by the central ATLAS detector. Proton-proton collision data recorded in 2017 at a center-of-mass energy of ffiffiffi s p¼13 TeV are analyzed, corresponding to an integrated luminosity of 14.6fb−1. A total of 57 (123) candidates in the ee þp(μμ þp) final state are selected, allowing the background-only hypothesis to be rejected with a significance exceeding 5 standard deviations in each channel. Proton-tagging techniques are introduced for cross-section measurements in the fiducial detector acceptance, corresponding to σeeþp¼11.02.6ðstatÞ1.2ðsystÞ0.3ðlumiÞand σμμþp¼7.21.6ðstatÞ0.9ðsystÞ0.2ðlumiÞfb in the dielectron and dimuon channel, respectively. DOI: 10.1103/PhysRevLett.125.261801 Electromagnetic fields sourced by protons at the Large Hadron Collider (LHC) are sufficiently intense to exceed the Schwinger limit of 1018 Vm −1[1–3] and produce lepton pairs via photon fusion, γγ →lþl−, where ldenotes electrons or muons [4–7]. This process occurs in a wide range of astrophysical phenomena, such as cosmic gamma rays [8,9] and neutron stars [10,11]. Measurements of γγ →lþl−at the LHC provide a unique laboratory probe of these natural phenomena and are fundamental tests of quantum electrodynamics [12–17]. These complement lower-energy probes using heavy-ion collisions [18–26] and high-intensity laser beams [27–30]. A hallmark prediction of photon fusion processes at the LHC is the forward scattering of incident protons. Near-beam instruments known as proton spectrometers can detect the scattered protons, which is a technique referred to as proton tagging. The CMS and TOTEM Collaborations reported protontagged dielectron (dimuon) production with 2.6σð4.3σÞ significance, which exceeds 5σwhen statistically combined [31], but no cross sections were measured. Previous measurements of γγ →lþl−by the ATLAS Collaboration were performed without proton tagging [4,5]. Measuring proton-tagged dilepton production, pp → pðγγ →lþl−ÞpðÞ, where pðÞ denotes a proton that remains intact or dissociates following electromagnetic excitation, is important for several reasons. Predictions of photon fusion processes have significant uncertainties associated with modeling strong-force interactions between scattered protons, which suppress cross sections by factors known as soft-survival probabilities [32–35]. This suppression is poorly constrained, especially at high γγ invariant masses important for new physics searches, as existing probes indirectly infer dissociation rates using only centraldetector information [4–7]. Proton tagging overcomes this longstanding experimental ambiguity by directly detecting the scattered protons. Detecting a proton also directly suppresses background processes and events involving proton dissociation, while providing information on the initial γγ system independently of central-detector information. The successful demonstration of proton-tagging techniques for cross-section measurements accomplishes the crucial first step toward a diverse program using proton tagging in measurements of Standard Model processes [36–41] and searches for new phenomena [42–46]. This Letter introduces proton tagging for cross-section measurements of pp →pðγγ →lþl−ÞpðÞ. The ATLAS Forward Proton (AFP) spectrometer detects one of the intact protons and the central ATLAS detector reconstructs the leptons. The dataset was collected in 2017 and corresponds to 14.6fb−1of ffiffiffi s p¼13 TeV proton-proton ðppÞcollisions. The average number of interactions per bunch crossing was 36. Several methods specific to proton tagging are introduced: in situ calibration of proton kinematics using the dimuon system, a novel data-mixing background estimation method, and tag-and-probe determination of the AFP reconstruction efficiency. The ATLAS experiment [47–49] is a general-purpose particle detector with nearly 4πcoverage [50] around the interaction point. It comprises an inner detector tracker, calorimeters, and a muon spectrometer. A two-level trigger *Full author list given at the end of the article. Published by the American Physical Society under the terms of the Creative Commons Attribution 4.0 International license. Further distribution of this work must maintain attribution to the author(s) and the published article’s title, journal citation, and DOI. Funded by SCOAP3. PHYSICAL REVIEW LETTERS 125, 261801 (2020) 0031-9007=20=125(26)=261801(21) 261801-1 © 2020 CERN, for the ATLAS Collaboration system [51] is employed to select events containing sameflavor lepton pairs, each lepton with peðμÞ T>17ð14ÞGeV [52–54], after which standard data-quality requirements are applied [55]. The AFP spectrometer [56,57] consists of four tracking units located along the beam pipe at z¼205 and 217 m, referred to as near and far stations, respectively. The þzð−zÞdirection is labeled side A(C). Each station houses a silicon tracker comprising four planes of edgeless silicon pixel sensors [58–61]. The sensors have 336 × 80 pixels with area 50 ×250 μm2. The direction normal to each sensor is tilted 14° relative to the beam to improve hit efficiency and x-position resolution, resulting in an overall spatial resolution of σx¼6μm[62]. Movable near-beam devices at each station, known as Roman pots, insert the tracker along the xdirection in the beam pipe. Data taking with the AFP commences once the trackers are at a position where the innermost silicon edge is within 2 mm of the beam center during stable beams. Data quality for this analysis requires that every AFP station has at least three silicon planes operational at high voltage, and the AFP data acquisition system [63] must report no problems. Simulated events of the exclusive signal pp → pðγγ →lþl−Þpwere produced using the HERWIG 7 Monte Carlo (MC) generator [64,65]. The single-dissociative signal pp →pðγγ →lþl−Þpwas generated using LPAIR 4.0 [66], with proton dissociation modeled using the Brasse et al. [67] and Suri-Yennie [68] structure functions interfaced with JETSET 7.408 [69,70]. Simulation of these processes is detailed in Ref. [5]. To model the centraldetector response, the exclusive signal sample underwent full detector simulation based on GEANT 4[71]. The singledissociative samples employed a fast simulation [72], which uses a parametrization of the calorimeter response [73]. The response of the AFP spectrometer is modeled by a fast simulation, where a Gaussian smearing is applied to track positions based on the AFP spatial resolution. Simulated samples include the effect on the central detector of multiple pp interactions in the same and neighboring bunch crossing (pileup), as detailed in Ref. [5]. Reconstructed events must contain at least one interaction vertex with two or more associated inner-detector tracks that satisfy pT>500 MeV, jηj<2.5, and the “Loose” criterion [74,75]. Electrons (muons) must satisfy pT> 18ð15ÞGeV, jηj<2.47ð2.4Þ,the“LooseAndBLayer”[76] (“Medium”[77]) identification criterion, and jz0sin θj< 0.5mm [78]. Electrons sharing an inner-detector track with a muon are discarded. To suppress fake and/or nonprompt lepton backgrounds, remaining electrons (muons) must satisfy transverse impact parameter significance jd0=σd0j< 5ð3Þand isolation requirements described in Ref. [79] (Ref. [80]). Electrons must also satisfy “Medium”identification [76]. Small corrections are applied to leptons in simulated samples to match reconstruction and trigger efficiencies measured in data, as described in Refs. [76,77]. Selected events must have exactly two same-flavor leptons with opposite electric charge (eþe−or μþμ−)and be matched to the leptons that triggered the event. To suppress quarkonia and Zboson resonances, the dilepton invariant mass must satisfy mll >20 and mll ∈½70;105GeV. To select events compatible with pp →pðγγ →lþl−ÞpðÞ processes based on the simulated signals, the dilepton transverse momentum must satisfy pll T<5GeV. This set of criteria is referred to as the preselection. Signal event candidates must additionally have small acoplanarity All ϕ¼1−jΔϕllj=π<0.01.These events must have no inner-detector tracks (N0.5mm tracks ¼0) that satisfy ΔRðtrack;lÞ>0.01 for both leptons and jztrack 0−zll 0j<0.5mm, where ztrack 0is the track z0position and zll 0¼ðzl1 0þzl2 0Þ=2with l1;2denoting the two leptons. The expected proton energy loss based on lepton kinematics ξll is determined from mll and the dilepton rapidity yll by momentum conservation ξll¼ðmll=ffiffiffi s pÞeyll ,whereþ (−) corresponds to the proton on side A(C). Reconstruction of scattered protons combines information from the AFP tracker and LHC magnet lattice [81]. Protons transported to the AFP leave hits in the silicon tracker, which are processed by clustering and track-finding algorithms detailed in Ref. [59]. Tracks are reconstructed from clusters in at least two planes. Small corrections of around 0.1 mm are applied to ensure the cluster positions between planes are compatible within the spatial resolution. The proton transport function xAFP ¼TðξAFPÞrelates the track xposition xAFP to the fractional energy loss of the scattered proton ξAFP ¼1−Escattered=Ebeam,whereEscattered (Ebeam)isthe scattered (beam) proton energy. The LHC magnets and beam optics [82] govern the form of TðξAFPÞ[83],whichis simulated in the MAD - X package [84,85] with further details discussed in Refs. [56,86,87]. Determination of ξAFP uses both the near and far stations if tracks are within their common acceptance, otherwise only the far station is used. The absolute scale of Escattered depends on the closest separation xs 0between each AFP station sand the beam center [87]. The beam positions relative to the detectors were determined in dedicated runs with beam-based alignment procedures [88] using beam loss monitors [89], and cross-checked with beam position monitor measurements [90]. There were three data-taking periods in 2017. In the first data-taking period, the xs 0values were initially set to −4.0ð−3.0Þmm on side Aand −3.8ð−2.9Þmm on side C for the near (far) stations; during a second data-taking period, all stations were moved 0.5 mm closer to the beam to improve acceptance. This first (second) data-taking period corresponds to 5% (17%) of the analyzed dataset. For the remaining dataset, the far stations were moved a further 0.2 mm toward the beam. The initially measured xAFP values relative to xs 0are calibrated in situ using the dimuon data sample passing the signal event selection. The xs ll −xs AFP distribution is peaked for signal processes due to the kinematic correlation between xs ll and xs AFP, where PHYSICAL REVIEW LETTERS 125, 261801 (2020) 261801-2 xll ¼TðξllÞis the expected position calculated using the transport function. Additive corrections are applied to xs AFP in data to center the maximum of the peak at zero. These corrections are found to be −0.28ð−0.34Þmm on side A and −0.17ð−0.36Þmm on side Cfor the near (far) stations. Selected dielectron events are used to verify that the signal is centered at zero. After applying these corrections, the lower value of the acceptance corresponds to ξA AFP > 0.028ð0.018Þon side Aand ξC AFP >0.026ð0.019Þon side Cfor the near (far) stations. The upper value of the acceptance is bounded by ξAFP <0.12 due to the presence of beam collimators [56]. To select events with one or more proton candidates, the ξll and ξAFP values for at least one AFP side are required to be within the range [0.02, 0.12]. If there is more than one proton candidate on the same AFP side, which occurs in 35% of selected events, the proton with ξAFP closest to ξll is chosen. Proton-tagged dilepton candidates, denoted ll þp, are selected by requiring kinematic matching on at least one AFP side, jξAFP −ξllj<0.005, which retains (rejects) more than 95% (85%) of the signal (background). The dominant source of background after this selection arises from lepton pairs produced in a pp interaction different from that of the detected proton. In this case, the lepton pairs are produced via the Drell-Yan mechanism, as well as γγ →lþl−processes, in which any outgoing protons are either outside the AFP acceptance or not reconstructed in AFP due to detector inefficiency. These events are collectively referred to as combinatorial backgrounds and are estimated using a data-driven method. A mixed-data sample is constructed by randomly pairing each measured ξll value, passing AFP acceptance ξAFP ∈½0.02;0.12, with 100 values of ξAFP from a large control sample of >106events. This control sample is constructed from the preselected events and requiring All ϕ>0.01. The 123 selected data events failing kinematic matching, jξAFP −ξllj>0.005, result mostly from combinatorial background processes, which are used to normalize the mixed-data sample using a background-only profile-likelihood fit [91,92]. Systematic uncertainties in the background normalization arise from the limited size of the data sample satisfying jξAFP −ξllj>0.005. An uncertainty in the background shape arises from kinematic changes in the control sample of protons due to the acoplanarity requirement. This uncertainty is estimated by replacing the All ϕ>0.01 condition with N0.5mm tracks ≥1and comparing the two background predictions in the region jξAFP −ξllj<0.005; they are found to differ by 14%. Further shape uncertainties arise from instrumental effects, which are expected to be dominated by the sensitivity to the number of interactions per bunch crossing μ. The background predictions for μ<35 and μ≥35 are found to differ by 8% in the jξAFP −ξllj<0.005 region. These two shape differences are assigned as additional uncertainties. The background estimation method is validated by applying it to the orthogonal mll ∈½70;105GeV region. The region jξAFP −ξllj>0.005 is dominated by Drell-Yan events, which have no correlated protons. In this region, the data and prediction from the mixed-data sample are found to be compatible within the uncertainties across the ξAFP − ξll range for both sides Aand C. After applying the event selection including kinematic matching, jξAFP −ξllj<0.005, a total of 57 (123) candidates in the ee þp(μμ þp) final state are observed compared with a background-only expectation of 6.2 1.2ð13.42.5Þevents. Using the asymptotic profilelikelihood method [91,92], the background-only hypothesis is rejected with a significance exceeding 5σin each channel [93]. This provides direct evidence of forward proton scattering in association with electron and muon pairs produced via photon fusion. The ξAFP −ξll distributions of data, signal, and background at detector level before kinematic matching are shown in Fig. 1. To illustrate 0.02−0 0.02 0.04 A ll ξ− A AFP ξ 0 10 20 30 40 50 60 70 Events / 0.0025 ATLAS 1− = 13 TeV, 14.6 fbs [70, 105] GeV∉ ll m < 0.12ξ, 0.02 < μμee+ Postfit 0.02−0 0.02 0.04 C ll ξ− C AFP ξ Data 2017 Uncertainty )pμμ→γγp(→pp ee)p→γγp(→pp )p*μμ→γγp(→pp ee)p*→γγp(→pp Combinatorial bkg. FIG. 1. Distributions of ξAFP −ξll with ξll and ξAFP satisfying [0.02, 0.12] for side A(left) and side C(right). The total prediction comprises the signal and combinatorial background processes, where pdenotes a dissociated proton. The simulated predictions are normalized to data to illustrate the expected signal composition. The first (last) bin includes underflow (overflow). The hatched band indicates the combined statistical and systematic uncertainties of the prediction. Error bars denote statistical uncertainties of the data. PHYSICAL REVIEW LETTERS 125, 261801 (2020) 261801-3 the expected composition of the signal, the simulated samples are normalized to data with sides Aand C combined and fit separately in the ee and μμ channels. Figure 2displays positions in the yll −mll plane of data candidates satisfying jξAFP −ξllj<0.005 on at least one side and the corresponding acceptance regions of the four AFP stations. The highest-mass ee candidate has an invariant mass mll ¼717 GeV and rapidity yll ¼0.252, so the scattered protons would be within the acceptance of both AFP sides if this were an exclusive process. However, it is found that the proton on side Afails kinematic matching jξAFP −ξllj<0.005, so this event is likely a single-dissociative process where the side Aproton candidate originates from a pileup interaction. The corresponding quantities for the highest-mass μμ candidate are mll ¼319 GeV and yll ¼0.255. Figure 3illustrates detector-level distributions of dilepton acoplanarity, mass, and rapidity after kinematic matching with the signal samples normalized to Nobs −Nbkg. Cross sections are measured in a fiducial region defined at particle level with an event selection similar to that applied at detector level [94]. To reliably estimate AFP reconstruction efficiencies using tag-and-probe techniques, the ξAFP and ξll values are restricted to a tighter range [0.035, 0.08] and each proton candidate is required to have an associated track in both near and far stations. The measured cross sections are defined by σfid. ¼ðNobs −NbkgÞ=ðL·Ccent ·CAFPÞ. Here, Nobs (Nbkg) is the number of observed data (expected background) events passing event selection, and Ccent (CAFP)is an overall correction factor accounting for the centraldetector (AFP) efficiency. The integrated luminosity, L¼14.6fb−1, is measured using the LUCID-2 detector [95] and the uncertainty is determined to be 2.4% [96].In this tighter region, Nobs is found to be 19 (23) for the ee (μμ) channel and Nbkg ¼1.70.3ð2.30.5Þ. The event rate between the two channels differs more for the ξ∈ ½0.02;0.12than ξ∈½0.035;0.08region because μμ events with low mll and high jylljhave greater selection efficiency due to trigger and reconstruction requirements. The Ccent factor is defined as the ratio of the number of MC events passing detector-level selection to the number passing the particle-level fiducial requirements. Uncertainties in Ccent are estimated by varying the electron (muon) energy (momentum) scale and resolution, and datato-MC correction factors described in Refs. [76,77], together with corrections applied to account for pileup modeling. The dominant uncertainties for ee events arise from pileup modeling (2%) and identification (1%), while for μμ events, these correspond to pileup modeling (3%), resolution (3%), and scale (2%); other sources such as trigger and isolation efficiencies contribute 1% or less. Using data-driven methods described in Ref. [5], a further correction of 0.89 0.04 is applied to Ccent to account for [GeV] ll m 10 2 10 3 10 4 10 ll y 8− 6− 4− 2− 0 2 4 6 8 Side A Side C ee μμ AFP acceptance None Near and Far stations Far station only Both sides ATLAS 1− = 13 TeV, 14.6 fbs AFP matched candidates FIG. 2. The 57 (123) ee (μμ) data event candidates in the dilepton rapidity yll vs mll plane satisfying event selection and kinematic matching, jξAFP −ξllj<0.005, on at least one side. Shaded (hatched) areas denote the acceptance (no acceptance) for the AFP stations indicated in the legend. Areas neither shaded nor hatched correspond to ξ∈½0;1. 0 0.002 0.004 0.006 0.008 0.01 ll φ A 0 20 40 60 80 100 120 Events / 0.001 Data 2017 Uncertainty )pμμ→γγp(→pp ee)p→γγp(→pp )p*μμ→γγp(→pp ee)p*→γγp(→pp Combinatorial bkg. ATLAS 1− = 13 TeV, 14.6 fbs < 0.12ξPostfit, 0.02 < 50 100 150 200 250 300 [GeV] ll m 0 20 40 60 80 100 Events / 20 GeV Data 2017 Uncertainty )pμμ→γγp(→pp ee)p→γγp(→pp )p*μμ→γγp(→pp ee)p*→γγp(→pp Combinatorial bkg. ATLAS 1− = 13 TeV, 14.6 fbs < 0.12ξPostfit, 0.02 < 3−2−1−0123 ll y 0 10 20 30 40 50 60 70 80 90 Events / 0.5 Data 2017 Uncertainty )pμμ→γγp(→pp ee)p→γγp(→pp )p*μμ→γγp(→pp ee)p*→γγp(→pp Combinatorial bkg. ATLAS 1− = 13 TeV, 14.6 fbs < 0.12ξPostfit, 0.02 < FIG. 3. Distributions of dilepton acoplanarity All ϕ(left), invariant mass mll (center), rapidity yll (right) satisfying ξll;ξAFP ∈½0.02;0.12, and jξAFP −ξllj<0.005 for at least one AFP side. Events with 70 <m ll <105 GeV are vetoed. The total prediction comprises the signal and combinatorial background processes, where pdenotes a dissociated proton. The simulated predictions are normalized to data to illustrate the expected signal composition. The rightmost bin of the mll distribution includes overflow. The hatched band indicates the combined statistical and systematic uncertainties of the prediction. Error bars denote statistical uncertainties of the data. PHYSICAL REVIEW LETTERS 125, 261801 (2020) 261801-4 differences between data and MC when modeling the luminous region at the interaction point. The 5% uncertainty in this correction is evaluated as the difference between either applying this data-driven method to simulated signal samples or imposing the N0.5mm tracks ¼0requirement on these samples. Overall, this results in Cee cent ¼0.12 0.01 ðCμμ cent ¼0.22 0.02Þfor the ee ðμμÞchannel. The CAFP factor is defined by the product ϵtrack ·ϵsmear. The track reconstruction efficiency ϵtrack is found to be 0.92 0.02 for sides Aand C. The near-station efficiency is estimated using a tag-and-probe method by first selecting events with exactly one track in the far (tag) station in the acceptance common to both stations, −12 <x AFP <−5mm. The efficiency is the fraction of these events that also have one or more tracks in the near (probe) station satisfying jxnear −xfarj<2mm. The tag and probe stations are inverted to measure the far-station efficiency. It is found that ϵtrack varies with ξAFP by 2%, which is assigned as an additional uncertainty. The proton resolution correction ϵsmear is found to be 0.98 0.02 (0.96 0.04) for the ee (μμ) channel. This is evaluated as the fraction of simulated signal events passing ξAFP;ξll ∈½0.035;0.08, and jξAFP −ξllj<0.005 out of those satisfying ξll ∈½0.035;0.08. Uncertainties in CAFP are dominated by global alignment (6%) evaluated by 0.3mm variations of xAFP and beam optics (5%) evaluated by varying the beam crossing angle by 50 μrad in the MAD - X package. Uncertainties involving track and cluster reconstruction are found to be less than 1%. The overall uncertainty in CAFP is 9%. The measured fiducial cross sections in the ee and μμ channels are σfid: eeþp¼11.02.6ðstatÞ1.2ðsystÞ0.3ðlumiÞ and σfid. μμþp¼7.21.6ðstatÞ0.9ðsystÞ0.2ðlumiÞfb, respectively. Table Icompares these with the combined HERWIG and LPAIR predictions assuming unit soft-survival factors Ssurv ¼1. Soft-survival effects are included using an mll-dependent reweighting of these predictions to Ssurv calculated for exclusive processes from Ref. [34]; LPAIR predictions are additionally scaled down by 15% to account for Ssurv being lower for single-dissociative processes [33]. SUPERCHIC 4[97] predictions include full kinematic dependence on Ssurv for exclusive, single-, and doubledissociative processes. The predictions for ee are higher than for μμ due to the looser ηðeÞrequirement [94]. In summary, forward proton scattering in association with lepton pairs produced via photon fusion, pp → pðγγ →lþl−ÞpðÞ, is observed with a significance exceeding 5σin both the ee þpand μμ þpfinal states using 14.6fb−1of ffiffiffi s p¼13 TeV pp collisions at the LHC. These results demonstrate that the ATLAS Forward Proton spectrometer performs well in high-luminosity data taking. Furthermore, proton tagging is introduced for crosssection measurements of photon fusion processes at the electroweak scale. We thank CERN for the very successful operation of the LHC, as well as the support staff from our institutions without whom ATLAS could not be operated efficiently. We acknowledge the support of ANPCyT, Argentina; YerPhI, Armenia; ARC, Australia; BMWFW and FWF, Austria; ANAS, Azerbaijan; SSTC, Belarus; CNPq and FAPESP, Brazil; NSERC, NRC and CFI, Canada; CERN; ANID, Chile; CAS, MOST and NSFC, China; COLCIENCIAS, Colombia; MSMT CR, MPO CR and VSC CR, Czech Republic; DNRF and DNSRC, Denmark; IN2P3-CNRS and CEA-DRF/IRFU, France; SRNSFG, Georgia; BMBF, HGF and MPG, Germany; GSRT, Greece; RGC and Hong Kong SAR, China; ISF and Benoziyo Center, Israel; INFN, Italy; MEXT and JSPS, Japan; CNRST, Morocco; NWO, Netherlands; RCN, Norway; MNiSW and NCN, Poland; FCT, Portugal; MNE/IFA, Romania; MES of Russia and NRC KI, Russia Federation; JINR; MESTD, Serbia; MSSR, Slovakia; ARRS and MIZŠ, Slovenia; DST/NRF, South Africa; MICINN, Spain; SRC and Wallenberg Foundation, Sweden; SERI, SNSF and Cantons of Bern and Geneva, Switzerland; MOST, Taiwan; TAEK, Turkey; STFC, United Kingdom; DOE and NSF, U.S. In addition, individual groups and members have received support from BCKDF, CANARIE, Compute Canada, CRC and IVADO, Canada; Beijing Municipal Science & Technology Commission, China; COST, ERC, ERDF, Horizon 2020 and Marie Skłodowska-Curie Actions, European Union; Investissements d’Avenir Labex, Investissements d’Avenir Idex and ANR, France; DFG and AvH Foundation, Germany; Herakleitos, Thales and Aristeia programs cofinanced by EU-ESF and the Greek NSRF, Greece; BSFNSF and GIF, Israel; La Caixa Banking Foundation, CERCA Programme Generalitat de Catalunya and PROMETEO and GenT Programmes Generalitat Valenciana, Spain; Göran Gustafssons Stiftelse, Sweden; The Royal Society and Leverhulme Trust, United Kingdom. The crucial computing support from all WLCG partners is acknowledged gratefully, in particular from CERN, the ATLAS Tier-1 facilities at TRIUMF (Canada), NDGF (Denmark, Norway, Sweden), CC-IN2P3 (France), TABLE I. Fiducial cross sections from the combined HERWIG and LPAIR predictions with Ssurv ¼1and Ssurv estimated using Refs. [33,34] as described in the main text. SUPERCHIC 4[97] predictions include fully kinematically dependent Ssurv. Uncertainties of 7% (17%) are assigned for predictions of the exclusive (single-dissociative) processes [98]. The bottom row displays the measured cross sections with statistical and systematic uncertainties combined. σHERWIGþLPAIR ×Ssurv σfid. eeþp(fb) σfid. μμþp(fb) Ssurv ¼115.51.213.51.1 Ssurv using Refs. 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Camerlingo,75a,75b D. Cameron,133 C. Camincher,36 S. Campana,36 M. Campanelli,95 A. Camplani,40 V. Canale,70a,70b A. Canesse,104 M. Cano Bret,78 J. Cantero,129 T. Cao,161 Y. Cao,173 M. Capua,41b,41a R. Cardarelli,74a F. Cardillo,174 G. Carducci,41b,41a I. Carli,142 T. Carli,36 G. Carlino,70a PHYSICAL REVIEW LETTERS 125, 261801 (2020) 261801-9 M. Testa,51 R. J. Teuscher,167,l N. Themistokleous,50 T. Theveneaux-Pelzer,19 D. W. Thomas,94 J. P. Thomas,21 E. A. Thompson,46 P. D. Thompson,21 E. Thomson,136 E. J. Thorpe,93 V. O. Tikhomirov,111,jj Yu. A. Tikhonov,122b,122a S. Timoshenko,112 P. Tipton,183 S. Tisserant,102 K. Todome,23b,23a S. Todorova-Nova,142 S. Todt,48 J. Tojo,88 S. Tokár,28a K. Tokushuku,82 E. Tolley,127 R. Tombs,32 K. G. Tomiwa,33e M. Tomoto,82,117 L. Tompkins,153 P. Tornambe,103 E. Torrence,131 H. Torres,48 E. Torró Pastor,174 M. Toscani,30 C. Tosciri,134 J. Toth,102,kk D. R. Tovey,149 A. Traeet,17 C. J. Treado,125 T. Trefzger,177 F. Tresoldi,156 A. Tricoli,29 I. M. Trigger,168a S. Trincaz-Duvoid,135 D. A. Trischuk,175 W. Trischuk,167 B. Trocm´e,58 A. Trofymov,65 C. Troncon,69a F. Trovato,156 L. Truong,33c M. Trzebinski,85 A. Trzupek,85 F. Tsai,46 P. V. Tsiareshka,108,y A. Tsirigotis,162,z V. Tsiskaridze,155 E. G. Tskhadadze,159a M. Tsopoulou,162 I. I. Tsukerman,124 V. Tsulaia,18 S. Tsuno,82 D. Tsybychev,155 Y. Tu,63b A. Tudorache,27b V. Tudorache,27b A. N. Tuna,36 S. Turchikhin,80 D. Turgeman,180 I. Turk Cakir,4b,ll R. J. Turner,21 R. Turra,69a P. M. Tuts,39 S. Tzamarias,162 E. Tzovara,100 K. Uchida,163 F. Ukegawa,169 G. Unal,36 M. Unal,11 A. Undrus,29 G. Unel,171 F. C. Ungaro,105 Y. Unno,82 K. Uno,163 J. Urban,28b P. Urquijo,105 G. Usai,8Z. Uysal,12d V. Vacek,141 B. Vachon,104 K. O. H. Vadla,133 T. Vafeiadis,36 A. Vaidya,95 C. Valderanis,114 E. Valdes Santurio,45a,45b M. Valente,168a S. Valentinetti,23b,23a A. Valero,174 L. Val´ery,46 R. A. Vallance,21 A. Vallier,36 J. A. Valls Ferrer,174 T. R. Van Daalen,14 P. Van Gemmeren,6S. Van Stroud,95 I. Van Vulpen,120 M. Vanadia,74a,74b W. Vandelli,36 M. Vandenbroucke,144 E. R. Vandewall,129 D. Vannicola,73a,73b R. Vari,73a E. W. Varnes,7 C. Varni,55b,55a T. Varol,158 D. Varouchas,65 K. E. Varvell,157 M. E. Vasile,27b G. A. Vasquez,176 F. Vazeille,38 D. Vazquez Furelos,14 T. Vazquez Schroeder,36 J. Veatch,53 V. Vecchio,101 M. J. Veen,120 L. M. Veloce,167 F. Veloso,139a,139c S. Veneziano,73a A. Ventura,68a,68b A. Verbytskyi,115 V. Vercesi,71a M. Verducci,72a,72b C. M. Vergel Infante,79 C. Vergis,24 W. Verkerke,120 A. T. Vermeulen,120 J. C. Vermeulen,120 C. Vernieri,153 P. J. Verschuuren,94 M. C. Vetterli,152,d N. Viaux Maira,146d T. Vickey,149 O. E. Vickey Boeriu,149 G. H. A. Viehhauser,134 L. Vigani,61b M. Villa,23b,23a M. Villaplana Perez,174 E. M. Villhauer,50 E. Vilucchi,51 M. G. Vincter,34 G. S. Virdee,21 A. Vishwakarma,50 C. Vittori,23b,23a I. Vivarelli,156 M. Vogel,182 P. Vokac,141 J. Von Ahnen,46 S. E. von Buddenbrock,33e E. Von Toerne,24 V. Vorobel,142 K. Vorobev,112 M. Vos,174 J. H. Vossebeld,91 M. Vozak,101 N. Vranjes,16 M. Vranjes Milosavljevic,16 V. Vrba,141 M. Vreeswijk,120 N. K. Vu,102 R. Vuillermet,36 I. Vukotic,37 S. Wada,169 P. Wagner,24 W. Wagner,182 J. Wagner-Kuhr,114 S. Wahdan,182 H. Wahlberg,89 R. Wakasa,169 V. M. Walbrecht,115 J. Walder,143 R. Walker,114 S. D. Walker,94 W. Walkowiak,151 V. Wallangen,45a,45b A. M. Wang,59 A. Z. Wang,181 C. Wang,60a C. Wang,60c H. Wang,18 H. Wang,3 J. Wang,63a P. Wang,42 Q. Wang,128 R.-J. Wang,100 R. Wang,60a R. Wang,6S. M. Wang,158 W. T. Wang,60a W. Wang,15c W. X. Wang,60a Y. Wang,60a Z. Wang,106 C. Wanotayaroj,46 A. Warburton,104 C. P. Ward,32 R. J. Ward,21 N. Warrack,57 A. T. Watson,21 M. F. Watson,21 G. Watts,148 B. M. Waugh,95 A. F. Webb,11 C. Weber,29 M. S. Weber,20 S. A. Weber,34 S. M. Weber,61a Y. Wei,134 A. R. Weidberg,134 J. Weingarten,47 M. Weirich,100 C. Weiser,52 P. S. Wells,36 T. Wenaus,29 B. Wendland,47 T. Wengler,36 S. Wenig,36 N. Wermes,24 M. Wessels,61a T. D. Weston,20 K. Whalen,131 A. M. Wharton,90 A. S. White,106 A. White,8M. J. White,1D. Whiteson,171 B. W. Whitmore,90 W. Wiedenmann,181 C. Wiel,48 M. Wielers,143 N. Wieseotte,100 C. Wiglesworth,40 L. A. M. Wiik-Fuchs,52 H. G. Wilkens,36 L. J. Wilkins,94 D. M. Williams,39 H. H. Williams,136 S. Williams,32 S. Willocq,103 P. J. Windischhofer,134 I. Wingerter-Seez,5E. Winkels,156 F. Winklmeier,131 B. T. Winter,52 M. Wittgen,153 M. Wobisch,96 A. Wolf,100 R. Wölker,134 J. Wollrath,52 M. W. Wolter,85 H. Wolters,139a,139c V. W. S. Wong,175 A. F. Wongel,46 N. L. Woods,145 S. D. Worm,46 B. K. Wosiek,85 K. W. Woźniak,85 K. Wraight,57 S. L. Wu,181 X. Wu,54 Y. Wu,60a J. Wuerzinger,134 T. R. Wyatt,101 B. M. Wynne,50 S. Xella,40 L. Xia,178 J. Xiang,63c X. Xiao,106 X. Xie,60a I. Xiotidis,156 D. Xu,15a H. Xu,60a H. Xu,60a L. Xu,29 R. Xu,136 T. Xu,144 W. Xu,106 Y. Xu,15b Z. Xu,60b Z. Xu,153 B. Yabsley,157 S. Yacoob,33a D. P. Yallup,95 N. Yamaguchi,88 Y. Yamaguchi,165 A. Yamamoto,82 M. Yamatani,163 T. Yamazaki,163 Y. Yamazaki,83 J. Yan,60c Z. Yan,25 H. J. Yang,60c,60d H. T. Yang,18 S. Yang,60a T. Yang,63c X. Yang,60a X. Yang,60b,58 Y. Yang,163 Z. Yang,60a W-M. Yao,18 Y. C. Yap,46 H. Ye,15c J. Ye,42 S. Ye,29 I. Yeletskikh,80 M. R. Yexley,90 E. Yigitbasi,25 P. Yin,39 K. Yorita,179 K. Yoshihara,79 C. J. S. Young,36 C. Young,153 J. Yu,79 R. Yuan,60b,mm X. Yue,61a M. Zaazoua,35e B. Zabinski,85 G. Zacharis,10 E. Zaffaroni,54 J. Zahreddine,135 A. M. Zaitsev,123,i T. Zakareishvili,159b N. Zakharchuk,34 S. Zambito,36 D. Zanzi,36 S. V. Zeißner,47 C. Zeitnitz,182 G. Zemaityte,134 J. C. Zeng,173 O. Zenin,123 T. Ženiš,28a D. Zerwas,65 M. Zgubič,134 B. Zhang,15c D. F. Zhang,15b G. Zhang,15b J. Zhang,6Kaili. Zhang,15a L. Zhang,15c L. Zhang,60a M. Zhang,173 R. Zhang,181 S. Zhang,106 X. Zhang,60c X. Zhang,60b Y. Zhang,15a,15d Z. Zhang,63a Z. Zhang,65 P. Zhao,49 Y. Zhao,145 Z. Zhao,60a A. Zhemchugov,80 Z. Zheng,106 D. Zhong,173 B. Zhou,106 C. Zhou,181 H. Zhou,7 M. Zhou,155 N. Zhou,60c Y. Zhou,7C. G. Zhu,60b C. Zhu,15a,15d H. L. Zhu,60a H. Zhu,15a J. Zhu,106 Y. Zhu,60a X. Zhuang,15a PHYSICAL REVIEW LETTERS 125, 261801 (2020) 261801-16 K. Zhukov,111 V. Zhulanov,122b,122a D. Zieminska,66 N. I. Zimine,80 S. Zimmermann,52 Z. Zinonos,115 M. Ziolkowski,151 L. Živković,16 G. Zobernig,181 A. Zoccoli,23b,23a K. Zoch,53 T. G. Zorbas,149 R. Zou,37 and L. Zwalinski36 (ATLAS Collaboration) 1Department of Physics, University of Adelaide, Adelaide, Australia 2Physics Department, SUNY Albany, Albany, New York, USA 3Department of Physics, University of Alberta, Edmonton, Alberta, Canada 4aDepartment of Physics, Ankara University, Ankara, Turkey 4bIstanbul Aydin University, Application and Research Center for Advanced Studies, Istanbul, Turkey 4cDivision of Physics, TOBB University of Economics and Technology, Ankara, Turkey 5LAPP, Universit´e Grenoble Alpes, Universit´e Savoie Mont Blanc, CNRS/IN2P3, Annecy, France 6High Energy Physics Division, Argonne National Laboratory, Argonne, Illinois, USA 7Department of Physics, University of Arizona, Tucson, Arizona, USA 8Department of Physics, University of Texas at Arlington, Arlington, Texas, USA 9Physics Department, National and Kapodistrian University of Athens, Athens, Greece 10Physics Department, National Technical University of Athens, Zografou, Greece 11Department of Physics, University of Texas at Austin, Austin, Texas, USA 12aBahcesehir University, Faculty of Engineering and Natural Sciences, Istanbul, Turkey 12bIstanbul Bilgi University, Faculty of Engineering and Natural Sciences, Istanbul, Turkey 12cDepartment of Physics, Bogazici University, Istanbul, Turkey 12dDepartment of Physics Engineering, Gaziantep University, Gaziantep, Turkey 13Institute of Physics, Azerbaijan Academy of Sciences, Baku, Azerbaijan 14Institut de Física d’Altes Energies (IFAE), Barcelona Institute of Science and Technology, Barcelona, Spain 15aInstitute of High Energy Physics, Chinese Academy of Sciences, Beijing, China 15bPhysics Department, Tsinghua University, Beijing, China 15cDepartment of Physics, Nanjing University, Nanjing, China 15dUniversity of Chinese Academy of Science (UCAS), Beijing, China 16Institute of Physics, University of Belgrade, Belgrade, Serbia 17Department for Physics and Technology, University of Bergen, Bergen, Norway 18Physics Division, Lawrence Berkeley National Laboratory and University of California, Berkeley, California, USA 19Institut für Physik, Humboldt Universität zu Berlin, Berlin, Germany 20Albert Einstein Center for Fundamental Physics and Laboratory for High Energy Physics, University of Bern, Bern, Switzerland 21School of Physics and Astronomy, University of Birmingham, Birmingham, United Kingdom 22aFacultad de Ciencias y Centro de Investigaciónes, Universidad Antonio Nariño, Bogotá, Colombia 22bDepartamento de Física, Universidad Nacional de Colombia, Bogotá, Colombia, Colombia 23aINFN Bologna and Universita’di Bologna, Dipartimento di Fisica, Italy 23bINFN Sezione di Bologna, Italy 24Physikalisches Institut, Universität Bonn, Bonn, Germany 25Department of Physics, Boston University, Boston, Massachusetts, USA 26Department of Physics, Brandeis University, Waltham, Massachusetts, USA 27aTransilvania University of Brasov, Brasov, Romania 27bHoria Hulubei National Institute of Physics and Nuclear Engineering, Bucharest, Romania 27cDepartment of Physics, Alexandru Ioan Cuza University of Iasi, Iasi, Romania 27dNational Institute for Research and Development of Isotopic and Molecular Technologies, Physics Department, Cluj-Napoca, Romania 27eUniversity Politehnica Bucharest, Bucharest, Romania 27fWest University in Timisoara, Timisoara, Romania 28aFaculty of Mathematics, Physics and Informatics, Comenius University, Bratislava, Slovak Republic 28bDepartment of Subnuclear Physics, Institute of Experimental Physics of the Slovak Academy of Sciences, Kosice, Slovak Republic 29Physics Department, Brookhaven National Laboratory, Upton, New York, USA 30Departamento de Física, Universidad de Buenos Aires, Buenos Aires, Argentina 31California State University, California, USA 32Cavendish Laboratory, University of Cambridge, Cambridge, United Kingdom 33aDepartment of Physics, University of Cape Town, Cape Town, South Africa 33biThemba Labs, Western Cape, South Africa 33cDepartment of Mechanical Engineering Science, University of Johannesburg, Johannesburg, South Africa 33dUniversity of South Africa, Department of Physics, Pretoria, South Africa PHYSICAL REVIEW LETTERS 125, 261801 (2020) 261801-17 33eSchool of Physics, University of the Witwatersrand, Johannesburg, South Africa 34Department of Physics, Carleton University, Ottawa, Ontario, Canada 35aFacult´e des Sciences Ain Chock, R´eseau Universitaire de Physique des Hautes Energies—Universit´e Hassan II, Casablanca, Morocco 35bFacult´e des Sciences, Universit´e Ibn-Tofail, K´enitra, Morocco 35cFacult´e des Sciences Semlalia, Universit´e Cadi Ayyad, LPHEA-Marrakech, Morocco 35dFacult´e des Sciences, Universit´e Mohamed Premier and LPTPM, Oujda, Morocco 35eFacult´e des sciences, Universit´e Mohammed V, Rabat, Morocco 36CERN, Geneva, Switzerland 37Enrico Fermi Institute, University of Chicago, Chicago, Illinois, USA 38LPC, Universit´e Clermont Auvergne, CNRS/IN2P3, Clermont-Ferrand, France 39Nevis Laboratory, Columbia University, Irvington, New York, USA 40Niels Bohr Institute, University of Copenhagen, Copenhagen, Denmark 41aDipartimento di Fisica, Universit`a della Calabria, Rende, Italy 41bINFN Gruppo Collegato di Cosenza, Laboratori Nazionali di Frascati, Italy 42Physics Department, Southern Methodist University, Dallas, Texas, USA 43Physics Department, University of Texas at Dallas, Richardson, Texas, USA 44National Centre for Scientific Research “Demokritos”, Agia Paraskevi, Greece 45aDepartment of Physics, Stockholm University, Sweden 45bOskar Klein Centre, Stockholm, Sweden 46Deutsches Elektronen-Synchrotron DESY, Hamburg and Zeuthen, Germany 47Lehrstuhl für Experimentelle Physik IV, Technische Universität Dortmund, Dortmund, Germany 48Institut für Kernund Teilchenphysik, Technische Universität Dresden, Dresden, Germany 49Department of Physics, Duke University, Durham, North Carolina, USA 50SUPA—School of Physics and Astronomy, University of Edinburgh, Edinburgh, United Kingdom 51INFN e Laboratori Nazionali di Frascati, Frascati, Italy 52Physikalisches Institut, Albert-Ludwigs-Universität Freiburg, Freiburg, Germany 53II. Physikalisches Institut, Georg-August-Universität Göttingen, Göttingen, Germany 54D´epartement de Physique Nucl´eaire et Corpusculaire, Universit´e de Gen`eve, Gen`eve, Switzerland 55aDipartimento di Fisica, Universit`a di Genova, Genova, Italy 55bINFN Sezione di Genova, Italy 56II. Physikalisches Institut, Justus-Liebig-Universität Giessen, Giessen, Germany 57SUPA—School of Physics and Astronomy, University of Glasgow, Glasgow, United Kingdom 58LPSC, Universit´e Grenoble Alpes, CNRS/IN2P3, Grenoble INP, Grenoble, France 59Laboratory for Particle Physics and Cosmology, Harvard University, Cambridge, Massachusetts, USA 60aDepartment of Modern Physics and State Key Laboratory of Particle Detection and Electronics, University of Science and Technology of China, Hefei, China 60bInstitute of Frontier and Interdisciplinary Science and Key Laboratory of Particle Physics and Particle Irradiation (MOE), Shandong University, Qingdao, China 60cSchool of Physics and Astronomy, Shanghai Jiao Tong University, KLPPAC-MoE, SKLPPC, Shanghai, China 60dTsung-Dao Lee Institute, Shanghai, China 61aKirchhoff-Institut für Physik, Ruprecht-Karls-Universität Heidelberg, Heidelberg, Germany 61bPhysikalisches Institut, Ruprecht-Karls-Universität Heidelberg, Heidelberg, Germany 62Faculty of Applied Information Science, Hiroshima Institute of Technology, Hiroshima, Japan 63aDepartment of Physics, Chinese University of Hong Kong, Shatin, N.T., Hong Kong, China 63bDepartment of Physics, University of Hong Kong, Hong Kong, China 63cDepartment of Physics and Institute for Advanced Study, Hong Kong University of Science and Technology, Clear Water Bay, Kowloon, Hong Kong, China 64Department of Physics, National Tsing Hua University, Hsinchu, Taiwan 65IJCLab, Universit´e Paris-Saclay, CNRS/IN2P3, 91405, Orsay, France 66Department of Physics, Indiana University, Bloomington, Indiana, USA 67aINFN Gruppo Collegato di Udine, Sezione di Trieste, Udine, Italy 67bICTP, Trieste, Italy 67cDipartimento Politecnico di Ingegneria e Architettura, Universit`a di Udine, Udine, Italy 68aINFN Sezione di Lecce, Italy 68bDipartimento di Matematica e Fisica, Universit`a del Salento, Lecce, Italy 69aINFN Sezione di Milano, Italy 69bDipartimento di Fisica, Universit`a di Milano, Milano, Italy 70aINFN Sezione di Napoli, Italy 70bDipartimento di Fisica, Universit`a di Napoli, Napoli, Italy PHYSICAL REVIEW LETTERS 125, 261801 (2020) 261801-18 71aINFN Sezione di Pavia, Italy 71bDipartimento di Fisica, Universit`a di Pavia, Pavia, Italy 72aINFN Sezione di Pisa, Italy 72bDipartimento di Fisica E. Fermi, Universit`a di Pisa, Pisa, Italy 73aINFN Sezione di Roma, Italy 73bDipartimento di Fisica, Sapienza Universit`a di Roma, Roma, Italy 74aINFN Sezione di Roma Tor Vergata, Italy 74bDipartimento di Fisica, Universit`a di Roma Tor Vergata, Roma, Italy 75aINFN Sezione di Roma Tre, Italy 75bDipartimento di Matematica e Fisica, Universit`a Roma Tre, Roma, Italy 76aINFN-TIFPA, Italy 76bUniversit`a degli Studi di Trento, Trento, Italy 77Institut für Astround Teilchenphysik, Leopold-Franzens-Universität, Innsbruck, Austria 78University of Iowa, Iowa City, Iowa, USA 79Department of Physics and Astronomy, Iowa State University, Ames, Iowa, USA 80Joint Institute for Nuclear Research, Dubna, Russia 81aDepartamento de Engenharia El´etrica, Universidade Federal de Juiz de Fora (UFJF), Juiz de Fora, Brazil 81bUniversidade Federal do Rio De Janeiro COPPE/EE/IF, Rio de Janeiro, Brazil 81cInstituto de Física, Universidade de São Paulo, São Paulo, Brazil 82KEK, High Energy Accelerator Research Organization, Tsukuba, Japan 83Graduate School of Science, Kobe University, Kobe, Japan 84aAGH University of Science and Technology, Faculty of Physics and Applied Computer Science, Krakow, Poland 84bMarian Smoluchowski Institute of Physics, Jagiellonian University, Krakow, Poland 85Institute of Nuclear Physics Polish Academy of Sciences, Krakow, Poland 86Faculty of Science, Kyoto University, Kyoto, Japan 87Kyoto University of Education, Kyoto, Japan 88Research Center for Advanced Particle Physics and Department of Physics, Kyushu University, Fukuoka, Japan 89Instituto de Física La Plata, Universidad Nacional de La Plata and CONICET, La Plata, Argentina 90Physics Department, Lancaster University, Lancaster, United Kingdom 91Oliver Lodge Laboratory, University of Liverpool, Liverpool, United Kingdom 92Department of Experimental Particle Physics, Jožef Stefan Institute and Department of Physics, University of Ljubljana, Ljubljana, Slovenia 93School of Physics and Astronomy, Queen Mary University of London, London, United Kingdom 94Department of Physics, Royal Holloway University of London, Egham, United Kingdom 95Department of Physics and Astronomy, University College London, London, United Kingdom 96Louisiana Tech University, Ruston, Louisiana, USA 97Fysiska institutionen, Lunds universitet, Lund, Sweden 98Centre de Calcul de l’Institut National de Physique Nucl´eaire et de Physique des Particules (IN2P3), Villeurbanne, France 99Departamento de Física Teorica C-15 and CIAFF, Universidad Autónoma de Madrid, Madrid, Spain 100Institut für Physik, Universität Mainz, Mainz, Germany 101School of Physics and Astronomy, University of Manchester, Manchester, United Kingdom 102CPPM, Aix-Marseille Universit´e, CNRS/IN2P3, Marseille, France 103Department of Physics, University of Massachusetts, Amherst, Massachusetts, USA 104Department of Physics, McGill University, Montreal, Quebec, Canada 105School of Physics, University of Melbourne, Victoria, Australia 106Department of Physics, University of Michigan, Ann Arbor, Michigan, USA 107Department of Physics and Astronomy, Michigan State University, East Lansing, Michigan, USA 108B.I. Stepanov Institute of Physics, National Academy of Sciences of Belarus, Minsk, Belarus 109Research Institute for Nuclear Problems of Byelorussian State University, Minsk, Belarus 110Group of Particle Physics, University of Montreal, Montreal, Quebec, Canada 111P.N. Lebedev Physical Institute of the Russian Academy of Sciences, Moscow, Russia 112National Research Nuclear University MEPhI, Moscow, Russia 113D.V. Skobeltsyn Institute of Nuclear Physics, M.V. Lomonosov Moscow State University, Moscow, Russia 114Fakultät für Physik, Ludwig-Maximilians-Universität München, München, Germany 115Max-Planck-Institut für Physik (Werner-Heisenberg-Institut), München, Germany 116Nagasaki Institute of Applied Science, Nagasaki, Japan 117Graduate School of Science and Kobayashi-Maskawa Institute, Nagoya University, Nagoya, Japan 118Department of Physics and Astronomy, University of New Mexico, Albuquerque, New Mexico, USA 119Institute for Mathematics, Astrophysics and Particle Physics, Radboud University Nijmegen/Nikhef, Nijmegen, Netherlands 120Nikhef National Institute for Subatomic Physics and University of Amsterdam, Amsterdam, Netherlands PHYSICAL REVIEW LETTERS 125, 261801 (2020) 261801-19 121Department of Physics, Northern Illinois University, DeKalb, Illinois, USA 122aBudker Institute of Nuclear Physics and NSU, SB RAS, Novosibirsk, Russia 122bNovosibirsk State University Novosibirsk, Russia 123Institute for High Energy Physics of the National Research Centre Kurchatov Institute, Protvino, Russia 124Institute for Theoretical and Experimental Physics named by A.I. Alikhanov of National Research Centre “Kurchatov Institute”, Moscow, Russia 125Department of Physics, New York University, New York, New York, USA 126Ochanomizu University, Otsuka, Bunkyo-ku, Tokyo, Japan 127Ohio State University, Columbus, Ohio, USA 128Homer L. Dodge Department of Physics and Astronomy, University of Oklahoma, Norman, Oklahoma, USA 129Department of Physics, Oklahoma State University, Stillwater, Oklahoma, USA 130Palacký University, RCPTM, Joint Laboratory of Optics, Olomouc, Czech Republic 131Institute for Fundamental Science, University of Oregon, Eugene, Oregon, USA 132Graduate School of Science, Osaka University, Osaka, Japan 133Department of Physics, University of Oslo, Oslo, Norway 134Department of Physics, Oxford University, Oxford, United Kingdom 135LPNHE, Sorbonne Universit´e, Universit´e de Paris, CNRS/IN2P3, Paris, France 136Department of Physics, University of Pennsylvania, Philadelphia, Pennsylvania, USA 137Konstantinov Nuclear Physics Institute of National Research Centre “Kurchatov Institute”, PNPI, St. Petersburg, Russia 138Department of Physics and Astronomy, University of Pittsburgh, Pittsburgh, Pennsylvania, USA 139aLaboratório de Instrumentação e Física Experimental de Partículas—LIP, Lisboa, Portugal 139bDepartamento de Física, Faculdade de Ciências, Universidade de Lisboa, Lisboa, Portugal 139cDepartamento de Física, Universidade de Coimbra, Coimbra, Portugal 139dCentro de Física Nuclear da Universidade de Lisboa, Lisboa, Portugal 139eDepartamento de Física, Universidade do Minho, Braga, Portugal 139fDepartamento de Física Teórica y del Cosmos, Universidad de Granada, Granada (Spain), Spain 139gDep Física and CEFITEC of Faculdade de Ciências e Tecnologia, Universidade Nova de Lisboa, Caparica, Portugal 139hInstituto Superior T´ecnico, Universidade de Lisboa, Lisboa, Portugal 140Institute of Physics of the Czech Academy of Sciences, Prague, Czech Republic 141Czech Technical University in Prague, Prague, Czech Republic 142Charles University, Faculty of Mathematics and Physics, Prague, Czech Republic 143Particle Physics Department, Rutherford Appleton Laboratory, Didcot, United Kingdom 144IRFU, CEA, Universit´e Paris-Saclay, Gif-sur-Yvette, France 145Santa Cruz Institute for Particle Physics, University of California Santa Cruz, Santa Cruz, California, USA 146aDepartamento de Física, Pontificia Universidad Católica de Chile, Santiago, Chile 146bUniversidad Andres Bello, Department of Physics, Santiago, Chile 146cInstituto de Alta Investigación, Universidad de Tarapacá, Chile 146dDepartamento de Física, Universidad T´ecnica Federico Santa María, Valparaíso, Chile 147Universidade Federal de São João del Rei (UFSJ), São João del Rei, Brazil 148Department of Physics, University of Washington, Seattle, Washington, USA 149Department of Physics and Astronomy, University of Sheffield, Sheffield, United Kingdom 150Department of Physics, Shinshu University, Nagano, Japan 151Department Physik, Universität Siegen, Siegen, Germany 152Department of Physics, Simon Fraser University, Burnaby, British Columbia, Canada 153SLAC National Accelerator Laboratory, Stanford, California, USA 154Physics Department, Royal Institute of Technology, Stockholm, Sweden 155Departments of Physics and Astronomy, Stony Brook University, Stony Brook, New York, USA 156Department of Physics and Astronomy, University of Sussex, Brighton, United Kingdom 157School of Physics, University of Sydney, Sydney, Australia 158Institute of Physics, Academia Sinica, Taipei, Taiwan 159aE. Andronikashvili Institute of Physics, Iv. Javakhishvili Tbilisi State University, Tbilisi, Georgia 159bHigh Energy Physics Institute, Tbilisi State University, Tbilisi, Georgia 160Department of Physics, Technion, Israel Institute of Technology, Haifa, Israel 161Raymond and Beverly Sackler School of Physics and Astronomy, Tel Aviv University, Tel Aviv, Israel 162Department of Physics, Aristotle University of Thessaloniki, Thessaloniki, Greece 163International Center for Elementary Particle Physics and Department of Physics, University of Tokyo, Tokyo, Japan 164Graduate School of Science and Technology, Tokyo Metropolitan University, Tokyo, Japan 165Department of Physics, Tokyo Institute of Technology, Tokyo, Japan 166Tomsk State University, Tomsk, Russia 167Department of Physics, University of Toronto, Toronto, Ontario, Canada PHYSICAL REVIEW LETTERS 125, 261801 (2020) 261801-20 168aTRIUMF, Vancouver, British Columbia, Canada 168bDepartment of Physics and Astronomy, York University, Toronto, Ontario, Canada 169Division of Physics and Tomonaga Center for the History of the Universe, Faculty of Pure and Applied Sciences, University of Tsukuba, Tsukuba, Japan 170Department of Physics and Astronomy, Tufts University, Medford, Massachusetts, USA 171Department of Physics and Astronomy, University of California Irvine, Irvine, California, USA 172Department of Physics and Astronomy, University of Uppsala, Uppsala, Sweden 173Department of Physics, University of Illinois, Urbana, Illinois, USA 174Instituto de Física Corpuscular (IFIC), Centro Mixto Universidad de Valencia—CSIC, Valencia, Spain 175Department of Physics, University of British Columbia, Vancouver, British Columbia, Canada 176Department of Physics and Astronomy, University of Victoria, Victoria, British Columbia, Canada 177Fakultät für Physik und Astronomie, Julius-Maximilians-Universität Würzburg, Würzburg, Germany 178Department of Physics, University of Warwick, Coventry, United Kingdom 179Waseda University, Tokyo, Japan 180Department of Particle Physics and Astrophysics, Weizmann Institute of Science, Rehovot, Israel 181Department of Physics, University of Wisconsin, Madison, Wisconsin, USA 182Fakultät für Mathematik und Naturwissenschaften, Fachgruppe Physik, Bergische Universität Wuppertal, Wuppertal, Germany 183Department of Physics, Yale University, New Haven, Connecticut, USA aDeceased. bAlso at Department of Physics, King’s College London, London, United Kingdom. cAlso at Instituto de Fisica Teorica, IFT-UAM/CSIC, Madrid, Spain. dAlso at TRIUMF, Vancouver, British Columbia, Canada. eAlso at Department of Physics and Astronomy, University of Louisville, Louisville, Kentucky, USA. fAlso at Physics Department, An-Najah National University, Nablus, Palestine. gAlso at Department of Physics, University of Fribourg, Fribourg, Switzerland. hAlso at Departament de Fisica de la Universitat Autonoma de Barcelona, Barcelona, Spain. iAlso at Moscow Institute of Physics and Technology State University, Dolgoprudny, Russia. jAlso at Department of Physics, Ben Gurion University of the Negev, Beer Sheva, Israel. kAlso at Universita di Napoli Parthenope, Napoli, Italy. lAlso at Institute of Particle Physics (IPP), Canada. mAlso at Department of Physics, St. Petersburg State Polytechnical University, St. Petersburg, Russia. nAlso at Borough of Manhattan Community College, City University of New York, New York, New York, USA. oAlso at Department of Physics, California State University, Fresno, USA. pAlso at Department of Financial and Management Engineering, University of the Aegean, Chios, Greece. qAlso at Centro Studi e Ricerche Enrico Fermi, Italy. rAlso at Department of Physics, California State University, East Bay, USA. sAlso at Institucio Catalana de Recerca i Estudis Avancats, ICREA, Barcelona, Spain. tAlso at Graduate School of Science, Osaka University, Osaka, Japan. uAlso at Physikalisches Institut, Albert-Ludwigs-Universität Freiburg, Freiburg, Germany. vAlso at University of Chinese Academy of Sciences (UCAS), Beijing, China. wAlso at Institute of Physics, Azerbaijan Academy of Sciences, Baku, Azerbaijan. xAlso at CERN, Geneva, Switzerland. yAlso at Joint Institute for Nuclear Research, Dubna, Russia. zAlso at Hellenic Open University, Patras, Greece. aaAlso at Center for High Energy Physics, Peking University, China. bbAlso at The City College of New York, New York, New York, USA. ccAlso at Dipartimento di Matematica, Informatica e Fisica, Universit`a di Udine, Udine, Italy. ddAlso at Department of Physics, California State University, Sacramento, USA. eeAlso at D´epartement de Physique Nucl´eaire et Corpusculaire, Universit´e de Gen`eve, Gen`eve, Switzerland. ffAlso at Institute for Nuclear Research and Nuclear Energy (INRNE) of the Bulgarian Academy of Sciences, Sofia, Bulgaria. ggAlso at Faculty of Physics, M.V. Lomonosov Moscow State University, Moscow, Russia. hhAlso at Institut für Experimentalphysik, Universität Hamburg, Hamburg, Germany. iiAlso at CPPM, Aix-Marseille Universit´e, CNRS/IN2P3, Marseille, France. jjAlso at National Research Nuclear University MEPhI, Moscow, Russia. kkAlso at Institute for Particle and Nuclear Physics, Wigner Research Centre for Physics, Budapest, Hungary. llAlso at Giresun University, Faculty of Engineering, Giresun, Turkey. mmAlso at Department of Physics and Astronomy, Michigan State University, East Lansing, Michigan, USA. PHYSICAL REVIEW LETTERS 125, 261801 (2020) 261801-21