Measurement of the Inelastic Proton-Proton Cross Section at √s=13 TeV with the ATLAS Detector at the LHC

Measurement of the Inelastic Proton-Proton Cross Section at ffiffi s p=13 TeV with the ATLAS Detector at the LHC M. Aaboud et al.* (ATLAS Collaboration) (Received 9 June 2016; published 26 October 2016) This Letter presents a measurement of the inelastic proton-proton cross section using 60 μb−1of pp collisions at a center-of-mass energy ffiffiffi s pof 13 TeV with the ATLAS detector at the LHC. Inelastic interactions are selected using rings of plastic scintillators in the forward region (2.07<jηj<3.86) of the detector. A cross section of 68.11.4mb is measured in the fiducial region ξ¼M2 X=s>10−6, where MXis the larger invariant mass of the two hadronic systems separated by the largest rapidity gap in the event. In this ξrange the scintillators are highly efficient. For diffractive events this corresponds to cases where at least one proton dissociates to a system with MX>13 GeV. The measured cross section is compared with a range of theoretical predictions. When extrapolated to the full phase space, a cross section of 78.12.9mb is measured, consistent with the inelastic cross section increasing with center-of-mass energy. DOI: 10.1103/PhysRevLett.117.182002 The rise of the total proton-proton (pp) cross section with center-of-mass energy ffiffiffi s p, predicted by Heisenberg [1] and observed at the CERN Intersecting Storage Rings [2], probes the nonperturbative regime of quantum chromodynamics (QCD). Arguments based on unitarity, analyticity, and factorization imply an upper bound on the high-energy behavior of total hadronic cross sections that prevents them from rising more rapidly than ln2ðsÞ[3–5]. Many experiments have measured σinel and found an increase with ffiffiffi s p[6]. The TOTEM and ATLAS collaborations determined σinel at ffiffiffi s p¼7and 8 TeV using the optical theorem and a measurement of the elastic cross section with Roman pot detectors [7–11]. Using a variety of alternative techniques, the ATLAS, CMS, ALICE, and LHCb experiments have made measurements of σinel at ffiffiffi s p¼7TeV [12–15] and ffiffiffi s p¼2.76 TeV (ALICE) [14]. The Pierre Auger Collaboration measured the inelastic p-air cross section at ffiffiffi s p¼57 TeV and extracted σinel using the Glauber model [16]. This Letter presents a measurement of the inelastic cross section σinel using pp collisions at ffiffiffi s p¼13 TeV with the ATLAS detector at the Large Hadron Collider (LHC). It is performed using two sets of scintillation counters in a data set corresponding to an integrated luminosity of 60.11.1μb−1collected in June 2015. In inelastic interactions, one or both protons dissociate as a result of colored (nondiffractive) or colorless (diffractive) exchange. The counters are insensitive to elastic pp scattering and diffractive dissociation processes in which neither proton dissociates into a system, X, of mass MX>13 GeV, or equivalently, ξ¼M2 X=s > 10−6. The cross-section measurement is reported in this fiducial region, ξ>10−6, and after extrapolation to the total inelastic cross section using models of inelastic interactions. The ATLAS detector is a cylindrical particle detector composed of several subdetector layers [17]. The inner tracking detector (ID) is immersed in a 2 T magnetic field provided by a superconducting solenoid. Around the tracker is a system of electromagnetic and hadronic calorimeters, which use liquid argon and lead, copper, or tungsten absorber for the electromagnetic and forward (jηj>1.7)[18] hadronic components of the detector, and scintillator-tile active material and steel absorber for the central (jηj<1.7) hadronic component. At z¼3.6m, thin plastic scintillation counters, the minimum-bias trigger scintillators (MBTS), are installed on the front face of each endcap calorimeter. These detectors cover the region 2.07 <jηj<3.86. They are similar to those described in Ref. [17] but were rebuilt during 2014, when the coverage was slightly extended from 2.08 <jηj<3.75 after the ffiffiffi s p¼7TeV run. The MBTS are divided into inner (4 counters in 149 <r<445 mm) and outer (8 counters in 444.5<r<895 mm) octagonal rings. The ATLAS experiment uses a multistage trigger to select events at about 1 kHz for offline analysis. Three trigger configurations were used to collect data for this analysis. The primary triggers use the MBTS detector and constant-fraction discriminators to select events when two proton bunches collide in the detector. To facilitate background studies, data were also collected with the same selection when no proton bunch (“empty”) or a single proton bunch from only one of the two beams (“single *Full author list given at the end of the article. Published by the American Physical Society under the terms of the Creative Commons Attribution 3.0 License. Further distribution of this work must maintain attribution to the author(s) and the published article’s title, journal citation, and DOI. PRL 117, 182002 (2016) PHYSICAL REVIEW LETTERS week ending 28 OCTOBER 2016 0031-9007=16=117(18)=182002(19) 182002-1 © 2016 CERN, for the ATLAS Collaboration beam”) was passing through the center of ATLAS. All of these triggers require at least one MBTS hit above threshold. Two additional triggers were used to collect data to determine the MBTS trigger efficiency, requiring either hits in a forward (5.6<jηj<5.9) Cherenkov detector (LUCID) or a far forward (jηj>8.4) tungsten-scintillator calorimeter detector (LHCf [19]) located at z¼17 m and 140 m, respectively. The LHCf detector is an independent detector, but for the runs considered in this analysis, its trigger signals were incorporated into the ATLAS readout. Monte Carlo (MC) simulation samples were produced to correct the fiducial measurement and to compare to the data. The detector response is modeled using a simulation based on G EANT 4[20–22]. The data and MC simulated events are passed through the same reconstruction and analysis software. The primary MC samples are based on the P YTHIA 8 generator [23,24] either with the A2 [25] set of tuned underlying-event parameters and the MSTW 2008 LO PDF set [26] or with the Monash [27] set of tuned parameters and the NNPDF 2.3 LO PDF set [28]. The samples are divided into four components: single-dissociation (SD, pp →pX), double-dissociation (DD, pp →XY), centraldissociation (CD, pp →pXp), all involving colorless exchange, and nondiffractive dissociation (ND) wherein color flow is present between the two colliding protons. For all dissociation event types, the Monash tune is used. P YTHIA 8 uses a pomeron-based diffraction model [29] to describe colorless exchange with a default pomeron flux model by Schuler and Sjöstrand (SS) [30,31]. Alternative MC samples are generated with the pomeron flux model of Donnachie and Landshoff (DL) [32] and with the minimum-bias Rockefeller (MBR) model [33]. In the DL model, the pomeron Regge trajectory is given by αðtÞ¼1þεþα0t, where εand α0are free parameters. In most samples used for this analysis, the value of α0is 0.25, the P YTHIA 8 default. The εparameter is varied from 0.06 to 0.10 (the P YTHIA 8 default is 0.085). An additional sample produced with α0¼0.35 is found to be statistically consistent with the α0¼0.25 default samples in each aspect of thisanalysis.Therangesofεandα0consideredaremotivated by previous total, inelastic, elastic, and diffractive crosssection measurements, including measurements of lowmass diffraction by the ATLAS and CMS collaborations [34,35]. For the DL and SS models the CD component is neglected. The MBR model is tuned to data as described in Ref. [33] and includes a small CD component. The E POS LHC and QGSJ ET -II event generators are also used to simulate pp collisions. E POS LHC [36] uses a “cut pomeron”model for diffraction and differs significantly from P YTHIA 8 in its modeling of hadronization and the underlying event. QGSJ ET -II [37,38] uses Reggeon field theory to describe pomeron-pomeron interactions. Both E POS LHC and QGSJ ET -II have been developed primarily to model cosmic-ray showering in the atmosphere. The fiducial region of the measurement is determined using MC simulation. In each generated event, the largest rapidity gap between any two final-state hadrons is used to define the boundary between two collections of hadrons. These collections define the dissociation systems in an event-generator-independent manner. The invariant mass of each collection is calculated, and the larger of the two masses, denoted MX, is used to define ξ¼M2 X=s. The variable ξis constrained to be >6×10−9by the elastic limit of m2 p=s where mpis the proton mass. This measurement is restricted to ξ>10−6, the region in which the event selection efficiency exceeds 50%. Two samples of data events passing the MBTS trigger requirements are selected: an inclusive sample and a singlesided sample. The inclusive selection requires at least two MBTS counters with a charge above 0.15 pC (nMBTS ≥2). This threshold is chosen to be well above the electronic noise level of the counters. Requiring two hits rather than one substantially reduces background due to collisioninduced radiation and activation. To constrain the diffractive component of the cross section and reduce the uncertainty in extrapolation to σinel, an additional singlesided selection is defined, requiring hits in at least two counters on one side of the detector and no hits on the other. In the data, 4 159 074 events pass the inclusive selection and 442 192 events pass the single-sided selection. The fiducial cross section is determined by σfid inelðξ>10−6Þ¼N−NBG ϵtrig ×L×1−fξ<10−6 ϵsel ;ð1Þ where Nis the number of observed events passing the inclusive selection, NBG is the number of background events, ϵtrig and ϵsel are factors accounting for the trigger and event selection efficiencies, 1−fξ<10−6accounts for the migration of events with ξ<10−6into the fiducial region, and Lis the integrated luminosity of the sample. Sources of background include interactions between the beam and residual gas in the beam pipe; interactions between the beam and collimators upstream of the detector, which can send charged particles through the detector parallel to the beam; collision-induced radiation; and activation backgrounds. Backgrounds from cosmic rays and instrumental noise are negligible. The mean number of pp collisions in the same LHC bunch crossing was 2.3×10−3for the recorded data set. Thus, the contribution from multiple collisions is also negligible. The beamrelated background components are extracted from single-beam events and dominate the total background. They are normalized by scaling the number of selected singlebeam events by a factor of 37=4×2, accounting for the 37 colliding pairs of bunches and 4 bunches producing the single-beam data in this run. The factor of 2 accounts for the presence of two colliding bunches. The number of protons per bunch producing these single-beam events PRL 117, 182002 (2016) PHYSICAL REVIEW LETTERS week ending 28 OCTOBER 2016 182002-2 agrees with that in the colliding bunches to within 10%. The radiation and activation-induced backgrounds are implicitly part of this background estimate. Doublecounting of these components is removed using estimates from empty events. The total background contributions to the inclusive and single-sided data samples are determined to be 1.2% and 5.8%, respectively. The classification of single-sided events as double-sided due to noise or other backgrounds is estimated to be below 0.1%. A systematic uncertainty of 50% is assigned to the background based on studies of the background composition and the relative contributions of the background components. This uncertainty is treated as fully correlated between the single-sided and inclusive selections. The trigger efficiency for events passing the inclusive selection, ϵtrig, is measured with respect to events selected with the LUCID detector after subtracting the background. A trigger efficiency of 99.7% (97.4%) is measured for the inclusive (single-sided) event sample. In both cases the statistical uncertainty is below 0.1%. The efficiency is also measured with events selected by the LHCf detector and agrees within 0.3% with the LUCID determination. This difference is taken as a systematic uncertainty. The ratio of the number of events passing the singlesided event selection to the number passing the inclusive selection (RSS) is used to adjust, for each model, the fractional contribution of the singleand double-diffractive dissociative cross section (σSD þσDD) to the inelastic cross section, fD¼ðσSD þσDDÞ=σinel [12]. The measured value is RSS ¼10.4% with a total uncertainty of 0.4%. The dominant systematic uncertainty arises from the background subtraction in the single-sided sample. For each MC model, fDis varied until it matches the observed RSS value in data. The data uncertainty is used to set the error in the constrained fDfor each model. An additional uncertainty in the ratio of singleto double-diffractive events is determined by taking the diffractive events to be entirely SD or to be evenly divided between SD and DD. Using this method, the fitted fDin the P YTHIA 8 samples is between 25% and 31%, depending on the model (the default value is 28%). For the QGSJ ET -II (E POS LHC) model the fitted fDis 35% (37%), differing significantly from the default value of 21% (28%). The observed RSS and the MC predictions of its dependence on fDare shown in Fig. 1. The fitted fDis used when determining the acceptance corrections ϵsel and fξ<10−6for each model. In Fig. 2the nMBTS distributions in data are compared to the ones from MC simulated samples utilizing the fitted fD values for both the inclusive and single-sided selections. The estimated background is subtracted from the measured distribution, and the trigger efficiency measured in data is applied to the simulation. The data distributions and MC simulation are peaked at high multiplicity values. In the single-sided case, nMBTS ¼12 corresponds to hits in all counters on one side of the detector. The data agree best with the DL models, particularly in the low-nMBTS range. The MBR-based distribution provides a slightly worse description of the data. The P YTHIA 8 sample using the SS model does not describe data well in the lowmultiplicity region. E POS LHC and QGSJ ET -II also do not describe the data well, particularly in the single-sided hit multiplicity distribution. Therefore, the P YTHIA 8 DL model with ε¼0.085 is chosen as the nominal MC model for the ϵsel and fξ<10−6corrections, and only the DL and MBR models are considered for systematic uncertainties related to the MC corrections. The event selection efficiency, ϵsel, depends upon the MBTS counter sensitivity. This sensitivity is tested using isolated charged particles, reconstructed as ID tracks in the region 2.07 <jηj<2.5where the coverages of the MBTS and ID overlap. Over the full coverage of the MBTS counters, the calorimeter is used to measure the counter efficiency with respect to particles that deposit sufficient energy in the calorimeter to seed a topological energy cluster [39]. Differences between the efficiencies in data and MC simulation are accounted for by adjusting the MBTS charge threshold in MC simulation until the simulated efficiencies match those observed in the data. The residual uncertainty in the counter efficiency after these corrections is 0.5% for the outer and 1.0% for the inner counters. Additionally, an uncertainty arising from the knowledge of the material in front of the MBTS detector is estimated using MC samples with an increased amount of material in front of the MBTS. Based on the MC samples, the uncertainty in the efficiency measurement due to modeling of hadronization and the underlying event is estimated to be negligible. After adjusting the counter charge threshold, ϵsel is determined from the nominal P YTHIA 8 DL MC simulations, using the fitted fDcorresponding to this model, to be 99.34% with a statistical uncertainty of 0.03%. The uncertainty in the MBTS counter efficiencies results in D f 0.1 0.15 0.2 0.25 0.3 0.35 0.4 SS R 0.04 0.06 0.08 0.1 0.12 0.14 0.16 0.18 Data 2015 Pythia8 SS =0.085 ε Pythia8 DL, =0.060 ε Pythia8 DL, =0.10 ε Pythia8 DL, Pythia8 MBR EPOS LHC QGSJET-II ATLAS -1 bμ=13 TeV, L=60.1 s FIG. 1. The ratio of the number of single-sided to inclusive events (RSS) as a function of the fraction of the cross section that is diffractive according to each model (fD). The default value of fDin each model is shown with a marker. PRL 117, 182002 (2016) PHYSICAL REVIEW LETTERS week ending 28 OCTOBER 2016 182002-3 only a 0.1% uncertainty in the overall event selection efficiency, because many counters are hit in typical events. In addition, an uncertainty of 0.2% in ϵsel arises from the knowledge of the material in front of the MBTS. The fraction of events passing the inclusive selection with ξ<10−6represents an additional background component in the fiducial cross-section measurement. It is determined using the same P YTHIA 8DLMC to be fξ<10−6¼ð1.37 0.05Þ%, where the uncertainty is statistical. Because the efficiency and migration corrections are correlated, they are combined in a single correction factor, CMC ¼ð1−fξ<10−6Þ=ϵsel, for which systematic uncertainties are assessed. The systematic uncertainties include the counter efficiency variations, the impact of the material uncertainty, the uncertainty in the fitted value of fD, and the variation in CMC found by comparing the P YTHIA 8DL and MBR models. Of these sources of uncertainty, the last is most important at 0.5%. The value of CMC is ð99.30.5Þ%. The uncertainty also implicitly contains an uncertainty due to the CD contribution, since this is included in only some of the models. The uncertainty in the integrated luminosity is 1.9%.It is derived, following a methodology similar to that detailed in Refs. [40,41], from a calibration of the luminosity scale using x-ybeam-separation scans performed in August 2015. This calibration uncertainty is slightly smaller than what has been reported in Ref. [42] because the lowluminosity data set used in this Letter is not affected by the uncertainties related to high-luminosity runs. The components of the fiducial cross-section calculation [Eq. (1)] are shown in Table Iwith their systematic uncertainties. The statistical uncertainties are negligible. The measured fiducial cross section is determined to be σfid inel ¼68.10.6ðexpÞ1.3ðlumÞmb; where the first uncertainty refers to all experimental uncertainties apart from the luminosity and the second refers to the luminosity only. The P YTHIA 8 DL model predicts values of 71.0 mb, 69.1 mb, and 68.1 mb for ε¼0.06, 0.085, and 0.10, respectively, all of which are compatible with the measurement. The P YTHIA 8 MBR model predicts 70.1 mb, also in agreement with the measurement. The E POS LHC (71.2 mb) and QGSJ ET -II (72.7 mb) predictions exceed the data by 2–3σ. The P YTHIA 8 SS model predicts 74.4 mb, and thus exceeds the measured value by ∼4σ. The extrapolation to σinel uses constraints from previous ATLAS measurements to minimize the model dependence of the component that falls outside the fiducial region. σinel can be written as σinel ¼σfid inel þσ7TeVðξ<5×10−6Þ ×σMCðξ<10−6Þ σ7TeV;MC ðξ<5×10−6Þ:ð2Þ The term σ7TeVðξ<5×10−6Þ¼σ7TeV inel −σ7TeVðξ> 5×10−6Þ¼9.92.4mb is the difference between σinel TABLE I. Inputs to the calculation of the measured cross section and their systematic uncertainties. Factor Value Relative uncertainty Number of events passing the inclusive selection (N) 4 159 074  Number of background events (NBG) 51 187 50% Integrated luminosity [μb−1](L) 60.1 1.9% Trigger efficiency (ϵtrig) 99.7% 0.3% MC correction factor (CMC) 99.3% 0.5% MBTS nd events n d events n 1 2− 10 1− 10 1 Data Pythia8 SS = 0.06 ε Pythia8 DL, = 0.085 ε Pythia8 DL, = 0.10 ε Pythia8 DL, MBR EPOS LHC QGSJET-II ATLAS -1 bμ13 TeV, 60.1 Inclusive selection MBTS n 2 4 6 8 1012141618202224 MC/data 0.5 1 1.5 MBTS nd events nd events n 1 1− 10 Data Pythia8 SS = 0.06 ε Pythia8 DL, = 0.085 ε Pythia8 DL, = 0.10 ε Pythia8 DL, MBR EPOS LHC QGSJET-II ATLAS -1 bμ13 TeV, 60.1 Single-sided selection MBTS n 2 4 6 8 10 12 MC/data 0.5 1 1.5 FIG. 2. The background-subtracted distribution of the number of MBTS counters (nMBTS) above threshold in data and MC simulation for (top) the inclusive selection and (bottom) the single-sided selection. The ratio of the MC models to the data is also shown. The experimental uncertainty is shown as a shaded band around the data points. The models shown here use the fD value determined from the RSS measurement. PRL 117, 182002 (2016) PHYSICAL REVIEW LETTERS week ending 28 OCTOBER 2016 182002-4 measured at 7 TeVusing the ALFA detector [8],σ7TeV inel , and σinel measured at 7 TeV for ξ>5×10−6using the MBTS [12] (The 7 TeV result is corrected upward by 1.9% following an improved luminosity calibration [40]). The uncertainties of the two measurements are uncorrelated. The P YTHIA 8 DL and P YTHIA 8 MBR MC samples are used to assess the systematic uncertainty in the MC-derived ratio of cross sections in Eq. (2), which is determined to be 1.015 0.081. (The value of the ratio arises from an approximately 20% increased cross section from increasing ffiffiffi s pwhich is largely compensated by a 15% decrease due to the change in the ξdistribution.) These models also agree with the measurement of σ7TeVðξ<5×10−6Þto within 2σ. The measured value for σinel is σinel ¼78.10.6ðexpÞ1.3ðlumÞ2.6ðextrapÞmb: This and other inelastic cross-section measurements are compared to several Monte Carlo models in Fig. 3. Additional predictions range between 76.6 and 81.6 mb [43–47]. Compared to the measurement with the ALFA detector at ffiffiffi s p¼7TeV the cross section is higher by ð94Þ%. In summary, a measurement of the inelastic cross section in 60 μb−1of proton-proton collision data at ffiffiffi s p¼13 TeV collected with the ATLAS detector at the LHC is presented. The measurement is performed in a fiducial region ξ>10−6, and the result is extrapolated to the inelastic cross section using measurements at ffiffiffi s p¼7TeV. The measured cross section agrees well with a variety of theoretical predictions and is consistent with the inelastic cross section increasing with center-of-mass energy, as observed at lower energies. We thank CERN for the very successful operation of the LHC,aswellasthesupportstafffromourinstitutionswithout 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; CONICYT, Chile; CAS, MOST and NSFC, China; COLCIENCIAS, Colombia; MSMT CR, MPO CR and VSC CR, Czech Republic; DNRF and DNSRC, Denmark; IN2P3-CNRS, CEA-DSM/IRFU, France; GNSF, Georgia; BMBF, HGF, and MPG, Germany; GSRT, Greece; RGC, Hong Kong SAR, China; ISF, I-CORE and Benoziyo Center, Israel; INFN, Italy; MEXT and JSPS, Japan; CNRST, Morocco; FOM and NWO, Netherlands; RCN, Norway; MNiSW and NCN, Poland; FCT, Portugal; MNE/IFA, Romania; MES of Russia and NRC KI, Russian Federation; JINR; MESTD, Serbia; MSSR, Slovakia; ARRS and MIZŠ, Slovenia; DST/ NRF, South Africa; MINECO, 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, United States of America. In addition, individual groups and members have received support from BCKDF, the Canada Council, CANARIE, CRC, Compute Canada, FQRNT, and the Ontario Innovation Trust, Canada; EPLANET, ERC, FP7, Horizon 2020 and Marie Skłodowska-Curie Actions, European Union; Investissements d’Avenir Labex and Idex, ANR, Région Auvergne and Fondation Partager le Savoir, France; DFG and AvH Foundation, Germany; Herakleitos, Thales and Aristeia programmes co-financed by EU-ESF and the Greek NSRF; BSF, GIF and Minerva, Israel; BRF, Norway; Generalitat de Catalunya, Generalitat Valenciana, Spain; the Royal Society and Leverhulme Trust, United Kingdom. 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Drechsler,56 M. Dris,10 Y. Du,35d J. Duarte-Campderros,153 E. Duchovni,171 G. Duckeck,100 O. A. Ducu,95,n D. Duda,107 A. Dudarev,32 A. Chr. Dudder,84 E. M. Duffield,16 L. Duflot,117 M. Dührssen,32 M. Dumancic,171 M. Dunford,59a H. Duran Yildiz,4a M. Düren,54 A. Durglishvili,53b D. Duschinger,46 B. Dutta,44 M. Dyndal,44 C. Eckardt,44 K. M. Ecker,101 R. C. Edgar,90 N. C. Edwards,48 T. Eifert,32 G. Eigen,15 K. Einsweiler,16 T. Ekelof,164 M. El Kacimi,135c V. Ellajosyula,86 M. Ellert,164 S. Elles,5F. Ellinghaus,174 A. A. Elliot,168 N. Ellis,32 J. Elmsheuser,27 M. Elsing,32 D. Emeliyanov,131 Y. Enari,155 O. C. Endner,84 J. S. Ennis,169 J. Erdmann,45 A. Ereditato,18 G. Ernis,174 J. Ernst,2M. Ernst,27 S. Errede,165 E. Ertel,84 M. Escalier,117 H. Esch,45 C. Escobar,125 B. Esposito,49 A. I. Etienvre,136 E. Etzion,153 H. Evans,62 A. Ezhilov,123 F. Fabbri,22a,22b L. Fabbri,22a,22b G. Facini,33 R. M. Fakhrutdinov,130 S. Falciano,132a R. J. Falla,79 J. Faltova,32 Y. Fang,35a M. Fanti,92a,92b A. Farbin,8A. Farilla,134a C. Farina,125 E. M. Farina,121a,121b T. Farooque,13 S. Farrell,16 S. M. Farrington,169 P. Farthouat,32 F. Fassi,135e P. Fassnacht,32 D. Fassouliotis,9M. Faucci Giannelli,78 A. Favareto,52a,52b W. J. Fawcett,120 L. Fayard,117 O. L. Fedin,123,o W. Fedorko,167 S. Feigl,119 L. Feligioni,86 C. Feng,35d E. J. Feng,32 H. Feng,90 A. B. Fenyuk,130 L. Feremenga,8P. Fernandez Martinez,166 S. Fernandez Perez,13 J. Ferrando,55 A. Ferrari,164 P. Ferrari,107 R. Ferrari,121a D. E. Ferreira de Lima,59b A. Ferrer,166 D. Ferrere,51 C. Ferretti,90 A. Ferretto Parodi,52a,52b F. Fiedler,84 A. Filipčič,76 M. Filipuzzi,44 F. Filthaut,106 M. Fincke-Keeler,168 K. D. Finelli,150 M. C. N. Fiolhais,126a,126c L. Fiorini,166 A. Firan,42 A. Fischer,2C. Fischer,13 J. Fischer,174 W. C. Fisher,91 N. Flaschel,44 I. Fleck,141 P. Fleischmann,90 G. T. Fletcher,139 R. R. M. Fletcher,122 T. Flick,174 A. Floderus,82 L. R. Flores Castillo,61a M. J. Flowerdew,101 G. T. Forcolin,85 A. Formica,136 A. Forti,85 A. G. Foster,19 D. Fournier,117 H. Fox,73 S. Fracchia,13 P. Francavilla,81 M. Franchini,22a,22b D. Francis,32 L. Franconi,119 M. Franklin,58 M. Frate,162 M. Fraternali,121a,121b D. Freeborn,79 S. M. Fressard-Batraneanu,32 F. Friedrich,46 D. Froidevaux,32 J. A. Frost,120 C. Fukunaga,156 E. Fullana Torregrosa,84 T. Fusayasu,102 J. Fuster,166 C. Gabaldon,57 O. Gabizon,174 A. Gabrielli,22a,22b A. Gabrielli,16 G. P. Gach,40a S. Gadatsch,32 S. Gadomski,51 G. Gagliardi,52a,52b L. G. Gagnon,95 P. Gagnon,62 C. Galea,106 B. Galhardo,126a,126c E. J. Gallas,120 B. J. Gallop,131 P. Gallus,128 G. Galster,38 K. K. Gan,111 J. Gao,35b,86 Y. Gao,48 Y. S. Gao,143,g F. M. Garay Walls,48 C. García,166 J. E. García Navarro,166 M. Garcia-Sciveres,16 R. W. Gardner,33 N. Garelli,143 V. Garonne,119 A. Gascon Bravo,44 K. Gasnikova,44 C. Gatti,49 A. Gaudiello,52a,52b G. Gaudio,121a L. Gauthier,95 I. L. Gavrilenko,96 C. Gay,167 G. Gaycken,23 E. N. Gazis,10 Z. Gecse,167 C. N. P. Gee,131 Ch. Geich-Gimbel,23 M. Geisen,84 M. P. Geisler,59a C. Gemme,52a M. H. Genest,57 C. Geng,35b,p S. Gentile,132a,132b C. Gentsos,154 S. George,78 D. Gerbaudo,13 A. Gershon,153 S. Ghasemi,141 H. Ghazlane,135b M. Ghneimat,23 B. Giacobbe,22a S. Giagu,132a,132b P. Giannetti,124a,124b B. Gibbard,27 S. M. Gibson,78 M. Gignac,167 M. Gilchriese,16 T. P. S. Gillam,30 D. Gillberg,31 G. Gilles,174 D. M. Gingrich,3,e N. Giokaris,9M. P. Giordani,163a,163c F. M. Giorgi,22a F. M. Giorgi,17 P. F. Giraud,136 P. Giromini,58 D. Giugni,92a F. Giuli,120 C. Giuliani,101 M. Giulini,59b B. K. Gjelsten,119 S. Gkaitatzis,154 I. Gkialas,154 E. L. Gkougkousis,117 L. K. Gladilin,99 C. Glasman,83 J. Glatzer,50 P. C. F. Glaysher,48 A. Glazov,44 M. Goblirsch-Kolb,25 J. Godlewski,41 S. Goldfarb,89 T. Golling,51 D. Golubkov,130 A. Gomes,126a,126b,126d R. Gonçalo,126a J. Goncalves Pinto Firmino Da Costa,136 G. Gonella,50 L. Gonella,19 A. Gongadze,66 S. González de la Hoz,166 G. Gonzalez Parra,13 S. Gonzalez-Sevilla,51 L. Goossens,32 P. A. Gorbounov,97 H. A. Gordon,27 I. Gorelov,105 B. Gorini,32 E. Gorini,74a,74b A. Gorišek,76 E. Gornicki,41 A. T. Goshaw,47 C. Gössling,45 M. I. Gostkin,66 C. R. Goudet,117 D. Goujdami,135c A. G. Goussiou,138 N. Govender,145b,q E. Gozani,152 L. Graber,56 I. Grabowska-Bold,40a P. O. J. Gradin,57 P. Grafström,22a,22b J. Gramling,51 E. Gramstad,119 S. Grancagnolo,17 V. Gratchev,123 P. M. Gravila,28e H. M. Gray,32 E. Graziani,134a Z. D. Greenwood,80,r C. Grefe,23 K. Gregersen,79 I. M. Gregor,44 P. Grenier,143 K. Grevtsov,5J. Griffiths,8 A. A. Grillo,137 K. Grimm,73 S. Grinstein,13,s Ph. Gris,36 J.-F. Grivaz,117 S. Groh,84 J. P. Grohs,46 E. Gross,171 J. Grosse-Knetter,56 G. C. Grossi,80 Z. J. Grout,79 L. Guan,90 W. Guan,172 J. Guenther,63 F. Guescini,51 D. Guest,162 O. Gueta,153 E. Guido,52a,52b T. Guillemin,5S. Guindon,2U. Gul,55 C. Gumpert,32 J. Guo,35e Y. Guo,35b,p R. Gupta,42 S. Gupta,120 G. Gustavino,132a,132b P. Gutierrez,113 N. G. Gutierrez Ortiz,79 C. Gutschow,46 C. Guyot,136 C. Gwenlan,120 PRL 117, 182002 (2016) PHYSICAL REVIEW LETTERS week ending 28 OCTOBER 2016 182002-9 35dSchool of Physics, Shandong University, Shandong, China 35eDepartment of Physics and Astronomy, Shanghai Key Laboratory for Particle Physics and Cosmology, Shanghai Jiao Tong University, Shanghai; (also affiliated with PKU-CHEP), China 35fPhysics Department, Tsinghua University, Beijing 100084, China 36Laboratoire de Physique Corpusculaire, Clermont Université and Université Blaise Pascal and CNRS/IN2P3, Clermont-Ferrand, France 37Nevis Laboratory, Columbia University, Irvington, New York, USA 38Niels Bohr Institute, University of Copenhagen, Kobenhavn, Denmark 39aINFN Gruppo Collegato di Cosenza, Laboratori Nazionali di Frascati, Italy 39bDipartimento di Fisica, Università della Calabria, Rende, Italy 40aAGH University of Science and Technology, Faculty of Physics and Applied Computer Science, Krakow, Poland 40bMarian Smoluchowski Institute of Physics, Jagiellonian University, Krakow, Poland 41Institute of Nuclear Physics Polish Academy of Sciences, Krakow, Poland 42Physics Department, Southern Methodist University, Dallas, Texas, USA 43Physics Department, University of Texas at Dallas, Richardson, Texas, USA 44DESY, Hamburg and Zeuthen, Germany 45Lehrstuhl für Experimentelle Physik IV, Technische Universität Dortmund, Dortmund, Germany 46Institut für Kernund Teilchenphysik, Technische Universität Dresden, Dresden, Germany 47Department of Physics, Duke University, Durham, North Carolina, USA 48SUPA—School of Physics and Astronomy, University of Edinburgh, Edinburgh, United Kingdom 49INFN Laboratori Nazionali di Frascati, Frascati, Italy 50Fakultät für Mathematik und Physik, Albert-Ludwigs-Universität, Freiburg, Germany 51Section de Physique, Université de Genève, Geneva, Switzerland 52aINFN Sezione di Genova, Italy 52bDipartimento di Fisica, Università di Genova, Genova, Italy 53aE. Andronikashvili Institute of Physics, Iv. Javakhishvili Tbilisi State University, Tbilisi, Georgia 53bHigh Energy Physics Institute, Tbilisi State University, Tbilisi, Georgia 54II Physikalisches Institut, Justus-Liebig-Universität Giessen, Giessen, Germany 55SUPA—School of Physics and Astronomy, University of Glasgow, Glasgow, United Kingdom 56II Physikalisches Institut, Georg-August-Universität, Göttingen, Germany 57Laboratoire de Physique Subatomique et de Cosmologie, Université Grenoble-Alpes, CNRS/IN2P3, Grenoble, France 58Laboratory for Particle Physics and Cosmology, Harvard University, Cambridge, Massachusetts, USA 59aKirchhoff-Institut für Physik, Ruprecht-Karls-Universität Heidelberg, Heidelberg, Germany 59bPhysikalisches Institut, Ruprecht-Karls-Universität Heidelberg, Heidelberg, Germany 59cZITI Institut für technische Informatik, Ruprecht-Karls-Universität Heidelberg, Mannheim, Germany 60Faculty of Applied Information Science, Hiroshima Institute of Technology, Hiroshima, Japan 61aDepartment of Physics, The Chinese University of Hong Kong, Shatin, N.T., Hong Kong, China 61bDepartment of Physics, The University of Hong Kong, Hong Kong, China 61cDepartment of Physics, The Hong Kong University of Science and Technology, Clear Water Bay, Kowloon, Hong Kong, China 62Department of Physics, Indiana University, Bloomington, Indiana, USA 63Institut für Astround Teilchenphysik, Leopold-Franzens-Universität, Innsbruck, Austria 64University of Iowa, Iowa City, Iowa, USA 65Department of Physics and Astronomy, Iowa State University, Ames, Iowa, USA 66Joint Institute for Nuclear Research, JINR Dubna, Dubna, Russia 67KEK, High Energy Accelerator Research Organization, Tsukuba, Japan 68Graduate School of Science, Kobe University, Kobe, Japan 69Faculty of Science, Kyoto University, Kyoto, Japan 70Kyoto University of Education, Kyoto, Japan 71Department of Physics, Kyushu University, Fukuoka, Japan 72Instituto de Física La Plata, Universidad Nacional de La Plata and CONICET, La Plata, Argentina 73Physics Department, Lancaster University, Lancaster, United Kingdom 74aINFN Sezione di Lecce, Italy 74bDipartimento di Matematica e Fisica, Università del Salento, Lecce, Italy 75Oliver Lodge Laboratory, University of Liverpool, Liverpool, United Kingdom 76Department of Physics, Jožef Stefan Institute and University of Ljubljana, Ljubljana, Slovenia 77School of Physics and Astronomy, Queen Mary University of London, London, United Kingdom 78Department of Physics, Royal Holloway University of London, Surrey, United Kingdom 79Department of Physics and Astronomy, University College London, London, United Kingdom 80Louisiana Tech University, Ruston, Los Angeles, USA 81Laboratoire de Physique Nucléaire et de Hautes Energies, UPMC and Université Paris-Diderot and CNRS/IN2P3, Paris, France PRL 117, 182002 (2016) PHYSICAL REVIEW LETTERS week ending 28 OCTOBER 2016 182002-16 82Fysiska institutionen, Lunds universitet, Lund, Sweden 83Departamento de Fisica Teorica C-15, Universidad Autonoma de Madrid, Madrid, Spain 84Institut für Physik, Universität Mainz, Mainz, Germany 85School of Physics and Astronomy, University of Manchester, Manchester, United Kingdom 86CPPM, Aix-Marseille Université and CNRS/IN2P3, Marseille, France 87Department of Physics, University of Massachusetts, Amherst, Massachusetts, USA 88Department of Physics, McGill University, Montreal, QC, Canada 89School of Physics, University of Melbourne, Victoria, Australia 90Department of Physics, The University of Michigan, Ann Arbor, Michigan, USA 91Department of Physics and Astronomy, Michigan State University, East Lansing, Michigan, USA 92aINFN Sezione di Milano, Italy 92bDipartimento di Fisica, Università di Milano, Milano, Italy 93B.I. Stepanov Institute of Physics, National Academy of Sciences of Belarus, Minsk, Republic of Belarus 94National Scientific and Educational Centre for Particle and High Energy Physics, Minsk, Republic of Belarus 95Group of Particle Physics, University of Montreal, Montreal, QC, Canada 96P.N. Lebedev Physical Institute of the Russian Academy of Sciences, Moscow, Russia 97Institute for Theoretical and Experimental Physics (ITEP), Moscow, Russia 98National Research Nuclear University MEPhI, Moscow, Russia 99D.V. Skobeltsyn Institute of Nuclear Physics, M.V. Lomonosov Moscow State University, Moscow, Russia 100Fakultät für Physik, Ludwig-Maximilians-Universität München, München, Germany 101Max-Planck-Institut für Physik (Werner-Heisenberg-Institut), München, Germany 102Nagasaki Institute of Applied Science, Nagasaki, Japan 103Graduate School of Science and Kobayashi-Maskawa Institute, Nagoya University, Nagoya, Japan 104aINFN Sezione di Napoli, Italy 104bDipartimento di Fisica, Università di Napoli, Napoli, Italy 105Department of Physics and Astronomy, University of New Mexico, Albuquerque, New Mexico, USA 106Institute for Mathematics, Astrophysics and Particle Physics, Radboud University Nijmegen/Nikhef, Nijmegen, Netherlands 107Nikhef National Institute for Subatomic Physics and University of Amsterdam, Amsterdam, Netherlands 108Department of Physics, Northern Illinois University, DeKalb, Illinois, USA 109Budker Institute of Nuclear Physics, SB RAS, Novosibirsk, Russia 110Department of Physics, New York University, New York, New York, USA 111Ohio State University, Columbus, Ohio, USA 112Faculty of Science, Okayama University, Okayama, Japan 113Homer L. Dodge Department of Physics and Astronomy, University of Oklahoma, Norman, Oklahoma, USA 114Department of Physics, Oklahoma State University, Stillwater, Oklahoma, USA 115Palacký University, RCPTM, Olomouc, Czech Republic 116Center for High Energy Physics, University of Oregon, Eugene, Oregon, USA 117LAL, Univ. Paris-Sud, CNRS/IN2P3, Université Paris-Saclay, Orsay, France 118Graduate School of Science, Osaka University, Osaka, Japan 119Department of Physics, University of Oslo, Oslo, Norway 120Department of Physics, Oxford University, Oxford, United Kingdom 121aINFN Sezione di Pavia, Italy 121bDipartimento di Fisica, Università di Pavia, Pavia, Italy 122Department of Physics, University of Pennsylvania, Philadelphia, Pennsylvania, USA 123National Research Centre “Kurchatov Institute”B.P.Konstantinov Petersburg Nuclear Physics Institute, St. Petersburg, Russia 124aINFN Sezione di Pisa, Italy 124bDipartimento di Fisica E. Fermi, Università di Pisa, Pisa, Italy 125Department of Physics and Astronomy, University of Pittsburgh, Pittsburgh, Pennsylvania, USA 126aLaboratório de Instrumentação e Física Experimental de Partículas—LIP, Lisboa, Portugal 126bFaculdade de Ciências, Universidade de Lisboa, Lisboa, Portugal 126cDepartment of Physics, University of Coimbra, Coimbra, Portugal 126dCentro de Física Nuclear da Universidade de Lisboa, Lisboa, Portugal 126eDepartamento de Fisica, Universidade do Minho, Braga, Portugal 126fDepartamento de Fisica Teorica y del Cosmos and CAFPE, Universidad de Granada, Granada, Spain 126gDep Fisica and CEFITEC of Faculdade de Ciencias e Tecnologia, Universidade Nova de Lisboa, Caparica, Portugal 127Institute of Physics, Academy of Sciences of the Czech Republic, Praha, Czech Republic 128Czech Technical University in Prague, Praha, Czech Republic 129Faculty of Mathematics and Physics, Charles University in Prague, Praha, Czech Republic 130State Research Center Institute for High Energy Physics (Protvino), NRC KI, Russia 131Particle Physics Department, Rutherford Appleton Laboratory, Didcot, United Kingdom PRL 117, 182002 (2016) PHYSICAL REVIEW LETTERS week ending 28 OCTOBER 2016 182002-17 132aINFN Sezione di Roma, Italy 132bDipartimento di Fisica, Sapienza Università di Roma, Roma, Italy 133aINFN Sezione di Roma Tor Vergata, Italy 133bDipartimento di Fisica, Università di Roma Tor Vergata, Roma, Italy 134aINFN Sezione di Roma Tre, Italy 134bDipartimento di Matematica e Fisica, Università Roma Tre, Roma, Italy 135aFaculté des Sciences Ain Chock, Réseau Universitaire de Physique des Hautes Energies—Université Hassan II, Casablanca, Morocco 135bCentre National de l’Energie des Sciences Techniques Nucleaires, Rabat, Morocco 135cFaculté des Sciences Semlalia, Université Cadi Ayyad, LPHEA-Marrakech, Morocco 135dFaculté des Sciences, Université Mohamed Premier and LPTPM, Oujda, Morocco 135eFaculté des sciences, Université Mohammed V, Rabat, Morocco 136DSM/IRFU (Institut de Recherches sur les Lois Fondamentales de l’Univers), CEA Saclay (Commissariat à l’Energie Atomique et aux Energies Alternatives), Gif-sur-Yvette, France 137Santa Cruz Institute for Particle Physics, University of California Santa Cruz, Santa Cruz, California, USA 138Department of Physics, University of Washington, Seattle, Washington, USA 139Department of Physics and Astronomy, University of Sheffield, Sheffield, United Kingdom 140Department of Physics, Shinshu University, Nagano, Japan 141Fachbereich Physik, Universität Siegen, Siegen, Germany 142Department of Physics, Simon Fraser University, Burnaby, BC, Canada 143SLAC National Accelerator Laboratory, Stanford, California, USA 144aFaculty of Mathematics, Physics & Informatics, Comenius University, Bratislava, Slovak Republic 144bDepartment of Subnuclear Physics, Institute of Experimental Physics of the Slovak Academy of Sciences, Kosice, Slovak Republic 145aDepartment of Physics, University of Cape Town, Cape Town, South Africa 145bDepartment of Physics, University of Johannesburg, Johannesburg, South Africa 145cSchool of Physics, University of the Witwatersrand, Johannesburg, South Africa 146aDepartment of Physics, Stockholm University, Sweden 146bThe Oskar Klein Centre, Stockholm, Sweden 147Physics Department, Royal Institute of Technology, Stockholm, Sweden 148Departments of Physics & Astronomy and Chemistry, Stony Brook University, Stony Brook, New York, USA 149Department of Physics and Astronomy, University of Sussex, Brighton, United Kingdom 150School of Physics, University of Sydney, Sydney, Australia 151Institute of Physics, Academia Sinica, Taipei, Taiwan 152Department of Physics, Technion: Israel Institute of Technology, Haifa, Israel 153Raymond and Beverly Sackler School of Physics and Astronomy, Tel Aviv University, Tel Aviv, Israel 154Department of Physics, Aristotle University of Thessaloniki, Thessaloniki, Greece 155International Center for Elementary Particle Physics and Department of Physics, The University of Tokyo, Tokyo, Japan 156Graduate School of Science and Technology, Tokyo Metropolitan University, Tokyo, Japan 157Department of Physics, Tokyo Institute of Technology, Tokyo, Japan 158Department of Physics, University of Toronto, Toronto, ON, Canada 159aTRIUMF, Vancouver, BC, Canada 159bDepartment of Physics and Astronomy, York University, Toronto, ON, Canada 160Faculty of Pure and Applied Sciences, and Center for Integrated Research in Fundamental Science and Engineering, University of Tsukuba, Tsukuba, Japan 161Department of Physics and Astronomy, Tufts University, Medford, Massachusetts, USA 162Department of Physics and Astronomy, University of California Irvine, Irvine, California, USA 163aINFN Gruppo Collegato di Udine, Sezione di Trieste, Udine, Italy 163bICTP, Trieste, Italy 163cDipartimento di Chimica, Fisica e Ambiente, Università di Udine, Udine, Italy 164Department of Physics and Astronomy, University of Uppsala, Uppsala, Sweden 165Department of Physics, University of Illinois, Urbana, Illinois, USA 166Instituto de Fisica Corpuscular (IFIC) and Departamento de Fisica Atomica, Molecular y Nuclear and Departamento de Ingeniería Electrónica and Instituto de Microelectrónica de Barcelona (IMB-CNM), University of Valencia and CSIC, Valencia, Spain 167Department of Physics, University of British Columbia, Vancouver, BC, Canada 168Department of Physics and Astronomy, University of Victoria, Victoria, BC, Canada 169Department of Physics, University of Warwick, Coventry, United Kingdom 170Waseda University, Tokyo, Japan 171Department of Particle Physics, The Weizmann Institute of Science, Rehovot, Israel 172Department of Physics, University of Wisconsin, Madison, Wisconsin, USA 173Fakultät für Physik und Astronomie, Julius-Maximilians-Universität, Würzburg, Germany PRL 117, 182002 (2016) PHYSICAL REVIEW LETTERS week ending 28 OCTOBER 2016 182002-18 174Fakultät für Mathematik und Naturwissenschaften, Fachgruppe Physik, Bergische Universität Wuppertal, Wuppertal, Germany 175Department of Physics, Yale University, New Haven, Connecticut, USA 176Yerevan Physics Institute, Yerevan, Armenia 177Centre de Calcul de l’Institut National de Physique Nucléaire et de Physique des Particules (IN2P3), Villeurbanne, France aDeceased. bAlso at Department of Physics, King’s College London, London, United Kingdom. cAlso at Institute of Physics, Azerbaijan Academy of Sciences, Baku, Azerbaijan. dAlso at Novosibirsk State University, Novosibirsk, Russia. eAlso at TRIUMF, Vancouver BC, Canada. fAlso at Department of Physics & Astronomy, University of Louisville, Louisville, KY, USA. gAlso at Department of Physics, California State University, Fresno, CA, USA. hAlso at Department of Physics, University of Fribourg, Fribourg, Switzerland. iAlso at Departament de Fisica de la Universitat Autonoma de Barcelona, Barcelona, Spain. jAlso at Departamento de Fisica e Astronomia, Faculdade de Ciencias, Universidade do Porto, Portugal. kAlso at Tomsk State University, Tomsk, Russia. lAlso at Universita di Napoli Parthenope, Napoli, Italy. mAlso at Institute of Particle Physics (IPP), Canada. nAlso at National Institute of Physics and Nuclear Engineering, Bucharest, Romania. oAlso at Department of Physics, St. Petersburg State Polytechnical University, St. Petersburg, Russia. pAlso at Department of Physics, The University of Michigan, Ann Arbor, MI, USA. qAlso at Centre for High Performance Computing, CSIR Campus, Rosebank, Cape Town, South Africa. rAlso at Louisiana Tech University, Ruston, LA, 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 Department of Physics, National Tsing Hua University, Taiwan. vAlso at Institute for Mathematics, Astrophysics and Particle Physics, Radboud University Nijmegen/Nikhef, Nijmegen, Netherlands. wAlso at Department of Physics, The University of Texas at Austin, Austin, TX, USA. xAlso at Institute of Theoretical Physics, Ilia State University, Tbilisi, Georgia. yAlso at CERN, Geneva, Switzerland. zAlso at Georgian Technical University (GTU), Tbilisi, Georgia. aaAlso at Ochadai Academic Production, Ochanomizu University, Tokyo, Japan. bbAlso at Manhattan College, New York, NY, USA. ccAlso at Hellenic Open University, Patras, Greece. ddAlso at Academia Sinica Grid Computing, Institute of Physics, Academia Sinica, Taipei, Taiwan. eeAlso at School of Physics, Shandong University, Shandong, China. ffAlso at Moscow Institute of Physics and Technology State University, Dolgoprudny, Russia. ggAlso at Section de Physique, Université de Genève, Geneva, Switzerland. hhAlso at Eotvos Lorand University, Budapest, Hungary. iiAlso at Departments of Physics & Astronomy and Chemistry, Stony Brook University, Stony Brook, NY, USA. jjAlso at International School for Advanced Studies (SISSA), Trieste, Italy. kkAlso at Department of Physics and Astronomy, University of South Carolina, Columbia, SC, USA. llAlso at School of Physics and Engineering, Sun Yat-sen University, Guangzhou, China. mmAlso at Institute for Nuclear Research and Nuclear Energy (INRNE) of the Bulgarian Academy of Sciences, Sofia, Bulgaria. nnAlso at Faculty of Physics, M.V.Lomonosov Moscow State University, Moscow, Russia. ooAlso at Institute of Physics, Academia Sinica, Taipei, Taiwan. ppAlso at National Research Nuclear University MEPhI, Moscow, Russia. qqAlso at Department of Physics, Stanford University, Stanford, CA, USA. rrAlso at Institute for Particle and Nuclear Physics, Wigner Research Centre for Physics, Budapest, Hungary. ssAlso at Flensburg University of Applied Sciences, Flensburg, Germany. ttAlso at University of Malaya, Department of Physics, Kuala Lumpur, Malaysia. uuAlso at CPPM, Aix-Marseille Université and CNRS/IN2P3, Marseille, France. PRL 117, 182002 (2016) PHYSICAL REVIEW LETTERS week ending 28 OCTOBER 2016 182002-19