Searches for physics beyond the SM at DANSS

DANSS in A336 Searches for physics beyond the SM at DANSS Petr Gorovtsov, UNIPD & INFN Padova On behalf of the DANSS collaboration 1 Motivation - there are several anomalies in neutrino physics •LSND & MiniBooNE result: 𝜈𝑒in the 𝜈𝜇beam (6𝜎): Δ𝑚2∼0.2−1e𝑉2? •MicroBooNE does not confirm this anomaly •Gallium anomaly (GA): deficit of 𝜈events in the calibration measurements in gallium experiments SAGE, GALLEX and BEST (5𝜎) •Reactor Antineutrino Anomaly (RAA): deficit of ҧ𝜈𝑒 from the reactors in comparison with theoretical predictions (2.8𝜎), tends to decrease 2 LSND, MiniBooNE, 29.05.2013, Annual Review of Nuclear and Particle Science vol 63 P. Arbatenko et al., (MicroBooNE), Phys. Rev. Lett. 130, 011801, 2023 V.V. Barinov et al, (BEST), Phys. Rev. Lett. 128, 232501, 2022 G. Mention et al, Phys. Rev. D 83, 073006, 2011 Possible explanations •Sterile neutrinos: at short distances we can consider only oscillations to sterile state 𝑃 ҧ𝜈𝑒→ ҧ𝜈𝑒≈1 −sin22𝜃𝑒𝑒 sin 1.267Δm41 2𝑒𝑉2𝐿 𝑚 𝐸𝑀𝑒𝑉 •Large Extra Dimensions (LED) (N. Arkani–Hamed, S. Dimopoulos, G. Dvali, Phys. Let. B, vol 429, issues 3-4, pages 263-272, 1998) •Extra dimensions renormalize Planck’s mass: 𝑀𝑃𝑙 2= 𝑀𝑃𝑙 ∗2+𝑛𝑎𝑛 •𝑛 ≥2needed for Hierarchy problem but one dimension can be bigger than others. In this approach survival probability for (anti)neutrino: 𝑃 ҧ𝜈𝑒→ ҧ𝜈𝑒=σ𝑖𝑈𝑒𝑖 2𝐴𝑖2 3 ∼1𝑒𝑉2 𝐴𝑖= 1−𝜋2 6𝑚𝑖 2𝑎22exp 𝑖𝑚𝑖 2𝐿 2𝐸 +2𝑚𝑖 2𝑎2exp 𝑖𝑚𝑖 2𝐿 𝐸෍exp 𝑖 𝑛2𝐿 2𝐸𝑎2 𝑛2,𝑚𝑎 ≪1 Kaluza-Klein towerAbsolute mass scale Size of the dominant dimension Detector of AntiNeutrino based on Solid Scintillator •Detector is placed under the reactor core at Kalinin NPP and consists of safe, nonflammable materials •The goal is to scrutinize the sterile neutrino hypothesis (and other BSM models) •A movable platform → spectral ratio analysis not sensitive to detector efficiency and antineutrino spectrum •Antineutrinos are detected in the IBD reaction: •The energy of antineutrino is determined by the energy of positron ∼5000𝑒𝑣𝑒𝑛𝑡𝑠/𝑑𝑎𝑦 Largest in the world antineutrino statistics, IBD is used ഥ𝜈𝑒+𝑝 → 𝑛+𝑒+ 𝐸𝜈𝑒≈𝐸𝑒++1.8𝑀𝑒𝑉 4 Positron →prompt signal Neutron →delayed signal (For the Top and Bottom agreement see the DANSS poster) Design of the detector •Shielding: muon veto, 8 cm of boron-doped polyethylene, 5 cm of lead, another 8 cm of borondoped polyethylene, and a 5 cm layer of copper •2500 scintillator strips coated with a gadoliniumcontaining layer for neutron capture. Light is collected with wavelength shifting fibers connected to SiPM and PMT •Currently the detector’s upgrade is coming: new scintillation counters, more of sensitive volume, better light collection 5 Acquired positron spectra •October 2016 –May 2025 •9.8×106events in [0.75−8]MeV •DANSS is moved once in 5-7 days in order to average the result by the fuel composition •Pure positron kinetic energy (no annihilation gammas) •𝜇-induced background due to the veto inefficiency is 1.8% of the signal only 6 First precise measurement of reactor power with antineutrino •Detection rate: 𝑑2𝑁 𝑑𝐸𝜈𝑑𝑡 =𝑁𝑝𝜎 𝐸𝜈𝜀 𝐸𝜈𝑑2𝜙 𝑑𝐸𝜈𝑑𝑡 1 4𝜋𝐿2P(E𝜈,L) 7 =1 •Uncertainty in flux models →normalization to flux during 1 month in 2016 •Corrections applied: •Change of the efficiency due to dead channels amount (<3%) •Variation of the dead time due to VETO rate (1%) •The fuel evolution (provided by KNPP) •Excellent agreement between DANSS and KNPP: 1.0%during 7 years •Statistical accuracy of each point is around 0.7% •Additional systematic between KNPP and DANSS measurements is 0.79%only! 2-3 days/point 7 days/point I. Alekseev et al, (DANSS), Phys. Let. B, vol 866, 139575, 2025 2 weeks/point First measurement of fission fractions with antineutrino spectrum 8 •The antineutrino spectrum is different for different isotopes •Correction for efficiency, dead time and neighbouring reactors (0.6%) •Fit doesn’t include 𝐸𝑒+∈ 3;5,5 𝑀𝑒𝑉due to theoretical uncertainties •5th campaign is used to fix energy calibration and 238𝑈and 241𝑃𝑢fractions (taken from KNPP) •Statistical error of IBD rate is 0.6% •ҧ𝜈𝑒spectra for isotopes are taken from HM or KI model. DANSS shows that results depend weakly on the choice of the model. KNPP data is based on the solving diffusion equation for neutron flux •Agreement with KNPP is within 2.1%although two methods based on the completely different physical processes I. Alekseev et al, (DANSS), Phys. Let. B, vol 866, 139575, 2025 𝜒2𝜃,𝜂 = ෍ 𝑏𝑖𝑛𝑠 𝑅𝑏𝑡 𝑜𝑏𝑠 −𝑅𝑏𝑡 𝑝𝑟𝑒(𝜃,𝜂) 2 𝜎2 +σ𝑏𝑖𝑛𝑠 𝑅𝑏𝑡 𝑜𝑏𝑠 −𝑅𝑏𝑡 𝑝𝑟𝑒; 𝑅𝑚𝑏𝑡 𝑜𝑏𝑠 −𝑅𝑚𝑏𝑡 𝑝𝑟𝑒 ⋅𝑊−1 ⋅𝑅𝑏𝑡 𝑜𝑏𝑠 −𝑅𝑏𝑡 𝑝𝑟𝑒 𝑅𝑚𝑏𝑡 𝑜𝑏𝑠 −𝑅𝑚𝑏𝑡 𝑝𝑟𝑒 +෍ 𝑠𝑦𝑠𝑡 𝜂−𝜂0 2 𝜎𝜂 2 •Data taking in 2 positions 𝑅𝑏𝑡 =𝑏𝑜𝑡𝑡𝑜𝑚/𝑡𝑜𝑝 •Data taking in 3 positions 𝑅𝑚𝑏𝑡 =𝑚𝑖𝑑𝑑𝑙𝑒/ 𝑏𝑜𝑡𝑡𝑜𝑚⋅𝑡𝑜𝑝 𝑊–covariance matrix •Penalty term for systematics: relative efficiency, background, energy scale, distance to reactor core Oscillation analysis 9 •For different points in parameter space 𝜃spectra ratios 𝑅were calculated •𝜃 =(sin22𝜃𝑒𝑒;Δ𝑚41 2)for sterile neutrino •𝜃 =(𝑎,𝑚0)for LED searches •𝜒2statistics is minimized over systematic parameters 𝜂 •Gaussian CLs method or confidence intervals (Wilks theorem assumed) were used BackUp •LSND result with LED •Probability of appearance is very low 16 Mass ordering •For the same 𝑚0in different ordering values of 𝑚1,𝑚2,𝑚3differ, hence, amplitudes are also different. They have different weights in the total probability 17 Survival probability: 𝑃𝑒𝑒 = ෍ 𝑈𝑒𝑖 2𝐴𝑖 2 𝑈𝑒1 ∼0.8 𝑈𝑒2 ∼0.5 𝑈𝑒3 ∼0.1 Fission fractions 18 Fission fraction provided by KNPP Antineutrino spectra for different isotopes List of systematics •𝜂0nominal values •𝜎𝜂standard deviations 19 Bump in positron spectra •Ratio of measured and predicted by HM spectra •3-5.5 MeV range is not included 20 bump Gaussian 𝐶𝐿𝑠method Significance of exclusion 𝐻1in comparison with 𝐻0without any suggestions on the structure of parameter space. 𝐻0is assumed to be true. •𝜒1 2−𝜒0 2(Δ𝑇)is distributed according to normal distribution with parameters determined from Asimov datasets. •Confidence level: 𝐶𝐿𝑠=1−𝑝1 1−𝑝0 21 Prediction of theory with experimental error Unfolding of the antineutrino spectrum 22 •Unfolding with SVD method