Improved exclusion limit for light dark matter from e+e− annihilation in NA64

Yu Andreev ,D Cooke,E Depero,I Tlisova,D Banerjee,M Jeckel,B Ketzer,L Marsicano,A Rubbia,N Charitonidis,H Sieber,P Crivelli,V Lysan,J Bernhard,A Gardikiotis,A Feshchenko,A Celentano,P Ulloa,B Radics,A Yu Trifonov,T Enik,Yu.v Mikhailov ,V.e Burtsev ,S Gerassimov ,N Krasnikov ,A.g Chumakov ,V Matveev ,M Kirsanov ,L Kravchuk ,M Hoesgen ,A Dermenev ,M Bondì ,S.v Donskov ,A Karneyeu ,Dmitry G Shchukin ,S Gninenko ,A Toropin ,L T Molina ,Valery E Lyubovitskij ,V.a Polyakov ,P Volkov ,V A Kramarenko ,V.n Kolosov ,D.v Peshekhonov ,D Kirpichnikov ,I Konorov ,V O Tikhomirov ,V.d Samoylenko ,G A Vasquez ,G D Kekelidze ,В Фролов ,R R Dusaev ,R A Rojas ,В Качанов ,B I Vasilishin ,S Kuleshov ,Sergey Kovalenko ,V Volkov

doi:10.1103/physrevd.104.l091701

Abstract

The current most stringent constraints for the existence of sub-GeV dark matter coupling to Standard Model via a massive vector boson $A^\prime$ were set by the NA64 experiment for the mass region $m_{A^\prime}\lesssim 250$ MeV, by analyzing data from the interaction of $2.84\cdot10^{11}$ 100-GeV electrons with an active thick target and searching for missing-energy events. In this work, by including $A^\prime$ production via secondary positron annihilation with atomic electrons, we extend these limits in the $200$-$300$ MeV region by almost an order of magnitude, touching for the first time the dark matter relic density constrained parameter combinations. Our new results demonstrate the power of the resonant annihilation process in missing energy dark-matter searches, paving the road to future dedicated $e^+$ beam efforts.

Highlights

The current most stringent constraints for the existence of sub-GeV dark matter coupling to Standard Model via a massive vector boson A0 were set by the NA64 experiment for the mass region mA0 ≲ 250 MeV, by analyzing data from the interaction of 2.84 × 1011 100-GeV electrons with an active thick target and searching for missing-energy events
By including A0 production via secondary positron annihilation with atomic electrons, we extend these limits in the 200–300 MeV region by almost an order of magnitude, touching for the first time the dark matter relic density constrained parameter combinations
Despite a few positive observations reported by different collaborations [5,6,7,8], the interpretation of these results as a dark matter (DM) signal is in contrast with null measurements reported by other experiments [9,10,11,12,13]

Summary

Published by the American Physical Society

Direct detection of heavy DM particles from the galactic halo, according to the so-called weakly interacting massive particles (WIMP) scenario [2]. We explicitly consider the case mχ < mA0=2, where mχ is the dark matter particles mass, resulting in an invisible decay of the A0 to LDM particles This scenario offers a predictive target through a combination of the LDM parameters that is capable of reproducing the presently observed. After applying all the selection cuts, determined through a blind-analysis approach by maximizing the experimental sensitivity, no events were found in the signal region, defined by the two requirements EECAL < 50 GeV and EHCAL < 1 GeV This result was translated to an exclusion limit in the A0 parameter space—mA0 vs ε -, considering only the socalled “A0-strahlung” production mechanism associated. The expected number of signal events with A0 energy greater than a threshold ECmUisTs is given by: Z

NA A

ECAL efficiency

Findings

These new results were also used to derive exclusion