Evidence for Higgs boson decays to a low-mass dilepton system and a photon in pp collisions at <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" altimg="si1.svg"><mml:msqrt><mml:mrow><mml:mi>s</mml:mi></mml:mrow></mml:msqrt><mml:mo linebreak="goodbreak" linebreakstyle="after">=</mml:mo><mml:mn>13</mml:mn></mml:math> TeV with the ATLAS detector
G. Aad, B. Abbott, D. C. Abbott, A. Abed Abud, K. Abeling, D. K. Abhayasinghe, S. H. Abidi, O. S. AbouZeid, N. L. Abraham, H. Abramowicz, H. Abreu, Y. Abulaiti, A.C. Abusleme Hoffman, B. S. Acharya, B. Achkar, L. Adámek, C. Adam Bourdarios, L. Adamczyk, L. Adámek, J. Adelman, A. Adıgüzel, S. Adorni, T. Adye, A. A. Affolder, Y. Afik, C. Agapopoulou, M. N. Agaras, A. Aggarwal, C. Agheorghiesei, J. A. Aguilar–Saavedra, A. Ahmad, F. Ahmadov, W. S. Ahmed, X. Ai, G. Aielli, S. Akatsuka, M. Akbiyik, T. P. A. Åkesson, E. Akilli, A. V. Akimov, K. Al Khoury, G. L. Alberghi, J. Albert, M. J. Alconada Verzini, S. Alderweireldt, M. Aleksa, I. N. Aleksandrov, C. Alexa, T. Alexopoulos, A. Alfonsi, F. Alfonsi, M. Alhroob, B. Ali, S. Ali, M. Aliev, G. Alimonti, C. Allaire, B. M. M. Allbrooke, P. P. Allport, A. Aloisio, F. Alonso, C. Alpigiani, E. Alunno Camelia, M. Alvarez Estevez, M. G. Alviggi, Y. Amaral Coutinho, A. Ambler, L. Ambroz, Christoph Amelung, D. Amidei, S. P. Amor Dos Santos, S. Amoroso, C.S. Amrouche, C. Anastopoulos, N. Andari, T. Andeen, J. K. Anders, S. Y. Andrean, A. Andreazza, V. Andrei, S. Angelidakis, A. Angerami, A. V. Anisenkov, A. Annovi, C. Antel, M. T. Anthony, E. Antipov, M. Antonelli, D. J. A. Antrim, F. Anulli, M. Aoki, J. A. Aparisi Pozo, M. A. Aparo, L. Aperio Bella, N. Aranzabal, V. Araujo Ferraz, C. Arcangeletti, A. T. H. Arce, Eloisa Arena, J-F. Arguin
Abstract
A search for the Higgs boson decaying into a photon and a pair of electrons or muons with an invariant mass m ℓ ℓ < 30 GeV is presented. The analysis is performed using 139 fb −1 of proton–proton collision data, produced by the LHC at a centre-of-mass energy of 13 TeV and collected by the ATLAS experiment. Evidence for the H → ℓ ℓ γ process is found with a significance of 3.2 over the background-only hypothesis, compared to an expected significance of 2.1 for the Standard Model prediction. The best-fit value of the signal-strength parameter, defined as the ratio of the observed signal yield to the one expected in the Standard Model, is μ = 1.5 ± 0.5 . The Higgs boson production cross-section times the H → ℓ ℓ γ branching ratio for m ℓ ℓ < 30 GeV is determined to be 8.7 − 2.7 + 2.8 fb.