Measurement of the TeV atmospheric muon charge ratio with the complete OPERA data set

N Agafonova,S Simone,C Göllnitz,N Mauri,M Kamiscioglu,V Tioukov,T Matsuo,V Matveev,M Tenti,H Pessard,J Kawada,T Hara,M Komatsu,S Ogawa,G Galati,M T Muciaccia,C Jollet,A Lauria,M Spinetti,A Zghiche,R Brugnera,L Consiglio,N Okateva,A Garfagnini,B Hosseini,A Anokhina,G De Lellis,S Dmitrievski,J Ebert,C S Yoon,P Del Amo Sanchez,N Kitagawa,L Votano,C Gustavino,F Pupilli,A Hollnagel,G Mandrioli,B Büttner,J H Kim,G Giacomelli,E Medinaceli,P Strolin,S Dusini,D Di Ferdinando,K Ozaki,I Kreslo,A Bertolin,M Pozzato,M De Serio,R A Fini,J Lenkeit,A Meregaglia,H Shibuya,S H Kim,D Duchesneau,A Di Crescenzo,J Goldberg,S Zemskova,Y Gornushkin,L Pasqualini,N Di Marco,K Kodama,C Kamiscioglu,P Monacelli,G Grella,G Sirri,A Buonaura,G Shoziyoev,C Pistillo,T Nakano,L Patrizii,C Hagner,A Longhin,I Shakiryanova,A Ariga,F Terranova,P Vilain,A Sheshukov,J L Vuilleumier,M Roda,T Shchedrina,Y Nakatsuka,S Mikado,I G Park,M Sioli,N D’Ambrosio,A Paoloni,S Tufanli,B Wonsak,T Omura,A Chukanov,N Naganawa,G Wilquet,B D Park,C Bozza,A Aleksandrov,N Starkov,T Ariga,T Dzhatdoev,S Buontempo,C Sirignano,N Polukhina,D Bender,K Ishiguro,P Loverre,Hiroki Rokujo ,M.c Montesi ,Tsutomu Fukuda ,Hirokazu Ishida ,Takashi Naka ,Д Подгрудков ,Satoru Takahashi ,Simona Maria Stellacci ,Keisuke Morishima ,L Stančo ,M Stipčević ,Т М Роганова ,Adam Schembri ,A S Malgin ,Takeshi Shiraishi ,O G Ryazhskaya ,Maša Malenica ,Shigeki Aoki ,M S Vladimirov ,U Köse ,Osamu Sato ,G De Rosa ,A Ljubičić ,K Jakovc̆ić ,M M Chernyavsky ,B Kliček ,Mitsuhiro Nakamura ,M Güler ,А.g Оlshevsky ,K Niwa,M Dracos,A Ereditato,A Pastore

doi:10.1140/epjc/s10052-014-2933-0

Abstract

The OPERA detector, designed to search for $\nu_{\mu} \to \nu_{\tau}$ oscillations in the CNGS beam, is located in the underground Gran Sasso laboratory, a privileged location to study TeV-scale cosmic rays. For the analysis here presented, the detector was used to measure the atmospheric muon charge ratio in the TeV region. OPERA collected charge-separated cosmic ray data between 2008 and 2012. More than 3 million atmospheric muon events were detected and reconstructed, among which about 110000 multiple muon bundles. The charge ratio $R_{\mu} \equiv N_{\mu^+}/N_{\mu^-}$ was measured separately for single and for multiple muon events. The analysis exploited the inversion of the magnet polarity which was performed on purpose during the 2012 Run. The combination of the two data sets with opposite magnet polarities allowed minimizing systematic uncertainties and reaching an accurate determination of the muon charge ratio. Data were fitted to obtain relevant parameters on the composition of primary cosmic rays and the associated kaon production in the forward fragmentation region. In the surface energy range 1-20 TeV investigated by OPERA, $R_{\mu}$ is well described by a parametric model including only pion and kaon contributions to the muon flux, showing no significant contribution of the prompt component. The energy independence supports the validity of Feynman scaling in the fragmentation region up to $200$ TeV/nucleon primary energy.

Highlights

Underground experiments detect the penetrating remnants of primary cosmic ray interactions in the atmosphere, namely muons and neutrinos
We have investigated the systematic uncertainty related to the alignment of the Precision Trackers (PT) system
The charge ratio of multiple muon events was computed using all the muon charges reconstructed in events with nμ > 1

Summary

Introduction

Underground experiments detect the penetrating remnants of primary cosmic ray interactions in the atmosphere, namely muons and neutrinos. These are the decay products of charged mesons contained in the particle cascade, mainly pions and kaons. Assuming the hypothesis of complete scaling we expect an energy independent charge ratio above the TeV energy region at sea level [1] once the kaon contribution to the muon flux reached its asymptotic value [2]. OPERA already reported a first measurement of the atmospheric muon charge ratio at TeV surface energies using the 2008 Run data [7]. The magnetic spectrometers were active only during the CNGS Physics Runs, being switched off during the CNGS winter shutdowns For nearly horizontal muons up to four bending angles can be measured in the two dipole magnets

Data analysis

Systematic uncertainties and unbiased charge ratio

Results

Conclusions