Study of the Bc+ → J/ψ Ds+ and Bc+ → J/ψ Ds*+ decays with the ATLAS detector

Abstract

Artículo escrito por un elevado número de autores, solo se referencian el que aparece en primer lugar, el nombre del grupo de colaboración, si le hubiere, y los autores pertenecientes a la UAM ; The decays Bc+ → J/ψ Ds+ and Bc+ → J/ψ Ds*+ are studied with the ATLAS detector at the LHC using a dataset corresponding to integrated luminosities of 4.9 and 20.6 fb−1 of pp collisions collected at centre-of mass energies √s = 7 TeV and 8 TeV, respectively. Signal candidates are identified through J/ψ → μ+μ− and Ds (∗)+→ φπ+(γ /π0) decays. With a two-dimensional likelihood fit involving the Bc+ reconstructed invariant mass and an angle between the μ+ and Ds+ candidate momenta in the muon pair rest frame, the yields of Bc+ → J/ψ Ds+ and Bc+ → J/ψ Ds*+, and the transverse polarisation fraction in Bc+ → J/ψ Ds+ and Bc+ decay are measured. The transverse polarisation fraction is determined to be ɼ±± (Bc+ → J/ψ Ds*+)/ ɼ(Bc+ → J/ψ Ds*+) = 0.38 ± 0.23 ± 0.07, and the derived ratio of the branching fractions of the two modes is Ɓ Bc+ → J/ψ Ds*+ /ƁBc+ → J/ψ Ds+ = 〖2.8〗_(-0.8 )^(+1.2 ) ± 0.3, where the first error is statistical and the second is systematic. Finally, a sample of Bc+ → J/ψ π+ decays is used to derive the ratios of branching fractions Ɓ Bc+ → J/ψ Ds+ /ƁBc+ → J/ψ π+ = 3.8 ± 1.1 ± 0.4 ± 0.2 and Ɓ Bc+ → J/ψ Ds*+ /ƁBc+ → J/ψ π+ = 10.4 ± 3.1 ± 1.5 ± 0.6, where the third error corresponds to the uncertainty of the branching fraction of Ds+→ φ(K+K-)π+ decay. The available theoretical predictions are generally consistent with the measurement ; 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, DNSRCand Lundbeck Foundation, Denmark; EPLANET, ERC and NSRF, European Union; IN2P3-CNRS, CEA-DSM/IRFU, France; GNSF, Georgia; BMBF, DFG, HGF, MPG and AvH Foundation, Germany; GSRT and NSRF, Greece; RGC, Hong Kong SAR, China; ISF, MINERVA, GIF, I-CORE and Benoziyo Center, Israel; INFN, Italy; MEXT and JSPS, Japan; CNRST, Morocco; FOM and NWO, Netherlands; BRF and RCN, Norway; MNiSW and NCN, Poland; GRICES and FCT, Portugal; MNE/IFA, Romania; MES of Russia and NRC KI, Russian Federation; JINR;MSTD, Serbia; MSSR, Slovakia; ARRS and MIZŠ, Slovenia; DST/NRF, South Africa; MINECO, Spain; SRC and Wallenberg Foundation, Sweden; SER, SNSF and Cantons of Bern and Geneva, Switzerland; NSC, Taiwan; TAEK, Turkey; STFC, the Royal Society and Leverhulme Trust, United Kingdom; DOE andNSF, United States of America. The crucial computing support from all WLCG partners is acknowledged gratefully, in particular from CERN and the ATLAS Tier-1 facilities at TRIUMF (Canada), NDGF (Denmark, Norway, Sweden), CC-IN2P3 (France), KIT/GridKA (Germany), INFNCNAF (Italy), NL-T1 (Netherlands), PIC (Spain), ASGC (Taiwan), RAL (UK) and BNL (USA) and in the Tier-2 facilities worldwide