Measurement of the SemileptonicCPAsymmetry inB0-B¯

Abstract

The inclusive charge asymmetry measured by the D0 Collaboration in events with the same charge dimuons [1] shows one of the largest discrepancies with the standard model, and it may be a first hint of physics beyond our current understanding (e.g., Refs. [2][3][4]). This asymmetry is sensitive to CP violation in the mixing of neutral B mesons. The neutral B 0 meson and its antiparticleB 0 are flavor eigenstates, formed from a mixture of two mass eigenstates. The time evolution of this two-state system results in flavor-changing B 0 →B 0 andB 0 → B 0 transitions. Violation of charge-parity (CP) symmetry may occur due to this process if the probability for a B 0 meson to transform into aB 0 meson is different from the reverse process. When a meson produced in the B 0 eigenstate decays semileptonically to a final state f, the charge of the lepton reveals the meson flavor at the time of decay. In such decays, "wrong-sign" transitions, like B 0 →f, can happen only due to the transition B 0 →B 0 →f. The flavorspecific (semileptonic) asymmetry is defined in terms of partial decay rates Γ as In this analysis, a d sl is measured by using semileptonicwhere X denotes any additional particles due to possible feed-down from τ þ decays into μ þ X and higher-resonance D decays into D ðÃÞ− X. The inclusion of charge-conjugate processes is implied. The signal is reconstructed from D ðÃÞ− μ þ pairs, with the charm mesons reconstructed fromsl using the quantities in Eq. (1) requires determining (tagging) the flavor of the B 0 meson at production. Since this is inefficient in hadron collisions, a d sl is instead determined from the untagged decay rates. The number of observed final states as a function of the B 0 decay time is expressed aswhere Γ d is the B 0 decay width and ζ ¼ þ1ð−1Þ for the f (f) final state. The asymmetry due to differences in detection efficiencies ε between f andf final states, A D ≡ ½εðfÞ − εðfÞ=½εðfÞ þ εðfÞ, is determined by using control samples of data, as described later. The asymmetry in theB 0 and B 0 effective production cross sections,

Measurement of theCPAsymmetry inBs0−B¯s0Mixing

“…The production asymmetry between B þ and B − mesons is A bkg ðB þ Þ ¼ ð−0.6 AE 0.6Þ%, obtained from the observed asymmetry in B þ → J=ψK þ decays [19], after correcting for the kaon detection asymmetry and the direct CP asymmetry [18]. For the B 0 background, there are contributions from the production asymmetry and from a d sl [20]. Both asymmetries are diluted when integrating over the B 0 decay time, resulting in A bkg ðB 0 Þ ¼ ð−0.18 AE 0.13Þ%.…”

“…This asymmetry largely cancels in A track ðK þ K − Þ due to the similar kinematic distributions of the positive and negative kaons. The kaon asymmetry is calculated using prompt [20,25]. For pions and muons, the charge asymmetry due to interactions in the detector material is assumed to be negligible, and a systematic uncertainty is assigned for this assumption [20].…”

“…The kaon asymmetry is calculated using prompt [20,25]. For pions and muons, the charge asymmetry due to interactions in the detector material is assumed to be negligible, and a systematic uncertainty is assigned for this assumption [20]. Effects from the track reconstruction algorithms and detector acceptance, combined with a difference in kinematic distributions between pions and muons, can result in a charge asymmetry.…”

“…There is a small correlation coefficient [20,[28][29][30][31][32]. The yellow ellipse represents the D0 dimuon measurement with ΔΓ d =Γ d set to its SM expectation value [5].…”

Search for Violations of Lorentz Invariance andCPTSymmetry inB(s)0Aaij1, Beteta2, Adeva3 et al. 2016Phys. Rev. Lett.Self Cite371190View full textAdd to dashboardCite

“…[26,27]. The corresponding uncertainties are included in the statistical uncertainty, while a possible momentum dependence of the production asymmetry is considered as a systematic uncertainty.…”