Semileptonic Mixing Asymmetry Measurements of A d SL and A s SL Martino Margoni Universita` di Padova and INFN on behalf of the BaBar Collaboration Motivation D0 Inclusive dilepton Analysis D0, LHCb, BaBar Flavor Specific Analyses Conclusions 1 FP FPCP , B , Buzi zios.R s.Rio.B .Brasi sil, 1 , 19- 9-24 24 M May 20 2013 M M.M .Margoni Un Universi sita ta` di di P Pado dova & I & INFN FN
Motivation 2 FP FPCP , B , Buzi zios.R s.Rio.B .Brasi sil, 1 , 19- 9-24 24 M May 20 2013 M M.M .Margoni Un Universi sita ta` di di P Pado dova & I & INFN FN
CPV in B 0 mixing New Particles in the boxes could modify SM expectations B 0 q - B 0 q oscillations & decay governed by an Effective Hamiltonian: [M ij ]= mass matrix [ Γ ij ]= decay matrix Physical Eigenstates with defined masses and widths: If |(q/p) q |=1 they would be also CP Eigenstates Neglecting o(m 2 b /M 2 W ): q ∣ ; q = L − H ≃ 2 ∣ 12 q ∣ cos q m q = m H − m L ≃ 2 ∣ M 12 q / 12 q q = arg − M 12 CP violating phase 3 FP FPCP , B , Buzi zios.R s.Rio.B .Brasi sil, 1 , 19- 9-24 24 M May 20 2013 M M.M .Margoni Un Universi sita ta` di di P Pado dova & I & INFN FN
CPV in B 0 mixing CP Asymmetry in B 0 mixing (time independent): (s) q ∣ 0 B q 0 , t − Prob B q 0 ,t q = Prob 0 4 = ∣ 12 4 = 1 − ∣ q / p ∣ B q B q q A CP sin q q ∣ 0 B q 0 , t Prob B q 0 ,t Prob 0 ∣ M 12 1 ∣ q / p ∣ B q B q q Experimentally: measure charge asymmetry in mixed semileptonic B 0 q decays: 0 l X − B q 0 l X q = 0 + - 0 B q CPV in mixing if: B q B q q = A SL A CP 0 0 l X + - 0 B q 0 l X B q B q B q A q S L ≠0 ↔ |q/p| q ≠1 ↔ Φ q ≠0 Stan andar dard Mo d Mode del predicts Be Beyo yond S d Stan andar dard Mo d Mode del (Nierste, arXiv:1212.5805 (2012)): (Lenz, Nierste, JHEP 0706, 072 (2007)) New Physics could modify and A q q M 12 B 0 d : A d SL = (-4.0±0.6)10 -4 SL leaving unchanged : q 12 Φ d =-4.9º±1.4º SM ,q q ; q = ∣ q ∣ e i q NP ,q = M 12 M 12 B 0 s : A s SL =(1.8±0.3)10 -5 q ∣ NP = ∣ 12 SM q sin q A SL Φ s =0.24º±0.06º ∣ M 12 SM ,q ∣ ∣ q ∣ 4 FP FPCP , Buzi , B zios.R s.Rio.B .Brasi sil, 1 , 19- 9-24 24 M May 20 2013 M M.M .Margoni Un Universi sita ta` di di P Pado dova & I & INFN FN
CPV in B 0 mixing T wo classes of measurements available: Inclusive dilepton asymmetry analyses: BaBar, Phys. Rev. Lett. 96 251802 (2006) Belle, Phys. Rev. D 73 112002 (2006) - - b = N b l l − N b l l + + D0, Phys. Rev. D 84,052007 (2011) A SL - - N b l l N b l l + + Hadron Colliders Experiments measure a combination of B 0 d & B 0 s CP b = C d A SL d C s A SL s A SL parameters: C d,s depend on B 0 d,s production rates & mixing probability +0.005 SM predicts: A b SL =(-0.028 )% -0.006 Flavor specific B 0 , B 0 s analyses: D0, Phys. Rev. D 86 072009 (2012) D0, Phys. Rev. Lett. 110, 011801 (2013) Reconstruction of B 0 D (*) lX, B 0 s D s lX LHCb, LHCb-CONF-2012-022 (2012) BaBar, arXiv:1305.1575 (2013) With or without flavor-tagging at production 5 FP FPCP , B , Buzi zios.R s.Rio.B .Brasi sil, 1 , 19- 9-24 24 M May 20 2013 M M.M .Margoni Un Universi sita ta` di di P Pado dova & I & INFN FN
Detector-related Asymmetries Current statistical precision of the experiments <0.5% requires very good control of spurious charge asymmetries from: Charge-asymmetric BKG: hadrons misidentified as leptons & leptons from light hadron decays (e.g. positive kaons have smaller interaction cross-section than negative kaons in matter) T rack reconstruction and lepton identification (detector anisotropy could affect efficiencies) Most crucial point of the analyses and biggest systematic uncertainty Effect reduced by inverting magnets polarities (D0, LHCb) Estimated on control samples (D0, LHCb) or determined directly in the fit to A SL (BaBar) 6 FP FPCP , B , Buzi zios.R s.Rio.B .Brasi sil, 1 , 19- 9-24 24 M May 20 2013 M M.M .Margoni Un Universi sita ta` di di P Pado dova & I & INFN FN
Inclusive dilepton Analyses D0: “Measurement of the anomalous like-sign dimuon charge asymmetry with 9 fb -1 of pp collisions”, (9 fb -1 ) Phys. Rev. D 84, 052007, 2011 7 FP FPCP , B , Buzi zios.R s.Rio.B .Brasi sil, 1 , 19- 9-24 24 M May 20 2013 M M.M .Margoni Un Universi sita ta` di di P Pado dova & I & INFN FN
D0 like-sign dimuons charge Asymmetry Phys. Rev. D 84,052007 (2011) Semileptonic asymmetry A b SL measured from inclusive single muon & like-sign dimuon charge asymmetries: μ - B 0 B 0 Only 3% of single muons + - a = n − n - X from decays of mixed B 0 + n n q μ - μ - + + b-hadr -hadron B 0 B 0 - - A = N − N N N + + - - X X bb Only 30% of equal- Challenge: understand contributions from: charge muons from Muons from other b decays, charm and decays of mixed B 0 q short-lived hadrons Detector-related charge asymmetries 8 FP FPCP , B , Buzi zios.R s.Rio.B .Brasi sil, 1 , 19- 9-24 24 M May 20 2013 M M.M .Margoni Un Universi sita ta` di di P Pado dova & I & INFN FN
D0 like-sign dimuons charge Asymmetry Phys. Rev. D 84,052007 (2011) BKG fractions and asymmetries from K, p, π μ determined using K* 0 K + π - , Φ K + K - , K S π + π - , Λ p π - control samples Observed single muon asymmetry agrees with BKG expectations: From the inclusive muon sample alone: Agrees with SM A b SL =(-1.04±1.30(stat)±2.31(syst))% 9 FP FPCP , B , Buzi zios.R s.Rio.B .Brasi sil, 1 , 19- 9-24 24 M May 20 2013 M M.M .Margoni Un Universi sita ta` di di P Pado dova & I & INFN FN
D0 like-sign dimuons charge Asymmetry Phys. Rev. D 84,052007 (2011) Observed like-sign dimuon asymmetry differs significantly from expectations From the dimuon sample alone: A b SL =(-0.808±0.202(stat)±0.222(syst))% Result obtained using a linear combination of single 3.9 σ from SM lepton and dilepton asymmetries to reduce prediction: uncertainty: A b SL =(-0.787±0.172(stat)±0.093(syst))% Systematics dominated by BKG fraction determination 10 FP FPCP , B , Buzi zios.R s.Rio.B .Brasi sil, 1 , 19- 9-24 24 M May 20 2013 M M.M .Margoni Un Universi sita ta` di di P Pado dova & I & INFN FN
D0 like-sign dimuons charge Asymmetry Phys. Rev. D 84,052007 (2011) Mixed B 0 (s) fractions depend on muon Impact Parameter b = C d A SL d C s A SL s A SL A b SL computed in the two regions: IP>120 μm, IP<120 μm Allows separate determination of A d SL =(-0.12±0.52)% A s SL =(-1.81±1.06)% 11 FP FPCP , B , Buzi zios.R s.Rio.B .Brasi sil, 1 , 19- 9-24 24 M May 20 2013 M M.M .Margoni Un Universi sita ta` di di P Pado dova & I & INFN FN
D0 like-sign Asymmetry: Interpretation Borissov, Hoeneisen, Phys. Rev. D 87, 074020 (2013) Results do not agree with SM only in dimuon charge asymmetry Search for any neglected source of CP violation which could affect the dimuon asymmetry leaving the single muon one uninfluenced B 0 (B 0 ) ccdd final states (e.g. D + D - ) accessible from both B 0 and B 0 Interference of decays with and without mixing results in CP violation which affects only the dilepton charge asymmetry: , x d = m d x d c d c d A c d =− sin 2 2 c d =− 0.045 ± 0.016 % d 1 x d Contribution of the ccdd channels in the inclusive dimuon sample Discrepancy with SM in like-sign asymmetry lowered from 2.8 σ to 2.3 σ Mandatory to perform measurements of flavor specific asymmetries 12 FP FPCP , B , Buzi zios.R s.Rio.B .Brasi sil, 1 , 19- 9-24 24 M May 20 2013 M M.M .Margoni Un Universi sita ta` di di P Pado dova & I & INFN FN
Flavor Specific Analyses D0: “Measurement of the semileptonic charge asymmetry in B 0 meson mixing with the D0 detector” (10.4 fb -1 ) Phys. Rev. D 86 072009 (2012) D0: “Measurement of the Semileptonic Charge Asymmetry using B 0 s D s μ X” (10.4 fb -1 ) Phys. Rev. Lett. 110, 011801 (2013) LHCb: “Measurement of the flavour-specific CP violating asymmetry A s SL in B 0 s decays” (1.0 fb -1 ) LHCb-CONF-2012-022 (2012), Preliminary BaBar: “Search for CP Violation in B 0 B 0 Mixing using Partial Reconstruction of B 0 D*Xl ν and a Kaon T ag” (425.7 fb -1 ) ArXiv: 1305.1575 (2013), Submitted to Phys. Rev. Lett. 13 FP FPCP , B , Buzi zios.R s.Rio.B .Brasi sil, 1 , 19- 9-24 24 M May 20 2013 M M.M .Margoni Un Universi sita ta` di di P Pado dova & I & INFN FN
Recommend
More recommend
