new measurements of sin(2) & cos(2) at BaBar

Transcription

1 new measurements of sin(2) & cos(2) at BaBar, UC Irvine For the BaBar collaboration ICHEP24 August 16th, Beijing

2 Decay rates of B mesons 2 Time-dependent rates for B (f + ) or B (f - ) decays to final state f: f f 2 Γt Γt 1 f 2 Im( f ) ± ( t) exp( Γt) cosh 2Re(f )sinh cos( mt) ± sin( mt) f 1+ f Γ m f = difference in total decay width between B H and B L = mass difference between B H and B L (~.5ps -1 ) q p A A f = >= p B > ± q B > Neglecting : f C } 2 1 f 2 Im( f ) ± ( t) exp( Γt) 1 cos( mt) ± sin( mt) f 1+ f B L / H If f is a CP eigenstate f CP then we have CP violation if f ±1: q/p 1 (CP violation in mixing, negligible) A f /A f 1 (direct CP violation, not expected here) Im( f ) (interference between mixing and decay) S } t= B mixing q p B A f decay A f t f

3 CP violation for cck decays B mixing q / p B B B decay * A V cb V cs K mixing q / K p K 3 K S q = p B B A A * VtbV = V V tb main decay amplitudes (tree and leading penguins) have same weak phase: no direct CP violation, no CP violation in mixing Im( K S K S = 1 K K S S ) = sin(2) td * td K K V V L * cb * cb V V * cs cs V V = = cs * cs K V V S K S * cd cd * VtbV = V V tb td * td V V cb * cb (L =,2)or+ V V * cd cd K S γ (L = 1) α

4 Experimental technique B J/ K S µ + µ Fully reconstruct decay to CP state 4 e - e + B Asymmetric energies produce boosted (4S), decaying into coherent BB pair Determine time between decays from vertices z=(c)t Determine flavor and vertex position of other B decay General principle: fully reconstruct decay to CP eigenstate use remaining tracks in event to determine initial flavor Measure t from position of both vertices (CP/tag) fit t distributions to determine amplitude of sin(mt) term = sin(2) l- K -

5 Resolution and tagging perfect tagging & time resolution realistic mistagging & finite time resolution B tag = B B tag = B B tag = B B tag = B Need to know mistag fraction andt resolution function R in order to measure CP asymmetry. Use large sample ( Bflav ) of fully reconstructed B decays to flavor eigenstates ( self-tagging decays ) : S=, C=1 5

6 Measurement method 6 Self-tagging ( BFlav ) signal events, C=1, S=: f Bflav ± ( f CP ± t') = ( t') = { exp( Γ t )[ 1± (1 2) cos( m t) ]} R( t t'; σ ( t)) + = unmixed (opposite flavor) - = mixed (same flavor) CP signal events, C=, S= F sin(2) : { exp( Γ t )[ 1 sin 2(1 2) sin( m t) ]} R( t t'; σ ( t)) + = B on tag side - = B on tag side Simultaneous maximum likelihood fit: observables t, (t), signal probability, tag flavor and category, Bflav flavor 65 free parameters in fit 9 parameters specific to CP sample f Common mistag fractions Common resolution function External physics parameters fixed: m=.52 ±.7 ps -1 (PDG24) (B)=1.536 ±.14 ps (PDG24) /= (varied to.2 as systematic =1 (floating in separate fit)

7 PEP-II performance Run4 PEP-II top luminosity: 9.2 x 1 33 cm -2 s -1 (more than 3x design goal 3. x 1 33 ) Run1 Run2 Run3 PEP-II delivered 254 fb -1 BaBar recorded 244 fb -1 In this analysis: Run1-4 data On peak 25 fb M BB pairs 7

8 The BaBar detector Electromagnetic Calorimeter! " π γ Instrumented Flux Return )! * +, µ + - " Cherenkov Detector (DIRC) π e + [3.1 GeV] Drift Chamber! #$% &'( e - [9 GeV] Silicon Vertex Tracker! *!! 8

9 Data sample CP modes yield signal region yield signal region 9 yield signal region BABAR M ES [GeV] J/ K L signal J/ X background Non-J/ background E [MeV] CP sample J/ K S (K S + - ) N TAG 2751 J/ K S (K S ) 653 (2S) K S (K S + - ) 485 c1 K S (K S + - ) 194 purity 96% 88% 87% 85% K (K c S S + - ) % Total for CP = % J/ K * (K * K S ) % J/ K L % Total % M ES [GeV] CP

10 Data sample BFlav modes yield yield M ES [GeV] M ES [GeV] BFlav sample D - + / + /a + 1 (6 decay modes) D* - + / + /a + 1 (12 decay modes) J/ K * (K * K + - ) (2 modes) Total N TAG purity 83.1% 89.4% 95.8% 1

11 Comparison with 22 Summer 22 (sin(2) =.741±.67±.34) Summer24 Data sample 88 M BB decays (run1+2) 227 M BB decays (run1-4) 2641 CP events (tagged, signal) 773 CP events (tagged, sig.) Flavor Tagger 4 tagging categories, Q=28.5% 6 tag categories, Q=3.5% Q = (1 2 2 i i) categories (sin(2)) 1 NQ Changes in analysis: More refined treatment of signal probabilities from m ES spectrum More floating parameters for the CP background: apparent CP content fraction of prompt (continuum) background 11

12 Fit results (cc) K S (CP odd) modes J/ K L (CP even) mode sin2 =.722 ±.4 (stat) ±.23 (sys) 12 (22 measurement: sin(2) =.741±.67±.34)

13 Consistency checks J/K S ( + - ) Lepton tags F =-1 modes 2 =11.7/6 d.o.f. Prob ( 2 )=7% 2 =1.9/5 d.o.f. Prob ( 2 )=86% 13

14 : direct CP violation no direct CP violation expected in Standard Model for (cc)k decays in nominal fit, assumed =1 results from fit (using (cc) K S modes) with floating and Im(): =.95 ±.31 (stat.) ±.13 Little effect on sin(2) measurement change in S of.5 w.r.t. =1-2% correlation between coefficient of sin term and cos term Fit projection on the t distributions with floating. The dashed line are the results from the nominal fit with =1 14

15 Systematic uncertainty σ(sin2β) σ( )) Description of background events.12.2 CP content of peaking background Background shape uncertainties Mistag differences between B CP and B flav samples.7.1 Composition and content of J/ψ K L background.11 N/A t resolution and detector effects.11.3 Silicon detector alignment uncertainty t resolution model Beam spot position.7.1 Fixed m,, /,.5.1 Tag-side interference/ DCSD decays.3.12 MC statistics/bias.3.3 TOTAL Steadily reducing systematic error: July 22 =.33 (better and more Monte Carlo) July 21 =.5 15

16 sin(2) & the unitarity triangle CKM fit without sin(2) measurement CKM fit with sin(2) measurement cos(2)< cos(2)> 16 Measured value of sin(2) in excellent agreement with Standard Model expectation Strong constraint on apex of Unitarity Triangle

17 cos(2) with B J/K * (K S ) J/K* (K S ) final state can be F =+1 or F =-1, depending on L=,1,2 F = +1 for L=,2 F = -1 for L=1 In nominal fit for sin2 we used averaged CP content of +.51 Full angular analysis allows for the separation of CP even and CP odd and amplitudes Many extra terms in time-dependent decay rate, two proportional to cos(2) : - t ± e f4() A A cos( - )cos(2)sin(mt) - t e f () A A cos( - )cos(2)sin(mt) ± 6 decay angles: = (cos( ),cos( K * tr ), tr angular amplitudes ) A A A = = = A A A e e e i i i (CP odd) (CP even) (CP even) angular amplitudes in transversity basis 17

18 Phases and amplitudes Angular amplitudes and strong phases, measured from B ± J/K* ± and B J/K* (K + - ) using time-integrated angular analysis: A A A =.566 ±.12 ±.5 =.24 ±.15 ±.5 =.23 ±.15 ± solution 1 solution 2 = ±.11±.52 =.184 ±.7 ±.46 OR - - = ±.11±.52 = ±.7 ±.46 discrete ambiguity in strong phases => sign ambiguity in (±)cos(2) 18

19 Breaking the ambiguity Central idea: include (K) S-wave in angular analysis Extra terms due to interference of S-wave and P-wave contributions to K final state: ± f8() A AS cos( -S)... ± f9() A AS cos( -S)... f () A A cos( - )... ± 1 S S S-wave amplitude & phase A = S A S e i S S changes sign between solution 1 and solution 2 but near K*(89): d(s - dm K ) < (consequence of Wigner causality) 19 only physical solution is the one for which S decreases with K mass near the K* resonance

20 Breaking the ambiguity solution 1: unphysical solution BABAR - - solution 1 = ±.11±.52 =.184 ±.7 ±.46 solution 2: physical solution LASS data OR - - solution 2 = ±.11±.52 = ±.7 ±.46 2

21 cos(2) results cos(2) from 14 tagged B J/ψ(K S π ) * decays: cos(2) = sin(2) =.1±.57 ( stat.) ±.27( syst.) (with floating sin(2)) h distribution of cos(2) results from a set of 2 data-sized Monte Carlo samples, generated with cos(2)=.68 cos(2 ) = cos(2 ) = 2.72 cos(2) = ( stat.) ±.27( syst.) (with sin(2) fixed to.731) cos(2) = 1 sin 2 (2) Estimation of confidence level excluding cos(2)=-.68 determined from distribution of 2 Monte Carlo experiments: =.68 excluded at 86.6% CL CL (cos(2 ) -.68) = h(+2.72) h(+2.72) + h(-2.72) 21

22 Conclusions New measurement of sin(2) on 2.6 times larger data sample sin(2) =.722 ±.4 (stat.) ±.23 (syst.) (22 measurement: sin(2) =.741 ±.67 (stat.) ±.34 (syst.)) Reduced systematic uncertainty Excellent agreement with Standard Model prediction No significant direct CP violation in (cc)k decays: =.95 ±.31 (stat.) ±.13 (syst.) Time-dependent angular analysis of J/K* gives cos(2)> at 86.6% CL new method to resolve strong phase ambiguity sign of cos(2) in agreement with Standard Model expectations 22

23 (Backup) Summary of t-fit parameters 23 Observables: t, (t), tag flavor, tag category (all), reco flavor (BFlav only) Free parameters in t-fit: 65 sin(2): 1 (CP sample only) mistag fractions for B and B in six tag categories: 12 (common) signal resolution function R( t ): 7 (common) tagging and reconstruction efficiency ratios: 7 (common) background-related (determined from sideband in mass spectrum): background mistag fractions: 24 (BFlav only) background resolution function: 3 (common) apparent CP and composition of CP background: 8 (CP only) background composition and lifetime of BFlav modes: 3 (BFlav only) External physics parameters fixed: m=.52 ±.7 ps -1 } (B PDG24 )=1.536 ±.14 ps /= (varied to 2% as systematic) =1 (floating in separate fit)

24 (Backup) Tagging performance 24 Tag cat Lepton Kaon I Kaon II Kaon-Pion Pions Other All Eff.(%) (%) 8.6±.1 3.2±.4 1.9±.1 4.6± ± ± ± ± ±.1 33.±.6 1.± ± ±.2 (%) -.2±.8 -.7±.9 -.7±.8 -.4±1. 5.1±1. 2.4±1.2 Q(%) 7.5±.2 9.±.2 8.1±.2 3.8±.2 1.7±.1.3±.1 3.5±.4

25 (Backup) Control sample fits Fit projections on the t distributions of the J/K + control sample sin(2)= 25

26 (Backup) K mass spectrum BABAR P-wave L = 82fb-1 Kπ mass from inclusive B J/ψK + π (+c.c.) (background subtracted) S-wave 26

27 (Backup) Sub-mode fits 27

28 (Backup) KL fits 28

29 (Backup) CP=-1 modes per tag cat 29

30 (Backup) Best or the rest 3