CP violation at Belle Kenkichi Miyabayashi for Belle collaboration (Nara Women’s University) 2003/Oct./14th BEAUTY2003
KM unitarity triangle and CPV parameter convention
Topics to be covered… sin2 (sin2 ) related (140/fb) ; –CPV golden mode; B 0 J/ K S –CPV in B 0 J/ 0 2 ( ) related (78/fb); –CPV in B 0 + -
Time dependent CP asymmetry
CP eigenstate reconstruction M bc (GeV) E(GeV) Two key variables; M bc = { (E CM /2) 2 - ( P i ) 2 } 1/2 B mass(5.28GeV) E = E i - E CM /2 0 Note; These are for full-reconstructable case. For the mode having missing or K L, different variables are used. Example; B 0 J/ K S
Vertex recon. to measure t BB system is boosted =0.425 ; t obtained by z Require consistent with run-dep. IP profile ( r =21 m). CP side vertex ·reconstructed by dilepton from J/ , + - pair, etc. Tag side vertex ·Impact parameter w.r.t CP side vertex < 500 m ·K S veto ·If reduced 2 > 20 … remove the track having largest 2 Resolution function ·including charmed meson lifetime, motion of B meson, ·Validation by lifetime measurement.
Inclusive Leptons: high-p l b c l intermed-p l + s l Inclusive Hadrons: high-p + B 0 D (*) +, D (*) +, etc. intermed-p K + K + X, low-p D 0 Flavor tagging by other B decay products Based on the calculated likelihood, q =+1 for B 0, -1 for B 0 (Tag side) r = from 0(no flav. info.) up to 1(perfectly confident tag).
Validation of flavor tagging B 0 D* - l + decay is self tagging; reconstructed with high purity Good tag Poor tag OF-SF asymmetry ~ (1-2w)cos( m t) w is also investigated. 1-2w
CP fit : unbinned max. likelihood fit Signal probability density function(PDF) is; P sig ( t, q, w l, w l ) = exp(-| t|/ B )/4 B {1-q w l +q(1-2w l )[S fCP sin( m t)+A fCP cos( m t)]} here, l is flavor tagging class(1,2,…6). For i-th event, likelihood value is; P i ( t i, S fCP, A fCP ) =(1-f ol )[f sig P sig ( t, q, w l, w l ) X R sig ( t i ) + f bg P bg X R bg ( t i )] + f ol P ol ( t i ) Free parameters : S fCP and A fCP Proper resolution func. : R ** B life and mixing : PDG values Fraction of each component : f **
sin2 1 (- CP S ccs )measurement B 0 charmonium + K recon. Mode CP NeventsPurity J/ K S ( + - ) J/ K S ( 0 0 ) ’(l + l - ) K S ’(J/ ) K S c1 K S c (K S K )K S c (KK )K S c (pp) K S J/ K *0 (K S 0 ) +1* J/ K L * 81%.
B 0 J/ K L (for sin2 1 measurement) Only K L direction known. In Upsilon(4S) rest frame, B has ~340MeV/c. Reconstruct it with two-body kinematics assumption.
CPV in B 0 charmonium+K 0 :sin2 1 sin2 1 = 0.733±0.057(stat)±0.028(syst) If is free in the fit, | |=1.007±0.041(stat) consistent with 1 Now precision measurement!
CPV in B 0 J/ 0 Decay caused by b ccd transition CP = +1 Tree has no complex phase if it dominates S J/ = -sin2 1 and A J/ = 0
Reconstruction of B 0 J/ 0 103events reconstructed. Relatively clean; purity=86±10% Backgrounds are separately est. for B J/ X and combinatorial.
Results for S J/ and A J/ After ftag and vtx, 91 events are used. S J/ = -0.72±0.42(stat)±0.08(syst) A J/ = -0.01±0.29(stat)±0.07(syst) B0B0 B0B0
CPV in B 0 + - If only tree contributes, V ub interferes V td (in mixing) extract 2 ! However, penguin looks significantly large (B 0 0 0, listen T.Higuchi’s talk) so that effect on CP asymmetry is there.
Event selection of + - LR>0.825 enhanced LR<0.825 = K enhanced To suppress cont. bg, Likelihood Ratio(LR) is calculated by event shape and B’s flight direction. Correlation with flav. tag is taken into account in the CP fit. 760 candidates; (163+24/-23 signals) are obtained by 78/fb.
Results for S and A S = -1.23±0.41(stat)+0.08/-0.07(syst) A = +0.77±0.27(stat)±0.08(syst)
Results for S and A (cont.) Our result is 3.4 away from CP conservation (i.e. S =A =0).
Conclusions and future sin2 =0.733±0.057(stat)±0.028(syst) –Moving into the precision measurement regime. –Relevant modes(b ccd) making progress. B 0 + - is away from CP conserv.(3.4 ) –Analysis using 140/fb is in progress. Now going to resume physics run with new SVD and smaller radius beampipe.
Backup slide
sin2 1 :charmonium + K S and J/ K L Opposite asymmetry by diff. CP eigenvalue is clearly seen!
B ± D CP K ± D1K-D1K- D1K+D1K+ D2K-D2K- D2K+D2K+ B DK decay can be caused via Vcb and Vub, if D decays into CP eigenstate(D 1 (K + K -, + - ), D 2 (K S 0, K S , K S , K S , K S ’)), possibility to access 3 A 1 =0.06±0,19(stat)±0.04(sys) A 2 =-0.19±0.17(stat)±0.05(syst)