CP violation at Belle
Kenkichi Miyabayashifor Belle collaboration
(Nara Women’s University)
2003/Oct./14th
BEAUTY2003
KM unitarity triangle andCPV parameter convention
Topics to be covered…
• sin2 (sin2) related (140/fb) ;– CPV golden mode; B0 J/ KS
– CPV in B0 J/ 0
• 2 () related (78/fb);– CPV in B0 +-
Time dependent CP asymmetry
CP eigenstate reconstruction
Mbc(GeV)
E(GeV)
Two key variables;Mbc = { (ECM/2)2 - ( Pi)2}1/2
B mass(5.28GeV)E = Ei - ECM/2
0
Note;These are for full-reconstructable case.For the mode having missing or KL, different variables are used.
Example; B0 J/ KS
Vertex recon. to measure t
BB system is boosted=0.425 ; t obtained by z
Require consistent with run-dep. IP profile (r=21m).
CP side vertex· reconstructed by dilepton from J/, +- pair, etc.
Tag side vertex · Impact parameter w.r.t CP side vertex < 500m· KS veto· If reduced 2 > 20 … remove the track having largest2
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 + B0D(*) +, D(*) +, etc.intermed-p K+ K+ X,
low-p D0
Flavor tagging by other B decay products
Based on the calculated likelihood, q =+1 for B0, -1 for B0 (Tag side)r = from 0(no flav. info.) up to 1(perfectly confident tag).
Validation of flavor tagging
B0 D*-l+ decay is self tagging;reconstructed with high purity
Good tag
Poor tag
OF-SF asymmetry ~ (1-2w)cos(mt)w is also investigated.
1-2w
CP fit : unbinned max. likelihood fit
Signal probability density function(PDF) is;Psig(t, q, wl, wl)= exp(-|t|/B)/4B{1-qwl+q(1-2wl)[SfCPsin(mt)+AfCPcos(mt)]}
here, l is flavor tagging class(1,2,…6).
For i-th event, likelihood value is;Pi(ti, SfCP, AfCP)=(1-fol)[fsig Psig(t, q, wl, wl) X Rsig(ti) + fbg Pbg X Rbg (ti)]
+ fol Pol(ti)
Free parameters : SfCP and AfCP Proper resolution func. : R**
B life and mixing : PDG values Fraction of each component : f**
sin21 (-CPSccs)measurement B0 charmonium + K recon.
Mode CPNevents Purity
J/ KS(+-) -1 1997 0.98
J/ KS(00) -1 288 0.82
’(l+l-) KS -1 145 0.93
’(J/) KS -1 163 0.88
c1 KS -1 101 0.96
c (KSK)KS -1 123 0.72
c (KK)KS -1 74 0.70
c (pp) KS -1 20 0.91
J/ K*0(KS0) +1* 174 0.93
J/ KL +1 2332 0.60* 81%.
B0 J/ KL
(for sin21 measurement)
Only KL direction known.In Upsilon(4S) rest frame,B has ~340MeV/c.Reconstruct it with two-bodykinematics assumption.
CPV in B0 charmonium+K0:sin21
sin21 = 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 B0 J/ 0
Decay caused by b ccd transition CP = +1
Tree has no complex phase if it dominates SJ/ = -sin21 and AJ/ = 0
Reconstruction of B0 J/ 0
103events reconstructed.Relatively clean; purity=86±10%
Backgrounds are separately est. for B J/ X and combinatorial.
Results for SJ/ and AJ/
After ftag and vtx, 91 events are used.SJ/ = -0.72±0.42(stat)±0.08(syst)AJ/= -0.01±0.29(stat)±0.07(syst)
B0
B0
CPV in B0 + -
If only tree contributes, Vub interferes Vtd(in mixing)extract 2!
However, penguin looks significantly large(B0 00, listen T.Higuchi’s talk)
so that effect on CP asymmetry is there.
Event selection of + -
LR>0.825
enhanced
LR<0.825=
Kenhanced
To suppress cont. bg,Likelihood Ratio(LR) is calculated by event shape and B’s flight direction.Correlation with flav. tag is taken intoaccount 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.• B0 +- is away from CP conserv.(3.4)
– Analysis using 140/fb is in progress.
Now going to resume physics run with newSVD and smaller radius beampipe.
Backup slide
sin21:charmonium + KS
and J/ KL
Opposite asymmetryby diff. CP eigenvalueis clearly seen!
B± DCP K±
D1K- D1K+
D2K-D2K+
B DK decay can be caused via Vcb and Vub, if D decays into CP eigenstate(D1(K+K-, +-), D2(KS0, KS, KS, KS, KS’)),
possibility to access 3
A1=0.06±0,19(stat)±0.04(sys) A2=-0.19±0.17(stat)±0.05(syst)