fully reconstructed B’s in B-factory experiments Tagging with fully reconstructed　B’s in B-factory experiments Takahiro Matsumoto, Belle Collaboration Tokyo Metropolitan University Dec 03 11:50-12:10

Fully reconstructed B tagging －Offline single B meson beams with known p（B）, flavor. －Large advantage to study decays including n and t Υ(4S) e- (8GeV) e+(3.5GeV) B p Interesting decays B → uln B → tn, Knn B → Dtn etc Full Recon. Full reconstruction efficiency = O(0.1%) Need large data sample ⇒　unique at B factories

The KEKB Collider (8 x 3.5 GeV, X angle) World record: L=(1.0 x 1034)/cm2/sec Accumulated 158/fb by this summer 152 million BBbar pairs KEKB Collider

Event display for fully reconstructed two B’s

Kinematic variables for the Υ(4S) Energy difference: Beam-constrained mass:

Fully reconstructed B tagging B decay patterns Hadronic : ~ 80% A lot of decay modes with Br ≤ O(1%) Semileptonic : ~20% Mainly for BD*(e,m)n (~10%), B momentum unknown Reconstruction Hadronic : Collect as many modes as possible Requires many CPU time due to multiple combination Semileptoic : Neutrino reconstruction with assumption of rest B at U(4s) CM frame Hadronic B decays B D(*)(p, r, a1)-, J/Y(KS, K*)… Semileptonic B decays B D(*) l n

B’s Reconstruction [Hadronic] Collect known major modes [Belle] [ low efficiency, but high purity ] BD(*)(p,r,a1)-, D(*)DS(*), (J/Y, Y(2s), cc1)K(*) Semi-inclusive reconstruction, BD(*)X [BaBar] [ high efficiency, but low purity ] X=n1p±n2K±n3KSn4p0, total charge ±1 n1 + n2≤ 5, n3≤2, n4≤2 Treatment of the multiple candidates Select the best reduced c2 events to each mode ( from M(D), M(D*)-M(D), DE etc.) Select the mode with the best purity

BD(*)(p,r,a1)- Main hadronic B decay sample [ Br ~ 1% ] D(*) is D0, D+, D*0 or D*+ [ recon. from D*D(p,g) and DKnp ] Recon. eff. : ~0.17% for B±, ~0.07% for B0 High purity ~0.8 w/ 152 million BBbar

BD(*)Ds(*) Br ~1%, but low yield due to D and Ds reconstruction Ds(*)+ is recon. from Ds*+Ds+g, Ds+K+K-p+,KsK+p+p-,KSK+ ~7% yield of BD(*)(p,r,a1)- Moderate purity ~ 0.6 Neutral B Charged B S= 4390 S= 8700 w/ 152 million BBbar

BCharmonium Color suppressed modes [ Br ~ 0.1% ] Reconstructed modes B- J/YK-, B0 (J/Y, Y(2s), cc1)KS, J/YK*0 ~9% yield of BD(*)(p,r,a1)- Very high purity ~0.95 [ due to clean recon. of J/Y l+l- ] Charged B Neutral B S= 9373 S= 7275 (CP modes= 3119) w/ 152 million BBbar

BD(*)X [ semi-inclusive , BaBar ] BD(*)（ n1p±n2K±n3KSn4p0）± In total, 1097 combinations! c.f. 64 combinations for BD(*)(p,r,a1)- Mbc w/ lepton (Pl*>1 GeV/c) High eff. ~0.5% for B±, ~0.3% for B0 Low purity: ~ 0.25 ~0.67 w/ lepton (P*l>1 GeV/c) in recoil B side S ~30k BD(*)X is categorized by Mx region depending on purity and select the best purity mode for each event ( also mode dep. threshold cut on purity is applied ). *hep-ex/0307062 for Vub paper with BXuln w/ 89 million BBbar

BHadronic, Summary BD(*)(p,r,a1)-, D(*)DS(*), (J/Y, Y(2s), cc1)K(*) eff. ~ 0.2% (0.1%) for charged (neutral) B 150k B±, 69k B0 in 152 million BBbar sample High purity ~ 0.81 BD(*)X eff. ~ 0.5 % (0.3%) for charged (neutral) B Low purity ~ 0.25 How to improve eff. and quality? Add more decay modes ex. D+  K-p+p+, KSp+ add ~50% with D+ K-p+p+p0 Study BD(*)X in detail. By understanding structure of X, we can optimize the selection criteria further Further cut tuning etc. Steady improvement will be possible

B’s reconstruction [Semileptonic] Reconstructed modes B- D0l-n ( Br=2.15±0.22% ) D0K-p+, K-p+p0, K-p+p+p-, KSp0 *B- D*0l-n ( Br= 6.5 ±0.5%) is automatically included in the sample

B- D(*)0l-n B± tagged events = 714k, eff. = 1.7% Purity for B- D(*)0l-n = 13.9% (Missing mass)2 for neutrino Large eff., but Large combinatoric backgrounds w/ 85 million BBbar

Application to physics analysis Fully reconstructed B tag sample is widely used for physics analysis since B-factory experiments succeeded to accumulate large sample of BBbar pairs BXuln ( for Vub analysis ) hep-ex/030762 [BaBar] BKnn, tn PRL86(2001)2950 [CLEO], BaBar conference paper For the decays with low multiplicity (BKnn, tn etc.), we can suppress combinatoric background significantly, then semileptonic B tag ( ~1% eff. ) sample can be also utilized Other interesting physics analyses are also expected BD(*)tn, Btt etc. or detailed study of inclusive B decays

Conclusions A large number of fully reconstructed B sample is already available in B-factory  Provide tools for innovative B physics analysis Reco. eff. ~ 0.15%(0.4%) for Hadronic B tag [ () is for BD(*)X ] ~ 1.7% for Semileptonic B tag* * useful for low multiplicity B decays We already have a sample of more than 105 fully reconstructed B mesons. We expect a lot of interesting physics results with these sample in near future