Takahiro Matsumoto,Belle CollaborationTokyo Metropolitan UniversityDec 03 11:50-12:10

Tagging with fully reconstructed　 B’s

in B-factory experiments

Fully reconstructed B tagging

－ Offline single B meson beams with known p （ B ） , flavor.

－ Large advantage to study decays including and

Υ(4S)e- (8GeV) e+(3.5GeV)

B

B

Interesting decays•B → ul•B → •B → D•etc

Full Recon.

Need large data sample ⇒ 　 unique at B factories

Full reconstruction efficiency = O(0.1%)

KEKB Collider

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

Event display for fully reconstructed two B’s

Kinematic variables for the Υ(4S)

Energy difference:

Beam-constrained mass:

2/

2 )()2(SKJCMbc ppEm

2/ CMKJ EEEES

Fully reconstructed B tagging

B decay patterns Hadronic : ~ 80%

• A lot of decay modes with Br ≤ O(1%) Semileptonic : ~20%

• Mainly for BD*(e,) (~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 Υ(4s) CM frame

Hadronic B decays B D(*)(, , a1)-, J/(KS, K*)…

Semileptonic B decays B D(*) l

B’s Reconstruction [Hadronic]

1. Collect known major modes [Belle]

[ low efficiency, but high purity ]

BD(*)(,,a1)-, D(*)DS(*), (J/, (2s), c1)K(*)

2. Semi-inclusive reconstruction, BD(*)X [BaBar]

[ high efficiency, but low purity ]

X=n1±n2K±n3KSn40, total charge ±1

n1 + n2≤ 5, n3≤2, n4≤2

Treatment of the multiple candidates Select the best reduced 2 events to each mode

( from M(D), M(D*)-M(D), E etc.) Select the mode with the best purity

BD(*)(,,a1)

Main hadronic B decay sample [ Br ~ 1% ] D(*) is D0, D+, D*0 or D*+ [ recon. from D*D(,) and DKn ] Recon. eff. : ~0.17% for B±, ~0.07% for B0

High purity ~0.8

w/ 152 million BBbar

BD(*)Ds(*)

Br ~1%, but low yield due to D and Ds reconstruction Ds

(*)+ is recon. from Ds*+Ds+, Ds

+K+K+,KsK++,KSK+

~7% yield of BD(*)(,,a1)

Moderate purity ~ 0.6Charged B Neutral B

S= 8700 S= 4390

w/ 152 million BBbar

BCharmonium

Color suppressed modes [ Br ~ 0.1% ] Reconstructed modes

B J/KB0 (J/, (2s), c1)KS, J/K*0 ~9% yield of BD(*)(,,a1)

Very high purity ~0.95 [ due to clean recon. of J/ l+l ]

Charged B Neutral B

S= 9373 S= 7275

w/ 152 million BBbar

(CP modes= 3119)

BD(*)X [ semi-inclusive , BaBar ]

BD(*) （ n1±n2K±n3KSn40 ） ±

In total, 1097 combinations! c.f. 64 combinations for BD(*)(,,a1)

Mbc w/ lepton (Pl*>1 GeV/c)

*hep-ex/0307062 for Vub paper with BXul

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

BD(*)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 ).

w/ 89 million BBbar

S ~30k

BHadronic, Summary

BD(*)(,,a1)-, D(*)DS(*), (J/, (2s), c1)K(*)

eff. ~ 0.2% (0.1%) for charged (neutral) B• 150k B±, 69k B0 in 152 million BBbar sample

High purity ~ 0.81 BD(*)X

eff. ~ 0.5 % (0.3%) for charged (neutral) B Low purity ~ 0.25

Steady improvement will be possible

How to improve eff. and quality? Add more decay modes

• ex. D+ K++, KS+ add ~50% with D+ K++0 Study BD(*)X in detail. By understanding structure of X, we can optimi

ze the selection criteria further Further cut tuning etc.

B’s reconstruction [Semileptonic]

Reconstructed modes B D0l( Br=2.15±0.22% )

• D0K+, K+0, K++, KS0

*B D*0l ( Br= 6.5 ±0.5%) is automatically included in the sample

B D(*)0l

B± tagged events = 714k, eff. = 1.7% Purity for B D(*)0l13.9%

w/ 85 million BBbar

(Missing mass)2 for neutrino

Large eff., butLarge combinatoric backgrounds

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 BXul( for Vub analysis )

• hep-ex/030762 [BaBar] BK,

• PRL86(2001)2950 [CLEO], BaBar conference paper For the decays with low multiplicity (BK, 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 BD(*), B 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 BD(*)X ] ~ 1.7% for Semileptonic B tag*

* useful for low multiplicity B decays We already have a sample of more than 105 fully reconstr

ucted B mesons. We expect a lot of interesting physics results with these sample in near future