Takahiro Matsumoto, Belle Collaboration Tokyo Metropolitan University Dec 03 11:50-12:10
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Transcript of Takahiro Matsumoto, Belle Collaboration Tokyo Metropolitan University Dec 03 11:50-12:10
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