radiative and rare b-decays at babar
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Radiative and Rare B-Decays at BaBar
All results are preliminary unless journal ref. is givenlimit values are 90% CL unless otherwise specified
Carsten Hast, SLACfor the BaBar Collaboration
Pittsburgh, October 17
Beauty 2003, October 17th Carsten Hast, SLAC 2
Overview
Since this talk is nicely framed between a theoretical introduction and a Belle summary and outlook I will focus on newer results and analysis techniques from BaBar
• FCNC b K
• Purely Leptonic Decaysb b
• b Kll and b K*ll • B Xsll
• Radiative Decays B0 K2
*0(1430) and B+ K2*+(1430)
Beauty 2003, October 17th Carsten Hast, SLAC 3
DIRC PID)144 quartz bars
11000 PMs
1.5 T solenoid EMC
6580 CsI(Tl) crystals
Drift Chamber40 stereo layers
Instrumented Flux Return
iron / RPCs (muon / neutral hadrons)
Silicon Vertex Tracker5 layers, double sided
strips
e+ (3.1 GeV)e- (9 GeV)
SVT+DCH: (pT)/pT = 0.13 % pT + 0.45 %, good dE/dx DIRC: K- separation 4.2 @ 3.0 GeV/c 2.5 @ 4.0 GeV/c EMC: Very good electron identification and 0 reconstructionIFR: Decent muon identification
The BaBar Detector
Beauty 2003, October 17th Carsten Hast, SLAC 4
On(off)-peakRun 1+2 82 (10)fb-1
Run 3 31 (4) fb-1
Run 4 6 (0)fb-1
Best PeformancePEPII peak Luminosity: 6.582x1033 cm-2 sec-1
Integrated Luminosity Shift: 135.2 pb-1 in 24 hours: 391.2 pb-1
124.1106 BB
89.7106 BB
82 fb-1 on-peak data for analysis
PEP- II Lumi Performance and Recorded BaBar Lumi
Beauty 2003, October 17th Carsten Hast, SLAC 5
e+e- (4S) BB B produced almost at rest in (4S) frameFor B decay with no missing particles use beam energy to constrain
mass and energy of the reconstructed B
**beamB EEE
background
signal
background
0 for signal0 for signal mB for signal**beamB EEE 22
BbeamES PEm
E and mES provide uncorrelated measurement of energy and mass
Standard Variables in (4S) Frame
Beauty 2003, October 17th Carsten Hast, SLAC 6
• The best upper limits (@90% CL):– CLEO: Br (BK) 2.410–4
– BABAR: Br (BK) 9.410–5
Semi-Leptonic B-tags: BDlX (X , 0 or nothing) 50.7 fb-1
• New search (80 fb-1) with hadronic B-tags
hep-ex/0207069PRL 86 2950 (2001)
Search
A rare flavour changing neutral current (FCNC) bs decaySM prediction: Br (BK) 410–6
Summed over all neutrino species
• B D0(*) () (K) (K0s) (0)
(D* D0 and D0 K , K0, K3, Ks)
• B constraining kinematic variables: E and mES
Beauty 2003, October 17th Carsten Hast, SLAC 7
• Identify tag B in signal E and mES area• All remaining tracks and neutrals belong to the recoiling signal-side B
• One well identified Kaon• no 0
• Missing momentum not in the beam pipe• “extra” Energy < 300 MeV
Data
BK MC
B+B MC B0B0 MC cc MC u,d,s MC
Search II
Beauty 2003, October 17th Carsten Hast, SLAC 8
Upper Limit
• Selected events: 3• Expected background events: 2.70.8
Br ( BBr ( B K K ) < 1.05 ) < 1.05 10 10 4 4 @ 90% CL @ 90% CL hep-ex/0304020
Br ( BBr ( B K K ) < 7.0 ) < 7.0 10 10 5 5 @ 90% CL @ 90% CL
• Combining this result with the previous, (Br (BK) 9.410–5) statistically independent BABAR result, yields a new limit:
Going to PRL
Beauty 2003, October 17th Carsten Hast, SLAC 9
SemiSemiLeptonic B-tagLeptonic B-tagB B Dl Dl X X
Hadronic B-tagHadronic B-tagB B D DXXhadhad
2 analyses of the 1999-2002 data sample: ~81 fb1
Reconstruct one B meson as
The remaining neutrals and tracks are signal candidates
The two samples of tag B mesons are statistically independent
(e, (e, ) ) (e, (e, ) ) (e, (e, ) ) (e, (e, ) )
((, , 00, , ) )
very clean but low efficiency (~ 0.25 – 0.30 %)
Search
Beauty 2003, October 17th Carsten Hast, SLAC 10
event veto• Only one charged track having low
impact parameter• Track is not identified as a kaon• Track is an identified lepton• Residual neutral energy is used to model PDFs to extract signal
and background contributions
• Three preselections • 1 track, 0 0
• 1 track, 1 0
• 3 tracks, 0 0
• Track is not identified as a kaon• Track is identified as lepton or pion• Additional cuts on
• Missing momentum• Residual neutral energy• Track momentum• Invariant masses
• Background mainly from Vcb events• Signal efficiency:Signal efficiency: 11.3% 11.3%
• Signal efficiencySignal efficiency: : 22.5%22.5%
SemiSemiLeptonic B-TagLeptonic B-Tag
Hadronic B-TagHadronic B-Tag
Signal Background
Eleft (GeV) Eleft (GeV)
Eve
nts/
0.07
GeV
Signal Selection
Beauty 2003, October 17th Carsten Hast, SLAC 11
Br ( BBr ( B ) < 7.7 ) < 7.7 10 10 4 4
hep-ex/0303034
hep-ex/0304030
SemiSemiLeptonic B-TagLeptonic B-Tag Hadronic B-TagHadronic B-Tag
Eleft (GeV)
Eve
nts/
0.07
GeV
Br ( BBr ( B ) < 4.9 ) < 4.9 10 10 4 4
47.7 47.7 7.0 7.0Observed events onpeak data
39.9 39.9 2.8 2.8Expected Bkg in onpeak data(sideband extrapolation)
40.9 40.9 3.8 3.8Expected Bkg from MC
3537.6 4.7 1.5All
108674
6.7 2.0 0.65.0 1.7 0.4
11.2 2.5 0.510.4 2.6 1.24.3 1.4 0.3
e e e e
0 0
Data candidates
Total BkgSelection
Results
Br ( BBr ( B ) < 4.1 ) < 4.110 10 4 4 @ 90% CL @ 90% CLSM prediction: SM prediction: < < 9.29.2101055
Combined limit
hep-ex/0305034
Beauty 2003, October 17th Carsten Hast, SLAC 12
Search
B rest frameB rest frame
CM frameCM frame
Signal Monte CarloData sample 1999–2002: ~81fb–1
Two Body decay p() ~ mB/2
• One well identified muon
• All the rest is from the companion B– do particle identification
– No additional leptons allowed
• After the companion B was found,
p() is re-reconstructed in the
signal B rest frame
Beauty 2003, October 17th Carsten Hast, SLAC 13
All other tracks and neutrals make the All other tracks and neutrals make the CompanionCompanion-B-B
Search
Signal Monte Carlo
Beauty 2003, October 17th Carsten Hast, SLAC 14
• Signal Selection efficiency: 2.09%• Selected events: 11• Expected background: 5.0
• Bg fluctuation prob. to the signal: 4%
DataB MC
Signal boxSignal box
SidebandSideband
B ( BB ( B ) < 6.6 ) < 6.6 10 10 6 6 @ 90% CL@ 90% CL
BABAR-CONF-03-007
+1.81.4
Upper Limit forData
Beauty 2003, October 17th Carsten Hast, SLAC 15
bK(*) l l
Reconstruct K+, Ks +-, K*0 K+ -, K*+ Ks +
Lepton identification for e+e- with p(e) > 0.5 GeV/c, +- with p() > 1.0 GeV/c
penguin diagram b s ll box diagram b s ll
Updated result on 113 fb-1 accepted by PRL
Beauty 2003, October 17th Carsten Hast, SLAC 16
bK(*) l l Peaking Background
Events with the same final state: B J/ K(*), ’ K(*)
Signal is scattered in this above area
500 fb-1 B J/ K(*), ’ K(*) Monte Carlo little to no contribution outside these veto bands
J/ veto ’ veto
Mll [Gev/c2] Mll [Gev/c2]
E [G
eV]
E [G
eV]
Beauty 2003, October 17th Carsten Hast, SLAC 17
bK(*) l l Peaking Background II
Background from lepton miss-identificationB h+h- K(*)
mES [Gev/c2] mES [Gev/c2]
# E
vent
s
# E
vent
s
h+h- K(*) events in data convolved with rates for h to fake e,
0.01 events 0.33 events
Included as part of the fit to data
Beauty 2003, October 17th Carsten Hast, SLAC 18
bK l l Results
2-D unbinned maximum LH fit to mES and Eon all 4 decays K+ee/ and Ks
0ee/
Br(bK ll) = (6.5 +1.4-1.3 +/- 0.4 ) 10-7
8.4 excess over background
accepted by PRL
Beauty 2003, October 17th Carsten Hast, SLAC 19
bK* l l Results
3-D unbinned maximum LH fit to mES, E and mK
Br(bK* ll) = (8.8 +3.3-2.9 +/- 1.0 ) 10-7
3.3 excess over background Constrain: K*ee = 1.33 X K* tot(B0) = 1.08 X tot(B+)
accepted by PRL
Beauty 2003, October 17th Carsten Hast, SLAC 20
bK(*) l l Results
Comparison of mll in data with simulation, normalized to the measured Br
Fits well
Beauty 2003, October 17th Carsten Hast, SLAC 21
Semi-Inclusive BXs l l
Sum of exclusive modes approach:reconstruct Xs with 1 K± or K0
s +-, # ( + 0) 2, # 0 110 modes, ~50% of BR(B Xs l+l-) (75% if assumed KS=KL)
Similar analysis as b K(*) ll but with higher combinatoric background
B Xs e+e- B Xs +-
mES [Gev/c2] mES [Gev/c2]
Beauty 2003, October 17th Carsten Hast, SLAC 22
Semi-Inclusive BXs l l Results
Mode Nsig
( stat)
Signifi-cance(stat)
Effici-ency
B Xs ee
29.0 8.3
4.0 2.5%
B Xs
12.4 6.2
2.2 1.2%
Sum 41.4
10.3
4.6
Br(B Xs ee) = (6.6 1.9 1.91.6) 106
Br(B Xs ) = (5.7 2.8 1.71.4) 106
Br(B Xs ll) = (6.3 1.6 1.81.5) 106
+ Data
Monte Carlo
Beauty 2003, October 17th Carsten Hast, SLAC 23
Br (B0 K2*0(1430) ) BaBar (12.2 +/- 2.5 +/- 1.1)10-6 (14.4 +/- 4.0 +/- 1.3)10-6 Belle ( 13 +/- 5 +/- 1) 10-6
Cleo (16.6 +/- 5.9 +/- 1.3) 10-6
B0 K2*0(1430) and B+ K2*+(1430)
Br (B+ K2*+(1430) )
BaBar Preliminary BaBar Preliminary
Beauty 2003, October 17th Carsten Hast, SLAC 24
Summary (1)
• FCNC b K3 bg
events expected 3 seen
• Purely Leptonic Decaysb difficultb looks quite interesting
• Radiative Decays B0 K2
*0(1430) and B+ K2*+(1430) BaBar is in the game
Beauty 2003, October 17th Carsten Hast, SLAC 25
Bs l l Summary
Next step: measure angular and kinematic distributions
…and have fun with the next talk covering all the other interesting rare results measured by Belle
Br(bs ll) in good agreement within experiments and prediction
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