Excited B states at LEP

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Excited B states at LEP
Peter Kluit (NIKHEF) DELPHI/LEP

• Introduction history
• Theory
• Experimental overview
• Excited Bu,d results
• Search for Bs and Sb()
• Summary

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Introduction History

• Boom of B physics at LEP
• around 1994
• vertex detectors
• exclusive reconstruction
• Discovery Bs meson at LEP
• B baryons
• Precision lifetimes
• Bd oscillations

Event Bs? yf?mm KK
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Inclusive B reconstruction

• New technique (1994)
• High rapidity particles
• Secondary vertex
• Energy-momentum constraint
• Estimate B four-momentum
• Physics result
• precision mass B?Bg
• Production V/(VP)0.75

g ?ee-
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Discovery of excited B states
OPAL 1995
Reconstruct B?B p Inclusive B fragmentation p
OPAL 1995
1995
Prel. 1997
Prel. 1997
BsSb()
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Theory HQET
l jq JP state Decay
0 ½ 0- 1- B B Bg
1 ½ 0 1 B0 B1 Bp Bp
1 3/2 1 2 B1 B2 Bp B()p
Heavy Q, light quark q sq ql ? jq sQ qjq ?
J Charm system measured
Broad
GBroad y 300 MeV
Expect B system Dm doublet Dmc mc/mb 13 MeV
Narrow

• Similar for Bs, decay to Bsp Isospin
  forbidden
• Dominant decay Bs? B() K, if above threshold

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B production at LEP
production fractions adjusted to world average
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Experimental overview Bud
Narrow states
Experiment method m(B) MeV s(B)/s(b)
OPAL 95 Incl 5712 11 0.22 0.05
DELPHI 95 Incl 5732 5 20 0.270.020.06
ALEPH 96 Incl 5734 3 16 0.140.010.03
L3 99 Incl B2 576856 0.320.030.06
CDF 01 Semi-excl B1 5710 20 0.220.050.02
ALEPH 98 Excl B25739116 0.240.070.05
Some numbers recomputed using common inputs
OPAL 01 Br(B?Bp X)0.850.260.12
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Experimental issues

• Crucial treatment of background
• Taken from MC, except ALEPH exclusive analysis
• Induces high production rate, shifted mass
  peaks, instabilities

ALEPH exclusive
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New DELPHI B analyses

• Focus on the background
• using control sample High efficiency
• Reduction by neural networks High purity
• Full LEP I statistics, reprocessed data, improved
  analysis techniques, inclusive B reconstruction

b and anti b tagging
B charge
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Analyses steps

• Reconstruct weakly decaying B and combine with p
  from primary vertex

Signal Background wrong sign
Bd ?Bp- Bp
Bu ?B0p B0p-

• Samples separated b/b tag qB vertex charge
• High Efficiency soft cuts, signal/wrong sign
  similar shape
• High Purity tight cuts, neural network

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High efficiency Analysis

• Simultanous fit to signal and background

B signal Narrow B2 mass and
Dm(B2-B1) free Br(B2 ?Bp/Bp)1.10.3 Broad
extrapol from Charm m(B1)m(B1),Dm(B1-B0)45
MeV G300(330) MeV
DELPHI
Enhancement at Q500 MeV, G300 MeV (2 s.d.)
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• High purity analysis
• Fit background MC times polynome
• Signal resolution free parameter

Significant deviations MC at low and high Q values

• Largest Systematics
• Background parametrisation
• Energy scale
• Cuts NN rapidity
• Modeling
• With/without 500-state
• Spin/state counting

B0
B
Fits not sensitive to Broad states and to
spin/state counting (lt 2 s.d.)
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Summary of B results

• Total rate s(Bud)/s(b) (broadnarrow)

DELPHI preliminary
Meth Total rate Narrow rate Q( B2 ) MeV Dm(B2-B1) MeV
HEff 0.1600.012 0.0200.025 0.0910.007 0.0130.011 3169 129 -215911
HPur 0.1530.017 0.0380.017 0.0880.009 0.0220.011 3237 139 1513106
Comb 0.1570.011 0.0220.019 0.0900.007 0.0130.011 3196 9 9 61176 (stat) (sys) (model)
m(B2)5738 14 MeV and m(B1)5732 20 MeV
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Comparison of LEP Results

• Rate s(Bud)/s(b) (narrow)factor 1.5-2 lower
• Due to background treatment, inclusive analyses
  at LEP overestimate the rate
• Compatible with ALEPH exclusive analysis
• m(B2)5739 10 MeV DELPHI5738 14 MeV
• Total rate0.240.070.05 DELPHI0.1570.0110.02
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• Compare to s(Dnarrow)/s(c) 0.17 0.05
• FUTURE recommend exclusive analyses extracting
  the background from data

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DELPHI Bs search

• Channel Bs ? B() K-
• Using neural networks for identification of kaon
  and B vertex charge
• Fit signal (Gaussian), free background

• Total Significance 3.8s
• systematics included
• Background shape
• Identification K/ NN
• Energy scale

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Interpretation discussion

• Most likely Bs2 ? B K-
• (BK reduced by factor 10)

Where is Bs1 ? BK? Dm 13 MeV
DELPHI preliminary
Bs1 Puzzle Large Dm? Enhanced Bs1 ?
Bsp? Results m(Bs2)5852 5 MeV OPAL
5800-5900 MeV Rate s(Bs2)/s(b)0.00930.00200.00
13 OPAL 0.020 0.006
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DELPHI Sb() search

• Channel Sb ()?Lbp
• Using neural networks for identification B
  baryon
• Fit signal, free background

Sqq J
Lb 0 ½
Sb 1 ½
Sb 1 3/2
Preliminary
Upper limit 95 CL s(Sb())/s(b) lt 0.012
Old prel. DELPHI result not confirmed
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Summary

• New DELPHI measurements for Bud
• Total production rate s(Bud)/s(b)0.1570.011
  0.029
• m(B2)5738 14 MeV and m(B1)5732 20 MeV
• New results factor 1.5-2 lower than previous
  due to background
• Compatible with ALEPH exclusive, and charm
  production
• Search for Bs
• Signal at 3.8s with m(Bs2)5852 5 MeV Bs1
  Puzzle
• Production rate s(Bs2)/s(b)0.00930.00200.00
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• Search for Sb()
• Limit production rate s(Sb())/s(b) lt 0.012
  at 95 CL

Preliminary