Mike Strauss

1
Rare Heavy Flavor Decays at DØ

• Mike Strauss
• for the DØ Collaboration
• The University of Oklahoma
• The Oklahoma Center for High Energy Physics

XXXIII International Conference on High Energy
Physics Moscow, Russia 26 July 2 August, 2006
2
Outline

• Search for D ? p m m
• FCNC in Charm Sector
• Search for Bs0 ? m m and Bs0 ? f m m
• FCNC in Bottom Sector

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FCNC in the Charm Sector

• Experimental limits exist for b?s and s?d
• Some models predict violations from SM in up
  quark sector, but not down quark sector

• RPV in the up sector
• Burdman et.al.
• hep-ph/0112234
• Little Higgs Models
• Fajfer et.al.
• hep-ph/0511048

SM
c ? u mm
4
c ? umm Analysis

• ?1 fb1 of data
• Find Ds ? pf ? pmm
• (100 of Ds ? pf)
• BF(Ds?pf) 0.0360.009
• BF(f ?mm)
• (2.8500.19)104
• Search for D ? pmm
• for m(mm) ? m(f)
• Add track to low mass dimuon candidate

w
f
5
Selection and Optimization Criteria

• Isolation ID p(D)/?pcone
• R (?h2 ?f2)½ lt 1.0
• Transverse flight length significance SD
• Collinearity angle QD
• Pion impact parameter significance Sp
• M c2vtx kp2 DRp2
• kp 1/pT(p)

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D ? pf ? pmm
0.96 lt m(m m) lt 1.06 GeV/c2
Resonance optimized cuts
Loose cuts
D
Ds
n(D) 26 9 n(Ds) 65 11
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Extracting the Resonant Branching Fraction
fc?D Fraction produced in fragmentation fp
Prompt fraction e Reconstruction efficiency
SM 1.77106 CLEO-c (f?ee)
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Nonresonant D ? p m m-
0.2 lt m(mm) lt 0.96 GeV/c2 1.06 lt m(mm) lt 1.76
GeV/c2
0.96 lt m(mm) lt 1.06 GeV/c2
BF(D ? p m m-) lt 4.7106 _at_ 90 C.L
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Bs0 ? m m

• FCNC with zero cross section at tree level
• SM Branching Fraction
• BF(Bs0 ? m m) (3.42 0.54) 109
• BF(Bd0 ? m m) (1.00 0.14) 1010
• Non-SM processes can enhance BF(Bs0 ? m m)
• MSSM enhances BF up to 3 orders of magnitude
• 2HDM, minimal supergravity, minimal SO(10) GUT,
  all have BF enhancements

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Search for Bs0 ? m m

• 300 pb-1 data analyzed (PRL 94, 071802 (2005))
• Sensitivity for 0.7 fb-1 determined
• Blind analysis to avoid bias
• Side bands used for background determination
• Normalize to resonant decay B ? J/y K

• pT(m) gt2.5 GeV/c
• h(m)lt 2
• c2vertex lt 10
• CFT hits gt 4
• SMT hits gt 3
• pT(Bs) gt 5 GeV/c
• dLxy lt 0.15 mm

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Analysis and Optimization

• Optimization using MC signal and background from
  data sidebands using
• Collinearity (Pointing) Angle
• Decay length significance
• Isolation

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Analysis and Normalization

• R BF(Bd)/BF(Bs) is small due to Vtd/Vts2
• eB/eBs efficiency
• eBd /eBs relative efficiency for Bd ?m m-
  versus Bs? m m-
• fs/fu fragmentation ratio

0.3 fb1
additional 0.4 fb1
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300 pb-1 Limit (published 2005)
Observed 4, expect 4.3 1.2
BF(Bs ? mm-) lt 5.0107 _at_ 95 C.L.
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DØ Sensitivity 0.7 fb-1
0.4 fb1

• For new dataset of 0.4 fb1
• Expect 2.2 0.7 background events
• Expect a sensitivity of about 3.0107 _at_ 95 C.L.
  
• Combined 0.7 fb1 sensitivity of 1.9107 _at_ 95
  C.L

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Search for Bs0 ? f m m

• ?0.45 fb1 of data
• Similar selection criteria to Bs0 ? m m
• 0.5 lt m(mm) lt 4.4 GeV/c2 excluding 5s around
  J/y y(2S)

• f ? K K
• pT (K)gt0.7 GeV/c
• 1.008 lt m(f) lt 1.032 GeV/c2

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Analysis Method

• Blind analysis Optimization using MC signal and
  background from data sidebands using
• Pointing Angle lt 0.1 rad
• Decay length significance gt 10.3
• Isolation gt 0.72

• Normalize to resonant decay Bs ? J/y f

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Bs0 ? f m m Results

• Expected background from sidebands 1.6 0.4
  events
• Observe zero events in signal region

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Bs0 ? f m m Results
_at_ 95 C.L
(10 times better than best limit)
Accepted for PRD Rapid Communication

• SM BF(Bs0 ? ? m m) 1.6 106 (30
  uncertainty)
• (Geng and Liu, J. Phys G 29, 1103 (2003)
• Accessible with about 4 fb1 of data

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Conclusions

• Searches for FCNC can give insight into physics
  beyond the Standard Model
• New DØ limits on D ? pmmand Bs0 ? ? m m are
  worlds best
• New limit on Bs0 ? m m should be coming soon