b Physics at the Tevatron part I: m and Dmd,s

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b Physics at the Tevatron part I m and Dmd,s

• Masses of b-hadrons,
• rare decays and
• oscillation measurements
• at CDF and D0

Saverio DAuria, University of Glasgow For the
CDF and D0 collaborations
XL Rencontres de Moriond EW
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Introduction CDF and D0 detectors
Tevatron performances see G. Bernardis
transparencies Great b-physics capabilities
D0 Excellent muon trigger Tracking coverage
? lt 2 Tracking Silicon SciFib,
CDF Excellent pT resolution, displaced track
trigger ? fully hadronic decay
modes Tracking Silicon Drift Chamber dE/dx,
ToF particle ID
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Trigger issues
CDF, D0
b Production cross section
y lt 1 CDF submitted to PRD hep-ex/0412071
Inelastic cross section ? 60 mb? factor 1/1000
trigger. Compare with b-factories s is 103
higher, L is pb -1 (TeVatron) vs. fb -1
(Y(4S))
s (mb) L cm-2 s-1 Integrated L b-events
Tevatron 29 1.2 ?1032 600 pb-1 ? 2 13.8 ?109
KEK 0.001 1.52?1034 371 fb-1 0.37 ?109
BaBar 0.001 0.95?1034 256 fb-1 0.25 ?109
e,m

• Trigger crucial point
• 2 m from J/y,
• soft lepton, (soft leptonnon prompt track)
• 2 non-prompt tracks (CDF)

(Track)
P.V.
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Relevance of mass measurements

• Spectroscopy of heavy-light quark system, to
  complement quarkonia
• Verify detailed calculation and hypothesis
  (potential, NRQCD .)
• Validation of Lattice QCD
• Spectroscopy of heavy-heavy mesons quarkonia vs.
  Bc.

Relevance of Bc

• Only meson to have 2 spectator-model weak decays
  with comparable amplitudes (b and c decays).
• Possible contamination for Bs decays
• Perfect source of flavour-tagged Bs
• Measure angle g in
  self-tagged decays

Masetti, Fleischer-Wyler,Kiselev
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b hadron masses
Fully reconstructed modes using J/y ? mm
trigger D0 more candidates CDF better mass
resolution (11 MeV, J/y mass constrained)
Calibration using J/y mass, checked against the
Y, systematics sub-MeV
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b hadron masses
B
Bs mass
Lb mass
B0
Systematics below 1 MeV for high statistics
channels Best single measurements of b-hadron
masses
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CDF Fully reconstructed Bc
m
m
Tevatron best place to measure Bc mass
precisely CDF Search for fully reconstructed mode
p
P.V.

• Trigger 2 ms from J/y, pT gt 1.5 GeV/c
• 2-body topology, reference mode B ? J/y K
• Blind search range semileptonic mass 2sm .
• Experimental issues
• lifetime, small BR, small sprod.
• expected 10-50 events, based on Run I rate.

• Background
• Prompt J/y associated to random prompt track
• ? require lifetime
• Secondary J/y with prompt track
• Secondary J/y with non prompt track
• ? require good vertexing

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CDF Fully reconstructed Bc
Hypothesis test set up before opening the box.
Score function
From toy Monte Carlo, P ? 1/1000 false positive
Threshold value
After box open scan search region with binned
likelihood fit mass fixed (scanned), Gaussian
width fixed (resolution), S,B fit parameters
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CDF Fully reconstructed Bc
Unbinned likelihood fit. Mass fit parameter,
width fixed.
Mass 6287.0 4.8(stat.) 1.1(syst.) MeV/c2
Main systematics Fit function/Background Momentum
scale pT spectrum
This result
Theory in very good agreement. Potential models,
NRQCD, LQCD Good topic for Moriond QCD
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D0 Semi-leptonic Bc decay

• Inclusive measurement Bc?J/y m X
• Same strategy, require 3rd track be a m.
• Inclusive measurement, no pointing constraint.
• No lifetime cut ? mass and lifetime measurement
• Depends on Monte Carlo for Probability Density
  Function and k-factor
• Control sample y(2S) m X?mm m X(expected low BR)
• Signal 951211 candidates,
• Significance likelihood ratio 60
• Mass MeV/c²

D0 ICHEP 04
Systematic uncertainties from MC sample
composition and decay model background fraction.
Larger than stat.
-2 log(Likelihood)
5.4 5.6 5.8 6.0 6.2 6.4 6.6 6.8
Mass (GeV/c²)
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b and c-mesons excited states
ICHEP 04
Evidence for the decay Bs ?Ds1(2536) m X Signal
18 5.5 candidates, 3.5 s
435pb-1
Studies of excited b-mesons for Same Side tagging
MC tuning Soft p from fragmentation and decay
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B-hadrons mass summary
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m
CDF/D0 Rare decays
b

• Bd,s ?mm- Flavour-Changing Neutral Currents.
• BR (3.4 0.54) 10-9 ? place to look for new
  Physics
• mSUGRA models enhanced 10 to 100? (Dedes,
  Dreiner, Nierste, hep-ph/0108037)
• SO(10) models 100? (Dermisek, Rabi et al.
  hep-ph/0304101)
• MSSM models enhanced 1000?
• D0 updated measurement to include 300 pb-1
• CDF uses 171 pb-1 Mass resolution 27 MeV/c2
• Limits on both Bd and Bs Both analyses blind

m
s
95 CL
BR (Bs ?mm- ) BR(Bd ?mm- )
D0 lt 3.7 10-7 ----------
CDF lt 7.5 10-7 lt 1.9 10-7
300 pb-1
D0 looking for BR (Bs ?mm-f ) Closed box
Attainable Sensitivity 1.2 10-5 (95 CL)
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Mixing measurements

• Reconstruct signal(s) flavor specific (selection
  cuts)
• Measure decay time for each candidate
• Establish flavor ( ) at production (?
  tagging)

Mixing Asymmetry
Need high statistics sample, well measured
lifetime.
Tagging production flavor

• Dms
• lower statistics Bs
• larger Dms

s.l.decays larger st
Statistics reduced by a factor eD2 N tagged
events eD2N useful events
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Flavor tagging

• Opposite side
• Soft-Lepton tag
• Flavor from the sign of the lepton (e or m)
  in semileptonic decays of accompanying b-meson.
• Source of dilution charm semi-leptonic cascade
  decays, oscillation in the opposite side.
• Kaon Tag
• Sign of the kaon in cascade decay b ? c ? s
• Jet Charge
• Sign of the momentum-weighted average charge of
  opposite jet.
• Same side
• Bs has preferentially a K close by, Bs has a
  K-, B0 has a p, B0 has a p-

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Flavor tagging
D0 use any m for tagging, use opposite side
fully reconstructed decays, semileptonic decays
for high statistics
Opposite side tagging is the same as for Bs
mixing use Dilution from Bd to fix this
parameter for Bs.
eD² () CDF s.l. D0 s.l. CDF had
SST (Bd) 1.04 0.35 0.06 1.00 0.36 ----
Soft m 0.56 0.05 1.00 0.38 0.46 0.11 0.03
Soft e 0.29 0.03 -- 0.18 0.06 0.02
Jet Qpt 0.16 0.03 0.03 ?1 0.24 0.09 0.01
Jet Qjp 0.150 0.03 0.02 0.11 0.06 0.02
Jet Qvtx 0.26 0.03 0.02 0.14 0.07 0.01
Combined 1.429 0.093 1.12 0.18 0.04
Overall fitter
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Dmd measurements
Expt (pb-1) channel Tag Result
D0 250 s.l. combined 0.456 0.034 (stat.) 0.024 (syst.)
D0 460 s.l. o.s.t. 0.558 0.048 (stat.) x.xxx (syst.)
CDF 355 s.l. o.s.t. 0.497 0.028 (stat) 0.015 (syst.)
CDF 355 f.r. o.s.t. 0.503 0.063 (stat) 0.015 (syst.)
NEW since la Thuile 05
460 pb-1
Main purpose tagging and fitting test preparing
for Dms Best measurement HFAG Dmd (0.506
0.006 0.008) ps-1
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Amplitude scan

• Fourier-transform method
• Fix frequency (Dm)
• Fit for the oscillation amplitude.
• Limit at 95 lowest value Dmlim
• P(A (Dmlim) ? 1) 5
• Sensitivity lowest value of Dm with error
  compatible with 1 (at 5)
• Measurement (range of) amplitude(s) compatible
  with 1 and not compatible with 0..value of Dm
  from asymmetry fit !
• Advantage easier to combine results

semileptonic
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Dms CDF sensitivity studies
World average Limit Dms gt 14.5 ps-1 Sensitivity
for Dms lt 18.3 ps-1
CDF 2
PDG 2004 HFAG
CDF Semileptonic Bs ? Ds l X , Ds ?
fp, KK, pp-p CDF hadronic Bs ? Ds p,
Ds ? fp, KK, pp-p
? 6700
? 700
D0 Semileptonic Bs ? Ds l X , ? 7000
Ds ? fp
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Dms D0 Preliminary results
Tagged 37631
Semi leptonic decays L 460 pb-1, opposite side
tag
D 0.47 0.01
Dms gt 5.0 ps-1 at 95 CL
Limit lt world average, but this is a first step
in the full analysis
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Other b-physics results

• CP Asymmetry in B ? fK
• PRL, hep-ex/0502044
• Evidence for the decay Bs? ff
• PRL, hep-ex/0502044
• CP Asymmetry in B ? hh (hp?,K?) ICHEP04

Bs penguin-diagram decay
ACP (B ? f K)
ICHEP 04
ICHEP 04
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Conclusions

• The Tevatron can produce unique results in B
  Physics and confirm/complement B factories.
• m u,d,s,c
• Best measurements of b-hadron masses, at 0.02
  level
• CDF first evidence of a fully reconstructed Bc
  decay mBc 6287.0 4.8 1.1 MeV/c²
• Run 2 confirmation of semileptonic Bc decay
• Rare decays improve limits on new Physics.
• Dmd
• Flavour taggers B0 mixing as a proof of
  principle.
• Amplitude scan method used for B0
• Dms
• D0 first preliminary Dms measurement from Run 2
  Dms gt 5.0 ps-1 at 95 CL
• G and DG see next talk
• Results improve faster than systematics
  and techniques.
• Including other decay modes, taggers, data.
  Moriond QCD

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Backup Slides
Aurora Borealis at Fermilab 9th November 2004, 3
a.m. 42N
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CDF Fully reconstructed Bc
Cut MC Efficiency N-1 data entries Background rejection
Lxy/s(Lxy) 42.0 11930 96.7
pT (p) 62.3 3043 87.1
?2(3D) 80.5 762 48.4
Pointing angle 85.4 768 48.8
?2vtx(p) 92.7 565 30.4
d0(Bc) 97.5 448 12.3
ct lt 98.7 410 4.1

• Summary of cut values used
• pT (p) gt 1.8 GeV/c
• Lxy/s(Lxy) gt 4.4
• ?2(3D) lt 9.0
• d0(Bc) lt 65 mm
• pointing angle lt 0.4 radians
• ?2vtx(p) lt 2.6
• ct lt 750 mm

S number of signal events from MC B average
number of background events (data) from whole
region in a window 2-sM wide (60.4 MeV/c2).
Maximized
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CDF Fully reconstructed Bc
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CDF Partially reconstructed hadronic Bc
No pointing cuts Relax vertex chi2
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D0 combined taggers, semileptonic decays, 250
pb-1 Dmd 0.456 0.034 (stat.) 0.024 (syst.)
ps-1 D0 combined opposite side taggers,
semileptonic decays, 460 pb-1 Dmd 0.558
0.048 (stat.) x.xxx (syst.) ps-1 CDF combined
opposite side taggers, semileptonic decays, 355
pb-1 Dmd 0.497 0.028 (stat) 0.015 (syst.)
ps-1 CDF combined opposide side taggers, fully
reco. decays, 355 pb-1 Dmd 0.503 0.063
(stat) 0.015 (syst.) ps-1
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Mixing Control sample Bu
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Mixing and CKM

• Dms time independent CP violation in Bs (g)
• Dms / Dmd well theoretically understood
• Dms / Dmd sensitive to new Physics
• Bs oscillations Dms,DGs

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