BTeV – A Dedicated B Physics Experiment at the Tevatron Collider
B physics at the Tevatron
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Transcript of B physics at the Tevatron
B. Abbott
B physics at the Tevatron
Brad AbbottUniversity of Oklahoma
SLAC April 19, 2005
B. Abbott
B physics at Hadron Colliders
Advantages:
Large cross sections ~100 b
Produce all B species: Bu, Bd
Bs, Bc, b,, ….
Incoherent production
Disadvantages:
Large backgrounds Triggering and reconstruction difficult
and 0 modes challenging
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Both Detectors
Silicon vertex detectorsCentral trackingHigh rate DAQCalorimetryMuon systems
CDF: Silicon vertex trigger Particle ID(dE/dx and TOF) Excellent mass resolution
DØ: Excellent electron and muon ID Large acceptance
DØ
CDF
Strengths
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Luminosity
Tevatron doing very well
Both experiments have~ 600 pb-1 on tape
CDF: 240-360 pb-1 for results
DØ: 220-460 pb-1 for results
Peak Luminosity doubled in 2004 1 x 1032 cm-2 s-1
Expect twice data in 2005
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Analyses:
• Focus on measurements complimentary to those at B-factories
• Bs, Bc, b, … (Modes not accessible at B-factories)
• Can contribute in a few places accessible to B-factories: B+ K+, Bd , lifetimes…
• Often use lifetimes, Bd mixing, etc. as calibration measurements.
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Analysis strategy
• Need to work with modes that can be triggered on
• J/ (trigger on dimuons)
• Semileptonic decays: trigger on lepton
• Hadronic decays (trigger on track impact parameter (CDF), trigger on lepton from “other” B.
Note: Need to apply Pt cuts on leptons to reduce rate and impact parameter triggerbiases lifetimes.
DØ strength
CDF strength
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Wide range of Analyses
• Measuring various B decays– Bc,B hh, b sss
• Lifetimes– B+/B0, b, Bs semileptonic
• Excited states– B**, D**, Bs Ds(2536)
• Rare decays– Bs/Bd , Bs
• Bs mixing, • Quarkonia, B hadron masses, Production cross sections,
bb correlations, hadronic moments, charm physics,…
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Bc
• Bc challenging. Low production rate
B+,B0:40%, Bs,B baryons: 10%, Bc~ .05%
• Factor of 3 shorter lifetime so cannot apply long lifetime cuts to reduce backgrounds
• First observed in 1998 by CDF in Bc J/ +lepton
• DØ observed Bc in this mode in 2004
• Want to measure properties of Bc
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Bc J/
• New CDF blind analysis
• “score” function S/(1.5+sqrt(B)) set in advance
• Reference mode B+ J/ K+
First evidence of Bc J/
Mass of Bc = 6.2870 ± 0.0048(stat) ± 0.0011(sys) GeV/c2
~ 100 times better than previous mass measurement
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Bc J/ e• Easy trigger: J/ • Can only partially
reconstruct due to M(Bc)=5.95 +0.14 – 0.13 ± 0.34 GeV/c2
Bc= 0.448 +0.123 – 0.096 ± 0.121 ps
95 ± 12 ± 11 signal events
114 ±15.5 ± 13.6 events
Critical issue is understanding backgroundbb, conversion e and fake e
J/ e X
J/ X
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B hh• Charmless two-body decays• Can measure BR and direct CP asymmetry• Signal is composed of 4 different decays
– Bd
– Bd K+
– Bs K+K-
– Bs K-
Displaced track trigger, PID and mass resolution critical
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B hh
mode Yield
Bd K 509 ± 28
Bd 134 ± 28
Bs KK 232 ± 29
Bs K 18 ± 27
)(11.050.0)(
)(sysstat
KBBRf
KKBBRf
dd
ss
)()(
)()(
KBNKBN
KBNKBNA
dd
dd
CP = -0.04 ± 0.08 (stat+sys)
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b sssBR(Bs ) = 1.4 ± 0.6 ±0.2 ± 0.5) x 10 -6
First observation of this mode
Acp(B± K±)= -0.07 ± 0.17(stat) ± 0.03(sys)
12 candidates on 1.95 expectedbackground events
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b lifetime
• Fully reconstructedb J/
DØ = 1.22 +0.22 – 0.18 ± 0.04 ps
World average: t=1.232 ± 0.072 ps
Good agreement with HQE
CDF =1.25 ± 0.26 ± 0.10 ps
DØ
DØ
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Observation of B D** X
• D** are orbitally excited D meson states
• In heavy quark limit– Two narrow states (D-
wave)– Two broad states(S-wave)
• Search for narrow states via– D0
1(2420) D*+ -
– D*02(2460) D*+ -
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M(D1) = 2021.7 ± 0.7 ± 0.6 GeV(D1)=20.0 ± 1.7 ± 1.3M(D2) = 2463.3 ± 0.6 ± 0.8 GeV(D2) = 49.2 ± 2.3 ± 1.3
DØ
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Branching ratio• Take experimentally measured number of D1
0 and D2*0 : N(D1)+N(D2*)=523 40
• Measure branching ratio of B D**(narrow) X, normalizing to known branching ratio (B D*+ X)
• Br(B {D10,D2*0} X • Br({D1
0,D2*0} D*+ ) = 0.280 0.021(stat) ± 0.088(sys) %
• Compare to LEP measurement of total D** Br (B D*+ X) = (0.48 0.10)%
• ~ half the rate through narrow states
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B**
Similar to D** decays, we canhave orbitally excited B’s2 narrow and 2 wide states
So far only narrow states have been found.
B** provide a good test of heavyQuark symmetry
Many properties of B** unknown
Soon can begin to measure manyproperties of B**
DØ RunII Preliminary
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Evidence for Bs Ds1(2536) X
3 significance.
Future hope to be able tomeasure its properties
DØ Run II Preliminary
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Bd,s
• Forbidden at
Tree Level in SM
BR(Bd l+l-) BR(Bs l+l-)
e (3.4 ± 2.3) 10-15 (8.0 ± 3.5) 10-14
(1.5 ± 0.9) 10-10 (3.4 ± 0.5) 10-9
(3.1 ± 1.9) 10-8 (7.4 ± 1.9) 10-7
Theoretical predictions
Experimental limits at 90% CL
BR(Bd l+l-) BR(Bs l+l-)
e < 5.9 10-6 < 5.4 10-5
< 1.5 10-7 < 5.8 10-7
< 2.5 % < 5.0%
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Bs in SUSY(Two Higgs-Doublet Model)
• BR depends only on charged Higgs mass and tan
• BR increases as tan4 (tan6) in 2HDM (MSSM)
• R parity violating models can give tree level contributions
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Blind analyses
• Isolation of the muon pair
• Opening angle between momentum vector of pair and vector pointing from primary vertex to vertex
• Decay length
• Optimize using signal MC and data sidebands
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Rare decays
DØ: (Bs ) < 3.7 X 10-7
CDF(Bs ) < 2.0 X 10-7
CDF(Bd ) < 4.9 x 10-8
World’s best limitsCDF new multivariate
analysis
No strong MSSM limits from Bs. Too many MSSM parameters
DØ Run II Preliminary
95% CL240 pb-1
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Bs
Signal box not yet openedExpected sensitivity = 1.2 x 10-5
DØ
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Dipion mass Spectrum of the X(3872)
• Nature of the X(3872) is still unknown.
• Seen by Belle, CDF, DØ and BaBar
• Still do not know its nature
• cc or DD molecule or ?...
• Found only in X J/
• Various interpretations lead to different M() distributions,
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X(3872) dipion mass distribution
Rule out some interpretations
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using Bs J/
Main measurement is lifetime difference in Bs system
We assume no CP violation in the Bs system and measure two Bs lifetimes, L and H, (or / and )
by simultaneously fitting the time evolution
and angular distribution of untagged Bs J/ decays
Exploring CP violation beyond SM
We allow for a free CP violating angle , and use the relation
between the measured , and SM prediction, SM,
= SM cos2() to extract
I. Dunietz, R. Fleischer, and U. Nierste, hep-ph/0012219
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Untagged Bs Rate in Time, Decay Angles
=transversity
CDF
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3 Angles 1 Angle
Inserting H( cos) =1, and F() =1 + J cos(2) + K cos2(2), and integrating over cos and , we obtain a 1-angle time evolution:
= 0.355 ± 0.066 (from CDF)
DØ
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CDF
h= 2.07 +.58 -.46 ± .03psL=1.05 + .16 - .13 ± .02 ps = 0.65 +.25 - .33 ± 0.01
=.47 + .19 - .24 ± .01 ps-1
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DØ Results
(in ps) ps) R / /
LL (in ps) (in ps) (in ps) (in ps)(CP odd fraction at t=0)
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Add in World Average based on semileptonic decays
Flavor specific final states (e.g. B0
slDs ) provide:
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New Physics?
We measure = SM cos2(), where SM = 0.12 ± 0.05 (Lenz)
SM predicts cos() ~ 1
Fit for cos2() gives:
Consistent with SM
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Bs mixing
• Important to measure ms
• Ratio of md to ms measures Vtd/Vts so we can apply tight constraints to Unitarity triangle
• Current limits ms > 14.4 ps-1 at 95% CL
• Expect ms < 24 ps-1
• New physics at 3 if ms > 30 ps-1 at 95% CL
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Measurement challenging• Large mixing
frequency
• Tagging quality
• Messy environment
BS
Se
DNmSig sms 2/)(
22
2)(
Bd mixing
Bs mixing ms=20
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Semileptonic vs hadronic modes
• Semileptonic
• Large yields• Poorer proper time
resolution
• If ms small, will find in semileptonic first
• Hadronic
• Smaller yields• Better proper time
resolution
• If ms large, will need to use hadronic modes
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Hadronic samples
• CDF: large samples but need to flavor tag
• (D2 ~ 1.12-1.43%)
• DØ small samples but each event has a high Pt muon to provide tag (D2 ~ 25%)
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Hadronic yields CDF
±±±
S/B 1.0 1.7 1.8
yields
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DØ hadronic modesL=250 pb-1
L=70 pb-1
Not many events but each event has a high Pt muon for flavor tagging
Bd D*
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Semileptonic modes
376 ± 31 events
Very Large sample
460 pb-1
Ds sample
DØ Run II Preliminary
events
Ds
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~ 7.6 K
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Biases due to trigger?
c = 413.8 ± 20.1 455.9 ± 11.9 422.6 ±25.7
Can correct for any trigger biases
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Fit and Results
400 pb-1
Green: signal Dotted line: background
=1.420 ± 0.043 (stat) ± 0.057 (syst) ps
World Average: 1.461 ± 0.057 ps
Dominant systematic: Background estimate, should be reduced in future
Bs Ds+ -
DØ Run II Preliminary
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Muon Tag
Mistag rate: 27.6 ± 2.1%
DØ Run II Preliminary
D*
Md consistent with world average
Flavor Tagging
Typical D2 ~1-1.5%
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Measurement currently has no stand alone sensitivity
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DØ Run II Preliminary
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Future improvements
Statistics and propertimeresolution!!!
CDF
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Future improvements to semileptonic ms measurement
DØ
Short term
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Future (longer term)• Proposal to increase bandwidth for B triggers
to allow us to lower prescales on triggers– 50 Hz additional bandwidth for B physics– Need to increase size of reconstruction farm– $500 K match from universities
• L0 Silicon to improve vertex resolution• Almost all B physics analyses are statistically
limited so almost all will benefit from increased bandwidth
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DØ
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Conclusions
• A lot of interesting B physics from Tevatron, I only touched on some topics
• Both experiments working well
• Many analyses statistically limited and expect ~ factor 10 more luminosity
• DØ much improved once Layer 0 silicon installed and if bandwidth upgrade approved by DOE