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

B. Abbott

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


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


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+ -


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Muon Tag

Mistag rate: 27.6 ± 2.1%


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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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

Documents

B physics at the Tevatron