# Presentation: 522342

## b Physics at CDF

**Shin-Shan Yu**
-  University of Pennsylvania
- for the CDF Collaboration
**Frontiers in Contemporary Physics –III, May 23-28, 2005 **

## Outline

- Why b
- CDF Detector, Trigger
- Previous b Results
- Lifetime and Mass:
- b  J/ 
- Branching Fractions:
- b  J/ b  pK, p
- b  c 
- New Results
- Branching Fractions:
- b  c b  c 
- First Observations:
- b  c* b  c 
- b  c
- 
- Future

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## Big Picture : Why b baryon?

-  This is all we know about b ...
-  Now, Fermilab Tevatron is the only
- facility that produces b and allows us to study b.

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## HQET and HQE

- Heavy Quark Effective Theory and Heavy Quark Expansion
* *HQET and HQE predict the b-hadron mass, branching fractions and lifetime
*  *Assuming mb >> QCD, the 3-body dynamics is reduced to 2-body
-              heavy vs. light system.
-   The b quark can be treated the same way as the nucleus in the atom.
-   Little interaction between the heavy and light system.
-   Relate the b-hadrons of different flavors
-  Difference of b-hadrons are expressed in the power of           and
-  Spin of di-quarks = 0, sub-leading order corrections are simpler than
-   those of B mesons.

**Measuring ********b**** mass, branching fractions, and lifetime tests HQET and HQE **
**independently from the B mesons.**

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## CDF Detector

- Solenoid
- 1.4 Tesla
- Silicon Tracker
- || < 2
- vertex ~ 30 m
- Central Outer Tracker (COT)
- 96 layers drift chamber, up to ||~1
- PT /PT~ 0.15% PT
- Particle ID with dE/dx
- Time of Flight
- Particle ID	of low momentum tracks
- Muon chamber
- 4 layers drift chamber outside the calorimeter
- || < 1

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## B Physics & B Triggers

- Huge production rates,  1000 times higher than at e+e-  (4S)
- (pp  bX, |y| < 0.6) = 17.6  0.4 (stat.)  2.5 (syst.) b  PRD 71, 032001
- Heavy states produced
- B0, B+, Bs, Bc, b, b
- Backgrounds are also 3 orders of magnitude higher
- Inelastic cross section 100 mb
- Challenge is to pick one *B* decay from ~103 QCD events
- Di-muon trigger  (lifetime, mass, branching ratios)
- pT() > 1.5 GeV/c, within J/mass window
- Two displaced-tracks trigger (branching ratios)
- pT > 2 GeV/c, 120 m ≤ d0 ≤ 1 mm, Lxy > 200 m,
-   pT > 5.5 GeV/c
- Lepton + displaced-track trigger (lifetime, fbaryon)
- pT(,e) > 4 GeV/c, 120 m ≤ d0 ≤ 1 mm, pT > 2 GeV/c

- Tracks/10 m

**Silicon Vertex Trigger**** Impact Parameter (cm)**

**Beam****=33 ********m**** **

**CDF Run II Preliminary**

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## Previous b Results 

## Lifetime, Mass, and Branching Fractions 

-  First measurement of (b) in a fully reconstructed mode b  J/ 
-     dimuon trigger data  ******= 1.25 ******** 0.26 ******** 0.10 ps**
**    **To be compared with the 2004 world average = 1.229  0.080 ps
-  Best single mass measurement b  J/ 
-     dimuon trigger data  ****** ********= 5619.7 ******** 1.2 ******** 1.2 MeV/c****2**
-      To be compared with the 2004 world average  = 5624.0  9.0 MeV/c2
-  Relative BR
-     dimuon trigger data
-      To be compared with the Run I result  Ratio = 0.27  0.12 (stat)  0.05 (syst)
-  Best upper limit on b charmless decays
-     two displaced track trigger data **B****(********b****→ pK+p********) < 2.2 x 10****-5 ****at 90% C.L**
-      To be compared with the 2004 world average B(b→ pK+p) < 5.0 x 10-5 at 90% C.L

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##  Branching Fraction b  c    c  p+ K- +

- Data come from two displaced track trigger
- Background shapes obtained from Monte Carlo simulation:
-        mis- or partially reconstructed b-hadron decays

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## New Results

## Why B(b  c)/B(b  c)  ?  

-  Similar Feynman diagrams. Theorists relate hadronic BR to easier and calculable semileptonic BR by factorization.
-  Differential semileptonic decay width is related to 6 form factors, reduced to one in HQET
-  Close form of (w) can be obtained using Large Nc Limits, QCD Sum Rules, and etc.
-  Predictions of Jenkins (***Nucl. Phys. B396, 38***), Huang, et al. (***hep-ph/0502004***) and
- Leibovich, Ligeti, Stewart, Wise (***Phys. Lett. B586, 337***) give a ratio of 15 with 10-30% error

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## How B(b  c)/B(b  c)  ? 

* *If hadronic BR is known, we can get Vcb from the semileptonic BR.
-  Four charged tracks in the final state
-  Control samples: similar decays in the B meson system
-                                         and

* *Relative BR is the yield ratio corrected for the efficiency, e.g:
- But since we can not reconstruct neutrinos, several    backgrounds can fake our semileptonic signals in the data ....

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## Control Sample   D*X, D*+  D0 +, D0  K-+ 

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## Control Sample   DX, D+  K-+ + 

- Inclusive  Semileptonic Signal

- Hadronic Signal

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## Signal Sample b  cX    c  p+ K- + 

- Inclusive  Semileptonic Signal

- Hadronic Signal

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## MC and Data Comparison 

* *We used MC to obtain relative efficiencies of signals and backgrounds.
-  Compare MC and background subtracted signal distribution in the data.
-  Tune our MC if MC and data disagree, e.g:  pT of b-hadron, M(c)

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## Where Are the Semileptonic Backgrounds From?

- Physics Background
- Muon Fakes
- QCD

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## Physics Background

- b-hadron decays into a charm, a  and additional particles, e.g:
- Reduced by the M(c) cut
- Normalize the amount to the measured hadronic signal
- BRs come from PDG, theoretical estimate and preliminary measurements
- 10~40% contribution

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## First Observation of b  c* b  c

- First observation of several b semileptonic decays that can fake the signal
- Estimate the BR based on the observation

- c(2625)
- c(2593)

- c++,+,0

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## How to Obtain B(b  c 

- Make use of previous CDF measurements
- However, a b  MC PT spectrum using fully reconstructed decay was not available
-       for CDF I
- Correct the CDF I fbaryon/fd using measured PT spectrum
- Acceptance correction
- Different PT thresholds affect the ratio:
-      10 GeV/c vs. 6 GeV/c

*Consistent with the prediction 0.45% (****Phys. Lett. B586, 337)***

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## Muon Fakes 

- Muon fakes
- p, K,  fake muons
- cand muon d0 cuts  suppress fakes from the primary vertex
- Our fakes mostly come from b decays.
- Weight “charm+TRKfail” events with muon fake prob.
- Fit the weighted mass
- ~5% contribution

****

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## QCD Pair Production 

-  QCD:
- charm and  come from different b- or charmed hadrons
- b, c quarks are pair produced and fragmented into two hadrons
- Suppressed due to the cand PT() cuts
- Rely on Pythia MC
- Most sensitive to gluon splitting
- Compare data and MC single hadron production -> 10~40% difference
- 1~2% contribution

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## Semileptonic Background Summary 

|                  |    Nbg/Ninclusive (%) |  |  |
| --- | --- | --- | --- |
|  | c  | D  | D*  |
|  Physics | 9.8 | 40.0 | 15.0 |
| Fakes | 3.2 | 4.9 | 4.3 |
|  | 0.2 | 1.2 | 0.9 |
| Total | 13.2 | 46.1 | 20.2 |

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## Relative BR with Statistical Uncertainty 

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## Systematics 

* *Physics background and hadronic signal branching fractions
-  Measured: from PDG
-  Estimated or Unmeasured
-      5% for charm decays
-  100% for b-hadron decays
-  Mass fitting model
-  Vary the constant parameters in the fit
-  Several background shapes come from inclusive MC
-  vary BR of the dominant decays
-  Muon fake estimate
-  Data sample size for the measurement of muon fake probability
-  Uncertainty of the proton, kaon, pion fractions in the hadron tracks
-  MC modeling of acceptance and efficiency
-  pT spectrum
-  muon reconstruction efficiency scaling
-  QCD process
-  detector material
-  c Dalitz structure, b lifetime, c and b polarizations
- b  semileptonic decay model

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## Uncertainty Summary 

|  |   fractional uncertainty (%) |  |  |
| --- | --- | --- | --- |
|  | 
 |  |  |
| Measured BR |   +3.5 -10.5 |  8.2 |  2.3 |
| Estimated BR |  2.5 |  9.2 |  6.2 |
| CDF Internal |  |  |  |
| Mass fitting |  3.2 |  4.1 | <  0.1 |
| Pt spectrum | +1.4-2.5 |  3.2 |  2.2 |
| Detector material |  1.1 |  1.7 |  1.3 |
| Muon fake |  0.9 |  0.7 |  0.4 |
|  scaling |  0.4 |  0.5 |  0.4 |
|  |  0.2 |  2.2 |  1.3 |
| c b polarizations |  1.9 | -- | -- |
| c Dalitz  |  0.4 | -- | -- |
| b lifetime |  1.1 | -- | -- |
| b decay model |  2.9 | -- | -- |
|  |  6.0 |  6.1 |  3.4 |
| Statistical |  15.0 |  10.2 |  13.0 |

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## Control Sample Result 

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## Signal Sample Result 

- Experimental Uncertainties
-    dominated by:
-  Data sample size
-  Measured BR  B (b  c
-  Reminder: physics backgrounds are normalized to hadronic signal
-   Dominated by the uncertainties on the production cross-section and
- B(c->pK)

**Leibovich**
**Ligeti**
**Stewart**
**Wise**

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## B(b  c 

- Combined the ratio of BR and *B(*b cwe have
-       Consistent with DELPHI result (Phys. Lett. B585, 63)
- Weighted average
-      Also in agreement with the theoretical prediction 6.6% *(****Phys. Lett. B586, 337)***
- |Vcb|  Exercise
- Plug in the weighted average and the theoretical slope parameter of the ISGW function into the formula for *B **(*bc
- Consistent with the |Vcb| from DELPHI measured with B->D*l decays
***(Eur. Phys. J C33, 213)***

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## First Observation of b  c 

- Data come from two displaced track trigger
- c Dalitz structure study in progress

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## Conclusions

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## What Do We Know About b Now?

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## Future

- Most analyses are still statistically limited, more data in the future will improve the result
- b  J/ lifetime analysis with 5x data expected
- TOF+dE/dx combined PID will be used in the search for b→ ph
- fbaryon/fd using the lepton+displaced track trigger data anticipated
- Lifetime and branching fraction measurement from b  c 
- b  c form factor
- b polarizations

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## Back Up Slides

## Tevatron & CDF Luminosity

- ~775 pb-1 on tape (Run I  100 pb-1)
- ~400 M events from the displaced track trigger

- Record peak luminosity
- 	1.27 x 1032 sec-1 cm-2
- 	*May** **12**, 200**5*

- ~975 pb-1 delivered
- ~775 pb-1 to tape

**Collider Run II Peak Luminosity**

- Year  2001     2002       2003      2004       2005
- Month 4  7 10 1 4  7 10 1 4 7 10 1 4 7 10  1  4

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##  Lifetime b  J/  J/  + -,   p+ -

- First measurement of (b) in a fully reconstructed mode dimuon trigger data
- 	******b**** ******** ********c****l******** (********c ******** pK********) ********= 1.33 ******** 0.15 ******** 0.07 ps**

**CDF Run I**

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##  Mass b  J/  J/  + -,   p+ -

- Best single mass measurement Data come rom the dimuon trigger
- Calibrate mass with the J/sample
- 	******b**** mass ********= 5621.0 ******** 4.0 ******** 3.0 MeV/c****2**

**CDF Run I**

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## Branching Fraction b  J/  J/  + -,   p+ -

- Data come from the dimuon trigger
- Pion from the is soft, can not rely on the MC to get the tracking efficiency for pT < 0.5 GeV/c.
- studied by embedding simulated signal hits in the J/data.

**CDF Run I**

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##  Search for b  pK, p

- Data come from two displaced track trigger
- Mohanta, Phys. Rev. D63:074001,2001 Prediction:
-  B(b→ pK)=(1.4~1.9)×10-6
-  B(b→ p)=(0.8~1.2)×10-6
*compare to *
*       **B**(B0**→**K****)= (18.5 ***** *1.1)×10**-6*
- Normalized to *B**(B0→K****)*
- Assigned  mass to both tracks to maximize the separation from *B→hh*
- Large CP assymetry O(10%) expected
- Improved previous upper limit

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## Control Sample Analysis Requirements 

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## Signal Sample Analysis Requirements

- Hadronic
- | MLc-MPDG| < 3 
- N = 179 ****** 19**

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## Consistency Check 

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