# Presentation: 743164

## Bc Results from CDF II

**Satyajit Behari** (For the CDF Collab.)
- Johns Hopkins Univ., Baltimore,USA

- 23rd Jul. 2005                        HEP2005 Europhysics Conference, Lisboa, Portugal

## Contents

- Introduction
- Interests in Bc Meson
- Measurements
- Mass in fully reconstructed Bc  J/Ψ π decay
- Cross-section×BR ratio in Bc  J/Ψ μν decay
- Cross-section×BR ratio in Bc  J/Ψ eνe decay
- Summary

- S.Behari, Bc Results from CDF II, HEP2005

- 23rd July 2005

## Heavy Flavor Physics at Tevatron

**Since ********(bb) << ********(pp)****    ********  ****Events have to be selected with specific ****triggers**
**Trigger requirements:**        large bandwidth, background suppression, deadtimeless

- Flavor Creation (annihilation)

**q**

**b**

- Flavor Creation
- (gluon fusion)

- Flavor Excitation

- Gluon Splitting

**b**

**g**

**g**

**g**

-  Tevatron is a source of all B-hadron
-    species, B**d**, B**u**, B**c**, B**s** and Λ**b**
**  ********b** = 29.4 **±** 0.6 **±** 6.2 ****b (|η| < 1) (**CDF**)
-  Huge cross-sections compared to the
-    the B-factories but proportionally large
-    backgrounds as well

- S.Behari, Bc Results from CDF II, HEP2005

- 23rd July 2005

## Triggers for Bc Analyses

- pT>1.5GeV, pT>2GeV, 0.6<1
-  < 2.5o and Muon ID cuts
-  Yields higher than Run I  (low pT threshold, increased acceptance)

**Triggers for B****c**** Analyses**

** ****Two track trigger**
** **2 opposite charged displaced     tracks
-   pT > 2 GeV, 120m < |IP| < 1mm
-  D* D0 ,  p 

- For Signal and Control Sample

- For particle ID studies

** ****Single electron trigger**
** **A track matched to a central electron cluster
-   pT > 8 GeV
-    e e

- S.Behari, Bc Results from CDF II, HEP2005

- 23rd July 2005

## What is interesting about Bc

-      Test of lattice QCD and potential models
- Unlike quarkonia it carries flavor
-      Probes heavy quark dynamics in new territories
- Spectroscopy of excited states
-      Possible observation, test of models

**What is interesting about B****c**

-  ̅

-  Production rate can shed light on
-    fragmentation mechanism
-  Gluon fusion diagram dominant
-  Recent cross-section calculation 7.4 nb
-          [Saleev et al, Phys. Lett. B605, 311 (2005)]

- S.Behari, Bc Results from CDF II, HEP2005

- 23rd July 2005

## Interests in Bc   Continued..

*B*S produced from *B*C decays
-       Estimate *B*C contribution to *B*S lifetime and mixing
- BC as a source of (lepton) tagged BS  BS mixing
- CP asymmetry measurement in D0DS+ decay mode

** ̅**

- c

- J/

- *l**l*...

- b

- c

- *l**l*...

- Bs*

- c

- W+

-  No annihilation decay channel for
-    BC  hadrons via gluons
-    ****** ****Only weak decays, large**
** ****lifetime**

**Long term...**

- S.Behari, Bc Results from CDF II, HEP2005

- 23rd July 2005

## CDF Run I Bc Measurements

**CDF Run I B****c**** Measurements**

- S.Behari, Bc Results from CDF II, HEP2005

- 23rd July 2005

## Bc  J/  Search

**Pros:**
- Exclusive mode; Precise mass measurement possible
- Same topology well known normalization mode: B+ J/ K+
**Cons:**
- B**c** lifetime is shorter than light *b*-mesons (charm decay dominates)
-      Need aggressive secondary vertex resolution
- Expected signal > 10 times smaller than the signal in the semileptonic decay.

** ****Analysis method:**
-  Reconstruct  vertex, **Constrain**** ******************** ****to**** J/********mass**
-  Attach a **third track** w/  pT threshold
-  Event-by-event primary vertex

- S.Behari, Bc Results from CDF II, HEP2005

- 23rd July 2005

## Cut Optimization

**Blind analysis:**
- Search range:
-       6.4 ±  2  = [5.6 to 7.2] GeV/c2
- Use MC for: optimizing cuts, estimate sensitivity, relative to B+
**Cut optimization:**
- Score function:                            (for 3 search)
- Signal from MC and background from data
- Tight vertex requirements using 3D 2, 2D decay length significance, pointing angle, impact parameter etc.

_**Backgrounds**_

- (Prompt J/Ψ + track from PV)

- (bb production from gluon splitting)

- -

- S.Behari, Bc Results from CDF II, HEP2005

- 23rd July 2005

## Peak Search Criteria

**390** data events within mass range
- Expected signal:
- Use Toy MC to determine criteria for seeing a significant peak:
- Yellow: Toy MC with no signal, corresponding to 0.1% prob. of background  fluctuation
- Blue: Toy MC for Nsig=30 events
**Score function threshold:  ****Σ**** > 3.5**

- S.Behari, Bc Results from CDF II, HEP2005

- 23rd July 2005

## Peak Evaluation

- A sliding fit is performed in the search region and the score function is estimated.   **Σ****max ****= 3.6**
- Probability for the background to give a peak at Σmax = 3.6 is estimated from Toy MC as 0.27%.
- As a consistency check compare partially reconstructed Bc yield with that for B+
- Study impact parameter of the pion with J/Ψ vertex
**Yield difference between upper and lower sidebands consistent with B****+**

- S.Behari, Bc Results from CDF II, HEP2005

- 23rd July 2005

## Bc Mass Measurement

**B****c**** Mass Measurement**

- Unbinned likelihood fit w/ width fixed in 6.180 < M < 6.480
**Sources of systematics:**
- Background shape  0.8 MeV/c2
- Momentum scale    0.6
- /K dE/dx             0.2
- Tracking                0.2
- pT                        0.5
-     **Total               1.1 MeV/c****2**

**M(B****c****) = (6287.0 ****± ****4.8****stat. ****± ****1.1****syst.****) MeV/c****2**

- S.Behari, Bc Results from CDF II, HEP2005

- 23rd July 2005

## σ×BR Ratio in BcJ/ψ μ 

- Analysed ~360 pb-1
- Normalization mode: B+ J/ψ K+
- Basic cuts:
- Good muons: 
- |M(μμ) – M(J/ψ)| < 50 MeV
- J/ψ mass constrained, Prob()> 1%,   c > 60m
- Third muon pT > 3 GeV
- Remove B+ J/ψ K+ within MB ± 50 MeV
**Backgrounds:**
**Fake muons from decay-in-flight of K,********,p**
- Estimated by assigning muon probabilities to the third track, obtained from PID quantities, dE/dx and ToF

- Predicted background: 16.3±2.9 events

- S.Behari, Bc Results from CDF II, HEP2005

- 23rd July 2005

## Background Predictions

**From bb fragmentation**
- Estimated relative contribution of QCD processes from a Pythia MC and compared to data
- Predicted background:
-        12.7 ± 1.7 ± 5.7 events
**Fake J/****ψ**** + a third muon**
- Estimated by matching a third muon with events in J/ψ sidebands
- Predicted background:
-        19.0 ± 3.0 events

-  ̅

- S.Behari, Bc Results from CDF II, HEP2005

- 23rd July 2005

## σ×BR Ratio Results

- Signal events: **60.0 ± 12.6**
- Background:   **46.0 ± 7.3**
- Significance:**  5.2****σ**

**For p****T****(B****c****) > 4 GeV, |********(B****c****)| < 1**

- S.Behari, Bc Results from CDF II, HEP2005

- 23rd July 2005

## σ×BR Ratio in BcJ/ψ e 

- 360 pb-1 data,
-      Normalization mode: B+ J/ψ K+
**Basic cuts:**
- Similar J/ψ selection as muon mode
- Soft electron identification:
- Good quality tracks, pT > 1 GeV, matched to central strip chambers and EM calorimeter
- Cut on a likelihood ratio variable constructed from 10 electromagnetic and tracking variables   Pe < 0.7
- Additional cut on specific ionization, dE/dx:

- Ze/σz > -1.3

- S.Behari, Bc Results from CDF II, HEP2005

- 23rd July 2005

## Backgrounds

- Fake electrons from decay-in-flight of K,,p
- From bb fragmentation
- From fake J/ψ
- Conversion electrons:
- Removed during J/ψ e sample selection
- Residual conversion electrons are found by pairing electron candidates with tracks, w/o electron requirement

** ̅**

- S.Behari, Bc Results from CDF II, HEP2005

- 23rd July 2005

## σ×BR Ratio Result

- Signal:     **114.9 ± 15.5 ± 13.6**
- Background: **63.6 ± 4.9 ± 13.6**
- Significance:**  5.9****σ**

- S.Behari, Bc Results from CDF II, HEP2005

- 23rd July 2005

## Summary

- A precise Bc mass measurement in Bc  J/Ψ π decay is in agreement with lattice QCD.
- σ*BR ratios of Bc measured in Bc  J/Ψ μ,e ν decays improve upon CDF Run I measurements.
- Update of mass and BR ratio measurements using high statistics  (~ 1 fb-1) are underway.
-  Lifetime and other studies to follow..

- S.Behari, Bc Results from CDF II, HEP2005

- 23rd July 2005

## Backup-1   DØ Run II (ICHEP2004)

**B****c**** ******** J/****ψ**** ****μ**** ****ν****:**
- 95 ± 12 ± 11 signal events
- L = 210 pb-1

**Backup-1****   D****Ø Run II (ICHEP2004)**

- S.Behari, Bc Results from CDF II, HEP2005

- 23rd July 2005

## Backup-2  Expected Bc Signal w.r.t B+ data

- All theoretical uncertainties are in the value of R2

- To evaluate the expected signal we use CDF Run I measurement and one ratio of *BR*.

**Backup-2  ****Expected B****c**** Signal w.r.t B****+**** data**

- S.Behari, Bc Results from CDF II, HEP2005

- 23rd July 2005