# Presentation: 798445

## Recent Results onB Physics at DØ 

**Recent Results on****B Physics ****at D****Ø**** **

**Heriberto Castilla**
**Cinvestav-IPN, Mexico City**
**Dzero Collaboration**
***Les Rencontres de Physique***
***De La Valle D’Aoste***
***March 9-15, 2003 at La Thuile, Aosta Valley***

## DØ B Physics Program

- B0s mixing: BsDs l X, BsDs(n)
- B Lifetimes
- Average B lifetime: b J/X
- b lifetime: bJ/0
- B0s lifetime and width: B0sJ/
- CP violation in B0d & B0s
- Rare decays, cross sections
- Ingredients for a Time-dependent B Physics program
- Reconstruct final states
- Reconstruct proper time distribution
- Tag the flavor of the b at production

## The Run II DØ Detector

## Strategy:   Measure +jet cross-section  Extract b-content using PTRel   Data selection & kinematic cuts   pT >6 GeV/c, || <0.8 (Muon PT measured in muon system only)   |jet| < 0.6 , Etcorr >20 GeV   0.5 cone  R(jet,) < 0.7

**Strategy:**** ****  ****Measure ********+jet cross-section****  Extract b-content using P****T****Rel****  **** ****Data selection & kinematic cuts**** ****  ****p****T******** ****>6 GeV/c, |************| <0.8 (Muon P****T**** measured in muon system only) ****  |********jet****| < 0.6 , E****t****corr**** >20 GeV ****  0.5 cone****  ********R(jet,********) < 0.7**

- jet

- 

- +jet

- pTRel

**Measured in Run1: 2-3 times higher than**
**predictions**

**B jet Cross Section**

**Muon + jet cross section**

**Lower in Jet E****T**
**so need muon and**
**jet trigger efficiencies**

- muon =55-70%

**Jet Energy scale**
**Correction ~ 1.8   0.13**

- Error on Jet Energy scale

##  + jet cross section

**Jet quality cuts applied**

**Data: 02/27/02 – 05/10/02 **
**          ****~ 3.4 pb****-1**

**Jet reco. Eff. 100% E > 20 GeV**
****** ****reco. Eff. 43.7****±****0.8(stat)****±****2.2(sys)%**

**Jet resolution: dijet p****T**** imbalance**
****** ****momentum resolution: from central tracks**

## B jet cross section

**20 GeV < E****T**** < 25 GeV**

**B fraction as a functionof  Jet E****T**

**Data unsmeared using ansatz function**

**Dominant error is due to jet**
**energy scale**

**B jet cross section**

-  **Fit p****T****rel**** templates to data in jet E****T**** bins**

## The J/

****** ****p****T  ****> 1.5 GeV & **
**      ****J/******** ****p****T**** > 3.0 GeV**** **
**SMT hits>3 & CFT hits>4**

**J/********’s: 75,013**

## The J/

****** ****e****+****e****-**** conversion**
**J/******** tracks p****T**** > 2 GeV **
****** ****tracks p****T**** > 1 GeV**
**J/******** mass window 2.8 – 3.3 GeV**
**J/********  and ******** vertex constrained**

- Reconstructing 0  

## Exclusive B decays

## Average B Hadron Lifetime

**J/******** Sources**

**(   ) states (prompt)**
**B ******** J/******

**Difference**

**                    ****decay**
**Prompt     ~  ****PV**
**J/********(B)      ~  ****SV**

**Transverse Decay Length Plot **

******B  ****through **********

**MC**

## Average B Hadron Lifetime

******B ****= 468 ****± 7(stat) ± 22(syst) ********m**
**B fraction: 17.3±0.5%**
**Prompt fraction: 82.7±0.6%**
**(********) = 1.561 ± 0.024(stat)±0.074(syst) ps**

**Transverse Decay Length Plot**
**Contributions**
**Zero lifetime component:**
**Prompt J/******** signal**
**Combinatorial Background**
**Both modeled as double Gaussians**
**Parameters from J/********  sidebands**
**Background fraction from fit to J/******** peak**
**Long lived component:**
**B ******** J/********  signal**
**Semileptonic Background**
**Both modeled as exponentials convoluted with gaussians**
**Background parameters and normalization determined from J/******** sideband**
**Signal parameters floated**

## Charged B Lifetime

**R: G****1**** ******** G****2**
**L: Right ******** E*G (B ********J/******** K****0*****)**
**P: Right ******** E****1*****G****1**** ******** E****2*****G****2**

**Left**

**Signal**

**Right**

## Flavor tagging

**Muon tagger:**
-  must have ΔR > 2.0 separation from reconstructed B
-  must have *p**T* > 1.9 GeV/*c*
***b****** *****flavor tagging:**
- charge of highest-*p**T* muon in event gives (opposite-side) *B*-tag

**Jet charge tagger:**
-  Remove daughter tracks from the reconstructed B
-  Remove tracks 2D impact parameter greater than 0.2cm
-  Remove tracks with |vtx_z – pvtxz| > 2. Cm, suppress minimum bias events
-  Use tracks left to calculate the jet charge Q by weighing on track pT
-  Events with |Q|>0.2 are counted as tagged, while the others are dropped

**Soft Muon Tag**

**Jet Charge Tagging**

## B Flavor Tagging

-  Errors in fractions of signal, bgd events
-   in mass window (from fit) are ignored

**D****Ø**** Run-II Preliminary**

**B Flavor Tagging**

**Soft muons**

**Average jet charge**

## Conclusions

**Latest Run IIa D0 B Physics results**
**B-jet cross section**
**B exclusive decays ( B+, B0d in two different channels)**
**Average B Lifetime**
**Preliminary Charged B lifetime measurement**
**Understanding Flavor Tagging**
**Improvements in the short term future****:**
**Track trigger and Silicon Trigger**
**Just the beginning of an exciting ****D****Ø**** ****B Physics program ...**

## Average B Hadron Lifetime

| Source | Uncertainty (m) |
| --- | --- |
| Boost Correction | ±15.9 |
| Background Shape | ± 3.0 |
| Flight Length dependence | ± 1.1 |
| Back. Normalization | ±  0.68 |
| Alignment bias | ± 4.1 |
| Fitting Bias | ±13 |
| Total | ±22 m |

**Systematic Uncertainties**

## V0 Finding 

## Flavor tagging

**Flavor ****tagging**