# Presentation: 448922

## Reconstruction of B-hadron final states at DØ

- Paul Balm
- April 21, 2002
- APS April Meeting

## B-physics at DØ in Run II

**Run II of the Tevatron has started March 2001**
**Detector improvements in Run II, e.g**
**Superconducting 2T solenoid installed, new Silicon detector and Fiber Tracker**
**Tracking out to |********| = ~3, muon coverage to |********| = ~2**
**Tevatron upgrade**
**Beam energy increase from 1.8 to 2.0 TeV, yields 20% increased bb production cross-section**
**Expected integrated luminosity Run IIa: 2 fb****-1**
**	****(factor 20 increase from Run I)**
**Much increased B-physics potential!**

- Paul Balm

- April 21, 2002

## pT resolution of tracker

- Paul Balm

- April 21, 2002

## Measurement of sin(2)

**Measure lifetime of B****d****-mesons decaying to J/********K****s**** and tag flavour (B****d**** or B****d****)**
**For ease of triggering: Require J/******** decay to two leptons, K****s**** to charged pions**

**p**

**p**

**B****d**

**K****s**

**J/******

****

****

**B meson**

******+**

******-**

- Paul Balm

- April 21, 2002

## J/ reconstruction

**J/******** in muon system:**
**Currently track-quality cuts only, ~70% eff.**
**Can use opening angle, scintillator timing, ... to improve S/B**

** “****muon system only” tracks**
** ****p****T**** > 3 GeV, “tight” quality**
** ****Fit result:**
** ****M(J/********) ****	****= 3.08 ± 0.04 GeV**
** ****width ****	****= 0.78 GeV**

- Paul Balm

- April 21, 2002

## J/ reconstruction

**J/******** in the trackers**
**	****	****	****(awaiting approval)**

- Paul Balm

- April 21, 2002

## Ks reconstruction

**K****s**** reconstruction**

**K****s**** from B****d**** decays low p****T**
**...****but K****s**** average decay**
**	****length is 5.8 cm**
**cut on**
**transverse decay length**
**vertex ********2**
**“****collinearity”**

- BJ/Ks MC

- Paul Balm

- April 21, 2002

## Ks selection criteria

**p**

**p**

**B****d**

**K****s**

****

****

**B meson**

****

****

**collinearity angle**

- Paul Balm

- April 21, 2002

## Ks mass peak

** ****decay length****T**** > 0.35 cm**
** ********+********-**** vertex ********2**** < 15**
** ****coll.angle < 0.8 deg**

- Paul Balm

- April 21, 2002

## Expected sin(2) resolution

**Uncertainty on sin(2 ********):**
**with signal-dilution factors:**
***D******mix***** due to B****d**** mixing**
***D******bgd***** due to background events**
**(***********D******2*****)*****tag****** *****is the tagging efficiency **
***N******rec****** (20k exp. in 2 fb******-1******)***** the number of reconstructed events**
**D******** expects**** (***********D******2*****)*****tag****** *****of 9.8% and S/B of 0.75 ******** **
**	****expect ****sin(2********) resolution of 0.04 (sys)**

- Paul Balm

- April 21, 2002

## Flavour tagging

| Tag | (D2) measured CDF Run I | (D2) expected CDF Run II | (D2) expected D Run II | relevant D difference |
| --- | --- | --- | --- | --- |
| same side | 1.8 ± 0.4 ± 0.3 | 2 | 2 | same |
| soft lepton | 0.9 ± 0.1 ± 0.1 | 1.7 | 3.1 | lepton coverage |
| jet charge | 0.8 ± 0.1 ± 0.1 | 3 | 4.7 | forward tracking |
| opp. side |  | 2.4 | 0 | no Kaon ID |
| combined |  | 9.1 | 9.8 |  |

- Paul Balm

- April 21, 2002

## Recent sin(2) measurements

**Preliminary measurements presented at Moriond conference (March 2002)**
**combination of many channels **
**	****(J/**KL, KS,...)
**Babar:****	****0.79 ****0.09 (stat) ******** 0.04 (sys)**
**Belle: ****	****0.82 **** ****0.12 (stat) ******** 0.05 (sys)**
**D****Ø expects**** 0.04 (stat) ****in the channel ****J/**KS**in 2 fb****-1**** of data (Run IIa)**

- Paul Balm

- April 21, 2002

## Conclusions

**Reconstruction of J/******** and K****s**** successful and improving**
**On track for a competitive measurement of sin(2********)**
**Plus many more B-physics measurements unique to the Tevatron**
**see talk by Raymond Gelhaus**

- Paul Balm

- April 21, 2002