25 April 2003DIS’03, St.Petersburg

1Alexander Khanov

Recent B Physics results from DØ

• The B Physics program in DØ Run II

• Current analyses – First results

• Conclusions

25 April 2003DIS’03, St.Petersburg

2Alexander Khanov

Tevatron at FermiLab

• 1992-1996: Run I (125 pb-1)– Discovered top

• 2001-2005: Run IIa (2 fb-1)– E=1.8 TeV

1.96 TeV

– L = 2 x 1031 cm-2 s-1

1 x 1032 cm-2 s-1

• 2005-2008: Run IIb (~10 fb-1)

Main Injector & Recycler

Tevatron

Chicago

p source

Booster

p

p

p p 1.96 TeV

CDFDØ

25 April 2003DIS’03, St.Petersburg

3Alexander Khanov

DØ: one of the two major detectors at Tevatron

• New in Run IIa:– Solenoid– Si + fiber tracker– Preshowers– Forward muon

system

25 April 2003DIS’03, St.Petersburg

4Alexander Khanov

DØ as a place to do B physics

• (pp bb) = 150 b at 2 TeV (~10 kHz)– Lots of B’s of all kinds (Bd, Bs, b, Bc, …)

• Rich B physics program– Cross section measurements

– Bs mixing

– B lifetime

– CP violation in Bd and Bs

– Rare decays

• In many cases Tevatron is complementary to B factories

25 April 2003DIS’03, St.Petersburg

5Alexander Khanov

Triggers

• Have to go down from 2.5 MHz crossing rate to 50 Hz writing to disk (0.25 MB/event)– Sophisticated 3-level trigger system

• Most useful triggers for B physics so far: dimuon triggers (simple and unprescaled)– Central (||<1): pT>3.5 GeV

– Forward (1<||<2): pT>2-2.5 GeV

• Coming soon (this summer):– L2 track trigger (track match to /e)

– L2 silicon trigger (displaced vertices)

25 April 2003DIS’03, St.Petersburg

6Alexander Khanov

B jet cross section (1)

• Step 1: Begin with in jet cross section

• Unlike most of the other analyses, this one is based on a relatively small data set (3.4 pb-1)

25 April 2003DIS’03, St.Petersburg

7Alexander Khanov

B jet cross section (2)

• Step 2: Extract b content via fit to pTrel distribution

– Large b mass high pTrel

T

+jet

25 April 2003DIS’03, St.Petersburg

8Alexander Khanov

B jet cross section (3)

• Step 3: Unfold jet energy resolution (unsmearing)

• Measured cross section consistent with Run I results (2-3 times higher than predictions)• Dominant error due to jet energy scale corrections

25 April 2003DIS’03, St.Petersburg

9Alexander Khanov

J/ data sample

• Exploit J/ +– mode• Results based on 40 pb-1 collected data (75k J/)• Calibration not finalized, mass not in good agreement with PDG

25 April 2003DIS’03, St.Petersburg

10Alexander Khanov

c reconstruction

• Observe c in c J/

• Low energy photons visible through e+e– conversions

• Cannot (yet?) separate c1 and c2 mass peaks

25 April 2003DIS’03, St.Petersburg

11Alexander Khanov

B Zoo

• We are able to reconstruct exclusive B decays– The first step towards CP violation measurements

25 April 2003DIS’03, St.Petersburg

12Alexander Khanov

B hadrons not produced at B factories

• Observe BsJ/ and b J/ – Can do B physics complementary to e+e– B factories

25 April 2003DIS’03, St.Petersburg

13Alexander Khanov

Inclusive B lifetime

• Begin with J/ transverse decay lengthcJ = Lxy M J/ / pT J/

• Infer cB from cJ/ by applying average MC correction

cB = cJ / <F(pT J/)>F: correction factor

<B> = 1.561 0.023(stat) 0.073(sys) ps (PDG : 1.564 0.014)

BJ/ X : 17 %Prompt fraction : 83 %

Systematic uncertainties: correction factor, fit bias

25 April 2003DIS’03, St.Petersburg

14Alexander Khanov

Charged B lifetime

• Full reconstruction (B± J/ K ±): no hadronization or momentum uncertainties

cB = Lxy M B / pT B

<B> = 1.76 0.24(stat) ps (PDG : 1.674 0.018)

25 April 2003DIS’03, St.Petersburg

15Alexander Khanov

B flavor tagging

• Method 1: soft muon tagging

Charge of highest pT muon in the event (excluding those from reconstructed B) gives (opposite-side) b-tag

• Method 2: jet charge tagging

Q= qi pTi / pTi, count events with |Q|>0.2Jet charge Soft muon

efficiency 55 ±4% 8 ±2%

dilution 21 ±11% 64 ±30%

D2 2.4 ±1.7% 3.3 ±1.8%

Tagging performance measure: D2

= (N right + N wrong) / N all:

efficiency

D = (N right – N wrong)/(N right + N wrong):

dilution

25 April 2003DIS’03, St.Petersburg

16Alexander Khanov

Conclusions

• Latest Run IIa D0 B physics results– b-jet cross section

– B lifetime

– Exclusive B decays

– Understanding flavor tagging

• Improvements in the future– Track and silicon triggers

– More calibration, data understanding underway

• Awaiting for large sets of data, lots of Physics ahead !

25 April 2003DIS’03, St.Petersburg

17Alexander Khanov

Summary slide

25 April 2003DIS’03, St.Petersburg

18Alexander Khanov

Recent B physics results from DØ

• With the DØ detector upgraded for Run II, our B physics program has started.

• Our first results based on 40 pb-1 of data include:– B-jet cross section measurement

– Observation of B exclusive decays

– B lifetime measurements

– Understanding of the flavor tagging

• In the near future, we’ll have our trigger improved, and we are awaiting for large data sets