1. Alexander Khanov 25 April 2003 DIS’03, St.Petersburg 1 Recent B Physics results from DØ The B Physics program in D Ø Run II Current analyses – First results Conclusions

2. Alexander Khanov 25 April 2003 DIS’03, St.Petersburg 2 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 10 31 cm -2 s -1  1 x 10 32 cm -2 s -1 2005-2008: Run IIb (~10 fb -1 ) Main Injector & Recycler Tevatron Chicago   p source Booster pp p p pp 1.96 TeV CDF DØ

3. Alexander Khanov 25 April 2003 DIS’03, St.Petersburg 3 DØ: one of the two major detectors at Tevatron New in Run IIa: –Solenoid –Si + fiber tracker –Preshowers –Forward muon system

4. Alexander Khanov 25 April 2003 DIS’03, St.Petersburg 4 DØ as a place to do B physics  (p  p  b  b) = 150  b at 2 TeV (~10 kHz) –Lots of B’s of all kinds (B d, B s,  b, B c, …) Rich B physics program –Cross section measurements –B s mixing –B lifetime –CP violation in B d and B s –Rare decays In many cases Tevatron is complementary to B factories

5. Alexander Khanov 25 April 2003 DIS’03, St.Petersburg 5 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 (|  | 3.5 GeV –Forward (1 2-2.5 GeV Coming soon (this summer): –L2 track trigger (track match to  /e) –L2 silicon trigger (displaced vertices)

6. Alexander Khanov 25 April 2003 DIS’03, St.Petersburg 6 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 )

7. Alexander Khanov 25 April 2003 DIS’03, St.Petersburg 7 B jet cross section (2) Step 2: Extract b content via fit to p T rel distribution –Large b mass  high p T rel T   +jet

8. Alexander Khanov 25 April 2003 DIS’03, St.Petersburg 8 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

9. Alexander Khanov 25 April 2003 DIS’03, St.Petersburg 9 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

10. Alexander Khanov 25 April 2003 DIS’03, St.Petersburg 10  c reconstruction Observe  c in  c  J/   Low energy photons visible through   e + e – conversions Cannot (yet?) separate  c1 and  c2 mass peaks

11. Alexander Khanov 25 April 2003 DIS’03, St.Petersburg 11 B Zoo We are able to reconstruct exclusive B decays –The first step towards CP violation measurements

12. Alexander Khanov 25 April 2003 DIS’03, St.Petersburg 12 B hadrons not produced at B factories Observe B s  J/   and  b  J/   –Can do B physics complementary to e + e – B factories

13. Alexander Khanov 25 April 2003 DIS’03, St.Petersburg 13 Inclusive B lifetime Begin with J/  transverse decay length c  J  = L xy M J/  / p T J/  Infer c  B from c  J/  by applying average MC correction c  B = c  J  / F: correction factor = 1.561  0.023(stat)  0.073(sys) ps (PDG : 1.564  0.014) B  J/  X : 17 % Prompt fraction : 83 % Systematic uncertainties: correction factor, fit bias

14. Alexander Khanov 25 April 2003 DIS’03, St.Petersburg 14 Charged B lifetime Full reconstruction (B ±  J/  K ± ): no hadronization or momentum uncertainties c  B = L xy M B / p T B = 1.76  0.24(stat) ps (PDG : 1.674  0.018)

15. Alexander Khanov 25 April 2003 DIS’03, St.Petersburg 15 B flavor tagging Method 1: soft muon tagging Charge of highest p T muon in the event (excluding those from reconstructed B) gives (opposite-side) b-tag Method 2: jet charge tagging Q=  q i p Ti /  p Ti, count events with |Q|>0.2 Jet chargeSoft muon efficiency55 ±4%8 ±2% dilution21 ±11%64 ±30% D2D2 2.4 ±1.7%3.3 ±1.8% Tagging performance measure:  D 2  = (N right + N wrong) / N all: efficiency D = (N right – N wrong)/(N right + N wrong): dilution

16. Alexander Khanov 25 April 2003 DIS’03, St.Petersburg 16 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 !

17. Alexander Khanov 25 April 2003 DIS’03, St.Petersburg 17 Summary slide

18. Alexander Khanov 25 April 2003 DIS’03, St.Petersburg 18 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