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Recent B Physics results from D Ø. The B Physics program in D Ø Run II Current analyses – First results Conclusions. Chicago . p. p. 1.96 TeV. Booster. p. CDF. DØ. Tevatron. p. p sou rce. Main Injector & Recycler. Tevatron at FermiLab. 1992-1996: Run I (125 pb -1 )
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Recent B Physics results from DØ • The B Physics program in DØ Run II • Current analyses – First results • Conclusions
Chicago p p 1.96 TeV Booster p CDF DØ Tevatron p p source Main Injector & Recycler 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 1031cm-2 s-1 • 1 x 1032 cm-2 s-1 • 2005-2008: Run IIb (~10 fb-1)
DØ: one of the two major detectors at Tevatron • New in Run IIa: • Solenoid • Si + fiber tracker • Preshowers • Forward muon system
DØ as a place to do B physics • s (pp bb) = 150 mb at 2 TeV (~10 kHz) • Lots of B’s of all kinds (Bd, Bs, Lb, 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
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 m/e) • L2 silicon trigger (displaced vertices)
B jet cross section (1) • Step 1: Begin with m in jet cross section • Unlike most of the other analyses, this one is based on a relatively small data set (3.4 pb-1)
m+jet T m B jet cross section (2) • Step 2: Extract b content via fit to pTrel distribution • Large b mass high pTrel
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
J/ data sample • Exploit J/ m+m– mode • Results based on 40 pb-1 collected data (75k J/) • Calibration not finalized, mass not in good agreement with PDG
c reconstruction • Observe cin c J/ g • Low energy photons visible through ge+e– conversions • Cannot (yet?) separate c1 and c2mass peaks
B Zoo • We are able to reconstruct exclusive B decays • The first step towards CP violation measurements
B hadrons not produced at B factories • Observe BsJ/ and Lb J/ L • Can do B physics complementary to e+e– B factories
Inclusive B lifetime • Begin with J/ transverse decay length • ctJ/y = Lxy M J/ / pTJ/ • Infer ctB from ctJ/ by applying average MC correction ctB = ctJ/y / <F(pTJ/)> F: correction factor BJ/ X : 17 % Prompt fraction : 83 % Systematic uncertainties: correction factor, fit bias <tB> = 1.561 0.023(stat) 0.073(sys) ps (PDG : 1.564 0.014)
Charged B lifetime • Full reconstruction (B± J/ K ±): no hadronization or momentum uncertainties • ctB = Lxy M B / pTB <tB> = 1.76 0.24(stat) ps (PDG : 1.674 0.018)
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=S qi pTi / S pTi, count events with |Q|>0.2 • Tagging performance measure: eD2 e = (N right + N wrong) / N all: efficiency D = (N right – N wrong)/(N right + N wrong): dilution
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 !
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-1of 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