1. B physics and X(3872) production at DØ  Introduction  DØ-Detector  Results on B physics  Results on X(3872)  Summary Frank Lehner U Zurich DIS 2004, Strbske Pleso 15-18 April, 2004 All results are preliminary

2. Accelerator Status  excellent performance of Tevatron in 2004  DØ recorded 70 pb -1 in 2004  important milestone: reprocessed full dataset in fall 2003  greatly improved tracking performance  good fraction processed off-site  current datasets  ~300 pb -1 on tape  ~200-250 pb -1 analyzed  ~100 pb -1 Run I

3. B production at Tevatron  Pro’s:  large cross section ~10 5 x larger than at present B-factories  (4S)  all kinds of b hadrons produced:  B d, B s, B c,  b,..  Con’s:  QCD background overwhelming  efficient trigger and reliable tracking necessary  soft p t spectrum, smaller boost than LEP  Key for B physics program at DØ:  Muon system  Muon trigger (single and dimuon triggers)  Silicon Vertex + Tracker

4. DØ detector  upgraded Run II DØ detector:  beamline shielding  reduce background  new Forward Muon + Central Muon Scintillators  excellent coverage |  |<2  Preshowers  helping for e-ID  Fiber Tracker  Silicon Detector  2T Solenoid

5. DØ tracking region  Silicon detector  6 barrels w/ 4 layers silicon- mostly double- sided silicon, axial and stereo  interspersed double-sided disks  large external area disks at end  tracking/vertexing up to |  |<3  Fiber Tracker  scintillating fibers Ø 0.82 mm  8 layers - each axial/stereo  R/O through VLPC in LHe

6. Tracking performance |  | for kaons from D*  D 0  p T spectrum of soft pion from D*  D 0  efficient muon and tracking system give us a large sample of semileptonic B decays Tracks are reconstructed over a wide  range starting from p T = 180 MeV Data from semileptonic decays (B   D X)

7. Benchmark: exclusive B decays & yields  accumulated large exclusive samples of B + and B 0  find in ~225 pb -1  B 0  J/  K * 1900 events  B +  J/  K + 4300 events  B 0  J/  K s 375 events  good S/B  Lifetime cuts applied

8. Benchmark: exclusive B decays & yields  b -> J/   52 events  B s -> J/   400 events  We have good potential in all B  J/  exclusive modes, work in progress on  Lifetime measurement of different B species  Studies of CP effects in B s & B d mesons 250 pb -1

9. Lifetime ratio  (B + )/  (B 0 ) from semileptonic decays  measure from semileptonic B decays directly lifetime ratio instead of absolute lifetimes  select following samples:  B   D 0 X  B   D* X  sample compositions:  “D 0 sample”:  + K +  - + anything  B + 82%, B 0 16%, B s 2%  “D* sample”:  + D 0  - + anything  B + 12%, B 0 86%, B s 2%  estimates based on measured BR and isospin relations  group events in 8 bins of visible proper decay length (VPDL) VPDL = L T / p T (  D 0 )  M B L T = transverse decay length

10. Lifetime ratio  (B + )/  (B 0 ) from semileptonic decays Measure ratio r= N(  + D* - )/N(  + D 0 ) in each bin i Combinatorial background with true D 0 in D* sample is subtracted using wrong-sign distribution  no need for parameterisation of background VPDL distribution Additional inputs to the fit: - sample compositions (previous slide) - K-factors (from simulation) K = p T (  D 0 ) / p T (B) (separately for different decay modes) - relative reconstruction efficiencies for different B decay modes (from simulation) - slow pion reconstruction efficiency [flat for p T (D 0 ) > 5 GeV (one of our cuts)] - decay length resolution (from simulation) -  (B + ) = 1.674  0.018 ps [PDG] one example VPDL bin

11. Lifetime ratio  (B + )/  (B 0 ) from semileptonic decays  systematics currently dominated by  time dependence of slow pion reconstruction efficiency  relative reconstruction efficiencies C Y  Br(B +   + D* -  + X)  K-factors  decay length resolution differences D 0  D* use binned  2 fit of event ratios to determine  (B + )/  (B 0 ) Preliminary result:  (B + )/  (B 0 ) = 1.093  0.021 (stat)  0.022 (syst)

12. Lifetime ratio  (B + )/  (B 0 ) from semileptonic decays New D Ø result (average not updated, plot not official or approved by HFAG) This is one of the most precise measurements to date:

13. B 0 /B 0 mixing  in SM B d mixing is explained by box diagrams  constrains V td CKM matrix element  mixing frequency  m d has been measured with high precision at B factories (0.502  0.007 ps -1 )  use our large sample of semileptonic B d decays to measure  m d  benchmark the initial state flavor tagging for later use in B s and  m s measurements

14. B 0 /B 0 mixing  initial flavor tagging  opposite side tight muon tag  muon p T > 2.5 GeV/c  cos  < 0.5  asymmetry of ‘oscillated’ and ‘non- oscillated’ B mesons as function of VPDL  use binned  2 fit for asymmetry  this is already one of the best measurements in hadron colliders  work in progress to reduce systematics  use other tagging methods  add more D 0 decay channels Preliminary results:  m d =0.506  0.055(stat)  0.049(syst) ps -1 Tagging efficiency: Tagging purity:

15. Towards B s mixing  semileptonic decays (B s ->  D s )  very good statistics  excellent yield: 9500 candidates in ~250 pb -1  if  m s  15 ps -1 a first indication of B s mixing might be possible with 500 pb -1  fully reconstructed hadronic decays:  poor statistics  excellent proper time resolution  need a few fb -1 of data to reach  m s  18 ps -1

16. Observation of B   D** X  D** are orbitally excited D meson states, see diagram  in heavy quark limit w/ L=1 expect two sets of doublet states  two broad (decay through S-wave)  two narrow (decay through D- wave)  narrow D**  D 0 1 (2420) -> D* +  -  D 2 * 0 (2460) -> D* +  -  D 1 0, D 2 * 0 have been observed and studied in several experiments, most recently by BaBar and Belle in B -  D** 0  -  we study D 1 0, D 2 * 0 produced in semileptonic B decays. Figure from Belle, hep-ex/0307021

17. Observation of B   D** X start from B   D*X sample, add another  + look at invariant mass of D* -  + system observed merged D 1 0 (2420) and D 2 * 0 (2460) excess in right-sign combinations can be interpreted as interfering D 1 0 and D 2 * 0 DØ’s preliminary result constrains the resonant contribution Work in progress: extract separate amplitude, relative phase Br(B  {D 1 0,D 2 * 0 }  X)  Br({D 1 0,D 2 * 0 }  D* +  - ) = 0.280  0.021 (stat)  0.088 (syst) %

18. B s   +  - sensitivity study  purely leptonic B decay is a flavor changing neutral current (FCNC)  forbidden at tree level  highly suppressed in SM  BR(B s ->  )~ 3·10 -9  BR grows with tan 6  in MSSM  very attractive probe for any new physics with extended Higgs sector (Two-Higgs Doublet models) SM: Two-Higgs Doublet models:

19. B s   +  - sensitivity study  blind analysis: optimization cuts using Random Grid Search based on mass sideband  discriminating variables  isolation of  pair  decay length  opening angle between  pair and decay length direction  expected signal is normalized to B + -> J/  K +  expect 7.3  1.8 background events in signal region Current expected limit (Feldman/Cousins): Br(B s   +  - ) < 1.0  10 -6 @ 95 % CL (stat + syst) The box has NOT been opened yet - Reoptimisation still in progress - further improvements expected

20. X(3872)  J/   +  -  last summer on LP ‘03, Belle announced new particle at ~3872 MeV/c 2  observed in B + decays:  B +  K + X(3872)  X(3872)  J/   +  -  Belle’s discovery has been confirmed by CDF and DØ  DØ preliminary:  300  61 events  4.4  effect  M = 0.768  0.004 (stat)  0.004 (syst) GeV/c 2

21. X(3872)  J/   +  -  nature of X(3872) is not known  mass surprisingly close to D*D threshold  could be charmonium, hybrid or meson molecule  compare sample of X particles to sample of  (2S) using  |  |<1 and 1<|  |<2 (plot)  decay length dl 0.2 mm  helicity of   isolation of X

22. X(3872)  J/   +  -  no significant differences between  (2S) and X have been observed  surviving fraction of X behaves similar to  (2S)  more useful once we have models of the production and decay of, e.g., meson molecules that predict the observables used in the comparison  Note that  observation of the charged analog X +  J/   +  0 would rule out cc hypothesis  observation of radiative decays X    c would favour cc hypothesis (Belle set limit). Use DØ’s calorimeter to identify low energy  0 and  : work in progress

23. Summary  Preliminary results from DØ:  precise measurement of  (B + )/  (B 0 )  measurement of  m d, benchmark flavour tagging  Observation of B   D** X at DØ  DØ’s sensitivity to B s     Observation of the X(3872) at DØ and study of its production properties  The exciting times have started; stay tuned for more

24. Spare slides

25. DØ tracking performance  (DCA)  53  m @ P T = 1 GeV and  15  m @ higher P T Can provide K/  separation for P tot < 400 MeV p/  separation for P tot <700 MeV NOT yet used for PID

26. Triggers  Robust and quiet single- and di-muon triggers  Large coverage |  <2  Variety of triggers based on  L1 Muon & L1 CTT (Fiber Tracker)  L2 & L3 filters  Typical total rates at medium luminosity (40 10 30 s -1 cm -2 )  Di-muons : 50 Hz / 15 Hz / 4 Hz @ L1/L2/L3  Single muons : 120 Hz / 100 Hz / 50 Hz @ L1/L2/L3  Rates before prescaling: typically single muon triggers are prescaled or/and used with raised p T threshold at L1  Muon purity 90% - all physics!  Current total trigger bandwidth 1600 Hz / 800 Hz / 60 Hz @ L1/L2/L3  B-physics semi-muonic yields are limited by L3 filters and L3 bandwidth

27. Calibrations using J/  sample Large J/  sample – currently 1.2 M events in 250 pb -1 J/  mass is shifted by 22 MeV Observe dependence on Pt and on material crossed by tracks Developed correction procedure based on field & material model Finalizing calibration of momentum scale using J/  Ks, D 0 NOT yet used Mass resolution 60 MeV/c 2 in agreement with expectations After magnetic field and material corrections Before corrections