Hot Topics at D0 David Buchholz (Northwestern Univ) On behalf of the DØ Collaboration

4/9/2006 D. Buchholz 2 D0 Results  D0 Talks at this conference-  b physics B mixing and lifetimes- Piedra B s decays and B leptonic decays- Van Kooten  t physics Top Physics – Clement  Many new b and t physics results  Watch for these in other talks  Hot Topics at D0  B s and B d mixing  CP violation result in B decays  Flavor Changing Neutral Current results (D ± → π ± μ + μ - )

4/9/2006 D. Buchholz 3 Excellent Tevatron Performance  Data sample corresponding to over 1 fb -1 of the integrated luminosity used for the Bs mixing analysis  Results are being reported on this 1 fb -1 sample

4/9/2006 D. Buchholz 4 D0 Detector B Physics Program based on excellent performance of 1) muon system, |η| 3,4,5 GeV 2) silicon microstrip tracker 3)Good single and dimuon triggers

4/9/2006 D. Buchholz 5 Unitarity Triangle- B Mixing Contribution Measurement of Δm s contributes to better determination of V td  m s ~ (lots of QCD) x |V ts |  m d ~ (lots of QCD) x |V td |  m s /  m d ~ (much less QCD) x |V ts |/|V td |

4/9/2006 D. Buchholz 6 Mixing and Oscillations

4/9/2006 D. Buchholz 7 Analysis Outline  Select B s candidate  Concentrate on the most clean decay mode B s  νμD s (  φπ)  For each B s candidate  B S flavor at decay time from muon sign at the reconstructed side  Transverse length L T and its error  Transverse momentum P T (B s ) (use P T (D s μ ))  B-hadron flavor at the opposite side (indicates B S flavor at production time) μ+μ+ π -π - K+K+ K-K- φ D-SD-S μ(e) B ν X Reconstructed Side Opposite Side LTLT

4/9/2006 D. Buchholz 8 Proper Decay Length  Proper Decay Length is determined from the Visible Proper Decay Length  K-factor takes into account the escaping neutrino and other missing particles  From MC for each decay mode- different excited states

4/9/2006 D. Buchholz 9 Resolution Calibration Using Data  Use J/ψ→ μμ sample  Fit pull distribution for J/ψ Proper Decay Length with 2 Gaussians  Resolution Scale Factor is 1.0 for 72% of the events and 1.8 for the rest  Confirmed by Impact Parameter tuning procedure in MC μ PV J/ψ vertex μ L±σLL±σL DØ Run II Preliminary resolutionresolution plus decays

4/9/2006 D. Buchholz 10 Efficiency Dependence on VPDL  From MC  Cross-checked and tuned using data  Note that efficiency at VPDL=0 is not 0

4/9/2006 D. Buchholz 11 Opposite Side Tagging PaPa  e Tagging side BsBs DsDs Primary Vertex Secondary Vertex K  e   B Reconstructed B-meson  Muon (electron) jet charge defined as:  Sum is taken over all tracks in the cone ΔR<0.5 around muon;  SV Charge:  Event charge:  all tracks with ΔR < 1.5 w.r.t. reconstructed B direction are used

4/9/2006 D. Buchholz 12 Calibration of Dilution Using B d  D *± μνX Increasing dilution Δm HFAG = ± ps -1

4/9/2006 D. Buchholz 13 Final Signal Selection  Use likelihood ratio method  Set of discriminating variables x i constructed for each event Helicity Angle (D s,K 1 )  D s Isolation p T (K 1 K 2 ) m(  D s )  2 of D s Vertex Fit m(K 1 K 2 or K 1  )  Construct likelihood ratio for each variable bgrd from m(D s ) sidebands signal from bgrd-sub peak  Combine into single variable  Use for final selection

4/9/2006 D. Buchholz 14 μ  D0 (~1 fb -1 ) μD s : 26,710±560 Opposite-side flavor tagging Tagging efficiency ~20% μD ± : 7,422±281 μD ± : 1,519±96 μD s : 5,601±102

4/9/2006 D. Buchholz 15 Cross-check Using B d  XμD ± (   )  The Amplitude Scan reveals the Bd oscillations  at correct place  no lifetime bias  with correct amplitude  correct dilution calibration Amplitude Scan DØ Run II Preliminary

4/9/2006 D. Buchholz 16 Event-by-Event Fit  Minimize the Likelihood function  Probability Density Functions (PDF) for each source  Proper Decay Length  Dilution  Proper Decay Length Error  Mass  Signal Selection Variable

4/9/2006 D. Buchholz 17 Vertex Resolution  Determined by vertex fitting procedure e.g. Period of 19ps -1 DØ Run II Preliminary Limit of sensitivity to mixing at 22ps -1

4/9/2006 D. Buchholz 18 Results of the Lifetime Fit  Different background models are used for cross-check and systematic errors  Trigger biases have been studied  Different efficiency models  Central values for cτ Bs = 404 − 416 μm  Statistical error ~10 μm  HFAG value cτ Bs = 438 ± 12 μm Most important region

4/9/2006 D. Buchholz 19 Amplitude Scan For B s  Deviation of the amplitude at 19 ps-1  2.5σ from 0  1.6σ from 1

4/9/2006 D. Buchholz 20 Log Likelihood Scan  m s < 21 ps 90% CL assuming Gaussian errors Most probable value of  m s = 19 ps -1 Systematic  Resolution  K-factor variation  BR (B s  D s X)  VPDL model  BR (B s  D s D s ) In agreement with the amplitude scan Have no sensitivity above 22 ps -1

4/9/2006 D. Buchholz 21 World -1 : 1.5σ  2.3σ HFAG Preliminary Correlated systematics not yet included With current D0 result

4/9/2006 D. Buchholz 22 Ensemble Tests  Using data  Simulate Δm s =∞ by randomizing the sign of flavor tagging  Probability to observe Δlog(L)>1.9 (as deep as ours) in the range 16 < Δm s < 22 ps -1 is 3.8% 5% using lower edge of syst. uncertainties band Region below 16 ps -1 is experimentally excluded No sensitivity above 22 ps -1  Using MC  Probability to observe Δlog(L)>1.9 for the true Δm s =19 ps -1 in the range 17 < Δm s < 21 ps -1 is 15%

4/9/2006 D. Buchholz 23 Impact on the Unitarity Triangle

4/9/2006 D. Buchholz 24 Impact on the Unitarity Triangle

4/9/2006 D. Buchholz 25 CP Violation in Mixing Three phenomenological signatures CPV in Mixing  K :  L   B : l  l   l  l   CPV in Decay  / /  : K L         A CP :         Mixing vs Decay  :  L    ?   : J/  s  First in K Last in B

4/9/2006 D. Buchholz 26 Analysis Strategy Goal is to measure   with part per mil precision by looking for asymmetry in like-sign dimuons How? Using independent spectrometers and reversing the polarities Toroid Solenoid Toroid    

4/9/2006 D. Buchholz 27 Tor*Sol polarity +1 N++177,950156,183 N--176,939156,148 N+-1,175,5471,029,604 Raw Results Now need the fraction of  from B After removing detector based asymmetries:

4/9/2006 D. Buchholz 28 Sample Composition signal Backgrounds that dilute the asymmetry Backgrounds with false asymmetries: Reaction K  N  Yπ (Y=Λ,Σ...) has no K + N analog b    b  b   b    b  c  

4/9/2006 D. Buchholz 29 Sample Composition signal Backgrounds that dilute the asymmetry Backgrounds with false asymmetries: Reaction K  N  Yπ (Y=Λ,Σ...) has no K + N analog b    b  b   b    b  c   Cross-check:

4/9/2006 D. Buchholz 30 Results Raw Asymmetry: Asymmetry from Mixing: CP Violation Parameter:

4/9/2006 D. Buchholz 31 Results (0.4±1.4±0.9)

4/9/2006 D. Buchholz 32 Flavor Changing Neutral Currents D +     m(      GeV) (1/  )(d  /dm 2 )  GeV -2 ) RPV in the up sector and not the down sector Burdman et al. hep-ph/ c  u     Little Higgs models with new up sector vector quark Fajfer et al. hep-ph/ factors of >1000 over SM not ruled out. Similar in magnitude to B s  but orthogonal parameter space Strict limits from b  s and s  d Possible to have effects in up sector and not down sector

4/9/2006 D. Buchholz 33 c  u     Analysis Strategy  First find D s   BF(D s   BF      (2.85 +/- 0.19) x  Product ~ 1 x  Then search for excess in the continuum region  D        with m(   Start with low mass dimuon candidate, add track to form D candidate  Reduce background with lifetime and topological cuts ~51k  ~55k    Dimuon invariant mass DØ Preliminary 1 fb -1

4/9/2006 D. Buchholz 34 Results for D  Results for D  n(D s ) = 65 ± 11 Optimized cuts n(D + ) = 26 ± 9 DØ : BF( D         (1.75 +/ /- 0.50) x CLEO-c: ( /- 0.2) x 10-6 Expected: 1.77 x 10-6 m(  GeV/c 2 for candidates with 0.96 < m(  ) < 1.06 GeV/c 2 DØ Preliminary 1 fb -1

4/9/2006 D. Buchholz 35 Results for D        DØ Preliminary 1 fb < m(  ) < 1.06 GeV/c < m(  ) < 0.96 GeV/c < m(  ) < 1.76 GeV/c 2 n(D  ) = 6 n(S+B) = 5.3 +/- 1.5 n(D s  ) = 3 n(S+B) = 4.6 +/- 0.7 Good agreement with expectations n(bkg) = /- 3.4

4/9/2006 D. Buchholz 36 Results for D        DØ Preliminary 1 fb < m(  ) < 0.96 GeV/c < m(  ) < 1.76 GeV/c 2 n = 17 n(bkg) = /- 3.4 Branching fraction limit D +        DØ: < 4.7 x (at 90%) CLEO-c(  e + e - ): 7.4x at 90% FOCUS: 8.8 x at 90% New limit on second generation RPV couplings

4/9/2006 D. Buchholz 37 Check of SM with Lifetimes and BR  In SM ( with CP conserved) eigenstates are CP specific- check decay portion of matrix  Measure of decay rates and widths in B s 0 -B s 0 system Γ s measures lifetime average 1/ΔΓ s measures off diagonal decay matrix element  Measure  Flavor specific, e.g.  Branching ratios  Lifetimes Differences

4/9/2006 D. Buchholz 38 1 Sigma Contours on ΔΓ s and 1/Γ s

4/9/2006 D. Buchholz 39 Conclusions  Tevatron’s first fb -1 opening up several new opportunities in flavor physics  Today, 3 world’s best results  Rare FCNC charm decays  CP Violation in B mixing  First double sided bound on  m s  More improvements this summer-  extend analysis and new hardware = layer 0 19 years after the observation of B d mixing and 12 years after the first lower limit on  m s, we now have first direct double sided bound on the B s oscillation frequency.  m s < 21 ps 90% CL

4/9/2006 D. Buchholz 40 Backup Slides

4/9/2006 D. Buchholz 41 Initial State Tagging  Get best estimate for reconstructed B meson to contain b(b) at origin  Definitions:  Efficiency:  Dilution:  Tagging power: use to compare the performance of taggers

4/9/2006 D. Buchholz 42 d pr Dilution  Determine dilution on event-by-event basis from B d  D *± μνX events  Use opposite side events  Plot d pr ( predicted) versus D measured