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SLAC Experimental Seminar 08 February 2007

Probing the Physics Frontier with Rare B Decays at CDF. Cheng-Ju S. Lin (Fermilab). SLAC Experimental Seminar 08 February 2007. Interesting time in particle physics with many exciting questions: - Origin of EW symmetry breaking - Nature of cosmological dark matter

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SLAC Experimental Seminar 08 February 2007

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  1. Probing the Physics Frontier with Rare B Decays at CDF Cheng-Ju S. Lin (Fermilab) SLAC Experimental Seminar 08 February 2007

  2. Interesting time in particle physics with many exciting questions: - Origin of EW symmetry breaking - Nature of cosmological dark matter - Nature of dark energy - + … To get a consistent picture would require physics beyond the Standard Model Tevatron could potentially uncover those mysteries. We can: - Look for things directly (e.g. production of new particles) - Look for deviations from the Standard Model predictions !!!

  3. Gold Mine for Heavy Flavor Physics New particles: X(3872), Xb, Pentaquarks, … B and D Branching ratios Lifetimes: DG, Lb, Bs, Bc, B+, Bd … Mixing: Bs, Bd, D0 Production properties: s(b), s(J/y), s(D0), … Mass measurements: Bc, Lb, Bs, … CP Violation: Acp(Bhh), Acp(D0Kp), … SURPRISES!? Rare decays: Bsm+m-, BK* m+m-, D0m+m- , … Focus of today’s talk

  4. Indirect Search of New Physics : Bsm+m- b s Bs = • Solid prediction from the Standard Model (SM) • In the SM, the decay of Bsm+m- is heavily suppressed SM prediction  ~ a few decays per 1 billion Bs produced • Bdmm is further suppressed by another factor of ~20 • SM prediction is well below the sensitivity of current generation of • experiments  no observation yet • New physics could significantly enhance the branching ratio •  Any signal would be a clear indication of NP

  5. Some Scenarios of NP m b R-parity violating SUSY ~ n l’i23 l i22 m s • - MSSM: Br(Bmm) is proportional • to tan6b. BR could be as large as • ~100 times the SM prediction • - Tree level diagram is allowed in • R-parity violating (RPV) SUSY • models. Possible to observe decay • even for low value of tanb. Either discovery or null result could shed light on the the structure of new physics !!!

  6. TEVATRON Collider Chicago Collide proton (p) and anti-proton (p) at the c.m. energy of ~2 TeV CDF p D0 p Tevatron Record luminosity: ~270E30 cm-2s-1 (design 300E30) Lots of Bs produced in the collision debris !

  7. Integrated Luminosity Close to 2fb-1 of data collected by CDF Analyses presenting today use from 780pb-1 to ~1fb-1 of data

  8. b b g g b g q b b b b b q g g g q q Flavor Excitation Flavor Creation (gluon fusion) Flavor Creation (annihilation) Gluon Splitting Heavy Flavor Physics in Hadron Environment b’s produced via strong interaction decay via weak interaction • Tevatron is great for heavy flavor: • Enormous b production cross-section, • x1000 times larger than e+e- B factories • All B species are produced (B0, B+,Bs, • Lb, Sb, etc…) • However, • Inelastic (QCD) background is about • x1000 larger than b cross-section • Online triggering and reconstruction is • a challenge: collision rate ~1MHz  • tape writing limit ~100Hz

  9. CDF II Detector Significant detector, trigger, and DAQ upgrades in Run II

  10. Looking for Bsmm with CDF Detector CMU: |h|<0.6 CMX 0.6<|h|<1.0 Measure muon track momentum and charge Look for Bs production and decay vertices

  11. CDF Trigger: Lifeline of B Physics Program • CDF has implemented a 3-tier trigger • Level-1 is a synchronous hardware trigger • - Can process one event every 132ns • - Input rate = 1.7MHz (396ns 36x36 bunches) • L1A rate ~ 30KHz (limited by L2) • Level-2 is a combination of hardware and • software trigger (asynchronous) • - Average Level-2 processing time is ~30ms • - L2A rate ~1KHz (limited by event-builder) • Level-3 is purely a software trigger • - Massive PC farm • - L3A rate ~ 100Hz (limited by tape writing) • Data reduction rate (L1+L2+L3)  1 : 17000

  12. Three Classes of B Physics Triggers at CDF X X X d0 } d0 } IP IP + (e+) + (e+) (1) Dimuon trigger: For triggering on J/ and rare B decays (e.g. Bsmm and BmmX) - (e-) IP (2) Two-track trigger (SVT): For triggering on hadronic B and charm decays. Both tracks are required to have an impact parameter d0> 120m. (D0mm, Bem, etc…) (3) Lepton+Displaced Track(SVT): For triggering on semileptonic B decays.

  13. Silicon Vertex Tracker (SVT) CDF is the first hadron collider experiment to be able to trigger on fully hadronic B events • SVT links drift chamber tracks from • Level-1 with silicon hits to compute the • impact parameter of the track. Track impact parameter Level-2 SVT Trigger • SVT d0 resolution is ~ 47m • (35m beamline  33m resol). • SVT revolutionized B and Charm • physics at CDF. -600 -300 0 300 600 SVT impact parameter (mm)

  14. SVT Performance • Our physics program • is dictated by what • triggers we have • In Run I, Bhh • physics was a fantasy • In Run II with SVT, • we are making world • class measurements • First observations of: • BsK+K- • BsK+p- • Lbpp- • LbpK+ • Did I mention Bs mixing too?

  15. ~540 Hz @ 200 E30 ~320 Hz @ 200 E30 RARE B TRIGGERS AT TEVATRON • Keeping trigger rates under control is a constant battle !!! • Main issue: trigger rate blows • up rapidly vs. luminosity • For illustration, the following • rare B dimuon triggers alone: • - CMU-CMU pT>1.5GeV • - CMU-CMX pT>1.5GeV • would take up the entire level-2 • trigger bandwidth at L=200E30 cm-2 s-1 • In the latest trigger table, there are more than 150 level-2 triggers that need to co-exist CDF L2 Dimuon Trigger Cross Section

  16. KEEPING RARE B TRIGGERS ALIVE • Handles to control rates: • - Tighter selection cuts (e.g. pT of muon) • - Apply prescales • (DPS, FPS, UPS, etc.) • - Improving trigger algorithm • - Upgrading trigger hardware • We’ve been using a combination of all four handles to control the trigger rate trading efficiency for purity • It’s been a great challenge keeping B and high pT triggers • alive at Tevatron • It’ll be an even greater challenge at the LHC !! Non-optimal for rare searches

  17. B  mm Data Sample • Using 780pb-1 of dimuon • trigger data: • CMU-CMU trigger • CMU-CMX trigger • Use this inclusive sample • to search for: • Bsm+m-(Mass Bs=5.37GeV) • Bdm+m- • Even if BR is x10 the • SM value, only expect • a hand full of signal events in • the signal region • Signal region is swamped with various • kinds of background: both from SM processes • and detector effect (fake muons) Search region Effective background rejection is the key to this analysis!!

  18. Analysis Overview Motto: reduce background and keep signal eff high Step 1: pre-selection cuts to reject obvious background Step 2: optimization (need to know signal efficiency and expected background) Step 3: reconstruct B+J/y K+ normalization mode (take into account Br of BJ/yK and J/ymm: >> 100million B+) Step 4: open the box  compute branching ratio or set limit

  19. CDF Pre-selection • Pre-Selection cuts: • 4.669 < mmm < 5.969 GeV/c2 • pT(m)>2.0 (2.2) GeV/c CMU (CMX) • pT(Bs cand.)>4.0 GeV/c • Track, muon and vertex quality cuts • 3D displacement L3D between primary and secondary vertex Bkg substantially reduced but still sizeable at this stage

  20. Background Rejection:Bsmm Decay Characteristics No other tracks from this vertex 2 muons point to a “common vertex” m- m+ Bs-flight distance Bs-mass: MBs=5.37 GeV p p • Background rejection cuts: • muons add up to Bs mass • muons are isolated and have common vertex • vertex is well separated from beam-spot

  21. B m+m-Signal vs Background Discrimination + L3D PT() - L3D di-muon vertex primary vertex • m+m- mass (Eenergy, P  momentum) • B vertex displacement: • Isolation (Iso): (fraction of pT from Bmm within DR=(Dh2+Df2)1/2 cone of 1) • “pointing (Da)”: (angle between Bs momentum and decay axis) • For each di-muon • candidate, we compute • the 4 variables: • M • l • Iso • Da

  22. Distribution of the Discriminating Variables • Blue = Bsmm signal • events from simulation • (Monte Carlo) • Black = expected bkg • distributions • Using l, Da and Iso • to construct a new • variable, likelihood • ratio: Ps(b)i is the probability distribution function for signal (background) for variable i, with i loops over l, Da, iso

  23. Likelihood Ratio (LR) Distribution Di-muon events with large LR (near 1) are more likely to be signal Events with LR near 0 are more likely to be background Signal distribution is based on simulation

  24. Background Estimate • Assume linear background shape • extrapolate # of background events in sidebands to signal • region (± 60 MeV signal window) • Use control samples to cross-check bkg estimate 1.) OS- : opposite-charge dimuon, l < 0 2.) SS+ : same-charge dimuon, l > 0 3.) SS- : same-charge dimuon, l < 0 4.) FM : fake muon sample (at least one leg failed muon stub chi2 cut)

  25. Cross Check BKG Estimate in Control Samples LR CMU-CMU CMU-CMX cut pred obsv prob pred obsv prob >0.50 489±12 483 41% 351±10 338 27% 28% OS- >0.90 62±4 73 12% 56±4 63 22% 7% >0.99 4.8±1.2 9 8% 3.9±1.1 8 7% 2% >0.50 5.4±1.3 4 40% 3.3±1.0 2 39% 27% SS+ >0.90 <0.10 0 - 0.9±0.5 0 43% 43% >0.99 <0.10 0 - <0.10 0 - - >0.50 6.6±1.4 7 49% 4.2±1.1 5 41% 40% SS- >0.90 0.6±0.4 1 45% 0.3±0.3 0 70% 57% >0.99 <0.10 0 - <0.10 0 - - >0.50 188±8 159 3% 33±3 37 29% 7% FM >0.90 34±3 24 7% 6±1 5 46% 6% >0.99 4.5±1.0 9 6% 0.6±0.4 0 55% 12% Combined prob • Using a wider ± 150 MeV signal window for cross-check (Probability factor in uncertainty on Poisson mean)

  26. Bhh Background • CDF signal region is also contaminated • by Bh+h- (e.g. BK+K-, K+p-, p+p-) • K,p muon fake rates measured from data using D* sample • Convolute fake rates with expected Bh+h- distributions to • to obtain Bhh bkg • Total bkg = Bhh + combinatorial LR > 0.99

  27. eLH(Bs) cut CMU-CMU CMU-CMX LR>0.90 (70+/-1)% (66+/-1)% LR>0.92 (67+/-1)% (65+/-1)% LR>0.95 (61+/-1)% (60+/-1)% LR>0.98 (48+/-1)% (48+/-1)% LR>0.99 (38+/-1)% (39+/-1)% Likelihood Ratio Efficiency for Bs Signal • determined from Bsmm MC • MC modeling checked by comparing eLH(B+) • between MC and sideband subtracted Data (stat uncertainties only) • Optimize analysis based on a-priori expected upper • limit  LR>0.99 !!!

  28. Now Look in the Bs and Bd Signal Windows Number of observed events in the signal box is consistent with bkg expectation  set branching ratio limit Bs Branching Ratio Limit: Br(Bsmm)<1.0×10-7 @ 95%CL Br(Bsmm)<0.8×10-7 @ 90%CL Bd Branching Ratio Limit: Br(Bdmm)<3.0×10-8 @ 95%CL Bsmm: Observed 1 candidate Expect ~1.3 background events Bdmm: Observed 2 candidates Expect ~2.5 background events Best limits in the world, but still no hints of new physics

  29. Branching Ratio Limits • Evolution of limits (in 95%CL): World’s best limits 90% CL

  30. SO(10) Grand Unification Model R. Dermisek et al., hep-ph/0507233 (2005) R. Dermisek et al., JHEP 0304 (2003) 037 Red arrows indicate exclusion from this result!!! Pink regions are excluded by either theory or experiments Green region is the WMAP preferred region Blue dashed line is the Br(Bsmm) contour Light blue region excluded by old Bsmm analysis Remaining white region is still not excluded by experiment tan(b)~50 constrained by unification of Yukawa couplings

  31. Implications on SUSY Flavor Violation J. Foster et al. Hep-ph/0604121 SUSY General Flavor Mixing (GFM) framework dxy parameters quantify variations from Minimal Flavor violating assumption Bsg, Bsmm, and Bs mixing severely constrain non-MFV

  32. Implications on SUSY Flavor Violation J. Foster et al. Hep-ph/0604121 SUSY General Flavor Mixing (GFM) framework 2-D scan over dxy space tanb=40 non-MFV SUSY phase space is severely constrained

  33. Sneak Preview of Bsmm • 1fb-1 update is near completion • Implemented NN selection to enhance signal • efficiency and bkg rejection: NN contains additional variables: pT(Bs), pT(muon), etc. For a given bkg level, NN signal eff is 15-20% higher than LR!!

  34. Sneak Preview of Bsmm • Apply improved muon selection and particle ID • to suppress fake muons and Bhh backgrounds • Instead of single-bin counting experiment, use • multi-bin parameterizations: • 780pb-1 1fb-1, only • about 30% increase in stat • Expect the sensitivity to • increase by a factor • of 2!!! Bs Signal Eff Neural Net Output

  35. CDF Projection Conservative projection based on our current (780pb-1) performance Improvement expected from 1fb-1 analysis Achievable in RunII

  36. s s s s s s b b Bu,d,sm+m-K+/K*/f • B Rare Decays Bm+m- h : • B+ mm K+ • B0mm K* • Bsmmf • Lbmm L • Penguin or box processes in the Standard Model: • Rare processes: predicted BR(Bsmmf)=16.1x10-7 PRD 73, 092001 (2006) PRL 96, 251801 (2006) observed at Babar, Belle not seen m- m+ m- m+ C. Geng and C. Liu, J. Phys. G 29, 1103 (2003)

  37. Standard Model Probe of New Physics • Probe various Wilson coefficients (bs) - Predicted in several new physics scenarios (e.g. SUSY) - Large forward backward asymmetry in B0mm K* decay expected Flipped signs • Need better statistics • In low q2 region • CDF may be able to • contribute to resolving this 37

  38. Discriminating Variables For BmmK • Using similar discriminating variables and analysis • strategy as Bsmm search • proper decay length (l) • significance • Pointing (Da) |fB – fvtx| • Isolation (Iso) SIGNAL SIDEBAND SIGNAL SIDEBAND SIGNAL SIDEBAND 38

  39. Bu,d,sm+m-K+/K*/f Results with 1fb-1 • Using similar discriminating variables and strategy • as Bsmm analysis Bum+m-K+Bdm+m-K*Bsm+m-f Signal Sideband Extrapolated fit • Note: bins are counted. Gaussian is for illustration of expected width only

  40. Bu,d,sm+m-K+/K*/f Summary With 1fb-1 of data: • We see evidence for the B+ mm K+ B0 mm K* rare modes • We are homing in on the Bs rare mode

  41. Summary • Tevatron heavy flavor physics program is in • full swing. What I’ve showed today is only the • “tip of the iceberg” • CDF could observe any modest enhancement of • Bsmmin Run II. CDF is also on the verge of • observing Bsmmf decay • For the next few years, Tevatron will continue • to search for new physics with direct and • indirect searches • The ultimate frontier machine will be the LHC. • We may finally have a first clean glimpse of the • physics beyond the Standard Model • Look forward to seeing what that new physics really is

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