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Ricerca delle oscillazioni del sistema a

Ricerca delle oscillazioni del sistema a. Sandro De Cecco INFN Roma Incontri di Fisica delle Alte Energie Catania, 31 marzo 2005. Outline. Highlights on B s mixing. CDF detector and triggers. B s mixing analysis: B s signals

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Ricerca delle oscillazioni del sistema a

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  1. Ricerca delle oscillazioni del sistema a Sandro De Cecco INFN Roma Incontri di Fisica delle Alte Energie Catania, 31 marzo 2005 Sandro De Cecco - INFN Roma

  2. Outline • Highlights on Bs mixing • CDF detector and triggers • Bs mixing analysis: • Bs signals • Lifetime measurement • Flavour tagging calibration • Bd mixing • Amplitude scan for Dms • Preliminary CDF result • Future prospects Sandro De Cecco - INFN Roma

  3. B0 meson flavour oscillations Flavour oscillations occur through 2nd order weak interactions Dmd (exp.)= 0.510+0.005 ps-1(HFAG 2005) Lattice-QCD: f2BdBBd = (223+33+12) MeV f2BsBBs = (276+38) MeV + |Vtd| determined at ~15% But in the ratio uncertainties cancels: Measuring Dms/Dmd determines |Vts|/|Vtd| at 5% precision x = 1.24+0.04+0.06 Sandro De Cecco - INFN Roma

  4. CKM Unitarity Triangle In SM, the CKM unitary matrix describes the weak decays of quarks, CPV allowed through phase h Unitarity relations: are represented as U.T. (area aCPV): ( since |Vcb|=|Vts|=Al2 ) Measurement of Bs mixing frequency Dms gives a precise determination of one side of UT  confirm CP violation Sandro De Cecco - INFN Roma

  5. 95% CL limit is : Dms > 14.5 ps-1 Sensitivity:18.2 ps-1 Experimental status on Dms Present limit (HFAG 2004) from: LEP / SLD / CDF run I Amplitude scan method discussed later Sandro De Cecco - INFN Roma

  6. Dms constraint to U.T. Fit with all constraints (winter 05): ρ= 0.190 ± 0.044 η = 0.349 ± 0.024 Experimental lower limit on Dms Sandro De Cecco - INFN Roma

  7. SM CKM-fit prediction for Dms (with all constraints) compatibility plot (Δms not used) Dms = 18.9 ± 1.6ps-1 [15.7, 23.0] @ 95% CL If Dms > 30 ps-1 New Physics @ 3s Δms = 20.5 ± 3.2ps-1 [14.4, 27.1] @ 95% CL Sandro De Cecco - INFN Roma

  8. The Collider Detector at Fermilab Sandro De Cecco - INFN Roma

  9. The Tevatron pp collider Superconducting proton-synchrotron: 36p36p bunches, crossing each 396 ns at √s = 1.96 TeV Luminosity……………………………..: record peak L =1.2  1032 cm-2 s-1 • @CDF : 240-360 pb-1 used for B physics • lost ~ 100 pb-1 due to COT crisis Sandro De Cecco - INFN Roma

  10. 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 B Physics at pp collider BB production mechanics in hadron collider: • Huge cross-section: 50-100 b • All B species produced: • Bu,Bd,Bs,Bc,b, b… • with production fractions: • fu : fd : fs : fL≈ 4 : 4 : 1 : 1 • BUT:(bb) << (pp) (~65 mb)  B events have to be selected with specific triggers • Trigger requirements:large bandwidth, background suppression, small dead-time Sandro De Cecco - INFN Roma

  11. The CDF II detector Tracking System Sandro De Cecco - INFN Roma

  12. ~ 1 mm b decays primary vertex secondary vertex Impact Parameter ( ~100mm) B physics triggers at CDF II With the NewSilicon Vertex Trigger Conventional at colliders (Run I) Di-Muon (J/) Pt() > 1.5 GeV J/ modes down to low Pt(J/)~0 (Run II) + Displaced track + lepton (e, ) 120 m < I.P.(trk) < 1mm PT(lepton) > 4 GeV Semileptonic modes 2-Displaced tracks PT(trk) > 2 GeV 120 m < I.P.(trk) < 1mm SpT> 5.5 GeV fully hadronic modes - CP violation - Masses, lifetimes - Quarkonia, rare decays - High statistics lifetimes - Sample for tagging studies - BSmixing - Charmless decays Sandro De Cecco - INFN Roma

  13. COT track ( 2 parameters) 5 SVX coordinates beam spot d Impact Parameter (transverse projection) SiliconVertexTracker: thehadronic B trigger • Online Impact parameter • Available at Level 2 trigger (20µs latency) • convolution of transverse size of the beam spot with the impact parameter resolution of the SVT: s≈47 um ≈ 35 um + 30 um SVT resolution Beam spot size Impact parameter distribution Compare to offline ~ 46 mm Sandro De Cecco - INFN Roma

  14. Searching for Bs mixing @ CDF Sandro De Cecco - INFN Roma

  15. Bs time evolution Ex. Dms=15 ps-1>>Dmd(=0.5ps-1) Mix and un-mix time dependent probabilities: Time dependent Asymmetry: Bs fully mixes in < 0.15 psSeveral oscillations per lifetime …. experimental challenge Sandro De Cecco - INFN Roma

  16. Significance of B0s mixing measurement • Since initial state flavour sign • is “far from ideally” known D where: Signal / Noise • Effective tagging power: • = efficiency of taggers •  eD2figure of merit vertexing and momentum resolution Sandro De Cecco - INFN Roma

  17. Kaon Analysis Strategy • Bs signal reconstruction • Flavour specific eigenstates • Bs decay time • proper time reconstruction • Lifetime measurement • Initial flavour of the Bs • Flavour tagging techniques • calibrate on Bd mixing  Bs Mixing • performed a “Blind Analysis” Sandro De Cecco - INFN Roma

  18. n p D D B B P.V. P.V. Two different Bs signatures: Fully reconstructed HADRONIC modes: • Complete momentum reconstruction • Good proper time resolution • High Bs mass resolution  high S/B • Selected by Two Track Trigger (SVT) • Two displaced tracks (w SVT Impact parameter) • LOW statistics s s Partially reconstructed SEMILEPTONIC modes: • Missing momentum carried by the n • Visible proper time corrected by K factor from MC • Proper time resolution diluted by missing momentum • Cannot reconstruct Bs mass  different S/B • Selected by dedicated trigger (l+SVT): • One displaced tracks (w SVT Impact parameter) • One Lepton m,e w pT >4 GeV/c • HIGH statistics m,e s s Sandro De Cecco - INFN Roma

  19. Hadronic Bs signals NBS = 526±33 S/B ~ 2 sM  15 MeV “Satellites”: ( Not used in this analysis ) Sandro De Cecco - INFN Roma

  20. Hadronic Bs signals (2) NBS = 254±21 NBS = 116±18 Sandro De Cecco - INFN Roma

  21. Calibration B0 and B+ hadronic signals Sandro De Cecco - INFN Roma

  22. Missing PT No Bs mass peak Use Ds mass signals Charge correlation between ℓ and Ds ℓ+ Ds- : “Right-sign” = signal ℓ+ Ds+: “Wrong-sign” = background Right-sign peak is not pure signal ~20% background: Ds + fake lepton from primary B0,B+g Ds D X with D gℓnX c-c backgrounds Semileptonic Bs Signals Sandro De Cecco - INFN Roma

  23. Semileptonic Bs Signals (2) 1573±88 events 1750±83 events Sandro De Cecco - INFN Roma

  24. B0B+ crosstalks: B0g l+nD- B+g l+nD**0 with (D**0g D-p+) Sample composition ℓ+ D+ : B0/B+ ~ 85/15 ℓ+ D*+ : B0/B+ ~ 85/15 ℓ+ D0 : B0/B+ ~ 20/80 Semileptonic B0 and B+ Signals ~52Kl+D- ~100Kl+D0 ~25Kl+D*- Sandro De Cecco - INFN Roma

  25. Signal yields summary (S/B) Hadronic Bs modes ~900 events O(104)calibration modes (S/B) Semileptonic Bs modes ~7700 events O(105)calibration modes Sandro De Cecco - INFN Roma

  26. Lifetime bias from SVT trigger SVT cuts on track Impact Parameter: 120 m < I.P.(trk) < 1mm Proper time distribution is sculpted Hadronic:2 SVT tracks Semileptonic:1 SVT track • Efficiency as a function of decay time is obtained using MonteCarlo: • B production (B p-spectrum from data), decay model (EvtGen) • full simulation of Detector & Trigger reproducing run-by-run conditions (alignments, beam line, …) • Check:emulate SVT sculpting on B+ gJ/Y K+unbiased sample Sandro De Cecco - INFN Roma

  27. Decay time actually measure transverse quantities: Lxy , PT(B) Un-binned likelihood fit Used: and Lifetime in the hadronic Bs modes Combinatorial background ct template from high mass sideband Sandro De Cecco - INFN Roma

  28. Lifetime in the B0 and B+hadronic modes B0 B+ Sandro De Cecco - INFN Roma

  29. Hadronic B-lifetimes results ± (stat) ± (syst) Systematic summary t(B+) = 1.66 ± 0.03 ± 0.01 ps t(B0) = 1.51 ± 0.02 ± 0.01 ps t(Bs) = 1.60 ± 0.10 ± 0.02 ps t(B+)/t(B0) = 1.10 ± 0.02 ± 0.01 t(Bs)/t(B0) = 1.06 ± 0.07 ± 0.01 Average lifetimes (exp.): Theory prediction: t(B+) = 1.653 ± 0.014 ps t(B0) = 1.534 ± 0.013 ps t(Bs) = 1.469 ± 0.059 ps t(B+)/t(B0) = 1.06 ± 0.02 t(Bs)/t(B0) = 1.00 ± 0.01 Sandro De Cecco - INFN Roma

  30. Measure the B decay distance L intersection of ℓ and Ds Observable momentum p* = p(ℓDs) Correct statistically for missing momentum factor ( from MC ) Lifetime in the semileptonic Bs modes K vsM(ℓDs) decay time pseudo decay time • Perform an unbinned Likelihood fit: • Ds meson mass, pseudo decay time, pseudo-decay time resolution • Integration over K-factor p.d.f. • Combinatorial background from Ds sidebands Sandro De Cecco - INFN Roma

  31. Lifetime in the semileptonic Bs modes ct = 455.9  11.9 mm ct = 413.8  20.1 mm ct = 422.6  25.7 mm Combined ℓ-Ds lifetime result:445.0  9.5 mm(W.A.: 438  17 mm) statistical err .only,NOT for Averages(DØ ’05: 426  13  17 mm) Real Ds backgrounds:prompt and physics Sandro De Cecco - INFN Roma

  32. Hadronic: <sct0>: ~ 30 mm (100 fs) sp/p < 1% Semileptonic <sct0>: ~ 50 mm (167 fs) sp/p ~ 15% (K factor) Bs decay time Resolution s(ct) Semileptonic Vertex resolution (constant) Momentum resolution (proportional to ct) Hadronic ct Sandro De Cecco - INFN Roma

  33. The amplitude of mixing asymmetry is diluted by a factor: Time resolution effect on mixing Semileptonic Dst = f(t) HadronicDst = const. Dm = 15 ps-1 st=167 fs sp/p ~ 15% Dm = 15 ps-1 st=100 fs Dst = 0.32 only first few oscillations Sandro De Cecco - INFN Roma

  34. Flavour tagging Opposite Side Jet Charge: the sum of charges of the b-Jet tracks is correlated to the b-flavour  Away Jet reconstruction Used for today results Soft Lepton (e,m) due to blnX The charge of the l is correlated to b-flavour  Search lepton from sec. vtx. Same Side NOT yet used SS Pion: B0d is likely to be accompanied close in DR by a p+ from fragmentation SS Kaon: for B0s is likely to be accompanied close in DR by a K+ (PID) search for p/K from Primary vertex Opposite Side K: due to bcs it is more likely that a B0 meson will contain in final state a K+ than a K-. (PID) search for K from secondary opposite vtx Sandro De Cecco - INFN Roma

  35. Statistical uncertainty for tagging efficiency: A typical tagging: e=0.1,D=0.4,eD2=1.6% 1000 events: eD2 =1.6+0.7% (44%) 100K events: eD2=1.60+0.07% (4.4%) Dividing events into classes based on tagging power improves eD2  Binned Dilution: needs statistics Solution: Lepton + Displaced track trigger ~1.4 M sample rich in semileptonic B High B purity Lepton Charge = Decay flavor of B Calibrating the taggers High b purity Sandro De Cecco - INFN Roma

  36. The soft electron and muon tagger are built in a Likelihood based aproach Dilution is binned as a function of the lepton transverse momentum wrt the B jet direction in the opposite hemisphere b g c+l- : High pTrel b g c g s+l+: Low pTrel (sequentials) B jet pTrel e Soft lepton tagging Soft electron tag Soft muon tag Sandro De Cecco - INFN Roma

  37. Measure the 5 taggers effective Dilutions in the ℓ + track calibration sample: Predict eD2event by event Test in Dm d measurement  Flavor Tagging Summary • Jet charge Q algorithms: • Jet with 2ndary vertex found • Jet containing displaced track • Highest momentum Jet e D Sandro De Cecco - INFN Roma

  38. Validation of the flavor tag calibration using B0 and B+ sample B0g Dp, B+g D0p B0g J/yK*0, B+g J/yK Event by event predicted dilution D from the flavor tag calibration Fit the “Dilution scale factor” S =1 if the tag calibration is correct. 5 scale factors for 5 tag types  Scale factors are then used for Bs mixing analysis in the hadronic B0 mixing in the hadronic channels B0 all Tags B+ all Tags Sandro De Cecco - INFN Roma

  39. Measure Dmd Extract 5 dilution scale factors  The dilution scale factors are used for semileptonic Bs mixing analysis B0 mixing in the semileptonic channels Muon Tag Sandro De Cecco - INFN Roma

  40. B0 mixing results • Dmd consistent with WA: 0.510±0.005 ps-1 • Total eD2: 1.1—1.4% • All dilution scale factors consistent with 1 • Hadronic: 15~25% uncertainty • Semileptonic: 5~15% uncertainty Sandro De Cecco - INFN Roma

  41. Standard cosine fit not very sensitive for high Dm (i.e. the Bs case) Method: Introduce “Amplitude” Ain Likelihood: perform “Amplitude Scan”(~AM band radio) Fit the amplitude A fixing Dm  Amplitude: A, uncertainty: sA Repeat the fit with a set of Dm values Amplitude A is consistent with: 1 if there is mixing 0 if there is no mixing Amplitude scan method, ex.: the B0 case Hadronic B0 A • Ex.: hadronic B0 • A = 1 at Dm = 0.5 ps-1 • A = 0 at Dm >> 0.5 ps-1 Sandro De Cecco - INFN Roma Dmdmeas.  1s

  42. “Blind Analysis”: Scrambling flavor tag decision  multiply the tag decision x (-1)Run Number Perform the blind amplitude scan to the Bs candidates: Amplitude A is randomized in the blind scan but: sA is not biased Evaluate sensitivity exclude Dms range where (1-A)>1.645∙ sA (95% C.L.) Systematic uncertainty Following the prescription by Moser, et.al. (NIM A 384 491) We use toy Monte-Carlo sample generated at each value of Dms in the amplitude scan Toy MC includes all variables and distributions used in Likelihood Take shifts in amplitude (DA) and statistical uncertainty (DsA). Derive systematic using formula Open the box after: Sensitivity estimation Systematic evaluation Dms amplitude scan road map Sandro De Cecco - INFN Roma

  43. Systematic Uncertainties Semileptonic Hadronic • Dilution scale factors and templates • systematic limited from control sample • statistics • Physics background at low Dms • Prompt background at high Dms **Systematic errors are negligible with respect to statistical in both cases** Sandro De Cecco - INFN Roma

  44. Amplitude Scan result (semileptonic) Sandro De Cecco - INFN Roma

  45. Amplitude Scan result (hadronic) Sandro De Cecco - INFN Roma

  46. CDF Combined Result • Sensitivity: 8.4 ps-1 • Limit: Dms > 7.9 ps-1@ 95% CL Sandro De Cecco - INFN Roma

  47. World Average + CDF Run II Sensitivity: 18.6 ps-1 Limit 14.5 ps-1 World Average (LEP, SLD, CDF run I) Sensitivity: 18.2 ps-1 Limit: 14.5 ps-1 CDF+World Combined Result Sandro De Cecco - INFN Roma

  48. Future perspectives • With the same data: • Add new tagging algorithm Same Side Kaon Tag • Add more channels • Add signals from other triggers • Improve decay time resolution with PV event by event • With new data: • Increased Luminosity • Use new trigger strategies • 2 SVT Tracks + tagging muon at trigger level • (already in place since summer 2004) Sandro De Cecco - INFN Roma

  49. Other channels, example • 13323 Bs candidates • Already used for lifetime • But not for mixing Sandro De Cecco - INFN Roma

  50. Same side Kaon tagging Exploits the charge correlation between the b quark and the leading product of b hadronization. B0 Already used in Dmd measurement, gives an eD2= 1.1  0.4 % p-K*0 B+ case is complicated by the contribution of excited Bd and Bs states B- p+K+ • SS Kaon tag possible with PID • “Simple case”: so excited states expected • Issues: • Need to know eD2 to set a limit on Dmd • Underlying event backgound Bs K-K*0 Sandro De Cecco - INFN Roma

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