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B S Mixing at Tevatron Donatella Lucchesi University and INFN of Padova On behalf of the CDF&D0 Collaborations First Workshop on Theory, Phenomenology.

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Presentation on theme: "B S Mixing at Tevatron Donatella Lucchesi University and INFN of Padova On behalf of the CDF&D0 Collaborations First Workshop on Theory, Phenomenology."— Presentation transcript:

1 B S Mixing at Tevatron Donatella Lucchesi University and INFN of Padova On behalf of the CDF&D0 Collaborations First Workshop on Theory, Phenomenology and Experiments in Heavy flavour physics May 29-31 2006, Capri, Italy

2 Donatella Lucchesi2 May 31, 2006 B s Mixing in The Standard Model In the ratio uncertainties cancels:   = 1.21+0.02 +0.035 -0.014 (M. Okamoto, hep-lat/0510113) Big uncertainties

3 Donatella Lucchesi3 May 31, 2006 Measurement Principle in a Perfect World B s vs. B d oscillation B lifetime Rather than fit for frequency perform a ‘Fourier transform’  m s [ps -1 ]  A

4 Donatella Lucchesi4 May 31, 2006 Road Map to  m s Measurement 1. Final state reconstruction 2. High resolution on proper decay length 3. Tag B flavor at production time Opposite Side fragmentation particle: , K… ,K

5 Donatella Lucchesi5 May 31, 2006 Adding all the realistic effects Proper time resolution Flavor tagging power

6 Donatella Lucchesi6 May 31, 2006 Road Map to  m s Measurement 1. Final state reconstruction 2. High resolution on proper decay length 3. Tag B flavor at production time Opposite Side fragmentation particle: , K… ,K measure efficiency  and dilution D:  D 2 gives the “effective” number of events

7 Donatella Lucchesi7 May 31, 2006 Primary Vertex Secondary Vertex d = impact parameter B Decay Length L  ~ 48  m includes 33  m of beam spot Triggers Used CDF: Two tracks displaced from PV D0:  Single inclusive muons o Pt>3,4,5 GeV  Dimuons: o Other muon for flavor tagging

8 Donatella Lucchesi8 May 31, 2006 B s Data sample B s  D s  D s   KK D s  K *0 K K *0  K  D s  3  B s  D s 3  D s  D s  K *0 K Signal B s  D s  D s  Partially reconstructed B mesons Combinatorial background B0 D-B0 D-

9 Donatella Lucchesi9 May 31, 2006 CDF Hadronic B s yields summary Decay channelYield B s  D s  D s  1570±43 B s  D s  D s  K *0 K857±32 B s  D s  D s  3  612±37 B s  D s 3  D s  493±37 B s  D s 3  D s  K *0 K204±26 Total3736±79 B +  D 0  ~ 26,000 B 0  D -  ~ 22,000

10 Donatella Lucchesi10 May 31, 2006 CDF Semileptonic samples B s  D s l X D s   KK D s  K *0 K K *0  K  D s  3  D s l ~ 53,000

11 Donatella Lucchesi11 May 31, 2006 Decay channel: B s  + D s - X D s -  - and  K + K - Cuts selected maximize N Bs = 26,710 ± 556(stat) +D-+D- +Ds-+Ds- D0 Semileptonic samples

12 Donatella Lucchesi12 May 31, 2006 Road Map to  m s Measurement 1. Final state reconstruction 2. High resolution on proper decay length 3. Tag B flavor at production time Opposite Side fragmentation particle: , K… ,K

13 Donatella Lucchesi13 May 31, 2006 Proper decay time reconstruction  Semileptonic decay ct = L xy lD M B /P t lD  K  Fully reconstructed events ct = L xy B M B /P t B CDF K=  P t lD /P t B  L xy B /L xy lD  It is needed to:  Measure the lifetime to establish the time scale  Determine the time resolution D0 K=  P t lD /P t B 

14 Donatella Lucchesi14 May 31, 2006 B Lifetime measurement c  (B s )=1.538±0.040(stat) ps Central value c  (B s )=404-416  m Statistical error ~10  m

15 Donatella Lucchesi15 May 31, 2006 Proper time resolution,  t  Lifetime measurement not very sensitive  In the  m s fit each event weighted by its resolution  Dedicated calibration needed Prompt Charm + track sample J/  +  - sample

16 Donatella Lucchesi16 May 31, 2006 Proper time resolution,  t

17 Donatella Lucchesi17 May 31, 2006 Road Map to  m s Measurement 1. Final state reconstruction 2. High resolution on proper decay length 3. Tag B flavor at production time Opposite Side fragmentation particle: , K… ,K measure efficiency , dilution D  D 2 gives the “effective” number of events N right -N wrong N right +N wrong D=D= = 2 P right -1

18 Donatella Lucchesi18 May 31, 2006 +D-+D- +Ds-+Ds- N = 5601 ± 102 (stat) -lepton (electron or muon) - Secondary Vertex - Event Charge Tags combined Opposite Side Taggers  Use data to calibrate the taggers and to evaluate D  Fit semileptonic and hadronic B d sample to measure: D,  m d  D 2 =2.48  0.21(stat.) (syst.)% +0.08 -0.06

19 Donatella Lucchesi19 May 31, 2006 Same Side Tagger B 0 s likely to have K B 0 /B ± likely to have  nearby Use PID to separate pion from kaon Tune Monte Carlo to reproduce B 0,B - distributions then apply to B s

20 Donatella Lucchesi20 May 31, 2006 Flavor Taggers performances  Exclusive combination of tags in OST  SSTK-OST combination assumes independent tagging information

21 Donatella Lucchesi21 May 31, 2006 Amplitude Scan notation  A is introduced:  A=1 when  m s measured =  m s true B 0 mixing in hadronic decay In the figure:  Points: A±  (A) from Likelihood fit for different  m  Yellow band: A±1.645  (A)  Dashed line: 1.645  (A) vs.  m   m excluded at 95% C.L. if A±1.645  (A)<1  Measured sensitivity: 1.645  (A)=1

22 Donatella Lucchesi22 May 31, 2006 D0 Results “favored value’’ = 19 ps -1 17<  m s <21 ps -1 at the 90% C.L.  m  19 ps -1 : A/  A=2.5 and A-1/  A=1.6 Sensitivity = 14.1ps -1  m s >14.8 at the 95% C.L.

23 Donatella Lucchesi23 May 31, 2006 Choice of Procedure Before un-blinding: p-value probability that observed effect is due background fluctuation. No search window. p-value<1%? make double sided confidence interval from  (ln( L )), measure  m s set 95% C.L. based on Amplitude Scan yes no ln[ L (A=1)/ln L (A=0)] Probability of random tag fluctuation estimated on data (randomized tags) and checked with toy Monte Carlo

24 Donatella Lucchesi24 May 31, 2006 CDF Amplitude Scans Sensitivity: 17.3 ps -1  m s > 15.9 ps -1 @ 95% CL Sensitivity: 25 ps -1  m s > 16.7 ps -1 @ 95% CL

25 Donatella Lucchesi25 May 31, 2006 CDF Combined Amplitude Scan Sensitivity better than the W.A. 20.1 ps -1 Rare case!!

26 Donatella Lucchesi26 May 31, 2006 Likelihood Profile & significance How often random tags produce a likelihood deep this dip? Probability of fake: p-value=0.5% Measure  m s !!!

27 Donatella Lucchesi27 May 31, 2006 Measurement of  m s  m s =17.33 + 0.42 ± 0.07 ps -1 -0.21 17.00 <  m s <17.91 ps -1 at 90% C.L. 16.94 <  m s <17.97 ps -1 at 95% C.L.

28 Donatella Lucchesi28 May 31, 2006 |V td |/|V ts | Determination Used as inputs:  m Bs /m Bd = 0.9830 PDG 2006   2 = 1.210 +0.47 ( M. Okamoto, hep-lat/0510113 )   m d = 0.507±0.005 PDG 2006 -0.35 |V td |/|V ts |=0.208 +0.008 (stat.+syst.) -0.007 |V td |/|V ts | = 0.199 +0.026 (stat) +0.018 (syst) -0.025-0.015 Latest Belle result b  s  ( hep-ex/050679 ):

29 Donatella Lucchesi29 May 31, 2006 Conclusions  1 fb -1 of data used for Bs oscillation study  D0:  2.5  deviation from 0 in the Amplitude Scan at  m s =19 ps -1  90% C.L. interval for  m s : 17-21 ps -1 o For the summer: Include D s  K*K, D s  K s K D s  3  and e+D s Include hadronic decays Include Same Side Tagging

30 Donatella Lucchesi30 May 31, 2006 Conclusions cont’d  CDF:  experimental signature for B s -B s oscillations  Probability of random fluctuation is 0.5%  First direct measurement of:  m s =17.33 + 0.42 ± 0.07 ps -1 -0.21 |V td |/|V ts |=0.208 +0.008 (stat.+syst.) -0.007 o Future: Include other decays (Partially recon. D s *  D s  /  ) Combine efficiently flavor tags Improve ct resolution

31 Donatella Lucchesi31 May 31, 2006 BACKUP

32 Donatella Lucchesi32 May 31, 2006 The Accelerator

33 Donatella Lucchesi33 May 31, 2006 Detector for the measurement: CDF Trigger: displaced tracks (SVT) Tagging Power: TOF & dE/dX (COT) Proper time Resolution: SVX and L00

34 Donatella Lucchesi34 May 31, 2006 Detector for the measurement: D0 Fiber and Silicon trackers in 2T Solenoid field Fine segmentation Liquid Ar Calorimeter & Preshower Three layers system & absorber Hermetic detector

35 Donatella Lucchesi35 May 31, 2006 Tevatron Luminosity 1fb -1 Used in the analysis

36 Donatella Lucchesi36 May 31, 2006 Parametrizing tag decision

37 Donatella Lucchesi37 May 31, 2006 Calibrating SSTK

38 Donatella Lucchesi38 May 31, 2006 Calibrating SSTK Tune MC to reproduce B 0/± dilution and then measure it for SSTK

39 Donatella Lucchesi39 May 31, 2006 D0 Procedure Correction factor due to missing neutrino Several effects taken into account:  Resolution scale factor for detector mismodeling  Reconstruction efficiency as function of decay length  Physical and combinatorial background contributions

40 Donatella Lucchesi40 May 31, 2006 Systematic Uncertainties Amplitude Scan Related to absolute value of A important when setting a limit Cancel out in A/  A Very small compared to statistical error

41 Donatella Lucchesi41 May 31, 2006 Combined Amplitude Scan: an other view

42 Donatella Lucchesi42 May 31, 2006 Systematic Uncertainties on  m s Fit Model: negligible Relevant only lifetime scale

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