03/19/2006 Md. Naimuddin 1 B s Mixing at the Tevatron Md. Naimuddin (on behalf of CDF and D0 collaboration) University of Delhi Recontres de Moriond 19 th March, 2006

03/19/2006 Md. Naimuddin 2 –Introduction to Mixing –Why study Mixing –Fermilab Tevatron –Data Taking –CDF and D0 Detectors –Analysis strategy –B s mixing at CDF –B s mixing at D0 –Results and Conclusions OUTLINE

03/19/2006 Md. Naimuddin 3 Mixing: The transition of neutral particle into it's anti-particle, and vice-versa Introduction First observed in the K meson system. In the B meson system, first observed in an admixture of B 0 and B s 0 by UA1 and then in B 0 mesons by ARGUS in These oscillations are possible because of the flavor-changing term of the Standard Model Lagrangian,

03/19/2006 Md. Naimuddin 4 Where V CKM is the CKM matrix; Wolfenstein parametrisation- expansion in ~ 0.22 CP violation in the Standard Model originates due to a complex phase in the CKM matrix (quark mixing). Introduction

03/19/2006 Md. Naimuddin 5 Mixing in B mesons Light and Heavy B mesons mass eigenstates differ from flavor eigenstates: Time evolution of B 0 and states In case  0,  mttP t e mu   cos1 1, 2

03/19/2006 Md. Naimuddin 6 standard model Expectation: Δm s = ps -1 Δm d = 0.5ps -1 measurement of Δm s /Δm d  V ts /V td constrain unitary triangle f 2 Bd B Bd = ( MeV) 2 |V td | from  m d limited by ~15%  consider ratio Determine |V ts |/|V td | ~ 5% precision Why B s mixing is important K mixing  direct & indirect CPV B d mixing  heavy top mass mixing  neutrino mass  0 B s mixing  ????

03/19/2006 Md. Naimuddin 7 Fermilab Tevatron Highest Luminosity achieved: 1.7x10 32 cm/s 2 Expected: 2 – 3 x cm/s 2

03/19/2006 Md. Naimuddin 8 Data Taking Excellent performance by the Tevatron and we are doubling our data set every year. Data taking efficiency is ~ 85%. We already have collected about 10 times of run 1 data. Pb -1

03/19/2006 Md. Naimuddin 9 CDF Detector Solenoid 1.4T Silicon Tracker SVX up to |  |<2.0 SVX fast r-  readout for trigger Drift Chamber 96 layers in |  |<1 particle ID with dE/dx r-  readout for trigger Time of Flight →particle ID

03/19/2006 Md. Naimuddin 10 D0 Detector 2T solenoid Fiber Tracker 8 double layers Silicon Detector up to |  |~3 forward Muon + Central Muon detectors excellent coverage |  |<2 Robust Muon triggers.

03/19/2006 Md. Naimuddin 11 We need to: Reconstruct the B s signal. Know the flavor of the meson at it’s production time (Flavor tagging) and get  D 2 Proper decay length resolution Analysis strategy  Measuring B s oscillations is much more difficult than B d oscillations because of the fast mixing frequency. In order to measure, Reconst- ruction Flavor tagging Proper time

03/19/2006 Md. Naimuddin 12  Semileptonic modes collected by the two track trigger Reconst- ruction Flavor tagging Proper time

03/19/2006 Md. Naimuddin 13  More than 2300 Bs signal candidates in 765 pb -1 Reconst- ruction Flavor tagging Proper time B s  D s - (  )  +

03/19/2006 Md. Naimuddin 14  Currently using only semileptonic decay of the Bs B s  D s  X (D s   ) (   K + K - ) Reconst- ruction Flavor tagging Proper time 26,710±560 7,422±281 5,601±102 1,519±96 UntaggedTagged

03/19/2006 Md. Naimuddin 15 Soft Lepton Tagging (  or e): Charge of the leptons provides the flavor of b. Jet Charge Tagging: Sign of the weighted average charge of opposite B jet provides the flavor of b. Same Side(Kaon) Tagging (New at CDF) B meson is likely to be accompanied by a close K/  particle Id helps b-hadronb-hadron Trigger lepton Fragmentation pion B PV D neutrino L xy Soft lepton Jet charge Opposite sideSame side e or   Reconst- ruction Flavor tagging Proper time

03/19/2006 Md. Naimuddin 16 Reconst- ruction Flavor tagging Proper time Opposite side Tagging: Same side Kaon Tagging:

03/19/2006 Md. Naimuddin 17 Reconst- ruction Flavor tagging Proper time  Using only Opposite side e, , secondary vertex or jet charge for tagging Tagger tuned using B d mixing measurement  m d = 0.506±0.020±0.014 ps -1

03/19/2006 Md. Naimuddin 18 Easier to calculate for Hadronic decays Proper decay time given as : Reconst- ruction Flavor tagging Proper time Distance from PV to SV in transverse plane Boost meson back to its rest frame Due to missing neutrino, it becomes little tricky in semileptonic sample Missing momentum  increased ct error (  ct ) Proper decay time given as: where from MC

03/19/2006 Md. Naimuddin 19 Reconst- ruction Flavor tagging Proper time Best estimate of errors used in track fitting, any additional scaling determined from data Scale factor = / (largest systematic) Pull of J/  vertex from the primary vertex for prompt J/  s

03/19/2006 Md. Naimuddin 20 Fitting procedure Amplitude Fitting approach:  Introduce amplitude  Fit for A at different  m s  Traditionally used for B s mixing search  Easy to combine experiments Likelihood approach:  Search for min, which minimizes the –ln(L), where min is the estimator of the true frequency.  Difficult to combine the results from different experiments.

03/19/2006 Md. Naimuddin 21 Amplitude fit method Fit to data - free parameter Obtain as a function of Measurement of gives and otherwise At 95% CL sensitivity excluded Systematics is given by

03/19/2006 Md. Naimuddin 22 Bs mixing limit Limit:  m s > 8.6 ps 95% confidence Sensitivity: 13.0 ps 95% confidence

03/19/2006 Md. Naimuddin 23 Bs mixing limit Dominant sources of systematic uncertainty: Scale factor, K factors and Sample composition Limit:  m s > 14.8 ps 95% confidence Expected Limit: 14.1 ps 95% confidence A clear deviation of 2.5  from 0 can be seen at  m s ~19 ps -1

03/19/2006 Md. Naimuddin 24 Likelihood scan  m s < 21 ps 90% CL Most probable value of  m s = 19 ps -1  Resolution  K-factor variation by 2%  BR (B s  D s X)  ccbar contamination  BR (B s  D s D s ) Syetematics

03/19/2006 Md. Naimuddin 25 Probability for this measurement to lie in the range 16 <  m s < 22ps -1 Given a true value:  m s > 22 ps -1 : 5.0%  m s = 19 ps -1 : 15% Simulate  m s = infinity by randomizing flavor tagging variable Consistent results from parameterized MC studies Significance Test

03/19/2006 Md. Naimuddin 26 CKM fit without new D0 result

03/19/2006 Md. Naimuddin 27 Disclaimer: Produced only yesterday by CKM group so I don’t have much information about the inputs. CKM fit with new D0 result

03/19/2006 Md. Naimuddin 28 CONCLUSIONS Excellent performance of the Tevatron. Development of Same Side Kaon Tagger which will ease the total tagging power by about 2.5 (CDF) D0 has excellent opposite side tagger performance. CDF preliminary: D0 Final (hep-ex/ , submitted to PRL): We are on the edge of B s mixing measurement and entering into the precision era. Limit:  m s > 8.6 ps 95% confidence Sensitivity: 13.0 ps 95% confidence  m s < 21 ps 90% CL Most probable value of  m s = 19 ps -1 Likelihood scan Limit:  m s > 14.8 ps 95% confidence Expected Limit: 14.1 ps 95% confidence Amplitude Scan

03/19/2006 Md. Naimuddin 29 FUTURE IMPROVEMENTS CDF: Improved selection in hadronic modes using Neural Networks Use semileptonic events from other triggers. Improve vertex resolution. Use same side Kaon tagger. Several major improvements are expected in the future: More data: On track for 4-8 fb -1 of data by D0: More decay modes (D s  K*K, 3 , K s , B s  e D s X ) Use of same side tagging. Use of hadronic modes. Additional Layer of silicon. Proposal to increase the bandwidth.

03/19/2006 Md. Naimuddin 30 Back-up slides

03/19/2006 Md. Naimuddin 31 Backup-1 Time evolution follows from a simple perturbative solution to the schrondinger’s equation Eigenvalues are, Measure of the amount by which |B L > and |B H > differ from CP eigenstates In case  0,

03/19/2006 Md. Naimuddin 32 In the limit of no CP violation in mixing (q/p =1), unmixed and mixed decay probabilities become  mttP te mu   cos1 1, These oscillations can be used to measure the fundamental parameters of the standard Model and have other far reaching effects such as breaking the matter anti-matter symmetry of the Universe. Constraining the CKM matrix redundantly using different measurements of the angles/sides is a sensitive probe of New Physics Backup-2

03/19/2006 Md. Naimuddin 33 Backup-3

03/19/2006 Md. Naimuddin 34 Backup-4

03/19/2006 Md. Naimuddin 35 Backup-5

03/19/2006 Md. Naimuddin 36 Backup-6

03/19/2006 Md. Naimuddin 37 Backup-7 WA+CDF+D0

03/19/2006 Md. Naimuddin 38 Comparison with other experiments at  m s =15 ps -1 Backup-8