Study of B s         Supreet Pal Singh Prof. Kajari Mazumdar Prof. J.B.Singh 1India-CMS Meeting 27th-28th March 2009

Introduction to Bs   K+K+ K-K-  .. PV SV B0sB0s B s decays in Secondary vertex 2  2 tracks from  (       BR ~ 50 %) B s mass = GeV 2India-CMS Meeting 27th-28th March 2009

The branching ratio has been predicted to be 1.6 x in Standard Model. source : C. Q. Geng and C. C. Liu, J. Phys. G 29, 1103 (2003). The latest update on the Upper limit is from D0 experiment which gives the upper limit as 3.2 x So,for 10 pb -1 luminosity corresponding we expect to see about 1000 events of the type Bs  . 3India-CMS Meeting 27th-28th March 2009

Work Done Signal events have been generated through full reconstruction chain in CMSSW_2_2_3 on the line of official data production. EvtGenLHC generator has been used to generate the signal sample with standard user_decay_file : “GeneratorInterface/EvtGenInterface/data/Bs_phimumu_KK.dec” The analysis has been done using PAT in CMSSW_2_2_5. 4India-CMS Meeting 27th-28th March 2009

Signal events Criteria : 1) MSEL =1, no pt thresholds. 2) 2 muons in the event with P T > 2.5 GeV and |  | < 2.5 Generator efficiency = 1.85 x No. of events analyzed = 8607 No. of reconstructed events with 0 muons = 351 No. of reconstructed events with 1 muons = 2098 No. of reconstructed events with 2 muons = 4364 No. of rec. events with more than 2muons = India-CMS Meeting 27th-28th March 2009

Background events Main source of background  QCD events. Not being able to submit the jobs for the dataset : “/InclusivePPmuX/Summer08_IDEAL_V9_v4/GEN-SIM-RECO “ For the present work the analysis has been done on : “/InclusiveBBmu_Pt20/Summer08_IDEAL_V9_v1/GEN-SIM-RECO “.  For this dataset: MSEL=1 At least one  in the event with P T > 5 GeV and |  | < 2.5 and b-bbar filter. No. of Background events analyzed = No. of reconstructed events with 0 muons = No. of reconstructed events with 1 muons = No. of reconstructed events with 2 muons = No. of rec. events with more than 2muons = India-CMS Meeting 27th-28th March 2009

Generator level plots for B s 0  vs P T Bs0Bs0 7India-CMS Meeting 27th-28th March 2009

ΔR between Generated and Reconstructed muons ΔR < 0.01 For ΔR < 0.01 signal efficiency = 87 % 8India-CMS Meeting 27th-28th March 2009

P T &  of reconstructed muons PTPT  We are loosing the muons in Central region due to low energy Leading pair of muons with opposite charge is selected for the analysis 9India-CMS Meeting 27th-28th March 2009

ΔR between leading pair of muons with opposite charge Signal efficiency = 93 % Bkgd. Efficiency = 59 % ΔR < India-CMS Meeting 27th-28th March 2009

Invariant mass of dimuon after ΔR <1.5 cut J/  For mass veto of 3.1 GeV: Signal efficiency = 92 % Bkgd. efficiency = 90 % 11India-CMS Meeting 27th-28th March 2009

Track Analysis 12India-CMS Meeting 27th-28th March 2009

Selection of tracks In the event those tracks (other than muons) are selected which lies in the opposite hemisphere of the leading jet (  jet.  track < 0) Kinematic constraint on tracks: Track P T > 400 MeV Track |  < 2.4 Tracks assigned mass = GeV The two tracks having opposite charge with invariant mass closest to M   (1.019 GeV) are chosen. 13India-CMS Meeting 27th-28th March 2009

Track P T and  distributions P T >0.4 GeV The tracks are for signal (B s   events  track P T track |  | < India-CMS Meeting 27th-28th March 2009

Invariant mass of track1 and track2 Two tracks with opp. charge and < M(tk + tk - ) < GeV are selected. Efficiency ~ 67 % 15India-CMS Meeting 27th-28th March 2009

Invariant mass of         16India-CMS Meeting 27th-28th March 2009

Future Plans Study the signal and QCD background simultaneously. Generate more signal events for high statistics. Study secondary vertex properties for B s meson by kinematical fitting of the vertex for dimuon and the Kaons. Put the kinematic selection cuts to increase the quality of the analysis and check the variation for both signal and background. 17India-CMS Meeting 27th-28th March 2009