Low p T Muon trigger studies for J/       Supreet Pal Singh (Panjab University, Chandigarh) Prof. J.B.Singh (Panjab University, Chandigarh) Prof. Kajari Mazumdar (TIFR, Mumbai) 1India-CMS Meeting 29th-30th July 2010

Motivation Study of quarkonium production at high energy collision is always interesting  testing ground of non-relativistic QCD including the technique of factorisation:  production of heavy quark-antiquark pair calculated in perturbative method.  non-perturbative effects which bind the heavy quark pair into a quarkonium  various models try to describe this, eg., colour singlet, colour octet, etc. Final state polarisation depends on the model as well as the transverse momentum of the produced J/ψ. Experimental data till now is unable to resolve various issues  at LHC physics of J/ψ will be pursued hot through differential cross-section d  (J/ψ)/ dP T, polarisation measurements, etc. 2India-CMS Meeting 29th-30th July 2010

New Trigger paths at HLT proposed At LHC startup the actual instantaneous luminosity is lower than anticipated  low p T physics can be studied using softer triggers than planned earlier. At high instantaneous lumi, low threshold triggers will have to be prescaled. J       event statistics should be high enough to be competitive with other experiments at the early stage of CMS. Need as low P T J  event sample as possible  produced in mid- rapidity regions atleast. In 70% of J  dimuons that CMS can reconstruct in minimum bias events, one of the muon can be only a tracker muon, and NOT a global muon Thus GT and TT samples are crucial to cover low pT range, especially for |  ~ India-CMS Meeting 29th-30th July 2010

Way out in CMS: devise a double muon trigger at HLT to catch low pt tracks from J/ ψ  Start with standard L1 info  L1 firmware remains unchanged Combine Global Muon + track of J/ψ  trigger rate < 10 Hz, tolerable. Distribution of J/ψ dimuons in phase space.

HLT_MuX_Track0_Jpsi  A new trigger configuration where a single L3 muon is combined to tracker track within invariant mass window of GeV/c 2. Different trigger configurations possible with transverse momentum cut on L3 muon.  HLT_Mu0_Track0_Jpsi : L3 Muon pT > 0 GeV/c,  HLT_Mu1p5_Track0_Jpsi : L3 Muon pT > 1.5 GeV/c,  HLT_Mu2_Track0_Jpsi : L3 Muon pT > 2 GeV/c,  HLT_Mu3_Track0_Jpsi : L3 Muon pT > 3 GeV/c,  HLT_Mu5_Track0_Jpsi : L3 Muon pT > 5 GeV/c,  This lowers the trigger rate and the signal statistics are not reduced much. Exercise for detremining gain of new path, evaluating trigger rates etc. during April, May, June of this year, strategy validated, trigger in place More work in progress.

p T distributions for different trigger Configurations Dimuon combinations: GG  global-global muons (black) GT  global-tracker muons (red) ; TT  tracker-tracker muons (blue) Global muons  Reconstruction starts from muon stations and matched to a track in tracker. Tracker muons  Reconstruction starts in tracker and matched to a tracklet in muon station. 6India-CMS Meeting 29th-30th July 2010

Muon trigger rate will change with evolving luminosity Maximum trigger rate should be about 25 Hz with change in trigger path once a month, almost.

Efficiencies and trigger rates for different trigger configurations of “HLT_MuX_Track0_Jpsi” pT min [GeV/c] of L3 Muon Trigger Rate [Hz] Going from Mu0 to Mu3 the trigger rates drops very strongly (good) but the signal efficiency also suffers. We could set the muon pT threshold at 2.0 Gev/c instead of 3.0 GeV/c, to keep a good low pT coverage for a longer period. 8India-CMS Meeting 29th-30th July 2010

Effect of changing the pT cut on pixel and tracker track (matched to L3 muon) in HLT_Mu0_Track0_Jpsi. Presently pT cut on pixel and tracker track  3.0 GeV To improve the signal efficiency new cuts on pixel and tracker track pT pixel > 2.2 GeV/c pT tracker > 2.5 GeV/c 9India-CMS Meeting 29th-30th July 2010

Efficiencies for different configurations of HLT for various pT cuts increase in the efficiency 10India-CMS Meeting 29th-30th July 2010 Before After

pT & rapidity distributions and the corresponding Efficiencies for various HLT triggers for CMS Data run numbers (certified) “Reference” trigger: HLT_L1MuOpen, Efficiencies of other trigger paths are calculated relative to the same for events passing the HLT_L1MuOpen trigger 11India-CMS Meeting 29th-30th July 2010

Mass distributions and the corresponding efficiencies CMS Data run numbers (certified) HLT_L1MuOpen is prescaled after run rumber  cannot be taken as a “default” trigger. HLT_Mu3 is good only for pT > 3 GeV. HLT_L1DoubleMuOpen is very efficient  can be taken as reference to study HLT_Mu0_Track0_Jpsi till it is prescaled. 12India-CMS Meeting 29th-30th July 2010

pT & rapidity distributions and the corresponding Efficiencies for HLT_Mu0_Track0_Jpsi for CMS Data run numbers (certified) India-CMS Meeting 29th-30th July 2010

2D efficiency plot of the HLT_Mu0_Track0_Jpsi trigger path w.r.t. HLT_L1DoubleMuOpen trigger HLT_Mu0_Track0_Jsi trigger is best suited for mid-rapidity region  No requirement for 2 nd muon in DT, while HLT_L1DoubleMuOpen require hits in at least “two” DT segments. HLT_L1DoubleMuOpen is efficient  but effected by background, cannot be used as unprescaled for long. HLT_Mu0_Track0_Jpsi  “Cleaner” trigger. 14India-CMS Meeting 29th-30th July 2010

Keep ψ(2S) in the game ! Increase HLT mass window from GeV to 2.7 – 3.9 GeV  the rate incrases by a factor of 1.5 Work in porgress

Summary New J  triggers in CMS: looser muon triggers (eg. no pt threshold) HLT_Mu0 + track in the J/  mass window  Good for all physics analyses with a J/  in the final state  Also gives a handle to measure all muon related efficiencies. Trigger rate for the different trigger configurations of HLT_Mu0_Track0_Jpsi has to be monitored carefully. The efficiency can be increased further by changing the pT cut on the pixel and tracker track to 2.2 GeV/c and 2.5 GeV/c. Data has started coming and HLT_Mu0_Track0_Jpsi has been included in the official HLT trigger paths. Favorable for polarization studies of low pT dimuons from J/   more statistics can be accumulated. Good Time ahead for physics with J/   muons 16India-CMS Meeting 29th-30th July 2010