J/   analysis: preliminary results and status report First results from J/ analysis: plots shown at ICHEP Towards a first paper Presentation based on: Several weekly discussions inside PWG3-muon and PWG3 The work of many people inside the muon group (calibration, alignment, analysis....) E. Scomparin – Physics Forum July 27, 2010

Data sample The following data samples have been analyzed: LHC10b (runs 114916-117222) – pass2 LHC10c1 (runs 118903-120242) – pass2 LHC10c2 (runs 120476-120824) – pass2 LHC10d (runs 122372-125296) – pass1 These periods correspond to slightly different configurations of the muon spectrometer. In particular, LHC10c has been splitted in two parts (LHC10c1: full trigger coverage, LHC10c2: problems in half of the trigger chambers) LHC10d includes data taken in very different luminosity conditions First days (LHC10d1): high luminosity Then, lower luminosity (LHC10d2) Relevant for normalization issues

Invariant mass spectrum With this statistics, the simple gaussian+exponential fit still does a good job Other approaches ready and working: Crystall Ball fit, NA60 fit (useful for systematics on signal extraction)

Transverse momentum bins Still good quality fits for various transverse momentum bins S/B and background shape are pT-dependent

Comparison with realistic Monte-Carlo Good agreement! Realistic Monte-Carlo includes, period by period: Evaluation of trigger/tracking efficiency Evalution of residual misalignment (~1 mm)

Transverse momentum distributions Raw pT spectrum Acc  eff J/ signal generation for MC based on “CDF pp 7” parameterization (CDF extrapolation for pT, CEM calculation for y, no polarization) Acceptance/efficiency correction performed with a 1D approach Preliminary results for ICHEP based on LHC10d period

Corrected J/ pT distribution No track/trigger matching required Results well within errors when asking 1 matched track

Fit of the pT spectrum Use a fitting function with high pT behaviour as a free parameter Fit converges towards x = 3.2  0.7 (in agreement with the high pT behaviour predicted by CEM calculation from Ramona, x = 3.25) Error on pT2 calculated from letting the 2 varying by one unit Complete systematic error evaluation still in progress

pT and pT2 Approximately linear behaviour of both pT and pT2 vs log(√s) ALICE result seems to follow this trend

ICHEP: a first comparison of results Very good agreement between ALICE and LHC-b ! (courtesy of C. Lourenco) We are still missing an absolute normalization

Preliminary rapidity distribution Fiducial range restricted to 2.7<y<3.8 to remove acceptance edges

Analysis of differential spectra: other approaches Try to quantify the systematic error related to the signal extraction First estimate gives a ~7% effect

1D vs 2D correction 2D approach 6 pT bins  3 y bins 1D approach (ICHEP) Good agreement, also on the extracted pT2

Normalization Fundamental issue, to arrive at a first publication Several approaches are being investigated Pile-up issues have a key role and must be understood, most of the statistics from high luminosity runs Main approaches currently investigated Use of CTP scalers Through “Golden muon” cross section Useful to investigate related systematic errors

The two methods in more detail CTP scalers trigger livetimes Golden muon with Livetime CMUS to correct N_J/psi, livetime CINT1B to correct N_V0AND (calculated in a single run, with low pile-up) The relative change on golden muon detection efficiency must be taken into account

Pileup Assuming a Poisson distribution The probability of having at least 1 interaction can be written as from CTP scalers One gets therefore and the pile-up correction factor is given by

Pileup vs time From CTP scalers, LHC10d period Number of tracks per CINT1B has a behaviour similar to , as expected

Effect of pile-up correction Tracks/CINT1B Before pile-up correction After pile-up correction Tracks/CINT1B still not flat after correction, issue being investigated Tracks/CMUS1B Much flatter, CMUS1B less sensitive to pileup

Pile-up: other approaches Work in progress to directly use SPD pile-up information to evaluate   still preliminary stage, being studied

Pileup factors, LHC10c1 Much smaller, as expected (lower luminosity) We are now considering the possibility of using for J/ absolute normalization the period LHC10d2 (low luminosity) which has anyway a non-negligible J/ statistics

Run selection The preliminary result released for ICHEP was based on a relatively loose run selection (keep maximum statistics) Efficiencies were anyway taken into account on a run per run basis We are now carrying out a systematic check of all our statistics in order to single out pathological runs and discard them A couple of example plots

Conclusions First results on J/ analysis released for ICHEP Very good agreement of differential spectra (shapes) between ALICE and LHC-b Analysis effort is progressing in order to converge soon towards a first paper Two main items under discussion Normalization  various approaches being tested Pile-up effects correction  under study