1. 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

2. Data sample The following data samples have been analyzed:
LHC10b (runs ) – pass2
LHC10c1 (runs ) – pass2
LHC10c2 (runs ) – pass2
LHC10d (runs ) – 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

3. 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)

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

5. 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)

6. 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

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

8. 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

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

11. 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

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

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

14. 1D vs 2D correction 2D approach 6 pT bins  3 y bins
1D approach (ICHEP)
Good agreement, also on the extracted pT2

15. 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

16. 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

17. 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

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

19. 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

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

21. 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

22. 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

23. 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