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J/   analysis: results for ICHEP

J/   analysis: results for ICHEP. Presentation based on: Several weekly discussions inside PWG3-muon and PWG3 The work of many people inside the muon group (calibration, alignment, analysis....). Today Summary of the main results that have been proposed

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J/   analysis: results for ICHEP

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  1. J/   analysis:results for ICHEP • Presentation based on: • Several weekly discussions inside PWG3-muon and PWG3 • The work of many people inside the muon group (calibration, • alignment, analysis....) • Today • Summary of the main results that have been proposed • to be shown next week at ICHEP E.S., July 15, 2010

  2. Data sample The following results are based on the data samples: • 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)

  3. Total available statistics  0 match 2 match  1 match Kinematic cut: 2.5<y<4 Fit: gaussian+exponential

  4. Statistics per period (1)

  5. Statistics per period (2) Current period(runs 122372-125296) Almost all these J/ were collected with the high intensity beams. Unfortunately, the amount of J/ collected with the displaced beams (Jul 1st – Jul 6th) is negligible (runs 124750 – 125296)

  6. Study of pT distributions 1<pT< 2 GeV/c 2<pT< 3 GeV/c 0<pT< 1 GeV/c (0 match) 3<pT< 4 GeV/c 4<pT< 5 GeV/c 5<pT< 10 GeV/c

  7. Comparison with “realistic” simulations • Invariant mass fits, in pT bins, with J/ pole and resolution • as free parameters • Simulations of the J/ signal now include • Residual misalignment • Realistic tracking/trigger efficiency, period by period Data Monte-Carlo Good agreement data vs Monte-Carlo, for the J/ mass resolution !

  8. Acceptance/efficiency calculation • Based on pure signal generation, with realistic kinematic • distributions • CDF pp 7 parameterization (AliGenMUONlib) • pT extrapolated from CDF results • y obtained from CEM calculations • No polarization ( = 0) Slightly lower efficiency of the tracking for the LHC10d period Does not vary strongly as a function of pT (0 match)

  9. pT spectra corrected for acceptance/efficiency LHC10c1 LHC10c2 LHC10d Integral of the spectra normalized to 1 • After correcting the spectrum corresponding to each period with its • own efficiency, we get a good relative agreement  sum the spectra • LHC10b discarded (too low statistics)

  10. Total pT spectrum • The efficiency corrected pT spectrum still misses an absolute • normalization. However, its shape can be compared with • Monte-Carlo and pT and pT2 can be computed • Our corrected J/ pT • spectrum is softer than • the CDF extrapolation Data Monte Carlo

  11. pT and pT2 • Two possibilities • Fit the pT spectrum with a suitable function • Advantage: can be extrapolated to pT  • Drawback: function-dependent • 2) Extract pT and pT2 directly from data • Advantage: not model dependent • Drawback: results depend on pT reach of the measurement • Previous experiments (including PHENIX) have used the function • First proposed by • Yoh et al., PRL 41 (1978) 684 • No physics content, only • phenomenological • With this choice one simlply has • pT2=p02/4, pT=(35/256)p0

  12. Fit of J/ pT distribution We get 2/ndf = 0.47 p0 = 6.0 ± 0.2 GeV/c which leads to pT2 = 9.08 ± 0.54 (GeV/c)2 pT = 2.59 ± 0.08 GeV/c • Can be compared with other experimental results, obtained with • a fitting approach

  13. Comparison with previous experiments

  14. Stability vs LHC period • As a test of our efficiency correction procedure, we can check if • pT2 and pT are stable with respect to the various considered • periods • Results are quite stable over the whole data taking

  15. Systematic errors • It is of course possible to extract the pT2 directly from the data, • as This gives pT2 = 8.2 (GeV/c)2 which is obviously smaller than the previous estimate, due to the fact that our pT reach is finite • If we truncate the function at our maximum pT reach, we get • pT2 = 7.8 (GeV/c)2, a value similar to the one quoted above

  16. Rapidity distribution • With the available statistics we can compute the rapidity • distribution of the J/ in 5 bins, using an approach identical • to the one adopted for the pT distributions dN/dy(a.u.) MC There are some deviations wrt the Monte-Carlo Data • Edge effect due to acceptance falling down at the upper and lower limit of our coverage ? • Suggestion: remove edges  we have now re-done this analysis in • 5 bins in the interval 2.7<y<3.8

  17. MC Data Rapidity distribution (2.7<y<3.8) Follows more closely the MC behaviour Probably healthier to remove the edges of the rapidity domain

  18. Data MC Monte Carlo Data Conclusions • Proposal for ICHEP presentation(s), as emerged from the • PWG3 rehearsal meeting of Tuesday 2/ndf = 0.47

  19. Backup

  20. Mass spectra -3.58<y<-3.36 -3.36<y<-3.14 -3.8<y<-3.58 -3.14<y<-2.92 -2.92<y<-2.7

  21. Comparison with Monte-Carlo • Rather good agreement of the mass resolution between data • and Monte-Carlo Data Monte-Carlo

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