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PWG3Muon – September 8 th 2010

J/  analysis update. Update on J/  cross section for the LHC10c1 period. systematics related to the evaluation of the J/  number acceptance x efficiency. First look to the LHC10e period. PWG3Muon – September 8 th 2010. LHC10c1 J/  cross section.

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PWG3Muon – September 8 th 2010

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  1. J/ analysis update Update on J/ cross section for the LHC10c1 period • systematics related to the evaluation of the J/ number • acceptance x efficiency First look to the LHC10e period PWG3Muon – September 8th 2010

  2. LHC10c1 J/ cross section J/ cross section evaluation for the LHC10c1 period (very low pile-up), normalized through the golden muon cross section presented at the last PWG3Muon (30/8/2010): J/(2.5<y<4) = (6.0 ± 0.7 (stat)) b (gaus+exp fit) (Crystal ball + double exponential fit) J/(2.5<y<4) = (6.9 ± 0.8 (stat)) b (preliminary error estimate obtained assuming same relative error as for the gaussian fit) Open points: • Systematics related to the signal extraction • Evaluation of the error on the signal • Discrepancy between Torino and Orsay acceptance x efficiency

  3. Acc x eff LHC10c1 acceptance x efficiency Based on realistic simulations (Livio, Jul10), using realistic y, pT distributions. Acceptance have been computed specifically for the LHC10c1 period Same cuts, as on the data, are applied Generated GEN: 61285 J/ with -4<y<-2.5, 0<pT<10 GeV REC: 24698 J/ with -4<y<-2.5, 0<pT<10 GeV, 1 muon matching the trigger Acc x eff (J/ 2.5<y<4, 0<pT<10) = 0.403 Reconstructed

  4. Acceptance x efficiency (2) realistic simulations used up to now are affected by a bug related to the tracking reject list.  results, after bug correction, should vary by ~3%, according to Matthieu Run selection was not applied in the reject list used in these simulations  negligible effect Next step: Livio will produce new realistic simulations with the new reject lists, and using only QA checked runs. (No updates to be done concerning the trigger efficiency)

  5. Number of J/ In order to study the systematics related to the signal extraction, we have performed different fits to the invariant mass spectrum, adopting the following functions:: • Gaussian+exponential • CrystalBall + 2 exponentials • “NA60” function + 2 exponentials Function parameters have been tuned on the realistic J/ simulation corresponding to the analyzed LHC period In order to better understand the differences between the fitting functions (reducing statistical fluctuations), the high statistics LHC10d sample is used.

  6. Simulated J/ signal Simulation based on realistic pT, y shapes, including misalignment, trigger/tracking efficiencies (Livio) Simulation done for each LHC period separately. Here we consider LHC10d Gaussian function Crystal Ball function The CB function assumes a gaussian tail on the right side of the pole  Fit unreasonable beyond 3.3 GeV/c2 (value already reached with ~100 J/) Gaussian fit the simulated spectrum only in a narrow region (2.9-3.3 GeV/c2)  Not used anymore in the following The CB function describes the simulated spectrum only for masses > 2.5 GeV/c2

  7. Simulated J/ signal (2) This is a function adopted for charmonia in NA50 and NA60 “NA60” function M1<M<M2 M<M1 M>M2 Gaussian shape with variable sigma: = • Right and left asymmetric tails are allowed • The function has many parameters (11) “NA60” function seems to better describe both right and left sides of the spectrum. Fit of the full mass spectrum converges with a 2 = 1.18

  8. Fit to the LHC10d spectrum Fits are performed assuming under two different assumptions: • crystal ball or the NA60 function for the signal • double exponential for the background • J/ function parameters fixed to the simulation (apart from the J/ mass) • J/ function parameters left free Fits performed with the likelihood and using the integral of the bins (to be independent on the bin width) Complicate error evaluation on the number of J/  the correlations between the parameters is taken into account using the covariance matrix Next step: study of the background shape, starting from the LHC09a18 production (LHC10d J/ are obtained after physics selection)

  9. CB fit to LHC10d CrystalBall function Fixed params No significant difference in the 2 values of the two fits Difference in the J/ number comes from the left tail description (already not properly described in the fit to the simulated J/) Fixed params Free params NJ/ error is smaller if parameters are fixed. Warning: if parameters are left free, large fluctuations in the error evaluation may happen, (because of param. errors larger than the param. value), even if the fit quality remains very good Crystal Ball function with free parameter should not be used with this reduced statistics

  10. “NA60” fit to LHC10d NA60 function Fixed params Since the MC signal shape is well described (over the full mass range), only J/ is left as free parameter Good quality in both (free/fix param) fits Fixed params Free params No difference in the resulting fitting functions NA60 function is less sensitive to free/fixed parameters Fit with free parameters may be used, in order to be able to take into account small differences between data and MC

  11. Fix CB Free CB Fix NA60 Free NA60 Comparison between fitting fz. Comparison of Crystal Ball and NA60 functions Quality of the fits is good  difficult to select according to the 2 Tails description is the main difference between the two functions If the fit parameters are fixed to the values tuned on the simulation  same number of J/ is extracted • However, the “NA60” function may be adopted, since • It describes the MC simulation over the full mass range • less sensitive to fixed/free fit parameters • it allows an asymmetric shape on the right of the J/ pole

  12. Fit to the LHC10c1 spectrum The LHC10c1 inv. mass spectrum is now fitted, having determined the J/ function parameters from a fit to the corresponding LHC10c1 simulation • 1 match Event selection • CMUS1B trigger • physics selection • 2.5<y<4 • 0<pT<10 GeV/c (on QA selected runs) CrystalBall function NA60 function

  13. J/ cross section (LHC10c1) J/ cross section evaluation, normalized through the golden muon cross section NJ/ extracted from different fitting functions N = 172598 golden muon reference computed by Daniel 85.3 ± 6.8 b 0.403 Obtained applying the same cuts used for the golden muon reference evaluation (PWG3Muon, 30Aug2010)

  14. J/ cross section (LHC10c1) Using the J/ number extracted from the “NA60” fit (free parameters) N J/ = 368 ± 42 (stat) We get: J/(2.5<y<4) = (7.6 ± 1.1 (stat)) b Systematic error obtained assuming NA60 function with free or fixed fit parameters ~6% Systematic error related to the difference between NA60 (free) and Crystal Ball (fixed parameters) ~9% Systematic error due to the signal extraction seems to apply only in the negative direction Very good agreement with the LHCb value (7.65 ± 0.19 ± 1.1) b

  15. LHC10e AODs • AOD for the high statistics LHC10e period have been produced • These AODs contain physics selected events • AODs, corresponding to ~ 170 runs, are stored in: /alice/cern.ch/user/a/arnaldi/Data7TeV_LHC10e/pass1/ Runs 127723 – 130850 WARNING: according to Cvetan (mail 27/8/2010): Runs reconstructed with aliroot <= v4-18-Rev-26  V0 does not remove background ev. because of a bug (in any case background contribution is very small) Runs reconstructed with aliroot > v4-18-Rev-26  bug corrected “First order correction” of the V0 seasonal drift at the CTP level

  16. LHC10e trigger definition trigger configuration is changed from run 127723 with respect to previous periods (almost all LHC10e has this new configuration): 1 minute Minimum Bias trigger (CINT1-B-NOPF-ALLNOTRD) 1 minute rare trigger: muon (CMUS1-B-NOPF-ALLNOTRD) or high multiplicity (CSH1-B-NOPF-ALLNOTRD) • (matching the CMUS1 trigger) can be collected also during the minimum bias minute (even if offline the event is flagged only with CINT1-B-NOPF-ALLNOTRD) different situation with respect to previous periods where muons were collected under different situations, flagged as CINT1B (MB, with muons not matching the muon trigger) CINT1B+CMUS1B (MB with muons matching the muon trigger) CMUS1B (muon matching the muon trigger)

  17. CMUS1 CMUS1 New Aliroot >4-18Rev-26 Ev after PS/ Ev before PS Old Aliroot <=4-18Rev-26 Physics Selection Effect of the physics selection on the LHC10e: PS rejects ~7% of the CINT1 events reconstructed with an old aliroot version and ~1% of the events reconstructed with a newer aliroot PS rejects <2% of the CMUS1 triggers  no bias induced in the data even if the PS is applied

  18.  0 match • 1 match =2 match Preliminary LHC10e mass spectrum First look to the LHC10e data in order to understand how many J/ have been collected No QA checks yet on these runs N CINT = 157 106 N CMUS = 19 106 Few runs still missing

  19. First LHC10e J/ Realistic simulations for the LHC10e period not yet available  Fit performed with the “NA60” function with free parameters “NA60”  1 match = 3.121 ± 0.003 GeV = 79 ±2 MeV 2= 1.2 S/B(2.9-3.3)= 2.3 Almost all J/ are collected during the rare triggers: N. J/ ( 1 match) collected during the rare triggers: 3271 ± 133 N. J/ ( 1 match) collected during the MB + rare triggers: 3564 ± 156 Should this high statistics sample be considered for the first publication?

  20. J/ resolution vs. time The value of the J/  depends on the adopted fitting function Value obtained from the “NA60” function is narrower with respect to the Crystal Ball and much smaller than those previously evaluated with a gaus+exp fit Performing fits with the NA60 function: NA60 fit parameters tuned on the LHC10d simulation for the moment No strong worsening with time of the J/ resolution

  21. Conclusions Systematic study of the extraction of the J/ number and its error • Fitting function parameters tuned on realistic MC simulation Crystal Ball: difficult to use it, on the data, without fixing the parameters (but the function does not properly describes the J/ tails in the MC) “NA60” function: better description of the J/ shape more stable results, leaving the J/  as a free parameter • Warning in the extraction of the error on NJ/ since we are extremely • sensitive to the error and the correlation on the parameters LHC10c1 cross section, based on NJ/ extracted from “NA60” function: J/(2.5<y<4) = (7.6 ± 1.1 (stat)) b Next steps: • cross section evaluation for the LHC10d period •  production AOD without physics selection is on-going • update of the results to the new realistic simulations What about the high statistics LHC10e period?

  22. Backup

  23. Fit to the LHC10c1 spectrum The LHC10c1 inv. mass spectrum is now fitted, having determined the J/ function parameters from a fit to the corresponding LHC10c1 simulation • 1 match Event selection • CMUS1B trigger • physics selection • 2.5<y<4 • 0<pT<10 GeV/c (on QA selected runs) CrystalBall function NA60 function

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