1PWG3Muon – September 8th 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

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LHC10c1 J/ cross section

J/(2.5<y<4) = (6.9 ± 0.8 (stat)) b (Crystal ball + double exponential fit)

(preliminary error estimate obtained assuming same relative error as for the gaussian fit)

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)

Open points:

• Systematics related to the signal extraction• Evaluation of the error on the signal• Discrepancy between Torino and Orsay acceptance x efficiency

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LHC10c1 acceptance x efficiency

Acc x eff (J/ 2.5<y<4, 0<pT<10) = 0.403

Based on realistic simulations (Livio, Jul10), using realistic y, pT distributions.

Acceptance have been computed specifically for the LHC10c1 period

GEN: 61285 J/ with -4<y<-2.5, 0<pT<10 GeVREC: 24698 J/ with -4<y<-2.5, 0<pT<10 GeV, 1 muon matching the trigger

Same cuts, as on the data, are appliedGenerated

Reconstructed

Acc

x e

ff

4

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)

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

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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::

Function parameters have been tuned on the realistic J/ simulation corresponding to the analyzed LHC period

• Gaussian+exponential• CrystalBall + 2 exponentials• “NA60” function + 2 exponentials

In order to better understand the differences between the fitting functions (reducing statistical fluctuations), the high statistics LHC10d sample is used.

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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 fit the simulated spectrum only in a narrow region (2.9-3.3 GeV/c2) Not used anymore in the following

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/)

The CB function describes the simulated spectrum only for masses > 2.5 GeV/c2

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Simulated J/ signal (2)

“NA60” function

“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

Gaussian shape with variable sigma:

This is a function adopted for charmonia in NA50 and NA60

298

165

273

143

3

1

1MMpp

MMpp

MMpp

MMpp

p

Right and left asymmetric tails are allowed The function has many parameters (11)

=

M1<M<M2

M<M1

M>M2

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Fit to the LHC10d spectrum Fits are performed assuming

under two different assumptions:

• J/ function parameters fixed to the simulation (apart from the J/ mass)• J/ function parameters left free

• crystal ball or the NA60 function for the signal • double exponential for the background

Next step: study of the background shape, starting from the LHC09a18 production

Fits performed with the likelihood and using the integral of the bins (to be independent on the bin width)

(LHC10d J/ are obtained after physics selection)

Complicate error evaluation on the number of J/ the correlations between the parameters is taken into account using the covariance matrix

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CB fit to LHC10dCrystalBall function

NJ/ J/ 2

Fixed param

1551 ± 56 93 MeV 1.1

Free params

1481 ± 97 86±5 MeV 1.2

Fixed params

No significant difference in the 2 values of the two fits

Fixed paramsFree params

Difference in the J/ number comes from the left tail description (already not properly described in the fit to the simulated J/)

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

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“NA60” fit to LHC10dNA60 function

NJ/ J/ 2

Fixed param

1577 ± 57 80 MeV 1.0

Free params

1564 ± 90 80±3 MeV 1.0

Fixed params

Fixed paramsFree 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

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

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Comparison between fitting fz.Comparison of Crystal Ball and NA60 functions

Fix CBFree CBFix NA60Free NA60

Tails description is the main difference between the two functions

Quality of the fits is good difficult to select according to the 2

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

NJ/ J/ 2

NA60 1577 ± 57 80 MeV 1.0

CB 1551 ± 56 93 MeV 1.1

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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

Event selection • CMUS1B trigger• physics selection

• 2.5<y<4 • 0<pT<10 GeV/c(on QA selected runs)

CrystalBall function

NA60 function

1 match

NJ/ J/ 2

Fixed param

345 ± 26 73 MeV 1.0

Free params

368 ± 42 78±5MeV 1.0

NJ/ J/ 2

Fixed param

336±24 83MeV 0.97

Free params

356±63 90±1MeV 1.08

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J/ cross section (LHC10c1)

ANDV

BCINTANDVJBCMUS

JJ N

N

AccN

N0

101

1

golden muon reference computed by Daniel

85.3 ± 6.8 b

J/ cross section evaluation, normalized through the golden muon cross section

0.403N = 172598

Obtained applying the same cuts used for the golden muon reference evaluation (PWG3Muon, 30Aug2010)

NJ/ extracted from different fitting functions

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J/ cross section (LHC10c1)

J/(2.5<y<4) = (7.6 ± 1.1 (stat)) b

Using the J/ number extracted from the “NA60” fit (free parameters)

Systematic error related to the difference between NA60 (free) and Crystal Ball (fixed parameters) ~9%

N J/ = 368 ± 42 (stat)

Systematic error due to the signal extraction seems to apply only in the negative direction

Systematic error obtained assuming NA60 function with free or fixed fit parameters ~6%

Very good agreement with the LHCb value (7.65 ± 0.19 ± 1.1) b

We get:

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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:

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

/alice/cern.ch/user/a/arnaldi/Data7TeV_LHC10e/pass1/

Runs 127723 – 130850

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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)

LHC10e trigger definition

(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 asCINT1B (MB, with muons not matching the muon trigger)CINT1B+CMUS1B (MB with muons matching the muon trigger)CMUS1B (muon matching the muon trigger)

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Physics Selection Effect of the physics selection on the LHC10e:

Ev

afte

r P

S/

Ev

befo

re P

S

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

CMUS1

CMUS1New Aliroot >4-18Rev-26

Old Aliroot <=4-18Rev-26

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Preliminary LHC10e mass spectrum

No QA checks yet on these runs

Few runs still missing

First look to the LHC10e data in order to understand how many J/ have been collected

N CINT = 157 106

N CMUS = 19 106

0 match1 match=2 match

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First LHC10e J/Realistic simulations for the LHC10e period not yet available Fit performed with the “NA60” function with free parameters

1 match

“NA60”

N. J/ ( 1 match) collected during the rare triggers: 3271 ± 133N. J/ ( 1 match) collected during the MB + rare triggers: 3564 ± 156

Almost all J/ are collected during the rare triggers:

= 3.121 ± 0.003 GeV = 79 ±2 MeV2= 1.2S/B(2.9-3.3)= 2.3

Should this high statistics sample be considered for the first publication?

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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

J/

LHC10c1 81 ± 6 MeV

LHC10d 80 ± 3 MeV

LHC10e 79 ± 2 MeV

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

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Conclusions

Next steps:

Systematic study of the extraction of the J/ number and its error

• Fitting function parameters tuned on realistic MC simulation

J/(2.5<y<4) = (7.6 ± 1.1 (stat)) b

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:

What about the high statistics LHC10e period?

• cross section evaluation for the LHC10d period production AOD without physics selection is on-going• update of the results to the new realistic simulations

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Backup

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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

Event selection • CMUS1B trigger• physics selection

• 2.5<y<4 • 0<pT<10 GeV/c(on QA selected runs)

CrystalBall function

NA60 function

1 match

NJ/ J/ 2

Fixed param

345 ± 26 73 MeV 1.0

Free params

368 ± 42 78±5MeV 1.0

NJ/ J/ 2

Fixed param

336±24 83MeV 0.97

Free params

356±63 90±1MeV 1.08