-- MarcelFigueredo - 08-Dec-2011

Dec 8, 2011

The first step towards the J/Psi correction for the LHC11d(triggered events) was performed.

1 - J/Psi Efficiency due to the EMCAL(L0) trigger.

A simulation was performed of J/Psi(e⁻e⁺), This simulation was used to estimate the J/Psi reconstruction due to the trigger. In order to do so, it was used a task already implemented into the AliRoot framework ( AliAnalysisTaskEMCALClusterizeFast.cxx in AliRoot/PWG4/UserTasks/EmcalTasks ), which emulates the behavior of the EMCal triggers (L1 and L0).

There was in the simulation one J/Psi per event. So the efficiency of J/Psi due to the trigger was estimated as the J/Psi that actually fired the trigger divided by all the J/Psi reconstructed. The plot below shows the behavior of this efficiency.

Figure 1(a) - J/Psi Efficiency due to the EMCal L0 trigger (threshold=4.8 GeV)

2 - Acceptance x Efficiency

For this first study, the values from the J/Psi paper [1] were used. Since they worked up to 5-7 pt bin. I used the value from this higher bin as an estimation for the LHC11d case. For the central barrel detectors, AxE = 0.120. Taking into account that the acceptance of the EMCal is different from that of the TPC, an extra acceptance factor was estimated.

AccepFactor = (DeltaEtaEMCAL/DeltaEtaTPC)x(DeltaPhiEMCAL/DeltaPhiTPC)=(1.4/1.8)x(100/360)=0.216

This factor should in principle be included in the results from trigger efficiency, since we considered the J/Psi to have at least on EMCal electron PID during the reconstruction.

3 - J/Psi Spectrum in LHC11d

For the J/Psi reconstruction, tracks were selected requiring dEdx>70. and at least one track with 0.9 < E/P < 1.1 and E> 4. GeV.

Figure 3(a) - J/Psi Reconstruction

Figure 3(b) - J/Psi Reconstruction for different pt bins

b.1 --> 6<Pt(J/Psi)<8 GeV/c b.2 --> 8<Pt(J/Psi)<10 GeV/c
InvMassSB_1.png;rev=1 InvMassSB_2.png;rev=1
b.3 --> 10<Pt(J/Psi)<14 GeV/c

Figure 3(c) - J/Psi Reconstruction Pt Spectrum

--++ 4 - First cross section estimation.

Considering the 3 previous sections, we have, if further hypotheses:

NEvents EMC-triggered ~ 6.6 M

B.R (J/Psi --> ee) = 0.0594

Assuming trigger gain factor = 2500 (100kHz --> 40 Hz)
NMB would be = 1.65E10 events

sigmaJ/Psi=NJ/Psi(corr)/BR(J/P-->ee) x sigmaMB/NMB

where sigma MB=62.3mb (from 2010 data) and NJ/Psi(corr)=NJPsi/AxE(EMCAL)    , where AxE(EMCAL)  was explained in section 2  



Considering the values above, we can make an estimation of the measured cross section for these LHC11d Data.

Figure 4(a) - J/Psi Cross section estimation

Preliminary Conclusions

The trigger correction was estimated using J/Psi from MC simulation and the ClusterizerFast(which emulates the behavior of the EMCal L0 trigger). The remaining corrections were estimated based on the 7 TeV paper values, considering an extra factor due to the EMCal Acceptance. Since this is a first estimation, the values attained seems very promising. if one compares the cross section estimated with that from ALICE paper in the 7 GeV/c bin, this first estimation is in the same order of magnitude. The other pt bins do not follow the behavior of the red points, which seems to be related to further corrections to be done. The Acceptance x Efficiency might vary as a function of pt, and so far, it was estimated as the same as that calculated for the 7 GeV/c bin of the paper. Probably, when doing a similar procedure with these, which means a pp J/Psi enhanced simulation with the full EMCAL included, these values will be accurately calculated.

Next Steps and questions

- in the last J/Psi paper --> Acceptance x efficiency was extract by MC procedure (J/Psi(CDF extracted)+MB events). They are: kinematic factor(both daughters inside ALICE Acceptance, pt > 1 GeV/c), reconstruction efficiency of pair ee, indentification efficiency, fraction of signal within the mass range 2.92-3.16 GeV/c².

- if we want to work with MC we need to think about a new JPsi enhanced production. The most recent production we have on the GRID for pp 7TeV does not have the 2011 EMCal's geometry. (we have on that is 2.76 TeV anchor, that might be a starting point).

- Since it seems that the EMCal PID is to be integrated in the Dielectron framework, the best way to study J/Psi efficiency might be by the use of the PWG3dielectron correction framework.

- We need to study EMCal behavior in MC (Track-cluster matching, E/P, etc).

- What is the best way to deal with trigger efficiency? Have we already had the efficiency curve as a function of cluster energy?

- Is it enough to use a J/Psi enhanced sample + ClusterizerFast in order to extract J/Psi efficiency by the L0 trigger? Is it worthy to integrate this with the Dielectron framework in such a way to extract a complete efficiency from MC?

- Is there any space for embedding?


[1] -- "Rapidity and transverse momentum dependence of inclusive J/Psi Production in pp colisions at sqrt(S)= 7 TeV" Physics Letters B 704 ( 2011) 442-455

Topic attachments
I Attachment History Action Size Date Who Comment
PNGpng InvMassSB_1.png r1 manage 42.1 K 2011-12-08 - 13:50 Marcelfigueredo  
PNGpng InvMassSB_2.png r1 manage 40.4 K 2011-12-08 - 13:50 Marcelfigueredo  
PNGpng InvMassSB_3.png r1 manage 40.5 K 2011-12-08 - 13:50 Marcelfigueredo  
PNGpng JPsiPt.png r1 manage 17.5 K 2011-12-08 - 13:50 Marcelfigueredo  
GIFgif Xsection.gif r2 r1 manage 10.3 K 2011-12-19 - 17:30 Marcelfigueredo  
PNGpng crystalBallFit.png r1 manage 29.2 K 2011-12-08 - 13:50 Marcelfigueredo  
GIFgif eff_1.gif r1 manage 6.0 K 2011-12-08 - 14:40 Marcelfigueredo  
PNGpng xsection.png r1 manage 15.1 K 2011-12-08 - 23:26 Marcelfigueredo  
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