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J/ y production in p-A collisions (a first step)

J/ y production in p-A collisions (a first step). Some plots with the 158 GeV data and status of the 400 GeV reconstruction. NA60 Collaboration Meeting 27/09/2006 Pedro Martins. Status of the 400 GeV data analysis. News since last meeting:

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J/ y production in p-A collisions (a first step)

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  1. J/y production in p-A collisions(a first step) Some plots with the 158 GeV data andstatus of the 400 GeV reconstruction NA60 Collaboration Meeting 27/09/2006 Pedro Martins

  2. Status of the 400 GeV data analysis • News since last meeting: • P. Cortese has been working on the alignment.The runs have been processed as soon as the setups become aligned. • Presently, we have processed ~40 runs taken with 400 GeV protons, with the “158 GeV setup”. • We have not yet performed “sanity checks” to evaluate data quality. • No plots from 400 GeV are included in this presentation

  3. Motivation • It is important to study the kinematical distributions of the J/y and how they change with the target nucleus. • Such differential analysis, as a function of pT and y, requires as many statistics as possible; hence the 400 GeV data sets will be the most suitable. • Since at this moment the 400 GeV data is not yet available, I started with the 158 GeV event sample, to get the macros tested on real data. • Anyway, comparisons between the results obtained at the two energies will be very relevant. • The pT and y distributions of the J/y are made for each target, as identified through the dimuon vertex information, after matching.

  4. Data source • All the 158 GeV data available on our na60tera1 (pA2004/prod1n/). • I used all the runs available there, except run 11348, which seems to have been reconstructed with a wrong setup (big mass shift).

  5. Matched dimuons mass distribution J/y OS LS • The number of events in the J/y peak was extracted by fitting the dimuon mass spectra to the superposition of an exponential with a Gaussian. • Dimuons are tagged as J/y’s if they are in the mass window [2.84, 3.25].

  6. J/y Z-vertex distribution Pb W Cu In U 3 x Be Al The In, Be and Pb targets should be less affected by geometrical acceptances than the others, placed at greater distances from the vertex tracker.

  7. Rapidity for the most downstream targets Pb In 3 x Be • The effect of the acceptance (not corrected for) is very clear in the rapidity distributions. The lead distribution is shifted to lower rapidities with respect to the events collected with Be or In targets.

  8. pT for the most downstream targets Pb In 3 x Be • The pT distributions are much less affected by acceptance effects. pT (GeV/c)

  9. Pb/Be pT ratio pT (GeV/c) • As expected, it seems that the pT distribution is flatter in Pb than in Be

  10. Nuclear dependence of the pT spectra • We can calculate the average pT2, <pT2>, for each target. • “A” is the mass number; A1/3 gives the dimension of the nucleus size... • These results are very preliminary, and haven’t been corrected for acceptances, etc. W In Pb U Al Cu 3 x Be

  11. Conclusions and perspectives • The results obtained so far do not indicate any abnormality with our data. • The Monte-Carlo study of the acceptance calculations will start now. • Results for 400 GeV will appear as soon as the reconstructed data become available

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