P. Cortese for the NA50 Collaboration 1

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? and Drell-Yan production in p-A collisionsat
450 GeV incident energy

• P. Cortese for the NA50 Collaboration
• B. Alessandro, C. Alexa, R. Arnaldi, M. Atayan,
  S. Beolè, V. Boldea, P. Bordalo, G. Borges, C.
  Castanier, J. Castor, B. Chaurand, B. Cheynis, E.
  Chiavassa, C. Cicalò, M.P. Comets, S.
  Constantinescu, P. Cortese, A. De Falco, N. De
  Marco, G. Dellacasa, A. Devaux, S. Dita, J.
  Fargeix, P. Force, M. Gallio, C. Gerschel, P.
  Giubellino, M.B. Golubeva, A.A. Grigorian, S.
  Grigorian, J.Y. Grossiord, F.F. Guber, A.
  Guichard, H. Gulkanyan, M. Idzik, D. Jouan, T.L.
  Karavitcheva, L. Kluberg, A.B. Kurepin, Y. Le
  Bornec, C. Lourenço, M. Mac Cormick, A.
  Marzari-Chiesa, M. Masera, A. Masoni, M. Monteno,
  A. Musso, P. Petiau, A. Piccotti, J.R. Pizzi, F.
  Prino, G. Puddu, C. Quintans, L. Ramello, S.
  Ramos, L. Riccati, H. Santos, P. Saturnini, E.
  Scomparin, S. Serci, R. Shahoyan, F. Sigaudo, M.
  Sitta, P. Sonderegger, X. Tarrago, N.S.
  Topilskaya, G.L. Usai, E. Vercellin, L. Villatte,
  N. Willis, T. Wu

- Università del Piemonte Orientale/INFN,
Alessandria, Italy - LAPP, CNRS-IN2P3,
Annecy-le-Vieux, France - LPC, Univ. Blaise
Pascal and CNRS-IN2P3, Aubière, France - IFA,
Bucharest, Romania - Università di Cagliari/INFN,
Cagliari, Italy - CERN, Geneva, Switzerland -
LIP, Lisbon, Portugal
- INR, Moscow, Russia, IPN - Univ. de Paris-Sud
and CNRS-IN2P3, Orsay, France - LLR, Ecole
Polytechnique and CNRS-IN2P3, Palaiseau, France -
Università di Torino/INFN, Torino, Italy - IPN,
Univ. Claude Bernard Lyon-I and
CNRS-IN2P3, Villeurbanne, France - YerPhI,
Yerevan, Armenia
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Physics motivation
Study of heavy flavours and quarkonia production
in p-A

• Test of theory of strong interactions
• probe the production aspects that are calculable
  in pQCD the dependence of the cross section on
  energy, pT, xF, ?CS polarization
• constrain theoretical approaches NRQCD and CEM
• parametrize non perturbative aspects color
  neutralization of the c-cbar, b-bbar pairs and
  absorption in nuclear matter

• Essential reference for the study of quarkonia
  suppression in hot and dense matter
• At SPS J/y suppression in Pb-Pb, In-In
• p-A collisions to measure normal nuclear
  absorption
• At RHIC J/y production in Au-Au, Cu-Cu
• p-p and d-Au collisions as a reference
• At LHC y and ? production from p-p to Pb-Pb

? absorption in normal nuclear matter not
systematically studied up to now even at fixed
target energies ? new data are useful in view of
future collider experiments
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Experimental overview of ? production in pp and pA
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p-A data taking at the NA50 dimuon spectrometer

• 5 nuclear targets Be, Al, Cu, Ag, W
• L 10 pb-1 per target
• 2 data sets at 450 GeV high luminosity and low
  luminosity
• 400 ? in the ???- channel in total

• Rapidity coverage -0.5 lt ycm lt 0.5
• For the ? corresponds to -0.36 lt xF lt 0.36
• ?Collins-Soper -0.5 lt cos(?CS) lt 0.5
• pT flat coverage

Transverse polarization for ? and ? is assumed
in this analysis Typical acceptances AJ/y? 14
ADY 21 (mmm gt 6 GeV) A? 25
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The opposite sign dimuon invariant mass spectra
Drell-Yan
Upsilons

• Mass resolution 4 at 10 GeV
• Combinatorial background and other contributions
  are negligible in this mass range

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Extracting the ? and DY signals
Fit to the opposite sign dimuon invariant mass
spectrum with a superposition of ? and Drell-Yan
signals

• Line shapes from MC simulation
• nDY and n? free parameters in the fit
• Relative weight of ? states fixed from CFS
  experiment at 400 GeV
• Good fit quality
• ?2/dof 0.9?1.5

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Nuclear dependence of Drell-Yan production
Drell-Yan cross section per nucleon-nucleon
collision for M?? gt 6 GeV Fit ?(Drell-Yan) with a
power law ? ?0 A? ?Drell-Yan 0.98 ?
0.02 ?2/dof 1.4 By imposing ? ? 1 we
get ?2/dof 1.3
Drell-Yan scales with nucleon-nucleon
collisions ? useful to normalize ? yield
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Nuclear dependence of ? production
a? 0.98 ? 0.08 (c2/dof 0.8) a?/DY 0.98 ?
0.09 (c2/dof 0.9) By imposing ? ? 1 we get
?2/dof 0.8
Weak nuclear absorption for the ? at mid-rapidity
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? nuclear absorption comparison of ?? with E772
Qualitative agreement with measurement by E772 at
800 GeV NA50 measurement at 450 GeV suggests low
absorption around xF 0
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Study of pT and ycm dependence of ? and DY
production
Too small statistics to divide the data sample
into pT or ycm bins
Strategy 1. Comparison of experimental spectra
with various simulated distributions obtained
with different MC parameters
Iterative procedure until we get self consistency
in the results
2. Build an estimator of the agreement between
data and Monte-Carlo taking into account that
data and MC have finite statistics (S. Baker and
R. Cousins Nucl. Instr. Meth. A221 (1984) 437)
?2
3. Find the value of the parameter that minimizes
?2 and get the corresponding error
4. Use the parameter obtained with this
minimization to get new line-shapes to be used in
the fits
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Drell-Yan transverse momentum
Path in nuclear matter of the projectile parton
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? transverse momentum
Statistics is too low to observe a clear nuclear
dependence Making an average on the 5 data
samples we get
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Mean pT for DY and ? comparison with other
experiments
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Rapidity / xF distribution
Results from previous experiments
NA50
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B?? d?(?) / dycm at ycm 0
Very good agreement with existing systematics
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Summary

• First measurement of ? production in p-A
  collisions at 450 GeV
• ? cross section at mid-rapidity is compatible
  with CEM calculations and with the available
  systematics
• We observed a small nuclear absorption for the ?
  at mid rapidity. a? 0.98 ? 0.08
• The ? rapidity distribution is compatible with
  measurements at 400 GeV
• Drell-Yan production cross section for 4.5 lt M lt
  8.0 GeV scales with nucleon-nucleon collisions
  confirming observations by NA38/50/51 the
  invariant mass range 2.9 lt M lt 7.0 GeV

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Experimental overview ? production in pp and pA
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The Drell-Yan pT spectra
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The ? pT spectra