QM2005 P. Cortese for the NA50 Collaboration 1

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

• 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/ suppression in Pb-Pb, In-In• p-A collisions to measure “normal” nuclear absorption

• At RHIC: J/ production in Au-Au, Cu-Cu• p-p and d-Au collisions as a reference

• At LHC: 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

Study of heavy flavours and quarkonia production in p-A

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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 < ycm < 0.5

For the corresponds to: -0.36 < xF < 0.36

• Collins-Soper: -0.5 < cos(CS) < 0.5

• pT ~ flat coverage

Transverse polarization for ’ and ’’ is assumed in this analysis

Typical acceptances: AJ/ 14% ADY ~ 21% (m > 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

• 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 = [0.91.5]

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

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Nuclear dependence of Drell-Yan production

Drell-Yan scales with nucleon-nucleon collisions

useful to normalize yield

Drell-Yan cross section per nucleon-nucleon collision for M > 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

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Nuclear dependence of production

= 0.98 0.08 (2/dof = 0.8)

DY = 0.98 0.09 (2/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 productionToo 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

3. Find the value of the parameter that minimizes 2 and get the corresponding error

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)

4. Use the parameter obtained with this minimization to get new line-shapes to be used in the fits

Iterative procedure until we get self consistency in the results

2

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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 distributionResults 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. = 0.98 0.08

• The rapidity distribution is compatible with measurements at 400 GeV

• Drell-Yan production cross section for 4.5 < M < 8.0 GeV scales with nucleon-nucleon collisions confirming observations by NA38/50/51 the invariant mass range 2.9 < M < 7.0 GeV

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References[Herb77] S. W. Herb et al., Pyhs. Rev. Lett. 39, 252 1977.[Yoh78] J. K. Yoh et al., Pyhs. Rev. Lett. 41, 684 1978.[Ueno79] K. Ueno et al., Phys. Rev. Lett. 42, 486 (1979).[Badier79] J. Badier et al., Phys. Lett. B86, 98 (1979).[Angelis79] A.L.S. Angelis et al., CCOR Collaboration, Phys. Lett. B87 (1979) 398.[Kourkoumelis80] C. Kourkoumelis et al., Phys. Lett. B91 (1980) 481.[Antreasyan80] D. Antreasyan et al., Phys. Rev. Lett. 45 (1980) 863.[Antreasyan81] D. Antreasyan et al., Phys. Rev. Lett. 47 (1981) 12.[Childress85] S. Childress et al., Phys. Rev. Lett. 55, 1962 (1985).[Albajar87] C. Albajar et al., Phys. Lett. B186, 237 (1987).[Yoshida89] T. Yoshida et al., Phys. Rev. D 39, 3516 (1989).[Moreno91] G. Moreno et al., Phys. Rev. D 43, 2815 (1991).[Alde91] D. M. Alde et al., Phys. Rev. Lett. 66, 2285 (1991).[Alexopoulos96] T. Alexopoulos et al., Phys. Lett. B374 (1996) 271.[Brown01] C. N. Brown et al., Pys. Rev. Lett. 86, 2529 (2001).[Acosta02] D. Acosta et al., Pys. Rev. Lett. 88, 161802 (2002).[Nedden04] M. Nedden et al., HERA-B Collaboration, hep-ex/0406042.

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Experimental overview: production in pp and pA