Transversity and the PAX collaboration GSI Alessandro Drago

Transversity and the PAX collaboration @ GSI Alessandro Drago University of Ferrara

• About the PAX proposal for the new GSI • Transversity distribution direct access to h 1 via ATT • Sivers distribution testing: (Sivers)DY = - (Sivers)DIS

PAX Collaboration Spokespersons: Paolo Lenisa Frank Rathmann lenisa@mail. desy. de f. rathmann@fz-juelich. de Yerevan Physics Institute, Yerevan, Armenia Department of Subatomic and Radiation Physics, University of Gent, Belgium University of Science & Technology of China, Beijing, P. R. China Department of Physics, Beijing, P. R. China Palaiseau, Ecole Polytechnique Centre de Physique Theorique, France High Energy Physics Institute, Tbilisi State University, Tbilisi, Georgia Nuclear Physics Department, Tbilisi State University, Georgia Forschungszentrum Jülich, Institut für Kernphysik Jülich, Germany Institut für Theoretische Physik II, Ruhr Universität Bochum, Germany Helmholtz-Institut für Strahlen- und Kernphysik, Bonn, Germany Physikalisches Institut, Universität Erlangen-Nürnberg, Germany Langenbernsodorf, UGS, Gelinde Schulteis and Partner Gb. R, Germany Department of Mathematics, University of Dublin, Ireland Università del Piemonte Orientale and INFN, Alessandria, Italy Dipartimento di Fisica dell’Università and INFN, Cagliari, Italy Università dell’Insubria and INFN, Como, Italy Instituto Nationale di Fisica Nuclelare, Ferrara, Italy

PAX Collaboration Dipartimento di Fisica Teorica, Universita di Torino and INFN, Torino, Italy Instituto Nationale di Fisica Nucleare, Frascati, Italy Andrej Sultan Institute for Nuclear Studies, Dep. of Nuclear Reactions, Warsaw, Poland Petersburg Nuclear Physics Institute, Gatchina, Russia Institute for Theoretical and Experimental Physics, Moscow, Russia Lebedev Physical Institute, Moscow, Russia Physics Department, Moscow Engineering Physics Institute, Moscow, Russia Laboratory of Theoretical Physics, Joint Institute for Nueclear Research, Dubna, Russia Laboratory of Particle Physics, Joint Institute for Nuclear Research, Dubna, Russia Laboratory of Nuclear Problems, Joint Institute for Nuclear Research, Dubna, Russia Budker Institute of Nuclear Physics, Novosibirsk, Russia High Energy Physics Institute, Protvino, Russia Institute of Experimental Physics, Slovak Academy of Science, Kosice Slovakia Department of Radiation Sciences, Nuclear Physics Division, Uppsala University, Uppsala, Sweden Collider Accelerator Department, Brookhaven National Laboratory, Broohhaven USA RIKEN BNL Research Center Brookhaven National Laboratory, Brookhaven, USA University of Wisconsin, Madison, USA Department of Physics, University of Virginia, USA 178 physicists 35 institutions (15 EU, 20 NON-EU)

The PAX proposal Jan. 04 LOI submitted 15. 06. 04 QCD PAC meeting at GSI 18 -19. 08. 04 Workshop on polarized antiprotons at GSI 15. 01. 05 Technical Report submitted 14 -16. 03. 05 QCD-PAC meeting at GSI Polarization enters in the core of FAIR

Principle of spin filter method σtot = σ0 + σ ·P·Q + σ||·(P·k)(Q·k) P beam polarization Q target polarization k || beam direction For initially equally populated spin states: (m=+½) and (m=-½) transverse case: longitudinal case: Unpolarized anti-p beam Polarized H target

Principle of spin filter method σtot = σ0 + σ ·P·Q + σ||·(P·k)(Q·k) P beam polarization Q target polarization k || beam direction For initially equally populated spin states: (m=+½) and (m=-½) transverse case: longitudinal case: Polarized Unpolarized anti-p beam Polarized H target

Meyer PRE 50 (1994) 1485 Rathmann et al. PRL 71(1993)1379

Polarization with hadronic pbar-p interaction P Model A: T. Hippchen et al. Phys. Rev. C 44, 1323 (1991) P 0. 20 0. 15 0. 10 0. 05 1 10 100 Kinetic energy (Me. V) 1 Model D: V. Mull, K. Holinde, Phys. Rev. C 51, 2360 (1995) 10 100 Kinetic energy (Me. V)

Beam Polarization P(2·τbeam) Beam Polarization Ψacc=50 mrad 0. 4 40 0. 3 EM only 30 20 10 0. 2 5 0. 1 0 1 10 Filter Test: T = 23 Me. V Ψacc= 4. 4 mrad 100 T (Me. V)

Staging: Phase I (PAX@CSR) Physics: EMFF pbar-p elastic Experiment: pol. /unpol. pbar on internal polarized target Independent from HESR running

Staging: Phase II (PAX@HESR) Physics: Transversity EXPERIMENT: 1. Asymmetric collider: polarized antiprotons in HESR (p=15 Ge. V/c) polarized protons in CSR (p=3. 5 Ge. V/c) 2. Internal polarized target with 22 Ge. V/c polarized antiproton beam.

Transversity in Drell-Yan processes PAX: Polarized antiproton beam → polarized proton target (both transverse) l+ q p q. L l- q 2=M 2 q. T p M invariant Mass of lepton pair

ATT for PAX kinematic conditions RHIC: τ=x 1 x 2=M 2/s~10 -3 → Exploration of the sea quark content (polarizations small!) ATT very small (~ 1 %) PAX: M 2~10 -100 Ge. V 2, s~45 -200 Ge. V 2, τ =x 1 x 2=M 2/s~0. 05 -0. 6 → Exploration of valence quarks (h 1 q(x, Q 2) large) ATT/a. TT > 0. 2 Models predict |h 1 u|>>|h 1 d|

Kinematics and cross section • M 2 = s x 1 x 2 • x. F=2 QL/√s = x 1 -x 2 2 k events/day collider 22 Ge. V M (Ge. V/c 2)

Energy for Drell-Yan processes "safe region": Fermilab E 866 800 Ge. V/c QCD corrections might be very large at smaller values of M: yes, for cross-sections, not for ATT K-factor almost spin-independent H. Shimizu, G. Sterman, W. Vogelsang and H. Yokoya, hep-ph/0503270

s=30 Ge. V 2 s=210 Ge. V 2 s=45 Ge. V 2 s=900 Ge. V 2

q l+ l– q l– J/ψ q all vector couplings, same spinor structure and, at large x 1, x 2 measure ATT also in J/ψ resonance region Mauro Anselmino, V. Barone, A. D. and N. Nikolaev PLB 594 (2004) 97

Estimated signal for h 1 (phase II) 1 year of data taking Collider: Fixed target: L=2 x 1030 cm-2 s-1 L=2. 7 x 1031 cm-2 s-1

Transversity in various quark models MIT CDM CQSM g 1 evol

Measuring the Sivers function Direct access to Sivers function usual parton distribution test QCD basic result: J. Collins process dominated by no Collins contribution usual fragmentation function same process at RHIC is dominated by Sivers function non-vanishing in gauge theories. Chiral models with vector mesons as gauge bosons can be used A. D. PRD 71(2005)057501. (Sivers)u = -(Sivers)d in chiral models at leading order in 1/Nc.

Conclusions • PAX Collaboration proposal @ GSI: First experiment with a polarized antiproton beam • Possibility of measuring h 1 in the valence region • Possibility of testing the gauge-theory dictated rule (Sivers)DY = - (Sivers)DIS