Transversityand the PAX collaboration @ GSI

Alessandro DragoUniversity of Ferrara

• About the PAX proposal for the new GSI

• Transversity distribution

direct access to h1 via ATT

• Sivers distribution testing: (Sivers)DY = - (Sivers)DIS

Yerevan Physics Institute, Yerevan, ArmeniaDepartment of Subatomic and Radiation Physics, University of Gent, Belgium

University of Science & Technology of China, Beijing, P.R. ChinaDepartment of Physics, Beijing, P.R. China

Palaiseau, Ecole Polytechnique Centre de Physique Theorique, FranceHigh Energy Physics Institute, Tbilisi State University, Tbilisi, Georgia

Nuclear Physics Department, Tbilisi State University, GeorgiaForschungszentrum Jülich, Institut für Kernphysik Jülich, Germany

Institut für Theoretische Physik II, Ruhr Universität Bochum, GermanyHelmholtz-Institut für Strahlen- und Kernphysik, Bonn, GermanyPhysikalisches Institut, Universität Erlangen-Nürnberg, Germany

Langenbernsodorf, UGS, Gelinde Schulteis and Partner GbR, GermanyDepartment of Mathematics, University of Dublin,Dublin, IrelandUniversità del Piemonte Orientale and INFN, Alessandria, ItalyDipartimento di Fisica dell’Università and INFN, Cagliari, Italy

Università dell’Insubria and INFN, Como, ItalyInstituto Nationale di Fisica Nuclelare, Ferrara, Italy

PAX CollaborationPAX CollaborationSpokespersons:Spokespersons:

Paolo LenisaPaolo Lenisa lenisa@mail.desy.deFrank RathmannFrank Rathmann f.rathmann@fz-

juelich.de

Dipartimento di Fisica Teorica, Universita di Torino and INFN, Torino, ItalyInstituto Nationale di Fisica Nucleare, Frascati, Italy

Andrej Sultan Institute for Nuclear Studies, Dep. of Nuclear Reactions, Warsaw, PolandPetersburg Nuclear Physics Institute, Gatchina, Russia

Institute for Theoretical and Experimental Physics, Moscow, RussiaLebedev Physical Institute, Moscow, Russia

Physics Department, Moscow Engineering Physics Institute, Moscow, RussiaLaboratory of Theoretical Physics, Joint Institute for Nueclear Research, Dubna, Russia

Laboratory of Particle Physics, Joint Institute for Nuclear Research, Dubna, RussiaLaboratory of Nuclear Problems, Joint Institute for Nuclear Research, Dubna, Russia

Budker Institute of Nuclear Physics, Novosibirsk, RussiaHigh Energy Physics Institute, Protvino, Russia

Institute of Experimental Physics, Slovak Academy of Science, Kosice SlovakiaDepartment of Radiation Sciences, Nuclear Physics Division, Uppsala University, Uppsala,

SwedenCollider Accelerator Department, Brookhaven National Laboratory, Broohhaven USA

RIKEN BNL Research Center Brookhaven National Laboratory, Brookhaven, USAUniversity of Wisconsin, Madison, USA

Department of Physics, University of Virginia, USA

178 physicists

35 institutions (15 EU, 20 NON-EU)

PAX CollaborationPAX Collaboration

The PAX proposalThe 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 methodPrinciple of spin filter methodP beam polarizationQ target polarizationk || beam direction

σtot = σ0 + σ·P·Q + σ||·(P·k)(Q·k)

transverse case:

Q0tot

longitudinal case:

Q)( ||0tot

For initially equally populated spin states: (m=+½) and (m=-½)

Unpolarized anti-p beam

Polarized H target

Principle of spin filter methodPrinciple of spin filter methodP beam polarizationQ target polarizationk || beam direction

σtot = σ0 + σ·P·Q + σ||·(P·k)(Q·k)

transverse case:

Q0tot

longitudinal case:

Q)( ||0tot

For initially equally populated spin states: (m=+½) and (m=-½)

Unpolarized anti-p beam

Polarized H target

Polarized anti-p beam

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

Polarization with hadronic Polarization with hadronic pbar-p interactionpbar-p interaction

Model A: T. Hippchen et al. Phys. Rev. C 44, 1323

(1991)

P

Kinetic energy (MeV)10 100 100

01

0.05

0.10

0.15

0.20

Model D: V. Mull, K. Holinde, Phys. Rev. C 51, 2360

(1995)

P

Kinetic energy (MeV)

10 100 1000

1

0.05

0.10

0.15

0.20

0.1

0.2

0.3

0.4B

eam

Pola

riza

tion P

(2·τ

beam)

10 T (MeV)100

EM only

5

10

30

20

40

Ψacc=50 mrad

0

1

Filter Test: T = 23 MeV Ψacc= 4.4 mrad

Beam PolarizationBeam Polarization

Staging: Staging: Phase I (PAX@CSR)Phase I (PAX@CSR)

Physics: EMFFpbar-p elastic

Experiment: pol./unpol. pbar on internal polarized target

Independent from HESR running

Staging: Staging: Phase II (PAX@HESR)Phase II (PAX@HESR)

EXPERIMENT:1. Asymmetric collider:

polarized antiprotons in HESR (p=15 GeV/c)polarized protons in CSR (p=3.5 GeV/c)

2. Internal polarized target with 22 GeV/c polarized antiproton beam.

Physics: Transversity

Transversity in Drell-Yan processesTransversity in Drell-Yan processes

p pqL

q

l+

l-q2=M2

qT

PAX: Polarized antiproton beam → polarized proton target (both transverse)

)M,x(q)M,x(qe

)M,x(h)M,x(he

add

ddA

22

q

21

2q

22

q1

q

21

q1

2q

TTTT

,...d,d,u,uq

M invariant Massof lepton pair

PAX: M2~10-100 GeV2, s~45-200 GeV2, τ=x1x2=M2/s~0.05-0.6

→ Exploration of valence quarks (h1q(x,Q2) large)

AATTTT for PAX kinematic conditions for PAX kinematic conditions

RHIC: τ=x1x2=M2/s~10-3 → Exploration of the sea quark content (polarizations small!) ATT very small (~ 1 %)

ATT/aTT > 0.2Models predict |h1

u|>>|h1d|

)M,x(u)M,x(u

)M,x(h)M,x(haA

21

21

21

u1

21

u1

TTTT

)qqqwhere( pp

Kinematics and cross sectionKinematics and cross section

q

22

21

22

21

2q

212

2

F2

2

M,xqM,xqM,xqM,xqe)xx(sM9

4

dxdM

d•M2 = s x1x2 •xF=2QL/√s = x1-x2

M (GeV/c2)

22 GeV

collider

2 k events/day

Energy for Drell-Yan processes

"safe region": /JMM

s

M J /2

τ

QCD corrections might be very large at smaller values of M:

yes, for cross-sections, not for ATT K-factor almost spin-independent

Fermilab E866 800 GeV/c

H. Shimizu, G. Sterman, W. Vogelsang and H. Yokoya, hep-ph/0503270

s=30 GeV2 s=45 GeV2

s=210 GeV2s=900 GeV2

J/ψq q

q

l+

l–

l+

l–

all vector couplings, same spinor structure

and, at large x1, x2

measure ATT also in J/ψ resonance region

llXJpp /

/2

/2

))((

JJ

Vl

Vq

MiMM

vuguvg

2

) )((

M

vueuveq

q

*

*/ ˆˆ TT

JTT aa

)()(

)()(

)()()(

)()()(ˆ

21

2111

212

21112

xuxu

xhxh

xqxqg

xhxhgaA uu

q

Vq

q qqVq

TTTT

Mauro Anselmino, V. Barone, A. D. and N. Nikolaev PLB 594 (2004) 97

Estimated signal for hEstimated signal for h1 1 (phase II)(phase II)

1 year of data taking

Collider:

L=2x1030 cm-2s-1

Fixed target:

L=2.7x1031 cm-2s-1

Transversity in various quark models

0.35 0.4 0.45 0.5 0.55 0.6x

0.5

1

1.5

2

h1u

MIT

CDM

CQSM

g1 evol

)(),( 2111Y-D xfkxfA TN

Sivers function usual parton distribution

Direct access to Sivers function

test QCD basic result: DIS1Y-D1 )()( TT ff J. Collins

qqTDXpp

N DfA )( 1

usual fragmentation function

process dominated by no Collins contribution

ccqq

same process at RHIC is dominated by ccgg

Measuring the Sivers function

Sivers function non-vanishing in gauge theories.Chiral models with vector mesons as gauge bosons can be used A.D. PRD71(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 h1 in the valence region

• Possibility of testing the gauge-theory dictated rule (Sivers)DY = - (Sivers)DIS