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 [email protected] 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