paolo lenisa – università and infn – ferrara, italy

P. Lenisa The PAX project 1

Paolo Lenisa – Università and INFN – Ferrara, ITALY

Trento, July 6th 2006

http://www.fz-juelich.de/ikp/pax

PAXPAXPolarized Antiproton Polarized Antiproton

ExperimentsExperiments


PAX CollaborationPAX Collaboration

TIMELINE

Jan. 04 Letter of Intent for FAIR

May 04 QCD-PAC meeting at GSI

Aug. 04 Workshop on polarized antiprotons at GSI

Jan. 05 Technical Proposal for FAIR

Mar. 05 QCD-PAC meeting at GSI

Nov. 05 LoI to CERN-SPSC to perform spin-filtering experiments with antiprotons at the AD ring

Apr. 06 LoI to COSY-PAC for spin filtering experiments with protons at COSY

180 physicists35 institutions (15 EU, 20 NON-EU)


… the PAC would like to stress again the uniqueness of the program with polarized anti-protons and polarized protons that could become available at GSI.

Evaluation by QCD-PAC (March 2005)Evaluation by QCD-PAC (March 2005)

The STI requests R&D work to be continued on the proposed asymmetric collider experiment with both polarized anti-protons and protons:t o demonstrate that a high degree of anti-proton polarization can be reached

The STI believes that PAX should become part of the FAIR core research program based on its strong scientific merit once the open problems are convincingly solved.

Recommendation of the STI of FAIR Recommendation of the STI of FAIR (Sept. (Sept. 2005)2005)


Physics MotivationsPhysics Motivations


Physics with polarized antiprotons at GSI-PAX

Transversity via Drell-Yan processes

TTA direct access to transversity

Transverse Single Spin Asymmetries

QCD “theorem”: (Sivers)D-Y = – (Sivers)DISNA

Time-like e.l.m. form factors

llpp form factors

Elastic processes

SLSSLLNNN AAA AA , , ,, spin mysteries like in pp ?

High Energy

Low Energy


h1 from pbar-p Drell-Yan at GSI

Similar predictions by Efremov et al.,

Eur. Phys. J. C35, 207 (2004)

PAX : M2s=x1x2~0.1-0.3 → valence quarks (ATT large ~ 0.2-0.4 )

Anselmino et al. PLB 594,97

(2004)

)()(

)()(ˆ

)()()()(

)()()()(ˆ

21

2111

21212

211121112

xuxu

xhxha

xqxqxqxqe

xhxhxhxheaA uu

TT

q q

q qqqqq

TTTT


10 % precision on the h1u (x) in the valence region

1 year of data taking at 15+3.5 GeV collider L = 2∙1030 cm-2s-1

Precision in hPrecision in h11 measurement measurement

(L~1031 reachable)


q q

q qqqqq

TTTT xqxqxqxqe

xhxhxhxheaA

)()()()(

)()()()(ˆ

dd

dd

21212

211121112

Barone, Calarco, Drago

Martin, Schäfer, Stratmann, Vogelsang

What about p-p?

h1q (x, Q2) small and with much slower evolution than

Δq(x, Q2) and q(x, Q2) at small x

h1q (x, Q2)- h1q (x, Q2)≠

RHIC: τ=x1x2~10-3 → sea quarks (ATT ~ 0.01 )

JPARC/U70: τ=x1x2~10-1 → valence and sea (ATT ~ 0.1 )

PAX: τ=x1x2~10-1 → valence and sea (ATT ~ 0.1 )


DY in p-p: ADY in p-p: ATT TT

•Aymmetry is large at PAX energy (> 0.1)

•Sign of the asymmetry will distinguish between the two models.

•It will give indications about calculation of sea distributions.

),(),( 2201 0QxqQxh

q

),(),( 2201 0QxqQxh

q

1

2Asymmetries evoluted from the

assumptions:

CDM

(~CQSM)

2

1

GeVs 10

A. Drago


pp-pbar-pbar

DY events distribution (√sDY events distribution (√s~15 GeV)~15 GeV)

p-pbar +p-p -> complete map of transversity

p-pp-p

Extraction of h1u for x>0.2x1=x2 ->ATT~h1u2

Direct measurement of h1u for 0.15<x<0.5

M2/s=x1x2~0.01-0.3


Val. scenario

Std. scenarioxF=x1-x2

q q

q q

LLDYLL

xqxqxqxqe

xqxqxqxqeaA

21212

21212

DY in p-p: ADY in p-p: ALL LL

•Large asymmetries expected

•Test of the assumptions of the fits

GeVs 10

Models:

oAA CDMCQSM

LLLL

Val. scenario: 0;

),(

),(2

2

ss

d

u

xu

xd

ssdduuQxq seasea ),( 2

Std. scenario:








llpp form factors

Elastic processes


High Energy

Low Energy


Single Spin Asymmetries (and their partonic

origin)

pq

Pq

π

k┴Collins effect = fragmentation of polarized quark

depends on Pq· (pq x k┴)

P

pk┴

Sivers effect = number of partons in polarized

proton depends on P · (p x k┴)

q

pk┴

Boer-Mulders effect = polarization of partons in

unpolarized proton depends on Pq · (p x k┴)

qPq

Collins: chiral-odd

Sivers: chiral-even

Boer-Mulders: chiral-odd

These effects may generate SSA

d d

d dNA


BNL-AGS √s = 6.6 GeV 0.6 < pT < 1.2 p↑p

E704 √s = 20 GeV 0.7 < pT < 2.0 p↑p

STAR-RHIC √s = 200 GeV 1.1 < pT < 2.5 p↑p

E704 √s = 20 GeV 0.7 < pT < 2.0 p↑p

SSA, pp → πX








llpp form factors

Elastic processes


High Energy

Low Energy


pp Elastic Scattering from ZGSpp Elastic Scattering from ZGS

Spin-dependence at large-PSpin-dependence at large-P (90°90°cmcm):):

Hard scattering takes Hard scattering takes place only with spins place only with spins ..

D.G. Crabb et al., PRL 41, 1257

(1978)

T=10.85 GeV

Similar studies in pp elastic scattering








llpp form factors

Elastic processes


High Energy

Low Energy


Proton Electromagnetic Proton Electromagnetic Formfactors Formfactors

• Single-spin asymmetry in pp → e+e-

– Measurement of relative phases of magnetic and electric FF in the time-like region

• Double-spin asymmetry in pp → e+e-

– independent GE-Gm separation

– test of Rosenbluth separation in the time-like region

2

p2

2E

22M

2M

*E

y

m4/q

/|G|)(sin|G|)(cos1

)GGIm()2sin(A

S. Brodsky et al., Phys. Rev. D69 (2004)


Experimental setupExperimental setup


PAX Accelerator SetupPAX Accelerator Setup

• Antiproton Polarizer Ring (APR)• Asymmetric Antiproton-Proton Collider (CSR) • High Energy Synchrotron Ring (HESR)


Antiproton Polarizer RingAntiproton Polarizer Ring

Energy 250 MeV

250 mm mrad

Circumf.

86 m


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:Asymmetric collider: polarized antiprotons in HESR (p=15 GeV/c)

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

Physics: Transversity

Second IP with minor interference with PANDA


Parameter Bunched Coasting

CSR HESR CSR HESR

Particles pbar p pbar p

Circum. [m] 183 574 183 574

Pmax [GeV/c] 3.65 15 3.65 15

smax [GeV2] ~ 200 ~ 200

No. bunches 10 30 - -

No. particles 5x1011 2.4x1012 5x1011 1x1013

Lifetime [hs] ~1500 ~300 ~1500 ~300

Lum. [cm-2s-

1]5x1030 1.2x1031

Polar. ↑↑,→→, ↑→ ↑↑,→→, ↑→

p-p yes yes

ParametersParameters


Symmetric colliderSymmetric collider

Circum.[m] 681

No. Bunches 10

No. p 1x1012

No pbar 1x1012

Smax [GeV2] ~900

Polar. ↑↑,→→

p-p no

Asymm. collider

Luminosity


PAX Detector Concept PAX Detector Concept Physics: h1 distribution sin2 EMFF sin2

pbar-p elastic high |t|

Detector: Extremely rare DY signal (10-7 p-pbar) Maximum Bjorken-x coverage (M interval) Excellent PID (hadron/e rejection ~ 104) High mass resolution (≤2 %)

Moderate lepton energies (0.5-5 GeV)

Azimuthally Symmetric:BARREL GEOMETRY

LARGE ANGLES

Experiment: Flexible Facility e+e-


Kinematics for Drell-Yan processes

QCD corrections might be very large at smaller values of M, for cross-sections, not for ATT: K-factor almost

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

V. Barone et al., in preparation

Fermilab E866 800 GeV/c

CERN NA51 450 GeV/c

"safe region"

/JMM

s

M J /2

Usually taken as

Q2>4 GeV2


PAX Detector Concept PAX Detector Concept Physics: h1 distribution sin2 EMFF sin2

pbar-p elastic high |t|

Magnet: Keeps beam polarization vertical Compatible with Cerenkov Compatible with polarized target

Detector: Extremely rare DY signal (10-7 p-pbar) Maximum Bjorken-x coverage (M interval) Excellent PID (hadron/e rejection ~ 104) High mass resolution (≤2 %)

Moderate lepton energies (0.5-5 GeV)

Azimuthally Symmetric:BARREL GEOMETRY

LARGE ANGLES

Experiment: Flexible Facility

TOROIDNO FRINGE FIELD

e+e-


PAX Detector Concept PAX Detector Concept

Designed for Collider but compatible with fixed target

Cerenkov(200 m)

(20 m)

GEANT simulation


2011-2013 APR final design and construction

Phase I: 2014-2017

APR+CSR @ GSI

Physics: EMFF, p-pbar elastic with fixed target.

Phase II: 2018 - …

HESR+CSR asymmetric collider

Physics: h1

The The (long) (long) way towards away towards apolarized antiproton colliderpolarized antiproton collider

Phase 0: 2006-2010

Pol. buildup measurements @ COSY and CERN


SIS18 HESR

RESR

APR

CSR

CSR

HESR CSR

CSR

HESR

Antiproton and Proton accelerators’ scheme

Energy

time

proton

antiproton


Higher energy p-p machineHigher energy p-p machine

GeVs 100

V. Barone, T. Calarco and A. Drago

Phys. Rev. D 56 (1997) 527

•s •Asymmetry

•√s @ PAX ideal


Transverse seaTransverse sea

M. Wakamatsu and T. KubotaPhys. Rev. D 63 (1999) 034020

V. Barone, T. Calarco and A. Drago

Phys. Lett. B 390 (1997) 287

CDM CQSM

•The two models predict different sign for (with comparable amplitude).

uh

1

dh

1

),(1 initu

Qxh),(

1 evoluQxh

),(1 initd

Qxh),(

1 evoldQxh

uh

1


Longitudinal seaLongitudinal sea

M. Glück et al.Phys. Rev. D 63 (2001) 094005

Models:

ouu CDMCQSM

ux

ux

dx

dx

sx

Gx

Val. scenario: 0;

),(

),(2

2

ss

d

u

xu

xd

ssdduuQxq seasea ),( 2

Std. scenario:

paolo lenisa – università and infn – ferrara, italy

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