P.Lenisa Polarized Antiprotons Experiments 1

dr. Paolo Lenisadr. Paolo LenisaUniversità di Ferrara and INFN - ITALYUniversità di Ferrara and INFN - ITALY

Project X WorkshopFNAL, 01/26/08

Polarized Antiprotons Polarized Antiprotons ExperimentsExperiments

The PAX Collaboration

178 Collaborators36 institutions (15 EU, 21 NON-EU)

P.Lenisa Polarized Antiprotons Experiments 2

Study of the Study of the proton spinproton spin

Physics with Physics with Polarized AntiprotonsPolarized Antiprotons

P.Lenisa Polarized Antiprotons Experiments 3

q h1

=

transversely polarisedquarks and nucleons

longitudinally polarisedquarks and nucleons

q

unpolarised quarksand nucleons

q

Quark structure of the nucleon

Well known

Known

Only glimpse

nxqxqxqx T1

55LTw2Corr Sγγ)(γ)(S)(

2

1)(

Study of the proton spinStudy of the proton spin

P.Lenisa Polarized Antiprotons Experiments 4

TransversityTransversity

- Probes relativistic nature of quarks- No gluon analog for spin-1/2 nucleon- Different evolution than - Sensitive to valence quark polarization

transversely polarisedquarks and nucleons

q1h

2Q q

Inclusive DIS Semi-inclusive DIS Drell-Yan

HERMES,COMPASS,JLab

h1 is chirally odd -> it needs a chirally odd partner

P.Lenisa Polarized Antiprotons Experiments 5

,...d,d,u,uq

M invariant Massof lepton pair /2 / 2

2121 sQxsMxxxxx LFF

)( )()( )(1

9

42121

2

212

2

2

2

xqxqxqxqexxsMdxdM

d

qq

F

sM 2

llqq *

Inclusive DIS Semi-inclusive DIS Drell-Yan

q q

q qqqqq

TTTT xqxqxqxqe

xhxhxhxheaA

)()()()(

)()()()(ˆ

dd

dd

21212

211121112

hh11 from p-p Drell-Yan from p-p Drell-Yan

P.Lenisa Polarized Antiprotons Experiments 6

EXPERIMENT:Asymmetric collider:

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

s=200 GeV2

The PAX proposal at FAIR (phase The PAX proposal at FAIR (phase II)II)

(Same “s” as Main Injector beam on fixed target)

P.Lenisa Polarized Antiprotons Experiments 7

hh11 from p-p Drell-Yan from p-p Drell-Yan

PAX : s=x1x2~0.02-0.3 valence quarks (ATT large ~ 0.2-0.3 )

)()(

)()(ˆ

21

2111

xuxu

xhxhaA uu

TTTT

q q

q qqqqq

TTTT xqxqxqxqe

xhxhxhxheaA

)()()()(

)()()()(ˆ

dd

dd

21212

211121112

• u-dominance• |h1u|>|h1d|

First direct measurement of h1 for valenc quarksNo competitive processes

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

P.Lenisa Polarized Antiprotons Experiments 8

Proton Proton electromagnetic form-electromagnetic form-

factorsfactors

Physics with Physics with Polarized AntiprotonsPolarized Antiprotons

P.Lenisa Polarized Antiprotons Experiments 9

Electromagnetic Form FactorsElectromagnetic Form Factors- Describe int. structure of the nucleon

-Information about proton ground state

-Test for models of nucleon structure

- Wavelength tunable with Q2:

< 0.1 GeV2 integral quantities

0.1-10 GeV2 internal structure

> 20 GeV2 pQCD scaling

k’k

p p’

q=k’-k

qiqFM

qFJ 22

21 2

• One-photon-exchange approximation: Pauli-Dirac (F1 and F2) or Sachs (GE and GM)GM(q2) = F1(q2) + F2(q2)GE(q2) = F1(q2) + F2(q2)=q2/4M2

• In the Breit reference system,

Sachs FFs are the Fourier transform of the charge and magnetization distributions

P.Lenisa Polarized Antiprotons Experiments 10

Space-like and Time-like regionsSpace-like and Time-like regions

•FFs are analytical functions. of t = q2 = -Q2.

)(lim)(lim 2222 qFqF TL

q

SL

q

e- + h => e-

+ h

Scattering

t=q2<0 (spacelike)real function

Annihilation

e+ + e- => h

+ h

_

_

t=q2>0 (timelike)

complex function

P.Lenisa Polarized Antiprotons Experiments 11

Polarization

Rosenbluth

Space-Like FFs: proton data

Proton Electromagnetic Form-Factors: Proton Electromagnetic Form-Factors: datadata

JLab results dramatically changed picture of the Nucleon:

- GEp/GM

p decreases with Q2

Time-Like FFs: proton data

- Q2 dependence suggests different charge and magnetization spatial distributions inside the nucleon

Is the proton round?

P.Lenisa Polarized Antiprotons Experiments 12

Time-Like FFs: proton data

Expected Q2 behaviour reached quite early, however ...... there is still a factor of 2between timelike and spacelike.

Proton Electromagnetic Form-Factors: Proton Electromagnetic Form-Factors: datadata

Polarization

Rosenbluth

Space-Like FFs: proton data

Is the proton round?

Additional direct measurement needed

P.Lenisa Polarized Antiprotons Experiments 13

The PAX proposal - Phase IThe PAX proposal - Phase I

EXPERIMENT:Fixed target experiment:

polarized antiprotons protons in CSR (Ek<2.5 GVe)fixed polarized protons target

“s” range covered by both Main Injector and Antiproton Accumulator beams on fixed target

P.Lenisa Polarized Antiprotons Experiments 14

•Most contain mduli GE, GM• Independent GE-GM separation• Test of Rosenbluth separation in the time-like region

•Access to GE-GM phase•Very sensitive to different models

Double polarized pbar-p annihilationDouble polarized pbar-p annihilation

E. Tomasi, F. Lacroix, C. Duterte, G.I. Gakh, EPJA 24, 419(2005)

P.Lenisa Polarized Antiprotons Experiments 15

Theoretical modelsTheoretical models

Spacelike Timelike

VDM : IJLF. Iachello..PLB 43, 191 (1973)

Extended VDM E.L.Lomon PRC 66, 045501 2002)

HohlerNPB 114, 505 (1976)

QCD inspiredBosted PRC 51, 409 (1995)

Electric Magnetic

neu

tron

pro

ton

Electric Magnetic

E. Tomasi, F. Lacroix, C. Duterte, G.I. Gakh, EPJA 24, 419(2005)

P.Lenisa Polarized Antiprotons Experiments 16

(Single Spin Asymmetry)(Single Spin Asymmetry)

A. Z. Dubnickova et al. Nuovo Cimento A109, 241 (1996)

S.J. Brodsky et al. PRD 69, 054022 (2004)

• Single-spin asymmetry in pp → e+e-

– Measurement of relative phases of magnetic and electric FF in the time-like region- Also sensitive to different models

P.Lenisa Polarized Antiprotons Experiments 17

Polarized Polarized pbar-p pbar-p

hard-scatteringhard-scattering

Physics withPhysics with Polarized AntiprotonsPolarized Antiprotons

P.Lenisa Polarized Antiprotons Experiments 18

Hard p-p polarized scatteringHard p-p polarized scattering

“One of the unsolved mysteries of hadron physics”(Brodsky, 2005)

It would be very interesting to perform these measurements with polarized antiprotons.

D.G. Crabb et al., PRL 41, 1257 (1978)

T=10.85 GeV

“The greatest asymmetries in hadron physics ever seen by a human being” (Brodsky)

Beam

Target

P

P.Lenisa Polarized Antiprotons Experiments 19

Physics withPhysics withPolarized AntiprotonsPolarized Antiprotons

•Spectroscopy of hadrons

•Use of polarization degrees of freedom to decrease number of contributing amplitudes

Further perspectives …

P.Lenisa Polarized Antiprotons Experiments 20

Fails in predicting polarization vs pT at CDF

J/J/,, production production

F. Maltoni et al., hep-ph/0601203

Fixed target exp

NRQCD

Able to reproduce the unpolarized xsec

P.Lenisa Polarized Antiprotons Experiments 21

Physics withPhysics with Polarized AntiprotonsPolarized Antiprotons

•Spectroscopy of hadrons

•Use of polarization degrees of freedom to decrease number of contributing amplitudes

Further perspectives …

•Low-t proton-antiproton scatteringInvestigation of spin and isospin dependence of nucleon-antinucleon interaction at low energy

P.Lenisa Polarized Antiprotons Experiments 22

More single-spin More single-spin asymmetriesasymmetries

P.Lenisa Polarized Antiprotons Experiments 23

pq

Pq

π

k┴Collins effect = fragmentation of polarized

quark depends on Pq· (pq x k┴)

Sivers effect = number of partons in polarized proton depends on P · (p x k┴)

P

pp

k┴

q

k┴

qPq

pp

Boer-Mulders effect = polarization of partons in unpolarized proton depends on Pq

· (p x k┴)

These effects may generate SSA

d d

d dNA

pq

P

k┴

Polarizing FF = polarization of hadrons from unpolarized partons depends on PL ·

(pq x k┴)

PDFs

FFs

Single-spin asymmetriesSingle-spin asymmetries

Correlation functions

P.Lenisa Polarized Antiprotons Experiments 24

)()()( 1T1siv zDxfA S )()()( 1T1siv zDxfA S

Sivers from SIDISSivers from SIDIS

ep→hX

Sivers from hadron Sivers from hadron scatteringscattering

E704 √s = 20 GeV 0.7 < pT < 2.0 p↑p

pp→X

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

P.Lenisa Polarized Antiprotons Experiments 25

The Sivers function The Sivers function

DYTTSIDISTT xfxf )p,()p,( 21

21

Test of Universality

A.V. Efremov et al.,

Phys. Lett. B 612, 233 (2005)

XeeppPAX :

y22/1 /

esMxM. Anselmino et al.,

Phys. Rev. D72, 094007 (2005)

XppE :704

XeepSIDIS :

P.Lenisa Polarized Antiprotons Experiments 26

• The physics case for polarization expeiments with antiprotons is outstanding

• Two options to perform polarization experiments with pbar at FNAL– Single spin-asymmetries

• Fixed target in AA or MI

– Double spin-asymmetries• Polarizer ring (F. Rathmann -> next talk) + experimental ring

SummarySummary

• The FNAL pbar-source is a pretious treasure for the world hadron-physics community– Factor 10 higher “real” intensity than the FAIR source “on the

paper” in ten years– Future of CERN pbar-source unclear

• AD ring low energy, no stacking capability