dr. Paolo Lenisa Università di Ferrara and INFN – ITALY on behalf of the PAX-Collaboration

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dr. Paolo LenisaUniversità di Ferrara and INFN – ITALY

on behalf of the PAX-Collaboration

Perspectives for Polarized Antiprotons

Polarized AntiprotonsP.Lenisa

XIV International Workshop on Polarized Sources, Targets and PolarimetrySt. Petersburg, 13.09.2011

Motivation:Missing tool for Hadron Physics

2Polarized AntiprotonsP.Lenisa

Polarized Antiprotons

Polarized Antiprotons 3

transversely polarisedquarks and nucleons

q

longitudinally polarisedquarks and nucleons

q

unpolarised quarksand nucleons

q

Quark structure of the nucleon

nxqxqxqx T1

55LTw2Corr Sγγ)(γ)(S)(

2

1)(

P.Lenisa

Well known Known Less known


Inclusive DIS Semi-inclusive DIS Drell-Yan

HERMES,COMPASS,JLab

transversely polarisedquarks and nucleons

q

longitudinally polarisedquarks and nucleons

q

unpolarised quarksand nucleons

q

nxqxqxqx T1

55LTw2Corr Sγγ)(γ)(S)(

2

1)(

Quark structure of the nucleon

P.Lenisa

Accesso to transversity through Drell-Yan

5

llqq *

q q

q qqqqq

TTTT xqxqxqxqe

xhxhxhxheaA

)()()()(

)()()()(ˆ

dd

dd

21212

211121112


Asymmetric (double-polarized)

proton (15 GeV/c) – antiproton (3.5 GeV/c) collider

6

pp

A double polarized pbar-p collider for FAIR


7

1 year run -> 10 % precision on the h1u (x) in the valence region

Pp=30%

Pp=10%


q q

q qqqqq

TTTT xqxqxqxqe

xhxhxhxheaA

)()()()(

)()()()(ˆ

dd

dd

21212

211121112

h1u from p-p Drell-Yan at PAX

• u-dominance• |h1u|>|h1d|

)()(

)()(ˆ

21

2111

xuxu

xhxhaA uuTTTT


Polarization

Rosenbluth

Space-Like FFs: proton data

Study of the Proton Electromagnetic Form-Factors

JLab results dramatically changed picture of the Nucleon:

- GEp/GM

p decreases with Q2

- data suggest GEp crosses 0 at Q2 8

GeV2

Time-Like FFs: proton data

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

Additional and more precise measurements needed

P.Lenisa

9

•Most contain moduli 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 annihilation:

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


10

Polarization and Models in T.L. Region

VDM : IJL

Ext. VDM

‘QCD inspired’

R

Ay Axx Ayy

AxzAzz

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


Method:The mechanism of spin-filtering



P. Lenisa PAX Status Report 12

Polarized antiprotons

Intense beam of polarized pbar never produced:

• Synchr. radiation ~ (4/R) -> pol ~107 y in 20 TeV pbar ring

• Conventional methods (ABS) not applicable

• Polarized pbar from antilambda decay• I< 1.5∙105 s-1 (P ≈ 0.35)

• Pbar scattering off liquid H2 target• I< 2∙103 s-1 (P ≈ 0.2)

Production of polarization in a stored beam

Two Methods: Loss versus spin flip

For an ensemble of spin ½ particles with projections + () and – ()


Spin-filtering

14P.Lenisa

Polarization build-up of a circulating particle beam by interaction with a polarized gas target


Unpolarized anti-p beam

Polarized target

Polarization Buildup

P.Lenisa 15

S beam-particle spinQ target polarizationk || beam direction

)ˆ)(ˆ()( 210 kQkSQStot

)/tanh()(

tNN

NNtP

fdQ t

1

~1

fQdt)~~(

1

1

||


Unpolarized anti-p beam

Polarized target

Polarized anti-p beam

P.Lenisa 16

Polarization BuildupS beam-particle spinQ target polarizationk || beam direction

)ˆ)(ˆ()( 210 kQkSQStot

)/tanh()(

tNN

NNtP

fdQ t

1

~1

fQdt)~~(

1

1

||


Optimum (black curve) after 2 lifetimes filtering

Spin-filtering at TSR: „FILTEX“ – proof-of-principle

Spin filtering works for protons

F. Rathmann et al., PRL 71, 1379 (1993)


PAX@AD/CERN:Antiproton polarization

PAX@COSY :Proton polarization

PAX@FAIR:Eexperiments with

pol. pbar

P.Lenisa 18Polarized Antiprotons

Polarized AntiprotonsExperimental program:

Measurements with pbar at AD-Ring

P.Lenisa 19

PAX target section

Measurements at AD (CERN)•Aim: 1st measurement of the spin-dependence of the pbar-p cross section•Method: measurement of polarization build-up by spin-filtering


Spin-dependence of the pbar-p interaction

P.Lenisa 20

Model A: T. Hippchen et al., Phys. Rev. C 44, 1323 (1991).

Model OBEPF: J. Haidenbauer, K. Holinde, A.W. Thomas, Phys. Rev. C 45, 952 (1992).

Model D: V. Mull, K. Holinde, Phys. Rev. C 51, 2360 (1995).


Expected polarizations after filtering for two lifetimes

transverse

A

D

21

longitudinal


• Measurement of the polarization buildup allows determination of σ1 and σ2

• Once pbar polarization available, spin-correlation coefficients accessible


More recent calculations…

PLB 690 (2010)

P.Lenisa

Cross sections

Projected polarizations

PAX@AD/CERN:Antiproton polarization

PAX@COSY :Proton polarization

PAX@FAIR:Experiments with pol. pbar


Polarized AntiprotonsExperimental program

Measurements with p at COSY-Ring (Germany)

WASA

e-cooler

ANKE

PAX

Spin-filtering at COSY

Main purpose:1. Commissioning of the experimental setup for CERN/AD2. Quantitative understanding of the machine parameters


Installation of low-β section (2009)

•Beam has to fit through storage cell target (dt=5x1013 atoms/cm2)•Increase acceptance angle at target position


• Model in good agreement with measurement: β ~ 0.3m -> beam fits through the cell!

• No negative impact on the COSY operation

Commissioning of the experimental setup (2010)I. Machine studies: Low- section


In case intra-beam scattering poses a limitation, increase of beam emittance should increase lifetime! (Touschek)

• Increase of beam emittance by tilting of electron cooler beam• Beam emittance measured with ionisation profle monitor


Commissioning of the experimental setup (2010)I. Machine studies: Studies of beam-lifetime

limitations

ABSABS

Breit-Rabipolarimeter

Breit-Rabipolarimeter

Spin filtering requires >1013 atoms/cm2 → ABS + openable storage cell

Analysis of target polarization by Breit-Rabi polarimeter (BRP) and a target gas analyzer (TGA)

Commissioning of the experimental setup (2010)II. Polarized Target


P.Lenisa Polarized Antiprotons 29

BRP: Continous monitoring of the target polarization

p D2

pd elastic scattering:detection in two (L-R) symmetric Silicon Tracking Telescopes

Commissioning of the experimental setup (2010)III. Beam Polarimeter


Deuteron identification

d

p


Commissioning of the experimental setup (Aug. 2011)

IV. Installation of NEG pump (12000 l/s)

In an ideal machine Single-Coulomb scattering at the target dominates beam loss

COSY beam

movable frame system

September 2011 ongoing beamtime:I Measurement of ring acceptance


September 2011 ongoing beamtime:II Ring polarization studies


I. Measurement of polarization lifetime: P>105sII. Measurement of spin-flip efficiency: =0.987

Spin-filtering cycle


PolarizationdP/dt 0.18%/h

Cycle

COSY measurement

revtpolpol

revtc0beam

fdQ

1

fd)(

1


To be continued ….

Ferrara - Castello EstenseSebastiano Filippi: “The spinning top game" – XVI cent.

Additional slides


pp interaction models


Nuclear polarization of the hydrogen target determined with the Breit-Rabi polarimeter after opening and closing of the storage cell a few times

Nuclear polarization of the hydrogen target determined with the Breit-Rabi polarimeter after opening and closing of the storage cell a few times

closed open

0penable storage cell•Atomic beam source provides polarized hydrogen target•Storage cell target to reach dt=5x1013 atoms/cm2


Polarisation buildup cross sections

Folie 34


Polarized antiprotons on fixed target

(PAX-Phase I)

EXPERIMENT:Fixed target experiment:

polarized antiprotons protons in CSR (p>200 MeV/c)fixed polarized protons target

P.Lenisa

Documents

dr. Paolo Lenisa Università di Ferrara and INFN – ITALY on behalf of the PAX-Collaboration