May 12, 2009 Paolo Lenisa and Frank Rathmann PAX collaboration

Mitg

lied

der H

elm

holtz

-Gem

eins

chaf

t

Measurement of the Spin-Dependence of the pp Interaction at the AD Ring

Polarizing antiprotons

May 12, 2009 Paolo Lenisa and Frank Rathmann PAX collaboration

New Opportunities in the Physics Landscape at CERN

Polarizing antiprotons 2

Introduction

We have proposed a method to polarize antiprotons by

„spin-filtering“

Frank Rathmann


(How) is it possible to provide polarized antiproton beams

in HESR ?High Energy Storage Ring (HESR)

for a beam of antiprotons

Frank Rathmann

Introduction

New initiative, driven by the FAIR-project at GSI

Polarizing antiprotons 4Frank Rathmann

Physics Case: Transversity distribution of the nucleon in Drell-Yan:

Last leading-twist missing piece of the QCD description of the partonic structure of the nucleon

Direct measurement of h1q

(x,Q2) of the proton for valence quarks (ATT in Drell-Yan >0.2)

transversely polarized proton beam or target () transversely polarized antiproton beam ()

+ other polarization observables in pp

HESRPAX → Polarized Antiprotons

QCD Physics at FAIR employs unpolarized Antiprotons


Plan of talk

Polarizing antiprotons …

Proposals, ideas, calculations, … Experiments

FILTEX (TSR)ep spin flip cross section measurement at COSYSpin-filtering at AD/CERN

Conclusion

Task taken on by the PAX-collaboration: ~100 members, 16 institutions Spokespersons: P. Lenisa (Ferrara), F. Rathmann (Jülich)

Frank Rathmann


Two Methods: Loss versus spin flip

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

Frank Rathmann


Proposed methods: Spin flip

→ Need for an experimental test of this idea!

Frank Rathmann


ep spin flip cross section measurement at COSY

No effect observed: measured cross sections at least 6 orders-of-magnitude smaller than predicted 1013 b.

0

4107

|Relative velocity of electrons in proton rest frame| (c)

dep

ol (b

arn)

Nominal proton energy in electron rest frame (keV)0 1 2 3

0 110-3 210-3 310-3

2107

-2107

-4107

Frank Rathmann

D.Oellers et al., Physics Letters B 674 (2009) 269

Meanwhile, Mainz group discovered numerical problems in the calculation → two errata.


Spin-filtering

Polarization build-up of an initially unpolarized particle beam by repeated passage through a polarized hydrogen target in a storage ring:

Frank Rathmann


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

→ Spin filtering works for protons

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

Frank Rathmann

PAX submitted new proposal to find out how well spin filtering works for antiprotons: Measurement of the Spin-Dependence of the pp Interaction at the AD Ring

(CERN-SPSC-2009-012 / SPSC-P-337)


PAX at the AD (the only place worldwide)

Frank Rathmann

PAX target sectionElectron cooler

Siberian snake


Experimental Setup

Atomic Beam Source

Six additional quadrupolesBreit-Rabi

Polarimeter

Target chamber:Detector system + storage cell


Expected Polarizations after filtering for two lifetimestransverse

A

D

Frank Rathmann

longitudinal

d (mm) Θacc (mrad)

8 8.610 10.812 13.0

• Measurement of the buildup equivalent to the determination of σ1 and σ2 • Once a polarized antiproton beam is available, differential double-spin

observables can be measured (50-500 MeV) → pp potential.• Protonium gave already first information about pp potential at rest.


Time plan (once approved)

Frank Rathmann

Phase Time Description

1 Shutdown 2009/102010

Installation of six magnets for the low-β insertion.Commissioning of the low-β section, carried out parasitically.

2a

2b

Shutdown 2010/112 weeks in 20113 weeks in 2011Shutdown 2011/122 weeks in 2012

Installation of the target chamber. Machine acceptance studies. Stacking studies (split in sessions).Installation of ABS, BRP, and detector system.Measurement of H target polarization with antiproton beam.

3 6 weeks in 2012 Spin-filtering measurements using H and D target up to 70 MeV with transverse beam polarization.

4 Shutdown 2012/13

4 weeks in 2013

Shutdown possibly extended up to six months. Implementation and commissioning of electron cooler upgrade to 300 keV.Commissioning of the electron cooler with beam.

5 6 weeks in 2013 Spin-filtering measurements using H and D target up to 430 MeV with transverse beam polarization.

6 Shutdown 2013/14 Implementation of the Siberian snake.

7 8 weeks in 2014 Spin-filtering measurements with H and D target up to 430 MeV with longitudinal beam polarization.

• PAX ready to set sequence into motion by installing low-β section into the AD end of this year!

Proof of compatibility with the other AD users.


Conclusions

• Clear task • Technically feasible• Expertise and commitment by PAX-collaboration• First measurements/achievements• High discovery potential

Now and here or never!

Frank Rathmann

→


Spare transparencies

Frank Rathmann


18

Expected antiproton beam polarization(in an ideal machine)

• AD machine acceptance: Ax=180 m, Ay=200 m

• Cooled 2 beam emittance = 1 m

• Realistic calculation of acc(mrad) using AD lattice functions and triangular density distribution in storage cell

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

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

Polarizing antiprotonsFrank Rathmann

0 2 4 6 8 100

10

20

Storage cell radius (mm)

Acc

epta

nce

angl

e (m

rad)

8


Beam lifetime

Frank Rathmann

d (mm) Θacc (mrad)

8 8.610 10.812 13.0


Target chamber, cell and detector system

Frank Rathmann

Storage cellSilicon strip detectors

Atomic beam

Stored beam


Phase 1

• Central quadrupole magnet (QDN15) remains in place until compatibility of the AD operation with other users is shown.

Frank Rathmann


Hadron Physics „Dream Machine“ for FAIR:

… an asymmetric (double-polarized) proton (15 GeV/c) – antiproton (3.5 GeV/c) collider

using HESR, CSR and APR

Frank Rathmann


Quark Transversity Distribution in Drell-Yan:

Double transverse spin asymmetry:

llqq *

First direct measurement: No competitive processes

Frank Rathmann


Proposed methods (1): Some history …

EPAC 1988

Stern-Gerlach splitting never tried (huge effort)

Frank Rathmann

Documents

May 12, 2009 Paolo Lenisa and Frank Rathmann PAX collaboration