May 12, 2009 Paolo Lenisa and Frank Rathmann PAX collaboration
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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
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Introduction
We have proposed a method to polarize antiprotons by
„spin-filtering“
Frank Rathmann
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(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
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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
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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
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Two Methods: Loss versus spin flip
For an ensemble of spin ½ particles with projections + () and – ()
Frank Rathmann
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Proposed methods: Spin flip
→ Need for an experimental test of this idea!
Frank Rathmann
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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.
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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
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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)
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PAX at the AD (the only place worldwide)
Frank Rathmann
PAX target sectionElectron cooler
Siberian snake
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Experimental Setup
Atomic Beam Source
Six additional quadrupolesBreit-Rabi
Polarimeter
Target chamber:Detector system + storage cell
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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.
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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.
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Conclusions
• Clear task • Technically feasible• Expertise and commitment by PAX-collaboration• First measurements/achievements• High discovery potential
Now and here or never!
Frank Rathmann
→
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Spare transparencies
Frank Rathmann
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Polarizing antiprotons 17Frank Rathmann
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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
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Beam lifetime
Frank Rathmann
d (mm) Θacc (mrad)
8 8.610 10.812 13.0
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Target chamber, cell and detector system
Frank Rathmann
Storage cellSilicon strip detectors
Atomic beam
Stored beam
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Phase 1
• Central quadrupole magnet (QDN15) remains in place until compatibility of the AD operation with other users is shown.
Frank Rathmann
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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
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Quark Transversity Distribution in Drell-Yan:
Double transverse spin asymmetry:
llqq *
First direct measurement: No competitive processes
Frank Rathmann
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Proposed methods (1): Some history …
EPAC 1988
Stern-Gerlach splitting never tried (huge effort)
Frank Rathmann