may 12, 2009 paolo lenisa and frank rathmann pax collaboration
DESCRIPTION
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. Introduction. - PowerPoint PPT PresentationTRANSCRIPT
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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
Polarizing antiprotons 2
Introduction
We have proposed a method to polarize antiprotons by
„spin-filtering“
Frank Rathmann
Polarizing antiprotons 3
(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
Polarizing antiprotons 5
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
Polarizing antiprotons 7
Proposed methods: Spin flip
→ Need for an experimental test of this idea!
Frank Rathmann
Polarizing antiprotons 8
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.
Polarizing antiprotons 9
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
Polarizing antiprotons 10
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
Polarizing antiprotons 12Frank Rathmann
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
Polarizing antiprotons 17Frank 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
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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
Polarizing antiprotons 22
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
Polarizing antiprotons 24
Proposed methods (1): Some history …
EPAC 1988
Stern-Gerlach splitting never tried (huge effort)
Frank Rathmann