PAX P olarized A ntiproton E X periment

PAXPAX PPolarizedolarized AAntiproton Entiproton EXXperimentperiment

PAX CollaborationPAX Collaborationwww.fz-juelich.de/ikp/pax

Spokespersons:

Frank Rathmann [email protected] Lenisa [email protected]

dr. Paolo Lenisa Universita’ and INFN - Sezione di Ferrara

PAXPAX Collaborators CollaboratorsMa Bo-Qiang

Department of Physics, Beijing, P.R. China

Klaus Goeke, Andreas Metz, and Peter SchweitzerInstitut für Theoretische Physik II, Ruhr Universität Bochum, Germany

Jens Bisplinghoff, Paul-Dieter Eversheim, Frank Hinterberger, Ulf-G. Meißner, and Heiko RohdjeßHelmholtz-Institut für Strahlen- und Kernphysik, Bonn, Germany

Sergey Dymov, Natela Kadagidze, Vladimir Komarov, Anatoly Kulikov, Vladimir Kurbatov, Vladimir Leontiev, Gogi Macharashvili, Sergey Merzliakov, Valerie Serdjuk, Sergey Trusov, Yuri

Uzikov, Alexander Volkov, and Nikolai Zhuravlev Laboratory of Nuclear Problems, Joint Institute for Nuclear Research, Dubna, Russia

Igor Savin, Vasily Krivokhizhin, Alexander Nagaytsev, Gennady Yarygin, Gleb Meshcheryakov, Binur Shaikhatdenov, Oleg Ivanov, Oleg Shevchenko, and Vladimir PeshekhonovLaboratory of Particle Physics, Joint Institute for Nuclear Research, Dubna, Russia

Wolfgang Eyrich, Andro Kacharava, Bernhard Krauss, Albert Lehmann, David Reggiani, Klaus Rith, Ralf Seidel, Erhard Steffens, Friedrich Stinzing, Phil Tait, and Sergey Yaschenko

Physikalisches Institut, Universität Erlangen-Nürnberg, Germany

Guiseppe Ciullo, Marco Contalbrigo, Marco Capiluppi, Paola Ferretti-Dalpiaz, Alessandro Drago, Paolo Lenisa, Michelle Stancari, and Marco StateraInstituto Nationale di Fisica Nucleare, Ferrara, Italy

Nicola Bianchi, Enzo De Sanctis, Pasquale Di Nezza, Delia Hasch, Valeria Muccifora, Karapet Oganessyan, and Patrizia Rossi

Instituto Nationale di Fisica Nucleare, Frascati, Italy

Stanislav Belostotski, Oleg Grebenyuk, Kirill Grigoriev, Peter Kravtsov, Anton Izotov, Anton Jgoun, Sergey Manaenkov, Maxim Mikirtytchiants, Oleg Miklukho, Yuriy Naryshkin, Alexandre

Vassiliev, and Andrey ZhdanovPetersburg Nuclear Physics Institute, Gatchina, Russia

Dirk Ryckbosch Department of Subatomic and Radiation Physics, University of Gent, Belgium

David Chiladze, Ralf Engels, Olaf Felden, Johann Haidenbauer, Christoph Hanhart, Andreas Lehrach, Bernd Lorentz, Nikolai Nikolaev, Siegfried Krewald, Sig Martin, Dieter Prasuhn, Frank

Rathmann, Hellmut Seyfarth, Alexander Sibirtsev, and Hans Ströher Forschungszentrum Jülich, Institut für Kernphysik Jülich, Germany

Ashot Gasparyan, Vera Grishina, and Leonid Kondratyuk Institute for Theoretical and Experimental Physics, Moscow, Russia

Alexandre Bagoulia, Evgeny Devitsin, Valentin Kozlov, Adel Terkulov, and Mikhail ZavertiaevLebedev Physical Institute, Moscow, Russia

N.I. Belikov, B.V. Chuyko, Yu.V. Kharlov, V.A. Korotkov, V.A. Medvedev, A.I. Mysnik, A.F. Prudkoglyad, P.A. Semenov, S.M. Troshin, and M.N. Ukhanov

High Energy Physics Institute, Protvino, Russia

Mikheil Nioradze, and Mirian TabidzeHigh Energy Physics Institute, Tbilisi State University, Tbilisi, Georgia

Mauro Anselmino, Vincenzo Barone, Mariaelena Boglione, and Alexei Prokudin Dipartimento di Fisica Teorica, Universita di Torino and INFN, Torino, Italy

Norayr Akopov, R. Avagyan, A. Avetisyan, S. Taroian, G. Elbakyan, H. Marukyan, and Z. HakopovYerevan Physics Institute, Yerevan, Armenia

(continued)(continued)

OutlineOutline• The Future GSI Facility• Physics Case

– Transversity– SSA– Electromagnetic Form Factors

• Antiproton Polarizer– Polarized Internal Target– Polarization Buildup– Beam lifetimes– Requirements for HESR

• Detector Concept– Forward Spectrometer– Large Acceptance Spectrometer

• Physics Performance• Conclusion

FLAIR:(Facility for very Low

energy Anti-protons and fully stripped Ions)

SIS100/300

HESR: PANDA and PAX

NESRCR-Complex

Future Int. Accelerator Facility at Future Int. Accelerator Facility at GSIGSI

HESR

Antiproton Production

Target

HESR (High Energy Storage Ring)• Length 442 m• Bρ = 50 Tm• N = 5 x 1010 antiprotons

High luminosity mode• Luminosity = 2 x 1032 cm-2s-1

• Δp/p ~ 10-4 (stochastic-cooling)

High resolution mode• Δp/p ~ 10-5 (8 MV HE e-cooling)• Luminosity = 1031 cm-2s-1

The Antiproton The Antiproton FacilityFacility

•Antiproton production similar to CERN •Production rate 107/sec at 30 GeV•Energy = 1.5 - 15 GeV/c

Gas Target and Pellet Target: cooling power determines thickness

SuperFRS

NESR

CRRESR

Cooling – e- and/or stochastic2MV prototype e-cooling at COSY

Spin-average

Helicity-difference

Twist-2 distribution functions

The Central Physics IssueThe Central Physics Issue

Helicity-flip

Status of knowledge Status of knowledge

Well known and well modeledKnown, but poorly modeled

Remains still unmeasured

Poorly modeled

Remains still unmeasured

Poorly modeled

Transversity, 1h

A review in:

Barone, Drago,Ratcliffe, Phys. Rep. 359 (2002) 1

TransversityTransversity

Chiral-odd: requires another chiral-odd partner

2Q

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

PropertiesProperties::

q

Transversity in Drell-Yan processesTransversity in Drell-Yan processes

p pqL

q

l+

l-q2=M2

qT

PAX: Polarized antiproton beam → polarized proton target (both transverse)

)M,x(q)M,x(qe

)M,x(h)M,x(he

add

ddA

22

q

21

2q

22

q1

q

21

q1

2q

TTTT

,...d,d,u,uq

M invariant Massof lepton pair

Elementary QED process

llqq

2cos

cos1

sina

2

2

TT

θ: polar angle of lepton in l+l- rest frame: azimuthal angle w.r.t. proton polarization

PAX: M2~10 GeV2, s~30-50 GeV2, τ=x1x2=M2/s~0.2-0.3

→ Exploration of valence quarks (h1q(x,Q2) large)

AATTTT in the Drell-Yan production at in the Drell-Yan production at PAXPAX

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

ATT/aTT > 0.3Models predict |h1

u|>>|h1d|

)M,x(u)M,x(u

)M,x(h)M,x(haA

21

21

21

u1

21

u1

TTTT

)qqqwhere( pp

Main contribution to Drell-Yan events at PAX from x1~x2~τ deduction of x-dependence of h1

u(x,M2)! xF=x1-x2

0 0.2 0.4 0.6

0.15

0.15

0.25TT

TT

a

A

Anselmino, Barone, Drago, Nikolaev(hep-ph/0403114 v1)

T=22 GeV

T=15 GeV

0.3

Single Spin AsymmetriesSingle Spin Asymmetries

Several experiments have observed unexpectedly large single spin asymmetries in pbar-p at large values of xF ≥

0.4 and moderate values of pT (0.7 < pT < 2.0 GeV/c)

E704 Tevatron FNAL 200GeV/c

xF

NN

NN

P

1A

beamN

π+

π-

Large asymmetries originate from valence quarks: sign of AN related to u and d-quark polarizations

Gauge Link structure: Gauge Link structure: Universality violation? Universality violation?

TTT SPSPf ,)(),0()0(,1 TTT SPSPf ,)(),0()0(,1

DYTDIST ff 11 DYTDIST ff 11

Gauge invariant definition of T-odd distribution function in DIS contains a future pointing Wilson line, whereas inDrell-Yan (DY) it is past pointing

DIS DY

Requires experimental checksCollins, PLB 536 (2002) 43

Proton Electromagnetic Proton Electromagnetic Formfactors Formfactors

• Measurement of relative phases of magnetic and electric FF in the time-like region– Possible only via SSA in the annihilation pp → e+e-

• Double-spin asymmetry– independent GE-Gm separation– test of Rosenbluth separation in the time-like

region

Polarized internal targetPolarized internal target

Interaction Region

point-like 5-10 mm free jet low density 1012 cm-2

extended 200-500 mm storage cell high density 1014 cm-2

Example: The HERMES targetExample: The HERMES target

Atomic Beam SourceNIM A 505, (2003) 633

The HERMES targetThe HERMES target



Pz+ = |1> + |4>

Pz- = |2> + |3>



Storage cellNIM A 496, (2003) 277

Diagnostics:

•Target Gas AnalyzerNIM A 508, (2003) 265

•Breit-Rabi Polarimeter

NIM A 482, (2002) 606

Target polarizationTarget polarization

• PT = total target polarization 0 =atomic fraction in absence of

recombination r =atomic fraction surviving recombination• Pa = polarization of atoms• Pm = polarization of recombined molecules

mrarT PPP )1(00

• Relation to measured quantities:• Sampling corrections

r = c rTGA

•Pa = cP PaBRP

Target performanceTarget performance

Longitudinal Polarization (B=335 mT)

•1996-1997 Hydrogen

•1999-2000 Deuterium

Pt = 0.845 ± 0.028


Longitudinal Polarization (B=335 mT)

•1996-1997 Hydrogen

•1999-2000 Deuterium

Pt = 0.845 ± 0.028


Tranverse Polarization (B=297 mT)

•2002 - … Hydrogen

PT = 0.795 0.033

Principle of Spin Filter MethodPrinciple of Spin Filter Method

For low energy pp scattering:

1<0 tot+<tot-

Expectation

Target Beam

For initially equally populated spin states: (m=½)

(m=-½)Q10tot

0kPif,0

210tot kQkPQP

P beampol.Q targetpol.k || beam

Filter Test at TSR with protonsFilter Test at TSR with protons

Experimental SetupExperimental Setup ResultsResults

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

T=23 MeV

Puzzle from FILTEX TestPuzzle from FILTEX Test

Observed polarization build-up: dP/dt = ± (1.24 ± 0.06) x 10-2 h-1

Expected build-up: P(t)=tanh(t/τ1),

1/τ1=σ1Qdtf=2.4x10-2 h-1

about factor 2 larger!

σ1 = 122 mb (pp phase shifts)Q = 0.83 ± 0.03dt = (5.6 ± 0.3) x 1013cm-2

f = 1.177 MHz

Three distinct effects:

1. Selective removal through scattering beyond θacc=4.4 mrad σR=83 mb

2. Small angle scattering of target protons into ring acceptance σS=52 mb

3. Spin transfer from polarized electrons of the target atoms to the stored protons

σE=-70 mb Horowitz & Meyer, PRL 72, 3981 (1994)

H.O. Meyer, PRE 50, 1485 (1994)

Spin transfer from electrons to Spin transfer from electrons to protonsprotons

epep

020

p2

ep2

e

pa2ln2sin

2C

mp

m14

2

1

Horowitz & Meyer, PRL 72, 3981 (1994)

H.O. Meyer, PRE 50, 1485 (1994)

α fine structure constantλp=(g-2)/2=1.793 anomalous magnetic momentme, mp rest massesp cm momentuma0 Bohr radiusC0

2=2πη/[exp(2πη)-1] Coulomb wave functionη=-zα/ν Coulomb parameter (neg. for anti-protons)v relative lab. velocity between p and ez beam charge number

Beam lifetimes in HESRBeam lifetimes in HESR

The lifetime of a stored beam is given byfd)(

1

t0Cb τ

2

1

2

1

vm2

ed

d

d2acc

42p0

4

.RuthC

max

min

)pp(tot0

(Target thickness =dt=5·1014 atoms/cm2)

1 400.8 800.6 1200.4 1600.2 20000

1

2

3

4

5

6

7

8

9

10

11

kinetic energy [MeV]

beam

lif

etim

e [h

]

10.89

0.214

τ T 20 103

τ T 10 103

τ T 5 103

τ T 1 103

2 1031 T

400 800 1200 T (MeV)

2

4

6

8be

am li

lfetim

e τ b

(h)

Ψacc = 1 mrad

5 mrad10 mrad

10 20 mrad

In order to achieve highest polarization in the antiproton beam, acceptance angles around Ψacc = 10 mrad are needed.

Polarization Build-upPolarization Build-up

Exploit spin transfer process σE

• works also if hadronic polarizing cross sections σR and σSturn out to be small

N(t)=N0exp(-t/τb) τb=(fdtσL)-1 I(t)=N(t) f

P(t)=1-exp(-t/τ1)~ σEdtfQt

Optimum filtering time: t=2τb (from d(P2I)/dt=0)

P(2τb )=2Q (σE/σL)

Estimate for σL from Indiana CoolerσL=4.75 107 T-2 mb , (Note: σE~T-1)

R.E. Pollock et al., NIM A 330, 380 (1993)

Antiproton PolarizerAntiproton Polarizer

spin-transfer cross section(electrons to antiprotons)

1 10 100 1 103

1 104

1 105

0.01

0.1

1

10

100

1 103

181.621

0.022

etr T

1.5 1045 T

10 100 1000 T (MeV)

e

(mba

rn)

100

10

1

0 5 10 15 20 25 300

0.01

0.02

0.03

0.04

0.05

0.06

0.07

beam lifetime [h]

Pol

ariz

atio

n

0.08

4.72 108

P2 t 800

P2 t 500

I t 10 3600

302.778 105 t

3600

antip

roto

n P

olar

izat

ion

(%)

Expected Buildup

t (h)5 10 15 20

8

6

4

2

T=500 MeV

T=800 MeV

dt=5·1014 atoms/cm2

Pelectron=0.9

Goal

Polarization Conservation in a Polarization Conservation in a Storage RingStorage Ring

HESR design must allow for storage of polarized particles!

Indiana CoolerH.O. Meyer et al., PRE 56, 3578 (1997)

Spin Manipulation in a Storage Spin Manipulation in a Storage RingRing

SPIN@COSY (A. Krisch et. al)– Frequent spin-flips reduce systematic errors– Spin-Flipping of protons and deuterons by artifical

resonance •RF-Dipole

– Applicable at High Energy Storage Rings (RHIC, HESR)

Stored protons:P(n)=Pi()n

=(99.3±0.1)%

PolarimetryPolarimetryDifferent schemes to determine target and beam polariz.

1. Suitable target polarimeter (Breit-Rabi or Lamb-Shift) to measure target polarization

2. At lower energies (500-800 MeV) analyzing power data from PS172 are available.

Therefrom a suitable detector asymmetry can be calibrated→ effective analyzing power

•Beam and target analyzing powers are identical• measure beam polarization using an unpolarized

target•Export of beam polarization to other energies

• target polarization is independent of beam energy

Detector ConceptDetector Concept

Two complementary parts:

Central Large Acceptance Detector• Measure angles and energies of medium

energy electromagnetic particles (Drell-Yan)

Forward detector (±8o acceptance) a la HERMES

•Identify unambiguously leading particles•Measure precisely their momenta

Forward DetectorForward Detector

Large Acceptance DetectorLarge Acceptance Detector

Physics PerformancePhysics Performance

• Luminosity– Spin-filtering for two beam lifetimes: P > 5%

– N(pbar) = 5·1011 at fr~6·105 s-1

– dt = 5·1014 cm-2

1231trp scm105.1dfN

10

1)0t(L

Time-averaged luminosity is about factor 3 lower • beam loss and duty cycle

Experiments with unpolarized beam• L factor 10 larger

Count rate estimateCount rate estimateUncertainty in ATT depends on target and beam polarization ( |P|>0.05, |Q|~0.9)

N

22

NQP

1TTA

Note: Conservative estimate

since hadronic buildup effect might be large as well

only non-resonant J/Ψ contribution

included

T = 15 GeV

T = 22 GeV

240 days

Extension of the “safe” regionExtension of the “safe” regionh1

q(x,Q2) not confined to „safe“ region M > 4 GeV!

eeqq

*qq

/Jqq unknown vector coupling, but same Lorentzand spinor structureas other two processes

Unknown quantities cancel in the ratios for ATT, but helicity structure remains!

Cross section increases by two orders from M=4 to M=3 GeV

→ Drell-Yan continuum enhances sensitivity of PAX to ATTAnselmino, Barone, Drago, Nikolaev(hep-ph/0403114 v1)

ConclusionConclusion

Challenging opportunities and new physics accessible with PAX at HESR– unique access to a wealth of new fundamental physics observables – polarized antiprotons (P>5%)– Central physics issue: h1

q (x,Q2) of the proton in DY processes

– Other issues:• Electromagnetic Formfactors• Polarization effects in Hard and Soft Scattering processes

– differential cross sections, analyzing powers, spin correlation parameters

Machine design (more beam!)Need separate target station HESR must be capable to store polarized antiprotonsPolarization buildup requires large acceptance angle (10 mrad)Storage cell target requires low-low-ββ section sectionSlow ramping of beam energy needed to optimize pol. build-up

PAX: The next stepsPAX: The next steps

Jan.2004 LOI submittedFormation of an advisory committee at GSI

Apr.-May 2004 Evaluation of LOI’s

(If approved)

15.12.2004 Techn. Report (with Milesones)

Evaluations & Green Light for Construction

2005-2008 Technical Design Reports (for Milestones)

2012 Commissioning of HESR

Documents

PAX P olarized A ntiproton E X periment