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PAX - Istituto Nazionale di Fisica Nucleare

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PAX - Istituto Nazionale di Fisica Nucleare
dr. Paolo Lenisa
Universita’ and INFN - Sezione di Ferrara
PAX
Polarized Antiproton EXperiment
PAX Collaboration
www.fz-juelich.de/ikp/pax
Spokespersons:
Frank Rathmann
Paolo Lenisa
[email protected]
[email protected]
PAX Collaborators
Ma Bo-Qiang
Department of Physics, Beijing, P.R. China
Klaus Goeke, Andreas Metz, and Peter Schweitzer
Institut für Theoretische Physik II, Ruhr Universität Bochum, Germany
Jens Bisplinghoff, Paul-Dieter Eversheim, Frank Hinterberger, Ulf-G. Meißner, and Heiko Rohdjeß
Helmholtz-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 Peshekhonov
Laboratory 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 Statera
Instituto 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
(continued)
Stanislav Belostotski, Oleg Grebenyuk, Kirill Grigoriev, Peter Kravtsov, Anton Izotov, Anton Jgoun,
Sergey Manaenkov, Maxim Mikirtytchiants, Oleg Miklukho, Yuriy Naryshkin, Alexandre Vassiliev, and
Andrey Zhdanov
Petersburg 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 Zavertiaev
Lebedev 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 Tabidze
High 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. Hakopov
Yerevan Physics Institute, Yerevan, Armenia
Outline
• 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
Future Int. Accelerator Facility at GSI
SIS100/300
HESR:
PANDA and PAX
FLAIR:
CR-Complex
NESR
(Facility for very Low energy
Anti-protons and fully
stripped Ions)
The Antiproton Facility
HESR (High Energy Storage Ring)
• Length 442 m
• Bρ = 50 Tm
• N = 5 x 1010 antiprotons
HESR
Antiproton
Production Target
CR
RESR
Super
FRS
NESR
•Antiproton production similar to CERN
•Production rate 107/sec at 30 GeV
•Energy = 1.5 - 15 GeV/c
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
Gas Target and Pellet Target:
cooling power determines thickness
Cooling – e- and/or stochastic
2MV prototype e-cooling at
COSY
The Central Physics Issue
Twist-2 distribution functions
Spin-average
Helicity-difference
Helicity-flip
Status of knowledge
Transversity,
h1
Remains still unmeasured
Poorly modeled
A review in:
Barone, Drago,Ratcliffe,
Phys. Rep. 359 (2002) 1
Well known and well modeled
Known, but poorly modeled
Transversity
Properties:
 Probes relativistic nature of quarks
 No gluon analog for spin-1/2 nucleon
2
 Different Q evolution than  q
 Sensitive to valence quark polarization
Chiral-odd: requires another chiral-odd partner
Transversity in Drell-Yan processes
PAX: Polarized antiproton beam → polarized proton target (both transverse)
l+
l-
q
p

A TT

d  d
 
 â TT

d  d
qT
p
qL
2 q
2
q
2
e
h
(
x
,
M
)
h
(
x
,
M
)
q1 1
1
2
q
 e q( x , M
2
q
1
2
)q ( x 2 , M 2 )
q
Elementary QED process
qq  l  l 
q2=M2
â TT 
sin 
cos 2
2
1  cos 
2
q  u, u, d, d,...
M invariant Mass
of lepton pair
θ: polar angle of lepton
in l+l- rest frame
: azimuthal angle
w.r.t. proton polarization
ATT in the Drell-Yan production at PAX
RHIC: τ=x1x2=M2/s~10-3
→ Exploration of the sea quark content (polarizations small!)
ATT very small (~ 1 %)
PAX: M2~10 GeV2, s~30-50 GeV2, =x1x2=M2/s~0.2-0.3
→ Exploration of valence quarks (h1q(x,Q2) large)
0.3
ATT/aTT > 0.3
Models predict |h1u|>>|h1d|
A TT  â TT
u
1
2
u
1
2
h ( x1 , M ) h ( x1 , M )
u ( x1 , M 2 ) u ( x1 , M 2 )
( where q p  q p  q)
A TT
â TT
0.25
0.15
T=22 GeV
0.15
Main contribution to Drell-Yan events
at PAX from x1~x2~τ
deduction of x-dependence of h1u(x,M2)!
T=15 GeV
Anselmino, Barone, Drago, Nikolaev
(hep-ph/0403114 v1)
0
0.2
0.4
xF=x1-x2
0.6
Single 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
π+
π-
xF
AN 
1
Pbeam
N  N
N  N
Large asymmetries originate
from valence quarks: sign of
AN related to u and d-quark
polarizations
Gauge Link structure: Universality
violation?
Gauge invariant definition of T-odd distribution function in
DIS contains a future pointing Wilson line, whereas in
Drell-Yan (DY) it is past pointing

f1T  P, ST  (0)(0,  )  ( ) P, ST
DIS
DY
f 

1T
DIS
 
  f1T
Collins, PLB 536 (2002) 43

DY
Requires experimental checks
Proton Electromagnetic 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 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 target
The HERMES target
Atomic Beam Source
NIM A 505, (2003) 633
The HERMES target
Atomic Beam Source
NIM A 505, (2003) 633
Pz+ = |1> + |4>
Pz- = |2> + |3>
The HERMES target
Atomic Beam Source
NIM A 505, (2003) 633
Storage cell
NIM A 496, (2003) 277
Diagnostics:
•Target Gas Analyzer
NIM A 508, (2003) 265
•Breit-Rabi Polarimeter
NIM A 482, (2002) 606
Target polarization
PT  a 0a r Pa  a 0 (1  a r ) Pm
•


•
•
PT = total target polarization
a0 =atomic fraction in absence of recombination
ar =atomic fraction surviving recombination
Pa = polarization of atoms
Pm = polarization of recombined molecules
• Relation to measured quantities:
• Sampling corrections
 ar = ca arTGA
• Pa = cP PaBRP
Target performance
Longitudinal Polarization (B=335 mT)
•1996-1997 Hydrogen
•1999-2000 Deuterium
Pt = 0.845 ± 0.028
Target performance
Longitudinal Polarization (B=335 mT)
•1996-1997 Hydrogen
•1999-2000 Deuterium
Pt = 0.845 ± 0.028
Target performance
Tranverse Polarization (B=297 mT)
•2002 - … Hydrogen
PT = 0.795  0.033
Principle of Spin Filter Method
  
 tot   0   1  P  Q   2  P k  Q  k
 0 , if P  k  0
For initially equally populated
spin states:  (m=½)
 (m=-½)
P beampol.
Q targetpol.
k || beam
 tot    0   1  Q
Expectation
For low energy pp scattering:
1<0  tot+<tot-
Target
Beam




Filter Test at TSR with protons
Experimental Setup
Results
T=23 MeV
F. Rathmann. et al.,
PRL 71, 1379 (1993)
Puzzle 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 ± 0.03
dt = (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
Horowitz & Meyer, PRL 72, 3981 (1994)
σE=-70 mb
H.O. Meyer, PRE 50, 1485 (1994)
Spin transfer from electrons to protons


pe  pe
e
2


4
a
1   p m e  2   
1
 2a ln 2pa 0 
 
 C 0    sin 
2

2 
p mp
2
a






Horowitz & Meyer, PRL 72, 3981 (1994)
H.O. Meyer, PRE 50, 1485 (1994)
α
λp=(g-2)/2=1.793
me, mp
p
a0
C02=2πη/[exp(2πη)-1]
η=-zα/ν
v
z
fine structure constant
anomalous magnetic moment
rest masses
cm momentum
Bohr radius
Coulomb wave function
Coulomb parameter (neg. for anti-protons)
relative lab. velocity between p and e
beam charge number
Beam lifetimes in HESR
The lifetime of a stored beam is given by
b 
 max
 1
e4
1
 d 


C   
d




2 4 
2
d  Ruth.
20 m p v  2 acc 2 
 min 
10.89
In order to achieve highest
polarization in the antiproton
beam, acceptance angles
around Ψacc = 10 mrad are
needed.
11
20 mrad
10
9
8
5 mrad
10 mrad
8
7
 T  20 10

beam lifetime [h]
(Target thickness =
dt=5·1014 atoms/cm2)
10
beam lilfetime τb (h)
0   tot (pp)
1
( C   0 )  d t  f
3

6
 T  10 10

3
 T  5 10

3

 T  1 10

3


6
5
4
4
Ψacc = 1 mrad
3
2
2
1
0.214
0
1
400.8
1
400
1200.4
800.6
T
kinetic energy [MeV]
800
1200
1600.2
2000
3
2 10
T (MeV)
Polarization Build-up
Exploit spin transfer process σE
• works also if hadronic polarizing cross sections
σR and σSturn out to be small
N(t)=N0exp(-t/τb)
τb=(fdtσL)-1
I(t)=N(t) f
P(t)=1-exp(-t/τ1)~ σEdtfQt
Optimum filtering time: t=2τb (from d(P2I)/dt=0)
 P(2τb )=2Q (σE/σL)
Estimate for σL from Indiana Cooler
σL=4.75 107 T-2 mb, (Note: σE~T-1)
R.E. Pollock et al.,
NIM A 330, 380 (1993)
Antiproton Polarizer
Expected Buildup
spin-transfer cross section
(electrons to antiprotons)
1 10
181.621
dt=5·1014 atoms/cm2
Pelectron=0.9
8
3
100
10
 etr T 
1
0.07
1
0.1
T=500 MeV
6
0.06
Goal
0.05
P2 t  800
10
Polarization
e (mbarn)
100
antiproton Polarization (%)
0.08
4
P2 t  500
0.04
I t  10 3600
0.03
T=800 MeV
2
0.02
0.01
8
4.72 10
0.022
0.01
1
5
10
1 10
3
100
T
10
100 1000
1 10
4
1 10
1.5 10
5
4
T (MeV)
0
0
2.778 10
5
5
5
10
10
15
15
t
3600
beam lifetime [h]
20
20
25
30
t (h)
30
Polarization Conservation in a Storage Ring
Indiana Cooler
H.O. Meyer et al.,
PRE 56, 3578 (1997)
HESR design must allow for storage of polarized particles!
Spin Manipulation in a Storage Ring
[email protected] (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)%
Polarimetry
Different 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 Concept
Two complementary parts:
Forward detector (±8o acceptance) a la HERMES
•Identify unambiguously leading particles
•Measure precisely their momenta
Central Large Acceptance Detector
• Measure angles and energies of medium energy
electromagnetic particles (Drell-Yan)
Forward Detector
Large Acceptance Detector
Physics 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
1
31
 2 1
L( t  0)   N p  f r  d t  1.5 10 cm s
10
Time-averaged luminosity is about factor 3 lower
• beam loss and duty cycle
Experiments with unpolarized beam
• L factor 10 larger
Count rate estimate
Uncertainty in ATT depends on target and beam polarization ( |P|>0.05, |Q|~0.9)
 A TT
1
22


PQ N
N
Note: Conservative estimate since
hadronic buildup effect might be
large as well
240 days
T = 15 GeV
only nonresonant J/Ψ
contribution
included
T = 22 GeV
Extension of the “safe” region
h1q(x,Q2) not confined to „safe“ region M > 4 GeV!
qq  J / 
qq   *
qq  e  e 
unknown vector coupling,
but same Lorentz
and spinor structure
as 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 ATT
Anselmino, Barone, Drago, Nikolaev
(hep-ph/0403114 v1)
Conclusion
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: h1q (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 antiprotons
Polarization buildup requires large acceptance angle (10 mrad)
Storage cell target requires low-β section
Slow ramping of beam energy needed to optimize pol. build-up
PAX: The next steps
Jan.2004
LOI submitted
Formation 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
Fly UP