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The PAX ProjectSpin Physics at GSI
Polarized Antiproton Experiments www.fz-juelich.de
/ikp/pax
Spokespersons Spokespersons Spokespersons
Paolo Lenisa Ferrara University lenisa_at_mail.desy.de
Frank Rathmann FZ-Jülich f.rathmann_at_fz-juelich.de
2
Central Physics Issue

• Transversity distribution of the nucleon
• last leading-twist missing piece of the QCD
  description of the partonic structure of the
  nucleon
• directly accessible uniquely via the double
  transverse spin asymmetry ATT in the Drell-Yan
  production of lepton pairs
• theoretical expectations for ATT in DY, 30-40
• transversely polarized antiprotons
• transversely polarized proton target
• definitive observation of h1q (x,Q2) of the
  proton for the valence quarks

3
Leading Twist Distribution Functions
Probabilistic interpretation in helicity base

f1(x)
q(x) spin averaged (well known)
-
Dq(x) helicity diff. (known)
g1(x)
No probabilistic interpretation in the helicity
base (off diagonal)
h1(x)
u? 1/?2(uR uL) u? 1/?2(uR - uL)
Transversity base
dq(x) helicity flip (unknown)
4
Evaluation by QCD Program Advisory Committee
(July 2004)

• STI Report
• Your LoI has convinced the QCD-PAC
• that Polarization must be included into the
  design of FAIR from the beginning, and
• that the presently proposed scheme is not
  optimized as to the physics. You are invited
  and encouraged to design a world-class facility
  with unequalled degree of polarization of
  antiprotons.
• Common Report
• The PAC considers the spin physics of extreme
  interest and the building of an antiproton
  polarized beam as a unique possibility for the
  FAIR Project.
• The unique physics opportunities, made
  possible with polarized antiproton beams and/or
  polarized target are extremely exciting,
  especially in double spin measurements.
• It would be very unfortunate if decisions
  about the facility, made now, later preclude the
  science.

5
Exploitation of Spin Transfer
PAX will employ spin-transfer from polarized
electrons of the target to antiprotons
(QED Process calculable)
Hydrogen gas target ?? in strong field (300 mT)
Pe0.993 Pz0.007
6
Antiproton Beam Polarization
Buildup in HESR (800 MeV)
F. Rathmann et al., PRL 94, 014801 (2005)
7
Transversity in Drell-Yan processes
Polarized Antiproton Beam ? Polarized Proton
Target (both transversely polarized)
l
Q2M2
l-
Q
QT
p
p
QL
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ATT for PAX kinematic conditions
RHIC tx1x2M2/s10-3 ? Exploration of the sea
quark content (polarizations small!) ATT very
small ( 1 )
PAX M210 GeV2, s30-50 GeV2, tx1x2M2/s0.2-0.3
? Exploration of valence quarks (h1q(x,Q2) large)
0.3
ATT/aTT gt 0.3 Models predict h1ugtgth1d
0.25
0.15
T15 GeV (?s5.7 GeV)
T22 GeV (?s6.7 GeV)
0.10
Anselmino et al. PLB 594,97 (2004)
Main contribution to Drell-Yan events at PAX
from x1x2?t deduction of x-dependence of
h1u(x,M2)
0
0.4
0.6
0.2
xFx1-x2
xFx1-x2
Similar predictions by Efremov et al., Eur.
Phys. J. C35, 207 (2004)
9
Towards an Asymmetric Polarized Hadron Collider

• CSR (COSY-like) at FAIR (3.5 GeV/c)
• Formfactor measurement pp? ? ee-
• unpolarized antiproton beam on polarized internal
  target
• CSR AP p?p? elastic
• Asymmetric Collider p?p? 3.5 GeV/c protons
  15 GeV/c antiprotons (also fixed target
  experiment possible)

10
Towards an Asymmetric Polarized Hadron Collider

• CSR at FAIR (3.5 GeV/c)
• Formfactor measurement pp? ? ee-
• unpolarized antiproton beam on polarized internal
  target
• CSR AP p?p? elastic
• Asymmetric Collider p?p? 3.5 GeV/c protons
  15 GeV/c antiprotons (also fixed target
  experiment possible)

11
Towards an Asymmetric Polarized Hadron Collider

• CSR at FAIR (3.5 GeV/c)
• Formfactor measurement pp? ? ee-
• unpolarized antiproton beam on polarized internal
  target
• CSR AP p?p? elastic
• Asymmetric Collider p?p? 3.5 GeV/c protons 15
  GeV/c antiprotons(also fixed target experiments
  possible)

12
ATT for PAX kinematic conditionsFixed Target vs
Collider
22 GeV/c fixed target
22 GeV/c
153.5 collider
153.5
15 15 collider
Anselmino et al. PLB 594,97 (2004)
Similar predictions by Efremov et al., Eur. Phys.
J. C35, 207 (2004)

• Collider Options for Transversity measurement
• 15 GeV/c 15 GeV/c ? s1000 GeV2, too high
• 15 GeV/c 3.5 GeV/c ? s220 GeV2, ideal

13
Conceptual Detector Design
3 m
14
Time schedule

• Jan. 04 LOI submitted
• 15.06.04 QCD PAC meeting at GSI
• 18-19.08.04 Workshop on polarized antiprotons at
  GSI
• 15.09.04 Additional PAX document on Polarization
  at GSI
• F. Rathmann et al., PRL 94, 014801 (2005)
• 15.11.04 Additional PAX document Number of IPs
  at HESR
• 21.12.04 Additional PAX document Asymmetric
  Collider
• 15.01.05 Technical Report (with Milestones)
• Design and Construction of APR at IKP of FZJ
• . . . . .
• Evaluations Green Light for Construction
• 2005-2008 Technical Design Reports (for
  Milestones)
• gt2012 Commissioning of HESR

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Conclusion

• Challenging opportunities and new physics
  accessible at HESR
• Unique access to a wealth of new fundamental
  physics observables
• 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
• Asymmetric Collider
• 15 GeV/c 3.5 GeV/c
• ideal conditions for Transversity measurements
• Calculation of Intrabeam and Beam-Beam Scattering
  (Meshkov/Sidorin using BETACOOL)
• Projections for HESR fed by a dedicated AP
• Pbeam gt 0.30
• 5.61010 polarized antiprotons
• Luminosity Fixed target L ? 2.7 1031 cm-2s-1
• Collider L ? 1030 cm-2s-1
  (first estimate)

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170 PAX Collaborators, 34 Institutions (17
inside, 17 outside EU)
Yerevan Physics Institute, Yerevan,
Armenia Department of Subatomic and Radiation
Physics, University of Gent, Belgium University
of Science Technology of China, Beijing, P.R.
China Department of Physics, Beijing, P.R.
China Centre de Physique Theorique, Ecole
Polytechnique, Palaiseau, France High Energy
Physics Institute, Tbilisi State University,
Tbilisi, Georgia Nuclear Physics Department,
Tbilisi State University, Tbilisi,
Georgia Forschungszentrum Jülich, Institut für
Kernphysik Jülich, Germany Institut für
Theoretische Physik II, Ruhr Universität Bochum,
Germany Helmholtz-Institut für Strahlen- und
Kernphysik, Bonn, Germany Physikalisches
Institut, Universität Erlangen-Nürnberg,
Germany Unternehmensberatung und Service Büro
(USB), Gerlinde Schulteis Partner GbR,
Langenbernsdorf, Germany Department of
Mathematics, University of Dublin, Dublin,
Ireland University del Piemonte Orientale and
INFN, Alessandria, Italy Dipartimento di Fisica,
Universita di Cagliari and INFN, Cagliari,
Italy Instituto Nationale di Fisica Nucleare,
Ferrara, Italy Dipartimento di Fisica Teorica,
Universita di Torino and INFN, Torino,
Italy Instituto Nationale di Fisica Nucleare,
Frascati, Italy Dipartimento di Fisica,
Universita di Lecce and INFN, Lecce, Italy Soltan
Institute for Nuclear Studies, Warsaw,
Poland Petersburg Nuclear Physics Institute,
Gatchina, Russia Institute for Theoretical and
Experimental Physics, Moscow, Russia Lebedev
Physical Institute, Moscow, Russia Bogoliubov
Laboratory of Theoretical Physics, Joint
Institute for Nuclear Research, Dubna,
Russia Dzhelepov Laboratory of Nuclear Problems,
Joint Institute for Nuclear Research, Dubna,
Russia Laboratory of Particle Physics, Joint
Institute for Nuclear Research, Dubna,
Russia Budker Institute for Nuclear Physics,
Novosibirsk, Russia High Energy Physics
Institute, Protvino, Russia Institute of
Experimental Physics, Slovak Academy of Sciences
and P.J. Safarik University, Faculty of Science,
Kosice, Slovakia Department of Radiation
Sciences, Nuclear Physics Division, Uppsala
University, Uppsala, Sweden Collider Accelerator
Department, Brookhaven National Laboratory,
USA RIKEN BNL Research Center, Brookhaven
National Laboratory, USA University of Wisconsin,
Madison, USA Department of Physics, University of
Virginia, Virginia, USA
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Outline

• WHY? Physics Case
• HOW? Polarized Antiprotons
• WHERE? FAIR Project at Darmstadt
• WHAT? Transversity Measurement
• WHEN? Time Schedule
• Conclusion

19
Transversity
Properties

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

Chiral-odd requires another chiral-odd partner
ep??eh?X
p?p??ll-X
Indirect Measurement Convolution with unknown
fragment. fct.
Impossible in DIS
Direct Measurement
20
Other Physics Topics

• Single-Spin Asymmetries
• Electromagnetic Form Factors
• Hard Scattering Effects
• Soft Scattering
• Low-t Physics
• Total Cross Section
• pbar-p interaction

21
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 ?
  ee-
• Double-spin asymmetry
• independent GE-Gm separation
• test of Rosenbluth separation in the time-like
  region

S. Brodsky et al., Phys. Rev. D69 (2004)
22
Study onset of Perturbative QCD
p (GeV/c)

• High Energy
• small t Reggeon Exchange
• large t perturbative QCD

• Pure Meson Land
• Meson exchange
• ? excitation
• NN potential models

• Transition Region
• Uncharted Territory
• Huge Spin-Effects in pp elastic scattering
• large t non- and perturbative QCD

23
pp elastic scattering from ZGS
Spin-dependence at large-P? (90cm) Hard
scattering takes place only with spins ??.
T10.85 GeV
Similar studies in pp elastic scattering at PAX
D.G. Crabb et al., PRL 41, 1257 (1978)
24
Outline

• WHY? Physics Case
• HOW? Polarized Antiprotons
• WHERE? FAIR Project at Darmstadt
• WHAT? Transversity Measurements
• WHEN? Time Schedule
• Conclusion

25
Spin Filter Method
P beam polarization Q target polarization k
beam direction
stot s0 s?PQ s(Pk)(Qk)
Time dependence of P and I
26
Polarization Buildup Optimum Interaction Time
statistical error of a double polarization
observable (ATT)
Measuring time t to achieve a certain error dATT
FOM P2I
(N I)
Optimimum time for Polarization Buildup given by
maximum of FOM(t) tfilter 2tbeam
27
Experimental Results from Filter Test
Results
Experimental Setup
T23 MeV
F. Rathmann. et al., PRL 71, 1379 (1993)
Expectation Expectation
Target Beam
? ?
? ?
Low energy pp scattering ?1lt0 ? ?totlt?tot-
28
1992 Filter Test at HD-TSR with protons
29
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/tpol),
1/tpols1Qdtf2.4x10-2 h-1 ? about factor 2
larger!
s1 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
• Selective removal through scattering beyond
  ?acc4.4 mrad sR?83 mb
• Small angle scattering of target protons into
  ring acceptance sS?52 mb
• Spin transfer from polarized electrons of the
  target atoms to the stored protons
• sEM?70 mb (-)

Horowitz Meyer, PRL 72, 3981 (1994) H.O. Meyer,
PRE 50, 1485 (1994)
30
Spin Transfer from Electrons to Protons
Horowitz Meyer, PRL 72, 3981 (1994) H.O. Meyer,
PRE 50, 1485 (1994)
a fine structure constant ?p(g-2)/21.793 ano
malous magnetic moment me, mp rest
masses p cm momentum a0 Bohr
radius C022p?/exp(2p?)-1 Coulomb wave
function ?za/? Coulomb parameter (negative for
antiprotons) v relative lab. velocity between p
and e z beam charge number
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Dedicated Antiproton Polarizer (AP)
Injection
Siberian Snake
HESR
AP
440 m
e-cooler
e-cooler
Internal Experiment
150 m
Extraction
ABS

Polarization Buildup in AP parallel to
measurement in HESR
Polarizer Target
F. Rathmann et al., PRL 94, 014801 (2005)
db?accß2?dtdt(?acc) lb40 cm (2ß) df1 cm,
lf15 cm
ß0.2 m q1.51017 s-1 T100 K Longitudinal Q
(300 mT)
32
Beam lifetimes in the AP
Beam Lifetime
Coulomb Loss
Total Hadronic
33
Optimum Beam Energies for Buildup in AP
Maximum FOM Maximum FOM Maximum FOM Maximum FOM
?acc (mrad) ?beam (h) P(2tbeam) T (MeV)
10 1.2 0.19 163
20 2.2 0.29 88
30 4.6 0.35 61
40 9.2 0.39 47
50 16.7 0.42 38
?acc 50 mrad
FOM
AP Space charge limit
15
40 mrad
10
30 mrad
5
20 mrad
10 mrad
T (MeV)
10
100
1
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Space-Charge Limitation in the AP
Before filtering starts Nreal 107 s-1 2tbeam
Nind.
1013
1012
1011
?acc 50 mrad
40 mrad
1010
30 mrad
Nreal
20 mrad
10 mrad
109
10 mrad
10
T (MeV)
100
1
35
Transfer from AP to HESR and Accumulation
Injection
Siberian Snake
HESR
AP
440 m
e-cooler
e-cooler
Internal Experiment
150 m
Extraction
ABS
COSY

Polarizer Target
36
Accumulation of Polarized Beam in HESR
PIT dt7.21014 atoms/cm2 tHESR11.5 h
Number accumulated in equilibrium independent of
acceptance
Npbar
No Depolarization in HESR during energy change
37
How about a Pure Polarized Electron Target?
Maxiumum sEM for electrons at rest (675 mb
,Topt 6.2 MeV) Gainfactor 15 over atomic e-
in a PIT

• Density of an Electron-Cooler fed by 1 mA DC
  polarized electrons
• Ie6.21015 e/s
• A1 cm2
• l5 m
• dt Iel(ßcA)-1 5.2108 cm-2

• Electron target density by factor 106 smaller,
• no match for a PIT (gt1014 cm-2)

38
Performance of Polarized Internal Targets
HERMES Stored Positrons
PINTEX Stored Protons
H
Fast reorientation in a weak field (x,y,z)
Transverse Field (B297 mT)
Targets work very reliably (many months of stable
operation)
39
Outline

• WHY? Physics Case
• HOW? Polarized Antiprotons
• WHERE? FAIR Project at Darmstadt
• WHAT? Transversity Measurement
• WHEN? Time Schedule
• Conclusion

40

• NEW Facility
• An International Accelerator Facility for Beams
  of Ions and Antiprotons
• Top priority of German hadron and nuclear physics
  community (KHuK-report of 9/2002) and NuPECC
• Favourable evaluation by highest German science
• committee (Wissenschaftsrat in 2002)
• Funding decision from German government in
• 2/2003 staging and at least 25 foreign
  funding
• to be build at GSI Darmstadt
• should be finished in gt 2011 (depending
  on start)
• FAIR
• (Facility for Antiproton and Ion Research)

41

• FAIR Prospects and Challenges
• FAIR is a facility, which will serve a large part
  of the nuclear physics community (and beyond)
• Nuclear structure ?? Radioactive beams
• Dense Matter ?? Relativistic ion beams
• Hadronic Matter ?? Antiprotons, (polarized)
• Atomic physics
• Plasma physics
• FAIR will need a significant fraction of the
  available man-power and money in the years to
  come
• 1 G ?? 10 000 man-years 100 man for 100
  years
• or (1000 x 10)

42
Facilty for Antiproton and Ion Research (GSI,
Darmstadt, Germany)

• Proton linac (injector)
• 2 synchrotons (30 GeV p)
• A number of storage rings
• ? Parallel beams operation

43
The FAIR project at GSI
SIS100/300
50 MeV Proton Linac
HESR High Energy Storage Ring PANDA (and PAX)
CR-Complex
FLAIR (Facility for very Low energy Anti-protons
and fully stripped Ions)
NESR
44
The Antiproton Facility

• HESR (High Energy Storage Ring)
• Length 442 m
• B? 50 Tm
• N 5 x 1010 antiprotons
• High luminosity mode
• Luminosity 2 x 1032 cm-2s-1
• ?p/p 10-4 (stochastic-cooling)
• High resolution mode
• ?p/p 10-5 (8 MV HE e-cooling)
• Luminosity 1031 cm-2s-1

SIS100/300
HESR
Super FRS
CR
Gas Target and Pellet Target cooling power
determines thickness
NESR
Antiproton Production Target
Beam Cooling e- and/or stochastic 2MV prototype
e-cooling at COSY

• Antiproton production similar to CERN
• Production rate 107/sec at 30 GeV
• T 1.5 - 15 GeV/c (22 GeV)

45
LoIs for Spin Physics at FAIR
SIS100/300
External ASSIA Extracted beam on PET
(Compass-like)
Internal PAX in HESR Polarized antiprotons PIT
46
The New Polarization Facility
HESR
APCOSY

• Conceptual Design Report for FAIR did not include
  Spin Physics
• Jan. 04 2 Letters of Intent for Spin Physics
• ASSIA (R. Bertini)
• PAX (P. Lenisa, FR)

47
Outline

• WHY? Physics Case
• HOW? Polarized Antiprotons
• WHERE? FAIR Project at Darmstadt
• WHAT? Transversity Measurement at PAX
• WHEN? Time Schedule
• Conclusion

48
Transversity in Drell-Yan processes at PAX
Polarized Antiproton Beam ? Polarized Proton
Target (both transversely polarized)
l
Q2M2
l-
Q
QT
p
p
QL
49
Estimated Luminosity for Double Polarization
Polarized Internal Target in HESR
In equilibrium
Qtarget 0.85 Pbeam 0.3 stot(15 GeV) 50 mb
(factor gt70 in measuring time for ATT with
respect to beam extracted on solid target)
50
Signal Estimate
Polarized Antiproton Beam ? Polarized Proton
Target (both transversely polarized)
2) Angular distribution of the asymmetry.
51
ATT asymmetry angular distribution

• Asymmetry is largest for angles 90
• Asymmetry varies like cos(2f).

Needs a large acceptance detector (LAD)
52
Detector Requirements

• Drell-Yan process requires a large acceptance
  detector
• Good hadron rejection needed
• 102 at trigger level, 104 after data analysis for
  single track
• Magnetic field
• Increased invariant mass resolution compared to
  calorimeter
• Improved PID through Energy/momentum ratio
• Separation of wrong charge combinatorial
  background
• Toroidal Field
• Zero field on axis compatible with polarized
  target

53
Expected precision of the h1 measurement
One year of data taking at 50 efficiency (180
days), ATT/aTT 0.3
Fixed Target 2.7?1031 cm-2s-1
Collider mode 5?1030 cm-2s-1
54
Extension of the safe region
Determination of h1q(x,Q2) not confined to the
safe region (M gt 4 GeV)
Anselmino et al. PLB 594,97 (2004)
Efremov et al., Eur.Phys.J. C35,207 (2004)
Cross section increases by two orders from M4 to
M3 GeV ? Drell-Yan continuum enhances
sensitivity of PAX to ATT
55
Outline

• WHY? Physics Case
• HOW? Polarized Antiprotons
• WHERE? FAIR Project at Darmstadt
• WHAT? Transversity Measurement
• WHEN? Time Schedule
• Conclusion

56
Final Remark
Polarization data has often been the graveyard of
fashionable theories. If theorists had their way,
they might just ban such measurements altogether
out of self-protection.
J.D. Bjorken St. Croix, 1987
57
Measurements at COSYElectron-Proton
Spin-Transfer

• 2005 Verification of sEM? at 40, 70 and 100 MeV
  using PIT at ANKE No additional equipment
  needed.
• weak transverse target guide field (10 G) QeQp
• Qp pp elastic using Spectator system
• electron cooling at injection, ANKE at 0
• gt2006 Direct measurement of sEM using
  HERMES-like PIT at TP1
• strong longitudinal target guide field (3 kG)
• needs measurement of Qe
• Snake in Cooler Telescope (Cooler Sol. WASA
  Sol.)
• adiabatically switched off after filtering
• Qp pp elastic using Spectator system

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Preliminary PYTHIA result (2109 events)

• Background higher for m than for e

• Background from charge conjugated mesons
  negligible for e.

60
Methods for Polarization Preservation

• lt 5 GeV conventional methods
• ? correcting dipoles ? tune jump
  quadrupoles
• ? Siberian snake (solenoid)
• 5 - 20 GeV adiabatic methods
• ? partial snake (helical dipole or solenoid)
  ? ac dipole
• gt 20 GeV Siberian snake concept
• ? Siberian snakes (helical dipole)

61
Depolarizing Resonances in the HESR
...
Resonance strength 10-6 - 10-2
Qy 8.14
62
Polarization Preservation at FAIR
AP ? 1 Tm solenoid COSY handled
already HESR ? 4 helical dipoles (2.5 Tesla)
15 Tm solenoid Other
Equipment several polarimeters 1 spin flipper
for HESR (AC dipole)
63
Siberian Snake for HESR
Helical snake
Helical solenoidal snake
? 4 helical dipoles (2.5 Tesla) and a 15 Tm
solenoid
64
Magnetic Field, Orbit and Spin
Solenoid
Helical dipoles
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66
HESR Accelerator Complex with Polarized
Antiprotons
Polarimeter
antiprotons
protons
Snake
(Spin-gymnastics)
HESR 1.5-15 GeV/c
COSY-Booster
AP
30 MeV Linac
Natural extension 15 GeV 15 GeV pbarp Collider
67
Double Polarization Experiments ? Azimuthal
Symmetry
Possible solution Toroid (6 superconducting
coils)

• 800 x 600 mm coils
• 3 x 50 mm section (1450 A/mm2)
• average integrated field 0.6 Tm
• free acceptance gt 80

Superconducting target field coils do not affect
azimuthal acceptance.
(8 coil system under study)
68
Background

• DY pairs can have non-zero transverse momentum
  (ltpTgt 0.5 GeV)
• ? coplanarity cut between DY and beam not
  applicable
• Larger Background in Forward Direction (where
  asymmetry is smaller).
• Background higher for m than for e (meson decay)
• ? hadronic absorber (needed for m) inhibits other
  reactions
• Sensitivity to charge avoids background from
  wrong-charge DY-pairs
• ? Magnetic field envisaged

69
Dream Option Collider (15 GeV)
Mgt4 GeV
___ 22 GeV
22 GeV
15 GeV
Collider 15 GeV15 GeV
Mgt2 GeV
___ Collider (15 GeV15GeV)
L gt 1030cm-2s-1 to get comparable rates
70
Theoretical prediction
Forward Part (FWD) qlab lt 8 Large Acceptance
Part (LAD) 8 lt qlab lt 50 Beam and Target
Polarization PQ1
Magnitude of Asymmetry
Angular modulation
0.3
0.25
T15 GeV
0.2
T22 GeV
LAD
0.15
0
0.4
0.2
0.6
xFx1-x2
71
Estimated signal

• 120k event sample
• 60 days at L2.1 1031 cm2 s-2, P 0.3, Q 0.85

ATT(4.3?0.4)10-2
Events under J/y can double the statistics. ?
Good momentum resolution required
72
ASSIA Collaboration Spokesperson
Raimondo Bertini bertini_at_to.infn.it
Participating Institutions Dzhelepov Laboratory
of Nuclear Problems, JINR, Dubna,
Russia Dipartimento di Fisica A. Avogadro and
INFN, Torino, Italy Dipartimento di Fisica
Teorica and INFN, Torino, Italy Universita and
INFN, Brescia, Italy Czech Technical Universiy,
Prague, Czech Republic Charles University,
Prague, Czech Republic DAPNIA, CEN, Saclay,
France Institute of Scientific Instruments,
Academy of Sciences, Brno, Czech Republic NSC
Kharkov Physical Technical Institute, Kharkov,
Ukraine Laboratoi Nazionali Frascati, INFN,
Italy Universita dell Insubria, Como and INFN,
Italy University of Trieste and INFN Trieste,
Italy
92 Collaborators, 12 Institutions (10 EU, 2
outside EU)
73
Depolarizing Resonances in the HESR

• Imperfection 25 ?
• 4, 5, 6, ... , 28
• Strong 8, 16, 24
• Intrinsic 50 ?
• -4, -3, ... , 20
• 12-, 13-, ..., 35-
• Strong 0, 8, 12, 16, 24-, 32, 36-
• Coupling 50 ?
• -4, -3, ... , 20
• 12-, 13-, ..., 36-

74
Average multiplicity 4 charged 2 neutral
particle per event. Combinatorial background
from meson decay.
Estimate shows for most processes background
under control.
75
Drell-Yan cross section and event rate

• M2 s x1x2
• xF2QL/vs x1-x2

22 GeV
15 GeV
Mgt4 GeV
Mgt2 GeV

• Mandatory use of the invariant mass region below
  the J/y (2 to 3 GeV).
• 22 GeV preferable to 15 GeV