spin physics at gsi
DESCRIPTION
SPIN Physics at GSI. Frank Rathmann Institut für Kernphysik Forschungszentrum Jülich. Outline. WHY? Physics Case HOW? Polarized Antiprotons WHERE? FAIR Project at Darmstadt WHAT? Transversity Measurement WHEN? Time Schedule Conclusion. Central Physics Issue. - PowerPoint PPT PresentationTRANSCRIPT
16th International Spin Physics Symposium, Trieste, Oktober 2004
SPIN Physics at GSISPIN Physics at GSI
Frank RathmannFrank RathmannInstitut für Kernphysik Institut für Kernphysik
Forschungszentrum JülichForschungszentrum Jülich
OutlineOutline
WHY?WHY? Physics CasePhysics Case
HOW?HOW? Polarized AntiprotonsPolarized Antiprotons
WHERE?WHERE? FAIR Project at DarmstadtFAIR Project at Darmstadt
WHAT?WHAT? Transversity MeasurementTransversity Measurement
WHEN?WHEN? Time ScheduleTime Schedule
ConclusionConclusion
Central Physics IssueCentral 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
Leading Twist Distribution Functions
1/2 1/2
L L
+f1(x)
h1(x)
proton
proton’
quark
quark’
u = 1/2(uR + uL)u = 1/2(uR - uL)
No probabilistic interpretation in the helicity base (off diagonal)
Probabilistic interpretation in helicity base:
q(x) spin averaged
(well known)
q(x) helicity diff.(known)
q(x) helicity flip(unknown)
1/2 1/2
R R
1/2 1/2
L L
-1/2 1/2
R R
g1(x)
Transversitybase
1/2 -1/2
R L
-
TransversityTransversity
Chiral-odd: requires another chiral-odd partnerChiral-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
Impossible in DIS Direct Measurement
ppl+l-X epe’hX
Indirect Measurement:Convolution of with
unknown fragment. fct.
Transversity in Drell-Yan processes
p pQL
Q
l+
l-Q2=M2
QT
Polarized Antiproton BeamPolarized Antiproton Beam → → Polarized Proton TargetPolarized Proton Target (both transversely polarized)
)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
Other TopicsOther Topics
• Single-Spin Asymmetries• Electromagnetic Form Factors• Hard Scattering Effects• Soft Scattering
– Low-t Physics– Total Cross Section– pbar-p interaction
Proton Electromagnetic Formfactors 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
2
p2
2E
22M
2M
*E
y
m4/q
/|G|)(sin|G|)(cos1
)GGIm()2sin(A
S. Brodsky et al., Phys. Rev. D69 (2004)
pp
pp
p (GeV/c)
Study onset of Perturbative QCDStudy onset of 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
High Energy• small t: Reggeon Exchange• large t: perturbative QCD
pp elastic scattering from ZGSpp elastic scattering from ZGS
Spin-dependence at large-PSpin-dependence at large-P (90°90°cmcm):):
Hard scattering takes Hard scattering takes place only with spins place only with spins ..
D.G. Crabb et al., PRL 41, 1257 (1978)
T=10.85 GeV
Similar studies in pp elastic scattering
OutlineOutline
WHY? WHY? Physics CasePhysics Case
HOW?HOW? Polarized AntiprotonsPolarized Antiprotons
WHERE? WHERE? FAIR Project at DarmstadtFAIR Project at Darmstadt
WHAT?WHAT? Transversity MeasurementsTransversity Measurements
WHEN? WHEN? Time ScheduleTime Schedule
ConclusionConclusion
P beam polarizationQ target polarizationk || beam direction
σtot = σ0 + σ·P·Q + σ||·(P·k)(Q·k)
polbeam
polbeam
tt
0
tt
0
ee2
I)t(I
ee2
I)t(I
transverse case:
Q0tot
longitudinal case:
Q)( ||0tot
For initially equally populated spin states: (m=+½) and (m=-½)
revtpolpol
revtc0beam
fdQ
1
fd)(
1
pol
t
0
pol
tcosheIII)t(I
ttanh
II
II)t(P
beam
Time dependence of P and I
Spin Filter MethodSpin Filter Method
1992 Filter Test at HD-TSR with protons1992 Filter Test at HD-TSR with protons
Experimental SetupExperimental SetupResultsResults
F. Rathmann. et al., PRL 71, 1379 (1993)
T=23 MeV
Low energy pp scattering
1<0 tot+<tot-
Expectation
Target Beam
Experimental Results from Filter TestExperimental Results from Filter Test
Puzzle from FILTEX TestPuzzle from FILTEX TestObserved polarization build-up: dP/dt = ± (1.24 ± 0.06) x 10-2 h-1
Expected build-up: P(t)=tanh(t/τpol),
1/τpol=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 Ψacc=4.4 mrad σR=83 mb
2. Small angle scattering of target protons into ring acceptance σS=52 mb
3.3. Spin transfer from polarized electrons of the target atoms to Spin transfer from polarized electrons of the target atoms to the stored protonsthe stored protons
σEM=70 mb (-)Horowitz & Meyer, PRL 72, 3981 (1994)
H.O. Meyer, PRE 50, 1485 (1994)
Spin Transfer from Electrons to ProtonsSpin Transfer from Electrons to Protons
epep
020
p2
ep2
EM
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 (negative for antiprotons)v relative lab. velocity between p and ez beam charge number
EM||EM 2
1 10 100 T (MeV)
σEM
|| (
mb
)
100
200
300
400
500
600
EM||EM 2
Pure Electrons
Atomic Electrons
Exploitation of Spin TransferExploitation of Spin Transfer
epep PAX will employ spin-
transfer from polarized electrons of the target to
antiprotonsHydrogen gas target: ①+② in strong field (300 mT)
Pe=0.993Pz=0.007
(QED Process: calculable)
Dedicated Antiproton Polarizer (AP)Dedicated Antiproton Polarizer (AP)
e-coolere-coolerAP
HESR
ABS
Polarizer Target
InternalExperiment
||EM||EM Q2
Siberian Snake
B
Injection
Extraction
150 m
440 m
Polarization Buildup in AP parallel to measurement in ESR
β=0.2 mq=1.5·1017 s-1
T=100 KLongitudinal Q (300 mT)
db=ψacc·β·2dt=dt(ψacc)
lb=40 cm (=2·β)
df=1 cm, lf=15 cm
Beam lifetimes in the APBeam lifetimes in the AP
10 100 1000 T (MeV)
40
30
25
ψacc(mrad)
20102
4
6
8
beam
lilf
eti
me τ
beam (
h)
10
Beam Lifetime
Coulomb Loss
Total Hadronic )T()T(
m4
)T(s1
)m4)T(s()T(s
m4)m2)T(s(4d
d
d),T(
pptot0
2p
2acc
22p
2
2p
22p2
.RuthaccC
max
min
)T(f)(d))T(),T((
1),T(
revacct0accCaccbeam
Beam PolarizationBeam Polarization
0.1
0.2
0.3
0.4
Beam
Pola
riza
tion
P(2
·τbeam)
10 T (MeV)100
EM only
5
10
30
20
40
Ψacc=50 mrad
0
1
Filter Test: T = 23 MeV Ψacc= 4.4 mrad
Buildup in HESR (800 MeV)
statistical error of a double polarization observable (ATT)
NQP
1TTA
Measuring time t to
achieve a certain error
δATT ~ FOM = P2·I
Polarization Buildup: Optimum Interaction TimePolarization Buildup: Optimum Interaction Time
(N ~ I)
Optimimum time forPolarization Buildup
given by maximum of FOM(t)
tfilter = 2·τbeam
0 2 4 6 t/τbeam
I/I 0
0.2
0.4
0.6
0.8
Beam
Pola
riza
tion
Optimum Beam Energies for Buildup in APOptimum Beam Energies for Buildup in AP
ψacc= 50 mrad
40 mrad
30 mrad
20 mrad
AP Space charge limit
F. Rathmann et al., physics/0410067 (2004)
1 10 T (MeV)100 10 mrad
FOM
5
10
15
Maximum FOM
Ψacc
(mrad)
Τbeam
(h)
P(2·τbeam
)
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
Space-Charge Limitation in the APSpace-Charge Limitation in the AP
10 mrad1 10 T (MeV)100
ψacc= 50 mrad40 mrad30 mrad20 mrad10 mrad
109
1010
1011
1012
1013
Nind.
Nreal
Before filtering starts:Nreal = 107 s-1 · 2τbeam
Transfer from AP to HESR and AccumulationTransfer from AP to HESR and Accumulation
e-coolere-coolerAP
HESR
ABS
Polarizer Target
InternalExperiment
Siberian Snake
B
Injection
Extraction
150 m
440 m
50 mrad40 mrad
30 mrad20 mrad10 mrad
20 40 60 t (h)80
4·1010
6·1010
8·1010
2·1010
0
Accumulation of Polarized Beam in HESRAccumulation of Polarized Beam in HESRPIT: dt=7.2·1014 atoms/cm2
τHESR=11.5 h
10
HESR2
7
p
106.5
e
s/p10N
Number accumulated in equilibrium independent of
acceptance
Np
bar
No Depolarization in HESR during energy change
Performance of Polarized Internal TargetsPerformance of Polarized Internal Targets
PT = 0.795 0.033
HERMES
H Transverse Field (B=297 mT)
HERMES
Dz
Dzz
PT = 0.845 ± 0.028
Longitudinal Field (B=335 mT)
HERMES: Stored Positrons PINTEX: Stored Protons
H
Fast reorientation in a weak field (x,y,z)
Targets work very reliably (many months of stable operation)
Estimated Luminosity for Double PolarizationEstimated Luminosity for Double Polarization
Polarized Internal Target in HESR
L= dt x frev x Npbar
dt = areal densityfrev = revolution frequencyNpbar = number of pbar stored in HESR
(factor >70 in measuring time for ATT with respect to beam extracted on solid target)
tot2
7
123110514
1
e
s/p10
scm107.2106.5108.6102.7L
Qtarget = 0.85Pbeam = 0.3σtot(15 GeV) = 50 mb
In equilibrium:
How about a Pure Polarized Electron Target?How about a Pure Polarized Electron Target?
1 10 100 T (MeV)
σEM
|| (
mb
)100
200
300
400
500
600
EM||EM 2
Pure Electrons
Atomic Electrons
Maxiumum σEM|| 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:
•Ie=6.2·1015 e/s•A=1 cm2
•l=5 mdt = Ie·l·(β·c·A)-1 = 5.2·108 cm-2
Electron target density by factor ~106 smaller, no match for a PIT (>1014 cm-2)
OutlineOutline
WHY? WHY? Physics CasePhysics Case
HOW? HOW? Polarized AntiprotonsPolarized Antiprotons
WHERE?WHERE? FAIR Project at DarmstadtFAIR Project at Darmstadt
WHAT?WHAT? Transversity MeasurementTransversity Measurement
WHEN? WHEN? Time ScheduleTime Schedule
ConclusionConclusion
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 > 2011 (depending on start)
FAIR(Facility for Antiproton and Ion Research)
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
FAIR – Prospects and ChallengesFAIR – 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)
• FAIR will have a long lead-time (construction, no physics) staging (3 phases)
FLAIR:(Facility for very Low energy
Anti-protons and fully stripped Ions)
SIS100/300
HESR: High Energy Storage Ring:PANDA (and PAX)
NESR
CR-Complex
The FAIR project at GSIThe FAIR project at GSI
50 MeV Proton Linac
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 FacilityThe Antiproton Facility
•Antiproton production similar to CERN
•Production rate 107/sec at 30 GeV•T = 1.5 - 15 GeV/c (22 GeV)
Gas Target and Pellet Target: cooling power determines thickness
SuperFRS
NESR
CR
Beam Cooling: e- and/or stochastic2MV prototype e-cooling at COSY
SIS100/300
HESR
AP
The New Polarization FacilityThe New Polarization Facility
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)
WE NEED MORE COLLABORATORS!
210 collaborators25 institutions
SIS100/300
Internal: PAX in HESRPolarized antiprotons +
PIT
LoI‘s for Spin Physics at FAIRLoI‘s for Spin Physics at FAIR
External: ASSIAExtracted beam on PET
(Compass-like)
Evaluation by Evaluation by QCD Program Advisory Committee (July QCD Program Advisory Committee (July
2004)2004)STI Report:Your LoI has convinced the QCD-PAC
a)that Polarization must be included into the design of FAIR from the beginning, and
b)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.
OutlineOutline
WHY? WHY? Physics CasePhysics Case
HOW? HOW? Polarized AntiprotonsPolarized Antiprotons
WHERE? WHERE? FAIR Project at DarmstadtFAIR Project at Darmstadt
WHAT?WHAT? Transversity Measurement at PAXTransversity Measurement at PAX– RatesRates
– Angular DistributionAngular Distribution
– BackgroundBackground
– Detector ConceptDetector Concept
WHEN? WHEN? Time ScheduleTime Schedule
ConclusionConclusion
Transversity in Drell-Yan processes at PAX
p pQL
Q
l+
l-Q2=M2
QT
Polarized Antiproton BeamPolarized Antiproton Beam → → Polarized Proton TargetPolarized Proton Target (both transversely polarized)
)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
AATTTT for PAX kinematic conditions for PAX kinematic conditions
RHIC: τ=x1x2=M2/s~10-3 → Exploration of the sea quark content (polarizations small!) ATT very small (~ 1 %)
TT
TT
a
A
T=22 GeV (s=6.7 GeV)
T=15 GeV(s=5.7 GeV)
Anselmino et al. PLB 594,97
(2004)
0.10
0.15
0.25
0.3
xF=x1-x2
0.2 0.4 0.60
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)
PAX: M2~10 GeV2, s~30-50 GeV2, =x1x2=M2/s~0.2-0.3
→ Exploration of valence quarks (h1q(x,Q2) large)
Similar predictions by Efremov et al.,
Eur. Phys. J. C35, 207 (2004)
xF=x1-x2
Signal EstimateSignal Estimate
q
22
21
22
21
2q
212
2
F2
2
M,xqM,xqM,xqM,xqe)xx(sM9
4
dxdM
d
1) Count rate estimate.
)M,x(u)M,x(u
)M,x(h)M,x(ha
dd
ddA
22
21
22
u1
21
u1
TTTT
2) Angular distribution of the asymmetry.
Polarized Antiproton BeamPolarized Antiproton Beam → → Polarized Proton TargetPolarized Proton Target (both transversely polarized)
p pQL
Q
l+
l-Q2=M2
QT
Drell-Yan cross section and event rateDrell-Yan cross section and event rate
q
22
21
22
21
2q
212
2
F2
2
M,xqM,xqM,xqM,xqe)xx(sM9
4
dxdM
d•M2 = s x1x2 •xF=2QL/√s = x1-x2
• Mandatory use of the invariant mass region below the J/ (2 to 3 GeV).
• 22 GeV preferable to 15 GeV
•x1x2 = M2/s
15 GeV22 GeV
M>2 GeV
M>4 GeV
22 GeV
15 GeV
M (GeV/c2)
2 k events/day
Extension of the “safe” regionExtension of the “safe” regionDetermination of h1
q(x,Q2) not confined to the „safe“ region (M > 4 GeV)
Cross section increases by two orders from M=4 to M=3 GeV → Drell-Yan continuum enhances sensitivity of PAX to ATT
eeqq
/Jqq unknown vector coupling, but same Lorentzand spinor structureas other two processes
Unknown quantities cancel in the ratios for ATT, but helicity structure remains!
Anselmino et al.PLB 594,97 (2004)
Efremov et al., Eur.Phys.J. C35,207 (2004)
Dream Option: Collider (15 GeV)Dream Option: Collider (15 GeV)
L > 1030cm-2s-1 to get comparable rates
AATTTT asymmetry: angular distribution asymmetry: angular distribution
)M,x(u)M,x(u
)M,x(h)M,x(haA
22
21
22
u1
21
u1
TTTT
Needs a large acceptance detector (LAD)
2cos)cos1(
sin),(
2
2
TTa
•Asymmetry is largest for angles =90°
•Asymmetry varies like cos(2).
Theoretical predictionTheoretical prediction
0.15
0.2
0.25TT
TT
a
A
T=22 GeV
T=15 GeV
0.3
0 0.6xF=x1-x2
0.40.2
Magnitude of Asymmetry
Angular modulation
FWD: lab < 8°
LAD: 8° < lab < 50°
P=Q=1
LAD
Estimated signalEstimated signal• 120k event sample
• 60 days at L=2.1 1031 cm2 s-2, P = 0.3, Q = 0.85
Events under J/y can double the statistics. Good momentum resolution
requested
LAD
LAD
ATT=(4.30.4)·10-2
Detector concept Detector concept
•Drell-Yan process requires a large acceptance detectorDrell-Yan process requires a large acceptance detector
•Good hadron rejection needed • 102 at trigger level, 104 after data analysis for single
track.
•Magnetic field envisagedMagnetic field envisaged• 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.
Double Polarization Experiments Double Polarization Experiments Azimuthal Azimuthal SymmetrySymmetry
(8 coil system under study)
• 800 x 600 mm coils
• 3 x 50 mm section (1450 A/mm2)
• average integrated field: 0.6 Tm
• free acceptance > 80 %
Superconducting target field coils do not affect azimuthal acceptance.
Possible solution: Toroid (6 superconducting coils)Possible solution: Toroid (6 superconducting coils)
OutlineOutline
WHY? WHY? Physics CasePhysics Case
HOW? HOW? Polarized AntiprotonsPolarized Antiprotons
WHERE? WHERE? FAIR Project at DarmstadtFAIR Project at Darmstadt
WHAT?WHAT? Transversity MeasurementTransversity Measurement
WHEN?WHEN? Time ScheduleTime Schedule
ConclusionConclusion
Time scheduleTime 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., physics/0410067 (2004)
15.01.05 Technical Report (with Milestones)o Experimental confirmation of spin transfer cross
section at COSY (Snake, Electron Polarimeter, strong B||)
o Design and Construction of AP at COSY. . . . .
Evaluations & Green Light for Construction
2005-2008 Technical Design Reports (for Milestones)
>2012 Commissioning of HESR
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, ItalyCzech 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, UkraineLaboratoi Nazionali Frascati, INFN, Italy
Universita dell’ Insubria, Como and INFN, Italy University of Trieste and INFN Trieste, Italy
ASSIA Collaboration:ASSIA Collaboration: Spokesperson: Spokesperson: Raimondo BertiniRaimondo Bertini
[email protected]@to.infn.it
92 Collaborators, 12 Institutions (10 EU, 2 outside EU)92 Collaborators, 12 Institutions (10 EU, 2 outside EU)
Participating Institutions 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. ChinaHigh Energy Physics Institute, Tbilisi State University, Tbilisi, Georgia
Forschungszentrum Jülich, Institut für Kernphysik Jülich, GermanyInstitut für Theoretische Physik II, Ruhr Universität Bochum, Germany
Helmholtz-Institut für Strahlen- und Kernphysik, Bonn, GermanyPhysikalisches Institut, Universität Erlangen-Nürnberg, Germany
Instituto Nationale di Fisica Nucleare, Ferrara, Italy Dipartimento di Fisica Teorica, Universita di Torino and INFN, Torino, Italy
Instituto Nationale di Fisica Nucleare, Frascati, ItalyPetersburg Nuclear Physics Institute, Gatchina, Russia
Institute for Theoretical and Experimental Physics, Moscow, RussiaLebedev Physical Institute, Moscow, Russia
Laboratory of Particle Physics, Joint Institute for Nuclear Research, Dubna, RussiaLaboratory of Nuclear Problems, Joint Institute for Nuclear Research, Dubna, Russia
High Energy Physics Institute, Protvino, RussiaDepartment of Radiation Sciences, Nuclear Physics Division, Uppsala University, Uppsala,
Sweden
PAX Collaboration:PAX Collaboration: Spokespersons: Spokespersons: Paolo LenisaPaolo Lenisa [email protected] RathmannFrank Rathmann [email protected]
123 Collaborators, 19 Institutions (9 EU, 10 outside EU)123 Collaborators, 19 Institutions (9 EU, 10 outside EU)
ConclusionConclusion
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
Projections for HESR fed by a dedicated AP:• Pbeam > 0.30• 5.6·1010 antiprotons• L 2.7 ·1031 cm-2s-1
Detector concept: 15 (22) GeV + PIT • Large acceptance detector with a toroidal magnet
Collider Option: Attractive far future perspective
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
BackgroundBackground
mbpp
50
nbDY 1 108-109 rejection factor against background
• DY pairs can have non-zero transverse momentum (<pT> = 0.5 GeV)
coplanarity cut between DY and beam not applicable
• Larger Background in Forward Direction (where asymmetry is smaller).
• Background higher for than for e (meson decay)
hadronic absorber (needed for inhibits other reactions
•Sensitivity to charge avoids background from wrong-charge DY-pairs
Magnetic field envisaged
Background for Background for Xeepp
Average multiplicity: 4 charged + 2 neutral particle per event.
Combinatorial background from meson decay.
Estimate shows for most processes background under control.
pp21hh X
eeK /0
/
ee0
eeK //0
ee
ee
21hh
…
• Background higher for than for e
Background for Background for Xeepp Preliminary PYTHIA result (2109 events)
• Background from charge conjugated mesons negligible for e.
e
x1000 x100
Total background
x1000 x100
e
Origin of Background