GLUON POLARISATION
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Transcript of GLUON POLARISATION
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GLUON POLARISATION
introduction
ΔG from inclusive data analysis
direct measurements of ΔG/G
1) method and previous measurements
2) recent results from COMPASS
3) measurements at RHIC
outlook
Fulvio Tessarotto
INFN – Trieste
EINN 2005
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Fulvio Tessarotto EINN 2005
Milos, 23 09 2005
In inclusive polarised DIS one can measure an asymmetry in the differential cross-section:
and extract the struture function g1.
In the QPM g1 has a simple interpretation:
In QCD at NLO g1 may depend explicitely
on G:
measuring Q2 variations of g1 we can try to
get G
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Fulvio Tessarotto EINN 2005
Milos, 23 09 2005
The nucleon spin
½= ½ΔΣ + ΔG + Lq + Lg
quarks gluons orb. mom.
Ellis-Jaffe: ΔΣ = a0 ≈ 0.6
experimentally: a0 ≈ 0.25
ΔΣ = a0 + 3(s/2)
ΔG
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Fulvio Tessarotto EINN 2005
Milos, 23 09 2005
0.43 0.80 ΔG
0.03 0.09 - Δs
0.04 0.43- Δd
0.03 0.84 Δu
0.06 0.32 ΔΣ
0.01 0.1 1
0.0
0.1
0.2
0.3
0.4
PD(g1
NLO/F1
NLO)
x
xG(x)
0.01 0.1 1
-0.4
-0.3
-0.2
-0.1
0.0
x
-x(d+d)
0.01 0.1 1
-0.2
-0.1
0.0
x
-x(s+s)
0.01 0.1 10.0
0.1
0.2
0.3
0.4
x
PD (g1
NLO + HT)
-x(u+u)
SLAC (E142, E143, E154, E155)CERN (EMC, SMC)DESY (HERMES)
185 exp. points
E. Leader, A. Sidorov, D. Stamenov Phys. Rev. D67 (2003) 074017
G not well constrained not extracted
dΔ ,uΔ
Spin-dependent PDFs
dp,1
dp,1
dn,p,1 /Fg ,A
1/2 = ½ + + Lz = 0.96 + Lz
Lz is negative
Two years ago …
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Fulvio Tessarotto EINN 2005
Milos, 23 09 2005
g and q were largely unconstrained
Direct Direct g g measurementmeasurement
Is this still true?
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Fulvio Tessarotto EINN 2005
Milos, 23 09 2005
final g1 data
- Very good statistics- Smearing (resolution and radiative corr.) →
correlation between x bins
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Fulvio Tessarotto EINN 2005
Milos, 23 09 2005
g1n(x) at high x from JLAB
• pQCD + no Lz →
u/u= d/d=1 at high x
• Very accurate A1n at high x
A1n > 0 at x > 0.5
• + world A1p → d/d < 0
so Lz not negligible ?
u/u
d/d
PRL 92, 012004 (2004)
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Fulvio Tessarotto EINN 2005
Milos, 23 09 2005
g1d(x) at low x
• new data : =0.202 (+0.042 -0.077) → 0.237 (+0.024 -0.029)
• COMPASS systematically > SMC at low x
PLB 612 (2005) 154
g1/F1
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Fulvio Tessarotto EINN 2005
Milos, 23 09 2005
NLO QCD fits with new data + new unpolarised PDFs
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Fulvio Tessarotto EINN 2005
Milos, 23 09 2005
to know G we still need to measure it
possible trend toward smaller G but the results are scattered:
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• Idea proposed by R.D.Carlitz, J.C.Collins and A.H.Mueller, Phys.Lett.B 214, 229 (1988)……..and many more
•revisited by A.Bravar,D.von Harrach and A.Kotzinian,Phys.Lett.B 421, 349 (1998)
• Method used in HERMES for photoproductionHERMES, A.Airapetian et al., Phys.Rev.Lett.84, 2584 (2000)
• Applied for DIS region by SMC (data with Q2 >1GeV2) SMC, B.Adeva et al.., Phys. Rev. D 70, 012002 (2004).
History:
Direct Measurements:
polarised p p collision: RHIC
semi-inclusive deep inelastic scattering: DESY, CERN (Photon Gluon Fusion)
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Fulvio Tessarotto EINN 2005
Milos, 23 09 2005
• Strategies to suppress background: 1) Open charm production: q = c unique, no background charm fragmentation, 1.2 D0 per event
D0 -> K- π+ (BR 4%), D*+(~20%) -> D0 π+
2) High-PT hadron pair production: q=u,d,s kT(intr) = 450 MeV/c
pT(frag) = 350 MeV/c
• pQCD scale set by: 1) ŝ > 4mc
2 or 2) ŝ > (pt1+pt2)2
ΔG/G from Photon-Gluon Fusion
Photon-Gluon Fusion
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Fulvio Tessarotto EINN 2005
Milos, 23 09 2005
HERMES & DESY
• 27.5 GeV e • Pure atomic H or D targets• Spectrometer with complete hadron identification
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Fulvio Tessarotto EINN 2005
Milos, 23 09 2005
Statistics decreases with pT
HERMES ALL from high pT hadron pairs
ehhXeNTeLL fAPP
NN
NNA
Proton target
Promising channel, but …
theoretical uncertainties
may be large
<xg> = 0.17
<Q2> = 0.06 (GeV/c)2
photoproduction
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Fulvio Tessarotto EINN 2005
Milos, 23 09 2005
ΔG/G from SMC
µ+ 190 GeV Pµ= -0.78±0.03
DIS eventsQ2 > 1 GeV2, 0.4<y<0.9
xF > 0.1, pT2 > 2.5
(GeV/c)2
1% of inclusive sample
∆G/G = -0.200.290.11
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Fulvio Tessarotto EINN 2005
Milos, 23 09 2005
COMPASS SPS
LHC
COMPASS EXPERIMENT
Beam: 2 . 108 µ+/ spill (4.8s / 16.2s)Luminosity: ~ 4 . 1032 cm-2 s-1 Beam polarisation: 76%Beam momentum: 160 GeV/c
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Fulvio Tessarotto EINN 2005
Milos, 23 09 2005
SM1 dipoleSM1 dipole
SM2 dipole
Polarised Target
HCAL1
Muon-filter1,MW1SPS 160 GeV 2.108/spill
Micromegas,DC,SciFi
Gems,SciFi,DCs,straws
MWPC Gems Scifi
trigger-hodoscopes
Silicon
Spectrometer 2002 -> 2004
RICH_1 Gem_11
ECAL2,HCAL2
straws,MWPC,Gems,SciFi
straws Muon-
filter2,MW2
DW45
SciFi
Veto
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New detector technologies
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Fulvio Tessarotto EINN 2005
Milos, 23 09 2005
ΔG/G from open charm
G
GaA LL
)s,x(G )s( sd
)s,x(G )s( sdccN
GPGF
GPGF
PGF at NLO:Bojak, Stratmann NPB 540 (1999) 345; A.P. Contogouris and G. Grispos, Phys. Rev. D 62 (2000). ŝ = m2
cc
D0 K- π+ (BR 4%)
D*+ D0 π+ + c.c.
Special trigger: quasi realphotoproduction
c
c
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Fulvio Tessarotto EINN 2005
Milos, 23 09 2005
D* tagging: D* D0 π (Kπ)π
KD0MeV/c2)
sK
M
eV/c
2 )
Cuts:
zD > 0.2
|cos *| < 0.85 (Background)
10 < pK < 35 GeV/c(RICH PID)
D0 K π
D*
D
0 π
no vertex detector(solid target!)
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Fulvio Tessarotto EINN 2005
Milos, 23 09 2005
ΔG/G from open charm
MC: Aroma + PolDis
ΔG/G = -1.08 ± 0.73
D0 (untagged, 2003) 4200 eventi
D*+→D0π+ (2003) 1100 eventi
<xg> ~0.15
0.73 0.43 with 2004 data
D0 → K π π0
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Fulvio Tessarotto EINN 2005
Milos, 23 09 2005
Pairs of hadrons with high pt and Q2 > 1 GeV/c
Photon Gluon Fusion
h1
h2
• current fragmentation:
• event cuts:
xF > 0.1z > 0.1
pt > 0.7 GeV/cpt1
2+pt22 > 2.5 (GeV/c)2
m(h1h2) > 1.5 GeV/c2
• 2 high pt hadrons:
N
Q2 > 1 (GeV/c)2
xBj < 0.050.1 < y < 0.9
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Fulvio Tessarotto EINN 2005
Milos, 23 09 2005
Result for high pt asymmetry
Aγ*d = -0.015 ± 0.080 (stat.) ± 0.013 (syst.)2002/03 data
Asymmetry for high-pt hadron pairs at Q2 > 1 (GeV/c)2:
Systematic uncertainty contains contributions from:• target and beam polarisation measurement (5% resp. 3%)• upper limit on false asymmetries (0.013)• determination of D and f (5% each)
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Fulvio Tessarotto EINN 2005
Milos, 23 09 2005
determination of ΔG/G
Photon Gluon Fusion QCD-Compton Leading Order
DISLOq
q
D
a
G
G
D
a
D
AA
tot
ComComLL
tot
PGFPGFLL
hhNLLd
ˆˆ
Relative Fractions determined by Monte Carlo (LEPTO)
05.074.0DaPGFLL
0qq
DaComLL
cut on xBj < 0.05:
0Ad1
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Fulvio Tessarotto EINN 2005
Milos, 23 09 2005
Data Monte Carlo comparision• Use LEPTO Monte Carlo for Q2>1 (GeV/c)2 including RADGEN
σPGF/σtot = 0.34 ± 0.07 (syst.)
Determination of thefraction of PGF eventsin LEPTO:
• Variation of the cut on pt2
• Standard and modified* set of fragmentation parameters
* SMC, B. Adeva et al., Phys. Rev. D70:012002, 2004
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Fulvio Tessarotto EINN 2005
Milos, 23 09 2005
10% ofstatistics
COMPASS result for ΔG/G
ΔG/G = 0.06 ± 0.31stat. ± 0.06syst.2002/03 dataQ2 > 1 (GeV/c)2
at <xg> = 0.13 ± 0.08
GSA,B,C: T. Gehrmann and W. Sterling, Z. Phys. C65 (1994) 461.
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Fulvio Tessarotto EINN 2005
Milos, 23 09 2005
ALL/D = Rpgf G/G aLLpgf
+ Rqcdc q/q aLLqcdc
all Q²
Pairs of hadrons with high pt and Q2 < 1 GeV/c
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Fulvio Tessarotto EINN 2005
Milos, 23 09 2005
+ Rqq q/q aLLqq q/q
Physical background
ALL/D = Rpgf G/G aLLpgf
+ Rqcdc q/q aLLqcdc
Q² < 1
all Q²
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Fulvio Tessarotto EINN 2005
Milos, 23 09 2005
+ Rqg G/G aLLqg q/q
Physical background
ALL/D = Rpgf G/G aLLpgf
+ Rqcdc q/q aLLqcdc
+ Rqq q/q aLLqq q/q
all Q²
Q² < 1
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Fulvio Tessarotto EINN 2005
Milos, 23 09 2005
+ Rgq q/q aLLgq (G/G)
Physical background
ALL/D = Rpgf G/G aLLpgf
+ Rqcdc q/q aLLqcdc
+ Rqq q/q aLLqq q/q
+ Rqg G/G aLLqg q/q
all Q²
Q² < 1
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Fulvio Tessarotto EINN 2005
Milos, 23 09 2005
+ Rgg G/G aLLgg (G/G)
Physical background
ALL/D = Rpgf G/G aLLpgf
+ Rqcdc q/q aLLqcdc
+ Rqq q/q aLLqq q/q
+ Rqg G/G aLLqg q/q
+ Rgq q/q aLLgq (G/G)
all Q²
Q² < 1
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Fulvio Tessarotto EINN 2005
Milos, 23 09 2005
Inputs:
-generation of Monte Carlo evts-parametrization (world data)-pQCD calculations
Physical background
ALL/D = Rpgf G/G aLLpgf
+ Rqcdc q/q aLLqcdc
+ Rqq q/q aLLqq q/q
+ Rqg G/G aLLqg q/q
+ Rgq q/q aLLgq (G/G)
+ Rgg G/G aLLgg (G/G)
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Fulvio Tessarotto EINN 2005
Milos, 23 09 2005
Resolved photon processes
polarised parton distribution functions of (virtual…) photon areunknown!
BUT:
-q(x,²) < q(x,²) < q(x,²)
leads to 2 extreme (min&max) scenarios
additional (theoretical) uncertainty
measured
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Fulvio Tessarotto EINN 2005
Milos, 23 09 2005
MC/data comparison
Q²
PYTHIA generator is used for Q²<1GeV²GEANT is used for spectrometer simulation
.data
- MC
data/MC
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Fulvio Tessarotto EINN 2005
Milos, 23 09 2005
MC/data comparison
pT
.data
- MC
.data
- MC
data/MC data/MC
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Fulvio Tessarotto EINN 2005
Milos, 23 09 2005
Results from MC
The Monte Carlo describes our data quite well!
Rpgf ≈ 31%
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Fulvio Tessarotto EINN 2005
Milos, 23 09 2005
Q2>1GeV2 :
Q2<1GeV2:
Gluon polarisation, high pT pairs 2002-2003
data
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Fulvio Tessarotto EINN 2005
Milos, 23 09 2005
G = 2.48
G = 0.62
G = 0.16
Gluon polarisation results:
ΔG/G (xg ≈ 0.1) is small G>1 disfavoured
GRSV2000NLO fits to g1
2 = 3 Gev2
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Fulvio Tessarotto EINN 2005
Milos, 23 09 2005
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Fulvio Tessarotto EINN 2005
Milos, 23 09 2005
ΔG/G from two jet events
LLAˆ
Hard Scattering Process
2P2 2x P
j 2f x
i 1f x1P
1 1x P
zhqDs
1ps
2ps
gggg gqgq qqqq
qg+gq
gg
0
Fraction
's produced
Pt [GeV/c]
Leading hadron used as jet tag
G
G
G
G
G
G
q
q
q
q
q
q
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Fulvio Tessarotto EINN 2005
Milos, 23 09 2005
Prompt photon production asymmetry• Gluon Compton Dominates
• At LOLO no fragmentation function• Small contamination from annihilation
•
2i i 2
i u,d,s
2i i 2
i u,d,s
LL1
1LL
e f (xg(
)
e f (A
x )a (gq
x )
g(x )q )
A1
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Fulvio Tessarotto EINN 2005
Milos, 23 09 2005
NSRL
2 superconducting rings3.8 km circumference
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Fulvio Tessarotto EINN 2005
Milos, 23 09 2005
RHIC – first polarized hadron collider
BRAHMS
STAR
PHENIX
AGS
LINACBOOSTER
Pol. H- Source
Spin Rotators(longitudinal polarization)
Solenoid Partial Siberian Snake
Siberian Snakes
200 MeV Polarimeter Internal Polarimeter
Rf Dipole
pC PolarimetersAbsolute Polarimeter (H jet)
pC Polarimeter
25% Helical Partial Siberian Snake
5% Helical Partial Siberian Snake
PHOBOS
Spin Rotators(longitudinal polarization)
Spin flipper
Siberian Snakes
Achieved ~ 50% beam polarization at 100 GeVAchieved ~ 30% beam polarization at 205 GeV on first try!
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Fulvio Tessarotto EINN 2005
Milos, 23 09 2005
New AGS helical snakes
2.6 m
2.6 m
25% s.c. helical snake build at BNL
Warm snake avoids polarization mismatch at AGS injection and extraction.
Cold strong snake eliminates all depolarizing resonances in AGS.
6 % helical snake build at Tokana Industries funded by RIKEN.
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Fulvio Tessarotto EINN 2005
Milos, 23 09 2005
STAR spin physics program: ∆G, ∆q/∆q, δq
Large acceptance TPC and EMC -1<η<2
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Fulvio Tessarotto EINN 2005
Milos, 23 09 2005
ΔG – Star: ALL for jets (2005)
STARSTAR
0 5 10 15 20 25 30
0.2
0.4
0.6
0.8
1.0
0.0
gg qq
qg
Inclusive Jets :LOW. Vogelsang
pT (GeV)
2005
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Fulvio Tessarotto EINN 2005
Milos, 23 09 2005
PHENIX Detector
• Central Arms: ||<0.35, =2900
Charged particle ID and tracking; photon ID
• Muon Arm:1.2<||<2.4Muon ID and tracking
• Global Detectors Collision triggerCollision vertex characterizationRelative luminosityLocal Polarimetry
Philosophy: High rate capability & granularity Good mass resolution and particle ID Sacrifice acceptance
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Fulvio Tessarotto EINN 2005
Milos, 23 09 2005
ppπ0/prompt + X
prompt γπ0
Excellent agreement with NLO & NLL
calculation with collider data !
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Fulvio Tessarotto EINN 2005
Milos, 23 09 2005
Outlook 2005/7
2003/4
PHENIX ALL for Inclusive 0 productionat √s=200 GeV, 2003 + 2004 data with about ∫Ldt~0.3pb-1 and <Pb>~0.3
Run 5 (April –June 2005):
absolute polarimeter: ∆Pb/Pb~7%
∫Ldt ~ 3pb-1, <Pb>~0.45
reduces statistical error by factor 7
pp -> 0 + X
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Fulvio Tessarotto EINN 2005
Milos, 23 09 2005
B. Jaeger et al. Phys. Rev. D67, 054005 (2003)
Y. Fukao, spin2004
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Fulvio Tessarotto EINN 2005
Milos, 23 09 2005
ΔG at RHIC – summary & outlook
• Various channels, large coverage in xg
- Jet/leading hadron production : First results of ALL pp 0 +X from PHENIX Very good perspective for +- at PHENIX and jets at STAR - Direct photon production: hard scale 100 GeV 2, xg reconstructed in STAR
- Heavy flavours, ...
• RHIC Spin program on track, major effort to reach performance
Run s1/2(GeV) Pbeam L(pb-1)
3 200 0.27 0.35
4 + 5 200 >0.40 10
>5 200 0.70 320
500 0.70 800
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Fulvio Tessarotto EINN 2005
Milos, 23 09 2005
Physics vs Luminosity and Polarization at RHIC
2005 2006 2007 2008 2009 …. 2012 (RHIC II)
10 pb-1 …………………………………… 275pb-1 …….. 950pb-1
√s= ……………………….. 200 GeV …………………......... 500 GeV|
P= 0.5 0.6 0.7 ……………………………………
Inclusive hadrons + Jets ~ 25% Transverse Physics Charm Physics direct photons bottom physics W-physics
ALL(hadrons, Jets) ALL(charm)
ALL(γ) AL(W)
L= 1x1031cm-2s-1 6x1031cm-2s-1 1.6x1032cm-2s-1
see Spin report to DOE http://spin.riken.bnl.gov/rsc/
@ 200GeV @ 500GeV
eRHIC
ELIC
Outlook
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Fulvio Tessarotto EINN 2005
Milos, 23 09 2005
PHENIX Forward Upgrade: W-physics and jet+photon
Muon Trigger Upgrade
RPC + FPGA based
trigger logic
Nose cone calorimeter
W-Si calorimeter
Trigger RPC Locations
RPC2
June 2005: $1.99M NSFMRI grant approved + $280k institutional support
UC Riverside, Abilene Christian, Iowa State, U. Illinois, U. Colorado, Columbia, Georgia Tech., RBRC, Kyoto, Peking U.,
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Fulvio Tessarotto EINN 2005
Milos, 23 09 2005
Final results on ∆G will come from combined NLO analysis of RHIC and DIS
RHIC measurements will span broad range in x with good precision. Multiple channels with independent theo. and exp. uncertainties.
Uncertainty through extrapolation to small x
s=200 GeV incl. 0 prod’n s=500 GeV incl. jet prod’n
∆G Measurements by 2012 see Spin report to DOE http://spin.riken.bnl.gov/rsc/
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Fulvio Tessarotto EINN 2005
Milos, 23 09 2005
COMPASS
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Fulvio Tessarotto EINN 2005
Milos, 23 09 2005
COMPASS upgrade in 20065
m5
m
6 m6 m3 m3 m
Photon Photon Detectors:Detectors:CsI MWPCCsI MWPC
mirrormirrorwallwall
vesselvessel
radiatorradiator::
CC44FF1010
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Fulvio Tessarotto EINN 2005
Milos, 23 09 2005
• 2002 – 2004 -> 2006• • FoM(G/G)
G/G)=1/FoM1/2
hard work to increase FoM
0
2
4
6
8
10
12
14
16
2002 2003 2004 2006
per year accumulated FoM
Figure of Merit for open charm
2006 will be a very important year
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Fulvio Tessarotto EINN 2005
Milos, 23 09 2005
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Fulvio Tessarotto EINN 2005
Milos, 23 09 2005
μ’
p’μ
DVCS μp μ’p’
Additional equipment to the COMPASS setup
At these energies (for μ, μ’, and ) the missing mass technique is not adapted
M2required = (mp+mπ)2-mp
2 = 0.25 GeV2
M2observed > 1 GeV2
ECal 1 or 2
12°
Nμ=2.108/SPS cycle(duration 5.2s, each 16.8s)
2.5m liquid H2 targetto be designed and built
L = 1.3 1032 cm-2 s-1
Recoil detector to insure exclusivityto be designed and built
+ additional calorimeter at larger angle
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Fulvio Tessarotto EINN 2005
Milos, 23 09 2005
COMPASS far future:
GPD’s, transversity, G/G and hadron programwill benefit from a possible upgrade of the SPS:
a Superconducting SPS (1 TeV) is better suited to LHC needs;
A bright future for G both at short and long term