experimental overview on exclusive processes
DESCRIPTION
Experimental overview on exclusive processes. Delia Hasch. 1 st Duality Workshop June 06-08, 2005; LNF-INFN, Frascati (Italy). Q 2. DVCS s asymm | VECTOR MESONS s asymm | PS MESONS s asymm. - PowerPoint PPT PresentationTRANSCRIPT
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Experimental overview on Experimental overview on exclusive processesexclusive processes
Delia Hasch
1st Duality Workshop June 06-08, 2005; LNF-INFN, Frascati (Italy)
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Q2
t
Q2>>, t<<
hard exclusive processeshard exclusive processes
• high luminosity ~1/Q4, 1/Q6
• high Q2 hard regime
• high resolution exclusivity
Quantum number of final state selects different GPDs:Vector mesons ( H EH E
Pseudoscalar mesons (: H E H E
DVCS () depends on H, E, H, EH, E, H, E~~ ~~
~~ ~~
prerequisities perspectives
DVCS asymm | VECTOR MESONS asymm | PS MESONS asymm
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Compass: 100-190 GeV
Jlab: HallA,Bup to 6 GeV e
H1, ZEUS distinct signature in 4 det.
HERMES, COMPASS, JLab:
missing mass/energy technique:
CLAS: MX ~ 30 MeV
HERMES: MX ~ 400 MeV
prerequisities perspectives
DVCS asymm | VECTOR MESONS asymm | PS MESONS asymm
Hall A: p , n Hall B: p, d
HERMES: p , d unpol. H, D, 4He, 14N, 20Ne, Kr, Xe
H1, ZEUS, HERMES:27.5 GeV e, e
H1, ZEUS: p (820 GeV)
Compass: d , p
prerequisitesprerequisites
CLAS
HERMES
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Deeply virtual Compton ScatteringDeeply virtual Compton Scattering
γpepe '' Bethe-HeitlerHallA,B HERMES H1/ZEUS
BHDVCS
prerequisities perspectives
DVCS asymm | VECTOR MESONS asymm | PS MESONS asymm
NLO analysis of H1, ZEUS cross sections
H H E ~
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DVCS cross section DVCS cross section first measurement oft –slope:d/dt = d/dt|t=0∙exp(-b t)
b 6.02±0.350.39 GeV2
|e)(),,( b|tq xqtxH |e)(),,( b|tg xgxtxH
[A.Freund, M. McDermott EPJC23(2002)]
absolute normalisation!
comparison to NLO QCD:
band width given by b measurement
prerequisities perspectives
DVCS asymm | VECTOR MESONS asymm | PS MESONS asymm
Hg Hq
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DVCS asymmetries DVCS asymmetries )τττ(τ |τ||τ|dσ BH
*DVCSDVCS
*BH
2DVCS
2BH
DVCS-BH interference leads to non-zero azimuthal asymmetry
BH
II
d
dd
)(d)(d
)(d)(d)(A
LU ~ sin∙Im{F1H + (F1+F2)H +kF2E}~
UL ~ sin∙Im{F1H + (F1+F2)(H + …}~
UT ~ sin∙Im{k(F2H - F1E) + … }
separating GPDs through polarisation: LU
beam target
= xB/(2-xB ),k = t/4M2 kinematically suppressed
H, H, E
H, H
H, E
~
~
prerequisities perspectives
DVCS asymm | VECTOR MESONS asymm | PS MESONS asymm
H H E ~
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beam spin asymmetrybeam spin asymmetryγpepe ''
V
[PRL87,2001] [PRL87,2001]
PRELIMINARY
(not for circulation)
0.15 < xB< 0.41.5 < Q2 < 4.5 GeV2
-t < 0.5 GeV2
- VanderhaeghenVanderhaeghen --
prerequisities perspectives
DVCS asymm | VECTOR MESONS asymm | PS MESONS asymm
H H E ~
CLAS
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BSA on nuclear targetsBSA on nuclear targets
… study dependence of coherent production on nuclei
heavier targets : 4He, 14N, 20Ne, Kr, Xe
prerequisities perspectives
DVCS asymm | VECTOR MESONS asymm | PS MESONS asymm
H H E ~
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target spin asymmetrytarget spin asymmetryγpepe ''
V
PRELIMINARY
(not for circulation)
prerequisities perspectives
DVCS asymm | VECTOR MESONS asymm | PS MESONS asymm
H H ~
CLAS
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target spin asymmetrytarget spin asymmetry
- VanderhaeghenVanderhaeghen --
transverse TSA: sensitivity to GPD E (Jq)
prerequisities perspectives
DVCS asymm | VECTOR MESONS asymm | PS MESONS asymm
H H E ~
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beam charge asymmetrybeam charge asymmetry(only @ HERA)
γpepe ''/- γpede ''/-
prerequisities perspectives
DVCS asymm | VECTOR MESONS asymm | PS MESONS asymm
H H E ~
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beam charge asymmetrybeam charge asymmetry(only @ HERA)
GPD calculations: different parametrisations for H
- VanderhaeghenVanderhaeghen (1999/02)(1999/02) ––
HERA: 2004/05 e beam (5x)
AC: high sensitivity to GPD models (tiny ep sample ~10pb-1)
… H1/ZEUS ?
prerequisities perspectives
DVCS asymm | VECTOR MESONS asymm | PS MESONS asymm
H H E ~
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DVCS DVCS DVMS DVMS
ρ0 2u+d, 9g/4
ω 2u-d, 3g/4
s, g
ρ+ u-d
prerequisities perspectives
DVCS asymm | VECTOR MESONS asymm | PS MESONS asymm
H H E ~
H E
DVCS theoretically cleanest process to study GPDs
- azimuthal asymmetries from interference term relate directly to amplitude
hard exclusive meson production: flavour separation
H E ~ ~
! factorisation theorem for L only !
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vs W in bins of Qvs W in bins of Q22 J/
• ~ Wwith • no dependence on Q2
general transition to hard behaviour at high Q2+M2
prerequisities perspectives
DVCS asymm | VECTOR MESONS asymm | PS MESONS asymm
H E
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LL separation from angular separation from angular distributiondistribution
if SCHC holds (VM retains * helicity):
0r0r 311
0411 Im
0400
0400
T
L
r1
r
δ)(ε
1
σ
σR
0
2002 < 10%
[Vanderhaegen et.al. (1999)]
--- 2-gluon exchange--- quark exchange
CLAS: analysis of L for 0 from 6 GeV data (higher W !) going on …
prerequisities perspectives
DVCS asymm | VECTOR MESONS asymm | PS MESONS asymm
H E
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00 transverse TSA transverse TSAinterference of H and E:
S ~ STsin S E∙H
- - Goeke, Polyakov & VanderhaeghenGoeke, Polyakov & Vanderhaeghen (2001)(2001) - -
EE related to JJqq TSA sensitive to J Jqq
0pepe ''
theorySS
SSS A
)(N)(N
)(N)(N
S
1)(A
TUT
same x-dependence behaviour asGPD calculations
prerequisities perspectives
DVCS asymm | VECTOR MESONS asymm | PS MESONS asymm
H E
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cross sectioncross sectionComparison with GPD model for L: [Vanderhaegen, Guichon, Guidal (1999)]
• Q2 dependence: in general agreement with the theoretical expectation• LO calculations too small
power corrections (k┴ ,soft overlap) overestimate data
Q2 dependence:
T suppressed by 1/Q2
prerequisities perspectives
DVCS asymm | VECTOR MESONS asymm | PS MESONS asymm
H E ~ ~
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cross section ratioscross section ratios
production: no-
pole
H dominates
[Mankiewicz,Piller & Radyushkin (1999)]
x
~measure at HERMES Jlab:
PRELIMINARY
(not for circulation)
prerequisities perspectives
DVCS asymm | VECTOR MESONS asymm | PS MESONS asymm
H E ~ ~
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++ transverse TSA transverse TSAinterference of H and E:
S ~ STsin S E∙H
~ ~
~~
gives access to relative size of H and E ~ ~
soon from HERMES Compass, Jlab …
TA
RG
ET
SP
IN A
SY
MM
ET
RY
L p → + n
- - Frankfurt, Pobylitsa, Polyakov & StrikmanFrankfurt, Pobylitsa, Polyakov & Strikman (1999)(1999) - -
- - Belitsky & MBelitsky & Müüllerller (2001)(2001) - -- - Frankfurt, Polyakov, Strikman & VanderhaeghenFrankfurt, Polyakov, Strikman & Vanderhaeghen (2000)(2000) - -
prerequisities perspectives
DVCS asymm | VECTOR MESONS asymm | PS MESONS asymm
H E ~ ~
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dedicated experimentsdedicated experiments
DVCS with recoil: 2006/07
background “free” DVCS:
• semi-inclusive bg: 5% <<1%
• associated bg: 10% 1%
prerequisities perspectives
DVCS asymm | VECTOR MESONS asymm | PS MESONS asymm
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JLab/Hall A JLab/CLAS
Inner Calorimetrer and supraconducting magnet within CLAS torus
e
e’p
γ
Dedicated, high statistics, DVCS experiments
→ Detection of 3 particles e, p and γ in final state
→ Firmly establish scaling laws (up to Q2 ~ 5 GeV2), if observed, or deviations thereof understood, first significant measurement of GPDs.
→ Large kinematical coverage in xB and t leads to femto-tomography of the nucleon
→ Opens the way for an ambitious program with JLab@12GeV (CLAS12 and other)
JLab dedicated DVCS experiments in 2004 - 2005JLab dedicated DVCS experiments in 2004 - 2005
M. Garcon
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conclusionsconclusions
prerequisities perspectives
DVCS asymm | VECTOR MESONS asymm | PS MESONS asymm
• first exciting results on DVCS and DVMS available
polarisation provides new observables sensitive
to different (combinations) GPDS
• dedicated experiments for DVCS measurements going
on at JLab or starting soon at HERMES
new facilities (high luminosity/energy/resolution) needed
to map GPDs in an global analysis of all hard exclusive
processes
H E ~ ~
H E H H E ~
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backup slidesbackup slidest – dependence of BSA for photon and pion production:
PRELIMINARY
(not for circulation)
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factorisation theorem factorisation theorem predictionprediction
for fixed xB and t
asymptotically
6Q
16Q
1LL
σ ),(QFactor Kin.σ red2
L x
4Q
1
2Q
12Q
1spins
2red |M|σ
fit: 1/Qp
p=1.9±0.5p=1.7±0.6p=1.5±1.0