Exclusive Vector Meson Electroproduction at 12 GeV
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Transcript of Exclusive Vector Meson Electroproduction at 12 GeV
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Exclusive Vector Meson Electroproduction
at 12 GeV
Paul Stoler Rensselaer Polytechnic Institute
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What do we want to do at 12 GeV?
(a) Approach to the small–size regime
(b) Learn about short–range nucleon and meson structure
Is 12 GeV the right energy?
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high xB
valence quarks
low xB
sea quarks
From valence quarks to sea quarks and gluons
From gluon dressed to bare quarks.
(Craig Roberts et al.)
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M N =M Ng +M Nq
M μ+,μ+Ni ∝ ea
a∑ Ca dx∫ Hμλ,μλ
i
λ∑ H i(x,ξ,t)
Hμλ ,μλi = dτ db ∫ αS Ψ̂V Fμλ,μλ
i e−S⎡⎣
⎤⎦
GPD’s
Hi =H ,E,H , %E HT ,ET ,HT ,%ET
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γL* p → pρ 0
VGGGK
VGG+D
JML
Example of world data
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GPD: n=3
γL* p → p φ
s
Example of CLAS 6 GeV date
s
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Q2=1-3 GeV2, W=2-3
Jlab 6 GeVJlab 12 GeV
f - ds/dt’
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γL* p → p ρ 0 γL
* p → p φ
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u =(pi − pp )2 smallt =(pi − pp )2 large
J.P Landsberg, B. Pire, L. Szymanowski
Elastic scattering from proton core in a dressed nucleon.
Backward angle (high -t) electroproduction
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Kinematic covered. W ~ 2 4.5 GeV➞
Q2 ~ 1 13 GeV➞ 2
−t’ ~ 0 to > 15 GeV2
Explore the transition from soft physics to the dominance of QCD quarks and gluons
CLAS12 Proposal
γ * + p → p + ρ° γ * + p → p + φ
γ * + p → n + ρ + γ * + p → p + ω
Exclusive Vector Meson Electroproduction with CLAS12
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γ * p → φ p φ → K +K − detect epK + and/or epK +K −
φ→ KS0KL
0 KS0 → π +π − detect pπ +π −
γ * p → ρ 0 p ρ 0 → π +π − detect ′e pπ + and ′e π −π +
γ * p → ρ +n ρ + → π + π 0 → π +γ γ
γ * p → ω p ω → π +π −π 0 detect epπ +π −
Meson Decay Modes
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Goals of the experiment
dσdt*dφ
=σT +εσL +εσTT cos(2φ* )+ 2ε(ε +1)σLT cosφ
* +h 2ε(ε −1)σL ′Tsinφ*
Goal-obtain information about all 5 structure functions available with polarized beam and unpolarized target
σT + εσ L( ) σ TT σ LT obtained from cos(f) and cos(2f) with h = 0
σT σ L –angular distribution of meson decay products.
Beam spin cross section differences
Δσ = dσuru
dt*dφ −
dσs uu
dt*dφ
σL ′T beam spin asymmetries
Structure Functions:
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W (cosθHS) = 38
1−r0004
( ) + 3r0004 −1( )cos
2θHS⎡⎣
⎤⎦
R = σ L
σ L
= 1ε
r0004
1−r0004.
L/T separation
H
Helicity Frame
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Simulations
Extensive simulations were carried out for all 4 mesons channels.
In general, statistics are quite good due to large acceptance, high luminosity and efficient PID
Compared with previously successful CLAS 6 GeV r0 r+ f and w experiments, statistics will increase by factor ~102
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r0 channel simulations
γ * + p → ρ 0 + p ρ 0 → π + + π −
MM ′e pπ +( ) ⇒ π − IM π +π −
( ) ⇒ ρ 0
MM ′e π +π +( )⇒ p IM π +π +
( )⇒ ρ 0 ← large - t
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0.1 xB
Q2
1 GeV2
13 GeV2
0.8
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0
ds/d
t ( m
b/G
eV2 )
-t (GeV2)10 20
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f simulations
γ * p → φp φ→ K + K −
1. MM ′e pK +( ) ⇒ K −
2.MM ′e K + K −( ) ⇒ p
3.Detect ′e K + K − p( )
⎧
⎨
⎪⎪
⎩
⎪⎪
⎫
⎬
⎪⎪
⎭
⎪⎪
IM K + K −( ) ⇒ φ
γ * p → φp φ→ KS0 KL
0
KS0 → π +π − MM pKS
0( ) → KL
0
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Acceptance - e p K+
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6 backup slides follow
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Statistics•Average acceptance ≃ 10 to 50%. (depending on kinematics)
SystematicsBackground subtraction~ few % (sharp state)Acceptance ~5-10 %
Net: s ~7-12%
Errors on cross sections
Statistics•⇒Statistics: very high•Average acceptance ≃ 10 to 30%. (depending on kinematics)
Systematics Background subtraction: systematics 10%
Net: s ~15%