Near threshold J/ψ photoproduction at
JLAB and LHCb proton-J/ψ bound states
S. Stepanyan (JLAB)
The Proton Mass
At the heart of most visible matter
Workshop at Temple U., March 28-29, 2016
2
Ø  Why J/ψ photoproduction
Ø  Photoproduction near threshold
Ø  JLAB experiment
• 
• 
E12-12-001
E12-11-005
0
b
Ø  LHCb (J/ψp) pentaquarks in Λ decay
Ø  Pentaquarks in photo- and electroproducion of J/ψ
Ø  Summary
S. Stepanyan, The proton mass
Workshop at Temple
Why J/ψ photoproduction?
§  There are no cc in nucleons, production of J/ψ goes via gluon exchange
§  Small size QQ state due to large mass of c-quark
§  Unique probe of the gluon field of the target
γ
J /ψ
γ
J /ψ
x1
x2
x1
N
N’
GPD
N
(a)
x2
N’
GPD
t
(b)
t (HERA,
(a)At high energies
FNAL) probes gluon GPDs
Near threshold (large momentum
(b)
transferred) probes gluonic form factor
S. Stepanyan, The proton mass
Workshop at Temple
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4
VDM picture of the production
mc ≈ 1.5 GeV ;
r⊥ ~
1
= 0.13 fm
mc
Close to the threshold, Eγ≈ 10 GeV
lc =
2Eγ
2
c
4m
≈ 0.4 fm; lF ≈
2EJ / ψ
(
2mc mψʹ − mJ / ψ
)
~ 1− 2 fm; b ~
1
~ 0.2 fm
−t
Favorable kinematics for studies of J/ψN scattering
S. Stepanyan, The proton mass
Workshop at Temple
J/ψ photoproduction near threshold
n 
The lowest published energy point is at
Eγ=11 GeV
n 
Production mechanisms, 2-gluon or 3gluon exchange
n 
Need precision data to sort this out
S.J. Brodsky, E. Chudakov, P. Hoyer, and J-M. Laget, Phys.Lett. B498, 23-28 (2001)
S. Stepanyan, The proton mass
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JLAB12 experiments
n 
With up to 12 GeV electron beam, the threshold region will be
studied in great detail with upgraded facilities in Halls A and B, as
well as in the new experimental Hall-D with GluEx
n 
Currently only two experiments have been approved:
q 
E12-12-001 on CLAS12 in Hall-B, 100 days approved
q 
E12-12-006 on SoLID in Hall-A, 50 days approved
n 
There more in the discussions (electroproduciton, production on
nuclear targets)
n 
The same experiments are well positioned to search and study
LHCb hidden charm pentaquarks
S. Stepanyan, The proton mass
Workshop at Temple
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SoLID in Hall-A, E12-12-006
Primary detection channels:
•  4-fold coincidence, which consists of detecting the scattered electron,
the recoil proton, and the (e+e−) from J/ψ decay
•  3-fold coincidence, without proton detection.
S. Stepanyan, The proton mass
Workshop at Temple
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SoLID projections
L=1037 cm-2 s-1, 50 days
2-gluon
3-gluon
4-fold
0.7K
2.9K
3-fold
2.1K
8.1K
S. Stepanyan, The proton mass
Workshop at Temple
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CLAS12 in Hall-B
FD
Forward Detector
Central Detector
CD
Angular range
Track
Photons
50 – 400
20 – 400
350 – 1250
---
Resolution
dp/p (%)
dθ (mr)
Δφ (mr)
< 1 @ 5 GeV/c
<1
<3
< 5 @ 1.5 GeV/c
< 10 – 20
< 5
Photon detection
Energy (MeV)
δθ (mr)
Neutron detection
>150
4 @ 1 GeV
Neff< 0.7
----Neff< 0.3
Particle ID
e/π π/p π/K
K/p π(η)gγγ
Full range
< 5 GeV/c
< 2.6 GeV/c
< 4 GeV/c
Full range
--< 1.25 GeV/c
< 0.65 GeV/c
< 1.0 GeV/c
---
L = 10 35cm−2 s−1
S. Stepanyan, The proton mass
Workshop at Temple
E12-12-001: TCS and J/ψ photoproduction
• 
• 
Quasi-real (untagged) photoproduction of lepton pairs
Only recoil proton and J/ψ decay leptons are detected
Scattered electron kinematics from the missing momentum analysis
+ −
2
"
"
ep
→
p
e
e
(
e
)
(
Q
≈0)
9.92 GeV ‹ E ‹ 11 GeV
!
J/ψ
10 2
Events/0.01 GeV
• 
BH - background
10
2
2.2
2.4
2.6
2.8
Me+e- (GeV)
3
3.2
3.4
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CLAS12 projections
Final state: ep → e + e − pX where X is scattered electron with Q2<0.01
GeV2 and σ ~ 1/Q4 and σ ~ e-1.2t
100 days @ 1035 cm-2 sec-1
<Eγ>=10.8 GeV
S.J. Brodsky, E. Chudakov, P. Hoyer, and
J-M. Laget, Phys.Lett. B498, 23-28 (2001)
<Eγ>=9. GeV
S. Stepanyan, The proton mass
Workshop at Temple
LHCb hidden charmed pentaquarks
R. Aaij et al. [LHCb Collaboration], Phys. Rev. Lett. 115, 072001
0
−
Amplitude analysis of the decay Λ b → K p J ψ with two interfering
0
modes of Λ b decay (with 14 Λ* states listed by PDG)
0
b
*
Λ →Λ J ψ
Two exotic
Λ 0b → K − Pc+
ccuud 5-quark states, Pc+ , were needed to converge
The significance of each of these resonances is more than 9σ.
S. Stepanyan, The proton mass
Workshop at Temple
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The new J/ψp pentaquark states, P
M-=4380±8±29 MeV
Γ-=205±18±86 MeV
JP=3/2M+=4449.8±1.7±2.5 MeV
Γ+=39±5±19 MeV,
JP= 5/2+.
Events/(15 MeV)
+
c
800
LHCb
(b)
700
600
500
400
300
200
100
0
4
4.2
4.4
4.6
4.8
5
mJ / ψp [GeV]
R. Aaij et al. [LHCb Collaboration], Phys. Rev. Lett. 115, 072001
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Interpretation of new states
Charmed Baryon and anti-charmed meson molecule:
• 
• 
• 
• 
• 
M. Karliner and J. L. Rosner, arXiv:1506.06386
L. Roca, J. Nieves, and E. Oset, arXiv:1507.04249
R. Chen, X. Liu, X.-Q. Li, and S.-L. Zhu, arXiv:1507.03704
H-X. Chen, W. Chen, X. Liu, T.G. Steele, and S-L. Zhu, arXiv:1507.0317
J. He, arXiv:1507.05200
• 
U.-G. Meiner and J. A. Oller,, arXiv:1507.07478. For P(4550)
• 
A. Mironov and A. Morozov, arXiv:1507.04694. Is NOT
*
*
*
c
D Σc−D Σ
χ c1 p
a molecule
A resonance state or reflection:
• 
F.-K. Guo, U.-G. Meiner, W. Wang, and Z. Yang, arXiv:1507.04950; Dominant decay to χ c1 p if real
• 
M. Mikhasenko, arXiv:1507.06552. Possible reflection in the complicated decay chain
Need independent verification with a different production mechanism
S. Stepanyan, The proton mass
Workshop at Temple
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•  The production of pentaquarks proceeds
as an s-channel resonance
•  VDM can be used to relate initial and
final states
,nb
Pentaquark photo-production
Br[Pc (4450) → p J ψ] = 0.01
V. Kubarovsky
1.4
35
1.2
30
1
25
0.8
J/
p
J/
Pc
20
0.6
p
15
0.4
10
0.2
5
9
9.5
10
10.5
E,GeV
9
9.5
10
10.5
E,GeV
Prediction of 2-gluon exchange model
for J/ψ elastic photoproduction
Q. Wang, X. H. Liu and Q. Zhao, arXiv:1508:00339.
V. Kubarovsky and M.B. Voloshin, arXiv:1508.00888.
M. Karliner and J.L. Rosner, arXiv:1508.01496.
S. Stepanyan, The proton mass
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SLAC single arm measurements
Flattening of cross section near the threshold
Can enhancement be due to a resonance?
S. Brodsky, SLAC-PUB-14985
2-g exchange
R.L. Anderson, SLAC-PUB-1741
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Workshop at Temple
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Search for pentaquarks in E12-12-001
Studies with Fast MC – field setting should be ≥75% to have at least 2σ of the
invariant mass resolution within Γ+
S. Stepanyan, The proton mass
Workshop at Temple
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E12-11-005: tagged J/ψ photoproduction
From A. Celentano’s talk
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E12-11-005: acceptance, resolution, rates
From A. Celentano’s talk
Expected rates – 1.5x103 σγ event/day/µbarn
S. Stepanyan, The proton mass
Workshop at Temple
J/ψ electroproduction with CLAS12 in Hall-B
•  Di-muon electroproduciton, ep → e"p"µ +µ −
•  CLAS12 FD will be blocked with heavy
shielding/absorber from electromagnetic and
hadronic backgrounds to be able to run at
luminosities ~1037 cm-2 s-1, and will be used
as a muon detector
•  Scattered electrons will be detected in a
compact PbWO4 calorimeter that is part of
the shielding
30o
Location
of HTCC
W shieldmirrors
500
Electron
calorimeter and
shield/absorber
30o
7o
S!
7o
5o
PbWO4
500
PbWO4 modules with APD readout - ~ 1500 modules S. Stepanyan, The proton mass
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Kinematics and mass resolutions for pentaquarks
•  Detector response is simulated with FastMC, events are generated with 1/Q4 and exponential t-dependence, b0=1.2 GeV-2
•  Recoil protons will not be detected
•  J/ψ will be identified in the invariant mass of µ+µ•  Proton will be identified in the missing mass of e’µ+µ•  Pentaquarks will be searched in the missing mass of e’
0.05
Constant
Mean
Sigma
45000
1462. / 18
0.4199E+05
0.1583E-03
0.1162E-01
40000
0.04
35000
Acceptance
30000
0.03
25000
20000
0.02
15000
10000
0.01
5000
0
3.8
4
4.2
4.4
4.6
4.8
0
-0.1 -0.08 -0.06 -0.04 -0.02
0
0.02 0.04 0.06 0.08 0.1
W (GeV)
W (GeV)
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Summary
n 
The energy reach of upgraded JLAB machine crosses the threshold of
charmonioum production on the nucleon
n 
Together with new experimental facilities this provides an opportunity for
detailed study production of ground state charmoniom, J/ψ
n 
Particular interest is the uncharted near threshold region, where different
mechanisms for the production have been proposed. In this region, J/ψ
production probes gluonic form factors of the nucleon
n 
Two experiments (in Halls A and B) for J/ψ photoproduction have already been
approved. One in Hall-B with CLAS12 is expected to produce results within
next two years.
n 
The same data sets can also be used to search and study LHCb hidden charm
pentaquark states in the pJ/ψ decay mode, Pc(4380) and Pc(4450)
n 
There are more discussions for new experiments, including J/ψ
electroproduciton, production on nuclei to study J/ψ N scattering. Pilot
measurements for these studies can be done with already approved beam
time.
S. Stepanyan, The proton mass
Workshop at Temple
J/ψ electroproduction rates
Electroproduction cross section can be presented as a sum of cross sections
for transversely (T ), and longitudinally (L) polarized photons
where
the virtual photon flux
the virtual photon polarization
VDM relation for transversely polarized (T)
and longitudinally polarized (L) photon cross sections
With 100 times of the CLAS12 nominal luminosity, for the 2-gluon exchange
model expecting 1/day in 40 MeV bin of W at 4.4 GeV
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