Measurement of the J/ψ photoproduction crosssection close to threshold
E.Chudakov1
1JLab, for GlueX collaboration
Presented at23-rd International Spin Symposium
SPIN2018, Ferrara, 10-14 Spetember 2018
E.Chudakov SPIN 2018, Ferrara J/ψ photoproduction 1 / 13
Motivation
Measured: σ(Eγ) for reaction γ + p → J/ψ + pat 8.22(threshold) < Eγ < 12 GeV
Existing data: two experiments from 1975 at E > 11 GeV
1 Photoproduction dynamicsσ(Eγ) is sensitive to high-x gluons in the nucleon
2 Spectroscopy: search for the LHCb pentaquarks-channel production γ + p → Pc(4450)→ J/ψ + p at 10.1 GeVThe Pc production would manifest itself as a peak in σ(Eγ)
The main topic of this presentation
E.Chudakov SPIN 2018, Ferrara J/ψ photoproduction 2 / 13
Motivation
Measured: σ(Eγ) for reaction γ + p → J/ψ + pat 8.22(threshold) < Eγ < 12 GeV
Existing data: two experiments from 1975 at E > 11 GeV
1 Photoproduction dynamicsσ(Eγ) is sensitive to high-x gluons in the nucleon
2 Spectroscopy: search for the LHCb pentaquarks-channel production γ + p → Pc(4450)→ J/ψ + p at 10.1 GeVThe Pc production would manifest itself as a peak in σ(Eγ)
The main topic of this presentation
E.Chudakov SPIN 2018, Ferrara J/ψ photoproduction 2 / 13
Motivation
Measured: σ(Eγ) for reaction γ + p → J/ψ + pat 8.22(threshold) < Eγ < 12 GeV
Existing data: two experiments from 1975 at E > 11 GeV
1 Photoproduction dynamicsσ(Eγ) is sensitive to high-x gluons in the nucleon
2 Spectroscopy: search for the LHCb pentaquarks-channel production γ + p → Pc(4450)→ J/ψ + p at 10.1 GeVThe Pc production would manifest itself as a peak in σ(Eγ)
The main topic of this presentation
E.Chudakov SPIN 2018, Ferrara J/ψ photoproduction 2 / 13
Exotic XYZ states: rich spectroscopy results
Belle, BaBar, CDF, D0, LHCb, BES have detected, mostly in B decaysmany mesonic states in c̄c, (b̄b) + X final states, as:χc1(3872) 0+(1++) Γ < 1.2 MeV → J/ψππ(> 3%), D̄∗0D0(> 30%) ... c̄c?Zc(3900) 1+(1+−) Γ = 28 MeV → J/ψπ±, D̄∗D... exotic (not a c̄c)
The masses are close to the thresholds of some reactions (say, D̄∗D)
The experimental evidence is very strong!
The interpretation is still uncertain:
Tetraquark: diquark-antidiquark 3̄c × 3c ∈ 1c
Molecule: meson-antimeson loosely bound 1c × 1c ∈ 1c“hadrocharmonium”
Cusp - kinematical effect
More information about their properties should help the interpretation
E.Chudakov SPIN 2018, Ferrara J/ψ photoproduction 3 / 13
LHCb Pentaquark
LHCb PRL, 115, 072001 (2015) Λ0b → K−(J/ψp)
No indications of Λ∗ → K−p reflections to J/ψpPWA leads to two states for P+
c → J/ψp:M1 = 4380± 30, Γ1 = 205± 90 MeV/c2
M2 = 4450± 3, Γ2 = 39± 20 MeV/c2
JPC : (32−, 5
2+
) or (32+, 5
2−
) or (52+, 3
2−
)
P2(4450)P1(4380)
M(J/ψp)
P2(4450)52+ P1(4380)3
2−
Threshold of Σc(2455)D̄∗(2007) = 4462 MeV/c2. The only mode detected J/ψpE.Chudakov SPIN 2018, Ferrara J/ψ photoproduction 4 / 13
Photoproduction of the Pentaquark: Predictions
t-channel s-channel
Eγ ∼ 10 GeV
In a Broad-band photon beamγ + p → J/ψ + p may includeγ + p → Pc → J/ψ + p
Addressed in a number of papers:M. Voloshin et al PRD 92, 031502 (2015)Q. Wang et al PRD 92, 034022 (2015)M. Karliner et al PL 752, 329 (2016)A. Hiller Blin et al PRD 94, 034002 (2016) JPAC
0
0.5
1
1.5
2
2.5
3
3.5
4
8.5 9 9.5 10 10.5 11Eγ GeV
σ(γp
→ J
/ψp
tota
l) nb JPAC
predictions
BR=0%, σ(10.1)=0.64 nb3/2- BR=3% Γ=40 MeV5/2+ BR=1% Γ=40 MeV3/2- BR=3% Γ=200 MeV5/2+ BR=1% Γ=200 MeV
• Pc → J/ψ p VMD⇒ γ p → Pc
• Interference of t- and s-channels• Using the measured Γ(Pc) the full
cross section is calculable with onefree parameter:
σγp→J/ψp(Epeak ) ∝ BR(Pc → J/ψp)2
http://cgl.soic.indiana.edu/jpac/PentaQ_JPsi.php
E.Chudakov SPIN 2018, Ferrara J/ψ photoproduction 5 / 13
CEBAF at 12 GeV
Beam runsyear EMAX , GeV
A B C D2016 10.9 - - 12.02017 10.6 10.6 8.5 11.72018 10.6 10.6 10.6 11.7
A B C
D
CHL
E.Chudakov SPIN 2018, Ferrara J/ψ photoproduction 6 / 13
Hall D/GlueX Meson Spectroscopy In Photoproduction
(GeV)PS E7.5 8 8.5 9 9.5 10 10.5 11 11.5
Pho
ton
Flu
x (A
rb. U
nits
)
1000
2000
3000
4000
5000
6000
7000 (a)Diamond: PARADiamond: PERPAluminum
Photon Beam Energy (GeV)7.5 8 8.5 9 9.5 10 10.5 11 11.5
Pol
ariz
atio
n
0
0.1
0.2
0.3
0.4
0.5
1.5% Syst. Uncert.
PARA
PERP
(b)
Photon Beam Spectrum
P ≈ 40%
9GeV
Flux
Pola
riza
tion
barrelcalorimeter
time-of-flight
forward calorimeter
photon beam
electronbeamelectron
beam
superconductingmagnet
target
tagger magnet
tagger to detector distanceis not to scale
diamondwafer
GlueX
central driftchamber
forward driftchambers
B = 2.0 T
30 cm LH2
E.Chudakov SPIN 2018, Ferrara J/ψ photoproduction 7 / 13
Hall D/GlueX Meson Spectroscopy In Photoproduction
(GeV)PS E7.5 8 8.5 9 9.5 10 10.5 11 11.5
Pho
ton
Flu
x (A
rb. U
nits
)
1000
2000
3000
4000
5000
6000
7000 (a)Diamond: PARADiamond: PERPAluminum
Photon Beam Energy (GeV)7.5 8 8.5 9 9.5 10 10.5 11 11.5
Pol
ariz
atio
n
0
0.1
0.2
0.3
0.4
0.5
1.5% Syst. Uncert.
PARA
PERP
(b)
Photon Beam Spectrum
P ≈ 40%
9GeV
Flux
Pola
riza
tion
Spectrometer parameters
I Acceptance: 1◦ < θ < 120◦
I Resolutions:h±: σp/p ∼ 1− 3%γ: σE/E ∼ 6%/
√E + 2%
I Beam energy tagging ∼0.1%I Trigger: energy in the calorimeters
E.Chudakov SPIN 2018, Ferrara J/ψ photoproduction 7 / 13
Hall D/GlueX Meson Spectroscopy In Photoproduction
(GeV)PS E7.5 8 8.5 9 9.5 10 10.5 11 11.5
Pho
ton
Flu
x (A
rb. U
nits
)
1000
2000
3000
4000
5000
6000
7000 (a)Diamond: PARADiamond: PERPAluminum
Photon Beam Energy (GeV)7.5 8 8.5 9 9.5 10 10.5 11 11.5
Pol
ariz
atio
n
0
0.1
0.2
0.3
0.4
0.5
1.5% Syst. Uncert.
PARA
PERP
(b)
Photon Beam Spectrum
P ≈ 40%
9GeV
Flux
Pola
riza
tion
Experiment GlueX
I Designed for light meson spectroscopyMain goal: search for hybrid mesons
I Data taking 80% completerun EMAX Int L status
GeV pb−1
2016 12.0 10 analyzed2017 11.7 45 analyzed2018 11.7 100 not yet analyzed
I Status of data analysis:complex final states reconstructedunderstanding the efficiencies: in progress
E.Chudakov SPIN 2018, Ferrara J/ψ photoproduction 7 / 13
Hall D/GlueX Meson Spectroscopy In Photoproduction
(GeV)PS E7.5 8 8.5 9 9.5 10 10.5 11 11.5
Pho
ton
Flu
x (A
rb. U
nits
)
1000
2000
3000
4000
5000
6000
7000 (a)Diamond: PARADiamond: PERPAluminum
Photon Beam Energy (GeV)7.5 8 8.5 9 9.5 10 10.5 11 11.5
Pol
ariz
atio
n
0
0.1
0.2
0.3
0.4
0.5
1.5% Syst. Uncert.
PARA
PERP
(b)
Photon Beam Spectrum
P ≈ 40%
9GeV
Flux
Pola
riza
tion
Example of event reconstruction:
η′f1(1285)/η(1295)
γp → pηπ0π0 → p6γ
M(6γ)
E.Chudakov SPIN 2018, Ferrara J/ψ photoproduction 7 / 13
Data Analysis for J/ψ
Reaction studied: γ p → J/ψ p, J/ψ → e+e−
σ(γp → ψp)× BR ∼ 30 pb ∼ 0.3 · 10−6 × σtot (γp → hadrons)
e+
p
e−
Event identification:
• PID for p: TOF, dEdx in drift chambers
• PID for e±: EM calorimeters (challenge: large BG from π+π−p events)• Kinematic fit using the photon energy measured with a 0.1% resolution
The Bethe-Heitler reaction γ p → (e+e−)p used for normalization(absolute efficiencies are not fully understood yet)
E.Chudakov SPIN 2018, Ferrara J/ψ photoproduction 8 / 13
Mass Spectrum of e+e−
GlueX Preliminary: not the final 2016+2017 data sample (about 70%).
All beam energies
BH normalization1.5 - 2.5 GeV
BH simulation from R.Paremuzyan, based on E.Berger et al, EPJC 23:675 (2002)E.Chudakov SPIN 2018, Ferrara J/ψ photoproduction 9 / 13
Mass Spectrum of e+e−
GlueX Preliminary: not the final 2016+2017 data sample (about 70%).
All beam energies
BH normalization1.5 - 2.5 GeV
/ ndf 2χ 62.38 / 65p0 0.172± 7.397 p1 0.163±2.709 − p2 12.8± 153 p3 0.001± 1.017 p4 0.000951± 0.009621
0.95 1 1.05 1.1
50
100
150
200
250
300 / ndf 2χ 62.38 / 65p0 0.172± 7.397 p1 0.163±2.709 − p2 12.8± 153 p3 0.001± 1.017 p4 0.000951± 0.009621
φ
φ736± 58
σ = 9.6 MeV
BH simulation from R.Paremuzyan, based on E.Berger et al, EPJC 23:675 (2002)E.Chudakov SPIN 2018, Ferrara J/ψ photoproduction 9 / 13
Mass Spectrum of e+e−
GlueX Preliminary: not the final 2016+2017 data sample (about 70%).
All beam energies
BH normalization1.5 - 2.5 GeV
/ ndf 2χ 31.53 / 35p0 15.96± 24.61 p1 5.112±7.307 − p2 5.5± 50.6 p3 0.001± 3.091 p4 0.000708± 0.007472
3 3.05 3.1 3.15 3.2
0
10
20
30
40
50
60 / ndf 2χ 31.53 / 35
p0 15.96± 24.61 p1 5.112±7.307 − p2 5.5± 50.6 p3 0.001± 3.091 p4 0.000708± 0.007472
ψJ/
J/ψ189± 16
σ = 7.5 MeV
BH simulation from R.Paremuzyan, based on E.Berger et al, EPJC 23:675 (2002)E.Chudakov SPIN 2018, Ferrara J/ψ photoproduction 9 / 13
Energy dependence of the cross section
10-1
1
10
8 10 12 14 16 18 20 22Eγ GeV
σ(γp
→ J
/ψp)
nb
Cornell 75SLAC 75
GlueX preliminary
30% system.GlueX
• SLAC:U.Camerini et al, PRL 35 (1975)Calculated from the measureddσdt |t=tmin assumingdσdt ∝ ea·t , a = 2.9±0.3 GeV−2
measured at 19 GeV
• Cornell:B.Gittelman et al, PRL 35 (1975)t-slope a = 1.25± 0.2 GeV−2
horizontal error bar representsthe acceptance
E.Chudakov SPIN 2018, Ferrara J/ψ photoproduction 10 / 13
Limit on the Pentaquark Production
0
0.25
0.5
0.75
1
1.25
1.5
1.75
2
2.25
2.5
8 8.5 9 9.5 10 10.5 11 11.5 12Eγ GeV
σ(γp
→ J
/ψp)
nb
GlueX
fit 2-g + 3-g model to GlueX points
JPAC for Γ=40MeV 3/2- BR=0.02
JPAC binned as experiment
Fit: 2 + 3-gluon exchangeBrodsky et al, PL 498 (2001)2 free parameters χ2/ndf = 0.8
Limit for Pc(4450) Γ = 40 MeVJPAC model, assumptions:σ(10.1) = 0.64 nb non-reson.no wide state Pc(4380) addedJPC BR 10.1± 0.6 GeV (2 bins)
JPAC experiment sepa-nb nb ration
σ(stat)3/2- 2.0% 0.81 0.58± 0.08 2.95/2+ 0.7% 0.81 0.58± 0.08 2.9
Systematic to be addressed:• t and s-channel interference• VMD model dependence• The wide state influence
E.Chudakov SPIN 2018, Ferrara J/ψ photoproduction 11 / 13
Limit on the Pentaquark Production
0
0.25
0.5
0.75
1
1.25
1.5
1.75
2
2.25
2.5
8 8.5 9 9.5 10 10.5 11 11.5 12Eγ GeV
σ(γp
→ J
/ψp)
nb
GlueX
fit 2-g + 3-g model to GlueX points
JPAC for Γ=40MeV 3/2- BR=0.02
JPAC binned as experiment
exclude peak areafrom the fit
Fit: 2 + 3-gluon exchangeBrodsky et al, PL 498 (2001)2 free parameters χ2/ndf = 0.1
Limit for Pc(4450) Γ = 40 MeVJPAC model, assumptions:σ(10.1) = 0.64 nb non-reson.no wide state Pc(4380) addedJPC BR 10.1± 0.6 GeV (2 bins)
JPAC experiment sepa-nb nb ration
σ(stat)3/2- 2.0% 0.84 0.58± 0.08 3.15/2+ 0.7% 0.84 0.58± 0.08 3.1
Systematic to be addressed:• t and s-channel interference• VMD model dependence• The wide state influence
E.Chudakov SPIN 2018, Ferrara J/ψ photoproduction 11 / 13
Unbinned distribution t vs E
The beam energy resolution is about 0.1%� 0.6 GeV binsThe Pc is expected to produce broad t-distribution
• JPAC: 52
+BR = 3%
• White dots: J/ψ events fromthe peak
• No indication of eventconcentration at 10.1 GeV
E.Chudakov SPIN 2018, Ferrara J/ψ photoproduction 12 / 13
Summary & Outlook
Summary of the preliminary GlueX results
The first measurement of the cross section of the reactionγp → J/ψp close to threshold has been reported.No statistically-significant evidence for the LHCb pentaquark hasbeen observed. The model-predicted yield fromPc(4450)( 3
2−
)→ J/ψp, BR=2% (or 52
+, BR=0.7%) is about
3σ(stat) above the experimental result.
Outlook
GlueX is planning to analyze the full data sample and finalize theresults before the end of the year. Also, we are planning to increasethe sensitivity to the Pc(4450) detection by using t − E unbinnedevent analysis. Later, the 2018 data is expected to triple thestatistics.Other experiments at JLab (CLAS12 and Hall C) have beenscheduled to the near future to measure the same process.Potentially, they would be able to reach a higher sensitivity.
E.Chudakov SPIN 2018, Ferrara J/ψ photoproduction 13 / 13
BACKUP
E.Chudakov SPIN 2018, Ferrara J/ψ photoproduction 14 / 13
Identification of e±
Using the track momentum p and the calorimeter energy E
0.7 0.8 0.9 1 1.1 1.2 1.3 1.4electron p/E
0.7
0.8
0.9
1
1.1
1.2
1.3
1.4
posi
tron
p/E
0
10
20
30
40
50
60
70
/ ndf 2χ 61.26 / 64p0 0.0028± 0.1052 p1 8.6± 144.9 p2 0.002± 1.062 p3 0.00286± 0.05108 p4 7.87± 21.92 p5 0.0183± 0.1327
0.8 0.9 1 1.1 1.2 1.3 1.4p/E
0
50
100
150
200
250 / ndf 2χ 61.26 / 64
p0 0.0028± 0.1052 p1 8.6± 144.9 p2 0.002± 1.062 p3 0.00286± 0.05108 p4 7.87± 21.92 p5 0.0183± 0.1327
data
sample)πnormalized backgr (from
Me+e−
1.5− 2.5 GeV
1 1.5 2 2.5 3), GeV-e+M(e
1
10
210
310
410
510
even
ts/1
0 M
eV
initial "pion" distribution
E/p cuts on both leptonsσ2
5% of data
1/5
000
BH normalization
Pion background for BH sample1.5 < M(e+e−) < 2.5 GeV
• One e± identified• p/E for pions - shape measured• Average background 36± 1.2%
• Energy-dependent BG correction
E.Chudakov SPIN 2018, Ferrara J/ψ photoproduction 15 / 13
Beam Flux Normalization
, GeVγE8.5 9 9.5 10 10.5 11 11.5 12
/20
MeV
-1lu
min
osity
, pb
0
0.2
0.4
0.6
0.8
Integral ∼50 pb−1
coherent peak
8.5 9 9.5 10 10.5 11 11.5 12, GeVγE
0
0.5
1
1.5
yie
ld/2
0 M
eV, a
.u.
ρflu
x no
rmal
ized
γp → ρp
• Beam flux is measured with thePair Spectrometer using e+e−
pair production with a ∼ 0.1%converter
• “Tagged flux” measures photonsin coincidence with the taggerdetectors
• The structure of the tagged flux iscaused by coherent peaks andthe tagger geometry/efficiency
• Flux-normalized yield of γp → ρpis smooth
E.Chudakov SPIN 2018, Ferrara J/ψ photoproduction 16 / 13
Systematic Error Budget
Systematic error source Estimate, %J/ψ to BH relative yield 18BH cross section calculation 10Pion contamination to BH 5ρ′ contamination to BH 5t-dependence of efficiency 9Total 24
E.Chudakov SPIN 2018, Ferrara J/ψ photoproduction 17 / 13
Exotic XYZ states: rich spectroscopy results
Belle, BaBar, CDF, D0, LHCb, BES have detected, mostly in B decaysmany mesonic states in c̄c, (b̄b) + X final states, as:χc1(3872) 0+(1++) Γ < 1.2 → J/ψππ(> 3%), D̄∗0D0(> 30%) ... c̄c?Zc(3900) 1+(1+−) Γ = 28 → J/ψπ±, D̄∗D... exotic (not a c̄c)
The masses are close to the thresholds of some reactions (say, D̄∗D)
e+e− → π±(Z∓C → π∓J/ψ)
BESIII PRL, 110, 252001 (2013)
e+e− → π±(Z∓C → (D̄∗D)∓)
BESIII PRL, 112, 022001 (2013)
E.Chudakov SPIN 2018, Ferrara J/ψ photoproduction 18 / 13