Measurement of the J/ photoproduction cross section close ... · Measurement of the J/ photoproduction cross section close to threshold E.Chudakov1 1JLab, for GlueX collaboration

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


Motivation







Motivation







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


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


http://cgl.soic.indiana.edu/jpac/PentaQ_JPsi.php

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


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



(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



Pol

ariz

atio

n

0

0.1

0.2

0.3

0.4

0.5

1.5% Syst. Uncert.

PARA

PERP

(b)


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



(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



Pol

ariz

atio

n

0

0.1

0.2

0.3

0.4

0.5

1.5% Syst. Uncert.

PARA

PERP

(b)


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



(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



Pol

ariz

atio

n

0

0.1

0.2

0.3

0.4

0.5

1.5% Syst. Uncert.

PARA

PERP

(b)


P ≈ 40%

9GeV

Flux

Pola

riza

tion

Example of event reconstruction:

η′f1(1285)/η(1295)

γp → pηπ0π0 → p6γ

M(6γ)


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)


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



All beam energies


/ 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




All beam energies


/ 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


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


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


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


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


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.


BACKUP


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


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


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


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)


Documents

Measurement of the J/ photoproduction cross section close ... · Measurement of the J/ photoproduction cross section close to threshold E.Chudakov1 1JLab, for GlueX collaboration