Search for the LHCb Charmed Pentaquark

in Photo-production at Hall C

Sylvester Joosten

J/ψ-007 Collaboration Meeting, October 2018

S. Joosten

The LHCb charmed “pentaquark” Pc: still a hot topic!

Slide from PAC talk (2016) Today: 579 citations

~200 citations/year for 2.9 years

2

S. Joosten

Discovery of the LHCb charmed “pentaquark” Pc

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⇤b ! ⇤⇤J/ ! (K�p)J/

⇤b ! K�Pc ! K�(pJ/ )

⇤b ! K�pJ/ Aaij, R, et. al (LHCb) PRL 115-7 (2015)

wide: Pc(4390) (9σ)

2 Pc states needed to describe results

narrow: Pc(4450) wide: Pc(4380)

spin/parity either: 5/2+, 3/2- (most likely!) 5/2-, 3/2+ 3/2-, 5/2+

narrow: Pc(4450) (12 σ)

S. Joosten

charmed “pentaquark” in photo-production

4

Possible explanations for LHCb observations: LHCb: 2 new charmed “pentaquark” (Pc) states alternative: kinematic enhancements through anomalous triangle singularity (ATS)

Photo-production ideal tool to distinguish between both explanations

if Pc real states, also created in photo-production kinematic enhancement through ATS not possible

Pc(4450) translates to narrow peak around Eγ = 10 GeV

Lui X-H, et al., PLB 757 (2016), p231 (and references therein)

Wang Q., et al., PRD 92-3 (2015) 034022-7 (and references therein)

JLab perfect place for this measurement!

S. Joosten 5

J/ψ photo-production: Direct photo-production Cornell ’75, SLAC ’75, CERN NA-14, FNAL E401, E687 Quasi-real production H1 and ZEUS Ultra-peripheral collisions LHCb ’14 (pp) and ALICE ’15 (pPb)

J/ψ photo-production: what do we know?

Well constrained above W > 15 GeV Dominated by t-channel 2-gluon exchange

Almost no data near threshold

γ,γ*J/ψ,Υ

l -

l+

p p’

q

q_

10 210 310W (GeV)

3−10

2−10

1−10

1

10

210

310

(nb)

ψJ/σ

Cornell '75SLAC '75CERN NA-14FNAL E401FNAL E687

*)γH1 Combined (*)γZEUS Combined (

LHCB '14 (UPC)

J/ψ

S. Joosten 6

Why the threshold region?

Near Threshold: Origin of proton mass, trace anomaly of the QCD energy-momentum tensor. Gluonic Van der Waals force, possible quarkonium-nucleon/nucleus bound states Mechanism for quarkonium production

10 210 310W (GeV)

3−10

2−10

1−10

1

10

210

310

(nb)

ψJ/σ

Cornell '75SLAC '75CERN NA-14FNAL E401FNAL E687

*)γH1 Combined (*)γZEUS Combined (

LHCB '14 (UPC)

J/ψ

[GeV]γE10 15 20

[nb]

σ

2−10

1−10

1

10

210

310Cornell 75

SLAC 75

SLAC 76 (Unpub.)

2-gluon fit

Pc?

LHCb charmed (charming) pentaquark

S. Joosten 7

S.J. Brodsky, et al., Phys.Lett. B498, 23-28 (2001)

Same as high energies (2-gluon)?

2-gluon 3-gluon

Production mechanism near threshold unknown

Or a partonic soft mechanism (power law 2-gluon form-factor)?

Frankfurt and Strikman., PRD66 (2002), 031502

partonic soft

Orders of magnitude difference 2-gluon fastest drop-off

Drives required luminosity for threshold measurement

Maybe 3-gluon exchange dominant?

S. Joosten

2-gluon fit near threshold

8

10 15 20 25 (GeV)γE

4−10

3−10

2−10

1−10

1

10

210

310

(nb)

ψJ/

σ

Cornell '75

SLAC '75

SLAC '76 (Unpublished)

2-gluon fit

J/ψ

Smallest cross section drives required precision and luminosity Use 2-gluon estimate for experimental projections near threshold

S. Joosten

Resonant J/ψ production through Pc decay

9

[GeV]γE8 8.5 9 9.5 10 10.5 11 11.5 12

[nb]

σ

0

0.2

0.4

0.6

0.8

1Cornell 75

SLAC 76 (Unpublished)

t-channel (2-gluon)

5/2+ (3% coupling)cP

3/2- (3% coupling)cP

sum

)θcos(1− 0.8− 0.6− 0.4− 0.2− 0 0.2 0.4 0.6 0.8 1

Arbi

trary

Uni

ts

0

1

2

3

4Ψt-channel J/

5/2+cP 3/2-cP 5/2-cP 3/2+cP

Cross section depends on coupling to (J/ψ, p) channel J/ψ angular distribution depends on Pc spin/parity

P c

s − channel

γ J/ ψ

(a)

P c

u − channel

γ J/ ψ

(b)P’P

P P’

s-channel u-channel

Leverage cos(θ) dependence to maximize S/B at low coupling!

d�

d cos ✓J/ (�p ! Pc ! J/ p)

3% coupling

Wang Q., et al., PRD 92-3 (2015) 034022-7

S. Joosten 10

To beamdump

1

3

D

QQ

Q

Incidentbeam

Hydrogentarget

e-

Detector Stacks:Tracking/ Timing:

1. Drift Chambers2. Hodoscopes

3. Gas erenkov4. Lead Glass Calorimeter

22

4

Particle ID:

9% Cu Radiator

D

QSHMS

HB

Argon/Neon Cerenkov

HGC

S1XS1Y

AGC

DC1

DC2

S2XS2Y LGC

A1

C4F10 Cerenkov

1 22

3

1

4

QQ

HMS

e+

Run with 2 settings: ”SIGNAL” Setting (9 days): minimizes accidentals and maximizes signal/background:

HMS: 34o, 3.25 GeV electrons SHMS: 13o, 4.5 GeV positrons

”BACKGROUND” Setting: (2 days): precise determination of the t-channel background

HMS: 20o, 4.75 GeV electrons SHMS: 20o, 4.25 GeV positrons

Setup similar to E-05-101(WACS) 50μA electron beam at 11GeV 10.6 GeV 9% copper radiator 15cm 10cm LH2 total 10% RL

electron in HMS

positron in SHMS

J/ �

High-impact experiment …will run February 2019!

Pentaquark search E12-16-007 in Hall C

S. Joosten

Photon Energy Reconstruction

11

Can unambiguously reconstruct the initial photon energy from the reconstructed J/ψ momentum and energy Assumptions:

photon beam along the z-axis proton target at rest 2 final state particles: a proton and a J/ψ

E� =M2 � 2EJMP

2(E �Mp � P cos ✓ )<latexit sha1_base64="wFhYCc1s5gP4TVZhwu/75FQTu0E=">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</latexit><latexit sha1_base64="wFhYCc1s5gP4TVZhwu/75FQTu0E=">AAACRnicbZBNSyNBEIZrortq9iu7HvfSGAT3kDATFvQiiEtAhECEjQqZ7FDT6Ukau2eG7pqFMOQv+Tv8AXvZg169eVu82hlzWD9eaHj6rSqq+41zJS35/l+vtrL65u3a+kb93fsPHz81Pn85tVlhuBjwTGXmPEYrlEzFgCQpcZ4bgTpW4iy++LGon/0Wxsos/UmzXIw0TlKZSI7krKhx1I3CCWqNbJ/Vw8QgL3tRmFv5q9PqdKPjXtSfl52dbuW1elHe6lcY8syGNBWE1fXbPGo0/bZfib2EYAlNWKofNW7DccYLLVLiCq0dBn5OoxINSa7EvB4WVuTIL3Aihg5T1MKOyurHc7btnDFLMuNOSqxy/58oUVs707Hr1EhT+7y2MF+rDQtK9kalTPOCRMofFyWFYpSxRXxsLI3gpGYOkBvp3sr4FF1s5EJ+soXr2MjJlBbJBM9zeAmnnXbgt4OT782Dw2VG6/AVtmAHAtiFAziCPgyAwyX8gWu48a68O++fd//YWvOWM5vwRDV4ANoJsQw=</latexit><latexit sha1_base64="wFhYCc1s5gP4TVZhwu/75FQTu0E=">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</latexit><latexit sha1_base64="wFhYCc1s5gP4TVZhwu/75FQTu0E=">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</latexit>

S. Joosten

Maximizing the sensitivity

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t-channel

Pc(4450) 5/2+

Use HMS and SHMS to maximize Pc signal over t-channel background

)θcos(1− 0.8− 0.6− 0.4− 0.2− 0 0.2 0.4 0.6 0.8 1

Arbi

trary

Uni

ts

0

1

2

3

4Ψt-channel J/

5/2+cP 3/2-cP 5/2-cP 3/2+cP

“SIGNAL” Setting

positron in SHMS

electron in HMS

S. Joosten

Resolution

13

[GeV]γE9 9.5 10 10.5 11 11.5 12

Cou

nts

0

100

200

300

Ψt-channel J/

3/2- (5.0% coupling)cP

5/2+ (5.0% coupling)cP

sum

[GeV]γE9 9.5 10 10.5 11 11.5 12

Cou

nts

0

100

200

Ψt-channel J/

3/2- (5.0% coupling)cP

5/2+ (5.0% coupling)cP

sum

Generated Reconstructed

[GeV]-e+eM3 3.02 3.04 3.06 3.08 3.1 3.12 3.14 3.16 3.18 3.2

Arbi

trary

Uni

ts

0

2

4

6

8

reconstructed J/ψ mass: σ = 5 MeV

S. Joosten

[GeV]γE9 9.5 10 10.5 11 11.5 12

Cou

nts

0

50

100

150Ψt-channel J/

3/2- (5.0% coupling)cP 5/2+ (5.0% coupling)cP

sum2 day estimate

BACKGROUND (2 days)

t-channel: 682 events 5/2+: 204 events 3/2-: 26 events

14

Projected results for “BACKGROUND” Setting

assuming 5% coupling value favored by existing photo-production data

(Corresponds to <1% coupling in V. Kubarovsky’s model)

2 days of beam time at 50μA able to separate 5/2+ from t-channel at low Eγ

Only 2 days!

]2t [GeV

6− 5− 4− 3− 2− 1− 0 1 2

Cou

nts

0

100

200

300 Ψt-channel J/ 3/2- (5.0% coupling)cP 5/2+ (5.0% coupling)cP

sum2 day estimate

First high-precision absolute cross section measurement near threshold!

Wang Q., et al., PRD 92-3 (2015) 034022-7

V. Kubarovsky, et al., PRD 92-3 (2015) 031502-4

J/ �

S. Joosten

Projected results for “SIGNAL” Setting

15

]2t [GeV

6− 5− 4− 3− 2− 1− 0 1 2

Cou

nts

0

50

100

150

200

Ψt-channel J/ 3/2- (5.0% coupling)cP 5/2+ (5.0% coupling)cP

sum9 day estimate

assuming 5% coupling value favored by existing photo-production data

(Corresponds to <1% coupling in V. Kubarovsky’s model)

9 days of beam time 5/2+ peak dominates the spectrum 26x reduction in t-channel background rate

Only 9 days!

Wang Q., et al., PRD 92-3 (2015) 034022-7

Significance > 20σ!

V. Kubarovsky, et al., PRD 92-3 (2015) 031502-4

[GeV]γE9 9.5 10 10.5 11 11.5 12

Cou

nts

0

100

200

Ψt-channel J/ 3/2- (5.0% coupling)cP 5/2+ (5.0% coupling)cP

sum9 day estimate

SIGNAL (9 days) t-channel: 120 events

5/2+: 881 events 3/2-: 266 events

J/ �

S. Joosten

Sensitivity for Discovery

16

coupling [%]1 1.5 2 2.5 3

]σ

Sens

itivi

ty [n

1

10

Projected Sensitivity

limitσ5

sensitivity calculated using a Δ-log-likelihood formalism 5 standard deviation level of sensitivity starting from 1.3% coupling!

What changed since the proposal?

S. Joosten

Changes since the proposal

18

10.6GeV beam instead of 11GeV beam 10cm LH2 target instead of 15cm LH2 target Smaller SHMS momentum acceptance Needed to re-tune the settings!

#1 is signal setting #2 is the original t-channel background setting #3 is a new background t-channel setting

P HMS Theta HMS P SHMS Theta SHMS#1: -3.45 32.8deg. 4.35 13.6deg.#2: -4.75 20.0deg. 4.25 20.0deg.#3: -4.95 18.6deg. 4.95 16.7deg.

S. Joosten

1 1.5 2 2.5 3 3.5 4 4.5 5 5.5coupling [%]

1

10

]σ

Sens

itivi

ty [n

Projected Sensitivity

limitσ5

Impact on sensitivity

19

1 1.5 2 2.5 3 3.5 4 4.5 5 5.5coupling [%]

1

10

]σ

Sens

itivi

ty [n

Projected Sensitivity

limitσ5

Significant loss in statistics From 5 sigma at 1.3% to 5 sigma at 1.7%

PAC NEW

S. Joosten

1 1.5 2 2.5 3 3.5 4 4.5 5 5.5coupling [%]

1

10

]σ

Sens

itivi

ty [n

Projected Sensitivity

limitσ5

Sensitivity assuming different models

20

Wang et al. Kubarovsky et al

0.2 0.4 0.6 0.8 1 1.2 1.4coupling [%]

1

10

]σ

Sens

itivi

ty [n

Projected Sensitivity (Kubarovsky)

limitσ5

Situation improved when using Kubarovsky’s model!

S. Joosten

Projected results (5% coupling)

21

8 8.5 9 9.5 10 10.5 11 11.5 12 [GeV]γE

1−10

1

10

[nb]

σ

"SIGNAL" Setting (15 days)"BACKGROUND" Setting 1 (4 days)"BACKGROUND" Setting 2 (2 shifts)Cornell 75SLAC 76 (Unpublished)

with Pc (5% coupling)ψJ/

8 8.5 9 9.5 10 10.5 11 11.5 12 [GeV]γE

1−10

1

10

[nb]

σ

"SIGNAL" Setting (18 days)"BACKGROUND" Setting (4 days)Cornell 75SLAC 76 (Unpublished)

(5% coupling)c with PψJ/

PAC NEW

S. Joosten

Summary

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High impact result will either confirm Pc resonance, or strongly exclude its existence

Strong sensitivity to the coupling down to 1.3% Will provide knowledge about J/ψ production (absolute cross section!) near threshold

Helps future experimental endeavors at CLAS12 and SoLID

Straightforward experiment, will run February 2019!

J/ �