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
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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
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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
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[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
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
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
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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=">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</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/ �
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