Recent Results From GlueX 2019 April APS Meeting Colin Gleason - - PowerPoint PPT Presentation

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Recent Results From GlueX 2019 April APS Meeting Colin Gleason Indiana University on Behalf of the GlueX Collaboration Work Supported by DE-FG02-05ER41374 April 10, 2019 Colin Gleason (IU) April 10, 2019 1 / 37 Overview 1. QCD and hybrid

slide-1
SLIDE 1

Recent Results From GlueX

2019 April APS Meeting Colin Gleason

Indiana University

  • n Behalf of the GlueX Collaboration

Work Supported by DE-FG02-05ER41374

April 10, 2019

Colin Gleason (IU) April 10, 2019 1 / 37

slide-2
SLIDE 2

Overview

  • 1. QCD and hybrid mesons
  • 2. The GlueX experiment
  • 3. Early Results
  • Beam Asymmetries
  • Spin Density Matrix Elements (SDMEs)
  • Cross sections and opportunistic measurements
  • Production of J/ψ at threshold
  • 4. Laying the foundation for exotic searches in GlueX
  • Identifying known resonances
  • Beginning searches in hybrids channels

Colin Gleason (IU) April 10, 2019 2 / 37

slide-3
SLIDE 3

GlueX and QCD

GlueX is a photoproduction experiment at Jefferson Lab whose goal is to understand how QCD builds hadrons from quarks and gluons

Colin Gleason (IU) April 10, 2019 3 / 37

slide-4
SLIDE 4

GlueX and QCD

GlueX is a photoproduction experiment at Jefferson Lab whose goal is to understand how QCD builds hadrons from quarks and gluons

q q q q q

  • “Traditional” hadrons are well known
  • Bound states of quarks interacting via

gluons

Colin Gleason (IU) April 10, 2019 3 / 37

slide-5
SLIDE 5

GlueX and QCD

GlueX is a photoproduction experiment at Jefferson Lab whose goal is to understand how QCD builds hadrons from quarks and gluons

q q q q q

  • “Traditional” hadrons are well known
  • Bound states of quarks interacting via

gluons q q q q q q q q q

  • Nothing in quark models forbidding

tetra and pentaquarks

  • Still in color singlet state

Colin Gleason (IU) April 10, 2019 3 / 37

slide-6
SLIDE 6

GlueX and QCD

GlueX is a photoproduction experiment at Jefferson Lab whose goal is to understand how QCD builds hadrons from quarks and gluons

q q q q q

  • “Traditional” hadrons are well known
  • Bound states of quarks interacting via

gluons q q q q q q q q q

  • Nothing in quark models forbidding

tetra and pentaquarks

  • Still in color singlet state
  • Λ0

b → J/ψK −p by LHCb (PRL 115, 072001 (2015))

  • Pc(4450) accessible at JLab energies via J/ψ

production

Colin Gleason (IU) April 10, 2019 3 / 37

slide-7
SLIDE 7

GlueX and QCD

GlueX is a photoproduction experiment at Jefferson Lab whose goal is to understand how QCD builds hadrons from quarks and gluons

q q q q q

  • “Traditional” hadrons are well known
  • Bound states of quarks interacting via

gluons q q q q q q q q q

  • Nothing in quark models forbidding

tetra and pentaquarks

  • Still in color singlet state
  • Λ0

b → J/ψK −p by LHCb (PRL 115, 072001 (2015))

  • 3 narrow states reported at Moriond QCD, Mar

26, 2019

Colin Gleason (IU) April 10, 2019 4 / 37

slide-8
SLIDE 8

Bound States in QCD

q q q q q

  • “Traditional” hadrons are well known
  • Bound states of quarks interacting via

gluons q q q q q q q q q

  • Nothing in QCD forbidding tetra and

pentaquarks

  • Still in color singlet state

g g q q g

  • Do gluonic degrees of freedom exist?
  • Can/how do we observe them?

Colin Gleason (IU) April 10, 2019 5 / 37

slide-9
SLIDE 9

Constructing Mesons

Conventional Meson

q q

  • Classify as JPC
  • J = L + S
  • P = (−1)L+1
  • C = (−1)L+S
  • Allowed: 0−+, 0++, 1−−, 1−+,

2++, ...

  • Forbidden: 0−−, 0+−, 1−+, 2+−,

...

Colin Gleason (IU) April 10, 2019 6 / 37

slide-10
SLIDE 10

Constructing Mesons

Conventional Meson

q q

  • Classify as JPC
  • J = L + S
  • P = (−1)L+1
  • C = (−1)L+S
  • Allowed: 0−+, 0++, 1−−, 1−+,

2++, ...

  • Forbidden: 0−−, 0+−, 1−+, 2+−,

...

Hybrid Meson

q q g

  • Excited gluon field coupled to q¯

q

  • Rich spectrum predicted by lattice

QCD

Colin Gleason (IU) April 10, 2019 6 / 37

slide-11
SLIDE 11

Constructing Mesons

Conventional Meson

q q

  • Classify as JPC
  • J = L + S
  • P = (−1)L+1
  • C = (−1)L+S
  • Allowed: 0−+, 0++, 1−−, 1−+,

2++, ...

  • Forbidden: 0−−, 0+−, 1−+, 2+−,

...

Hybrid Meson

q q g

  • Excited gluon field coupled to q¯

q

  • Rich spectrum predicted by lattice

QCD

  • Detection of forbidden JPC → non

q¯ q structure

Colin Gleason (IU) April 10, 2019 6 / 37

slide-12
SLIDE 12

Lattice QCD

500 1000 1500 2000 2500 3000

Positive Parity Negative Parity Exotics

Dudek, PRD 88 (2013) no.9, 094505 Colin Gleason (IU) April 10, 2019 7 / 37

slide-13
SLIDE 13

Lattice QCD

500 1000 1500 2000 2500 3000

Lightest hybrid mesons

q q g

Positive Parity Negative Parity Exotics

Dudek, PRD 88 (2013) no.9, 094505 Colin Gleason (IU) April 10, 2019 8 / 37

slide-14
SLIDE 14

Lattice QCD

500 1000 1500 2000 2500 3000

Lightest hybrid mesons

Observation of exotic JPC would be signal for non qq

Exotics

η0

1

η1 π1

The goal of GlueX is to study the spectrum hybrid mesons

Colin Gleason (IU) April 10, 2019 9 / 37

slide-15
SLIDE 15

Global Spectroscopy Program

electromagnetic probes hadron probes colliding beam fixed target

completed/analysis completed/analysis

  • ngoing/future
  • ngoing/future

Colin Gleason (IU) April 10, 2019 10 / 37

slide-16
SLIDE 16

The GlueX Experiment

Colin Gleason (IU) April 10, 2019 11 / 37

slide-17
SLIDE 17

The GlueX Experiment

barrel calorimeter time-of

  • flight

forward calorimeter photon beam electron beam electron beam superconducting magnet target tagger magnet tagger to detector distance is not to scale diamond wafer

GlueX

central drift chamber forward drift chambers start counter DIRC

Linearly polarized photon beam Large acceptance

Colin Gleason (IU) April 10, 2019 12 / 37

slide-18
SLIDE 18

The GlueX Experiment

75 m Collimator

select < 25 r polarized photons

Hall-D

Diamond Radiator

​"↑− "%→&​"↑− % Tagger Area

Photon Tagger Pair Spectrometer GlueX Spectrometer Photon Beam Dump Electron Beam Dump East ARC North LINAC

Hall D

Triplet Polarimeter

Colin Gleason (IU) April 10, 2019 13 / 37

slide-19
SLIDE 19

The GlueX Experiment

75 m Collimator

select < 25 r polarized photons

Hall-D

Diamond Radiator

​"↑− "%→&​"↑− % Tagger Area

Photon Tagger Pair Spectrometer GlueX Spectrometer Photon Beam Dump Electron Beam Dump East ARC North LINAC

Hall D

Triplet Polarimeter

Measured Flux

Photon Beam Energy (GeV)

7.5 8 8.5 9 9.5 10 10.5 11 11.5 0 7.5 8 8.5 9 9.5 10 10.5 11 11.5

Photon Flux (Arb. Units)

1000 2000 3000 4000 5000 6000 7000

(a)

Diamond: PARA Diamond: PERP Aluminum Polarization Colin Gleason (IU) April 10, 2019 13 / 37

slide-20
SLIDE 20

The GlueX Experiment

75 m Collimator

select < 25 r polarized photons

Hall-D

Diamond Radiator

​"↑− "%→&​"↑− % Tagger Area

Photon Tagger Pair Spectrometer GlueX Spectrometer Photon Beam Dump Electron Beam Dump East ARC North LINAC

Hall D

Triplet Polarimeter

Measured Flux

Photon Beam Energy (GeV)

7.5 8 8.5 9 9.5 10 10.5 11 11.5 0 7.5 8 8.5 9 9.5 10 10.5 11 11.5

Photon Flux (Arb. Units)

1000 2000 3000 4000 5000 6000 7000

(a)

Diamond: PARA Diamond: PERP Aluminum Polarization

Polarization

7.5 8 8.5 9 9.5 10 10.5 11 11.5

Photon Beam Energy (GeV)

7.5 8 8.5 9 9.5 10 10.5 11 11.5

Polarization

0.1 0.2 0.3 0.4 0.5

3% Syst. Uncert.

PARA PERP

(b)

Colin Gleason (IU) April 10, 2019 13 / 37

slide-21
SLIDE 21

First Physics: Beam Asymmetries

  • First priority is to understand how known mesons (π, η, ρ, φ,) are

produced

Colin Gleason (IU) April 10, 2019 14 / 37

slide-22
SLIDE 22

First Physics: Beam Asymmetries

  • First priority is to understand how known mesons (π, η, ρ, φ,) are

produced

  • Beam asymmetry Σ is sensitive to the production mechanisms
  • Want to understand how known mesons are produced and use this

information in our search for hybrids

Colin Gleason (IU) April 10, 2019 14 / 37

slide-23
SLIDE 23

First Physics: Beam Asymmetries

  • First priority is to understand how known mesons (π, η, ρ, φ,) are

produced

  • Beam asymmetry Σ is sensitive to the production mechanisms
  • Want to understand how known mesons are produced and use this

information in our search for hybrids

Σ = |ω+ρ|2−|h+b|2

|ω+ρ|2+|h+b|2

1−− : !, ρ 1+− : b, h

Exchange JPC

JPAC, PRD 92, 074013

Colin Gleason (IU) April 10, 2019 14 / 37

slide-24
SLIDE 24

First Physics: Beam Asymmetries

  • First priority is to understand how known mesons (π, η, ρ, φ,) are

produced

  • Beam asymmetry Σ is sensitive to the production mechanisms
  • Want to understand how known mesons are produced and use this

information in our search for hybrids σpol(φ) = σunpol(1 − PγΣ cos 2φ) = σunpol(1 −

Y⊥−FRY|| Y⊥+FRY|| )

  • Pγ = beam polarization
  • Σ= beam asymmetry
  • φ= azimuthal angle of scattered meson w.r.t

polarization plane

  • Y⊥,|| are yields at different polarizations
  • FR is the photon flux ratio between ⊥ and ||

Colin Gleason (IU) April 10, 2019 15 / 37

slide-25
SLIDE 25

π0 and η Beam Asymmetries

2

) c (GeV/

  • t

0.2 0.4 0.6 0.8 1 1.2 1.4 1.6 1.8 2

Σ

0.2 0.4 0.6 0.8 1 1.2 1.4 <9.0 GeV

γ

GlueX 8.4<E =10 GeV

γ

E SLAC

π p → p γ

(a)

2.6% Norm. Uncert.

2

) c (GeV/

  • t

0.2 0.4 0.6 0.8 1 1.2 1.4 1.6 1.8 2

Σ

  • 0.4
  • 0.2

0.2 0.4 0.6 0.8 1 1.2 1.4 Laget [5,6] JPAC [7,8] Donnachie [9] Goldstein [4]

η p → p γ

(b)

  • First results from GlueX: Σ vs. −t for

π0 and η production (PRC 95, 042201 (2017))

Colin Gleason (IU) April 10, 2019 16 / 37

slide-26
SLIDE 26

π0 and η Beam Asymmetries

2

) c (GeV/

  • t

0.2 0.4 0.6 0.8 1 1.2 1.4 1.6 1.8 2

Σ

0.2 0.4 0.6 0.8 1 1.2 1.4 <9.0 GeV

γ

GlueX 8.4<E =10 GeV

γ

E SLAC

π p → p γ

(a)

2.6% Norm. Uncert.

2

) c (GeV/

  • t

0.2 0.4 0.6 0.8 1 1.2 1.4 1.6 1.8 2

Σ

  • 0.4
  • 0.2

0.2 0.4 0.6 0.8 1 1.2 1.4 Laget [5,6] JPAC [7,8] Donnachie [9] Goldstein [4]

η p → p γ

(b)

  • First results from GlueX: Σ vs. −t for

π0 and η production (PRC 95, 042201 (2017))

  • Insight to production mechanisms:

Σ = |ω+ρ|2−|h+b|2

|ω+ρ|2+|h+b|2

  • Σ=1 indicates vector exchange at

Eγ = 9 GeV

  • Only includes data from 2016 (≈ 5% of

expected data set)

Colin Gleason (IU) April 10, 2019 16 / 37

slide-27
SLIDE 27

η and η′ Beam Asymmetries

  • Expand results to include 2017 dataset
  • Vector exchange dominates at Eγ = 9 GeV
  • Ratio of

Ση′ Ση provides information about s¯

s exchange

η, η0

ρ, ! η0/η → π+π−π0 η0/η → π0π0π0

η0/η → γγ

JPAC Model 1 JPAC Model 2

JPAC Model: PLB 774 (2017) 362-367 Colin Gleason (IU) April 10, 2019 17 / 37

slide-28
SLIDE 28

π−∆++

Unnatural exchange favored (e.g. !) Natural exchange favored (e.g. ", %&) ± 7% *+,-. /*01,2%3*24

5 6 → !8Δ:: (~8.5 GeV)

B.G. Yu (Korea Aerospace U.),PLB 769 262 (16GeV)

  • J. Nys (JPAC) PLB 779, 77 (8.5 GeV)

∆++

π−

t

  • Charge Exchange: production mechanism depends on t
  • Data will help constrain the theoretical models

Colin Gleason (IU) April 10, 2019 18 / 37

slide-29
SLIDE 29

Vector Meson production: SDMEs

  • Spin-1 kinematics are more complicated
  • Additional angular components
  • Angular distributions described by spin density matrix elements

(SDMEs)

  • 9 SDMEs can be defined for a linearly polarized photon beams

Colin Gleason (IU) April 10, 2019 19 / 37

slide-30
SLIDE 30

Vector Meson production: SDMEs

  • Spin-1 kinematics are more complicated
  • Additional angular components
  • Angular distributions described by spin density matrix elements

(SDMEs)

  • 9 SDMEs can be defined for a linearly polarized photon beams
  • Much better statistical

precision when comparing to previous SLAC measurements

  • As −t → 0:
  • ρ1

1−1 → 0.5

  • Imρ2

1−1 → −0.5

  • Others →0

)

2

/c

2

  • t (GeV

0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1

1 1-1

ρ

)

2

/c

2

  • t (GeV

0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1 1 − 0.9 − 0.8 − 0.7 − 0.6 − 0.5 − 0.4 − 0.3 − 0.2 − 0.1 −

2 1-1

ρ Im

SCHC JPAC Model GlueX 2017 SLAC (Ballam et al.)

Colin Gleason (IU) April 10, 2019 19 / 37

slide-31
SLIDE 31

Ongoing Measurements: Presented in Session H09

“Low” energy cross sections

  • Special two-week run period to

collect data for 3 < Eγ < 6 GeV:

  • 1. Compare with measurements

from CLAS

  • 2. Bridge gap between these and

GlueX (6-12 GeV) measurements

  • Interested in low mass mesons:

ρ, ω, φ, η, η′

  • “Preliminary results for η, η′

cross sections between 3 and 6 GeV at the GlueX experiment”

Colin Gleason (IU) April 10, 2019 20 / 37

slide-32
SLIDE 32

Ongoing Measurements: Presented in Session H09

“Low” energy cross sections

  • Special two-week run period to

collect data for 3 < Eγ < 6 GeV:

  • 1. Compare with measurements

from CLAS

  • 2. Bridge gap between these and

GlueX (6-12 GeV) measurements

  • Interested in low mass mesons:

ρ, ω, φ, η, η′

  • “Preliminary results for η, η′

cross sections between 3 and 6 GeV at the GlueX experiment” Σ for γp → K +Σ0

Σ

−t (GeV2)

  • “Measurement of the Photon

Beam Asymmetry Σ for γp → K +Σ0 at Eγ = 8.5 GeV in GlueX”

Colin Gleason (IU) April 10, 2019 20 / 37

slide-33
SLIDE 33

Σ, dσ

dt , and SDMEs for Other Channels

γp → K +Λ(1520)

1.4 1.5 1.6 1.7 1.8 1.9 2 2.1 2.2 2.3 2.4 )

2

p inv. mass (GeV/c

  • K

200 400 600 800 1000 1200 1400 1600 1800 2000 2200

Λ(1520) Λ∗s M(K−p) GeV/c2

  • Lots of Λ∗, Σ∗ states
  • Measurements of Σ, SDMEs,

and σ underway for γp → K +Λ(1520)

Colin Gleason (IU) April 10, 2019 21 / 37

slide-34
SLIDE 34

Σ, dσ

dt , and SDMEs for Other Channels

γp → K +Λ(1520)

1.4 1.5 1.6 1.7 1.8 1.9 2 2.1 2.2 2.3 2.4 )

2

p inv. mass (GeV/c

  • K

200 400 600 800 1000 1200 1400 1600 1800 2000 2200

Λ(1520) Λ∗s M(K−p) GeV/c2

  • Lots of Λ∗, Σ∗ states
  • Measurements of Σ, SDMEs,

and σ underway for γp → K +Λ(1520) γp → ηπ0π0p

M(ηπ0π0) GeV/c2

  • Work ongoing for cross sections
  • f η′ production
  • Awaiting full GlueX dataset

Colin Gleason (IU) April 10, 2019 21 / 37

slide-35
SLIDE 35

J/ψ Production at GlueX

  • Able to make measurements of J/ψ production at threshold

(8.2 GeV)

  • Data sparse from previous measurements
  • Significant interest due to LHCb pentaquarks

Pc(4380) and Pc(4450) (2015)

  • Would be seen in s-channel production
  • Can set upper limit on Pc(4450) → J/ψp

branching ratio

  • New report from LHCb of three pentaquark states

(Pc(4312), Pc(4440), Pc(4457)) at Moriond QCD, Skwarnicki, Mar 26, 2019

  • Can also study:
  • gluon dynamics at threshold

Colin Gleason (IU) April 10, 2019 22 / 37

slide-36
SLIDE 36
  • Example event display for J/ψ production
  • large momentum transfer (t) to proton → High momentum proton
  • J/ψ is heavy → large opening angle between e+e−

Colin Gleason (IU) April 10, 2019 23 / 37

slide-37
SLIDE 37

J/ψ Yield

First observation of charmonium at JLab!

1 1.5 2 2.5 3 3.5 ), GeV

  • e

+

M(e 50 100 150 200 250 events/5MeV

/ ndf

2

χ 60.43 / 55 p0 10.98 ± 43.15 p1 3.6 ± 12.4 − p2 4.77 ± 70.98 p3 0.001 ± 3.091 p4 0.00077 ± 0.01281

2.9 2.95 3 3.05 3.1 3.15 3.2 ), GeV

  • e

+

M(e 20 40 60 80 events/5MeV

/ ndf

2

χ 60.43 / 55 p0 10.98 ± 43.15 p1 3.6 ± 12.4 − p2 4.77 ± 70.98 p3 0.001 ± 3.091 p4 0.00077 ± 0.01281

  • Available dataset: 464±25 J/ψ events
  • Normalize to Bethe-Heitler (γp → e+e−p) process to calculate cross

section

Colin Gleason (IU) April 10, 2019 24 / 37

slide-38
SLIDE 38

J/ψ Cross section

8 10 12 14 16 18 20 , GeV

γ

E

1 −

10 1 10 p), nb ψ J/ → p γ ( σ

GlueX SLAC Cornell GlueX data 25% syst. uncertainty

  • SLAC measurements

calculated at dσ

dΩ|t=tmin

(U.Camerini et al, PRL 35 (1975))

  • Cornell (B. Gittelman et al.,

PRL 35, 1975)

  • horizontal error

bar represents the acceptance

Colin Gleason (IU) April 10, 2019 25 / 37

slide-39
SLIDE 39

J/ψ Cross section

8 10 12 14 16 18 20 , GeV

γ

E

1 −

10 1 10 p), nb ψ J/ → p γ ( σ

GlueX SLAC Cornell GlueX data 25% syst. uncertainty

  • SLAC measurements

calculated at dσ

dΩ|t=tmin

(U.Camerini et al, PRL 35 (1975))

  • Cornell (B. Gittelman et al.,

PRL 35, 1975)

  • horizontal error

bar represents the acceptance

  • Shape of σ at threshold sheds light on

gluon dynamics

Colin Gleason (IU) April 10, 2019 25 / 37

slide-40
SLIDE 40

J/ψ Cross section: Pc Upper Limits

(GeV)

γ

E 8 8.5 9 9.5 10 10.5 11 11.5 12 p) (nb) ψ J/ → p γ ( σ

2 −

10

1 −

10 1 10

Gluex Preliminary (4450) J=3/2 BR=2%

c

P (4450) J=5/2 BR=2%

c

P

GlueX data 25% syst. uncertainty

  • Little sensitivity to

P+

c (4380) due to large

width and would be seen where σ drops steeply

  • Set upper limit on

B(Pc(4450) → J/ψp) at ≈ 2% by fitting to JPAC model for JP = 3

2 −, less

for JP = 5

2 −

  • New LHCb result does not

report the JP of the 3 Pc states

  • Would have to make

assumptions when trying to set upper limits Model: JPAC, PRD 94,034002 (2016)

Colin Gleason (IU) April 10, 2019 26 / 37

slide-41
SLIDE 41

Early Spectroscopy

  • Unprecedented statistical precision provide ample opportunity to search for new states
  • ≈ 20% of expected GlueX Phase 1 dataset exceeds previous datasets by several
  • rders of magnitude

ρ’? SLAC:

PRL 53, 751 (1984)

Eγ = 20 GeV

γp → π+π−p

Colin Gleason (IU) April 10, 2019 27 / 37

slide-42
SLIDE 42

Opportunistic Measurements: Cascades

M(π−Λ) GeV/c2

Ξ⁻(1320)

Ξ⁻(1820)?

M(K−Λ) GeV/c2

  • Opportunity to study cascade states

with high statistics

  • Poorly understood spectrum... why

have we seen so few states?

  • γp → K +K +Ξ−
  • Goal is to measure beam asymmetry

(Σ) and cross sections of Ξ(1320)−

  • 3σ peak in region of Ξ(1820)
  • γp → K +K +(K −Λ)
  • Should be able to study higher mass

states with full dataset

  • Both plots only have ≈ 10% of

expected data from GlueX Phase 1

Colin Gleason (IU) April 10, 2019 28 / 37

slide-43
SLIDE 43

Opportunistic Measurements: γp → Λ¯ Λp

M(π+¯ p) GeV/c2 M(π−p) GeV/c2

¯ Λ → π+¯ p

Λ → π−p

  • Able to study baryon–antibaryon

production

  • Never before seen in

photoproduction

  • Have access to both t and u

channnels

  • Shown here is ≈ 20% of data from

GlueX Phase 1... full dataset needed

Colin Gleason (IU) April 10, 2019 29 / 37

slide-44
SLIDE 44

Foundation for Exotic Searches at GlueX: η(′)π Channels

  • Next step with GlueX data is to analyze known resonances:

a0(980) → ηπ, a2(1320) → ηπ

  • η(′)π channels have been analyzed before in exotic searches
  • Relatively simple channel
  • Only have 20% of expected data from GlueX Phase 1

0.5 1 1.5 2 2.5 3 3.5 4 500 1000 1500 2000 2500 3000 Counts/10 MeV 0.5 1 1.5 2 2.5 3 3.5 4 1000 2000 3000 4000

γp → ηπ0p

η → γγ η → γγ

γp → ηπ−∆++

Counts/10 MeV

M(ηπ0) [GeV/c2] M(ηπ−) [GeV/c2]

Colin Gleason (IU) April 10, 2019 30 / 37

slide-45
SLIDE 45

COMPASS Results for π−p → ηπ− and η′π−

ϑ cos

  • 1
  • 0.8
  • 0.6
  • 0.4
  • 0.2

0.2 0.4 0.6 0.8 1 Intensity (a.u.) 0.05 0.1 0.15 0.2 0.25 0.3 0.35 0.4

S P

1

P D

1

D

cos θGJ

Intensity (a.u.)

η0

π−

yGJ

θGJ

Rest Frame of X

p0

π−

i = zGJ

where X → η0π−

Colin Gleason (IU) April 10, 2019 31 / 37

slide-46
SLIDE 46

COMPASS Results for π−p → ηπ− and η′π−

ϑ cos

  • 1
  • 0.8
  • 0.6
  • 0.4
  • 0.2

0.2 0.4 0.6 0.8 1 Intensity (a.u.) 0.05 0.1 0.15 0.2 0.25 0.3 0.35 0.4

S P

1

P D

1

D

cos θGJ

Intensity (a.u.)

η0

π−

yGJ

θGJ

Rest Frame of X

p0

π−

i = zGJ

where X → η0π−

  • Clear D–wave (L = 2) structure at

≈ 1300 MeV in ηπ− system (a2(1320))

  • Some D–wave structure around

1500-2000 MeV → need PWA to understand

PLB 740, 303 (2015) Colin Gleason (IU) April 10, 2019 31 / 37

slide-47
SLIDE 47

COMPASS Results for π−p → ηπ− and η′π−

ϑ cos

  • 1
  • 0.8
  • 0.6
  • 0.4
  • 0.2

0.2 0.4 0.6 0.8 1 Intensity (a.u.) 0.05 0.1 0.15 0.2 0.25 0.3 0.35 0.4

S P

1

P D

1

D

cos θGJ

Intensity (a.u.)

η0

π−

yGJ

θGJ

Rest Frame of X

p0

π−

i = zGJ

where X → η0π−

  • Forward/backward asymmetry

attributed to interference between odd and even waves

Colin Gleason (IU) April 10, 2019 32 / 37

slide-48
SLIDE 48

COMPASS Results for π−p → ηπ− and η′π−

ϑ cos

  • 1
  • 0.8
  • 0.6
  • 0.4
  • 0.2

0.2 0.4 0.6 0.8 1 Intensity (a.u.) 0.05 0.1 0.15 0.2 0.25 0.3 0.35 0.4

S P

1

P D

1

D

cos θGJ

Intensity (a.u.)

η0

π−

yGJ

θGJ

Rest Frame of X

p0

π−

i = zGJ

where X → η0π−

  • Forward/backward asymmetry

attributed to interference between odd and even waves

  • L=1,3,5 (exotic waves) suppressed in

ηπ− with respect to η′π−

  • Only report P-wave amplitude

PLB 740, 303 (2015) Colin Gleason (IU) April 10, 2019 32 / 37

slide-49
SLIDE 49

COMPASS Results: JPAC Coupled-Channel Fit (PRL 122, 042002)

ηπ

P-wave P-wave

ηπ

η0π η0π

D-wave D-wave

  • Coupled channel fit to both ηπ and η′π amplitudes from COMPASS PWA
  • Pole positions for a2, a′

2, and π1 (exotic P-wave) determined

  • π1 consistent with lightest exotic in JPC and mass
  • π1(exotic): M = 1564 ± 24 ± 86 MeV, Γ = 492 ± 54 ± 102 MeV

Colin Gleason (IU) April 10, 2019 33 / 37

slide-50
SLIDE 50
  • Comparable statistical precision

with GlueX Phase 1 in η → π+π−π0

  • Expect more in η → γγ decay

)

2

Invariant Mass (GeV/c π η 0.5 1 1.5 2 2.5 3 3.5 ϑ cos 1 − 0.8 − 0.6 − 0.4 − 0.2 − 0.2 0.4 0.6 0.8 1

cos θGJ

M(ηπ0) GeV/c2

1 2 3 1 − 0.5 − 0.5 1

)

  • π

η M( θ cos

M(ηπ−) GeV/c2

cos θGJ

Colin Gleason (IU) April 10, 2019 34 / 37

slide-51
SLIDE 51

Summary and Outlook

  • Presented beam asymmetries for π0, π−, η(′), ρ SDMEs, and σ for

J/ψ photoproduction at theshold

  • Progress towards understanding how known mesons are produced
  • Focus on how well we know the detector acceptance, the photon flux,

and backgrounds

  • Looking to make opportunistic measurements unique to GlueX

Colin Gleason (IU) April 10, 2019 35 / 37

slide-52
SLIDE 52

Summary and Outlook

  • Presented beam asymmetries for π0, π−, η(′), ρ SDMEs, and σ for

J/ψ photoproduction at theshold

  • Progress towards understanding how known mesons are produced
  • Focus on how well we know the detector acceptance, the photon flux,

and backgrounds

  • Looking to make opportunistic measurements unique to GlueX
  • Identify known resonances (a0, a2, ...) through amplitude analysis
  • Developing amplitude analysis procedure will lay foundation for analysis
  • f exotics

Colin Gleason (IU) April 10, 2019 35 / 37

slide-53
SLIDE 53

Summary and Outlook

  • Presented beam asymmetries for π0, π−, η(′), ρ SDMEs, and σ for

J/ψ photoproduction at theshold

  • Progress towards understanding how known mesons are produced
  • Focus on how well we know the detector acceptance, the photon flux,

and backgrounds

  • Looking to make opportunistic measurements unique to GlueX
  • Identify known resonances (a0, a2, ...) through amplitude analysis
  • Developing amplitude analysis procedure will lay foundation for analysis
  • f exotics
  • Hybrid searches: amplitude analysis of ηπ, η′π, πππ, etc final states
  • Need full GlueX data set! 20% being analyzed now. Expect 100% to

be available by end of 2019

  • GlueX Phase 1 finished data taking in December 2018!
  • Phase 2 begins this Fall with the DIRC to improve K +/− identification

and will have better statistical precision

Colin Gleason (IU) April 10, 2019 35 / 37

slide-54
SLIDE 54

The GlueX Experiment

Colin Gleason (IU) April 10, 2019 36 / 37

slide-55
SLIDE 55

Vector Meson production: SDMEs

  • Spin-1 kinematics are more complicated
  • Additional angular components
  • Angular distributions described by spin density matrix elements

(SDMEs)

  • For a linearly polarized photon beam, the intensity, W (cos θ, φ, Φ), is

given as:

W (cos θ, φ, Φ) = W 0(cos θ, φ) − Pγcos2ΦW 1(cos θ, φ) − Pγsin2ΦW 2(cos θ, φ) W 0(cos θ, φ) = 3 4π 1 2 (1 − ρ0

00 + 1

2 (3ρ0

00 − 1))cos2θ −

√ 2Reρ0

10 sin 2θ cos φ − ρ0 1−1sin2θ cos 2φ)

W 1(cos θ, φ) = 3 4π

  • ρ1

11 sin 2θ + ρ1 00 cos2 θ −

√ 2ρ1

10 sin 2θ cos φ − ρ1 1−1 sin2 θ cos 2φ)

W 2(cos θ, φ) = 3 4π √ 2Imρ2

10 sin 2θ sin φ + Imρ2 1−1 sin2 θ sin 2φ)

Schilling [Nucl. Phy. B, 15 (1970) 397]

Colin Gleason (IU) April 10, 2019 37 / 37