light-meson spectroscopy at jefferson...

IntroductionThe GlueX Experiment

Gluonic ExcitationsOther Physics (at GlueX)

Summary and Outlook

Light-Meson Spectroscopy at Jefferson Lab

Volker Credé

Florida State University, Tallahassee, Florida

PANDA Collaboration Meeting

Uppsala, Sweden

06/10/2015

V. Credé First Round of Experiments in Hall D



Summary and Outlook

Outline

1 Introduction

2 The GlueX ExperimentDetector and Commissioning StatusLight-Meson Spectroscopy

3 Gluonic ExcitationsLattice QCD and Hybrid MesonsExperimental Evidence

4 Other Physics (at GlueX)

5 Summary and Outlook




Summary and Outlook

Non-Perturbative Quantum Chromodynamics (QCD)

QCD is the theory of the strong nuclear forcewhich describes the interactions of quarksand gluons making up hadrons.

Strong processes at larger distances and atsmall (soft) momentum transfers belong tothe realm of non-perturbative QCD.

Quarks are confined within hadrons.

Confinement of quarks and gluons within hadrons is anon-perturbative phenomenon, and QCD is extremelyhard to solve in non-perturbative regimes: Knowledgeof internal structure of hadrons is still limited.




Summary and Outlook

Non-Perturbative QCD

How does QCD give rise to excited hadrons?

1 What is the origin of confinement?

2 How are confinement and chiralsymmetry breaking connected?

3 What role do gluonic excitations play inthe spectroscopy of light mesons, and canthey help explain quark confinement?

Hadron Spectroscopy: (Baryons) What are the effective degrees of freedominside the nucleon? (Mesons) What are the properties of the predicted statesbeyond simple quark-antiquark systems (hybrid mesons, glueballs, ...)?

Ü Gluonic Excitations provide a measurement of the excited QCD potential.Hybrid baryons are possible but do not carry “exotic” quantum numbers.




Summary and Outlook

Detector and Commissioning StatusLight-Meson Spectroscopy

Outline

1 Introduction








Summary and Outlook


Hadron Spectroscopyπ + Nucleus

γ p Photoproduction

e+ e−

p̄ p

The GlueX Collaboration110 members, 21 institutions(USA, Canada, Chile, Armenia, Greece, Russia, UK)

Commissioning in full swingFirst physics in 2016

DIRC quartz bars: 2018+

Ü




Summary and Outlook


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

startcounter

BoxBox

Search for exotic mesons:

Linearly-polarized photons;coherent edge at 9 GeV.

High intensity (2017+).Goal: 5 x 107 γ/s (coh. peak)

Sophisticated analysis tools.Ü Partial Wave Analysis (PWA)

∼ 75 m




Summary and Outlook


May 2014

Hall D

Jefferson Lab Upgrade to 12 GeV

10.1 GeV achieved, Fall 2014

Hall D complete




Summary and Outlook


Coh. Peak: 8.4 - 9.0 GeV

~γ σE/E ∼ 0.1 %, P∼ 40 %

h± σp/p ∼ 1- 3 %

γ σE/E ∼ 6 %/√

E ⊕ 2 %

Goniometer:20 µm diamond

Barrel CALorimeter (BCAL):48 4-m long modules

CDC: 28-layerstraw-tube chamber

FCAL: 2800 lead glassblocks

FDC: four six-planeforward drift chambers

TOF: two planes of2.5 cm scintillator bars

2.0 T superconducting solenoid

Ü

Ü

Ü

Ü Ü




Summary and Outlook


GlueX Upgrade: Focusing DIRC Detector

DIRC DetectorDetection of Internally ReflectedCherenkov lightUse 48 of BaBar DIRC quartz barsSeparation of π/K up to 4 GeVInstallation in FY 2018

Physics Motivation A study of decays tostrange final states with GlueX in Hall Dusing components of the BaBar DIRC.arXiv:1408.0215 [physics.ins-det].

DIRC bars

DIRC bars




Summary and Outlook


Commissioning: Fall 2014 and Spring 2015

Vertexreconstructionfrom tracking

Data from all subsystems

Signal coincidence& hit correlation

between detectors

z Vertex [cm]

βTOF: positive tracks

p [GeV/c]

p [GeV/c]dE

/dx

[a.u

.]

p

Ü

π

p

π

p

Particle ID




Summary and Outlook


Quark-Model Classification: Ordinary & Exotic Mesons

Quantum Numbers JPC ≡ 2S+1L J

Parity: P = (−1)L+1

Charge Conjugation: C = (−1)L+S

(defined for neutral mesons)

G parity: G = C (−1)I

12 GeV CEBAF upgrade has high priority(DOE Office of Science, Long Range Plan)“[key area] is experimental verification of thepowerful force fields (flux tubes) believed to beresponsible for quark confinement.”

L = 0, S = 0 :

e.g. π, η (JPC = 0−+)

L = 0, S = 1 :

e.g. ρ, ω, φ (JPC = 1−−)

Forbidden States (Exotics):JPC = 0+−, 0−−, 1−+, 2+− · ··




Summary and Outlook

Lattice QCD and Hybrid MesonsExperimental Evidence

Outline

1 Introduction








Summary and Outlook


Hybrid Meson Decays and Interesting Channels

0+− h0 → b1π → π+π−π0π0π0; h1η

b0 → π(1300)π; h1π

1−+ η1 → a1π → 2π+2π−; π(1300)π

π1 → f1π → ηπππ; b1π, πρ, ηa1

2+− h2 → ρπ → πππ; b1π, ωη

b2 → a2π; a1π, h1π, ωπ

Ü Multi-particle final states withneutral and charged particles!

Ideas on Hybrid-Meson Decays:(angular momentum in the flux tube stays in one of the daughter mesons)

Lattice calculations:(lightest hybrid) M 1−+ ≈ (1.9±0.2) GeV/c2

L = 1

L = 0

Evidence for JPC = 1−+ waveÜ Interpretation controversial ...




Summary and Outlook


Meson Spectroscopy on the Lattice

0.5

1.0

1.5

2.0

2.5

exotics

isoscalar

isovector

YM glueball

negative parity positive parity

Ü 0−+

Ü 1−−

mπ = 396 MeV

→ isoscalar

→ isovector

exoticspositive paritynegative parity

J. J. Dudek et al., Phys. Rev. D 84, 074023 (2011)




Summary and Outlook


Meson Spectroscopy on the Lattice

0.5

1.0

1.5

2.0

2.5

exotics

isoscalar

isovector

YM glueball

negative parity positive parity exoticspositive paritynegative parity

Big Box

Ü 0−+

Ü 1−− Lattice QCD Predictions

Constituent glue with JPC = 1+−

Ü Lightest nonet: 1−−, (0−+, 1−+, 2−+)

J. J. Dudek et al., PRD 84, 074023 (2011)




Summary and Outlook


Experimental Searches for Hybrid MesonsThere is convincing evidence for an exotic JPC = 1−+ wave.Ü The interpretation remains controversial.

Exotic waves are (all) observed in diffraction-like reactions.Ü Observation of π1(1400)→ ηπ in pp̄ remains exception.

1 π1(1400)→ ηπ Ü Tetraquark? Nothing? (too low in mass for hybrid)

2 π1(1600) Appears to be robust signal.

Diffractive Production Process

Natural parity exchange: JP = 0+, 1−, 2+, ...

Unnatural parity exchange: JP = 0−, 1+, 2−, ...Same production mechanism, Mε, expectedfor all decay modes.

Review: C. Meyer & Y. Van Haarlem, PRC 82, 025208 (2010)




Summary and Outlook


The JPC = 1−+ Exotic Wave: E852 ExperimentThere is convincing evidence for an exotic JPC = 1−+ wave.

1 π1(1400)→ ηπ

2 π1(1600) → η ′π; f1(1285)π Ü Natural-parity exchange.

π1(1600) → b1π Ü Unnatural-parity exchange dominates.

π1(1600) → ρπ

π(1600)→ ρπ(E852 : π−p → π+2π− p)

M = 1598± 8+29−47 MeV

Γ = 168± 20+150−12 MeV

Mε = 0−, 1− Mε = 1+

?

Ü Better understanding requiresa spectrum of hybrid mesons.




Summary and Outlook


COMPASS Experiment (1): π− Pb → π−π−π+ (Pb)

)2 System (GeV/c+π-π-πMass of 0 0.5 1 1.5 2 2.5 3

)2E

ven

ts /

(5

MeV

/c

0

0.5

1

1.5

2

2.5

3

3.5

310×

(1260)1a

(1320)2a

(1670)2π

event distribution

background wave

)2 System (GeV/c+π-π-πMass of 0.6 0.8 1 1.2 1.4 1.6 1.8 2 2.2 2.4

)2In

tens

ity

/ (40

MeV

/c

0

100

200

300

400

500

600

700

800 Pπρ+1-+1 (d)

)2 System (GeV/c+π-π-πMass of 0.6 0.8 1 1.2 1.4 1.6 1.8 2 2.2 2.4

Phas

e (d

egre

es)

-200

-150

-100

-50

0

50

100

150

S)π2f+0-+ P - 2πρ+1-+ (1φ∆

(b)P

∆φ (1−+ − 2−+)

π1, π2 → constant ∆φ?

M. Alekseev et al., PRL 104, 241803 (2010)

1−+ Exotic Wave

1−+1+ρπ P

Based on ∼ 420,000 events using a 180 GeV π beam:

π1(1600): M = 1660 MeV π2(1670): M = 1658 MeVΓ = 269 MeV Γ = 271 MeV

Ü Exotic 1−+ wave dominantly produced in natural-parity (Mε = 1+) exchange.




Summary and Outlook


COMPASS Experiment (2): π− p → η(′) π− (p)

m(η′π−) [GeV/c2]

Entries

/20M

eV/c2

1.5 2 2.5 3 3.5 4 4.5 50

100

200

300

400

500

600

121416

Acceptance

[%

]

Events

/40M

eV/c2

m(η′π−) [GeV/c2]

1.2 1.6 2 2.4 2.80

1000

2000

3000

4000

5000

Φ1−

Φ2

[deg]

m(η(′)π−) [GeV/c2]

0.8 1.2 1.6 2 2.4 2.8

-50

0

50

100

150

200

250

C. Adolph et al., PLB 740, 303 (2015)

1−+ Exotic Wave

η′π− P-wave,L = 1

Collaboration refrains from proposing resonance parameters for exotic P wave.

Odd partial waves with L = 1,3,5 (non-qq̄ QN) suppressed in ηπ− withrespect to η′π−. Even partial waves similar (intensity & phase behavior).

Dominant 8⊗ 8 (ηπ) & 1⊗ 8 (η′π) nature of SU(3) flavor configurationsÜ gqq̄ and qq̄qq̄ configurations predicted to have 1⊗ 8 character.




Summary and Outlook


Meson Spectroscopy in Photoproduction: CLAS

Even

ts/4

0 M

eV

10

20

30

40

50

60

70310×

a.P,F

)/l(-+

2

) (GeV)-/+/+/M(1 1.2 1.4 1.6 1.8 2

Even

ts/4

0 M

eV

05

101520253035404550

310×

c.S

)/l(++

1

b.S

)/2

(f-+

2

) (GeV)-/+/+/M(1 1.2 1.4 1.6 1.8 2

d.P

)/l(-+

1(1600)?1/

CLAS does not observe a resonantstructure in the 1−+ (ρπ)P partial wave.

Results on light mesons from CLAS at Jefferson Lab

Search for the photo-excitation of exotic mesons in the π+π+π− system:(M. Nozar et al., Phys. Rev. Lett. 102, 102002 (2009))

charge exchange

CLAS

neutral exchange

E852

p

π−

P ?P




Summary and Outlook


Meson Spectroscopy in Photoproduction: CLAS

A JPC = 1−+ gluonic hybrid should bephoto-produced at the same rate as thea 2(1320), whereas in pion production itshould be suppressed by a factor of 10.(Close & Page, Phys. Rev. D 52, 1706 (1995))

Upper limit for the π1(1600) of 13.5 nb, less than 2 % of the a 2(1320).

Recent CLAS-g12 data have an order of magnitude more statistics.Ü e.g. γp → n π+π+π−, γp → p π+π−π0 (JPC = 1−+ isoscalar production?)

Results on light mesons from CLAS at Jefferson Lab

Search for the photo-excitation of exotic mesons in the π+π+π− system:(M. Nozar et al., Phys. Rev. Lett. 102, 102002 (2009))

charge exchange

CLAS

neutral exchange

E852

p

π−

P ?P




Summary and Outlook


First GlueX “Physics”: Observation of vector mesons

) 2 Invariant Mass (GeV/c-π+π 0 0.2 0.4 0.6 0.8 1 1.2 1.4

Eve

nts

0

100

200

300

400

500 GlueX Commissioning: Fall 2014

(p)-π+π →p γ

Data

) 2 Invariant Mass (GeV/c0π-π+π 0 0.2 0.4 0.6 0.8 1 1.2 1.4

Eve

nts

0

20

40

60

80

100

120

140 GlueX Commissioning: Fall 2014

(p)0π-π+π →p γ

Data0π-π+π → ω

γ p → p π+π−π0

Proton PID based on dE/dxExclusive process (missing mass cut)

π → γγ: reconstructed from forward calorimeter Ü(σ ∼ 11 MeV, calibration ongoing)

ω ρ

π0




Summary and Outlook


First GlueX “Physics”: Observation of KS and Λ

)2 Invariant Mass (GeV/c-πp 1.1 1.2 1.3 1.4 1.5 1.6 1.7 1.8 1.9 2

Even

ts

0

50

100

150

200

250

300GlueX Commissioning: Fall 2014

-π p → Λ

2 = 1115.68 MeV/cPDGm

2max bin center: 1116.25 MeV/c)2 Invariant Mass (GeV/c-π +π

0.2 0.4 0.6 0.8 1 1.2 1.4 1.6 1.8 2

Even

ts

0

100

200

300

400

500

600

700

800GlueX Commissioning: Fall 2014

-π +π → SK

1.2 MeV±width: 13.0 2 1.0 MeV/c± = 497.7 fitm

2 = 497.65 MeV/cPDGm 109.8±counts: 1461.3

No direct K± meson ID, yet. But

KS → π+π−

Λ→ pπ−

clearly observed.

Reconstruction

p & π± PID based on dE/dx, β

Detached vertices




Summary and Outlook


First GlueX “Physics”: Polarized ρ Photoproduction

XXXX

coh. peakat 3 GeV

Studies of diamond radiator in beamconfirmed understanding andcontrol of photon polarizationand diamond orientation.

Ü 2.5h of pol. beam (∼10 nA),P max = 65 %, P ave = 47 %

8-fold peaking (symmetries):

Lattice planes:[022], [022̄], [004], [040]

Each plane: φ, φ+ π

Ü

ÜE γ

Enhanced “Polarized”Photon Spectrum

ρ → π+π−

CrystalAlignment

Enh

ance

men

t

Eve

nts

Eγ [GeV]

π+π− Invariant Mass [GeV/c2]




Summary and Outlook


First GlueX “Physics”: Polarized ρ PhotoproductionPolarized ρ Production with the Hall D Photon Beam

�p ! ⇢0p ! ⇡+⇡�p

-150 -100 -50 0 50 100 150

Even

ts

0

20

40

60

80

100

DiamondAmorphous

Spring 2015 Commissioning(a few hours of beam)

Angle Between Polarization and Decay Planes: s (deg.)

Energy of Beam Photon (GeV)0 1 2 3 4 5

Even

ts

0

50

100

150

200

250

300

DiamondAmorphous


Energy of Beam with Di!erent Radiators for apAlp Events

coherent bremsstrahlung peak has high degree of

linear polarization

l Decay Plane

l

s

/

/<

a

Photon Beam Polariz

ation Plane

p

p

Polarization P is preserved

in l�production.

(1 + P cos 2s)dmds

Energy of Beam Photons [GeV]

Eve

nts

Eve

nts




Summary and Outlook


First GlueX “Physics”: Initial AnalysesPolarized ρ Production with the Hall D Photon Beam

�p ! ⇢0p ! ⇡+⇡�p

-150 -100 -50 0 50 100 150

Even

ts

0

20

40

60

80

100

DiamondAmorphous


Angle Between Polarization and Decay Planes: s (deg.)

Energy of Beam Photon (GeV)0 1 2 3 4 5

Even

ts

0

50

100

150

200

250

300

DiamondAmorphous


Energy of Beam with Di!erent Radiators for apAlp Events

coherent bremsstrahlung peak has high degree of

linear polarization

l Decay Plane

l

s

/

/<

a

Photon Beam Polariz

ation Plane

p

p

Polarization P is preserved

in l�production.

(1 + P cos 2s)dmds

Eve

nts Ü

Detector Understanding:γp → p π0

γp → p ηγp → p ργp → p ω Initial Exoticγp → p η ′ Hybrid Searchesγp → p φ γp → ηπ (n, p)

γp → η ′π (n, p)γp → ρπ (n, p)γp → ωπ (n, p)γp → ωππ (n, p)γp → ηππ (n, p)

Strange Baryons: γp → K +Λ, K Σ, KK Ξ




Summary and Outlook

Outline

1 Introduction








Summary and Outlook

Gluonic Excitations on the Lattice

0

500

1000

1500

2000

The mass scale is m − mρ formesons and m−mN for baryons.

Common scale of ∼ 1.3 GeV for gluonic excitation.

J. J. Dudek and R. G. Edwards, Phys. Rev. D 85, 054016 (2012)

mπ = 524 MeV mπ = 396 MeV




Summary and Outlook

Gluonic Excitations on the Lattice

0

500

1000

1500

2000

The mass scale is m − mρ formesons and m−mN for baryons.

Letter of Intent to JLab PAC 43Ü Search for Hybrid Baryons with CLAS 12 in Hall B

J. J. Dudek and R. G. Edwards, Phys. Rev. D 85, 054016 (2012)

mπ = 524 MeV mπ = 396 MeV




Summary and Outlook

Opportunities for Baryon Spectroscopy at GlueX

8F Ξ

10F Ξ(1530)

Ξ(1820)

Spectroscopy of |ssn〉 Ξ baryons:Very few established statesHardly any JP measuredPossibly narrow resonances

The multi-strange baryons providea missing link between light-flavorand heavy-flavor baryons.

Program on Cascades involves:Measurement of Ξ−−Ξ0 splittings.JP measurements.Search for new states.




Summary and Outlook

Planned Experiments at Jefferson LabBroad and rich physics program in Hall D using the GlueX detector:

Mapping the Spectrum of Light-Quark Mesons and Gluonic Excitationswith Linearly-Polarized Photons. (arXiv:)A study of decays to strange final states with GlueX in Hall D usingcomponents of the BaBar DIRC. (arXiv:1408.0215)

Precision Measurement of η Radiative Decay Width via Primakoff Effect.

Measuring the Charged-π Polarizibility in the γγ → π+π− Reaction.

Symmetry Tests of Rare η Decays to All-Neutral Final States.

Spectroscopy Program in Hall B with CLAS 12:

Search for hybrid mesons.

Study of very (doubly) strange baryons; hybrid baryon program.




Summary and Outlook

Outline

1 Introduction








Summary and Outlook

Summary

The GlueX experiment is ideally suited to study the spectrum of light-flavormesons up to M ≈ 2.8 GeV and – if existing – the pattern of the gluonicexcitations produced in γp collisions:

It is important to establish the existence and the nonetnature of the 1−+ state (and of 0+−, 2+−)

For a given produced resonance, linear polarizationwill allows us to distinguish between naturalities of exchanged particles.

About 70 % of the photoproduction cross section in the energy regionEγ ∼ 7− 12 GeV has multiple neutrals and is completely unexplored.Ü Many opportunities for GlueX to make key experimental advances

in our knowledge of excited mesons and baryons.

Advances in both theory and experiment will allow us to finally understandQCD and confinement.


light-meson spectroscopy at jefferson...

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