1 Overview of Spectroscopy Results in Meson Photoproduction with Polarization Observables M. Dugger,...

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Overview of Spectroscopy Results in Meson Photoproduction

with Polarization Observables

M. Dugger, HADRON, September 2015

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Outline

• Motivations

• Helicity amplitudes

• Reactions and results

• PDG then and now


3

Nucleon resonances

γ p → π+ n

• The nucleon resonance spectrum has many broad

overlapping states, making disentangling the spectrum difficult


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Resonance Rating SystemNucleon resonances are rated using stars:* Poor evidence of existence** Fair evidence of existence*** Likely evidence of existence, or certain and properties need work**** Existence is certain and properties well explored


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Resonance status for N* and Δ

26 N* states: • 10 with **** • 5 with ***• 8 with **• 3 with *

Nucleon

22 Δ states: • 7 with **** • 3 with ***• 7 with **• 5 with *

• Nearly half the states have only fair or poor evidence!

• Most states need more work to learn details

• Are there missing states?M. Dugger, HADRON, September 2015

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Resonances

• Masses, widths, and coupling constants not well known for many resonances

• Many models: quark model, Goldstone-boson exchange, diquark and collective models, instanton-induced interactions, flux-tube models, lattice QCD…

• Big Puzzle: Most models predict

more resonance states than observed


Brief look at the non-relativistic quark model

• Harmonic oscillator states

• Non-harmonic perturbation

• Spin-spin hyperfine interaction including tensor part

ji

ij

ijjiji

ijijji

ji

sijhyp SS

r

rSrS

rrSS

mmH

23

3 31

3

8

3

2

Spin-spin interaction Tensor interactionM. Dugger, HADRON, September 2015

Oscillator + spin-spin interaction

Oscillator +

spin-spin + tensor interaction

Brief look at the non-relativistic quark model

Oscillator state: N = 1; S = 1/2 ,3/2; negative parity; P wave

Notation: X2S+1LπJP, where π is permutation symmetry

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R.G. Edwards et al. Phys. Rev. D84 074508 (2011)

Example: Lattice QCD results for N* resonances

Mass(π) = 524 MeV

Mass(π) = 396 MeV

• Noticeable change as the π mass becomes more realistic

• Number of low-lying states (boxed regions) remains the same for the two π-masses, and is the same as the non-relativistic quark model


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Low-lying Resonance States

Lattice QCD is consistent with non-relativistic quark model for number of low-lying states

Negative parity Positive parity

Missing resonances

More than resonances

t

Born t-channel

• Born term: nucleon propagator

• t-channel: vector meson propagator

• The ρ0, ω, and φ have same quantum numbers as the photon → Vector Meson Dominance

• The meson-NN coupling can be extracted from the Born term

11M. Dugger, HADRON, September 2015

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Outline

• Motivations



• PDG then and now


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• 8 helicity states: 4 initial, 2 final → 4∙2 = 8 • Amplitudes are complex but parity symmetry reduces independent numbers to 8• Overall phase unobservable → 7 independent numbers • HOWEVER, not all possible observables are linearly independent and it turns out

that there must be a minimum of 8 observables / experiments

Helicity amplitudes for γ + p → p + pseudoscalar

4321

2121

21

23

HH

HHA

helicity +1 photons (ε+): helicity -1 photons (ε-):

1221

3421

23

21

HH

HHA

,, AeA

Parity symmetry →

2221

1211

AA

AAA

Initial helicity Fin

al helicity


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The alphabet soup of observables for pseudo-scalar photoproduction

• Most experiments are done with photon and/or target polarization

• Hyperons are “self analyzing” and allow for recoil polarization measurements without using recoil polarimeter


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Helicity amplitudes and observables for single pseudoscalar photoproduction

Differential cross section

Beam polarization S

Target asymmetry T

Recoil polarization P

Double polarization observables • Need at least 4 of the double

observables from at least 2 groups for a “complete experiment”

• π0p, π+ n, and η p will be nearly complete

• K+ Λ will be complete!

Lon

gitu

din

al t

arge

t

Tra

nsv

erse

tar

get

+P

olar

ized

p

hot

ons


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Finding missing resonances requires lots of different observables.

Cross sections are not enough!


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Outline

• Motivations



• Conclusions


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Status of CLAS meson photoproduction σ Σ T P E F G H Tx Tz Lx Lz Ox Oz Cx Cz

Proton target

pπ0 ✔ ✔ ✓ ✓ ✓ ✓ ✓ ✓

nπ+ ✔ ✔ ✓ ✓ ✓ ✓ ✓ ✓

pη ✔ ✓ ✓ ✓ ✓ ✓ ✓ ✓

pη’ ✔ ✓ ✓ ✓ ✓ ✓ ✓ ✓

K+Λ ✔ ✓ ✓ ✔ ✓ ✓ ✓ ✓ ✓ ✓ ✓ ✓ ✓ ✓ ✔ ✔

K+Σ0 ✔ ✓ ✓ ✔ ✓ ✓ ✓ ✓ ✓ ✓ ✓ ✓ ✓ ✓ ✔ ✔

K0Σ+ ✔ ✓ ✓ ✓ ✓ ✓ ✓ ✓ ✓ ✓ ✓ ✓ ✓ ✓ ✔ ✔

“Neutron” target

pπ- ✔ ✓ ✓ ✓

K+Σ- ✓ ✓ ✓ ✓

K0Λ ✓ ✓ ✓ ✓ ✓ ✓ ✓ ✓ ✓ ✓ ✓ ✓ ✓ ✓

K0Σ0 ✓ ✓ ✓ ✓ ✓ ✓ ✓ ✓ ✓ ✓ ✓ ✓ ✓ ✓

✔ - published ✔ - acquired

Not shown in table: ω, ρ and multi-meson observables


• See Priyashree Roy, Thursday at 11:05 (session 2) for ω and ρ CLAS results

Data from first round of double polarization measurements


Polarization observables from the proton CBELSA/TAPS

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Data• There are several labs performing polarization measurements

• There are too many reactions and observables for me to do justice to the work that has been performed

• I will just show some examples of reactions specific features along with samples of data

Talks at HADRON that include polarization observables:• Helicity Asymmetry Measurements for π0 photoproduction on the CLAS Frozen Spin Target: Igor

Strakovsky, Thursday at 9:35 (session 1) • Polarization Observables in Vector Meson Production decaying to Multi-pion-Final States using a

Transversely Polarized Target and Polarized Photons at CLAS, Priyashree Roy, Thursday at 11:05 (session 2)• Baryon Spectroscopy – Recent Results from the CBELSA/TAPS Experiment, Jan Hartmann, Thursday at

11:45 (session 2)• Polarization Observables in η and π Production using a Polarized Target with the Crystal Ball/TAPS at

MAMI, Natalie Walford, Thursday at 12:05 (session 2) • Baryon spectroscopy from JLab, David Ireland, Thursday at 3:10 (plenary session)


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Isospin combinations for reactions involving π0 and π+

21

321

21

323

21

321

21

3230

,3/2,3/1:

,3/1,3/2:

IIIIn

IIIIp

Δ+ N*

• Differing isospin compositions for N* and Δ+ for the π0 p and π+ n final states

• The π0 p and π+ n final states can help distinguish between the Δ and N*


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Isospin photo-couplings

• Using both proton and neutron targets allows decomposition of iso-singlet and iso-vector photo-couplings C0, C1

γp→nπ+: *32*1

310

32 CNCC

*32*1

310

32 CNCCγn→pπ-:

Example:


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T for γ p → n π+

• Preliminary results

• CLAS results agree well with previous data

G9b: FROST

(new)

(new)

(new)


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F for γ p → n π+

• Early stage results• Predictions get much worse at

higher energies• SAID13 are predictions based

on preliminary fits to CLAS pion Σ measurements

(new) (new)

(new)

G9b: FROST


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E for γ p → p π0

• ELSA results

Black solid: BnGa fitBlack dashed: BnGa previous to fitBlue solid: MAIDRed solid: SAID (CM12)Red dashed: SAID (SN11)

• See Igor Strakovsky, Thursday at 9:35 (session 1) for CLAS results and more about this observable

M. Gottschall et al., PRL 112, 012003 (2014)

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E for γ p → π+ n

S. Strauch, CLAS Collaboration, submitted to PRC

Blue short dash: Julich (14E)Blue long dash: Julich (14 prediction)Green solid: SAID (st14E)Green dash-dotted: SAID (st14 prediction)

• Models needed data to obtain reasonable agreement

• See Dave Ireland, Thursday at 3:10 (plenary session) for more CLAS π observables

27M. Dugger, HADRON, September 2015

• Preliminary CLAS results (Tsuneo Kageya)

• Deuteron target: HD-ICE

• Red: SAID prediction• Blue: BnGa prediction

E for γ n → π- p

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G for γ p → p π0

A. Thiel et al., PRL 109, 102001 (2012)

• ELSA resultsBlue dotted: MAIDRed dashed: SAIDBlack solid: BnGa

• Discrepancies between the different model predictions can be traced to the E0+ and E2- multipoles

• See Jan Hartmann’s talk (Thursday session 2) for more CBELSA/TAPS results

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“Isospin filters”

• The ηp, and ωp systems have isospin ½ and limit one-step excited states of the proton to be isospin ½. Final states like ηp, ωp act as isospin filters to the resonance spectrum.

γ p → π+ n γ p → η p


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T and F for η photoproduction

C.X. Akondi et al., PRL 113, 102001 (2014)

• See Natalie Walford, Thursday at 12:05 (session 2) for more about MAMI results and these observables

Black circles: MAMIPink triangles: Bonn

Red dashed: MAIDGreen long dashed: GissenBlack dash dotted: BG2011-02Blue dotted: SAID GE09Black: Legendre fits

• Model predictions do not reproduced results of the data

• CLAS results coming soon

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E-observable for η photoproduction on proton

I. Senderovich, CLAS Collaboration, submitted to PRL

• Cross section for γ n → η n shows strong enhancement in narrow region around W = 1685 MeV not seen in cross sections of γ p → η p

• Looking for structure near W = 1685 MeV in other observables for the γ p → η p reaction

Hint of structure at W = 1685 MeV but not conclusive evidence of narrow resonance

Flavor-singlet Goldberger-Treiman relation

)()( 00222

GNNF

NNAN gN

mFFgGm

• mN = mass of nucleon

• GA(0) = nucleon flavor-singlet axial charge

• F = invariant decay constant (reduces to Fπ if UA(1) anomaly were turned off)

GA(0) = 0.213 ± 0.138 Taking F = Fπ and NF = 3 allows a rough calculation of gGNN given gη´NN

• NF = Number of flavors

• gη´NN = η´-nucleon-nucleon coupling constant

• gGNN = gluon-nucleon-nucleon coupling constant

• The η' is the only isosinglet pseudoscalar meson. This property can be used to indirectly probe gluonic coupling to the proton

The η´ isosinglet

Needed to go from η0 to physical η´

M. Dugger, HADRON, September 2015 32

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Beam asymmetry for γ p → η´ p

1. F. Huang, H. Haberzettl and K. Nakayama, Phys. Rev. C 87, 054004 (2013).2. W.-T. Chiang, S. N. Yang, L. Tiator, M. Vanderhaegen and D. Drechsel , Phys. Rev. C 68, 045202 (2003).3. X.-H. Zhong and Q. Zhao, Phys. Rev. C 84, 065204 (2011).4. V. A. Tryasuchev, Phys. Part. Nucl. Lett. 10, 315 (2013).

Blue dashed: [1]Red dotted: [2]Green dot-dashed: [3]Orange long dashed: [4]Black: a sin2θ cosθ

• GRAAL data: P. Levi Sandri et al., arXiv: 1407.6991v2

• Predictions do not match the data

• CLAS data coming soon

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Photoproduction of π π p states

• 64 observables• 28 independent relations related to helicity amplitude magnitudes• 21 independent relations related to helicity amplitude phases• Results in 15 independent numbers

Good for discovering resonances that decay into other resonances!


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A small sample of Is for γ p → p π0 π0

V. Sokhoyan, et al., CBELSA/TAPS Collaboration, Eur. Phys. J. A 51, 95 (2015)

• σ = σ0{1+ Pγ[Is sin(φ) + Ic cos(φ)]}

• CBELSA/TAPS data• Much more data than shown• Ic not shown

• Black: BnGa full fit• Green: BnGa without N(1900)3/2+


Dalitz plot

• Clear evidence for intermediate states: • Δ(1232)π• N(1520)3/2- π• N(1680)5/2+ π• N f0(980)

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N(1900)JP →N(1520)3/2- π0


3/2+

5/2-

3/2-

5/2+

7/2+

JP

Best fit


• Data from region II

• See Jan Hartmann’s talk (Thursday session 2) for more CBELSA/TAPS results

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Interpretation of the p π0 π0 data using ρ λ oscillators


L=2

L=1

ρ = (x1 – x2)/sqrt(2) Antisymmetric under 1↔2λ = (x1+x2-2x3)/sqrt(6) Symmetric under 1↔2

• If L=2 with both ρ and λ oscillators excited, then there must be an intermediate state

• Resonances where only one oscillator is excited have a much reduced chance to decay into an intermediate resonance

• High mass resonances should have a three-particle component that excludes a simple quark-diquark picture of baryon resonances


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Self-analyzing reaction K+ Y (hyperon)

• The weak decay of the hyperon allows the extraction of the hyperon polarization by looking at the decay distribution of the baryon in the hyperon center of mass system:

cos1)(cos 21

YPI

where I is the decay distribution of the baryon, α is the weak decay asymmetry (αΛ= 0.642 and αΣ0 = -⅓ αΛ), and PY is the hyperon polarization.• We can obtain recoil polarization information without a

recoil polarimeter and the reaction is said to be “self-analyzing”


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The alphabet soup of observables for pseudo-scalar photoproduction

• Most experiments are done with photon and/or target polarization

• Hyperons are “self analyzing” and allow for recoil polarization measurements without using recoil polarimeter


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Observables Cx and Cz for γ p → K+ Λ

Without P13(1900) With P13(1900)

• Open circles: Cz

• Filled circles: Cx

• Inclusion of P13(1900) helped improve fit

• Data: R. Bradford et al., CLAS Collaboration, PRC 75, 035205 (2007)• Fits: V.A. Nikonov et al., Phys. Lett. B 662, 245 (2008)


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Spin and parity of the Λ(1405)

K. Moriya et al., CLAS Collaboration, Phys. Rev. Lett. 112, 082004 (2014)

• Reaction: γ p→K+ Λ(1405) where Λ(1405) →Σ+ π- • 2.55 < W < 2.85 GeV and 0.6 < cos(θc.m

K+) < 0.9• Polarization = 0.45• Decay distribution consistent with J = 1/2

Q is the polarization transfer:• Odd: independent of θΣ

• Even: dependent on θΣ

odd parity even parity

JP = ½-

JP = ½+

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T observable for γ p → K+ Λ

Data:• Red: CLAS (preliminary from Natalie Walford)• Black: Bonn78• Green GRAAL09

Models:• Red: RPR-Ghent• Blue: MAID• Purple dashed: BnGa

• GRAAL and CLAS data agree fairly well

• More observables for this reaction and K+ Σ0 coming soon

• See Dave Ireland, Thursday at 3:10 (plenary session) for more CLAS hyperon observables

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New experiment coming online: BGO-OD at ELSA


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PDG: then and nowSince 2010:• Eight resonance states have been added:

• N(1685) ?? *• N(1860)5/2+ **• N(1875)3/2- ***• N(1880)1/2+ **• N(1895)1/2- **• N(2040)3/2+ *• N(2060)5/2- **• N(2120)3/2- **

• Three resonance states have been removed:• N(2080)D13 **

• N(2090)S11 *

• N(2200)D15 **• The N(1900)3/2+ has been upgraded from ** to ***• The Δ(1940)3/2- has been upgraded from * to **


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Thanks for your time


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Title


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Title


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Temporary


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Experiment

Baryon models

Reaction modelAmplitude analysis

Linking experiment and theories

cross sectionsspin observables

LQCDquark models

etc…

multipole amplitudesphase shifts

effective Lagrangiansisobarsetc…


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Circ

ular

pol

ariza

tion

Circular polarization from 100% polarized electron beam

• Circular photon beam from longitudinally- polarized electrons

• Incident electron beam polarization

> 85%

2

2

344

4

kk

kkPP e

Circular beam polarization

k = Eγ/Ee

Cou

nts

H. Olsen and L.C. Maximon, Phys. Rev. 114, 887 (1959) M. Dugger, HADRON, September 2015

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Linearly polarized photons

• Coherent bremsstrahlung from 50-μ oriented diamond

• Two linear polarization states (vertical & horizontal)

• Analytical QED coherent bremsstrahlung calculation fit to actual spectrum (Livingston/Glasgow)

• Vertical 1.3 GeV edge shown


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FROST target • Butanol composition: C4H9OH

• C and O are even-even nuclei → No polarization of the bound nucleons

• Carbon target used to represent bound nucleon contribution of butanol


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• Frozen spin butanol (C4H9OH)

• Pz ≈ 80%

• Target depolarization: τ ≈100 days

Performance: target polarization

• For g9a (longitudinal orientation) 10% of allocated time was used polarizing target

• For g9b (transverse orientation) 5% of allocated time was used polarizing target


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HDICE target

A.M. Sandorfi

• Deuteron+Hydrogen target

• Neutron and proton polarization possible


✦ Look at the matrix element:

✦ Approximate the axial current as being conserved:

✦ Obtain 2 mN F(q2) = q2G(q2)

✦ Take as q → 0: G(q2) → fπ (1/q2) gπNN , where fπ is the pion decay constant and mπ = 0

✦ Goldberger-Treiman: 2 mN F(0) = f π gπNN , Note: F(0) is the isotriplet axial-vector form factor at q2 = 0

✦ Do the same calculation for the flavor singlet axial current to get:2 mN GA(0) = f gη0NN , where η0 is the unphysical flavor singlet goldstone boson

Goldberger-Treiman

)()()()( 25255 puqGqqFpupNJpN

05 J


Why do baryon spectroscopy ?

Continuous spectrum

Absorption spectrum

Emission spectrum

Atomic spectroscopy: H + γ → H* → H + γ

Intensity vs. wavelength

Atomic spectroscopy was a veryuseful tool in determining the quantum description of the atom.

Quantum mechanics for H* → H + γreproduces the observed spectrum

Ne + H

Ne Only

350nm 700nmn1

n4n3

n2

Baryon models must also be tested experimentally


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pi0 beam asymmetry


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γ p → p π π

Next slide

Linear beam and unpolarized target: Λi = δʘ = 0


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Conclusion


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Title


1 Overview of Spectroscopy Results in Meson Photoproduction with Polarization Observables M. Dugger,...

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