1 overview of spectroscopy results in meson photoproduction with polarization observables m. dugger,...
TRANSCRIPT
1
Overview of Spectroscopy Results in Meson Photoproduction
with Polarization Observables
M. Dugger, HADRON, September 2015
2
Outline
• Motivations
• Helicity amplitudes
• Reactions and results
• PDG then and now
M. Dugger, HADRON, September 2015
3
Nucleon resonances
γ p → π+ n
• The nucleon resonance spectrum has many broad
overlapping states, making disentangling the spectrum difficult
M. Dugger, HADRON, September 2015
4
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
M. Dugger, HADRON, September 2015
5
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
6
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
M. Dugger, HADRON, September 2015
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
9
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
M. Dugger, HADRON, September 2015
10
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
12
Outline
• Motivations
• Helicity amplitudes
• Reactions and results
• PDG then and now
M. Dugger, HADRON, September 2015
13
• 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
M. Dugger, HADRON, September 2015
14
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
M. Dugger, HADRON, September 2015
15
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
M. Dugger, HADRON, September 2015
16
Finding missing resonances requires lots of different observables.
Cross sections are not enough!
M. Dugger, HADRON, September 2015
17
Outline
• Motivations
• Helicity amplitudes
• Reactions and results
• Conclusions
M. Dugger, HADRON, September 2015
18
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
M. Dugger, HADRON, September 2015
• See Priyashree Roy, Thursday at 11:05 (session 2) for ω and ρ CLAS results
Data from first round of double polarization measurements
M. Dugger, HADRON, September 2015
Polarization observables from the proton CBELSA/TAPS
20
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)
M. Dugger, HADRON, September 2015
21
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*
M. Dugger, HADRON, September 2015
22
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:
M. Dugger, HADRON, September 2015
23
T for γ p → n π+
• Preliminary results
• CLAS results agree well with previous data
G9b: FROST
(new)
(new)
(new)
M. Dugger, HADRON, September 2015
24
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
M. Dugger, HADRON, September 2015
25
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)
26
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
28
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
29
“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
M. Dugger, HADRON, September 2015
30
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
31
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
33
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
34
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!
M. Dugger, HADRON, September 2015
35
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+
M. Dugger, HADRON, September 2015
Dalitz plot
• Clear evidence for intermediate states: • Δ(1232)π• N(1520)3/2- π• N(1680)5/2+ π• N f0(980)
36
N(1900)JP →N(1520)3/2- π0
M. Dugger, HADRON, September 2015
3/2+
5/2-
3/2-
5/2+
7/2+
JP
Best fit
V. Sokhoyan, et al., CBELSA/TAPS Collaboration, Eur. Phys. J. A 51, 95 (2015)
• Data from region II
• See Jan Hartmann’s talk (Thursday session 2) for more CBELSA/TAPS results
37
Interpretation of the p π0 π0 data using ρ λ oscillators
M. Dugger, HADRON, September 2015
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
V. Sokhoyan, et al., CBELSA/TAPS Collaboration, Eur. Phys. J. A 51, 95 (2015)
38
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”
M. Dugger, HADRON, September 2015
39
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
M. Dugger, HADRON, September 2015
40
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)
M. Dugger, HADRON, September 2015
41
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+
42
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
43
New experiment coming online: BGO-OD at ELSA
M. Dugger, HADRON, September 2015
44
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 **
M. Dugger, HADRON, September 2015
45
Thanks for your time
M. Dugger, HADRON, September 2015
46
Title
M. Dugger, HADRON, September 2015
47
Title
M. Dugger, HADRON, September 2015
48
Temporary
M. Dugger, HADRON, September 2015
49
Experiment
Baryon models
Reaction modelAmplitude analysis
Linking experiment and theories
cross sectionsspin observables
LQCDquark models
etc…
multipole amplitudesphase shifts
effective Lagrangiansisobarsetc…
M. Dugger, HADRON, September 2015
50
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
51
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
M. Dugger, HADRON, September 2015
52
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
M. Dugger, HADRON, September 2015
53
• 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
M. Dugger, HADRON, September 2015
54
HDICE target
A.M. Sandorfi
• Deuteron+Hydrogen target
• Neutron and proton polarization possible
M. Dugger, HADRON, September 2015
✦ 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
M. Dugger, HADRON, September 2015
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
M. Dugger, HADRON, September 2015
57
pi0 beam asymmetry
M. Dugger, HADRON, September 2015
58
γ p → p π π
Next slide
Linear beam and unpolarized target: Λi = δʘ = 0
M. Dugger, HADRON, September 2015
59
Conclusion
M. Dugger, HADRON, September 2015
60
Title
M. Dugger, HADRON, September 2015