Supported in parts by the U.S. National Science Foundation: NSF PHY-1205782
Steffen Strauch for the CLAS Collaboration University of South Carolina
Nucleon Resonances: From Photoproduction to High Photon Virtualities, ECT*, Trento, Italy, October 12 - 16, 2015
Baryon spectroscopy with polarization observables from CLAS
1. Unpolarized target 2. Polarized proton target (FROST) 3. Polarized neutron target (HDice) 4. CLAS 12 Forward Tagger
Relevant degrees of freedom and missing resonance problem
2
Quark Models
• Constituent Quark Models predict many more of excited states than have been observed; some of the states may only couple weakly to πN.
• Quark-Diquark Models predict fewer states. • Quark and Flux-Tube Models predict increased number of states.CQM: U. Löring, B.C. Metsch, and H.R. Petry, Eur. Phys. J. A10 395 (2001)
Degr
ees
of f
reed
om
π2T 2J
L P11
D13 1 11 1 13 1 11 1 13
S DF F G I IH H191715
K11 13 15 17 19
GP
1720
1535
1675
1440
939
1900
19902000
2700
2090
1650
1520
1700
2600
1710
2100
1680
2190
2250
2200
2080
2220
1986
1897 1895
1/2+ 3/2+ 5/2+ 7/2+ 9/2+ 11/2+ 13/2+ 1/2- 3/2- 5/2- 7/2- 9/2- 11/2- 13/2-J
Mass [
MeV
]
1000
1500
2000
2500
3000
****
*
**
****
**
* **
****
**
***
S **
***
****
****
**
****
****
****
****
***
****
****
S S
N Resonance Spectrum — the low-energy signature of QCD
MB
3* or 4*
Resonance spectrum in Lattice QCD
3R.G. Edwards, J.J. Dudek, D.G. Richards, and S.J. Wallace, Phys. Rev. D 84, 074508 (2011)
LQCD predicts states with the same quantum numbers as CQMs with underlying SU(6) x O(3) symmetry; more states than have been identified experimentally.
0.6
0.8
1.0
1.2
1.4
1.6
1.8
2.0
N(938)
Δ(1232)1 1
2 3 2 1
2 2 1
4 5 3 1
mπ = 396 MeV
Hadron spectrum collaboration
Extracting nucleon-resonance information from experimental data
4
DataReaction Theory
Amplitude Analysis
N*, Δ*
LQCD
Models
QCD
Extraction of physics
Nucleon resonance information: mass, spin, parity, coupling constants, decay parameters, …
Cross sections and polarization observables
Coupled-channel analysis especially important
What we measure with CLAS
5
γ p→ π 0p,π +nγ p→ηp, ′η pγ p→ KY (K +Λ,K +Σ0,K 0Σ+ )γ p→ π +π − p,ω p, ρ p,φp…
γ n→ π − pγ n→ π +π −nγ n→ Σ−K + ,ΛK 0
…
Prot
on tar
get
Neut
ron
targ
et
Unpolarized, circularly polarized, linearly polarized beam
Unpolarized, longitudinally polarized, transversally polarized target
Recoil polarization (asymmetry in the weak decay of the hyperon)
Cross section and polarization observables
e.g. CLAS frozen spin target (FROST)
e.g. unpolarized deuterium target (g13), polarized HD-Ice target (g14)
Observables in pseudoscalar meson photoproduction
4 complex amplitudes ⇒ 16 possible (not independent) observables
6A.M. Sandorfi, S. Hoblit, H. Kamano and T.-S.H. Lee, J. Phys. G, Nucl. Part. Phys. 38, 053001 (2011)
e.g, FROST and HDice
e.g, Hyperon weak decay
Beam
Target Recoil Target + Recoil
x’ y’ z’ x’ x’ x’ y’ y’ y’ z’ z’ z’
x y z x y z x y z x y z
unpolarized dσ0 T P Tx’ Lx’ Σ Tz’ Lz’
PLγ sin(2φγ) H G Ox’ Oz’ Cz’ E F -Cx’
PLγ cos(2φγ) Σ -P -T -Lx’ Tz’ -dσ0 Lx’ -Tx’
circular Pcγ dσ0 F -E Cx’ Cz’ -Oz’ G -H Ox’
-
double pion photoproduction fills empty cells in the table
coherent and incoherent Bremsstrahlung
CEBAF Large Acceptance Spectrometer in Hall B (1997 - 2012)
7
Polarized electron beam Energies up to Ee = 6 GeV (now up to 11 GeV)
CEBAF Large Acceptance
Spectrometer (CLAS)
Photon TaggerTarget unpolarized p or d, polarized FROST, HDiceEγ = Ee − E ′e
B.A. Mecking et al., Nucl. Instr. and Meth. A 503, 513 (2003).
Beam asymmetry Σ for π+ and π0 photo production on the proton
Largest changes from previous fits are for “well known” Δ(1700)3/2- and Δ(1905)5/2+ states.
8
dσdΩ
⎛⎝⎜
⎞⎠⎟ =
dσdΩ
⎛⎝⎜
⎞⎠⎟ 01− PL
γ Σcos(2ϕγ )( )
M. Dugger et. al (CLAS Collaboration), Phys. Rev. C88, 065203 (2013)
γ
p
π0
p
θcmπ
Models: SAID DU13 (CM12), MAID07, BG2011-02
high-energy π0 data: 1904 MeV < W < 2091 MeV
!γ p→ π 0p
θ (deg)
Polarization Transfer Observables Cx, Cz
9
Cx (•), Cz () for K+Λ channel
!γ p→ K +!Λ
Bonn-Gatchina coupled-channel isobar model: N(1900)P13 needed in PWA of Nikonov et al. Strongest contributions to γp → KΛ: S11-wave, P13(1720), P13(1900), P11(1840)
with N(1900)P13
without N(1900)P13
CLAS Data: R. Bradford, et al., Phys. Rev. C 75, 035205 (2007). Analysis: V.A. Nikonov et al., Phys. Lett. B 662, 245 (2008)
State confirmed in more recent analyses.
N(1900)P13 found in qqq models, not expected in quark-diquark models.
Recoil Polarization P
10
γ p→ K +!Λ
Kaon-MAID model (green) Single-channel BW resonance fits No longer up-to-date
Data: M. McCracken et al, (CLAS) Phys. Rev. C 81, 025201 (2010).
F.X. Lee et al., Nucl. Phys. A695, 237 (2001)
Bonn-Gatchina model (blue) Multi-channel, unitary, BW resonance fit Large suite of N* contributions Was not predictive for recoil polarization
R. Schumacher, CIPANP Vail 2015
BnGa: A.V. Sarantsev et al., Eur. Phys. J., A 25, 441 (2005).
Simultaneous fit to five polarization observables: Σ, P, T, Ox, and Oz.
11
g8 analysis:Dave Ireland (U. of Glasgow)
prelim. CLAS g8 data
dσdΩ
⎛⎝⎜
⎞⎠⎟ =
dσdΩ
⎛⎝⎜
⎞⎠⎟ unpol
1− PLγ Σcos(2ϕγ )(
+Px 'R PL
γOx ' sin(2ϕγ )⎡⎣ ⎤⎦+Py '
R P − PLγT cos(2ϕγ )⎡⎣ ⎤⎦
−Pz 'R PL
γOz ' sin(2ϕγ )⎡⎣ ⎤⎦ )
Hyperon photoproduction with linearly polarized photons
!γ p→ K +Σ
!γ p→ K +!Λ1700 MeV < W < 2200 MeV
Self-analyzing weak hyperon decay gives access to recoil polarization.
W (GeV)
W (GeV)
The FROST Target
12
Through dynamic nuclear polarization the high electron polarization is transferred to the proton spin system via microwave induced transitions.
Thermal equilibrium polarization of a spin-1/2 particle
superconducting holding coils (0.5 T)
transverse polarization (g9b)
longitudinal polarization (g9a)
Target: Frozen beads of butanol (C4H9OH) at 50 mK
Temperature (K)
-210 -110 1 10210
Pola
rizat
ion
-310
-210
-110
1
B = 5 T
proton
electronDNP
P = tanh µB2kT
⎛⎝⎜
⎞⎠⎟
FROST Target: C.D. Keith et al., Nucl. Instrum. and Methods A 684, 27 (2012)
The simple idea of the experiment
• Measure polarized free-proton and unpolarized bound-nucleon yield off butanol.
• Measure simultaneously unpolarized bound-nucleon yield off 12C target.
• Determine the polarized proton yield in the difference.
13
N p ≈ NB −αNC
12C CH2Butanol
γ p→π +XW = 1240 − 2260 MeV−0.9 ≤ cos(θπ
cm ) ≤ +0.9
ΔW = 20 MeV, ncosθ = 30
• Data analysis in 900 bins
!γ !p→ π +n
S.S. et al. (CLAS Collaboration), PLB 750, 53 (2015)
Double Polarization Observable E in π+n
14
Partial Wave Analyses Good overall description after fit, however, not with identical results. S.S. et al. (CLAS Collaboration), PLB 750, 53 (2015)
!γ !p→ π +n
)cm
πθcos(
-0.5 0 0.5
E
-0.5
0
0.5W = 1.640 - 1.660 GeVSAID ST14Juelich14BnGa11E
)cm
πθcos(
-0.5 0 0.5
E
-0.5
0
0.5W = 1.640 - 1.660 GeVSAID ST14EJuelich14EBnGa14E
)cm
πθcos(
-0.5 0 0.5
E
-0.5
0
0.5W = 1.900 - 1.940 GeV
)cm
πθcos(
-0.5 0 0.5
E
-0.5
0
0.5W = 1.900 - 1.940 GeV )
cm
πθcos(
-0.5 0 0.5
E
-0.5
0
0.5W = 2.140 - 2.200 GeV
)cm
πθcos(
-0.5 0 0.5
E-0.5
0
0.5W = 2.140 - 2.200 GeV
beforeafter
W = 1.650 GeV W = 1.920 GeV W = 2.170 GeV
dσdΩ
⎛⎝⎜
⎞⎠⎟ =
dσdΩ
⎛⎝⎜
⎞⎠⎟ 01− PzP⊙E( ) W = 1240 − 2260 MeV
−0.9 ≤ cos(θπcm ) ≤ +0.9
Is chiral symmetry effectively restored in highly excited mesons and baryons?
15
An important consequence of the spontaneous breaking of the chiral symmetry is the large mass gap between chiral partners:
ρ(770)
a1(1260)Jp = 1+
Jp = 1-500 MeV
N(938)
N*(1535)Jp = 1/2-
Jp = 1/2+
600 MeV
Mesons and baryons at higher masses are often observed in parity doublets.Example: four positive-parity and four negative-parity ∆∗ resonances at about 1900 MeV
Δ(1910)1 / 2+ Δ(1920)3 / 2+ Δ(1905)5 / 2+ Δ(1950)7 / 2+ (****)Δ(1900)1 / 2− Δ(1940)3 / 2− Δ(1930)5 / 2− Δ(2200)7 / 2− (*)
A.V. Anisovich et al., arXiv:1503.05774 [nucl-ex]
New evidence forΔ(2200)7/2- resonance
16A.V. Anisovich et al., arXiv:1503.05774 [nucl-ex]
Δ(1950)7/2+ **** Δ(2200)7/2- *
Parity partner of Δ(1950)7/2+ is poorly known.
Evidence found for ∆(2200)7/2− in a preliminary analysis of the Bonn/Gatchina group.
M(Δ7/2-) ≈ 2180 MeV
… and not ≈ 1950 MeV.Chiral symmetry is not restored in high-mass hadrons.
BnGa analysis of CLAS and CBELSA/TAPS data
0
0.5
1 2142dσ/dΩ, µb/sr
γp → π0p
2142dσ/dΩ, µb/sr
γp → π+n
-0.5
0
0.52085
T2131
T
-0.5
0
0.52092
Σ
2093
Σ
-0.5
0
0.52157E 2191E
-0.5
0
0.5
-1 -0.5 0 0.5 1
2208E
cos θ-1 -0.5 0 0.5 1
2227E
cos θ
FROST π+ data
with Δ(2200)7/2-
without
χ2 in
crea
se
0
200006r2 total7/2+ 7/2<
0
100006r2 /0p
0
2000
40006r2 /+n
0
1000
6r2 KY
0
10006r2 /0/0p
0
200
1800 1900 2000 2100 2200 2300
6r2 /0dp
M, MeV
0
200
400
0
200
400
0
100
200
0
25
50
0
50
100
0
5
7/2-7/2+
All isospin channels are important to constrain coupled-channel analyses: two examples for π0p
17
)0
π (θcos-1.0 -0.8 -0.6 -0.4 -0.2 0.0 0.2 0.4 0.6 0.8 1.0
F
-1.0
-0.5
0.0
0.5
1.0
CLAS preliminarySN11MAID2007BG2011-02
W = 1.87 GeV
)0
π (θcos-1.0 -0.8 -0.6 -0.4 -0.2 0.0 0.2 0.4 0.6 0.8 1.0
T
-1.0
-0.5
0.0
0.5
1.0
CLAS preliminarySN11MAID2007BG2011-02
W = 1.87 GeV
Polarized beam and target (up/down)Polarized target (left/right)
dσdΩ
⎛⎝⎜
⎞⎠⎟ =
dσdΩ
⎛⎝⎜
⎞⎠⎟ 01+ PyT + PxP⊙F
g9 analysis: Hao Jiang (USC)
transverse polarized target
γ
p
π0
p
θcmz
xy
γ
p
π0
p
θcmz
xy
T F
!γ !p→ π 0p
Helicity asymmetry E in eta photoproduction on the proton
η photoproduction isolates N*(I=1/2) states in the resonance spectrum.
Narrow structure seen in MAMI γp → ηp cross section data. [predicted in πN PWA: Phys. Rev. C 69, 035208 (2004)]
Present CLAS E data do not demand the presence of a narrow resonance with a width of 40 MeV or less at about 1.7 GeV.
18
!γ !p→ηp
-1
-0.5
0
0.5
1
1.5 <-0.8cmθ-1.0<cos
Juelich 2014 (fit)
1500 1600 1700 1800 1900 2000 2100-1
-0.5
0
0.5
1
1.5 <0.0cmθ-0.4<cos
<-0.4cmθ-0.8<cos
1500 1600 1700 1800 1900 2000 2100
<0.4cmθ 0.0<cos
W (MeV)
E(W)
E
E
W (MeV)I. Senderovich et al. (CLAS Collaboration), arXiv:1507.00325 [nucl-ex]
19
CLAS g9b preliminary —— RPR-Ghent —— KAON-MAID …… Bonn-Gatchina
g9 analysis:Natalie Walford (CUA, now Basel)
First measurement of the polarization observable F up to 2.30 GeV.
no sufficient previous constraints exist; all models fail to describe the data.
1.85 < W < 1.90 GeV1.80 < W < 1.85 GeV1.70 < W < 1.80 GeV
2.00 < W < 2.05 GeV1.85 < W < 2.00 GeV1.90 < W < 1.85 GeV
2.15 < W < 2.20 GeV2.10 < W < 2.15 GeV2.05 < W < 2.10 GeV
2.20 < W < 2.30 GeV
γ
p
K+
Σ0
θcmz
xy
!γ !p→ K +Σ0Hyperon photoproduction
FFROST data for Λ, Σ photoprouction
Double-pion photoproduction as a tool in the study of excited nucleons
Nππ is a dominant decay channel of highly excited nucleons.
Essential part in coupled-channel calculations.
Allows for the study of sequential decays.
20
γ p→ N * →πΔγ p→ N * → ρp
cm
kp'
π+
π−
z’x’
θθ∗φ∗
p α
transversely polarized target
circularly polarized beam
d 5σdm(π +π − ) dΩπ+
* d cosθ
Example:
Parity conservation yields to symmetry properties of observables
21
* [degrees]φ0 90 180 270 360
I
-0.04
-0.03
-0.02
-0.01
0
0.01
0.02
0.03
0.04
* [degrees]φ0 90 180 270 360
xP
-0.1
-0.05
0
0.05
0.1
* [degrees]φ0 90 180 270 360
yP
-0.25
-0.2
-0.15
-0.1
-0.05
0
0.05
0.1
0.15
* [degrees]φ0 90 180 270 360
xP
-0.1
-0.05
0
0.05
0.1
0.15
0.2
0.25
0.3
* [degrees]φ0 90 180 270 360
yP
-0.4
-0.2
0
0.2
0.4
M −λN − ′λN−λγ (θ ,θ1,φ1) = (−1)
λγ −λN + ′λN M λN ′λNλγ (θ ,θ1,2π −φ1)
I⊙ Px
Py Py⊙
Px⊙
g9 analysis: Aneta Net (USC)
odd observables: do not exist in single
meson final states. even observables:
Py and Px⊙ correspond
to T and F, respectively.
circ
ular
ly p
olar
ized
pho
tons
-
tran
sver
sely
polar
ized
tar
get
γ p→ π +π − p
Preliminary results (g9a) for Pcz
22
A. Fix and H. Arenhövel, Eur. Phys. J. A 25, 115 (2005); Preliminary data: Yuqing Mao (USC)
Yuqing Mao (USC)
cm
kp'
π+
π−
z’x’
θθ∗φ∗β
p
I = I0 1+ ΛzPz ++δ ℓ sin2β I s + ΛzPz
s( )+δ ℓ cos2β I c + ΛzPz
c( )
* * *N N N∆
π πρ
ππ σ
ππ
Effective Lagrangian Model (A. Fix)
Exchange mesons, π,ρ,σ, and resonances, Δ(1232), N*(1440), N*(1520), N*(1535), Δ(1620), N*(1675), N*(1680), Δ(1700), N*(1720), Nucleon and Delta Born terms; Resonance terms:
𝝓* (deg)
Pola
rizat
ion
Obs
erva
ble
Pc zPo
lariza
tion
Obs
erva
ble
Pcz
W = 1.46 MeV to W = 2.30 GeV
γ p→ π +π − p
Preliminary results (g9b) for Px and Py
23
g9 analysis: Priyashree Roy (FSU)
) <-0.8+πθ-1.0< cos(
) <0.2+πθ0.0< cos(
) <-0.6+πθ-0.8< cos(
) <0.4+πθ0.2< cos(
) <-0.4+πθ-0.6< cos(
) <0.6+πθ0.4< cos(
) <-0.2+πθ-0.4< cos(
) <0.8+πθ0.6< cos(
) <-0.0+πθ-0.2< cos(
) <1.0+πθ0.8< cos(
) <-0.8+πθ-1.0< cos(
) <0.2+πθ0.0< cos(
) <-0.6+πθ-0.8< cos(
) <0.4+πθ0.2< cos(
) <-0.4+πθ-0.6< cos(
) <0.6+πθ0.4< cos(
) <-0.2+πθ-0.4< cos(
) <0.8+πθ0.6< cos(
) <-0.0+πθ-0.2< cos(
) <1.0+πθ0.8< cos(
1100 MeV < Eγ < 1200 MeV
cm
kp'
π+
π−
z’x’
θθ∗φ∗
p α
Data binned in Eγ, Φ*, and cos θ*,
fit with Fourier series.
I = I0 1+ Λcos(α )Px +Λsin(α )Py( )
γ p→ π +π − p
Intermediate Δ(1232) Resonance
24
π
N(1520)
(1232)∆
p = N(938)π−
+
CLAS Data: S.S. et al (CLAS Collaboration), Phys. Rev. Lett 95, 162003 (2005); Model: A. Fix and H. Arenhövel, Eur. Phys. J. A 25, 115 (2005)
I⊙ = ak sin(kφ)∑Fourier coefficients of the angular distribution
Example of sequential decays
-0.5
-0.25
0
0.25
0.5a 1
W = 1.520 GeV
-0.2
-0.1
0
0.1
0.2
1.1 1.2 1.3 1.4M(pπ+) (GeV)
a 2
-0.5
-0.25
0
0.25
0.5
a 1
W = 1.520 GeV
-0.2
-0.1
0
0.1
0.2
1.1 1.2 1.3 1.4M(pπ-) (GeV)
a 2
N(1520)→ π −Δ++ → pππ N(1520)→ π +Δ0 → pππγ p→ N * → πΔ
γ p→ π +π − p
Beam and target asymmetries inomega photoproduction (g9b)
25
Prelim
inary
Σ
-1
-0.8
-0.6
-0.4
-0.2
0
0.2
0.4
0.6
0.8
1
E: 1150 MeV
FROST (g9b-linear)
GRAAL (2013)
GRAAL (2006)
c.m.ωΘ
0 20 40 60 80 100 120 140 160 180-1
-0.8
-0.6
-0.4
-0.2
0
0.2
0.4
0.6
0.8
1
0 20 40 60 80 100 120 140 160 180
E: 1250 MeV
E: 1450 MeVE: 1350 MeVPre
limina
ry: 1250 MeVγE
: 1650 MeVγE
: 2050 MeVγE
: 1350 MeVγE
: 1750 MeVγE
: 2150 MeVγE
: 1450 MeVγE
: 1850 MeVγE
: 2250 MeVγE
: 1550 MeVγE
: 1950 MeVγE
: 2350 MeVγE
-0.8
0
0.8
-0.8
0
0.8
-0.8
0
0.8
-1 -0.5 0 0.5 1-1 -0.5 0 0.5 1-1 -0.5 0 0.5 1-1 -0.5 0 0.5 1c.m.
)ωΘcos(
T
γ p→ω p
g9 analysis: Priyashree Roy (FSU)
Beam asymmetry Target asymmetry
All isospin channels are important to constrain coupled-channel analyses
26Figs. A.M. Sandorfi, Spin’2014 Symposium
g14 analysis: Tsuneo Kageya (Jlab)PWA solutions (already outdated) show need to measure all isospin channels.
Beam-Target helicity asymmetry (observable E) for proton and neutron targets
!γ !p→ π +n
W = 1900 MeVW = 1880 MeV
!γ !n(p)→ π − p(p)
Double pion beam-helicity asymmetry for proton and neutron targets
27
g14 analysis: Peng Peng (UVa)
γ p→ π +π − pγ p(n)→ π +π − p(n) γ n(p)→ π +π −n(p)
I ⊙ I ⊙
φ * (rad) φ * (rad)
Integrated Io asymmetries off proton and neutron targets are comparable.
preliminarypreliminary
Moller Shield
Calorimeter
Tracker
Scintillation
Hodoscope
HTCC Moller
cup
CAD implementation
CLAS 12 Forward Tagger
28
• Small angle e- scattering (2.5o to 5o) • Eγ = 6.5 - 10.5 GeV • 0.01 (GeV/c)2 < Q2 < 0.3 (GeV/c)2 virtual photon, (almost) real photon • Quasi real photons are linearly polarized wrt to scattering plane • High luminosity
e- beam
Fig. from M.Battaglieri, ECT* Workshop Lattice QCD and hadronic physics (2014)
e
ForwardTagger
CLAS12
Nγ∗
e’
Quasi-Real Photoproduction with CLAS12
Baryon Spectroscopy
• E12-11-005A - Cascade, γp → K+K+Ξ-
(millions of reconstructed Ξ) - Omega, γp → K+K+K0Ω-
(4,000 reconstructed Ω)
• LOI12-15-004 - Search for Hybrid Baryons
(focus on lowest mass hybrid baryons)
29
L. Guo et al., Phys. Rev. C 76, 025208 (2007)
)2) (GeV/c+K+MM(K1.1 1.2 1.3 1.4 1.5 1.6 1.7 1.8
)2C
ount
s/(5
MeV
/c0
500
1000
1500
2000
2500 Ξ−
Ξ− (1530)
γ p→ K +K +X
presentCLAS data
L. Guo et al., Jefferson Lab Experiment E12-11-005A, “Photoproduction of the Very Strangest Baryons on a Proton Target in CLAS12” V. Burkert et al., Jefferson Lab LOI12-15-004, “Search for Hybrid Baryons with CLAS12 in Hall B"
Summary and outlook
New CLAS polarized photoproduction data off
polarized and unpolarized, proton and neutron targets
contribute to complete or nearly complete experiments.
Evidence of new states found in coupled-channel analyses.
Large impact expected as data analyses are being finalized.
30
PDG
bary
on s
ummar
y ta
ble
for
N* r
eson
ance
s
Table adapted from: V. Crede and W. Roberts, Rep. Prog. Phys. 76 (2013) 076301
future
… f
utur
e up
date
s …