Photoproduction experiments with the Crystal Barrel/TAPSdetector at ELSA
U.Thoma, Bonn University
• Introduction
• The Crystal Barrel / TAPS detector at ELSA
• η- photoproduction at the proton and neutron
• 2π0- photoproduction
• π0η- photoproduction
• Polarisation
• Current experiments - double polarisation -
• Summary
funded by the DFG within the
SFB/TR16
Introduction
Electromagnetic Interaction Strong Interaction
γ
e
e
pp
↔ QED u
d
u
d
π+g
↔ QCD
“color“
⇒ 8 Gluons
- Gluons carry “color charge“
⇒ Running coupling
constantαs
QCD: Effects of the running coupling constantαs:
Abstand [m]
Confinement
?
asymptotische Freiheit
αs small⇒ QCD-processes calculable (perturbation theory)
αs big ⇒ perturbation theory notapplicable
→ Baryons (qqq)
→ Mesons (qq)
Better understanding of strong QCD and the structure of hadrons:
• What are the relevant degrees of freedom ?
• And the effective forces ?
⇒ Baryon spectroscopy
baryons, e.g.: or ?
Spectroscopy - Electromagnetic interaction -
Galaxie
1021 m
Materie
10-1 m
DNA
10-8 m
Kristall
10-9 m
Atom
10-10 m
Atomkern
10-14 m
Nukleon
10-15 m
⇔ Remember the atom:
Emissionlines
Absorptionlines
n=1
2
3
4
S1/2
S1/2 1/2, P
P3/2
P3/2 3/2, DD5 /2
S1/2 1/2, P
S1/2
S1/2
P1/2
P3/2
D5 /2
P1/2
S1/2
P3/2
D3/2
F =0
F =1
F =0F =1
B o h r Dira c Q ED H F S
0
E
1 420 M H z
17 8 M H z
8 17 3 M H z
2 46 6 T H z
43,5 G H z
Lamb−Shift
QEDDiracBohr
⇒ Discrete spectrum of absorption and emission lines
- Bohr model of the atom- Quantum mechanics- QED ...
⇔ Study strong QCD through the excitation spectrum of the nucleon
but:N∗- spectral-lines do not really look like this:
Ebut more like this:
E
Heisenberg’s uncertainty principle:
∆E · ∆t ≥ ~
⇔ Baryon-resonances are broad and overlapping
N∗- resonances in the quark model
Galaxie
1021 m
Materie
10-1 m
DNA
10-8 m
Kristall
10-9 m
Atom
10-10 m
Atomkern
10-14 m
Nukleon
10-15 m
U. Loering, B. Metsch, H. Petry et al. (Bonn)
π2T 2JL P11 D13 1 11 1 13 1 11 1 13S DF F G I IH H191715 K 11 13 15 17 19GP
1720
1535
1675
1440
939
1900
19902000
2700
2090
1650
1520
1700
2600
1710
2100
1680
2190
22502200
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
Mas
s [M
eV]
1000
1500
2000
2500
3000
****
*
**
****
**
* **
****
**
***
S **
***
****
****
**
****
****
****
****
***
****
****
S S
?
?
proton
??
↔
Constituentquarks
Confinement-potential
Residualinteraction
Baryon spectroscopy
Symmetric quark models:
→ many more resonances expected than observed yet- certain configurations completely missing !
• Certain configurations not realised by strong QCD ? Why ?
• Experimentally not found yet (resonances might decouple from πN)
↔ Big discovery potential of photoproduction experimentsinvestigating e.g. γp → Nη, Nη′, Nω, ∆π, Nρ, ∆η, ∆ω
Experimentally:Broad and strongly overlappingresonances
Important:→ Measurement of polarisation observables
(unambigiuos PWA)
→ Investigation of different final states
γp → pπ0 γp → pη
Photoproduction cross sections
Eγ/GeV
σ/barn
1
1.2 1.6 1.8 2.0 2.2 2.4
0 2 3
µ
10−1
210
10
1
1.4
π 0π 0ppγ π 0ppγ η
γ p ηpγ pp + −K K
+γ πpp −π π0
πpp −π+γ
p−>pXγ
γ p π 0p
K Σ+0γ p
γ p K+Λγ p K+Σ
– CB-ELSA data ,– SAPHIR data (ELSA) ,– other experiments
At high excitation energies:Multi-meson final states play a role of increasing importance
The Crystal Barrel / TAPS Experiment at ELSA
e
6.6m
inner detector
Eγ = E0 − E tagger
ELSA provides electrons
up to E=3.5 GeVTAPS
γCrystal Barrel goniometer
tagging system
• Unpolarised photons:Scattering of unpolarised electronsfrom an amorphous radiator→ production of Bremsstrahlung∼ 1/Eγ distribution
Tagging system:
- 14 Scintillators- 480 scintillating fibres- wire chamber (208 wires)
tagged range: 22 - 92% of E0
• Linearly polarized photons:
Production of linearly polarized photonsby coherent Bremsstrahlung off a diamondcrystal- coherent scattering if momentum transfercorresponds to a reciprocal lattice vectorplane fixed → linear polarisation
• Circularly polarized photons:
Scattering of longitudinally polarizedelectrons from an amorphous radiator
0
0.2
0.4
0.6
0.8
1
0.2 0.4 0.6 0.8 1
Pci
rc / P
e
Eγ / Eo
0
( Polarisation transfer, calculation: H.Olsen, L.C. Maximon)
Erzeugung von
polarisierten
Photonen
Christian
Hammann
Polarisierte
Photonen
Erzeugung
unpolarisierter
Photonen
Bremsstrahlung
Kinematik
linear polarisierte
Photonen
Impulsubertrag aufKristall
reziprokes Gitter
Bestimmung desPolarisationsgrads
Messen derPhotonpolarisation
zirkular
polarisierte
Photonen
Polarisationsubertrag
Bestimmung derElektronpolarisation
Messen derPhotonpolarisation
Spektrum der Erzeugten Photonen
The Crystal Barrel / TAPS Experiment at ELSA
γγ
p
γ
γp → N∗ →pη→pγγ
TAPS:
- 528 BaF2-crystals (6-30)
- 12 rad. length (τ=0.9/630ns)
- fast trigger, timing (σ=210ps)
- Energy resolution:σE/E = 0.79%/
p
E[GeV] + 1.8%
- charged identification via scintillators
Crystal Barrel:
- 1260 CsI(Tl) crystals
- 16 rad. length (τ= 0.9/7µs)
- angular resolution 1.2
- Energy resolution:σE/E = 2.5% /E1/4[GeV]
The Crystal Barrel / TAPS Experiment at ELSA
γ
p
γ
Crystal Barrel
- 1260 CsI(Tl) crystals
- 16 rad. length (τ= 0.9/7µs)
- angular resolution 1.2
- Energy resolution:σE/E = 2.5% /E1/4[GeV]
Inner detector:→ charged identification
- 3 layers of scintillating fibres(513 fibres, 2mm diameter)
- provides an intersection point ofcharged particle trajectories
- trigger, timing
η - Photoproduction
CB-ELSA:
] 2 [MeV/cγ γ m100 200 300 400 500 600
102
103
104
105
106
400 500 600
1000
2000
3000
4000
5000
6000
~ 78000 (a)γ 2 → η
400 500 600
500
1000
1500
2000
2500~ 21000 (b)
0π 3 → η
γ 2 → 0π~ 2.6 million
→ Photons aredetected
→ Proton directionmeasured
1000 15000
1000
2000
mass [MeV]
CBELSA/TAPS
γp → p η :
η → γγ
η → 3π0
CLAS (Jefferson Lab.):
→ Proton detected
→ η from missing mass
η′ → π0π0η
η - Photoproduction ( γp → N∗ →pη→pγγ )
DS11 13
1535
2090
1650
1520
1700
2080
1897 1895
1/2− 3/2−
* **
****
****
****
***
S S
3000
π2T 2JL 11P
1440
939
1710
2100
1986
1/2+J
Mas
s [M
eV]
1000
1500
2000
2500
****
*
S
***
****
γ
η
γ
ηProton
] 2 [MeV/cγ γ m100 200 300 400 500 600
102
103
104
105
106
400 500 600
1000
2000
3000
4000
5000
6000
~ 78000 (a)γ 2 → η
400 500 600
500
1000
1500
2000
2500~ 21000 (b)
0π 3 → η
γ 2 → 0π~ 2.6 million
CB-ELSA
→ photonsdetected (E,Θ, φ)
→ proton directionmeasured (Θ, φ)
⇒
1.6 1.8 2 2.2 2.4
5
10
1520 1 1.5 2 2.5
W [GeV]
[GeV]γEb]µ [ totσ
TAPS
GRAAL
CLASCB−ELSA
3rd S11 ?
FIT
⇔
E
broad and overlapping resonances
η - photoproduction
⇒ additional information necessary:
π2T 2JL P11 13 F15P
1720
1440
939
1900
2000
1710
2100
1680
1986
1/2+ 3/2+ 5/2+J
Mas
s [M
eV]
1000
1500
2000
2500
3000
****
*
**
****
S
***
****
****
**
DS D11 13 15
1535
1675
2090
1650
1520
1700
2200
2080
1897 1895
1/2− 3/2− 5/2−
* **
****
**
****
****
****
***
S S
⇔ Baryons have different properties
⇒ 1.) Measurement of angular distributions
γ
p
p
η
Θ
decay angular distribution
η
p
γ
LRp
helicity coupling
s−channel
(Breit−Wigner)resonance
Differential cross sections γp → pη
V.Crede, O.Bartholomy et al.,PRL 94, 012004 (2005)
CB-ELSA 4 GRAAL CLAS ? TAPS —– CB-ELSA fit
750 − 800 800 − 850 850 − 900 900 − 950 950 − 1000 1000 − 1050
1050 − 1100 1100 − 1150 1150 − 1200 1200 − 1250 1250 − 1300 1300 − 1350
1350 − 1400 1400 − 1450 1450 − 1500 1500 − 1550 1550 − 1600 1600 − 1650
0.5
1
1.5
2
0.2
0.4
0.6
0.2
0.4
0.6
−0.5 0 0.5 1−0.5 0 0.5 1−0.5 0 0.5 1−0.5 0 0.5 1−0.5 0 0.5 1−1 −0.5 0 0.5 1
cmθcos
b/sr]µ [Ω/dσd
W=1800W=1700
γ
p
p
η
Θ
η
pp
γ
R
s−channel
γ
p p
η
ρ,ω
t−channel
Total cross section γp → pηV.Crede, O.Bartholomy et al.,PRL 94, 012004 (2005)
1.6 1.8 2 2.2 2.4
5
10
1520 1 1.5 2 2.5
W [GeV]
[GeV]γEb]µ [ totσ
TAPS
GRAAL
CLASCB−ELSA
3rd S11 ?
FIT
CB-ELSA Isobar model fit:
Data included:
• γp → pη, γp → pπ0 (CB-ELSA)
• γp → pη (TAPS)
• Σ(~γp → pη), Σ(~γp → pπ0) (GRAAL)
• Σ(~γp → pπ0), σ(γp → nπ+) (SAID)
⇒ S11(1535), D13(1520), S11(1650), F15(1680), P13(1720), D13(2080)+ ... + ρ -,ω -t-channel exchange
+ new D15: m = 2068 ± 22 MeV,Γ = 295 ± 40 MeV
↔ No need for a 3rd S11!
New D15 -state
- D15(2060 ± 30, 340 ± 50):
! !" #$ % & ' %( ! ') *"+,- ./0 0 10 234 5- 6 67 - 4 - 8 . 1 2- 79 :; - 5- / 8 6 < 8- 0 = 64 0 , /> - ?- - 23 . 14 4 - 79
@ BA A C C ) %" !ED F GH " % ' @ BA A C C ) %" !ED F GH " % ' @ BA A C C ) %" !ED F GH " % ' @ BA A C C ) %" !ED F GH " % '
IJKL M NPOQR S TUV L W MXY Z T Y MV X V U W W MXY[ \ \] ^_ `ab cde b `[ \ \] ^_ `ab cde b `[ \ \ ] ^_ `a b c de b `[ \ \ ] ^_ `a b c de b `f \ \ g `h h ij klm e npo qsr tu \
i\v i\ w ^b x] a xy i\ clm e nz r nzf \ ae ] | i\ klm e npo qsr tu \
iv j \ ] ` h `_ ~ f clm e nz r nz m
\v ge b c | c w f klm e nz r z n z
@ A A C C ) %" !ED F GH " % F # !@ A A C C ) %" !ED F GH " % F # !@ A A C C ) %" ! D F GH " % F # !@ A A C C ) %" ! D F GH " % F # !
IJKL M NPOQR S TUV L W MXY Z T Y MV X V U W W MXY
j \ g `h h ij klm e npo qsr tu \
\ \v \ \ w ^b x] a xy i\ clm e nz r nz \ ae ] | i\ klm e npo qsr tu \
j \v \ ] ` h `_ ~ f clm e nz r nz m
~ v j f ge b c | c w f klm e nz r z n z
varies strongly !
⇔ Results vary strongly!
Multiparticle final states: γp → pπ0π0 , γp → pπ0η
Search for N∗/∆∗ → ∆π , ∆∗ → ∆η : CB-ELSA
γp → p4γ:
⇒ γp → pπ0π0
and γp → pπ0ηclearly observed
γp → N∗/∆∗ → ∆π0 → pπ0π0
γp → ∆∗ → ∆η → pπ0η
isospin selective ⇒ investigation ofthe ∆∗-spectrum
N*
π
π0
0
γ
Proton
∆(1232)
*∆,
, ηγp → pπ0η
) 0πm(p1000 1500 20000
500
1000
1500
2000
∆(1232)
• γp → N∗/∆∗ → Xπ0 → pπ0π0
0
20
40
60
80
100
120
140
) 0π(p2m1000 2000 3000
3x10
) 0 π
(p2
m
1000
2000
3000
3x10 ): 1800−2000 MeV0π0πm(p
13D (1520)
∆ (1232)
13D (1520)
) 0πm(p1000 1500 20000
1000
2000
3000
): 1800-1200 MeV0π0πm(p
X = ∆(1232)
X = D13(1520)
0
10
20
30
40
50
60
70
80
90
) 0π(p2m1000 2000 3000 4000
3x10
) 0 π
(p2
m
1000
2000
3000
4000
3x10 ): 2000−2200 MeV0π0πm(p
(1232)∆
X(1660)
D13(1520)
) 0πm(p1000 1500 20000
500
1000
1500): 2000-2200 MeV0π0πm(p
X = ∆(1232)
X = D13(1520)
X = X(1660)
γp → pπ0π0
U. Thoma et al., PLB 659 (2008) 87
0
2
4
6
8
10
1.2 1.3 1.4 1.5 1.6 1.7 1.8
M(γp), GeV/c2
σ tot ,
µb
CB−ELSA
GRAAL
TAPS
(ππ)sp
∆π
Results contradicting naive expectation:e.g.: D13(1520) → ∆π decay with L=0 ≈ L=2
D13(1700) → ∆π decay with L=0 < L=2
D33(1700) → ∆π decay with L=0 or L=2→ Measurement of double polarisation
observables necesarry
CB-ELSA Fit including additional data from:- single meson photoproduction,- π−p→n2π0 (CBall),- P11, S11, P33, D33- πN-partial waves
↔ Event based maximum likelihood fit
⇒ Determination of resonance properties:m , Γi (∆π0,Nσ,P11π,D13π,+...)
0
5
10
15
20
1.1 1.2 1.3 1.4 1.5 1.6
M(πp), GeV/c2
Nev
/ 20
MeV
x1033*1
0Phase space
FIT
DATA
0
1
2
3
4
5
6
7
0.2 0.4 0.6 0.8
M(ππ), GeV/c2
Nev
/ 20
MeV
x103
3*1
0
γp → pπ0ηI. Horn, Bonn
πP P33 S D31 F F D GH G II3 1135 37 39 H3 11 3 13 3 15 3 1333 35 37 3931KKL2T 2J
1232
20001950
1700
2150
1940 1930
2200
2750
1620
23502400
1900
2300
2420
2950
2390
19051920
1600
1750
1910
J 1/2+ 3/2+ 5/2+ 7/2+ 9/2+ 11/2+ 13/2+ 15/2+ 1/2- 3/2- 5/2- 7/2- 9/2- 11/2- 13/2- 15/2-
Mas
s [M
eV]
1000
1500
2000
2500
3000
*
********
*****
****
**
**
****
***
**
**
****
**
**
*
*
*
*
*******
***
*∆− resonances
?
U. Loering et al.
• γp → ∆∗ → ∆(1232)η → pπ0η
) 0πm(p1000 1500 20000
500
1000
1500
2000
∆(1232) ⇒ ∆(1232) clearly observed !
but there are also additionalinteresting structures :
0
2
4
6
8
10
12
14
16
) 0π(p2m1500 2000 2500 3000 3500
3x10
) η(p
2m
3000
4000
5000
3x10 ): 2200−2400 MeVη0πm(p
(1232)∆S (1535)11
) η0πm(600 800 1000 12000
500
1000 a0(980)
γp → pπ0η CB-ELSAI.Horn, Bonn
πP P33 S D31 F F D GH G II3 1135 37 39 H3 11 3 13 3 15 3 1333 35 37 3931KKL2T 2J
1232
20001950
1700
2150
1940 1930
2200
2750
1620
23502400
1900
2300
2420
2950
2390
19051920
1600
1750
1910
J 1/2+ 3/2+ 5/2+ 7/2+ 9/2+ 11/2+ 13/2+ 15/2+ 1/2- 3/2- 5/2- 7/2- 9/2- 11/2- 13/2- 15/2-
Mas
s [M
eV]
1000
1500
2000
2500
3000
*
********
*****
****
**
**
****
***
**
**
****
**
**
*
*
*
*
*******
***
*∆− resonances
?
U. Loering et al.
Total cross section
2γ
σµb
M( p) GeV/c
CB−ELSANabakayashiet al, PRC 2006
∆η
S11π
2.42.22.01.81.6 2.6
5
4
3
2
1
0
tot
−1 −0.5 0 0.5 10
200
400
600
800
1000
1200
1400
1.2 1.4 1.6 1.8 2 2.20
500
1000
1500
2000
2500
3000
−1 −0.5 0 0.5 10
200
400
600
800
1000
1200
1400
0.8 1 1.2 1.4 1.6 1.80
200
400
600
800
1000
1200
1400
1600
cos Θη cos Θp
π0π0π0m(p ) π0m( )η
Fit, +: data, phasespace
Event based maximum likelihood fit:
⇒ D33(1940) clearly contributes
~γp → pπ0η - CBELSA/TAPS -
0πφ
-150 -100 -50 0 50 100 1500
500
1000
1500
2000
2500
dσdΩ
=(
dσdΩ
)
0(1 − δl(Σ cos 2φ+ Is sin 2φ))
— PWAprediction
E. Gutz et al,
EPJ A35, (2008) 291
~γp → pη - CBELSA/TAPS -
· CB/TAPS beam-asymmetries ⇔ provide additional information for the PWA
P (1720)13
13D (1520)
BoGa−PWA
13D (1520)
P (1720)13
η −MAID
D.Elsner et al.,EPJ. A33 (2), 147 (2007)
Single pseudoscalar meson photoproduction
Complete experiment→ ≥ 8 observables needed
(W.-T. Chiang, F.Tabakin, PRC55, 2054 (2007))
Double pseudoscalar meson photoproduction
→ ≥ 15 observables needed(Roberts, Oed)
⇒ double polarisation experiments needed !
Crystal Barrel/TAPS at ELSA:
Experiments with longitudinally polarised targetand polarised beam started
Polarisation observables:
Photon Target Recoil Target–Recoil
x′ y′ z′ x′ x′ z′ z′
x y z x z x z
unpolarized σ 0 T 0 0 P 0 Tx′ -Lx′ Tz′ Lz′
linear -Σ H (-P ) -G Ox′ (-T ) Oz′ (-Lz′) (Tz′) (-Lx′) (-Tx′)
circularly 0 F 0 -E Cx′ 0 Cz′ 0 0 0 0
1 unpolarised measurement, 3 single polarisation observables,12 double polarisation observables
Example: Beam polarisation Σ
- along y-axis: dσ⊥
- along x-axis: dσ||
Σ =σ⊥ − σ||
σ⊥ + σ||
,
0πφ
-150 -100 -50 0 50 100 1500
500
1000
1500
2000
2500
dσ
dΩ=
dσ
dΩ0· (1 − PlΣcos(2φ))
Photoproduction of two pseudoscaler mesons
Double pol. experiments with: - linear or circular polarised beam- longitudinal polarised target
Single pseudoscalar meson photoproduction
dσdΩ
= σ0 1 − δ lΣ cos 2ϕ − Λ z ( − δ lG sin 2ϕ + δ E)
Double pseudoscalar meson photoproduction
dσdxi
= σ0 ( 1 − Λz · Pz ) + δ (I − Λz · E )
− δ l [ sin 2ϕ ( I s − Λz ·G )
+ cos 2ϕ ( Σ − Λz · Pzc ) ]
bcm
a
k2
b1
zx
pθ
φ θ
⇒ Multi-meson final states or final states with non-spin-0-mesons:
much more complicated
~γp → pη - CBELSA/TAPS -
· CB/TAPS beam-asymmetries ⇔ provide additional information for the PWA
P (1720)13
13D (1520)
BoGa−PWA
13D (1520)
P (1720)13
η −MAID
D.Elsner et al.,EPJ. A33 (2), 147 (2007)
Single pseudoscalar meson photoproduction
Complete experiment→ ≥ 8 observables needed
(W.-T. Chiang, F.Tabakin, PRC55, 2054 (2007))
Double pseudoscalar meson photoproduction
→ ≥ 15 observables needed(Roberts, Oed)
⇒ double polarisation experiments needed !
Crystal Barrel/TAPS at ELSA:
Experiments with longitudinally polarised targetand polarised beam started
Circularly polarized beam + longitudinally polarized targetη-photoproduction
Predictions:
η-MAID / BoGa-PWA
dσ(3/2−1/2)
dΩ=dσ3/2
dΩ−dσ1/2
dΩ
1500
0
1
2
dσ/dΩ [µb/sr] (helicity 1/2 - 3/2)
1600 1700
18001
0.5
0
1900 2000
21000.5
0
2200 2300
24000.5
-0.5
0
-1
0-1 1
2500
0-1 1
2600
0-1 1
cos θcm
Double Polarisation Experiments at ELSA
Experiments with: - linear or circular polarised beam- longitudinal polarised target (frozen spin butanol)
TAPS
Forward Detector
Crystal Barrel
+ Inner detector
Goniometer
Tagging system
Beam DumpPhoton intensity
monitor
Gas-Cherenkov
Polarized Target
The central detector:
γγ
p
Forward plug :- 90 CsI(Tl) crystals (∼12-30)- Photomultiplier readout- 1st-level trigger capabilities- timing
Crystal Barrel :- 1230 CsI(Tl) crystals (∼30-156)- Readout via photodiodes on WLS- 2nd-level trigger capabilities only
inner detector:charged part. identification
- charged identification (FP):180 scintillators in 2 layers
Double Polarisation Experiments at ELSA
Experiments with: - linear or circular polarised beam- longitudinal polarised target (frozen spin butanol)
TAPS
Forward Detector
Crystal Barrel
+ Inner detector
Goniometer
Tagging system
Beam DumpPhoton intensity
monitor
Gas-Cherenkov
Polarized Target
Mean Pol ~ 70%
Double Polarisation Experiments at ELSA
Online spectra: circularly polarised beam, longitudinally polarised target
γp → pη:
g p
g p
proton
500 1000 1500 2000
mass [MeV]
2000
4000
6000
8000
10000
0
co
un
ts
difference unpolarised difference
=⇒
1800
1400
1000
600
200
0
-200500 1000 1500 2000
mass [MeV]
Dc
ou
nts 1800
1400
1000
600
200
0
-200500 1000 1500 2000
mass [MeV]
Dc
ou
nts
h gg
h gg300
co
un
ts
200
100
0100 200 300 400 500 600
mass [MeV]
x103
co
un
ts 14000
12000
10000
8000
6000
4000
2000
0400 450 500 550 600 650 700
mass [MeV]
p0 gg γp → pγγ
⇒ First asymmetries observed
Double Polarisation Experiments
First online spectra: linearly polarised beam, longitudinally polarised targetdσdΩ
=(
dσdΩ
)
0(1 − δl(Σ cos 2φ− ΛzG sin 2φ))
)Θcos(-1 -0.8 -0.6 -0.4 -0.2 0 0.2 0.4 0.6 0.8 1
φ
-150
-100
-50
0
50
100
150
0
2
4
6
8
10
12
14
16
18
20
)Θcos(-1 -0.8 -0.6 -0.4 -0.2 0 0.2 0.4 0.6 0.8 1
φ
-150
-100
-50
0
50
100
150
0
2
4
6
8
10
12
14
16
18φφ −45° +45°
cos( )θ cos( )θ
200
400
600
800
1000
1200
1400
1600
1800
2000
400
600
800
1000
1200
1400
1600
1800
2000
−150 −100 −50 0 50 100 1500 −150 −100 −50 0 50 100 1500
200
projection on φ projection on φ
φ φ−45° +45°
~γ~p → pπ0
(Eγ=750-1200 MeV)
−150 −100 −50 0 50 100 1500
500
1000
1500
2000
2500
3000
3500
sum
φ
Double Polarisation Experiments
First online spectra: linearly polarised beam, longitudinally polarised targetdσdΩ
=(
dσdΩ
)
0(1 − δl(Σ cos 2φ− ΛzG sin 2φ))
−150 −100 −50 0 50 100 1500
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
−150 −100 −50 0 50 100 1500
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
φ φ
−45° +45°Target − Target −
−150 −100 −50 0 50 100 1500
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
−150 −100 −50 0 50 100 1500
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8Target + −45° Target + +45°
φ φ
~γ~p → pπ0
(Eγ=750-1200 MeV)
⇒ Clear effect
fromG observed
= further information for thepartial wave analysis !
The ” new ” states - a comparison with the quark model -
π2T 2JL P11 13 F15P
1720
1440
939
1900
2000
1710
2100
1680
1986
1/2+ 3/2+ 5/2+J
Mas
s [M
eV]
1000
1500
2000
2500
3000
****
*
**
****
S
***
****
****
**
DS D11 13 15
1535
1675
2090
1650
1520
1700
2200
2080
1897 1895
1/2− 3/2− 5/2−
* **
****
**
****
****
****
***
S S D13(1875)
11(1840)P
+ πp π electroproduction (CLAS)
P (1900)13
D15(2070)
2 states ?
Quark model calculations by:
U. Loring, B. Metsch, H. Petry et al.
... important : further polarisationexperiments!
→ confirmation ofnew resonances
↔ higher sensitivityon resonance contri-butions !
The ∆∗- states
πP P3331 F F H35 37 39 H3 11L2T 2J
1232
20001950
2300
24202390
19051920
1600
1750
1910
J 1/2+ 3/2+ 5/2+ 7/2+ 9/2+
Mas
s [M
eV]
1000
1500
2000
2500
3000
*
********
*
****
**
**
*******
***
S D D G G I3 1133 35 37 3931
1700
2150
1940 1930
2200
1620
23502400
1900
1/2− 3/2− 5/2− 7/2− 9/2− 11/2−
****
***
**
**
****
*
*
*
*
11/2+
****
Quark model
U. Loring, B. Metsch,
H. Petry et al.
model∼ 2n+ `
The ∆∗- states
πP P3331 F F H35 37 39 H3 11L2T 2J
1232
20001950
2300
24202390
19051920
1600
1750
1910
J 1/2+ 3/2+ 5/2+ 7/2+ 9/2+
Mas
s [M
eV]
1000
1500
2000
2500
3000
*
********
*
****
**
**
*******
***
S D D G G I3 1133 35 37 3931
1700
2150
1940 1930
2200
1620
23502400
1900
1/2− 3/2− 5/2− 7/2− 9/2− 11/2−
****
***
**
**
****
*
*
*
*
11/2+
****
?
in CB−ELSAdata
⇔ Additional experimental information needed !!
Quark model
U. Loring, B. Metsch,
H. Petry et al.
model∼ 2n+ `
data∼ n+ ` ?
↔ Paritydoublets ?
Summary
• High quality baryon spectroscopy data has been taken
→ Determination of resonances properties
→ First evidence for new resonances D15(2070) → pη
→ Evidence for D33(1940) → ∆η
→ Decays via higher mass resonances observed(baryon cascades e.g. D13(1520)π0, S11(1535)π0)
⇔ Already very interesting !
But there is a lot more to be discovered+ cross check new states
⇔ Polarisation experiments
⇒ Better understanding of the hadron spectrum
⇒ Detailed testing ground for quark models,lattice QCD calculations ...