Daniel Elsner 1 Baryonspektroskopie mit polarisierten Photonenstrahlen – aktuelle Ergebnisse der Experimente an ELSA Daniel Elsner Physikalisches Institut Universität Bonn für die CBELSA/TAPS-Collaboration DPG Frühjahrstagung - Münster 21.-25. März 2011 funded by the DFG within the SFB/TR16
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Daniel Elsner 1
Baryonspektroskopie
mit polarisierten Photonenstrahlen –
aktuelle Ergebnisse
der Experimente an ELSA
Daniel ElsnerPhysikalisches InstitutUniversität Bonn
für die CBELSA/TAPS-Collaboration
DPG Frühjahrstagung
-
Münster 21.-25. März 2011
funded
by
the
DFGwithin
the
SFB/TR16
Daniel Elsner 2
Outline
•
Introduction
•
Experimental setup–
polarised
photon
beams
at ELSA
–
longitudinally
polarised
target–
Crystal Barrel detector
setup
•
Resultssingle
meson
photo
production
+ single
& double polarisation
observables
•
Summary
Daniel Elsner 3
Motivation baryon
spectroscopy
ener
gy
eV
MeV
atom
nucleon
Daniel Elsner 4
Motivation photo
production
Xp
p
p +
+
+ p p + +
+ p p +
+ p p + + p K+
+
Eγ
/ GeV
W / GeV
Daniel Elsner 5
Motivation baryon
spectroscopy
Löhring, Metsch, Petry, EPJ A10, 395(2001)
?
??
?
Daniel Elsner 6
Motivation photo
production
• avoid
artificial
selection
(e.g. πN coupling) → photo
production, measure
many
decay
channels
• sensitivity
to „low
intensity“
resonances→ polarisation
observables
,,,,,, K
?,,,, N
Daniel Elsner 7
- - - - x´
y´
z´
x´
x´
z´
z´-
x y z -
-
-
x z x z
photon
target
recoil
(target
+ recoil)
unpolarised
σ0
0 T
0 0 P
0 Tx´
-Lx´
Tz´
Lz´
linearly
pol. -Σ
H (-P) -G
Ox´
(-T) Oz´
(-Lz´) (Tz´) (-Lx´) (-Tx´)
circularly
pol. 0 F 0 -E
-Cx´
0 -Cz´
0 0 0 0 Knöchlein, Drechsel, Tiator
Z.Phys. A 352 (1995)
Observables
in meson
photo
production
single
pseudoscalar
meson
photo
production
dσ
= dσ0
[ 1-
Pγlin
( Σ
cos
2Φ
-
G
PT,z
sin 2Φ) -
E
Pγcirc
PT,z
]dσ
= dσ0
[ 1-
Pγlin
( Σ
cos
2Φ
-
G
PT,z
sin 2Φ) -
E
Pγcirc
PT,z
]
Linearly polarised photons: Pγlin
Circularly polaris. photons: Pγcirc
Longitudinally polaris. protons: PT,z
Example:
Daniel Elsner 8
Electron
Stretcher
Accelerator
0.5 GeV
to 3.5 GeV(polarised) electron
beam
electron
polarisation72% @ 1.9 GeV65% @ 2.4 GeV
BGO -
ODBGO
ELSA talks:HK 26.4HK 26.5
Daniel Elsner 9
Coherent
BS linearly
polarised
photons
structure
(diamond
crystal)Laue-Bragg
condition q=ng
kinematical
constraint
0.25 0.5 0.75 1.0 E /E0
ddE
incoherentcoherent
coh./incoh.
E =E0-Ee-
E0,p0
E ,k
T,q
Ee-,p
Incoherent
BS
Linearly
polarised
photons
via Coherent
Bremsstrahlung
Daniel Elsner 10
Linearly
polarised
photons
via Coherent
Bremsstrahlung
x
z
z h
x v
Pol
aris
atio
nsgr
ad
r
elat
ive
Inte
nsitä
t
Polmax
≈
61% Polmax
≈
58% Polmax
≈
54%
Daniel Elsner 11
Circularly
polarised
photons
& Møller
–
polarimetry
A = N - NN Nzz
+
beam
polarisation
P = Azz
P aTzz•
B
counting
rate asymmetry
• longitudinally polarised
electrons • helicity
transfer to photon
• measurement
of electron
polarisationusing
Møller
polarimeter
Pol
aris
atio
n / %
Date
Daniel Elsner 12
Experimental hall
Crystal Barrel set-up BGO -
Open Dipole set-up
Daniel Elsner 13
Crystal Barrel / Taps setup
electron beam
Daniel Elsner 14
60 m
mbeam
target
internal superconducting 'holding coil’liquid helium from the still
100 mmButanol (C4
H9
OH)
Frozen
spin
target
-
polarisation: Dynamic
Nuclear
Polarisation at high B-field
(2.5 T)-
target
material: chem. endowed
Butanol (C4
H9
OH)
-
„freeze“
up the
spin
(0.4 T) at 50 mK-
horizontal
cryostat
(→ 4π
accept.) with
integrated
solenoid
(∆B/B ~10-4), NMR
-
relaxation
time T~500h- ~75% long. polarisation(max. 83%)
Bonn: H. Dutz, S. GoertzBochum: W. Meyer, S. Reichertz
Daniel Elsner 15
Frozen
spin
target
-
polarisation: Dynamic
Nuclear
Polarisation at high B-field
(2.5 T)-
target
material: chem. endowed
Butanol (C4
H9
OH)
-
„freeze“
up the
spin
(0.4 T) at 50 mK-
horizontal
cryostat
(→ 4π
accept.) with
integrated
solenoid
(∆B/B ~10-4), NMR
-
relaxation
time T~500h- ~75% long. polarisation(max. 83%)
Bonn: H. Dutz, S. GoertzBochum: W. Meyer, S. Reichertz
Daniel Elsner 16
Frozen
spin
target
Daniel Elsner 17
Frozen
spin
target
Daniel Elsner 18
Frozen
spin
target
Daniel Elsner 19
Frozen
spin
target
Daniel Elsner 20
Frozen
spin
target
Daniel Elsner 21
Frozen
spin
target
Daniel Elsner 22
Frozen
spin
target
Daniel Elsner 23
Frozen
spin
target
Daniel Elsner 24
Crystal Barrel setup
• Crystal Barrel detector1230 CsI
crystals
•
forward
detector
(FWPlug)90 CsI
crystals
with
PM’s,
12 deg. –
30 deg.
• Inner-detectorcylinder
of 513 scintillating
fibers
•
forward
detector
(MiniTAPS)216 BaF2
, 1 deg. -12 deg.(not
shown)
Close to 4π
coverage
Daniel Elsner 25
Polarisation observables
at ELSA
Linearly polarised photons: Pγlin
Circularly polaris. photons: Pγcirc
Longitudinally polaris. protons: PT,z
Transversally polaris. protons: PT,x
& PT,y
dσ
= dσ0
[ 1-
Pγlin
( Σ
cos
2Φ
-
G
PT,z
sin 2Φ)
-
E
Pγcirc
PT,z
]
dσ
= dσ0
[ 1-
Pγlin
( H
PT,x
sin 2Φ
+ P
PT,y
cos
2Φ)
+ F
Pγcirc
PT,x
+ T
PT,y
]
photophoto
productionproduction
qq22
= 0 = 0 →→
real real photonsphotons
Daniel Elsner 26
CB double pol. observables @ DPG Frühjahrstagung
2011
Vahe
Sokhoyan
(Bonn) –
HK 4.2:Measurment
of polarization
observables
Is
und Ic
in the
reaction
γ
p → p π0π0
with
the
CBELSA/TAPS experiment
Jan Hartmann (Bonn) –
HK 4.3:Messung von Polarisationsobservablen
in der Meson‐Photoproduktion mit linear polarisiertem Strahl und transversal polarisierten Target (γ
p → p π0
/ p η)
Annika Thiel (Bonn) –
HK 4.4:Messung der Doppelpolarisationsobservablen
G in π0
‐ und η‐Photoproduktion
Manuela Gottschall (Bonn) –
HK 4.5:Bestimmung der Doppelpolarisationsobservablen
E für die Reaktion γ
p → p π0
Thomas Jude (Bonn) –
HK 4.7:Meas. of the
beam‐target
double polarization
observable, E for
γ(pK0)Σ+
with
the
CBELSA/TAPS experiment
Holger Eberhardt (Bonn) –
HK 17.6:Messung von Polarisationsobservablen
in der ω
Photoproduktion
Daniel Elsner 27
η-photoproduction
(γp
→ pη) photon
beam
asymmetry
Elsner D. et al., EPJ A 33, 147 (2007)
θηcm
Σ
BnGa
η-MAIDsensitive not sens.
D13(1520) MAID/BnGaD15(1675) MAID BnGaP11(1710) MAID BnGaP13(1720) BnGa MAID
CBELSA/TAPS dataset
2003
Daniel Elsner 28
Double polarisation
observable
G γ
+ p → p + π0
linearly polarised
photonslongitudinally polarised
proton
__
BoGa
__ SAID
__ MAID
G
A. Thiel -
HK 4.4
Prediction partialwave analysis
• pol. target
(C4
H9
OH ) → effective
dilution
factor
!
G
E
=967 MeV E
=1067 MeVPreliminary
results
CBGRAAL data
Daniel Elsner 29
Double polarisation
observable
G γ
+ p → p + η A. Thiel -
HK 4.4
Preliminary
results
CB
GRAAL data
linearly polarised
photonslongitudinally polarised
proton
CB data
2003
__
BoGa
__ SAID
__ MAID
Eγ= 1050 MeV
G
Daniel Elsner 30
Helicity dependent
cross section γ
+ p → p + π0
circularly
polarised
photon
beasm
longitudinally
polarised
proton
target
P33 (1232)
N1/
2 -N
3/2
´
M. Gottschall -
HK 4.5
with acceptance correction no normalisation
Daniel Elsner 31
Helicity dependent
total cross section γ
+ p → p + η
circularly
polarised
photon
beasm
longitudinally
polarised
proton
target
S11 (1535)
Preliminary
results
(J. Müller)
P11 (1710)
P13 (1720)
N1/
2 -N
3/2
no acceptance correction
Daniel Elsner 32
Polarisation observables
at ELSA
Linearly polarised photons: Pγlin
Circularly polaris. photons: Pγcirc
Longitudinally polaris. protons: PT,z
Transversally polaris. protons: PT,x
& PT,y
dσ
= dσ0
[ 1-
Pγlin
( Σ
cos
2Φ
-
G
PT,z
sin 2Φ)
-
E
Pγcirc
PT,z
]
dσ
= dσ0
[ 1-
Pγlin
( H
PT,x
sin 2Φ
+ P
PT,y
cos
2Φ)
+ F
Pγcirc
PT,x
+ T
PT,y
]
photophoto
productionproduction
qq22
= 0 = 0 →→
real real photonsphotons
Daniel Elsner 33
Motivation: Target asymmetry
in γ
+ p → p + η
Daniel Elsner 34
Target asymmetry
T γ
+ p → p + η
•
unpolarized
beam•
transversely
polarized
target
(direction
of pol.: β
= 99°)
Jan Hartmann HK 4.3
Recoil
Polarization
P and Observable
H
transversely
polarized
target+ linearly
polarized
photon
beam
Daniel Elsner 35
Electromagnetic
excitation
off the
neutron
Example:Cross section
for
γ
+ n → n + η
Jaegle, Phys. Rev. Lett. 100:252002 (2008)
Narrow
structure
in the
excitation
function
GRAAL W≈1680 MeV, Γ<30MeV
Tohoku-LNS
W≈1666 MeV, Γ<40MeV
ELSA W≈1685 MeV, Γ<60MeV
MAMI-C W≈1675 MeV, Γ<40MeV
-
New narrow state with stronger photo-coupling to the neutron ?
-
Interference effect of resonances ?- …
→ polarisation
observables needed !
→ running beam time
Daniel Elsner 36
•
linearly
and circularly
pol. photon
beams
available
at ELSA →
degree
of polarisation: Plin
max
= 50 –
60 %, Pcircmax
= 65%
•
first
round
of double polarisation
experiments
with
Crystal Barrel at ELSA
•
with
longitudinally
and transversally
polarised
target
→ high quality data for double polarisation
observables
→ preliminary
results
for
the
double polarisation
observables:Σ,G, E and T,P,H
→ different final states
•
essential for model independent PWA (complete experiment)
Summary
Daniel Elsner 37
Crystal Barrel talksVahe
Sokhoyan
(Bonn) –
HK 4.2:Meas. of polarization
observables
Is
und Ic
in the
reaction
γ
p ‐> p π0 π0 with
the
CBELSA/TAPS experiment
Jan Hartmann (Bonn) –
HK 4.3:Messung von Polarisationsobservablen
in der Meson‐Photoproduktion mit linear polarisiertem Strahl und transversal polarisierten Target
Annika Thiel (Bonn) –
HK 4.4:Messung der Doppelpolarisationsobservablen
G in π0 ‐ und η‐Photoproduktion
Manuela Gottschall (Bonn) –
HK 4.5:Bestimmung der Doppelpolarisationsobservablen
E für die Reaktion γ
p ‐> p π0
Thomas Jude (Bonn) –
HK 4.7:Meas. of the
beam‐target
double polarization
observable, E for
γ(pK0)Σ+ with
the
CBELSA/TAPS experiment
Mariana Nanova
(Giessen) –
HK 11.8:In‐Medium Properties
of the
η’‐Meson
Holger Eberhardt (Bonn) –
HK 17.6:Messung von Polarisationsobservablen
in der ω
Photoproduktion
Frieda Dietz (Giessen) –
HK 17.7 :ω‐Photoproduction
off Protons and Neutrons with
CBELSA/TAPS
Martin Urban (Bonn) –
HK 39.2 :Kompensation der Temperaturabhängigkeit von APDs
für eine neue Auslese des CB‐Kalorimeters
Karoly Makonyi
and Stefan Friedrich (Giessen) –
HK 43.4
:Search
for
ω‐mesic
nuclei
Daniel Elsner 38
Chiang & Tabakin, PRC55 (97) 2054
λ=
±1 ±½ ±½
0
4 x 2
parity conservation4
complex amplitudes
Complete
experiment
BACKUP
γ
+ p →
p
+ η
≥7
independent quantitiesno discrete ambiguities:
8
↔
well chosen observablesd2σ/dΩ, Σ, T, P, G, F, Tx, Lz.
Daniel Elsner 39
circularly
polarised
photons
Solenoid DipolElsa
Exp
Daniel Elsner 40
Circularly
polarised
photons Møller
–
polarimetry, formalism
dσcm
ij cm·[1+ a (θ ) P · P ]dΩ =cm
dσdΩ
0 B Ti j
asymmetry
coefficientsaij
θ
A = N - NN Nzz
+
counting
rate asymmetry
beam
polarisation
P = Azz
P aTzz•
B
counting
rate asymmetry
Daniel Elsner 41
Daniel Elsner 42
Daniel Elsner 43
Daniel Elsner 44
Daniel Elsner 45
Daniel Elsner 46
Daniel Elsner 47
Bonn frozen
spin
target
Daniel Elsner 48
Helicity dependent
total cross section γ
+ p → X
circularly
polarized
photonslongitudinally
polarized
proton
MAMI data: J. Ahrens et al., Phys. Tev. Lett. 87 (2001) 022003ELSA data: H. Dutz
et al., Phys. Rev. Lett. 91 (2003) 192001
Daniel Elsner 49
η-photoproduction
(γp
→ pη) total cross section
V. Crede, O. Bartolomy
et al.PRL 94 (2005) 012004,EPJ A33 (2007) 133V. Crede, A. McVeigh
et al.,PRC submitted
2009CLASGRAAL
TAPS
γp
→ pγγ
γp
→ pπ0π0π0
π0
η
BoGa
PWA
S (1535), D (1520), S (1650), F (1680), P (1720), D (2080)
+ ... + -, -t-channel exchange
+
11 13 11 15 13 13
new D15:m = 2068 ± 22MeV,
= 295 ± 40MeV
Daniel Elsner 50
Extraction
of polarisation
observables
Σ
& G
dσ
= dσ0
[ 1-
Pγlin
( Σ
cos
2Φ
-
G
PT,z
sin 2Φ) ]
• each
energy
& angular
bin →
fit modulation
of azimuth
angle
• each
single
event: photon
energy
→ photon
polarisation→ event-weighted
average
polarisation
(Pγ
lin)
first
online spectraγ
+ p → p + π0
Φlinpol
= Φlinpol
=π0 π0
Daniel Elsner 51
TargetasymmetryTargetasymmetry
in pin p
Daniel Elsner 52
Recoil
Polarization
P and Observable
H
•
linearly
polarized
photon
beam
(angle of pol. plane: α
= 45°) •
transversely
polarized
target
(direction
of pol.: β
= 99°)
f = eff. dilution
factor
Jan Hartmann HK 4.3
Daniel Elsner 53
Pol. obs. in double meson
production
See next
talk
(V. Sokhoyan) γ
+ p → p + π0
π0
• multi
meson
production
important
at higher
energies• access
to high excited
resonances
and their
decays
• η
acts
as isospin
filter
But
for
complete
experiment
in pseudoscalar
meson
prod.15/64 observables
needed
(1-
meson
8/16)
example: γ
+ p → p + π0
η E. Gutz
et al. Phys. Lett. B
687 (2010) 11
3 body
kinematic
→ 2nd decay
plane
if
angle Φ* is
integrated
out → Is
vanishes, Ic
= Σ
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