baryonspektroskopie mit polarisierten …...daniel elsner 1 baryonspektroskopie mit polarisierten...

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