Photoproduction of mesons off nuclei - unibas.ch...η-production data from the proton: larger...

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Photoproduction of mesons off nuclei B. Krusche, U. Basel, CBELSA/TAPS, CBALL/TAPS collaborations Introduction excited states of the nucleon meson nucleus interactions Experimental setups Crystal Barrel & TAPS @ ELSA Crystal Ball & TAPS @ MAMI Experimental results photoproduction of mesons off quasi-free nucleons: η , η , π o π o , π o η ,... coherent photoproduction of mesons off light nuclei: π o η , π o π o , π o π o π o search for η -mesic nuclei Conclusions Collaboration 2 a B. Krusche, Giessen, November 2009

Transcript of Photoproduction of mesons off nuclei - unibas.ch...η-production data from the proton: larger...

Page 1: Photoproduction of mesons off nuclei - unibas.ch...η-production data from the proton: larger ηN-scattering lengths 1991 - 2002: T. Ueda, C. Wilkin, S.A. Rakityanski and others: suggestions

Photoproduction of mesons off nucleiB. Krusche, U. Basel, CBELSA/TAPS, CBALL/TAPS collaborations

Introductionexcited states of the nucleon

meson nucleus interactions

Experimental setupsCrystal Barrel & TAPS @ ELSA

Crystal Ball & TAPS @ MAMI

Experimental resultsphotoproduction of mesons off quasi-free nucleons: η, η′, πoπo, πoη,...

coherent photoproduction of mesons off light nuclei: πoη, πoπo, πoπoπo

search for η-mesic nuclei

ConclusionsCollaboration

2a

B. Krusche, Giessen, November 2009

Page 2: Photoproduction of mesons off nuclei - unibas.ch...η-production data from the proton: larger ηN-scattering lengths 1991 - 2002: T. Ueda, C. Wilkin, S.A. Rakityanski and others: suggestions

Photoproduction of mesons off nuclei - what can we learn?

breakup (quasi-free)

πo

γ + A → πo + A′ + N + ...

dσdΩ ∝ ∑ |A|2 × ...

& nuclear effects & FSI & ...

photo-excitation ofquasi-free neutrons

in-medium propertiesof hadrons, meson FSI...

coherent

γ

πo

A, ~q γ + A → πo + A

dσdΩ ∝ | ∑ A|2 × F 2(q2) × ...

& nuclear effects & FSI & ...

spin/iso-spin filters

meson - nucleusbound states...

∆ in-medium properties

nuclear form factors

incoherent

γ

πo

γ′

A, ~q γ + A → πo + A⋆

→ πo + A + γ

transition form factors

∆ in-medium properties

spin/iso-spin selection

Page 3: Photoproduction of mesons off nuclei - unibas.ch...η-production data from the proton: larger ηN-scattering lengths 1991 - 2002: T. Ueda, C. Wilkin, S.A. Rakityanski and others: suggestions

Structure of the Nucleoncomplex many body system

models - effective dof’s:

valence quarks

sea quarks

gluons

3 equivalent constituentquarks

quark - diquark models(fewer states)

quarks - flux tubes etc.(more states)

chiral soliton models(anti-decuplet states)

coupled channel dynamics(molecule-like states) ...

comparison: known excited states -constituent quark model (Capstick & Roberts)

1000

1200

1400

1600

1800

2000

2200

2400

P11(939)

P11(1440)

D13(1520)S11(1535)

S11(1650)D15(1675)F15(1680)D13(1700)P11(1710)P13(1720)P13(1900)

F17(1990)F15(2000)D13(2080)S11(2090)P11(2100)G17(2190)D15(2200)H19(2220)G19(2250)

P33(1232)

P33(1600)S31(1620)

D33(1700)P31(1750)S31(1900)F35(1905)P31(1910)P33(1920)D35(1930)D33(1940)F37(1950)F35(2000)S31(2150)

H39(2300)D35(2350)F37(2390)H3,11(2420)

Mass/(MeV/c2)N(I=1/2) ∆(I=3/2)

exp expQM QM

ordering of (low-lying) states?

missing resonance problem?

Page 4: Photoproduction of mesons off nuclei - unibas.ch...η-production data from the proton: larger ηN-scattering lengths 1991 - 2002: T. Ueda, C. Wilkin, S.A. Rakityanski and others: suggestions

low lying excited states

P11(939)

P11(1440)

D13(1520)S11(1535)

S11(1650)D15(1675)F15(1680)D13(1700)

P33(1232)

P33(1600)S31(1620)

D33(1700)

N(I=1/2) ∆(I=3/2)

η σ π ρ π

Notation:

L2I2J ; L=0(S),1(P),2(D),...

ππ ηπ

B. Krusche, Giessen, November 2009

Page 5: Photoproduction of mesons off nuclei - unibas.ch...η-production data from the proton: larger ηN-scattering lengths 1991 - 2002: T. Ueda, C. Wilkin, S.A. Rakityanski and others: suggestions

Experimental Options:

Final states: Observables: Isospin: neutron targets

single meson production:γp → pπ, η, η′, ω...; ΣK(⋆)...

0

10

20

30

40

500 1000

σ[µb

]

γp→pπo

D13

P11S11

F15

0

5

10

15

20

500 1000

γp→pηS11(1535)

S11(1650)

photon energy [MeV]

multiple meson production:

N*, ∆

N(938)

N*, ∆

N* ∆

N*

N*

N*,∆

N*

ππ πη

ρ σπ

π

π

η

π

η

η

π

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ang. distributions−→ dσ/dΩ

Dalitz plots−→ M(N, mi), M(m1, m2)

polarization dof:

- linearely pol. beams

- circularly pol. beams

- longitudinally pol. targets

- transversely pol. targets

- recoil polarization

−→ I⊙

−→ Σ, R, T

−→ E, G, H , F

−→ ...

elm. excitationsisospin dependent

quasifree off the deuteron

coherent off the deuteron

Page 6: Photoproduction of mesons off nuclei - unibas.ch...η-production data from the proton: larger ηN-scattering lengths 1991 - 2002: T. Ueda, C. Wilkin, S.A. Rakityanski and others: suggestions

electromagnetic excitation off the neutron

importance of measurements off the neutron:

• different resonance contributions

• needed for extraction of iso-spin composition of elm. coupl ings

complications due to use of nuclear targets (deuteron):

• Fermi motion

• nuclear effects like FSI, re-scattering, coherent contrib utions

B. Krusche, Giessen, November 2009

Page 7: Photoproduction of mesons off nuclei - unibas.ch...η-production data from the proton: larger ηN-scattering lengths 1991 - 2002: T. Ueda, C. Wilkin, S.A. Rakityanski and others: suggestions

πo-mesons in the ∆-resonance: coherent - breakup - FSI

large coherent cross section, strong FSI γd → Xπo vs. γp → pπo

0

1

2

3

4

5

6

200 300 400 500

σ [1

00µb

]

d(γ,πo)d

d(γ,πo)np

photon energy [MeV]

γd→ ppπ−

0

10

20

30

40

0 60 120 180

dσ/d

Ωπ

b/sr

]

0

10

20

30

40

0 60 120 180

dσ/d

Ωπ

b/sr

]

θπ [deg] θπ [deg]

ωγlab=310 MeV

π- pp

ωγlab=330 MeV

π- pp

γd→ npπo

0

20

40

60

0 60 120 180

dσ/d

Ωπ

b/sr

]

θπ* [deg] θπ

* [deg]

ωγlab=285 MeV

π0 np

0

20

40

60

0 60 120 180

dσ/d

Ωπ

b/sr

]ωγlab=285 MeV

π0 np π0 np

ωγlab=285 MeV

π0 np π0 np

ωγlab=285 MeV

π0 np π0 np

ωγlab=285 MeV

π0 np

ωγlab=324 MeV

π0 np

cos(Θπ)

Eγ=340 MeV

Eγ=260 MeV

Eγ=215 MeV

Eγ=530 MeV

Eγ=460 MeV

Eγ=395 MeV0

2

4

0

10

0

5

10

(1/A

)dσ/

dΩ[µ

b/sr

]

0

5

0

20

-1 -0.5 0 0.5 10

2

4

-1 -0.5 0 0.5 1

strong FSI: breakup cross sections no good estimate for free nucleon xs

N2

N1

N2

N1

γ π

N2

N1

N2

N1

γ π

a bN2

N1

γ π

N1

N2c

breakup + coherent ≈quasi-free without FSI

B. Krusche, Giessen, November 2009

Page 8: Photoproduction of mesons off nuclei - unibas.ch...η-production data from the proton: larger ηN-scattering lengths 1991 - 2002: T. Ueda, C. Wilkin, S.A. Rakityanski and others: suggestions

simpler case: quasi-free η-production in the S 11-range

no complication from coherent process, no significant FSI ef fects,controllable Fermi motion effects

γd → ηX γp → pη, γd → pη(n)

10-2

10-1

1

620 640 660 680

coherent threshold

breakup

Eγ [MeV]

σ tot [

µb]

0

5

10

15

20

25

600 700 800

σ tot [

µb]

5

10

15

600 800 1000 1200 1400

σ[µb

]

Eγ[MeV]

σ(ηp), free proton

σ(ηp), quasi-free

σ(ηp), unfolded

significant FSI-effects only very close to threshold!

perfect agreement between free and quasi-free proton cross sections aftercorrection for Fermi motion!

B. Krusche, Giessen, November 2009

Page 9: Photoproduction of mesons off nuclei - unibas.ch...η-production data from the proton: larger ηN-scattering lengths 1991 - 2002: T. Ueda, C. Wilkin, S.A. Rakityanski and others: suggestions

resonance excitations in

quasi-free and coherent photoproduction of mesons

motivations:investigate/find resonances that are stronger excited on th e neutronthan on the proton (Moorehouse rules)

investigate spin/iso-spin structure of electromagnetic r esonance excitations

tools & status & problems:quasi-free production ⇒ neutron excitationsso far mainly results for π,η-production (differential cross sections)partly not well understood ‘deuteron’ effects

coherent production ⇒ spin/iso-spin filtersso far almost only for πo and sparse results for η

in most cases very small cross sections, difficult to separat e from breakup

B. Krusche, Giessen, November 2009

Page 10: Photoproduction of mesons off nuclei - unibas.ch...η-production data from the proton: larger ηN-scattering lengths 1991 - 2002: T. Ueda, C. Wilkin, S.A. Rakityanski and others: suggestions

interaction of mesons in nuclear matter

results from inclusive (quasi-free) pion photoproductionA-scaling of cross sections as function of kinetic energy T:

σ(A) ∝ Aα(T )α ≈ 1: ’volume’, no absorptionα ≈ 2/3: ’surface’, strong absorption

0.5

0.6

0.7

0.8

0.9

1

10 102

α

πo

η

transparent∆-resonance(black)

T[MeV]

πo-mesons: strongly absorbed atenergies sufficient to excite ∆;but only very weak interactionat small momenta−→ no bound-states possible

η-mesons: strong interaction also atvery small momenta due to s-waveS11(1535) resonance at threshold−→ strong enough for

(quasi)-bound states?

B. Krusche, Giessen, November 2009

Page 11: Photoproduction of mesons off nuclei - unibas.ch...η-production data from the proton: larger ηN-scattering lengths 1991 - 2002: T. Ueda, C. Wilkin, S.A. Rakityanski and others: suggestions

‘history’ of η-mesic nuclei1985: Bhalerao & Liu:attractive η-nucleus interaction for A ≥12

1986: Liu & Haider:suggestion of η-nucleus bound states

experiments: inconclusive e.g.:Chrien et al. (1988): π+ +16 O → p +15

η O

Johnson et al. (1993): π+ +18 O → π− +18η Ne

1993 - 2002: analysis of newη-production data from the proton:larger ηN-scattering lengths

1991 - 2002: T. Ueda, C. Wilkin,S.A. Rakityanski and others:suggestions of bound2H-, 3H-, 3He-, 4He-η states

experiments:threshold behaviorof η-production

p + d → 3He + η

d + d → 4He + η

pd→3Heηγ3He→3Heη

|f|2 [a

.u.]

1

10

10 2

0 0.5 1 1.5pη[fm-1]

B. Krusche, Giessen, November 2009

Page 12: Photoproduction of mesons off nuclei - unibas.ch...η-production data from the proton: larger ηN-scattering lengths 1991 - 2002: T. Ueda, C. Wilkin, S.A. Rakityanski and others: suggestions

GDH

MøllerPolarimeter

Crystal Barrel

M Q BPM

Quadrupole

Combined-Function Magnet

Dipole (horizontal)Dipole (vertical)

Radio FrequencySolenoid

SextupoleSkew Quadrupole

pol. esource

(50 keV)

Mottpolarimeter

LINAC 2

electrongun

(26 MeV)

LINAC 1(20 MeV)

detectortests

skewquadrupoles

tune jumpquadrupole

injection septa

bending magnetbeamlines for

SR experimentsBN3

BN2

BN1

FZK laboratory

DORIS cavity

PETRA cavity

tune jumpquadrupole

extraction septa

superconductingsolenoid

medium energyphysics

experiments

boostersynchrotron

DESY cavity

BN0

0.5 - 1.6 GeV

half cell of ELSA

-

0.5 - 3.5 GeVstretcher ring

EKS

0 m 5 m 10 m 15 m

Electron Stretcher Accelerator (ELSA)

ComptonPolarimeter

Page 13: Photoproduction of mesons off nuclei - unibas.ch...η-production data from the proton: larger ηN-scattering lengths 1991 - 2002: T. Ueda, C. Wilkin, S.A. Rakityanski and others: suggestions

MAMI accelerator in Mainz

4. Stage: Harmonic Double Sided Microtronmaximum energy: 1.5 GeV

B. Krusche, Giessen, November 2009

Page 14: Photoproduction of mesons off nuclei - unibas.ch...η-production data from the proton: larger ηN-scattering lengths 1991 - 2002: T. Ueda, C. Wilkin, S.A. Rakityanski and others: suggestions

Mainz accelerator lab

Page 15: Photoproduction of mesons off nuclei - unibas.ch...η-production data from the proton: larger ηN-scattering lengths 1991 - 2002: T. Ueda, C. Wilkin, S.A. Rakityanski and others: suggestions

experiments: Crystal Ball & Crystal Barrel with TAPS

10 cm

Bonn ELSA accelerator:Crystal Barrel (CsI),TAPS (BaF2) forward wall,inner detectors

Eγ ≤ 3.5 GeV,lin. pol.: available,circ. pol.: available

Mainz MAMI accelerator:Crystal Ball (NaJ),TAPS (BaF2) forward wall,inner detectors

Eγ ≤ 1.5 GeV,lin. pol.: available,circ. pol.: available

B. Krusche, Giessen, November 2009

Page 16: Photoproduction of mesons off nuclei - unibas.ch...η-production data from the proton: larger ηN-scattering lengths 1991 - 2002: T. Ueda, C. Wilkin, S.A. Rakityanski and others: suggestions

Experimental setup: Crystal Barrel and TAPS

γ7

30o

magnet

radiator

electronbeam

beamdump

fibers

proportional wire chamber

unscatteredelectrons

beamphoton

scintillators

electronsscattered

B. Krusche, Giessen, November 2009

Page 17: Photoproduction of mesons off nuclei - unibas.ch...η-production data from the proton: larger ηN-scattering lengths 1991 - 2002: T. Ueda, C. Wilkin, S.A. Rakityanski and others: suggestions

B. Krusche, Giessen, November 2009

Page 18: Photoproduction of mesons off nuclei - unibas.ch...η-production data from the proton: larger ηN-scattering lengths 1991 - 2002: T. Ueda, C. Wilkin, S.A. Rakityanski and others: suggestions

TAPS Crystal Ball - at MAMI

B. Krusche, Giessen, November 2009

Page 19: Photoproduction of mesons off nuclei - unibas.ch...η-production data from the proton: larger ηN-scattering lengths 1991 - 2002: T. Ueda, C. Wilkin, S.A. Rakityanski and others: suggestions

resonances coupling to η photoproduction off the protonbranching ratios and elm. couplings (PDG):

state bη [%] Ap1/2 Ap

3/2 An1/2 An

3/2

• D13(1520): 0.23±0.04 -24 166 59 139• S11(1535): 30 - 55 90 -46• S11(1650): 3 - 10 53 -15• D15(1675): 0±1 19 15 -43 -58• F15(1680): 0±1 -15 133 29 -33• D13(1700): 0±1• P11(1710): 6.2±1.0• P13(1720): 4±1

D15(1675) has stronger electromagneticcoupling to neutron than to protonbut parameters quite uncertain:

An1/2=-(21-57), An

3/2=-(30-77)

bη=0-1% (PDG), bη=17% (ETA-MAID, Chiang et al.)

interference structure in S 11-sector?

γp → ηp

1.6 1.8 2 2.2 2.4

5

10

1520 1 1.5 2 2.5

W / [GeV]

/ [GeV]γ Eb]µ / [ totσ

Data:

• TAPS: B. Krusche et al., PRL74 (1995) 3736• GRAAL: F. Renard et al., PLB528 (2002) 215• CLAS: M. Dugger et al., PRL89 (2002) 222002• Crystal Barrel: V. Crede et al., PRL94 (2005) 012004

⇑⇓

S11

S11

D15?

P11, P13

B. Krusche, Giessen, November 2009

Page 20: Photoproduction of mesons off nuclei - unibas.ch...η-production data from the proton: larger ηN-scattering lengths 1991 - 2002: T. Ueda, C. Wilkin, S.A. Rakityanski and others: suggestions

what is expected for n(γ, η)n - why is it interesting?

total cross sections for protonand neutron from MAID modelwith and without D 15(1675)(Eta-MAID, W.T. Chiang et al., NPA 700 (2002) 429)

0

10

1500 1600 1700 1800

σ[µu

b]

W[MeV]

full model MAID, protonno D15(1675), proton

full model MAID, neutronno D15(1675), neutron

previous data from MAMI only atlower incident photon energies

0.5

1

1.5

700 800 900 1000

σ n/σ p Kaiser et al.

MAID full model

MAID only S11(1535)

d(γ,η)X, σn/σp(Eγ)d(γ,η)X, σn/σp(Eγ)

d(γ,η)X, σn/σp(E*d(γ,η)X, σn/σp(Eγ)

4He(γ,η)X, σn/σp(Eγ)4He(γ,η)X, σn/σp(Eγ)4He(γ,η)X, σn/σp(E

*4He(γ,η)X, σn/σp(Eγ)

Eγ[MeV]B. Krusche, Giessen, November 2009

Page 21: Photoproduction of mesons off nuclei - unibas.ch...η-production data from the proton: larger ηN-scattering lengths 1991 - 2002: T. Ueda, C. Wilkin, S.A. Rakityanski and others: suggestions

quasifree eta photoproduction from p,n: results from GRAAL

recoil neutron recoil proton

0

0.2

0.4

0.6

0.8

1.5 1.6 1.7 1.8 1.9W,GeV

dσ/d

Ω, a

.u.

0

0.5

1

1.5 1.6 1.7 1.8 1.9W,GeV

dσ/d

Ω, a

.u.

0

0.2

0.4

0.6

0.8

1.5 1.6 1.7 1.8 1.9W,GeV

dσ/d

Ω, a

.u.

0

0.5

1

1.5 1.6 1.7 1.8 1.9W,GeV

dσ/d

Ω, a

.u.

0

0.2

0.4

0.6

0.8

1.5 1.6 1.7 1.8 1.9W,GeV

dσ/d

Ω, a

.u.

0

0.5

1

1.5 1.6 1.7 1.8 1.9W,GeV

dσ/d

Ω, a

.u.

V. Kouznetsov for the GRAAL collaboration,proceedings NSTAR 2004, page 197

proton cross section in agree-ment with free proton results

narrow structure in quasifreeneutron cross section atW =1675, width Γ ≈ 40 MeV

predicted properties ofnucleon-like pentaquark

Θ |2 _

[ud] s >+

|2 _

[us] d >3/2+Ξ

N |2 _

[ud] d >+

N |s_

[ud][su] s>+

+

Σ |2 _

[su] s >+

s

Σ |_

[ud][su] d >+

+

|2 _

[ds] u >3/2--Ξ

B. Krusche, Giessen, November 2009

Page 22: Photoproduction of mesons off nuclei - unibas.ch...η-production data from the proton: larger ηN-scattering lengths 1991 - 2002: T. Ueda, C. Wilkin, S.A. Rakityanski and others: suggestions

identification of η-meson production (exclusive)

decay channel: η → 3πo → 6γ

select events with 7 hits

invariant mass off all photon pairs

cut on πo invariant mass

select best combination of6γ to 3πo by χ2-test

use πo mass as constraint,construct 3 πo invariant mass

cut on 3 πo invariant mass

missing mass analysis toremove ηπ final states etc.treat recoil nucleon as missingparticle:

m2 = (Pγ + PN − Pη)2

[MeV]oπoπoπm400 600 800 1000

Cou

nts

[a.u

.]

800 MeV≤ γ E≤779 MeV

[MeV]neutronm800 1000 1200 1400

Cou

nts

[a.u

.]

data

n(p) +η

sim.πNNη

n(p) sim.η

sim.πNNη

[MeV]oπoπoπm400 600 800 1000

Cou

nts

[a.u

.]

1000 MeV≤ γ E≤950 MeV

[MeV]neutronm800 1000 1200 1400

Cou

nts

[a.u

.]

data with

background

[MeV]oπoπoπm400 600 800 1000

Cou

nts

[a.u

.]

1600 MeV≤ γ E≤1400 MeV

[MeV]neutronm800 1000 1200 1400

Cou

nts

[a.u

.]

B. Krusche, Giessen, November 2009

Page 23: Photoproduction of mesons off nuclei - unibas.ch...η-production data from the proton: larger ηN-scattering lengths 1991 - 2002: T. Ueda, C. Wilkin, S.A. Rakityanski and others: suggestions

B. Krusche, Giessen, November 2009

Page 24: Photoproduction of mesons off nuclei - unibas.ch...η-production data from the proton: larger ηN-scattering lengths 1991 - 2002: T. Ueda, C. Wilkin, S.A. Rakityanski and others: suggestions

B. Krusche, Giessen, November 2009

Page 25: Photoproduction of mesons off nuclei - unibas.ch...η-production data from the proton: larger ηN-scattering lengths 1991 - 2002: T. Ueda, C. Wilkin, S.A. Rakityanski and others: suggestions

quasifree η-photoproduction off the deuteroncross section for γn → ηn from analyses with very different systematics:(1) η in coincidence with recoil neutrons(2) difference of inclusive data and η in coincidence with recoil protons

1

10

500 1000 1500 2000 2500

σ[µb

]

Eγ[MeV]

σ(npη)

σ(pη)

σ(nη)

σ(npη)-σ(pη)

0

5

10

1000 1500 2000 2500

σ[µb

]

Eγ[MeV]

nη*3/2

pη, nη, MAID

0.5

1

1.5

1000 1500 2000 2500

σn/σp

σ n/σ p

B. Krusche, Giessen, November 2009

Page 26: Photoproduction of mesons off nuclei - unibas.ch...η-production data from the proton: larger ηN-scattering lengths 1991 - 2002: T. Ueda, C. Wilkin, S.A. Rakityanski and others: suggestions

comparison of free and quasi-free cross sections

quasi-free total cross sections‘corrected’ for Fermi smearing(correction factors from foldingETA-MAID model with momentumdistribution of bound nucleons)

result:in S11(1535) peak below 0.9 GeV perfectagreement between free and quasi-freeproton data and quasi-free neutron datascaled by 2/3

Fit parameters for S 11 Breit-Wigner:

proton:W =1538 MeV, Γ=157 MeV, Ap

1/2=103

neutron:W =1538 MeV, Γ=148 MeV, An

1/2=85

narrow structure around 1 GeV inneutron/proton ratio,width is only upper bound

0

5

10

15

1000 1500 2000 2500

σ[µb

]

Eγ[MeV]

ηp, free protonηp

ηn ηnp-ηpσ(ηn)/(2/3)

0.5

1

1.5

2

1000 1500 2000 2500Eγ[MeV]

σ n/σ p

B. Krusche, Giessen, November 2009

Page 27: Photoproduction of mesons off nuclei - unibas.ch...η-production data from the proton: larger ηN-scattering lengths 1991 - 2002: T. Ueda, C. Wilkin, S.A. Rakityanski and others: suggestions

quasi-free angular distributions

700 MeV

750 MeV 800 MeV 850 MeV

900 MeV

950 MeV 1000 MeV

1100 MeV 1200 MeV 1300 MeV

1400 MeV 1500 MeV 1600 MeV 1700 MeV 1800 MeV

1900 MeV 2000 MeV 2100 MeV 2200 MeV 2400 MeV

cos(Θη)cos(Θ*

ηp, qf ηn, qf ηp, free folded

0

0.5

1

0

0.2

0.4

0.6

0

0.2

0.4

dσ/d

Ω[µ

b/sr

]

0

0.2

0.4

-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 -0.5 0 0.5 1

cos(Θ) =- 1.0 - -0.6

cos(Θ) =- 0.6 - -0.2

cos(Θ) =- 0.2 - +0.2

cos(Θ) =+ 0.2 - +0.6

cos(Θ) =+ 0.6 - +1.0

Eγ[MeV]

0

1

0

1

0

1

dσ/d

Ω[µ

b/sr

]

0

1

0

1

1000 1500 2000 2500

I. Jaegle et al., Phys. Rev. Lett. 100 (2008) 252002

B. Krusche, Giessen, November 2009

Page 28: Photoproduction of mesons off nuclei - unibas.ch...η-production data from the proton: larger ηN-scattering lengths 1991 - 2002: T. Ueda, C. Wilkin, S.A. Rakityanski and others: suggestions

fit of angular distributionsfit with:

dσdΩ = q⋆

k⋆× Σ AiPi(cos(Θ⋆))

result:

all coefficients similar for protonand neutron above 1.25 GeV

Ao coefficient:dominance of S 11 resonances,for neutron small shoulderaround 1 GeV

A1 coefficient:interference S 11, P11?

A2 coefficient:interference S 11 - D13 resonance

Ao A1

A2 A3

Eγ[GeV]

0

1

2

31.5 1.7 1.9 2.1 W[GeV]

-0.5

-0.25

0

0.25

1.5 1.7 1.9 2.1 W[GeV]

-0.5

0

0.5

1 1.5 2 2.5

Ai [

µb/s

r]

-0.5

-0.25

0

0.25

1 1.5 2 2.5

10-1

1

1 2

• quasifree neutron • quasifree proton — free proton (Ff)

— q.f. neutron (Maid) — q.f. neutron (Shklyar et al.)

B. Krusche, Giessen, November 2009

Page 29: Photoproduction of mesons off nuclei - unibas.ch...η-production data from the proton: larger ηN-scattering lengths 1991 - 2002: T. Ueda, C. Wilkin, S.A. Rakityanski and others: suggestions

Bonn-Gatchina model analysis

basis: coupled channel isobar analysis with background ter ms

0

2

4

6

8

10

12

1500 1600 1700 1800 1900 2000 2100

M(γn) [MeV]

σtot [µb]

CB-ELSA

0

2

4

6

8

10

12

1500 1600 1700 1800 1900 2000 2100

M(γn) [MeV]

σtot [µb]

CB-ELSA

0

2

4

6

8

10

12

1500 1600 1700 1800 1900 2000 2100

M(γn) [MeV]

σtot [µb]

CB-ELSA

different scenarios to reproduce ’bump’ structure:

left: interference in S 11-sector: adjusting phases etc.

middle: introduction of conventional (broad) P 11 resonance

right: introduction of very narrow P 11 resonanceA. Anisovich et al., EPJA 41 (2009) 13

B. Krusche, Giessen, November 2009

Page 30: Photoproduction of mesons off nuclei - unibas.ch...η-production data from the proton: larger ηN-scattering lengths 1991 - 2002: T. Ueda, C. Wilkin, S.A. Rakityanski and others: suggestions

s-wave coupled channel models-wave coupled channel model with dynamical generation of S 11(1535) pole

free cross sections quasi-free cross sections

700 800 900 1000 1100 1200Eγ [MeV]

0

5

10

15

20

σ [µ

b]

KΣKΛ

700 800 900 1000 1100 1200Eγ [MeV]

0

5

10

15

20

σ [µ

b]

s1/2

=1535 MeVs

1/2=m

N+mη

cross section ratio

700 12000

1

2

700 800 900 1000 1100 1200Eγ [MeV]

0

0.5

1

1.5

2

σ n / σ p

structure in σn/σp due to K Λ, KΣ threshold effects(intermediate strangeness states in loop-diagrams)

M. Doring. K. Nakayama, nucl-th:0909.3538v1

B. Krusche, Giessen, November 2009

Page 31: Photoproduction of mesons off nuclei - unibas.ch...η-production data from the proton: larger ηN-scattering lengths 1991 - 2002: T. Ueda, C. Wilkin, S.A. Rakityanski and others: suggestions

‘de-folding’ of Fermi smearing

for events with neutron in TAPS(cos (Θ⋆

η) < -0.1)neutron energy from time-of-flight

comparsion: W from photonenergy (Fermi smeared) -W from nucleon - meson4-vectors (resolution smeared)

de-folded proton cross sectionsimilar to free proton,de-folded neutron cross sectionshows structure around 1.7 GeV:

position: W =1683 MeVwidth: Γ=60±10 MeV(resolution dominated)

WB[MeV] WR[MeV]

0

2

4

1500 1600 1700 1800

dσ/d

Ωac

c[µb/

sr]

ηpηn

0

2

4

1500 1600 1700 1800

I. Jaegle et al.,Phys. Rev. Lett. 100 (2008) 252002

B. Krusche, Giessen, November 2009

Page 32: Photoproduction of mesons off nuclei - unibas.ch...η-production data from the proton: larger ηN-scattering lengths 1991 - 2002: T. Ueda, C. Wilkin, S.A. Rakityanski and others: suggestions

new preliminary results from MAMI C: reaction identificatio n

raw invariant mass cut on co-planarity

co-planarity

B. Krusche, Giessen, November 2009

Page 33: Photoproduction of mesons off nuclei - unibas.ch...η-production data from the proton: larger ηN-scattering lengths 1991 - 2002: T. Ueda, C. Wilkin, S.A. Rakityanski and others: suggestions

preliminary excitation functions

W = f(Eγ), 130 < ∆Φ < 220 W = f(n, η), 130 < ∆Φ < 220

W = f(Eγ), 170 < ∆Φ < 190 W = f(n, η), 170 < ∆Φ < 190

B. Krusche, Giessen, November 2009

Page 34: Photoproduction of mesons off nuclei - unibas.ch...η-production data from the proton: larger ηN-scattering lengths 1991 - 2002: T. Ueda, C. Wilkin, S.A. Rakityanski and others: suggestions

structure also seen for 3He target nuclei

nucleons bound in deuteron nucleons bound in 3He

0

0.5

1

1500 1600 1700 1800 1900

γ3He→(np)pη

γ3He→(pp)nη

W[MeV]σ[

a.u.

]

B. Krusche, Giessen, November 2009

Page 35: Photoproduction of mesons off nuclei - unibas.ch...η-production data from the proton: larger ηN-scattering lengths 1991 - 2002: T. Ueda, C. Wilkin, S.A. Rakityanski and others: suggestions

Summary

narrow structure in excitation function of γn → nη:

GRAAL: W ≈ 1680 MeV, Γ <30 MeV

Tohoku-LNS: W ≈ 1666 MeV, Γ <40 MeV

ELSA: W ≈ 1685 MeV, Γ <60 MeV

MAMI-C: W ≈ 1675 MeV, Γ <40 MeV

so far no information about quantum numbersof possible resonanceor whatever nature of the structure

B. Krusche, Giessen, November 2009

Page 36: Photoproduction of mesons off nuclei - unibas.ch...η-production data from the proton: larger ηN-scattering lengths 1991 - 2002: T. Ueda, C. Wilkin, S.A. Rakityanski and others: suggestions

coherent η-photoproduction: search for light - η-mesic nuclei

η-photoproduction dominated by excitation of S 11(1535):

γ(E1) + N → S11 → N + η

Jz: -1 +1/2 -1/2 -1/2 0 → spin-flip transition

isospin structure: AIS1/2/A

p1/2 ≈0.09 → dominantly isovector

expectation for light nuclei:

1) 4He: J=0, I=0, isoscalar, non spin-flip → very small signal(not seen, only upper bounds, V. Hejny et al.)

2) 2H: J=1, I=0, isoscalar, spin-flip → small signal(seen, almost in agreement with expectations)

3) 3He: J=1/2, I=1/2, isovector, spin-flip → ’large’ signal

B. Krusche, Giessen, November 2009

Page 37: Photoproduction of mesons off nuclei - unibas.ch...η-production data from the proton: larger ηN-scattering lengths 1991 - 2002: T. Ueda, C. Wilkin, S.A. Rakityanski and others: suggestions

η-photoproduction from 3He - threshold behavior

photon energy / MeV

σ tot /

µba

rn

coherent threshold

quasifree threshold

quasifree cross sectioncoherent cross section

10-2

10-1

1

10

600 620 640 660 680 700 720 740

0

20

-1 -0.5 0 0.5 1cos Θη

*

dσ/

/ nb

/sr

600 - 625 MeV

expectedangular dependence

cos Θη*

625 - 745 MeV

expectedangular dependence

-25

0

25

50

75

100

-1 -0.5 0 0.5 1

M. Pfeiffer et al., PRL 92 (2005) 252001

evidence for strong finalstate interaction of the η-meson

⇐= threshold enhancement ofcoherent part

istropic angular distributionof coherent part at threshold =⇒

B. Krusche, Giessen, November 2009

Page 38: Photoproduction of mesons off nuclei - unibas.ch...η-production data from the proton: larger ηN-scattering lengths 1991 - 2002: T. Ueda, C. Wilkin, S.A. Rakityanski and others: suggestions

search for η-mesic nuclei

G. Sokol et al., search in: γ +12 C → N +η (A − 1) → N + π+ + n + (A − 2)

similar principle for photoproduction from 3He:

0

100

200

300

400

500

600

700

800

250 500 750

50

100

150

200

250

600 800

170o-180o

150o-170o170o-180o

150o-170o

E[MeV]E[MeV]

170o-180o

(150o-170o

subtracted)

-5

0

5

10

15

20

25

30

35

600 800E[MeV]

→ search for back-to-backπo - p pairs

excess of πo-pback-to-backemission at theη-threshold(3.5σ)

B. Krusche, Giessen, November 2009

Page 39: Photoproduction of mesons off nuclei - unibas.ch...η-production data from the proton: larger ηN-scattering lengths 1991 - 2002: T. Ueda, C. Wilkin, S.A. Rakityanski and others: suggestions

new 3He experiment - improved statistics

reaction identification:invariant mass analyses for η → 2γ and η → 3πo → 6γ

missing energy analysis for coherent kinematics:

-10 0 100

50

100

< 600 MeVγ592 < E

-10 0 100

50

100 < 608 MeVγ600 < E

-10 0 10 200

50

100

150 < 617 MeVγ609 < E

-60 -40 -20 0 200

200

400

< 697 MeVγ689 < E

Missing Energy[MeV]

Cou

nt(a

.u)

-20 -10 0 10 200

20

40

< 600 MeVγ592 < E

-10 0 10

0

20

40

< 608 MeVγ600 < E

-20 -10 0 10 20

0

20

40 < 617 MeVγ609 < E

-50 00

50

100 < 697 MeVγ689 < E

Missing Energy[MeV]

Cou

nt(a

.u)

η → 2γ η → 6γ

PhD thesis F. Pheron

B. Krusche, Giessen, November 2009

Page 40: Photoproduction of mesons off nuclei - unibas.ch...η-production data from the proton: larger ηN-scattering lengths 1991 - 2002: T. Ueda, C. Wilkin, S.A. Rakityanski and others: suggestions

new 3He experiment - coherent η-production

[MeV]γE600 650 700

bµ/ ησ

0

0.1

0.2

0.3

γ2→ηγ6→0π3→η

Coh. Thres.

Qf. Thres.

-1 -0.5 0 0.5 10

0.005

0.01

0.015

0.02 = 602.0 MeVγE

-1 -0.5 0 0.5 10

0.005

0.01

0.015 = 606.3 MeVγE

-1 -0.5 0 0.5 10

0.005

0.01

0.015 = 610.5 MeVγE

-1 -0.5 0 0.5 10

0.02

0.04

= 686.6 MeVγE

)*ηΘ cos(

b/sr

]µ [

Ω/dσd

preliminary cross sections:very steep rise of total cross section at threshold confirmed

rather flat angular distributions at threshold

B. Krusche, Giessen, November 2009

Page 41: Photoproduction of mesons off nuclei - unibas.ch...η-production data from the proton: larger ηN-scattering lengths 1991 - 2002: T. Ueda, C. Wilkin, S.A. Rakityanski and others: suggestions

new 3He experiment - coherent η-production

[MeV]γE600 650 700

bµ/ ησ

0

0.1

0.2

0.3

γ2→ηM.Pfeiffer et al[1]

γ6→0π3→η

Coh. Thres.

Qf. Thres.

-1 -0.5 0 0.5 10

0.005

0.01

0.015

0.02 = 602.0 MeVγE

-1 -0.5 0 0.5 10

0.005

0.01

0.015 = 606.3 MeVγE

-1 -0.5 0 0.5 10

0.005

0.01

0.015 = 610.5 MeVγE

-1 -0.5 0 0.5 10

0.02

0.04

= 686.6 MeVγE

)*ηΘ cos(

b/sr

]µ [

Ω/dσd

preliminary cross sections:very steep rise of total cross section at threshold confirmed

rather flat angular distributions at threshold

B. Krusche, Giessen, November 2009

Page 42: Photoproduction of mesons off nuclei - unibas.ch...η-production data from the proton: larger ηN-scattering lengths 1991 - 2002: T. Ueda, C. Wilkin, S.A. Rakityanski and others: suggestions

new 3He experiment

πo-p back-to-back pairs:peak structure at coherent threshold also confirmedwith much better statistics

/MeV γ E400 500 600 700 800

yie

ld/ a

.u.

0

100

200

°-180° = 170pπ

ψ

°-170° = 150pπ

ψ

/MeV γ E400 500 600 700 800

yie

ld/ a

.u.

0

5

10

Coh. Thres.η

/MeV γ E400 500 600 700 800

yie

ld/ a

.u.

0

100

200 °-180° = 165pπ

ψ

°-165° = 150pπ

ψ

/MeV γ E400 500 600 700 800

yie

ld/ a

.u.

0

5

10

Coh. Thres.η

Summary: new data confirme previous results with much betterstatistics - further analysis under way

B. Krusche, Giessen, November 2009

Page 43: Photoproduction of mesons off nuclei - unibas.ch...η-production data from the proton: larger ηN-scattering lengths 1991 - 2002: T. Ueda, C. Wilkin, S.A. Rakityanski and others: suggestions

the reaction γp → πoηp - πoη-pairs off the protonIdentification

Total cross section

Invariant mass distributions

dominant final states:−− ∆(1232)η, −.− N(1535)π, ... pao(980)

I. Horn et al. (ELSA)

←−

B. Krusche, Giessen, November 2009

Page 44: Photoproduction of mesons off nuclei - unibas.ch...η-production data from the proton: larger ηN-scattering lengths 1991 - 2002: T. Ueda, C. Wilkin, S.A. Rakityanski and others: suggestions

threshold region of πoη dominated by D 33(1700)V. Kashevarov et al. (MAMI)

⇐ best model fitsfor P 33 or D35 isobars

⇐ model fitsfor D 33 isobar

analysis of threshold region in terms of isobar model(Fix et al.) indicates strong dominance of D 33(1700)

extracted amplitudes allow specific predictions forcoherent production of πoη-pairs of light nuclei (Fix et al.)

B. Krusche, Giessen, November 2009

Page 45: Photoproduction of mesons off nuclei - unibas.ch...η-production data from the proton: larger ηN-scattering lengths 1991 - 2002: T. Ueda, C. Wilkin, S.A. Rakityanski and others: suggestions

coherent photoproduction of πoη-pairs: d(γ, ηπo)d

Proton / Deuteron5 10

Ene

rgy

depo

site

d [M

eV]

200

400

600

Neutron TOF [ns]5 10

200

400

600

[MeV]γγ0 200 400 600

Cou

nts

[a.u

.]

0

50

100

150 2.5× = 12.8 MeVoπσ

= 31.1 MeVησ

m [MeV]∆−50 0 50

Cou

nts

[a.u

.]

0

20

40

= 15 MeVm∆σ

time-of-flight versus energyfor deuteron identification

invariant mass (two-photon)for reaction identificationand missing mass(deuteron treated as missingparticle) for verificationof coherent kinematics

B. Krusche, Giessen, November 2009

Page 46: Photoproduction of mesons off nuclei - unibas.ch...η-production data from the proton: larger ηN-scattering lengths 1991 - 2002: T. Ueda, C. Wilkin, S.A. Rakityanski and others: suggestions

d(γ, ηπo)d: total cross section, kinetic energy distributions

total cross section kinetic energy

[MeV]γE1000 1500 2000 2500

b]µ [σ

0

0.05

0.1

0.15 A. Fix

[MeV]kin.cmT

0 50 100 150 200

[nb

/ MeV

]ki

n.cm

/dT

σd

0

1

2 oπη

= 900 − 1100 MeVγEW = 2628 − 2767 MeV

[MeV]kin.cmT

0 200 400

[nb

/ MeV

]ki

n.cm

/dT

σd

0

0.5

1

1.5

)ηps T()oπps T(

)η* T(∆)oπ* T(∆

= 1100 − 1600 MeVγEW = 2767 − 3088 MeV

[MeV]kin.cmT

0 200 400 600 [n

b / M

eV]

kin.

cm/d

Tσd

0

0.2

0.4

0.6

0.8 = 1600 − 2000 MeVγEW = 3088 − 3322 MeV

total cross section in reasonable agreement with predictio ns

T distributions support dominant ∆⋆ → ∆(1232)η → Nηπo contribution:

T (πo) peaks around 100 MeV ( ∆(1232) → Nπ), T (η) rises with E γ

B. Krusche, Giessen, November 2009

Page 47: Photoproduction of mesons off nuclei - unibas.ch...η-production data from the proton: larger ηN-scattering lengths 1991 - 2002: T. Ueda, C. Wilkin, S.A. Rakityanski and others: suggestions

very preliminary: 3He(γ, ηπo)3He

identification via missing mass preliminary total cross section

0

0.5

1

0 100 200

data

πoη 3He, simu

πoη NX, simu

sum simulations

Eγ=765 - 1400 MeV

∆m[MeV]

coun

ts[a

.u.]

[MeV]γE800 1000 1200

b]µ [σ

0

0.05

0.1

0.15

0.2He − A23ηoπ→He3γ

d − CBELSA/TAPSηoπ→dγ He − A. Fix3ηoπ→He3γ

d − A. Fixηoπ→dγ

qualitative agreement with isotope dependence from Fix’ mo del

B. Krusche, Giessen, November 2009

Page 48: Photoproduction of mesons off nuclei - unibas.ch...η-production data from the proton: larger ηN-scattering lengths 1991 - 2002: T. Ueda, C. Wilkin, S.A. Rakityanski and others: suggestions

quasi-free photoproduction of πoη pairs...preliminary results

[MeV]γE800 1000 1200 1400

b]µ [σ

0

2

4

6 p), I. Horn et al., CBELSAηoπ(pσFree p folded with d Fermi motion

He Fermi motion3Free p folded with , CBELSA−TAPSp)ηoπ(dσ

p),A2ηoπ(dσp)/2ηoπ(He3σ

[MeV]γE1000 1500 2000 2500

b]µ [σ

0

2

4

6 p), I. Horn et al., CBELSAηoπ(pσFree p folded with d Fermi motion

He Fermi motion3Free p folded with , CBELSA−TAPSp)ηoπ(dσ

p),A2ηoπ(dσp)/2ηoπ(He3σ

[MeV]γE800 1000 1200 1400

b]µ [σ

0

2

4

6

8 pn)ηoπ(dσ

p)ηoπ(dσ

n)ηoπ(dσ

p)ηoπ(σpn) − ηoπ(dσp)ηoπ(σpn) − ηoπ(He3σ

pn)/(3/2)ηoπ(He3σ

/2p)ηoπ(He3σ

n)ηoπ(He3σ

[MeV]γE1000 1500 2000 2500

b]µ [σ0

2

4

6

8 pn)ηoπ(dσ

p)ηoπ(dσ

n)ηoπ(dσ

p)ηoπ(σpn) − ηoπ(dσp)ηoπ(σpn) − ηoπ(He3σ

pn)/(3/2)ηoπ(He3σ

/2p)ηoπ(He3σ

n)ηoπ(He3σ

deuteron results fromMAMI and ELSA consistent

quasi-free proton andneutron results fromdeuteron and 3Heconsistent

quasi-free protoncross section roughly50 % smaller than freeproton cross section.Not yet understood. FSI ?

quasi-free proton andneutron cross sectionsvery similar as expected

Page 49: Photoproduction of mesons off nuclei - unibas.ch...η-production data from the proton: larger ηN-scattering lengths 1991 - 2002: T. Ueda, C. Wilkin, S.A. Rakityanski and others: suggestions

results for many more channels, e.g. quasi-free η′

0

0.5

1

1.5

1.25 1.5 1.75 2 2.25 2.5

γd→(n)pη,

γd→(p)nη,

γd→(p)(n)η,

γd→dη, x 100

Eγ[GeV]

σ[µb

]

W[GeV] 1.9 2.0 2.1 2.2 2.3

Ao

A1 A2 A3

Eγ[GeV]

0

0.1

0.2

0.3 γp→pη,

γd→(n)pη,

Ai [

µb/s

r]

0

0.1

-0.1

0

0.1

-0.1

0

0.1

0

0.1

0.2

1.5 2 2.5

γd→(p)nη,

0

0.1

1.5 2 2.5

-0.1

0

0.1

1.5 2 2.5

-0.1

0

0.1

1.5 2 2.5

⇐ total cross sections,

model calculations

K. Nakayama et al.

Legendre coefficients

of angular distributions ⇓

very good agreementbetween quasi-freeand free protoncross section

angular distributionsdominated by s-waves

reasonable agreementwith model calculations

broad structure inneutron cross sectionbetween2.0 GeV< W < 2.5 GeVwhich is lesspronounced for proton

Page 50: Photoproduction of mesons off nuclei - unibas.ch...η-production data from the proton: larger ηN-scattering lengths 1991 - 2002: T. Ueda, C. Wilkin, S.A. Rakityanski and others: suggestions

...and single πo quasi-free and coherent...

total cross sections

[MeV]γE400 600 800 1000 1200

b]

µ [σ

10

210np)0π(σ

n)0π(σ p)0π(σ

n) Folded0π(σMAID

p) Folded0π(σMAID

[MeV]γE500 600 700 800 900 1000 1100 1200 1300 1400

b]

µ [σ

0

10

20

30

40

50

60

n)0π(σ p)0π(σ d)0π(σ

quasi-free off proton and neutron: contriutions from diffe rent N ⋆-resonancs

coherent off deuteron:only ∆-resonances, N ⋆ forbidden due to isospin conservation

B. Krusche, Giessen, November 2009

Page 51: Photoproduction of mesons off nuclei - unibas.ch...η-production data from the proton: larger ηN-scattering lengths 1991 - 2002: T. Ueda, C. Wilkin, S.A. Rakityanski and others: suggestions

... double πo quasi-free and coherent...

total cross sections

[MeV]γE0 200 400 600 800 1000 1200 1400

b)

µ (σ

0

2

4

6

8

10

NeutronProton

cross section ratio

[MeV]γE500 1000

pσ / nσ

0

0.5

1

p)oπoπ(He3σn) / oπoπ(He3σ×2p)oπoπ(He3σp)) / oπoπ(He3σppn) ­ oπoπ(

He3σ(×2

p)oπoπ(dσn) / oπoπ(dσ

coherent contribution

[MeV]γE500 1000

b]µ [σ0

0.02

0.04

0.06

0.08

A2

CBELSA/TAPS

A. Fix

quasi-free off proton and neutron:some difference in resonance bump structure

coherent off deuteron:only N ⋆-resonances, ∆-resonances forbiddendue to isospin conservation

Page 52: Photoproduction of mesons off nuclei - unibas.ch...η-production data from the proton: larger ηN-scattering lengths 1991 - 2002: T. Ueda, C. Wilkin, S.A. Rakityanski and others: suggestions

polarization observables - example: beam-helicity for 2 π

beam-helicity asymmetry (circularly polarized beam, unpo larized target)

p

n

π+

πo

Φγ z

z’

y

I⊙(Φ) ≡ dσ+−dσ−

dσ++dσ−

γp → pπ+π− γp → nπoπ+ γp → pπoπo

575 - 605

605 - 635

635 - 665

665 - 695

700 - 730

745 - 815

Φ[o]

-10

0

10

-10

0

10

-10

0

10

0 100 200 300 100 200 300

I⊙[%

]

520 - 570

570 - 620

620 - 670

670 - 720

720 - 770

770 - 820

Φ[o]

-20

0

20

-20

0

20

-20

0

20

0 100 200 300 100 200 300

I⊙[%

]

560 - 620

620 - 680

680 - 745

745 - 810

Φ[o]

-10

0

10

-10

0

10

0 100 200 300 100 200 300

I⊙[%

]proton results so far not understood!

Page 53: Photoproduction of mesons off nuclei - unibas.ch...η-production data from the proton: larger ηN-scattering lengths 1991 - 2002: T. Ueda, C. Wilkin, S.A. Rakityanski and others: suggestions

...free and quasi-free (off deuteron) proton results...

preliminary quasi-free data from protons bound in deuteron alreadyin good agreement with free proton data

]o [Φ−150 −100 −50 0 50 100 150

[%]

° I

−15

−10

−5

0

5

10

15700 − 800 MeV

Free pQuasiree pFree p FermiFolded

­20

0

20

Free P n+π 0π p ­> γ

Fermi folded P

[770 ­ 820]∈ γE

­100 0 100

­20

0

20

]o[Φ

[%]

° I

γp → pπoπo γp → nπoπ+

B. Krusche, Giessen, November 2009

Page 54: Photoproduction of mesons off nuclei - unibas.ch...η-production data from the proton: larger ηN-scattering lengths 1991 - 2002: T. Ueda, C. Wilkin, S.A. Rakityanski and others: suggestions

...quasi-free proton and quasi-free neutron...

­100 0 100

­10

0

10

[720 ­ 770]∈ γE ProtonNeutron

­100 0 100

­10

0

10

[770 ­ 820]∈ γE ProtonNeutron

­100 0 100

­10

0

10

[820 ­ 900]∈ γE ProtonNeutron

­100 0 100

­10

0

10

[900 ­ 1000]∈ γE ProtonNeutron

­100 0 100

­10

0

10

[1000 ­ 1080]∈ γE ProtonNeutron

­100 0 100

­10

0

10

[1080 ­ 1160]∈ γE ProtonNeutron

­100 0 100

­10

0

10

[1160 ­ 1220]∈ γE ProtonNeutron

­100 0 100

­10

0

10

[1220 ­ 1280]∈ γE ProtonNeutron

­100 0 100

­10

0

10

[1280 ­ 1340]∈ γE ProtonNeutron

­100 0 100­100 0 100­100 0 100

­10

0

10

­10

0

10

­10

0

10

]o[Φ

[%]

° I

­20

0

20

n+π 0π p ­> γ p­π 0π n ­> γ

[720 ­ 770]∈ γE

­20

0

20

n+π 0π p ­> γ p­π 0π n ­> γ

[770 ­ 820]∈ γE

­20

0

20

n+π 0π p ­> γ p­π 0π n ­> γ

[820 ­ 900]∈ γE

­100 0 100

­20

0

20

n+π 0π p ­> γ p­π 0π n ­> γ

[900 ­ 1100]∈ γE

­100 0 100

­20

0

20

n+π 0π p ­> γ p­π 0π n ­> γ

[1100 ­ 1200]∈ γE

­100 0 100

­20

0

20

n+π 0π p ­> γ p­π 0π n ­> γ

[1200 ­ 1400]∈ γE

­100 0 100­100 0 100­100 0 100

­20

0

20

­20

0

20

]o[Φ

[%]

° I

almost identical results forγp → pπoπo and γn → nπoπo

less similarities forγp → nπoπ+ and γn → pπoπ−

B. Krusche, Giessen, November 2009

Page 55: Photoproduction of mesons off nuclei - unibas.ch...η-production data from the proton: larger ηN-scattering lengths 1991 - 2002: T. Ueda, C. Wilkin, S.A. Rakityanski and others: suggestions

ConclusionsSystematic investigation of meson production

off 2H and 3He:

η-photoproduction off deuteron:large difference for resonance contributions to p(γ, η)p and n(γ, η)n

narrow structure in excitation function off neutron

η-photoproduction off 3He:evidence for (quasi)-bound η-nucleus state

other channels:iso-spin dependence of the elm. nucleon excitation

outlook:upcoming program to measure quasi-free(double) polarization observables

I. JaegleI. KeshelashviliT. RostomyanF. PheronY. MaghrebiD. WerthmullerTh. ChallandeR. TrojerM. DieterleM. OberleL. Witthauer

B. Krusche, Giessen, November 2009