Helicity dependent meson photoproduction on 3 He in the -resonance - - PowerPoint PPT Presentation

Helicity dependent meson photoproduction on

3He in the Δ-resonance region

Paolo Pedroni

INFN-Sezione di Pavia, Italy For the CBMAMI and A2 collaborations

Physics motivations Results Outlook

SUMMARY

for 150 < Eγ < < 500 MeV (Mainz)

⎪ ⎩ ⎪ ⎨ ⎧ → π γ N ppn X e H r r 3

• Exp. check of the GDH sum rule

Determination of the N* properties

⎩ ⎨ ⎧ First data First data

nucleus-spin photon-spin nucleus-spin photon-spin

σa σp

2 2 2 2

4 ( ( k M e S dv v E E I

thr

a p GDH

π = ) σ − ) σ = ∫

∞ ν γ γ

Anomalous magnetic moment

Experimental verification of the GDH sum rule

⎩ ⎨ ⎧ = (nuclei) threshold tegration photodisin (nucleon) threshold production π ν thr

Proposed in 1966 by Gerasimov-Drell-Hearn Prediction on the absorption of circularly polarized photons by longitudinally polarized nucleons/nuclei

spin

GDH sum rule: Fundamental check of our knowledge of the γN interaction

The only “weak” hypothesis is the assumption that Compton scattering γN → γ → γ’ N’ becomes spin independent when ν → ν → ∞ A violation of this assumption can not be easily explained

Important comparison for photoreaction models Helicity dependence of partial channels (pion photoproduction) is an essential tool for the study of the baryon resonances (interference terms between different electromagnetic multipoles) Valid for any system with k ≠ 0 ≠ 0 (2H, 3He) . “Link” between nuclear and nucleon degrees of freedom

D13(1520)

X p → r r γ

F15(1680) F35(1905)

Δ(1232)

200 MeV

unpolarized c.s.

Experimental status IGDH

GDH (p) = 211 ±

(p) = 211 ± 5 ± ± 12 2 µb

MAMI-Mainz ELSA-Bonn

GDH sum rule: predictions

Nρ : Zhao et al., PRC 65, 032201 (03) Nππ ππ : Fix, Arenhoevel EPJA 25, 114 (2005) KΛ(Σ) : Sumowidagdo et al., PRC 65,0321002 (02) Nπ : SAID-FA07K [MAID07] Nη : MAID

Proton IGDH (µb) Neutron IGDH (µb) γ γ p → Nπ 172 172 [164] [164] γ γ p → → Nππ ππ 94 94 γ γ p → Nη

• 8

γ γ p → → KΛ Λ (Σ) -4 γ γ p → Nρ(ω) 0 Regge contrib. -14 (Eγ > 2 Gev) γ γ n → Nπ 147 147 [131] [131] γ γ n → Nππ ππ 82 82 γ γ n → Nη

• 6

γ γ n → K Λ(Σ) 2 γ γ n → Nρ(ω) 2 Regge contrib. 20 (Eγ > 2 Gev) TOTAL 239 [231] TOTAL 244 [231] GDH 205 GDH 233

Regge : Bianchi-Thomas , PLB 450,439(99)

GDH sum rule on the neutron

No Free neutron target available Model dependent results from nuclear targets Our experimental goal: to have a “small” and “realiable” model dependence Two different (and complementary) targets =) deuteron (data from Mainz –Bonn) =) 3He (no data up to now) Measurement of partial channels like

NNN e H NN d π γ π γ → → r r r r

3

GDH sum rule on the neutron

2H:

µ ∼ µp + µn ⇒ ΙGDH

Deut ∼ 0.93•ΙGDH neutron+0.93•ΙGDH proton

3He: µ ∼ µn ⇒

(S-state with ∼ 90% prob.)

ΙGDH

He3 ∼ 0.87•ΙGDH neutron-0.026•ΙGDH proton

3He better suited to measure ΙGDH

neutron (inclusive method)

2H better suited to measure partial reaction channels

n p PWIA approach Eγ

γ > mπ

n p p

Status of the deuteron results

X d → r r γ

AFS model from Ahrenhoevel, Fix and Schwamb

Facility

tagged photon facility of the MAMI accelerator in Mainz

Beam

circularly polarised photons produced by bremsstrahlung of longitudinally polarised electrons Eelectron = 525 MeV 150 < Eγ < 500 MeV

Target Polarised 3He gas First feasibility test Detector the large acceptance (93%) Crystal Ball (CB) photon spectrometer in combination with the TAPS detector

TAPS CRYSTAL BALL PID MWPC

3He Experimental set-up

3He polarisation

MEOP: Metastability Exchange Optical Pumping

Ground state Metastable state

11S0 23S1 23P0

1083 nm σ+ transition

B = 0 B ≠ 0 mF = +½ mF = -½ mF = +½ mF = -½

Excited state

(F = ½) (F = ½)

Polarisation transfer to the 3He ground state by atomic collisions

( ) ( ) ( ) ( )

1 3 1 3 3 1 3 1 3 3

1 2 1 2 S e H S He S He S e H r r + → +

RF discharge Laser J.Krimmer et al., NIMA 648, 35 (2011)

Polarised

3He gas target

Cylindrical cell (gas polarised via MEOP) Length: 20 cm diameter: 6 cm Made of quartz glass (thickness: 2 mm) Titanium entrance and exit windows (50 µm) provide the necessary gas tightness (4 bar) give long relaxation time (∼20 hrs) of the gas polarisation

3He polarisation measurements carried out via NMR

technique; field provided by Helmholtz coils γ-beam Vacuum chamber Helmholtz coils solenoid in collaboration with PI, Mainz

3He gas

Ti windows All charged particle events (P-A) difference

Natoms ∼ 1021/cm2 ∼102 times less than in a solid/liquid target

Charged Particle Z-Vertex from MWPCs

X He →

3

γ

“Inclusive” analysis method

(NO partial channel separation) Only hadron counting and empty target subtraction Extrapolation from quasi-free pion production and MAID cross sections Extrapolation from Schwamb model for ppn Data from CB detector ONLY Overall Extrapolation is about 5 %

• f the measured yields

Good agreement with previous data

Unpolarised data

X He π γ →

3

200 400 600 800

π0 X

σ (µb)

200 400 600 800 200 300 400 500

Eγ (MeV) σ (µb)

π± X

σ (µb)

• A. Fix (nuclear model)

MAID (free nucleons)

• A. Fix model:

Input: Free γN→πN amplitudes from MAID Free Amplitudes embedded inside

3He wave function

• FSI taken into

account in an approximate way

• As expected , FSI

play a bigger role in the π0 case

X π X

±

π

First data First data

Differential unpolarised cross section

X He

3

π γ →

Eγ = 418 MeV Eγ = 400 MeV Eγ = 381 MeV Eγ = 361 MeV

θLAB π CB CB π0X

• A. Fix
• A. Fix

MAID MAID

First data First data

) ° ( θ

20 40 60 80 100 120 140 160 180

b) µ ( Ω /d σ d

20 40 60 80 100 120

diff_cross_sec_5

) ° ( θ

20 40 60 80 100 120 140 160 180

b) µ ( Ω /d σ d

20 40 60 80 100

diff_cross_sec_6

) ° ( θ

20 40 60 80 100 120 140 160 180

b) µ ( Ω /d σ d

20 40 60 80 100 120

diff_cross_sec_7

) ° ( θ

20 40 60 80 100 120 140 160 180

b) µ ( Ω /d σ d

10 20 30 40 50 60 70 80 90

diff_cross_sec_8

Differential unpolarised cross section

X He

±

→ π γ 3

Eγ = 418 MeV Eγ = 381 MeV Eγ = 400 MeV Eγ = 361 MeV

θLAB π CB CB π±X

• A. Fix
• A. Fix

MAID MAID

First data First data

ppn He →

3

γ

No model estimation available for this channel “Quasi-deuteron” approximation (γ 3He → pnps) evaluated from the Schwamb γd → pn model

Discrepancy between data and the quasi- deuteron model mostly due to 3-body absorption effects

First data First data

• 200

200 400 200 300 400 500

Eγ (MeV) Δσ (µb)

CB-Inclusive method

X e H → r r 3 γ

Extrapolation from quasi-free pion production and MAID cross sections Model: Prediction based on

MAID

p n

σ σ σ Δ ⋅ − Δ ⋅ = Δ 05 . 87 .

“Inclusive” analysis method

(NO partial channel separation) Extrapolation from quasi-free pion production and MAID cross sections Extrapolation from Schwamb model for ppn

) ( b

a p

µ σ σ σ − = Δ

Polarised data

First data First data

˝MAID Inspired˝ model

A Fix model: Nuclear structure contribution (FSI, …) less important than for the unpolarised case

X e H π γ → r r 3

05 . 87 .

p n MAID

σ σ σ Δ ⋅ − Δ ⋅ = Δ

100 200 300

π0 X

Δσ (µb)

• 200
• 100

100 200 300 400 500

Eγ (MeV) σ (µb)

π± X

Δσ (µb)

• A. Fix (nuclear model)

MAID (free nucleons)

X π X

±

π

) ( b

a p

µ σ σ σ − = Δ

First data First data

Differential polarised cross section

Eγ = 418 MeV Eγ = 400 MeV Eγ = 381 MeV Eγ = 361 MeV

θLAB π CB CB π0X

• A. Fix
• A. Fix

MAID MAID

X e H

3

π γ → r r

First data First data

) ° ( θ

20 40 60 80 100 120 140 160 180

b) µ ( Ω /d σ d

• 25
• 20
• 15
• 10
• 5

5 10 15

diff_cross_sec_5

) ° ( θ

20 40 60 80 100 120 140 160 180

b) µ ( Ω /d σ d

• 40
• 30
• 20
• 10

10

diff_cross_sec_6

) ° ( θ

20 40 60 80 100 120 140 160 180

b) µ ( Ω /d σ d

• 25
• 20
• 15
• 10
• 5

5 10 15 20

diff_cross_sec_7

) ° ( θ

20 40 60 80 100 120 140 160 180

b) µ ( Ω /d σ d

• 20
• 10

10 20

diff_cross_sec_8

Differential polarised cross section

Eγ = 418 MeV Eγ = 400 MeV Eγ = 381 MeV Eγ = 361 MeV

θLAB π CB CB π0X

• A. Fix
• A. Fix

MAID MAID

X e H

±

→π γ r r 3

First data First data

ppn e H → r r 3 γ

No model estimation available for this channel “Quasi-deuteron” approximation (γ 3He → pnps) evaluated from the Schwamb γd → pn model

• First data

First data

Very rough derivation of

Conclusions

This first test has proved the feasibility of the use of polarised 3He gas target to check the GDH sum rule on the neutron Unprecedented data and preliminary results for unpolarised and polarised photoabsorption cross section on

3He

Good agreement for the unpolarised inclusive cross section between the CB-MAMI data and the DAPHNE data Importance of the data in providing additional constraints for nuclear and subnuclear models Further measurements to improve statistics and to investigate a wider energy range are needed The game has just started ……

B.M.K.Nefkens, S.N.Prakhov, and A.Starostin University of California, Los Angeles, CA, USA J.Ahrens, H.J.Arends, D.Krambrich S.Scherer, S.Schumann, A.Thomas, L.Tiator, M.Unverzagt, M.Ostrick P. Bartolome Aguar Institut fur Kernphysik, University of Mainz, Germany A.Braghieri, S.Costanza P.Pedroni, INFN Sezione di Pavia Italy J.R.M.Annand, D.Glazier, K.Livingston, J.McGeorge, I.J.D.MacGregor, D.Protopopescu Department of Physics and Astronomy, University of Glasgow, Glasgow, UK E.Downie and W.Briscoe George Washington University, Washington, USA S.Cherepnya, L.Fil'kov, and V.Kashevarow Lebedev Physical Institute, Moscow, Russia

• I. Kashelashvili, B.Krusche , T.Rostomyan and F.Zehr, Institut fur Physik University of Basel, Basel, Ch

D.P.Watts School of Physics, University of Edinburgh, Edinburgh, UK V.Lisin, R.Kondratiev and A.Polonski Institute for Nuclear Research, Moscow, Russia R.Miskimen, A.Mushkarenkov University of Massachusetts, Ahmerst , USA D.Hornidge Mount Allison University, Sackville, Canada M.Manley Kent State University, Kent, USA

• M. Korolija and I. Supek Rudjer Boskovic Institute, Zagreb, Croatia
• D. Sober Catholic University, Washington DC

CB@MAMI collaboration

RISERVA

GDH sum rule on the deuteron

b 230 93 . ) ( µ ≈ ⇓ ⋅ + =

neutron GDH proton GDH neutron GDH Deuteron EXP

I I I I

Running GDH integral for the deuteron

200 400 500 1000 1500

Eγ (MeV) IGDH (µb)

GDH Mainz GDH Bonn AFS model

between [0.2-1.8 GeV] Effects neglected : FSI+other nuclear mechanisms PWA approach

452 9 24 μb

± ±

∫

γ

) σ − ) σ =

γ γ E MeV a p GDH

dv v E E I

200

( (

200 400 600 800 1000 1200 1400 200 300 400

Eγ (MeV) σ (µb)

MacCormick et al. Inclusive method Sum of partial channels

b)

• 250

250 500 200 300 400 500

Eγ (MeV) Δσ (µb)

CB-Inclusive method CB-Sum of partial

channels

Eγ (GeV) IGDH (µb) 0.14-0.20 * MAID03 SAID04

• 29
• 28

0.20-2.90 Measured (Mainz+Bonn) 254 5 12 > 2.90 (Regge approach) Simula et al. Bianchi-Thomas

• 13
• 14

Total 211 5 12 GDH sum rule 205

GDH sum rule on the proton

* Low energy theorems in the Nπ threshold

region (multipole analyses are quite reliable ...)

± ± ± ± ± ±

Susanna Costanza 32

Differential Differential unpolarised cross section unpolarised cross section ··

E = 341 E = 341 MeV MeV E = 319 MeV E = 319 MeV E = 297 MeV E = 297 MeV E = 275 MeV E = 275 MeV

CB CB π0X

• A. Fix
• A. Fix

MAID MAID

Photon polarization Target polarization Recoil nucleon Polarization Target and Recoil polarizations X Y Z(beam) X’ Y’ Z’ X’ X’ Z’ Z’ X Z X Z unpolarized linear Circular σ Σ

• T
• H

(-P) G F - E

• P
• Ox

(-T) Ox Cx

• Cz

Tx Lx Tz Lz (-Lz) (Tz) (Lx) (-Tx)

• Towards the “complete” Nπ experiment
• Linearly /circularly polarized photons
• Longitudinally / transversally polarized p,d targets
• Longitudinally polarized 3He target
• Recoil polarimeter
• MAMI-C Eγ

γ ≤ 1.5 GeV

• CB-TAPS-Inner tracker

In preparation First beam test performed

Polarised

3He gas target

Cylindrical cell (Polarised via MEOP) Length: 20 cm diameter: 6 cm Made of quartz glass (thickness: 2 mm) Titanium entrance and exit windows (50 µm) provide the necessary gas tightness (4 bar) give long relaxation time (∼20 hrs) of the gas polarisation

3He polarisation measurements carried out via NMR

technique; field provided by Helmholtz coils γ-beam Vacuum chamber Helmholtz coils