Recent Results from the CB@MAMI Programme at the Glasgow Tagged Photon

Spectrometer in Mainz

E. J. Downie

University of Glasgow

Introduction

Introduction to the CB@MAMI experimental series

Physics highlights of first round➔ Experiment to measure the MDM of (1232)

Glasgow Photon Tagger upgrade / MAMI-C

Anticipated physics of round II

The Need for CB@MAMI Experiments

Detailed information on nucleon & resonances test QCD

N resonances: short lifetime difficult to measure properties

Large Breit Wigner widths can't accurately determine spect.

Need more experimental information

Unique capabilities of CB@MAMI

Well understood probe: photon

Ability to accurately separate final states: good det. resolution

Sensitivity to small processes: 4 detection, large flux

Access to polarisation observables: pol. beam, target, recoil

The CB@MAMI Set-up – Electron BeamMAMI B

Up to 883 MeV e- beam

100 % duty factor

Current up to 100A

Polarised e-

Very stable beam

MAMI-A180 MeV

MAMI-B883 MeV

The CB@MAMI Set-up – Photon BeamGlasgow Photon Tagging Spectrometer

Pass e- beam through radiator

Magnetic spectrometer for e-

“Tags” bremsstrahlung

Photon beam enters expt.

Timing coincidence

Polarised e- 80%circ. pol.

Crystalline rad. lin. pol.

The CB@MAMI Detector Set-up

High rate 2MeV resolution tagged photon beam

Liquid H2/D2, 208Pb, 40Ca, 16O, 12C and other nuclear targets

Two EM calorimeters 4 spectrometer set-up

MWPC & PID for tracking and ID of charged particles

Ideal for high precision / low cross section measurements

GlasgowPhotonTaggingSpectrometer

The CB@MAMI Detector Set-up

High rate 2MeV resolution tagged photon beam

Liquid H2/D2, 208Pb, 40Ca, 16O, 12C and other nuclear targets

Two EM calorimeters 4 spectrometer set-up

MWPC & PID for tracking and ID of charged particles

Ideal for high precision / low cross section measurements

The CB@MAMI Detector Set-up – The PID

Pions

Protons

Built by Glasgow & Edinburgh

E (PID) / E (CB)

2mm scint. barrel

Identified p / +/- / e- / d

PID II by Edinburgh & Glasgow

The Magnetic Dipole Moment of the +(1232)

Nucleon structure very difficult to probe

Predictions of very sensitive to the baryon model used

EM properties of nucleon excited states largely unmeasured

Spin precession in a magnetic field wholly unsuitable

➔ Experimental test of theoretical models

The Magnetic Dipole Moment of the +(1232)

Tagged photon beam on liquid H2

+ lifetime 10-24s large Breit-Wigner width

Created + at upper end of B-W width

+ radiatively decays to another +

++

P

0

p(uud) +(uud)

The Magnetic Dipole Moment of the +(1232)

Comprehensive measurement required:

Measure two channels: p(,'0p), p(,'+n)

Measure several observables: ➔ Five-fold differential cross section

➔ Linearly polarised photon asymmetry➔ Circularly polarised photon asymmetry

p(,'0p) Experimentally difficult channel:

~50nb cross section

Backgrounds: p(,0p), 318b; p(,00p), 1.5b

The Magnetic Dipole Moment of the +(1232)

M(initial +)M(final +)M(sum)

Emiss. dataEmiss. sim.

M2miss.(

0p) dataM2

miss.(0p) sim.

The Magnetic Dipole Moment of the +(1232)

Total cross section of p(,'0p)

Expect improvement in statistical error: kinematic fitting

background subtraction improvement

This Work - preliminary Kotulla et al. P.R.L. 89 (2002)

The Magnetic Dipole Moment of the +(1232)

Differential of p(,'0p)

Improvement in acceptance calculation expected

Fully diff. being calculated by Mainz / Basel students

S. Schuman, Mainz Kotulla et al. P.R.L. 89 (2002)

The Magnetic Dipole Moment of the +(1232)

Linearly polarised photon asymmetry of p(,'0p)

Variation with E(') important model constraint

First ever measurement!

The Magnetic Dipole Moment of the +(1232)

Chiang et al. P.R.C. 71 (2005)Pascalutsa & Vanderhaeghen P.R.L. 94 (2005)

The Magnetic Dipole Moment of the +(1232)

p(,'+n) results

PID & shower shape Good + energy determination

Can measure n+ decay of + with CB !!

Proof of principle established more detailed meas. planned

D. Glazier & D. Watts, Edinburgh

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ola

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rise

d)

Other CB@MAMI Round I Physics Highlights

mass determination

➔ Find prod.threshold

A. Nikolaev, Bonn

WithoutAcceptanceCorrection

2

2 2c

Emmmm

thr

ppp

mass determination

p(,00p) production

➔ Test of PT

➔ Circ. asymmetry

➔ Reaction mechanism?

➔ N resonance properties?

A. Nikolaev, Bonn

WithoutAcceptanceCorrection

Bernard et al. Phys. Lett. B382 (1996)Kotulla et al. Phys. Lett. B578 (2004)F. Zehr, Basel

Double 0 Excitation Function

Other CB@MAMI Round I Physics Highlights

D. Krambrich, Mainz

mass determination

p(,00p) production

p(,0p) photon asymmetry

➔ Massive statistics

➔ High resolution

➔ EM properties of ➔ E2/M1 ratio

E. Downie

R. Leukel, Mainz, 2001E. Downie, Glasgow

VERY PRELIMINARY>0.5 of data set

Other CB@MAMI Round I Physics Highlights

Coherent 0 production➔ Do heavy stable nuclei have a neutron skin?

➔ Fundamental property of nuclear physics➔ Size of skin gives direct information on neutron rich equation of state➔ Skin size also gives important new insights into neutron star physics

(cooling mechanisms, mass radii relationships) ➔Accuracy < 0.05 fm

➔ C. Tarbert, D. Watts, Edinburgh ➔ See D. Watts talk

CB@MAMI Highlights I

16O

6.1 MeV

12C

4.4 MeV

See low E nuclear decay 's

In coincidence !➔ 550 MeV invariant mass➔ 135 MeV 0 invariant mass➔ 4.4 MeV Carbon decay photon

New possibilities for range of nuclear physics studies e.g. transition matter form factors

0

C. Tarbert, Edinburgh

C. Tarbert, Edinburgh

CB@MAMI Highlights I

MAMI-C / Photon Tagger Upgrade

MAMI-A

MAMI-B

MAMI-A180 MeV

MAMI-B883 MeV

MAMI-C / Photon Tagger Upgrade

MAMI – C

Now Operational!

MAMI-A

MAMI-B

MAMI-A180 MeV

MAMI-B883 MeV

MAMI–C1.5 GeV

MAMI-C / Photon Tagger Upgrade

Tagger

Tagger has to bend 1.5 GeV

Need to increase B to 1.8T

Complete Tagger dismount

➔ Reduce pole gap

➔ Increase return yoke

Tagger reassembled

2T field achieved

Sucessfully running @ 1.5GeV!

MAMI-C / Photon Tagger Upgrade

MAMI-C / Photon Tagger Upgrade

1.5 GeV Beam Spot

See Eillidh McNicoll's talk

High flux allows possibility of recoiling nucleon polarimetry Graphite scatterer + PID/Tracking detectors

Scatter > 10: Hadronic interaction n(,) =no(){1+A()[Pycos()–Pxsin()]}

First “complete measurement” of meson (p,n..) production Enable first fully constrained PWAs

CB@MAMI Future Facilities: Edinburgh Recoil Polarimeter

n() =no(){1+A()[Pycos()–Pxsin()]}

Recoil polarisation expts. Frozen spin target – double pol. experiments

S11(1535) Magnetic Moment Threshold strangeness production

Short range correlations Tests of fundamental symmetries , ' decays

Medium modification of mesons (ral sym. restoration) Sum rules – GDH ...

Vector meson production -mesic nuclei

VERY PRELIMINARY>0.5 of data set

CB@MAMI 1.5GeV Expected Future Highlights

Initial round of CB@MAMI experiments complete

Results are approaching publication

MAMI C running at 1.5GeV

Tagger upgrade sucessfully complete

Broad range of nuclear and hadronic physics planned

Watch this space for interesting physics!

Conclusions

The CB@MAMI Detector Setup – The PID

Designed and build by Edinburgh / Glasgow Universities