electromagnetic probes mami, jefferson lab & max-lab daniel watts university of edinburgh

Electromagnetic probes MAMI, Jefferson Lab & MAX-Lab

Daniel WattsUniversity of Edinburgh

Scope of talk

• Outline the present engagement of the Glasgow and Edinburgh groups at these facilities.

• No attempt to be comprehensive

• Choose two topics reflecting current research:

Neutron skins The nucleon excitation spectrum

Timelines, upgrades & UK investment

2005

2010

2015

2020

2025Facility upgrade

MAX@0.25 GeV106s-1MeV-1

MAMI@1.5 GeV105s-1MeV-1

JLab@12 GeV108 s-1

Timelines, upgrades and investment

2005

2010

2015

2020

2025

MAX@0.25 GeV106s-1MeV-1

UK Hardware at Max-lab

Edinburgh Ge-6 Array

Glasgow active target

Timelines, upgrades and investment

2005

2010

2015

2020

2025Facility upgrade

MAMI@1.5 GeV105s-1MeV-1

UK investment at MAMI• Glasgow photon tagger

• Edinburgh Particle-ID detector

• Edinburgh nucleon polarimeter

• Glasgow photon beam profiler

Timelines & Upgrades

2005

2010

2015

2020

2025

JLab@12 GeV108 s-1

UK Investmentat Jefferson Lab

Polarised beam setup (Glasgow)

Big bite focal plane array(Glasgow)

Part of neutron polarimeter for Gen (Glasgow)

Nucleon polarimetry R&D (Edinburgh)

Neutron Skins

Our knowledge of the shape of stable nuclei is presently incomplete

e.g. 208Pb: RMS charge radius known to < 0.0001 fm

RMS neutron radius only known to ~0.2 fm !! Horowitz PRC63 025501 (2001)

New techniques to attack this fundamental problem are important and timely

URCA Cooling

n → p + e- +

e- + p → n +

Relativistic mean field

Skyrme HF

• Angular distribution of 0 → accurate information about matter distribution

d/dA2(q/k)P32|F

m(q)|2sin2

Neutron skins

Photon probe Interaction well understood

0 meson – produced with ~equal probability on

protons AND neutrons.

Select reactions which leave nucleus in ground state

Reconstruct

from →2decay

No neutron skin0.2fm neutron skin

208Pb(,0)E=185±5 MeV

1st m

inim

a N

o s

kin

2nd M

ax.

No

ski

n

Neutron Skins :Preliminary analyses

One of over 30 spectra!!

• A primary motivation of the new EM beam facilities → better establish the nucleon excitation spectrum

• Use meson photoproduction reactions

+ N → N* →

• small → resonances are broad (E ~ ħ)

Excitation spectrum of nucleon

0.5 1.0 1.5

Cro

ss s

ecti

on

E (GeV)

P33

N(1440)P11

N(1520)D13

N(1535)S11

(1600)P33

The way forward – double polarisation

Polarisation of

target recoil

Observable

Edinburgh Recoil Polarimeter: Cx, OX, T, P

Graphite scattererHydrogen target cell

n() =no(){1+A()[Pycos()–Pxsin()]

Edinburgh Recoil Polarimeter: Cx, OX, T, P

First proof of principle for a 4 nucleon polarimeter !!

1000 hours of approved → pion photoproductionFuture multipion etc.

SAID PWAMAID PWA

p(,p)0

Worldwide activityDouble polarisation at Jefferson Laboratory

Frozen spin polarised target development – beam-target experiments start 2008 (Glasgow, Edinburgh)

Strange meson photoproduction e.g. + p → K+ + 0

Self-analysing (weak) decay → recoil polarimetry !!

Beam-recoil experiments under analysis (Glasgow)

Polarised target will enablecomplete measurement

C.Gordon, K. Livingston et. al.

Worldwide activitySummary

New generation of EM beam facilities offer unique opportunities to address fundamental questions in

nuclear and hadron physics

Other EM beam research programmes with UK leadership

Magnetic moments of nucleon resonances Nuclear three-body forces

Nuclear short-range correlations Tests of chiral perturbation theory in strange

quark sector Search for multiquark states

Exotic hybrid mesons and glueballs Nucleon form factors