electromagnetic probes mami, jefferson lab & max-lab daniel watts university of edinburgh
TRANSCRIPT
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
[email protected] GeV106s-1MeV-1
[email protected] GeV105s-1MeV-1
JLab@12 GeV108 s-1
Timelines, upgrades and investment
2005
2010
2015
2020
2025
[email protected] 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
[email protected] 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