Active Target Experimental Possibilities
at MAX-lab
J.R.M. Annand
Department of Physics and Astronomy
Active Target Experimental Possibilities, J.R.M. Annand, PAC Meeting, MAX-lab October 2008
Experimental Possibilities at Low Energy
and Momentum Transfer
How does Lund fit in the European/US Scheme?
Lund MAX-lab
Tagged Photons 10 – 200 MeV
UK funding “problematic” after March 2009
MAMI @ Mainz
Electrons 180 – 1508 MeV
Tagged Photons 20 – 1400 MeV
Polarised target/beam/recoil programme dominates next few years
Jefferson Lab
Electrons 500 – 6000 MeV, Hall-A p(e,e'p)0 Q2  0.04 - 0.15 GeV2
Low energy experiments before upgrade ?? (partial summer shutdown)
HIGZ
Higher energy range attainable in practise?
Active Target Experimental Possibilities, J.R.M. Annand, PAC Meeting, MAX-lab October 2008
New Measurements @ MAX-lab
Tagged Photons E = 10 – 120 MeV
➢
➢
➢
Main broad-band tagger, SAL FP array, 450 keV E resolution.
Total Photoabsorption cross section of 3,4He (1% stat. ~2hr gas sc.)
Both gas scintillators and SSD/MWPC active targets
Partial photoreaction cross sections of 3,4He
Gas scintillator and MWPC/SSD active targets, TOF arrays
6,7
Li total photoabsorption (see D. Middleton)
➢
➢
Compton scattering with active 3,4He target and large NaI array
Separate coherent scattering from quasi-free?
Rates?
Near threshold pion photoproduction on
3,4
He ?
Active Target Experimental Possibilities, J.R.M. Annand, PAC Meeting, MAX-lab October 2008
4
He Total Photoabsorption
& Active Target Analysis
Pilot Experiment MAX-Lab 2000
EIHH + LIT Calculation
Gazit et al PRL 96,112301,2006
Realistic Potential
AV18 2-N + Urbana IX 3-N
(,n) Nilsson X 2
(,n)+(,p) Shima
Necessary Corrections
Window background
Detection efficiency
Target thickness uncertainty
GEANT-4 MC model
Active Target Experimental Possibilities, J.R.M. Annand, PAC Meeting, MAX-lab October 2008
High Pressure Gas-Scintillator Active Target for MAX-lab
4 Optically isolated chambers
4 PMT readout per chamber
2 containment chambers
...isolate window events
1-2 MPa
pressure
~500 ppm N2
0.5 mm Be
outer window
5m Al-Mylar
inner windows
52-104 mg/cm2
target thickness
Operational pressure 1-2 MPa
Alternative gas mixtures
under test (He-Xe)
Geant-4 computer model
under construction
Active Target Experimental Possibilities, J.R.M. Annand, PAC Meeting, MAX-lab October 2008
Setup for Test Beam October 2008
16 3.5/2.5 l liquid scintillator Nordball low-energy n
10 300 x 20 x 10 cm plastic scintillator
3 Very large NaI(Tl)
Various 10” NaI(Tl)
Active Target Experimental Possibilities, J.R.M. Annand, PAC Meeting, MAX-lab October 2008
Compton Scattering at MAX-lab
S.Beane et al, 2004
PT O(Q4)
3 Large NaI CATS, BUNI, DIANA
Neutron polarisabilities main focus
Coherent Compton on 2H
MAX energy range low for QF
Need good energy resolution
Also proposals for 4He and 12C
2
H(,) Data
M.Lucas, PhD Thesis U.Illinois 1994
D.Hornidge et al, PRL84(2000),2334
M.Lundin et al, PRL(2003),192501
Current MAX-lab programme
L.Myers et al.
Active Target Experimental Possibilities, J.R.M. Annand, PAC Meeting, MAX-lab October 2008
Compton Scattering on 3He
Choudhury et al.,
PRL98(2007)232303
120 MeV
60 MeV
80 MeV
Alternative “take” on neutron
polarisabilities
Polarised 3He ~ polarised
neutron...neutron spin polarisabilities?
PT calculations @ NLO of coherent
3
He(,) now available
Consistent framework for analysis of 2H
and 3He data?
No data available
What could MAX-lab do?
Zero  sensitivity
@ 90 deg.
Active Target Experimental Possibilities, J.R.M. Annand, PAC Meeting, MAX-lab October 2008
Alternative Techniques for Compton Scattering
test at MAMI July 2008
Unshielded 4
Detector
Crystal Ball
Select single  events (with recoil p)
Single  from 0
contaminates
signal.
Clean up by
proton detection
Proton energy
unreliable @
lower E
Angular
correlation
seems to be
sufficient
Neutron signal
possible?
Compton Signal
Possibilities for Experiments at Low Energy and Momentum Transfer
Preliminary Computer Studies of Coherent 3He(,3He)
Geant-4 Simulation
Crude model of detector
geometry and materials
Active Target
3 of 10” NaI + Pb collimator
5 of “Nordball” n-detector
E = 20 - 140 MeV
Phase-space generator
of events
Will include realistic model
of non-active elements
Realistic event generators
Active Target Experimental Possibilities, J.R.M. Annand, PAC Meeting, MAX-lab October 2008
Preliminary MC Calculations 3He(,3He)
Uncollimated 10” NaI
Active Target Experimental Possibilities, J.R.M. Annand, PAC Meeting, MAX-lab October 2008
Preliminary MC Calculations 3He(3He) 3He(pd)
15 cm  Collimator on 10” NaI @ 90o
Elastic
Inelastic
Active Target Experimental Possibilities, J.R.M. Annand, PAC Meeting, MAX-lab October 2008
Counting Rate
Tagged-Photon Intensity 0.5 MHz/MeV
10 MeV bin = 5 MHz
Target thickness
@ 20 bar = 20 x 0.1786 x 10-3 x ¾ x 32.8 gcm-2
Compton rate in target
52 events/hr per b cross section
Effective photon detector acceptance
250 msr
Compton rate @ 90o for  = 25 nb/sr
0.325/hr
Experiment with bremsstrahlung?
Pre-upgrade single-cell active-target interrupt ~ 100 Hz
Active Target Experimental Possibilities, J.R.M. Annand, PAC Meeting, MAX-lab October 2008
+3He ppn
R. Skibinsky et al., PRC67,054002,2003
d5/d1d2dS |{NN+3NF}-{NN}|
Faddeev AV18 + U-IX, Siegert, E=120 MeV
CD Bonn + MT', Siegert, E=120 MeV
Skibinski et al, PRC72,044002,2005, Data Belyaev et al, Sov.JNP44,181,1986
E=120 MeV
Full AV18 + UIX
Dashed AV18 Only
E=200 MeV
Present Fadeev calculations not valid
above pion production threshold
Energies slightly low for Mainz detectors
Yerevan Active target?
Large angle acceptance + good
energy/angle resolution
Angle range sufficient?
Increased operating pressure?
Ge-6 array + Si-strips + L3He target
Possibilities for Experiments at Low Energy and Momentum Transfer
Experimental Outlook Summary
MAX-lab Lund
Active target activity resumed in 2007
Start beam studies of active 4He target October 2008
Include Nordball TOF for (,n) signal
Include 10” NaI detectors for Compton signal
Continue Target development in Glasgow.....
in combination with development of Geant-4 models as quantitative
analysis tools
4
He production runs early 2009....also 1st
3
He runs?
Yerevan active target ? (funding Yerevan group...EU)?
Investigate 3He photodisintegration with Yerevan target?
Complementary Compton scattering programme with MAMI ?
Possibilities for Experiments at Low Energy and Momentum Transfer