Crystal Ball at MAMI
Daniel Watts,
Univ. of Edinburgh (UK)
For the CB@MAMI Collaboration
CB@MAMI: Main physics objectives
(mainly involving low cross sections and/or precision measurements)
•
Precision spectroscopy of low lying baryon states:
m( (1232)) from p p0 ’ p and p+ ’ n
m(S11(1535)) from ph ’ p reaction
• Threshold meson production: (test of LET/ ChPT):
Strangeness ( N →LK)
p0 photoproduction at threshold
• Ambiguity free amplitude analysis of meson photoproduction
Requires Double polarization measurements:
N→Np(p); Nh (r,…) channels
• Tests of fundamental symmetries (C,CP,CPT…)
Rare h, h/ decays
• In medium properties of hadrons & nuclear physics:
Meson photo production on nuclei
The MAMI facility
•
•
•
100% duty factor electron microtron
MAMI-C 1.5 GeV upgrade (2006)
(MAMI-B 0.85 GeV)
Crystal Ball - A2 hall
(tagged photon beam)
One of the MAMI-C magnets

e
Photon Tagger upgrade
Photon beam facilities
Legs
B
C
Emax
Imax
(GeV)
(s-1MeV-1) (FWHM)
(MeV)
ΔE
Pollin
Polcirc
(%)
(%)
3.5
≈ 104
5
70
80
1.5
≈ 103
15
100
100
5.4
≈ 104
5
70
80
0.45
≈ 103
5
100
100
0.8
1.5
3.0
≈ 105
1
70
80
≈ 103
30
100
100
Crystal Ball history
1996-2002
BNL-AGS
(Ecm = 1.2 – 1.53 GeV)
1982-1986
DORIS
(Ecm = 9 -10 GeV)
1976
Conceived
1978 -1981
SPEAR
(Ecm = 3 - 7 GeV)
2002
MAMI
(Ecm = 1.2 -1.9 GeV)
Crystal Ball arrives at Frankfurt
Setup at MAMI
Tracker & Particle-ID
Good angular and
energy resolution,
close to 4p acceptance
Tracker & Particle-ID
320mm
2mm thick
EJ204
scintillator
s(q) ~ 1.5o
s(f) ~ 1.3o
• Two cylindrical wire chambers
• 480 anode wires, 320 strips
• Adapted from DAPHNE
• New MWPC tracker under
construction (2006)
MWPC & Particle-ID in situ
Setup at MAMI
Tracker & Particle-ID
Good angular and
energy resolution,
close to 4p acceptance
MAMI Photo Gallery
CB
with
PMTs
CB
TAPS
CB
TAPS
Panoramic view of MAMI setup

Targets at MAMI
Liquid hydrogen (deuterium) target
Polarised 3He gas target
(~2008)
Frozen spin Target
butanol / deuterated butanol
(~2007)
Liquid 3He target (2006)
CB@MAMI – timetable
Nov '02:
Nov '03:
Mar '04:
Apr '04:
May '04:
Jun'04-Apr '05 :
Crystal Ball moved to Mainz
Crystal Ball installed at photon beam at MAMI
TAPS installed
MWPC and PID installed
First test run tests with the complete setup
First production runs
E=0.1-0.8 GeV: unpolarized H2 or D2 targets, nuclear targets
Apr '05-Jan'06 :
'06 onwards
MAMI-C upgrade, photon tagger upgrade
: Second production runs
E=0.1-1.5 GeV: unpolarized, polarised, nuclear targets
Selection of
preliminary spectra
from first round of
experiments
E = 0.1 – 0.8 GeV
Preliminary analyses: p0, h identification
h  3p0  
s~25 MeV
p0  
s~11 MeV
h  
s~23 MeV
Preliminary analyses: Ags(,p0)Ags
coherent p0 photoproduction from nuclei
•
ds/dW ~
•
E=220 MeV
Clear diffraction patterns for 208Pb,
40Ca, 16O, 12C
208Pb
sinq ~ 1.22 l/D
Rm ~ 5.75 fm
(Rc ~ 5.50 fm)
A2(q/k)P32|Fm(q)|2sin2qp
Matter form factor,  properties in
the medium
33o
Also see coincident low energy Nuclear Decay Photons !!
C. Tarbert, D. Watts
12C
4.4 MeV
16O
40Ca
3.7MeV
6.1 MeV
Preliminary analyses: (, p)p0
Photon Asymmetry S:
ds
ds
(q , f ) 
(q )(1  p  S cos( 2f ) )
dW
dW
A. Starostin
Preliminary analyses: p(,p)p0p0
• High statistics measurement
• With  beam polarisation → S , Scirc
F.Zehr
E dependence of
p0p0 yield
(not acc. corrected)
Preliminary analyses: p(,p)p0 to measure m(+)
m(+)
´


p
p
+

p0
p
p

p
dominant
´

+
p0
small
´
p0
p
coherent addition...
MAMI pilot measurement with TAPS only
M. Kotulla et al., PRL 89 (2002) 272001
p(,p)p0 to measure m(+)
• 100 in statistics
• measure  beam polarisation observables
• Both pp0 and np+ decay of +
m= 0.79mp
m=3mp
m=5mp
m=3mp
m=1mp
Future plans
with MAMI-C
E = 0.1 – 1.5 GeV
Double-polarisation in pseudo-scalar meson photoproduction
Polarisation of
Observable

target
recoil
Beam-target observable: E
 p → p p0  p → p h
 n → n p0  n → n h
Butanol frozen spin target
Deuterated butanol frozen spin target
Circularly polarised photons + longitudinally polarised protons (or neutrons)
 n → n p0
qp=90o
 p → p p0
qp=90o
E
Expected
data
accuracy
qp±10o
E±10 MeV
250 hrs
E (MeV)
E (MeV)
Previous E measurement for  p → p p0 led to significant revision of helicity
amplitudes for D13(1520) [ PRL 88, 232002 (2002)]
Neutron targets: different resonance contributions, isospin structure
Also get pp channels – mechanisms, contributions to GDH integrand
Beam-target observable: G
 p → p p0
 p → n p+
linearly polarised photons + longitudinally
polarised protons
Expected Data
accuracy
qp±10o
E±10 MeV
600 hrs
Variable well suited to studies of Roper resonance ( P11(1440) )
Beam-Recoil Observables: Cx, OX, T, P
Useful scattered event
Select events with scattering angles
larger than ~10 degrees : arising
from nuclear interaction
Initial path of proton
Polarimeter acceptance : ±20o polar angle (target at centre)
Most events suffer only coulomb scattering
Hydrogen target cell
 beam
TAPS
Graphite sheet
(~7cm thick) Crystal Ball
n(q,f) =no(q){1+A(q)[Pycos(f)–Pxsin(f)]
Beam-Recoil Observables- p(,p0)p
qp(cm)=130o
300 hrs Ee=0.85 GeV
500 hrs Ee=1.5 GeV
Summary
~4p detector system
Very good neutral (and charged) particle
detection capabilities
Excellent properties of MAMI beam
Availability of polarized targets
Recoil nucleon polarimetry possibilities
High quality data for meson photoproduction
for E up to ~1.5 GeV can be expected
J.Brudvik, J. Goetz, B.M.K.Nefkens, S.N.Prakhov, A.Starostin, I. Saurez, University of California, Los Angeles, CA, USA
J.Ahrens, H.J.Arends, D.Drechsel, D.Krambrich, M.Rost, S.Scherer, A.Thomas, L.Tiator, D. von Harrach and Th.Walcher
Institut fur Kernphysik, University of Mainz, Germany
R. Beck, M. Lang, A. Nikolaev, S. Schumann, M. unverzagt, Helmholtz-Institut fur strahlen und Kernphysik, Universitat Bonn,
Germany
S.Altieri, A.Braghieri, P.Pedroni, A.Panzeri and T.Pinelli INFN Sezione di Pavia and DFNT University of Pavia, Italy
J.R.M.Annand, R.Codling, E.Downie, D.Glazier, J. Kellie, K.Livingston, J.McGeorge, I.J.D.MacGregor, R. Owens
D.Protopopescu and G.Rosner Department of Physics and Astronomy, University of Glasgow, Glasgow, UK
C.Bennhold and W.Briscoe George Washington University, Washington, USA
S.Cherepnya, L.Fil'kov, and V.Kashevarow Lebedev Physical Institute, Moscow, Russia
V.Bekrenev, S.Kruglov, A.Koulbardis, and N.Kozlenko Petersburg Nuclear Physics Institute, Gatchina, Russia
B.Boillat, B.Krusche and F.Zehr, Institut fur Physik University of Basel, Basel, Ch
P. Drexler, F. Hjelm, M. Kotulla, K. Makonoyi, R.Novotny, M. Thiel and D. Trnka II. Phys. Institut, University of Giessen,
Germany
D.Branford, K.Foehl, C.M.Tarbert and D.P.Watts School of Physics, University of Edinburgh, Edinburgh, UK
V.Lisin, R.Kondratiev and A.Polonski Institute for Nuclear Research, Moscow, Russia
J.W. Price California State University, Dominguez hills, CA, USA
D.Hornidge Mount Allison University, Sackville, Canada
P. Grabmayr and T. Hehl Physikalisches Institut Universitat Tubingen, Tubingen, Germany
D.M. Manley Kent State University, Kent, USA
M. Korolija and I. Supek Rudjer Boskovic Institute, Zagreb, Croatia
D. Sober Catholic Catholic University, Washington DC
CB@MAMI
CB@MAMI: Main physics objectives
•
(mainly involving low cross sections and/or precision
measurements)
Precision spectroscopy of low lying baryon states:
m( (1232)) from p p0 ’ p and p+ ’ n
m(S11(1535)) from ph ’ p reaction
• Threshold meson production: (test of LET/ ChPT):
Strangeness ( N →LK)
p0 photoproduction at threshold
• Ambiguity free amplitude analysis of meson photoproduction
Requires Double polarization measurements:
N→Np(p); Nh (r,…) channels
• Tests of fundamental symmetries (C,CP,CPT…)
Rare h,h/ decays
• In medium properties of hadrons:
Meson photo production on nuclei
p(,p)p0 to measure m(+)
• 100 in statistics
• measure  beam polarisation observables
• Both pp0 and np+ decay of +
m= 0.79mp
m=3mp
m=5mp
m=3mp
m=1mp
Double-polarisation: theory background
Polarisation of
Observable

target
recoil
•
•
•
•
4 complex amplitudes – 16
observables in meson
photoproduction
Each double polarisation
observable gives different
combination of amplitudes
To fix the 4 amplitudes
unambiguously → 8 real
quantities
Cannot choose from the same
set
Cx’ ( + recoil) – theoretical predictions
• Predicted sensitivity to
poorly established
resonances
• Resonance parameters
from quark model
(Capstick and Roberts)
Solid – SAID
Dashed – background + ****
Dotdash- background + **** +N-3/2(1960)
Dutta, Gao and Lee, PRC 65, 044619 (2002)
Previous experimental data – SAID
database
Data for all CM breakup angles
Ox’
Cx’
Recent JLAB data
not in database
P
T
Recent Cx’ measurement at JLab
• MAID & SAID
poor description
of new data
Polarisation transfer Cx’
• First determination
p(,p)p0 in 2002
Hall A JLab
Photon energy (MeV)
The proposed experimental setup
Useful scattered event
Select events with scattering angles
larger than ~10 degrees : arising
from nuclear interaction
Initial path of proton
Polarimeter acceptance : ±20o polar angle (target at centre)
Most events suffer only coulomb scattering
Hydrogen target cell
 beam
TAPS
Graphite sheet
Crystal Ball
n(q,f) =no(q){1+A(q)[Pycos(f)–Pxsin(f)]
GEANT simulation of polarimeter
No Graphite
With Graphite scatterer
• Simulation includes realistic
smearing of energy deposits due to
experimental energy resolution
and proper cluster finding algorithms
• Finite target size and E resolution
included
Angle between qN(E,qp) and TAPS hit
Kinematic acceptance of polarimeter
qp(CM) >~130o
E=150 MeV
E=200
Eg=300
E=500
E=750
E=1000
E=1500
Pion angle in CM (deg)
p(,p)N
Polarimeter
acceptance
Nucleon angle in lab (deg)
Kinematic acceptance of polarimeter
•
More forward recoils than for pion
production.
•
Almost all recoils are incident on
polarimeter up to ~0.8 GeV
CM h angle (degrees)
p(,h)N
Polarimeter
acceptance
Eg=720
Eg=820
Eg=920
Eg=1520
Lab nucleon angle (degrees)
Cx’ – Extraction and expected
accuracy
Cx’
0
180
360
Photon energy (MeV)
P=0.7, E=±25MeV, qp=130±10
Plot difference in f distributions for two helicity
states (cut on region of q with reasonable A(q))
Left with simple sin(f)
Dependence. Extract Px
s ~ 1 mb/sr → Cx ~ 0.015
s ~ 0.1 mb/sr → Cx ~0.05
Greatly improved data quality
Polarimetry basics
• Measure direction of nucleon before and after the
scatterer with sufficient accuracy to determine an
analysing reaction has taken place.
qscat
Qscat=5-20o
For incident protons also
have multiple (coulomb)
scattering
CB@MAMI: Future programme
•
Magnetic dipole moments:
 (1232) from p p0 ’ p and p+ ’ n
S11(1535) from ph ’ p) reaction
• Threshold meson production: (test of LET/ ChPT):
Strangeness ( N →LK)
p0 photoproduction at threshold
• Double polarization measurements: (properties of baryon resonances/GDH)
N→Np(p); Nh (r,…) channels
• Mass of h-meson and rare h decays
• Meson photo production on nuclei: medium mod., nuclear properties
Doublepolarisation in
pseudo-scalar
meson
photoproduction
Polarisation of
Observable

target
recoil
• 4 complex amplitudes
→16 observables in meson
photoproduction
→ need 8 well chosen
measurements to fix the 4
amplitudes
• Each double polarisation
observable gives a different
combination of amplitudes
MWPC tracker
• Adapted from
MWPCs used with
the DAPHNE detector
• New dedicated
MWPC tracker under
construction
(Complete early 2006)
s(q) ~ 1.5o
s(f) ~ 1.3o
Scattered nucleon detection in
TAPS
• 1 TAPS block ~ position resolution for hit
• TAPS~0.9m from scatterer
N
Straight through
10o scatter
20o scatter
p
Detrimental side-effects of
scatterer material
• To hit polarimeter
TN>100 MeV in (p,p)N
above the 
• Proton energy loss
Tp exit proton (MeV)
1000
100
Tp after graphite
Energy loss
10
1
<10 MeV for Tp>100 MeV.
• Multiple scattering
<1o
FWHM for Tp>100 MeV
• 0.37 radiation lengths
 conversion ~ 30%
FWHM scattering angle (deg)
0
100
200
300
400
Tp incident proton (MeV)
500
3
2.5
2
Coulomb scattering
1.5
Series1
1
0.5
0
0
200
400
600
800
1000
Proton energy (MeV)
1200
Crystal Ball history
1996-2002
BNL-AGS
(Ecm = 1.2 – 1.53 GeV)
N*, , L*, S,
h decays, medium. mod
1976
Conceived
1978 -1981
SPEAR
(Ecm = 3 - 7 GeV)
y,y spectroscopy
radiative f decays
t decays
D decays,
→ ,
h, h, f
1982-1986
DORIS
(Ecm = 9 -10 GeV)
Y spectroscopy
radiative  decays
2002
MAMI
(Ecm = 1.2 -1.9 GeV)
Particle-ID detector
24 of 2x10x320mm
EJ204 scintillator
Small light
attenuation
Good separation of
p, p with little
overhead in
material before
MWPC and CB
detectors
24 Hamamatsu
f=10mm PMT
Hadron Structure: + Magnetic Moment
recent calculation:
includes pN
rescattering loops
W.-T. Chiang, M. Vanderhaeghen, S. N. Yang, D. Drechsel,
PRC 71,015204 (04)
Hadron Structure: + Magnetic Moment
Connection between Np ’N and Np N
ds
1 ds

 (kin. factor)
'
'
'
dE dWp E 0 E dWp
p0 p
p+ n
Hadron Structure: + Magnetic Moment
TAPS – first
 p → p+ p ’ data
M. Kotulla et al., PRL 89 (2002) 272001
1 ds '
R
E
'
s p dE
m  2.7  1.2 (stat)  1.5 (sys)  3.0 (model )
(units: mN)
m=1
(units:
m=7
mN)
Hadron Structure: + Magnetic Moment
sensitivity to angular
differential cross section
with cut on ´ energy
sensitivity to beam
asymmetry (linearly
polarized photon beam)
m  (1 +  )m N
Setup at MAMI
Good angular and energy
resolution, close to 4p acceptance for charged and neutral final states