Crystal Ball at MAMI

1
Crystal Ball at MAMI

• Daniel Watts,
• Univ. of Edinburgh (UK)
• For the CB_at_MAMI Collaboration

2
CB_at_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 g p
  and p g n
• m(S11(1535)) from ?p?h g p
  reaction
• Threshold meson production (test of LET/ ChPT)
  
• Strangeness (g N ?LK)
• p0 photoproduction at threshold
• Ambiguity free amplitude analysis of meson
  photoproduction
• Requires Double polarization
  measurements
• gN?Np(p) Nh (r,) channels
• Tests of fundamental symmetries (C,CP,CPT)
• Rare ?, h/ decays
• In medium properties of hadrons nuclear
  physics
• Meson photo production on nuclei

3
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)

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Photon Tagger upgrade
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Photon beam facilities
Egmax (GeV) Igmax (s-1MeV-1) ?Eg (FWHM) (MeV) Polglin () Polgcirc ()
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 1.5 105 1 70 80
3.0 103 30 100 100
Legs
B
C
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Crystal Ball history

• 1982-1986
• DORIS
• (Ecm 9 -10 GeV)

1996-2002 BNL-AGS (Ecm 1.2 1.53 GeV)
1976 Conceived 1978 -1981 SPEAR (Ecm 3 - 7
GeV)

2002 MAMI (Ecm 1.2 -1.9 GeV)
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Crystal Ball arrives at Frankfurt
8
Setup at MAMI
Tracker Particle-ID
Good angular and energy resolution, close to 4p
acceptance
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Tracker Particle-ID
2mm thick EJ204 scintillator
320mm
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)

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MWPC Particle-ID in situ
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Setup at MAMI
Tracker Particle-ID
Good angular and energy resolution, close to 4p
acceptance
12
MAMI Photo Gallery
CB with PMTs
CB
TAPS
TAPS
CB
Panoramic view of MAMI setup
g
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Targets at MAMI
Polarised 3He gas target (2008)
Liquid hydrogen (deuterium) target
Frozen spin Target butanol / deuterated butanol
(2007)
Liquid 3He target (2006)
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CB_at_MAMI timetable
Nov '02 Crystal Ball moved to
Mainz Nov '03 Crystal Ball
installed at photon beam at MAMI Mar '04
TAPS installed Apr '04
MWPC and PID installed May '04
First test run tests with the complete
setup Jun'04-Apr '05 First production runs
Eg0.1-0.8 GeV unpolarized H2 or D2
targets, nuclear targets

• Apr '05-Jan'06 MAMI-C upgrade, photon tagger
  upgrade
• '06 onwards Second production runs
• Eg0.1-1.5 GeV
  unpolarized, polarised, nuclear targets

15
Selection of preliminary spectra from first round
of experiments Eg 0.1 0.8 GeV
16
Preliminary analyses p0, h identification
h ? 3p0 ? 6g s25 MeV
h ? gg s23 MeV
p0 ? gg s11 MeV
17
Preliminary analyses Ags(g,p0)Ags coherent p0
photoproduction from nuclei

• Clear diffraction patterns for 208Pb, 40Ca, 16O,
  12C
• ds/dW A2(q/kg)P32Fm(q)2sin2qp
• Matter form factor, D properties in the medium

Also see coincident low energy Nuclear Decay
Photons !!
C. Tarbert, D. Watts
16O
12C
40Ca
3.7MeV
4.4 MeV
6.1 MeV
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Preliminary analyses (g, p)p0
Photon Asymmetry S
A. Starostin
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Preliminary analyses p(g,p)p0p0

• High statistics measurement
• With g beam polarisation ? S , Scirc

F.Zehr
Eg dependence of p0p0 yield (not acc.
corrected)
5 of total statistics
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Preliminary analyses p(g,p)p0g to measure m(D)
MAMI pilot measurement with TAPS only M. Kotulla
et al., PRL 89 (2002) 272001
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p(g,p)p0g to measure m(D)

• ?100 in statistics
• measure g beam polarisation observables
• Both pp0 and np decay of D

22
Future plans with MAMI-C Eg 0.1 1.5 GeV
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Double-polarisation in pseudo-scalar meson
photoproduction
Polarisation of g
target recoil
Observable
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Beam-target observable E
g p ? p p0 g p ? p h g n ? n p0 g n
? n h Circularly polarised photons
longitudinally polarised protons (or neutrons)
Butanol frozen spin target
Deuterated butanol frozen spin target
g n ? n p0 qp90o
g p ? p p0 qp90o
Expected data accuracy qp10o Eg10 MeV 250
hrs
E
Eg (MeV)
Eg (MeV)
Previous E measurement for g 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
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Beam-target observable G
Expected Data accuracy qp10o Eg10 MeV 600 hrs
Variable well suited to studies of Roper
resonance ( P11(1440) )
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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
g beam
TAPS
Graphite sheet (7cm thick)
Crystal Ball
n(q,f) no(q)1A(q)Pycos(f)Pxsin(f)
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Beam-Recoil Observables- p(g,p0)p
qp(cm)130o
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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 Eg up to 1.5 GeV can be
  expected

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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 M. Vanderhaeghen,
College of William and Mary, Williamsburg, USA
CB_at_MAMI
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CB_at_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 g p
  and p g n
• m(S11(1535)) from ?p?h g p
  reaction
• Threshold meson production (test of LET/
  ChPT)
• Strangeness (g N ?LK)
• p0 photoproduction at threshold
• Ambiguity free amplitude analysis of meson
  photoproduction
• Requires Double polarization
  measurements
• gN?Np(p) Nh (r,) channels
• Tests of fundamental symmetries (C,CP,CPT)
• Rare ?,h/ decays
• In medium properties of hadrons
• Meson photo production on nuclei

31
p(g,p)p0g to measure m(D)

• ?100 in statistics
• measure g beam polarisation observables
• Both pp0 and np decay of D

mD5mp
mD3mp
mD1mp
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Double-polarisation theory background
Polarisation of g target
recoil
Observable

• 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

34
Cx (g 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)
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Previous experimental data SAID database
Data for all CM breakup angles
Ox
Cx
Recent JLAB data not in database
36
Recent Cx measurement at JLab

• First determination
• p(g,p)p0 in 2002
• Hall A JLab
• MAID SAID
• poor description
• of new data

Polarisation transfer Cx
Photon energy (MeV)
37
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
g beam
TAPS
Graphite sheet
Crystal Ball
n(q,f) no(q)1A(q)Pycos(f)Pxsin(f)
38
GEANT simulation of polarimeter

• Simulation includes realistic
• smearing of energy deposits due to experimental
  energy resolution
• and proper cluster finding algorithms
• Finite target size and Eg resolution included

No Graphite With Graphite scatterer
Angle between qN(Eg,qp) and TAPS hit
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Kinematic acceptance of polarimeter p(g,p)N
Polarimeter acceptance

• qp(CM) gt130o

Pion angle in CM (deg)
Eg150 MeV Eg200 Eg300 Eg500 Eg750 Eg1000 Eg
1500
Nucleon angle in lab (deg)
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Kinematic acceptance of polarimeter p(g,h)N
Polarimeter acceptance

• More forward recoils than for pion production.
• Almost all recoils are incident on polarimeter up
  to 0.8 GeV

CM h angle (degrees)

Eg720 Eg820 Eg920 Eg1520
Lab nucleon angle (degrees)
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Cx Extraction and expected accuracy
Cx
0 180 360
Photon energy (MeV)

• Pg0.7, Eg25MeV, qp13010
• s 1 mb/sr ? DCx 0.015
• s 0.1 mb/sr ? DCx 0.05
• Greatly improved data quality

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
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Polarimetry basics

• Measure direction of nucleon before and after the
  scatterer with sufficient accuracy to determine
  an analysing reaction has taken place.

For incident protons also have multiple
(coulomb) scattering
Qscat5-20o
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CB_at_MAMI Future programme

• Magnetic dipole moments
• ??(1232) from ?p? p0 g p and
  p g n
• S11(1535) from ?p?h g p) reaction
• Threshold meson production (test of LET/
  ChPT)
• Strangeness (g N ?LK)
• p0 photoproduction at threshold
• Double polarization measurements (properties of
  baryon resonances/GDH)
• gN?Np(p) Nh (r,) channels
• Mass of ?-meson and rare ? decays
• Meson photo production on nuclei medium mod.,
  nuclear properties

45
Double-polarisation in pseudo-scalar meson
photoproduction
Polarisation of g target
recoil
Observable

• 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

46
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
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Scattered nucleon detection in TAPS

• 1 TAPS block position resolution for hit
• TAPS0.9m from scatterer

N
Straight through 10o scatter 20o scatter
p
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Detrimental side-effects of scatterer material

• To hit polarimeter
• TNgt100 MeV in g(p,p)N above the D
• Proton energy loss
• lt10 MeV for Tpgt100 MeV.
• Multiple scattering
• lt1o FWHM for Tpgt100 MeV
• 0.37 radiation lengths
• g conversion 30

Tp after graphite Energy loss
Tp exit proton (MeV)
Tp incident proton (MeV)
Coulomb scattering
FWHM scattering angle (deg)
Proton energy (MeV)
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Crystal Ball history

• 1982-1986
• DORIS
• (Ecm 9 -10 GeV)
• Y spectroscopy
• radiative ? decays

1996-2002 BNL-AGS (Ecm 1.2 1.53 GeV) N,
D, 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, gg? gg, h, h?, f

2002 MAMI (Ecm 1.2 -1.9 GeV)
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Particle-ID detector
24 of 2x10x320mm EJ204 scintillator

• Good separation of p, p with little overhead
  in material before MWPC and CB detectors

Small light attenuation
24 Hamamatsu f10mm PMT
53
Hadron Structure D Magnetic Moment
W.-T. Chiang, M. Vanderhaeghen, S. N. Yang, D.
Drechsel, PRC 71,015204 (04)
recent calculation
includes pN rescattering loops
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Hadron Structure D Magnetic Moment
Connection between ?N?p gN and ?N?p N
p n
p0 p
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Hadron Structure D Magnetic Moment
TAPS first g p ? p p g data
M. Kotulla et al., PRL 89 (2002) 272001
(units mN)
mD1
(units mN)
mD7
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Hadron Structure D Magnetic Moment
sensitivity to angular differential cross section
with cut on g energy
sensitivity to beam asymmetry (linearly
polarized photon beam)
57
Setup at MAMI
Good angular and energy resolution, close to 4p
acceptance for charged and neutral final states