p(,n reaction measured with the Crystal Ball at MAMI
Dan Watts, Derek GlazierUniversity of Edinburgh
Richard Codling, John AnnandUniversity of Glasgow
Crystal Ball Collaboration meeting, Mainz, 2007
Why measure p(,n’
• Independent test of theoretical treatment of reaction amplitudes and rescattering effects in radiative photoproduction
• radiated from + lines (rather than proton lines as in p0’) – brem production has different strength/angular behaviour
• Give additional sensitivity to MDM?
Blue lines : + p →n + + + 'Black lines : + p →p + 0 + '
Theoretical predictions p(,n+’)
• Predictions presently available in unitary model (and EFT presently in development)
Main features:
1) Cross sections ~5x larger than p(,p0’) 2) Linear asymmetries large and positive3) Sensitivity to MDM marginal (in sampled kinematics)4) But helicity asymmetry shows promise as complimentary determination of MDM
Tree levelUnitary model
+ detection in the Crystal Ball:Achieving good energy determination
Utility of Crystal Ball for detection well understood but energy determination unexploredExpect some challenges:
1) Separation from proton/electron events 2) Hadronic/nuclear interactions 3) Unstable decay products }GEANT simulation to indicate
CB response
Particle-ID detector
● (~26 ns)
ee (~2 s)
Michel spectrumof e+ energies
● Use shower shape to help identify event types
● Reject many of , NI events with simple restriction on Ncryst<=4
Good Event
Muon decay event
Nuclear interaction
Geantsimulation: + shower shapes
Geant simulation: 150 MeV + signals in the CB
Cou
nts
Energy contained in cluster (GeV)
Cou
nts
Energy contained in cluster (GeV)
Split off clusters
Muon decay
Hadronicinteractions
No shower size restriction <=4 crystals in the shower
p(,n+’) : Outline of data analysis
Accept events with: 1+, 2 neutral clusters in CB/TAPS1+, 1 neutron TAPS, 1 other neutralp(,n+’) total 4-mom kinematic fit (CL>10-1)
If two neutrals assume either is photon or neutron, analyse both combinations
Reject events with:2 neutrals pass M0 kinematic fit (CL>10-3) - p0,n+0
M+miss = Mn Kin. Fit (CL>10-3) - n+
n+ Total 4 momentum fit (CL>10-2) - n+
+ shower condition <=4 crystals
Data used in next plots: all MDM data at Ee=885 MeV July/Sep/JanTotal p(,n+’) events – 70,000
p(,n+’) : Simulation data
• Run event generators through Monte Carlo of CB/TAPS
• Predicted energy deposits smeared according to observed experimental energy resolutions
Event generators:p(,n+p(,n+- split off clusters from n/+p(,n+0– Missed/combined from 0 decay
All phase space distributions at the moment!’) :
p(,n+’) : Analysis results
N.B
. K
inem
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eje
ct
backg
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rela
xed
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ese p
lots
!!ExperimentSimulated n+Simulated n+
Simulated no
Mmass of the mass of the system recoiling system recoiling
from the pionfrom the pionminusminus the neutron the neutron
massmass
M M
M M
p(,n+’) : Analysis results
ExperimentSimulated n+Simulated n+
Simulated no
p(,n+’) : Linear asymmetry E= 360 ± 20 MeV
CM = 0o-70o
CM = 70o-110o
CM = 110o-180o
= 50-80 MeV = 80-110 MeV
= 110-140 MeV
p(,n+’) : Linear asymmetry E=420 ± 20 MeV = 50-80 MeV = 80-110
MeV = 110-140 MeV
CM = 0o-70o
CM = 70o-110o
CM = 110o-180o
E = 320 ±20 MeV
E = 360 ±20 MeV
E = 420 ±20 MeV
o(CM) < 110o
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ear
Asym
metr
y
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metr
y
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metr
y p(,n+’) : Analysis results (Linear Asymmetry)
Unitary model (=2)
Unitary model normalised to agreein soft photon limit
Rescattering not included
E = 320 ±20 MeV
E = 360 ±20 MeV
E = 420 ±20 MeV
o(CM) < 70o
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Asym
metr
y
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metr
y
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Asym
metr
y p(,n+’) : Analysis results (Linear Asymmetry)
Unitary model (=2)
Unitary model normalised to agreein soft photon limit
Rescattering not included
E = 320 ±20 MeV
E = 360 ±20 MeV
E = 420 ±20 MeV
o(CM) < 180o
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ear
Asym
metr
y
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Asym
metr
y
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y p(,n+’) : Analysis results (Linear Asymmetry)
Unitary model (=2)
Unitary model normalised to agreein soft photon limit
Rescattering not included
p(,n+’) : Helicity dependence E=420 ± 20 MeV
CM = 0o-70o
CM = 70o-110o
CM = 110o-180o
= 50-90 MeV = 90-130 MeV
= 130-170 MeV
in CM framez = beam
y = x beam
= 50-90 MeV = 90-130 MeV
= 130-170 MeV
CM = 0o-70o
CM = 70o-110o
CM = 110o-180o
p(,n+’) : Helicity dependence E=460 ± 20 MeV
CM = 0o-70o
CM = 70o-110o
CM = 110o-180o
= 50-90 MeV = 90-130 MeV
= 130-170 MeV
p(,n+’) : Helicity dependence E=620 ± 20 MeV
p(,n+’) : Analysis results (Helicity dependence)
Helicity shows sin (dependence
Assumption:Fit distributions with sin() - extract amplitude to give helicity asymmetry at phi =90o
p(,n+’) : Analysis results (Helicity dependence)
Unitary model = 1 = 3 = 5
Experimental data:E = 420±20 MeVAll (CM)(CM) = 90o
CM = 110o-180o
CM = 70o-110oCM = 0o-70o
Unitary model integratedover appropriate (CM) ranges
(at fixed (CM) = 90o)
cir
c
cir
c
cir
c
p(,n+’) : Analysis results (Helicity dependence)
Unitary model = 1 = 3 = 5
Experimental data:E = 470±20 MeVAll (CM)(CM) = 90o
CM = 110o-180o
CM = 70o-110oCM = 0o-70o
Unitary model integratedover appropriate (CM) ranges
(at fixed (CM) = 90o)
cir
c
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c
cir
c
Summary
• We see a promisingly clean p(,n+’) signal
• Extracted linear polarisation observables will give important constraints on the theoretical modelling of radiative pion photoproduction
• Helicity asymmetry may show promising additional route to gain sensitivity to MDM - future dedicated beamtime ?
• Need to pass theoretical predictions through detector acceptance before publication (Unitary, CEFT?)
p(,n+’) : Analysis results
E = 470±20 MeV(CM) = 90±??o
(CM) = 90o
Unitary model = 1 = 3 = 5
CM = 0o-70o CM = 70o-110o
CM = 110o-180o Unitary model
integratedover appropriate (CM) ranges
p(,n+’) : Analysis results
Only keep data which haveoverall p(,n+’) 4-momentum
with confidence level > 0.1
All plots: E = 400 ± 20 MeV
Importance of MDM determination of (1232)
Present knowledge
CB@MAMI
Outline
● Motivation
● Count rate estimate
● n (Deuterium data)
● + detection – preliminary analysis of experimental data
Count rate estimate● Detection efficiencies +
~25% n~30% ~90%
(p0 0~85% p~70% ~90% )
● Electron count rate 5x105 s-1MeV-1
● Tagging efficiency ~50%
● Tagged photon flux 2.5x105 s-1MeV-1
● 5cm long proton target 2.1x1023 cm-2
● Data acquisition live time ~70%
● d/dE ~0.5 nb/MeV
● Total count rate ~0.7x105 events (with '=30-150 MeV Eg=340-490 MeV)
p(,n+’) : Analysis results (Helicity dependence)
Unitary model = 1 = 3 = 5
E = 420±20 MeV(CM) = 90 ±?? o
(CM) = 90o
CM = 110o-180o
CM = 70o-110oCM = 0o-70o
Unitary model integratedover appropriate (CM) ranges
+ detection in the Crystal Ball : Tracker & Particle-ID detector
~ 1.5o
~ 1.3o
• Two cylindrical wire chambers• 480 anode wires, 320 strips
2mm thickEJ204 scintillator
320m
m
p(,n+’) : Analysis results
E(MeV)
(b
arn
s)*
10
-6A
ccep
tan
ce x
10
-3
E(MeV)
E(MeV)E(MeV)
Accep
tan
ce
Accep
tan
ce x
10
-3
CB – data analysis parameters ● Threshold for cluster finding = 5 MeV
● Individual crystal threshold given by TDC (~1.5 MeV).
● Do not include clusters near to edge of CB - 30 - 150 deg
● Require PID hit within =±10 deg of cluster centre
● 2-D region cut on plot of PID energy versus CB cluster energy
Energy of cluster in CB(MeV)E
nerg
y de
posi
ted
in P
ID
Pion cut
Protons
MWPC & Particle-ID in situ
p(,n+’) : Analysis results
E = 470±20 MeV(CM) = 90±??o
(CM) = 90o
Unitary model = 1 = 3 = 5
CM = 0o-70o CM = 70o-110o
CM = 110o-180o Unitary model
integratedover appropriate (CM) ranges
+ - Selection of energy tagged events
● Use two-body kinematics + p → n + +
● Select n and + events back-to-back in phi plane
● Calculate + energy from pion angleand E
●Note that wire chamber tracking NOT included – uncertainty from reaction vertex
Good angular and energy resolution, close to 4acceptance
Setup at MAMI
Tracker & Particle-ID
GeV)
~41cm
~25cm
sin
Preliminary + signals
● Ecalculated – E
Measured
● No restriction on shower size
0-2525-5050-7575-100
100-125125-150150-175175-200
Preliminary + signals
● Ecalculated – E
Measured
● 4 or less crystals in the + shower
0-2525-5050-7575-100
100-125125-150150-175175-200
Preliminary + signals
● Ecalculated – E
Measured
● 2 or less crystals in the + shower
0-2525-5050-7575-100
100-125125-150150-175175-200
Energy resolution
●Includes uncertainties in reaction vertex, energy loss … as well as intrinsic CB resolution
Fraction with good energy determination
●Look at fraction of events within
Conclusions
●+ p → n + + events identified
● Energy tagged + events indicate CB gives reasonable energy signal
● MWPC software now implemented – further studies
● Develop improved shower shape algorithm which exploits correlation of energy deposits and shape in pion induced shower.
● Look at sampling after pulse - see time dependence of positron decays?
Magnetic moment of the + via the + p n + + + ' reaction
Daniel Watts – University of EdinburghPh.D student Richard Codling – University of Glasgow
p n
+
Preliminary + signals in CB
●Plot Ecalculated - E
Measured
● Shift of peak - energy losses?
● Simple shower shape restrictions give noticeable effect on response shape
● Development of better shower algorithms underway
No. cryst <4 No. cryst < 16
0-2525-5050-7575-100
100-125125-150150-175175-200
Michel spectrum
+ - Comparison of calculated and measured energies
● Rough tagger random subtraction included
● All angles summed over
Incident + energy (GeV)
Hig
hest
clu
ster
ene
rgy
(GeV
)
No restriction on shower sizeNcryst<3 & no neighbours
+ decay
Nuclear interaction
Geant simulation: + signals in the CB
Theoretical background● m - quark spins & currents.
● Test validity of theoretical hadron description in NPQCD
● Long lived particles - precession in B-field
● Short lived - Radiative decay
● Pioneered in p++p D++ D++g'
● TAPS@MAMI - proof of principle g+p D+ D+g' pp0
Energy
s
pp+
Theory mD+ / m
N
LQCD 2.20 0.4QCDSR 2.19 0.5Latt 2.26 0.31XPT 2.40 0.2RQM 2.38 NQM 2.73XQSM 2.19XB 0.75
Theoretical Background
● Reaction has important background terms
● Different for pp0 and np+ final states
● Simultaneous measurement also tests pN rescattering
D terms
Born terms
Black lines : g + p ->p + p0 + g' Blue lines : g + p ->n + p+ + g'
w exchange
Theoretical model● Effective lagrangian
● Integral s : sensitivity to mD+
● Kinematics can suppress brem.
● Simultaneous unitarised description
Experiment● CB : 672 * 0.5m NaI
TAPS : 540 * 0.25m BaF2
● Tracker: MWPC
● PID: 2mm plastic scint. Barrel
● >1 cluster trigger: Measure g + p ->n + p+ + g' and g + p ->p + p0 + g' (Expt. A2-1-02) simultaneously.
Neutron detection
● Neutron detection capabilities of CB established (BNL-AGS) p- p p0n
● en~10-40%
● Dqn< 10o; Df
n< 20o
Stanislaus, Koetke et. al., NIM
A462 463 (2001)
p+ decay● p+ m+ + nm (~26
ns)e+ n
e nm (~2 ms)
● NaI: t ~1ms tr~
0.1ms
Energy of positron (MeV)500
e+
n
en
m
Michel spectrum
No.
of
coun
ts
e+ ne nm (~2 ms)
+ signals in Crystal Ball
● 150 MeV + - isotropic
● Spectra sensitive to time over which energy deposits are recorded
● See signal at Tp.......but with
background
Michel spectrumt~infinite
Energy deposited in Ball (GeV)
Nuclear intn.+ absorbed
Nuclear intn.
t<1ms!!
0 150 300
4000
14000
0 150 300
Neutron detection in the CB
Neutron kinetic energy (MeV)
Dete
ctio
n e
ffici
en
cy
Neutron difference (deg)
~5o
E = 320 ±20 MeV
E = 360 ±20 MeV
E = 420 ±20 MeV
o(CM) < 70o
o(CM) < 110o
o(CM) < 180o
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y p(,n+’) : Analysis results (Linear Asymmetry)
p+ signals in CB
● Simple cut on shower size. N
cryst (HE clust) <3 &
No neighbouring clusters
● Get peak with manageable background!
● Eff ~25% at 100MeV
Summary
● Simultaneous measurement of np+g' with pp0g' improves confidence in model dependent extraction of mD+
● Measurement requires no extra beam time
● Establishing p+ detection capabilities of CB - opens perspectives for other future measurements