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p( g ,n p + g / ) reaction measured with the Crystal Ball at MAMI. Dan Watts, Derek Glazier University of Edinburgh Richard Codling, John Annand University of Glasgow. Crystal Ball Collaboration meeting, Mainz, 2007. Why measure p( g ,n p + g ’ ) ??. Independent test of - PowerPoint PPT Presentation
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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
ati
c c
uts
to r
eje
ct
backg
rou
nd
rela
xed
in
th
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
Lin
ear
Asym
metr
y
Lin
ear
Asym
metr
y
Lin
ear
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) < 70o
Lin
ear
Asym
metr
y
Lin
ear
Asym
metr
y
Lin
ear
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
Lin
ear
Asym
metr
y
Lin
ear
Asym
metr
y
Lin
ear
Asym
metr
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
cir
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
Lin
ear
Asym
metr
y
Lin
ear
Asym
metr
y
Lin
ear
Asym
metr
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
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