00 cooler csb observation of dd απ 0 csb–vii trento, italy june 13-17, 2005 ed stephenson...
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Cooler CSBObservation of ddαπ0
CSB–VIITrento, Italy
June 13-17, 2005
Ed StephensonIndiana University Cyclotron Facility
Review of the experiment
Getting d + d → 4He + π0 rightEd StephensonIndiana University Cyclotron FacilityBloomington, IN
Workshop on Charge Symmetry BreakingTrentoJune 13-17, 2005
Before you start, remember the history…
suggested by Lapidus [JETP 4, 740 (’57)]
review by Banaigs [PRL 58, 1922 (’87)]
upper limitat 0.8 GeV
positive claim by Goldzahl [NP A 533, 675 (’91)]
double radiative capture by Dobrokhotov [PRL 83, 5246 (’99)}
Be prepared for… very low cross sections ( ~ pb) interference from double radiative capture
PLAN
Search just above threshold (225.5 MeV) (No other π channel open for d+d.) Capture forward-going 4He. Pb-glass arrays for π0 γγ. Efficiency on two sides ~ 1/3. Insensitive to other products (γbeam = 0.51)
6 bend in Cooler straight section Target upstream, surrounded by Pb-glass Magnetic channel to catch 4He (~100 MeV) Reconstruct kinematics from channel time of flight and position. (Pb-glass energy and angle too uncertain for π0 reconstruction. αγγ looks the same.)
Target density = 3.1 x 1015
Stored current = 1.4 mALuminosity = 2.7 x 1031 /cm2/s
Expected rate ~ 5 /day
… thanks to Andy Bacher, Mark Pickar, and Georg Berg
Crucial features:Pb-glass has low backgroudWindowless targetChannel with good TOF
Target
D2 jet
Pb-glass array
256 detectorsfrom IUCF andANL (Spinka) +scintillators forcosmic trigger
228.5 or 231.8 MeVdeuteron beam
Separation Magnet
removes 4He at 12.5from beam at 6
20 Septum Magnet
FocussingQuads
MWPCs
Scintillator
E-1
Scintillators
E-2EVeto-1Veto-2
MWPC
COOLER-CSB MAGNETIC CHANNELand Pb-GLASS ARRAYS
•separate all 4He for total cross section measurement•determine 4He 4-momentum (using TOF and position)•detect one or both decay ’s from 0 in Pb-glass array
ActualPb-glassarrangement
SEPARATION OF 0 AND EVENTS
MWPC1 X-position (cm)
Y-p
osi
tion
(c
m)
Time of Flight (ΔE1 - ΔE2) (ns)
needed TOFresolution
GAUSS = 100 ps
MWPCspacing= 2 mm
Calculate missing mass from the four-momentum measured in the magnetic channel alone, using TOF for z-axis momentum and MWPC X and Y for transverse momentum.
[Monte Carlo simulation for illustration. Experimental errors included.] 0 peak
TOT = 10 pb
background(16 pb)
predictionfrom Gårdestig
Difference is due to acceptance of channel.Acceptance widths are: angle = 70 mr (H and V) momentum = 10%
missing mass (MeV)
Cutoff controlledby availableenergy abovethreshold.
.
Major physicsbackground is from double radiative capture.
COMMISSIONING THE SYSTEM using p+d 3He+π0 at 199.4 MeV3He events readily identifiedby channel scintillators.
Recoil cone on first MWPC
Channel time of flight
Construction of missingmass from TOF andposition on MWPC.
FWHM = 240 keV
130 134 138
Pb-glass energy sumsnearest neighbors.
Response matched toGEANT model. Efficiency(~ 1/3) known to 3%.
data
Monte-Carlo
NOTE: Main losses inchannel from random veto,multiple scattering, andMWPC multiple hits.
It is important toidentify lossmechanisms.
IDENTIFICATION OF 4He IN THE CHANNELE2
E
E1-C
E2
[online spectra for 5-hour run]
We absolutely needcoincidence with thePb-glass (decay )to extract any signalat all.
Proton rate from breakup ~ 105 /s.Handle this with: veto longer range protons set timing to miss most protons reduce MWPC voltage to keep Z=1 tracks below threshold divide ΔE-1 into four quadrants
Set windows around 4He group.Rate still 103 too high.
The 4He flux, most likely from(d,α) reactions, is smooth inmomentum and angle. Itrepresents the part of phase space sampled by the channel.
SINGLE AND DOUBLE GAMMA SIGNALSdata for all of July run
corr
ecte
d
time
cluster energy
A single may be difficult to extract.
But select on thesimilar locus on theother side of thebeam, and thesignal becomes clean.
Beam left-side array
Many ’s come frombeam halo hittingdownstream septum.
List of requirements: > correct PID position in channel scintillator energy > correct range of TOF values > correct Pb-glass cluster energies and corrected times
We will require two ’s.
keep above here
RF frequency (MHz)
Co
ole
r ci
rcu
mfe
ren
ce (
m)
averagecircumference= 86.786 ± 0.003 m
3H
e c
on
e o
pe
nin
g a
ng
le (
de
g)OTHER ITEMS
Stuff you have to get right!
Energy of Cooler beam known from ringcircumference and RF frequency (~ 16 keV)
Calculation of He momentum depends ongood model of energy loss in channel. Thisis also needed to set channel magnets.
Calculation of time of flight required knowingthe time offsets for each scintillator PMT andtracking changes through the experiment.Final adjustments were made in replay.
Run plan: started in June at 228.5 MeV to keep cone in channel during 1-week break decided to raise energy to 231.8 MeV
demonstrate that peak stayed at pion massprovide two cross sections to check energy dependence
(Limits were luminosity, rate handling, available time.)
Time Stability ProblemFor good resolution, we need FWHM ~ 0.2 ns.
PMT signal transit time drifts and occasionallyjumps as the tube ages, responding to heat.
Timing is affected when people change PMT voltage or swap other equipment.
This is also connected to missing massreconstruction errors arising from 6° magnetdispersion, pulse height, and position effects.
A narrow peak helps 0 separation statistically.
E1
E2
AB
CD
There are 6 PMTsused for TOF.
Mean-timing theones for E2leaves 4 freetime parameters.
To make run-by-run corrections to TOF, we need a marker.We use deuterons that stop and the back of the E scintillator.
Choose Energy Choose Trajectory
deuteron gate
p
d
E2
E
XY-1
XY-2
XY-3
Resulting TOF peaksE1 scintillator:
A
B
C
D
Results for June run:
1 ns
beam
44° 25°
deuterontelescope(present onlyfor calibration)
tapered/displacedscintillator pair foradded position info.
Calibrating the luminosity of the IUCF Cooler
PLAN: Monitor with d+d elastic.Measure ratio of d+d crosssection to d+p (known) withmolecular HD target.
Reference d+pcross sections:thesis of KarstenErmisch, KVI,Groningen (‘03).
dot = 108 MeVcircle = 120 MeVX = 135 MeV
line = adoptedcross sectionat 116 MeV
NOTE: Target distribution monitoredusing position sensitive silicondetector looking at recoildeuterons from small-anglescattering. Detector acceptance determinedusing Monte-Carlo simulations.
dσ/dΩ(mb/sr)
θc.m.
Recent measurements by the Japanese confirm their old crosssection values at 135 MeV and disagree with the data from the KVI.
KVI dataJapanese data original d-beam data from RIKEN remeasurements from RIKEN and RCNP.
An independent measurement is needed !
beam
target
position-sensitivesilicon detector
½-inch copperabsorbers delta-
EE
siliconposition E energy
Forward scintillator – silicon system
distinguish H from D bypulse height in silicon
H
D
Issues include reaction losses and multiple scattering.
Position becomes templatefor target distribution.
beam
Detail on second luminosity monitoring system
oppositely taperedscintillators forX-position
two halves displacedvertically to checkvertical centering
results not satisfactory,relied on transitalignment
protons
deuterons
position span
Scintillator spectra:(44° – 44° coincidence)
44° scintillator, back vs. front pulse height(zero suppressed to remove no-hits)
F – BF + B
x =
angle beamz-position
angle beam z-position
cut
left
right
xL by xR gated on deuterons
average
0 0.1 0.20
50
100
η = pπ/mπ
σTOT/η
RESULTS
231.8 MeV50 events
σTOT = 15.1 ± 3.1 pb
228.5 MeV66 events
σTOT = 12.7 ± 2.2 pb
missing mass (MeV)
Events in these spectra must satisfy: correct pulse height in channel scintillators usable wire chamber signals good Pb-glass pulse height and timing
Background shape based on calculateddouble radiative capture, corrected byempirical channel acceptance using 4He.
Cross sections are consistentwith S-wave pion production.
Spectra are essentiallyfree of random background.
Systematic errors are6.6% in normalization.
Peaks give the correctπ0 mass with 60 keVerror.
XY-1 position
T = 228.5 MeV, max = 1.20° T = 231.8 MeV, max = 1.75°
EXISTENCE? For the candidate events, check to see whether there is any cone.
XY-1 position
T = 228.5 MeV, max = 1.20° T = 231.8 MeV, max = 1.75°
EXISTENCE? For the candidate events, check to see whether there is any cone.
Circles with these centers also minimize the missing mass width.
missing mass (MeV 100)
rawTOF
135MeV
IS IT CORRECT? The missing mass should be independent of the TOF.
In fact, the time adjustmentsare made separately for each segment of E1.
A B
C D
T = 231.8 MeVT = 228.5 MeV
V. Anferov, G.P.A. Berg, and C.C. Foster,Indiana University Cyclotron Facility, Bloomington, IN 47408
B. Chujko, A. Kuznetsov, V. Medvedev, D. Patalahka, A. Prudkoglyad, and P.A. Semenov, Institute for High Energy Physics, Protvino, Moscow Region, Russia 142284
S. Shastry, State University of New York, Plattsburgh, NY 12901
spokesperson for CE-82 and letter of intentpost-doctechnical managerstudent
Experimental (active):
C. Allgower, A.D. Bacher, C. Lavelle, H. Nann, J. Olmsted, T. Rinckel, and E.J. Stephenson, Indiana University Cyclotron Facility, Bloomington, IN 47408
M.A. Pickar, Minnesota State University at Mankato, Mankato, MN 56002
P.V. Pancella, Western Michigan University, Kalamazoo, MI 49001
A. Smith, Hillsdale College, Hillsdale, MI 49242
H.M. Spinka, Argonne National Laboratory, Argonne, IL 60439
J. Rapaport, Ohio University, Athens, OH 45701
Technical support:
J. Doskow, G. East, W. Fox, D. Friesel, R.E. Pollock, T. Sloan, and K. Solberg, Indiana University Cyclotron Facility, Bloomington, IN 47408
Experiment (historical):
Underline did June/July shift work
Theoretical:
Antonio Fonseca, Lisbon
Anders Gardestig, Indiana
Christoph Hanhart, Juelich
Chuck Horowitz, Indiana
Jerry Miller, Washington
Fred Myhrer, South Carolina
Jouni Niskanen, Helsinki
Andreas Nogga, Arizona
Bira van Kolck, Arizona