0

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