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p 0. Cooler CSB. Observation of dd  απ 0. Ed Stephenson Indiana University Cyclotron Facility. CSB –VII Trento, Italy June 13-17, 2005. Review of the experiment. Getting d + d → 4 He + π 0 right. Ed Stephenson Indiana University Cyclotron Facility Bloomington, IN

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P 0

p0

Cooler CSB

Observation of ddαπ0

Ed Stephenson

Indiana University Cyclotron Facility

CSB–VII

Trento, Italy

June 13-17, 2005

Review of the experiment


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Getting d + d → 4He + π0 right

Ed Stephenson

Indiana University Cyclotron Facility

Bloomington, IN

Workshop on Charge Symmetry Breaking

Trento

June 13-17, 2005

Before you start, remember the history…

suggested by Lapidus [JETP 4, 740 (’57)]

review by Banaigs [PRL 58, 1922 (’87)]

upper limit

at 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


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… thanks to Andy Bacher, Mark Pickar, and Georg Berg

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)

Crucial features:

Pb-glass has low backgroud

Windowless target

Channel with good TOF

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 mA

Luminosity = 2.7 x 1031 /cm2/s

Expected rate ~ 5 /day


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  • COOLER-CSB MAGNETIC CHANNEL

  • and Pb-GLASS ARRAYS

  • separate all 4He for total cross section measurement

  • determine 4He 4-momentum (using TOF and position)

  • detect one or both decay g’s from p0 in Pb-glass array

Scintillators

DE-2

E

Veto-1

Veto-2

Pb-glass array

256 detectors

from IUCF and

ANL (Spinka) +

scintillators for

cosmic trigger

Scintillator

DE-1

Focussing

Quads

MWPC

MWPCs

228.5 or 231.8 MeV

deuteron beam

Target

D2 jet

20 Septum Magnet

Separation Magnet

removes 4He at 12.5

from beam at 6

Actual

Pb-glass

arrangement


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SEPARATION OF ap0 AND agg EVENTS

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.

Major physics

background is from

double

radiative

capture.

MWPC

spacing

= 2 mm

Y-position (cm)

[Monte Carlo simulation for

illustration. Experimental

errors included.]

ap0 peak

sTOT = 10 pb

MWPC1 X-position (cm)

agg prediction

from Gårdestig

agg

background

(16 pb)

needed TOF

resolution

sGAUSS = 100 ps

missing mass (MeV)

Difference is due to

acceptance of channel.

Acceptance widths are:

angle = 70 mr (H and V)

momentum = 10%

Cutoff controlled

by available

energy above

threshold.

Time of Flight (ΔE1 - ΔE2) (ns)

.


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COMMISSIONING THE SYSTEM using p+d  3He+π0 at 199.4 MeV

3He events readily identified

by channel scintillators.

Pb-glass energy sums

nearest neighbors.

It is important to

identify loss

mechanisms.

Recoil cone on first MWPC

Construction of missing

mass from TOF and

position on MWPC.

data

FWHM

= 240 keV

Monte-

Carlo

130

134

138

NOTE: Main losses in

channel from random veto,

multiple scattering, and

MWPC multiple hits.

Response matched to

GEANT model. Efficiency

(~ 1/3) known to 3%.

Channel time of flight


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IDENTIFICATION OF 4He

IN THE CHANNEL

[online spectra for 5-hour run]

DE2

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.

DE1-C

E

We absolutely need

coincidence with the

Pb-glass (decay g)

to extract any signal

at all.

The 4He flux, most likely from

(d,α) reactions, is smooth in

momentum and angle. It

represents the part of phase

space sampled by the channel.

DE2


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SINGLE AND DOUBLE GAMMA SIGNALS

data for all of July run

Beam left-side array

A single g may be

difficult to extract.

But select on the

similar locus on the

other side of the

beam, and the

signal becomes

clean.

corrected g time

keep above here

g cluster energy

We will require two g’s.

List of requirements:

> correct PID position in channel scintillator energy

> correct range of TOF values

> correct Pb-glass cluster energies and corrected times

Many g’s come from

beam halo hitting

downstream septum.


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OTHER ITEMS

Stuff you have to get right!

Energy of Cooler beam known from ring

circumference and RF frequency (~ 16 keV)

3He cone opening angle (deg)

Calculation of He momentum depends on

good model of energy loss in channel. This

is also needed to set channel magnets.

RF frequency (MHz)

Calculation of time of flight required knowing

the time offsets for each scintillator PMT and

tracking changes through the experiment.

Final adjustments were made in replay.

Cooler circumference (m)

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 mass

provide two cross sections to check energy dependence

(Limits were luminosity, rate handling, available time.)

average

circumference

= 86.786

± 0.003 m


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For good resolution, we

need FWHM ~ 0.2 ns.

Time Stability Problem

PMT signal transit time

drifts and occasionally

jumps as the tube ages,

responding to heat.

A narrow peak helps p0 separation statistically.

DE2

Timing is affected

when people change

PMT voltage or swap

other equipment.

There are 6 PMTs

used for TOF.

Mean-timing the

ones for DE2

leaves 4 free

time parameters.

A

This is also connected

to missing mass

reconstruction errors

arising from 6° magnet

dispersion, pulse height,

and position effects.

B

C

D

DE1


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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

E

XY-1

Resulting TOF peaks

DE1 scintillator:

A

d

p

B

DE2

XY-2

C

XY-3

D


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Results for June run:

1 ns


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Calibrating the luminosity of the IUCF Cooler

PLAN: Monitor with d+d elastic.

Measure ratio of d+d cross

section to d+p (known) with

molecular HD target.

44°

25°

beam

deuteron

telescope

(present only

for calibration)

tapered/displaced

scintillator pair for

added position info.

Reference d+p

cross sections:

thesis of Karsten

Ermisch, KVI,

Groningen (‘03).

dσ/dΩ

(mb/sr)

NOTE:

Target distribution monitored

using position sensitive silicon

detector looking at recoil

deuterons from small-angle

scattering.

Detector acceptance determined

using Monte-Carlo simulations.

dot = 108 MeV

circle = 120 MeV

X = 135 MeV

line = adopted

cross section

at 116 MeV

θc.m.


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Recent measurements by the Japanese confirm their old cross

section values at 135 MeV and disagree with the data from the KVI.

Japanese data

original d-beam data from RIKEN

remeasurements from RIKEN and RCNP

KVI data

.

An independent measurement is needed !


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Forward scintillator – silicon system

position-sensitive

silicon detector

distinguish H from D by

pulse height in silicon

beam

target

½-inch copper

absorbers

delta-

E

E

H

silicon

position

D

E energy

Position becomes template

for target distribution.

Issues include reaction losses

and multiple scattering.


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Detail on second luminosity monitoring system

oppositely tapered

scintillators for

X-position

beam

two halves displaced

vertically to check

vertical centering

results not satisfactory,

relied on transit

alignment


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Scintillator spectra:

(44° – 44° coincidence)

right

F – B

F + B

x =

xL by xR gated on deuterons

44° scintillator, back vs. front pulse height

(zero suppressed to remove no-hits)

beam

z-position

angle

left

position

span

angle

beam z-position

deuterons

cut

protons


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RESULTS

Events in these spectra must satisfy:

correct pulse height in channel scintillators

usable wire chamber signals

good Pb-glass pulse height and timing

228.5 MeV

66 events

σTOT = 12.7 ± 2.2 pb

Background shape based on calculated

double radiative capture, corrected by

empirical channel acceptance using 4He.

Cross sections are consistent

with S-wave pion production.

σTOT/η

231.8 MeV

50 events

Systematic errors are

6.6% in normalization.

100

σTOT = 15.1

± 3.1 pb

average

Peaks give the correct

π0 mass with 60 keV

error.

50

Spectra are essentially

free of random

background.

η = pπ/mπ

0

0.1

0

0.2

missing mass (MeV)


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EXISTENCE?

For the candidate events, check to see whether there is any cone.

XY-1 position

T = 228.5 MeV, qmax = 1.20°

T = 231.8 MeV, qmax = 1.75°


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EXISTENCE?

For the candidate events, check to see whether there is any cone.

XY-1 position

T = 228.5 MeV, qmax = 1.20°

T = 231.8 MeV, qmax = 1.75°

Circles with these centers also minimize the missing mass width.


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missing mass (MeV  100)

T = 228.5 MeV

T = 231.8 MeV

135

MeV

raw

TOF

IS IT CORRECT?

The missing mass should be

independent of the TOF.

A

B

In fact, the time adjustments

are made separately for

each segment of DE1.

C

D


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Experimental (active):

Theoretical:

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

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

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):

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 intent

post-doc

technical manager

student

Underline did June/July shift work


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