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• TRIUMF:
differential cross sections at 20 – 68 MeV→ Roman Tacik
• PSI:
1. Analyzing powers of scattering at 45 – 90 MeV
2. Total SCX cross sections at 40 – 250 MeV
Measurements of Total π--p Charge Exchange Cross Sections at Low Energies
p
Pion-nucleon scattering at low energies
Johannes Breitschopf , Physikalisches Institut Universität Tübingen
Aim: Reliable data base for π p scattering below 100 MeV
• σ-term • πNN coupling constant • strong isospin breaking
p
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A_y at PSI with LEPS
PyA 1
Analyzing power measurement at PSI: Principle
Analyzing power measurement at PSI: Principle
Background suppression:
Active polarized target
Background suppression:
Active polarized target
T
Beam
±p
Polarized Proton Target
Detector+
-
p p
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Active targetActive polarized targetActive polarized target
B. van den Brandt et al., NIM A446 (2000)
BC 800 lightguide
quarz-adapter
scintillator
PM
800m
m,
12m
m
18 mm
18 m
m
5 mm
Hel
mho
ltz
coil
s
targetcell / mixing chamber
wave-guide
light-guide
beam
3He/4He
4He
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Background suppressionActive polarized target for background suppressionActive polarized target for background suppression
π+ scattering at Tπ = 68.6 MeV, θcm = 81.3°
Focal plane spectrum
1. without constraint
2.-4. with increasing size of active target signal.
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Results A_y pi+
Wieser et al., PRC54 (1995)LEPS/PSI Phys. Lett. B588 (2004) 155
KH80 SAID FA02
+p
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LEPS/PSI Phys. Lett. B588 (2004) 155
KH80 SAID FA02
J. D. Patterson et al., Pys. Rev. C66 (2002) 025207
-p
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Total SCX cross sectionTotal cross section for π-p →π0n (SCX)
Δ-r
eson
ance
reg
ion
L
ow e
ner
gy r
egio
n
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Test of isospin breakingTest of isospin breaking
20
AAA elastic
App
App
π p elastic scattering
00 Anp
SCX
SCXA0
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Pri
nci
ple
of
Mea
sure
men
tP
rin
cip
le o
f ex
per
imen
t
4 π s
cin
till
atio
n d
etec
tor
I 0I
=I 0e
-ασ
π-
neu
tral
s: S
CX
π- p
π
0 n
π-
π-
bea
m d
efin
itio
nco
un
ters
T a r g e t
←
20 c
m
→
← 10 cm →
→ ←
2 m
m
7m
m
→
←
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Dat
a ac
qu
siti
on?
Dat
a ac
qu
isit
ion
CH2
58 2
70 4
14 p
ions
57 7
68 9
18
pion
s se
en i n
box
neut
rals
58
270
414
- 57
768
918
= 5
01 2
23 n
eutr
als
tran
smis
sion
0.99
1398
(12)
DA
Q:
All
para
met
ers
(TD
C, A
DC
, FA
DC
) ev
ent-
by-e
vent
(to
tal o
f 3.
5 T
B)
Typ
ical
exa
mpl
e:
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i = C, CH2 0 = empty targetα = target thickness
iieTTi
0
iii T
T0log1
)(22
1_ CCHtotalH
events Beam
events DetectedBeam on Transmissi
Typical target dimensions:3.5 cm x 4.0 cm x 7.6 mm (CH2) 3.5 cm x 4.0 cm x 4.5 mm (C)
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Detector and correctionsModeling of the detector in GEANT3
Corrections:GEANT 3 and 4
• detection of neutrals: γ’s (5.5%), n’s (2%), π0-Dalitz (1.2%)
• muons
In addition
• π - – capture
• randoms
•efficiencies
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Corretions_all
Cor
rect
ion
s fo
r d
etec
tion
of
neu
tral
s
GE
AN
T3
πE3
πM1
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Pre
limin
ary
resu
lts
from
πM
1 ch
ann
el
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Per
cen
t d
evia
tion
fro
m S
AID
FA
02
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Com
par
ison
wit
h o
ther
dat
a an
d p
red
icti
ons
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Per
cen
t d
evia
tion
fro
m S
AID
FA
02 in
co
mp
aris
on w
ith
oth
er d
ata
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Summary1
1. @PSI:
Analyzing powers 45 – 90 MeVR. Meier, M. Cröni et al.,Phys. Lett. B588 (2004) 155
p
Summary and outlook I
•No strong deviations from KH80 or SAID FA02.•Experimental data tend to be below predictions at the lowest energies.
Similar findings for @TRIUMF
J. D. Patterson et al., Phys. Rev. C66 (2002) 025207
p
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πE3 channel: 40 – 80 MeV
• Of particular interest for isospin breaking
Summary2Summary and outlook II
2. SCX @PSI: Total SCX cross sectionsTransmission on CH2 and C in event mode (3.5 TB)
πM1 channel: 60 – 250 MeV, ~ 2% statistical error ~ 1 – 2% systematical error
Findings (preliminary):
•Confirms Bugg et al. data•About 3% above Friedman et al. data •Excellent agreement with SAID SM95/FA02•Below KH80 up to 170 MeV
•Analysis in progress
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Collaboration
R. Meier, M. Cröni, R. Bilger, J. Breitschopf, H. Clement, H. Denz, J. Pätzold, G. J. Wagner
Physikalisches Institut, Univ. Tübingen, Tübingen, Germany
B. van den Brandt, P. Hautle, J. A. Konter, S. MangoPaul Scherrer Institut, Villigen, Switzerland
G. J. Hofman, M. PavanTRIUMF, Vancouver, British Columbia, Canada
J. Comfort Arizona State University, Tempe, Arizona, USA
K. FöhlSchool of Physics, Univ. of Edinburgh, UK
E. FriedmanRacah Inst. of Physics, The Hebrew University, Jerusalem, Israel
Analyzing powers Analyzing powers
J. Breitschopf, M. Bauer, H. Clement, M. Cröni, H. Denz, R. Meier, G.J. Wagner
Physikalisches Institut, Univ. Tübingen, Tübingen, Germany
E. FriedmanRacah Inst. of Physics, The Hebrew University, Jerusalem, Israel
E. GibsonCalifornia State University, Sacramento, USA
Supported by BMBF (06Tü9871) and DFG (European Gradudate School Basel – Tübingen)
SCXSCX