• 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

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

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

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.

Results A_y pi+

Wieser et al., PRC54 (1995)LEPS/PSI Phys. Lett. B588 (2004) 155

KH80 SAID FA02

+p

LEPS/PSI Phys. Lett. B588 (2004) 155

KH80 SAID FA02

J. D. Patterson et al., Pys. Rev. C66 (2002) 025207

-p

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

Test of isospin breakingTest of isospin breaking

20

AAA elastic

App

App

π p elastic scattering

00 Anp

SCX

SCXA0

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

→

←

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:

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)

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

Corretions_all

Cor

rect

ion

s fo

r d

etec

tion

of

neu

tral

s

GE

AN

T3

πE3

πM1

Pre

limin

ary

resu

lts

from

πM

1 ch

ann

el

Per

cen

t d

evia

tion

fro

m S

AID

FA

02

Com

par

ison

wit

h o

ther

dat

a an

d p

red

icti

ons

Per

cen

t d

evia

tion

fro

m S

AID

FA

02 in

co

mp

aris

on w

ith

oth

er d

ata

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

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

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