Measurements of Total π - -p Charge Exchange Cross Sections at Low Energies

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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 p

description

Pion-nucleon scattering at low energies Johannes Breitschopf , Physikalisches Institut Universität Tübingen. Measurements of Total π - -p Charge Exchange Cross Sections at Low Energies. TRIUMF: differential cross sections at 20 – 68 MeV → Roman Tacik PSI: - PowerPoint PPT Presentation

Transcript of Measurements of Total π - -p Charge Exchange Cross Sections at Low Energies

Page 1: Measurements of Total  π - -p Charge Exchange Cross Sections at Low Energies

• 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

Page 2: Measurements of Total  π - -p Charge Exchange Cross Sections at Low Energies

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

Page 3: Measurements of Total  π - -p Charge Exchange Cross Sections at Low Energies

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

Page 4: Measurements of Total  π - -p Charge Exchange Cross Sections at Low Energies

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.

Page 5: Measurements of Total  π - -p Charge Exchange Cross Sections at Low Energies

Results A_y pi+

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

KH80 SAID FA02

+p

Page 6: Measurements of Total  π - -p Charge Exchange Cross Sections at Low Energies

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

KH80 SAID FA02

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

-p

Page 7: Measurements of Total  π - -p Charge Exchange Cross Sections at Low Energies

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

Page 8: Measurements of Total  π - -p Charge Exchange Cross Sections at Low Energies

Test of isospin breakingTest of isospin breaking

20

AAA elastic

App

App

π p elastic scattering

00 Anp

SCX

SCXA0

Page 9: Measurements of Total  π - -p Charge Exchange Cross Sections at Low Energies

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

Page 10: Measurements of Total  π - -p Charge Exchange Cross Sections at Low Energies

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:

Page 11: Measurements of Total  π - -p Charge Exchange Cross Sections at Low Energies

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)

Page 12: Measurements of Total  π - -p Charge Exchange Cross Sections at Low Energies

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

Page 13: Measurements of Total  π - -p Charge Exchange Cross Sections at Low Energies

Corretions_all

Cor

rect

ion

s fo

r d

etec

tion

of

neu

tral

s

GE

AN

T3

πE3

πM1

Page 14: Measurements of Total  π - -p Charge Exchange Cross Sections at Low Energies

Pre

limin

ary

resu

lts

from

πM

1 ch

ann

el

Page 15: Measurements of Total  π - -p Charge Exchange Cross Sections at Low Energies

Per

cen

t d

evia

tion

fro

m S

AID

FA

02

Page 16: Measurements of Total  π - -p Charge Exchange Cross Sections at Low Energies

Com

par

ison

wit

h o

ther

dat

a an

d p

red

icti

ons

Page 17: Measurements of Total  π - -p Charge Exchange Cross Sections at Low Energies

Per

cen

t d

evia

tion

fro

m S

AID

FA

02 in

co

mp

aris

on w

ith

oth

er d

ata

Page 18: Measurements of Total  π - -p Charge Exchange Cross Sections at Low Energies

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

Page 19: Measurements of Total  π - -p Charge Exchange Cross Sections at Low Energies

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

Page 20: Measurements of Total  π - -p Charge Exchange Cross Sections at Low Energies

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