55. Jahrestagung der ÖPG, September 2005 Pionischer Wasserstoff: Präzisionsmessungen zur starken...

55. Jahrestagung der ÖPG, September 2005

Pionischer Wasserstoff: Präzisionsmessungen zur starken Wechselwirkung

J. MartonStefan Meyer Institut der ÖAW

on behalf of the Pionic Hydrogen Collaboration


Physics Goals

N coupling constant (using Goldberger Miyazawa Oehme sum rule)

pion-nucleon sigma term (measure of chiral symmetry breaking)

High precision values for the hadronic shift and width of the 1s ground state of pionic hydrogen

pion-nucleon scattering lengths (isoscalar, isovector) with an accuracy at the percent level

scattering lengths basis for comparison of changes in the nuclear medium


Pion-Nucleon Scattering Lengths

21

1

)(

a

aa

s

s

shift data from pionic hydrogen and deuterium, width from pionic hydrogen (Schröder et al.,2001)

)1(1

41

1e

h

ppBs

s arE

20

1

1 ))1()(1

1(8 0

h

npBs

s aPr

Q

E

>>> W. Thirring 1954


Electromagnetic Cascade of p

1observables:

shift and width

1s state

Pion decay~10-8 s slow compared to reaction rates

precise QED calculationsadvanced cascade theory

p is not an isolated system interaction with hydrogen


Principle of Set-Up

high stop density

high X - ray line yields

bright X - ray source

position & energy resolution

background reduction by analysis of CCD hit pattern

spherically bent Bragg crystal

ultimate energy resolution


SET-UP at PSI

crystal spectrometer

spherically bent crystals

CCD X-ray detector

2 3 matrix

X-ray tube

cryogenic target

cyclotron trap II


Experimental Method

Braggcrystal

CCD X-raydetector

Target and cyclotron trap


Cyclotron Trap with Target and Degraders

X - rays

beam

stop efficiencyfstop density 1% @ stp

109 /s

super-conducting split coil magnet


Spherically curved Bragg crystal

100 mm


Large - Area Focal Plane CCD Detector

N. Nelms et al., Nucl. Instr. Meth 484 (2002) 419

2 3 CCD 22 array

pixel size 40 m 40 m

600 600 pixels per chip

operated at – 100°C

150 eV @ 4 keVX 90%

image area

storage area

flexible boards

cooling (LN2)


high pion flux in E5 at PSI

p=112 MeV/c, ~ 109 -/s

cyclotron trap for small stop volume and high stopping efficiency

Light weight cryogenic target for wide density range

spherically bent Bragg crystals characterization by ECRIT X-ray source

position sensitive X-ray detection with CCD array: CCD-22 background reduction by shielding and pixel analysis of CCD data

calibration lines (pionic oxygen) measured in parallel

Features of the Experiment


πp Hadronic Shift and Width

e.m. transitionwithout strong

interaction

attractive shift

Goals: Shift 0.2% Width 1%

Molecular effects

Doppler broadeningCoulomb deexcitation

required resolution:1:100000

careful study ofsmall effects

Stability & Calibration

)1()1( .1 snpEsnpE electrmeass


extention of parameter space: measurements of shift and width with different

Doppler broadening of width to be measured with muonic hydrogen X-rays (no hadronic interaction)

Experimental Procedure

densities

X-ray transitions (4p-1s, 3p-1s, 2p-1s)

Investigations on

molecular effects

Coulomb transitions

effecting the width


H(3p-1s) energy no density dependence identified

1s = + 7.116 0.008 0.007 eV

EQED = ± 0.006 eV P. Indelicato, priv. comm.

piH shift

7,00

7,10

7,20

1 10 100 1000

density equivalent / bar

/ eV

previous experiment

LH2

previous experiment ETHZ-PSI H.-Ch.Schröder et al.

Eur.Phys.J.C 1(2001)473

Density Effect ?

Molecular formation ("Vesman“ mechanism)

p + H2 [(pp) p] ee


Electron Cyclotron Resonance Ion Trap

cyclotron trap (4) + hexapole magnet (2)

(D. Hitz et al., Rev. Sci. Instr., 71 (2000) 1116)

large mirror ratioBmax / Bmin !

argon / oxygen (1/9)1.410-6 mbar

HF 6.4 Ghz

Response Function

H- and He-like electronic atomsTion 5 eV "cold" plasma

narrow X-ray transitions

X = 10 - 40 meV

high X-ray intensity: short measuring time

First plasma inside ECRIT


ECRIT and Crystal SpectrometerD.F.Anagnostopoulos et al., Nucl. Instr. Meth. B 205 (2003) 9

CCD detector

aperture

6.4 GHz, 450 W

= 10–8 s

M1 transitions in He-like S, Cl and Ar

response function very well understood


total line width

800

1000

1200

1400

1994 2000 2001 2001 2001 2002year of measurement

/

meV (2-1)

(3-1)

(4-1)

preliminary

previous experiment H.-Ch.Schröder et al.Eur.Phys.J.C 21 (2001) 473

notcorrected for

Coulomb de-excitation

crystal resolution subtracted

15 3.5 3.5 28.5 LH2 10 bar

Line Width Analysis


Hadronic Width (preliminary)

Hadronic width – corrected for Doppler effect due to Coulomb de-excitation

Preliminary average value for the hadronic width

1s = 785 ± 27 meV



low-energy component


high-energy components

Muonic Hydrogen

----- Crystal response ECRIT 2004

µH R-98.01 December 2004


PSI Experiment R98-01

previous exp. 1. step goal

1s /1s 0.5% 0.2% 0.2% reached

1s /1s 7 % 3 % 1%

Results on Pionic Hydrogen

Work in progress:

H Coulomb de-excitation analysis H high statistic run


Status of πp Experiment

• Density dependence studies of the 1s

no effect of molecular effects at our accuracy found

value consistent with result of previous experiment

• Measurement of transitions from 4p, 3p and 2p to 1s

influence of cascade processes on width

(due to Coulomb de-excitation) visible Doppler effect

• ECRIT response function extracted

• Precision measurement of µp X-ray spectrum study of the Doppler broadening due to Coulomb transitions


Outlook

Analysis in progress

High statistics measurement / high resolution crystal

Thank you for your attention

55. Jahrestagung der ÖPG, September 2005 Pionischer Wasserstoff: Präzisionsmessungen zur starken...

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