J. Marton, FB18, August 21 24, 2006, Santos, Brasil 1 Precision Studies on Strong Interaction in Pionic Hydrogen J. Marton Stefan Meyer Institut (SMI)

1J. Marton, FB18, August 21 – 24, 2006, Santos, Brasil

Precision Studies on Strong Interaction in Pionic Hydrogen

J. MartonStefan Meyer Institut (SMI) / ÖAW

on behalf of the Pionic Hydrogen Collaboration @ PSI

Coimbra – Debrecen – Ioannina – Jülich – Paris – PSI – SMI/Vienna


Outline

• Motivation

• Pionic hydrogen: Cascade

• Scattering lengths

• Layout of the experiment

• Measurements

• Preliminary results: Shift, width

• Summary and outlook


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 ε1s and width 1s of the 1s ground state of pionic hydrogen p

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

scattering lengths basis for comparison of changes in the nuclear medium

2

1

1

3

1

1

10~

102~

s

s

s

s


Electromagnetic Cascade of p

precise QED calculations ~ 10-3

advanced cascade theory

p is not an isolated system interaction with hydrogen atoms

QED

n n -1I = 0

1 2

1

2

3

4

~16

π0 n

+ γ

n

Stark mixing

EKα ~ 2.5 keV

QED + Strong interaction

X-ray transitions

external Auger transitions

Coulomb transition

QEDsnp

meassnps EE 1

.11


Strong Interaction in p

• Principal interaction: electromagnetic• Transition energies 4p-1s, 3p-1s, 2p-1s (QED)

Transition Energy [eV] QED Energy [eV] QED + strong interaction

2p – 1s 2429.506 2436.6143p – 1s 2878.808 2885.9164p – 1s 3036.094 3043.202

eVeV

s

s

1~7~

1

1


Extraction of a+ and a-

)1(141

1e

hpp

Bs

s arE

20

1

1 ))1()(11(8 0

h

npBs

s aPr

QE

21

1

)(

a

aa

s

s

= (-7.2 2.9) 10-2 J. Gasser et al., Eur. Phys. J. C26 (2003) 13

= (0.6 0.2) 10-2 P. Zemp, Proc. Workshop Hadatom05

Accuracy of a+ strongly dependent on !

Deser formulae:


Pion-Nucleon Scattering Lengths

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

Tomozawa-Weinberg – current algebra (chiral limit)a+ = 0a- = 0.079 m

-1


Scheme of Experimental 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 -Target - 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 m600 600 pixels per chip

operation at – 100°C

150 eV @ 4 keVX 90%

image area

storage area

flexible boards

cooling (LN2)


high pion flux in E5 at PSIp=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


p Hadronic Shift and Width

e.m. transitionwithout strong

interaction

attractive shift

Goals: Shift 0.2% Width 1%

Molecular effects

Doppler broadeningCoulomb deexcitation

Precision in small effects ~10-5EB

careful study ofsystematic effects

Stability & Calibration

)1()1( .1 snpEsnpE electrmeass


Extention of parameter space measurements of shift and width with different

Experimental Procedure

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

Investigations on molecular effects

Coulomb transitionseffecting the width

high statistic measurement


mixture H2 / 16O2

(98%/2%)85K at 1.2 bar

4 bar equivalent density

H2

20K at 2 bar 28.5 bar equivalent density

H2

17K at 1 bar LH2

first time measurement

Shift Measurement: Density Dependence


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

1s = + 7.120 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

/ e

V

previous experiment

LH2

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

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

Density Effect in ε1s ?

Molecular formation ("Vesman“ mechanism)

p + H2 [(pp) p] ee


Hadronic Width

Low background (tails)

High statistics

• Well-known response function

• Correction of Doppler effect (em cascade)

Requirements for precise determination of 1s :


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


NEUTRON - TOF (– p)ns 0 n

non-radiative transitions

quasi-discrete velocity profile

n – TOF / ns

A. Badertscher et al., Eur. Phys. Lett. 54 (2001) 313

(–H)n + H=H (–H)n-1 + H + H + kinetic energy

Coulomb Transitions: PSI experiment


Coulomb Transitions

Energy gain from Coulomb transitions

2p-1s3p-1s4p-1s

Example: 3p-1s


Width – Doppler Corrected

907±34 meV

775±40 meV

812±60 meV

1s 82319 meV (2.3%)

Fit results including Dopplerboxes with free weights

Boxes:0-2 eV2-20 eV29-33 eV65-75 eV210-220 eV

Boxes:0-2 eV2-20 eV29-33 eV65-75 eV

Boxes0-2 eV3-15 eV27-34 eV(same apparatus, 10bar)


High Statistics Data

Measurement (2005)of the X-ray transition 2p 1s in pionic hydrogen

1 ch = 28.9 meV

in analysis



low-energy component


high-energy components

Muonic Hydrogen

----- Crystal response ECRIT 2004

µH R-98.01 December 2004


a++a- = (93.2±2.9) [10-3mπ-1]

ε1s : Extraction of scattering lengths dominated by ChPT correction = (-7.2 2.9)% * J. Gasser et al., Eur. Phys. J. C 26, 13 (2003)

ChPT correction = (0.60.2)% * P. Zemp, Proceedings hadatom05, arXiv:hep-ph/0508193 (2005) p.16

a- = (86.4 ) [10-3mπ-1] pion nucl. coupling constant

+0.99 -1.02

a+ = (6.8±3.1) [10-3mπ-1]

* δε depend on three LEC: c1,f1,f2; f1 badly known, depends on f2 only

1s = 82319 meV (2.3%) (Preliminary result 2005)

a+ and a- (preliminary results)


Pion-nucleon Coupling Constant

GMO sum rule

f2πN = 0.5712 a- [mπ] + 0.02488 J [mb-1] = 0.0763

M.L. Goldberger, H. Miyazawa, R. OehmePhys. Rev. 99, 986 (1955)

gπNN = 47.66 fπN = 13.165

J = - (1.082 0.032) mb T. E. O. Ericson et al. Phys. Rev. C 66, 014005 (2002)

[ g2πNN /4π=13.79 ± ]0.164

0.180

+ 0.0009 - 0.0010

+ 0.077

- 0.087

02222

2

)(2

)()(

21

)2/(2)1(

dk

k

kk

Mmmf

ma

Mm

totp

totpN

J


Pion-nucleon Coupling Constant

preliminaryPSI 2006

M. Saino


PSI Experiment R98-01

previous exp. present goal 1s /1s 0.5% 0.2% 0.2% reached

1s /1s 7 % 2 % 1%

Results on Pionic Hydrogen

Work in progress:

H Coulomb de-excitation analysis H high statistic measurement (2005) analysisD measurements in 2006 – additional information


Status of p 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 Doppler effect

• ECRIT response function extracted

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

• High statistic measurement 2005 – now in analysis


Outlook

Thank you for your attention

Measurement program is finalized.Analysis of the data set is in progress. We are approaching our goal in accuracy of 1s.

Documents

J. Marton, FB18, August 21 24, 2006, Santos, Brasil 1 Precision Studies on Strong Interaction in Pionic Hydrogen J. Marton Stefan Meyer Institut (SMI)