Precision Muon Physics Group

muon capture on proton - + p + n

to 1 %

muon capture on proton - + p + n

to 1 %

Nucleon form factors, chiral symmetry of QCD

Cap experimentgP to < 7% (3%)

muon decay+ e++e+

+ to 1 ppm

muon decay+ e++e+

+ to 1 ppm

Fermi Coupling Constant

Lan experiment

GF to < 1ppm

muon capture on deuteron

- + d + n +n

to 1 %

muon capture on deuteron

- + d + n +n

to 1 %

Basic EW two nucleon reaction, calibrate v-d reactions

D project

K.D. Chitwood, P. Debevec, S. Clayton, D. Hertzog, P. Kammel, B. Kiburg, R. McNabb, F. Mulhauser, C. C. Polly, A. Sharp, D. Webber

Scientific case

Cap

QCD is the theory of strong interactions

• non Abelian Gauge theory, running coupling constant,

• Precision tests at high energies

• strong coupling, confinement at “everyday” energies

Theoretical approaches to low energy domain

• QCD inspired models

• Lattice QCD

• Effective field theories (chiral perturbation theory) systematic expansion around chiral limit “spontaneous broken” symmetry governs dynamics mass generation accurate QCD prediction and QCD foundation for models model independent predictions of important reactions

QCD is the theory of strong interactions

• non Abelian Gauge theory, running coupling constant,

• Precision tests at high energies

• strong coupling, confinement at “everyday” energies

Theoretical approaches to low energy domain

• QCD inspired models

• Lattice QCD

• Effective field theories (chiral perturbation theory) systematic expansion around chiral limit “spontaneous broken” symmetry governs dynamics mass generation accurate QCD prediction and QCD foundation for models model independent predictions of important reactions

Quarkhandedness conserved

n

p

-

W

Cap

d

u

-

W

- + p + nelementary level

nucleon level

J = <n| V - Ap>

VgV(q2) + igM(q2)/2M q

AgA(q2) + gP(q2) q/m

J = <n| V - Ap>

VgV(q2) + igM(q2)/2M q

AgA(q2) + gP(q2) q/m

JJ

J = <d| u> J = <d| u>

QCD

pseudoscalar form factor gP

n

p

-

gNN

F

W

• fundamental and least known weak nucleon FF

• solid theoretical prediction at 2-3% level

• basic test of QCD symmetries

• experiments not precise, controversial, 4 discrepancy to theoryT. Gorringe, H. Fearing, Induced pseudoscalar coupling of the proton weak interaction, nucl-th/0206039, Jun 2002

V. Bernard et al., Axial Structure of the Nucleon, Nucl. Part. Phys. 28 (2002), R1

D project + d n + n +

• fundamental EW 2-body reaction

• high impact for fundamental astrophysics reactions

• 10x precision improvement feasible by Cap techniques

• fundamental EW 2-body reaction

• high impact for fundamental astrophysics reactions

• 10x precision improvement feasible by Cap techniques

D

n

d

-

W

n

EFT: Class of axial current reactions related by single unknown parameter L1A

• basic solar fusion reaction

p + p d + e+ +

• key reactions for solar neutrino detection and supernova neutrino

+ d p + p + e

+ d p + n +

• short distance, axial two body currents,

ab-inito EFT(NNLO) vs. SNPA vs. MEEFT

d capture close terrestrial analogued capture close terrestrial analogue

dp

e

e+W

p• soft enough ?

• precision measurement

possible ?

n

d

-

W

n

D

MEC

EFTL1A

Precision Measurement of Muon Capture on the Proton“Cap experiment”

- + p + n - + p + n

www.npl.uiuc.edu/exp/mucapture/

Petersburg Nuclear Physics Institute (PNPI), Gatchina,RussiaPaul Scherrer Institut, PSI, Villigen, Switzerland

University of California, Berkeley, UCB and LBNL, USAUniversity of Illinois, Urbana-Champaign, USA

Universite Catholique de Louvain, BelgiumTU Munich,Garching, Germany

Boston University, USAUniversity of Kentucky, USA

@ PSICap

experimental challenges

e+e+

- p () + n p

(Rich) physics effects

• Interpretation: where does capture occur ?

Critical because of strong spin dependence of V-A interaction

• Background: Wall stops and diffusion Transfer to impurities p+Z Z +p

• Rate and statistics (BR = 10-3)

• SR effect for +

TS

pp

pp

pp

ortho

para

F=0 F=1

J=1

J=0

n+

n+

n+

Cap

- = heavy electron

Cap experimental strategy I

Cap

New idea: active target of ultra-pure H2 gas 10 bar measure +

and - S = 1/- - 1/+ , to 10-5

New idea: active target of ultra-pure H2 gas 10 bar measure +

and - S = 1/- - 1/+ , to 10-5

eSCe

“Lifetime” or “Disappearance” Method

Our experiment observes e+ and e– decay products. Muon capture reduces the μ– lifetime compared to the μ+ lifetime by 0.15% !

High precision measurement of the lifetime difference:

1 1

( )' ( )'s

TPC

ePC1

ePC2log(counts)

time

μ+

μ –

1010

events

Cap experimental strategy II

Physics

• Unambigous interpretation At low density (1% LH2) mostly capture from p(F=0) atomic state.

• Clean muon stop definition: Wall stops and diffusion eliminated by 3-D muon tracking

• In situ gas impurity control (cZ<10-8, cd<10-6) hydrogen chambers bakeable to 150 C, continuous purification TPC monitors impurities in-situ 10-8 sensitivity with gas chromatograph

• +SR: calibrated with transverse field 70 G

Statistics

• 1010 statistics: Complementary analysis methods Cap

ppP

ppO

p

pp

ppP

ppP

ppO

ppO

time (s)

100% LH2 1 % LH2 10% LH2

Cap experimental setup Key ideas: active target of ultra-pure H2 gas 10 bar for muons, separate large tracking detector for electrons.

Key ideas: active target of ultra-pure H2 gas 10 bar for muons, separate large tracking detector for electrons.

Cap

SC(t = 0)

PC1

PC2

TPC

ePC2ePC1 eSC (Hodoscope)

μ

MuonDetectors

ElectronDetectors e

Cap experimental setup: TPC

The time projection chamber (TPC), is our active gas-filled target. It detects in muons and reaction products in 3D.

stop

rare impurity capture +Z Z’+n+

2003 run

Cap

Assembly: March → August

Data-Taking:

September → mid-October.

commissioning / first physics

time spectra 2003

Cap status and plans

Planned schedule Cap

• technical proposal spring 2001, received “high priority status”

• commissioning 2003

• final detector upgrades 2004

• data run 2003 4% precision

• data run 2004 1% precision

• …. Cap II or d project

Planned schedule Cap

• technical proposal spring 2001, received “high priority status”

• commissioning 2003

• final detector upgrades 2004

• data run 2003 4% precision

• data run 2004 1% precision

• …. Cap II or d project

Cap

Steve’s and Tom’s thesis

Contact me if you are interested !

Experimental facility

Muon Source• PSI accelerator (ring cyclotron) generates 590 MeV proton beam • protons hit graphite target and produce pions • pions decay to muons

Muon Beam Properties• Particles: μ+ or μ–

• Momentum ~ 30-40 MeV/c• rate ~ 50 kHz

LocationPaul Scherrer Institute (PSI),Switzerland