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Precision Muon Physics Group. K.D. Chitwood, P. Debevec, S. Clayton, D. Hertzog, P. Kammel, B. Kiburg, R. McNabb, F. Mulhauser, C. C. Polly, A. Sharp, D. Webber. Nucleon form factors, chiral symmetry of QCD m Cap experiment g P to < 7% (3%). muon capture on proton  - + p   m + n

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Precision Muon Physics Group

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Precision muon physics group

Precision Muon Physics Group

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

Nucleon form factors, chiral symmetry of QCD

m Cap experimentgP to < 7% (3%)

muon capture on proton- + p  m+ n

L to 1 %

Basic EW two nucleon reaction, calibrate v-d reactions

mD project

muon capture on deuteron - + d  m+ n +n

L to 1 %

Fermi Coupling Constant

m Lan experiment

GF to < 1ppm

muon decay+  e++ne+m

t+ to 1 ppm


Scientific case

Scientific case

  • 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 generationaccurate QCD prediction and QCD foundation for modelsmodel independent predictions of important reactions

Quarkhandedness conserved

mCap


P m n

- + p  m+ n

nucleon level

elementary level

Ja

Ja

d

p

n

u

W

W

QCD

nm

m-

m-

nm

Ja = <n|Va- Aa |p>

Va= gV(q2) ga + igM(q2)/2M sab qb

Aa= gA(q2) gag5 + gP(q2) qa/m g5

Ja = <d|ga (1-g5) |u>

  • fundamental and least known weak nucleon FF

  • solid theoretical prediction at 2-3% level

  • basic test of QCD symmetries

  • experiments not precise, controversial, 4 s discrepancy to theory

  • T. 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

gpNN

n

p

p

pseudoscalar form factor gP

Fp

W

m-

nm

mCap


M d project m d n n n

mD project m + d  n + n + n

n

d

n

W

nm

m-

  • fundamental EW 2-body reaction

  • high impact for fundamental astrophysics reactions

  • 10x precision improvement feasible by mCap techniques

mD


P eft class of axial current reactions related by single unknown parameter l 1a

MECEFT

L1A

pEFT: 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 pEFT(NNLO) vs. SNPA vs. MEEFT

md capture close terrestrial analogue

  • soft enough ?

  • precision measurement possible ?

p

n

d

d

p

n

W

W

e+

nm

m-

ne

mD


Precision measurement of muon capture on the proton m cap experiment

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

- + p  m+ n

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

Petersburg Nuclear Physics Institute (PNPI), Gatchina,Russia

Paul Scherrer Institut, PSI, Villigen, Switzerland

University of California, Berkeley, UCB and LBNL, USA

University of Illinois, Urbana-Champaign, USA

Universite Catholique de Louvain, Belgium

TU Munich,Garching, Germany

Boston University, USA

University of Kentucky, USA

@ PSI

mCap


Experimental challenges

experimental challenges

- p ()  m+ n

m- e+ne+m

p

- = heavy electron

  • (Rich) physics effects

  • Interpretation: where does capture occur ?

  • Critical because of strong spin dependence of V-A interaction

m

LS

LT

pm

pm

n+n

F=0

F=1

Lortho

  • Background:Wall stops and diffusionTransfer to impurities mp+Z mZ+p

  • Rate and statistics (BR = 10-3)

  • mSR effect for m+

ppm

n+n

J=1

Lpara

ppm

n+n

J=0

mCap


M cap experimental strategy i

log(counts)

ePC2

μ+

ePC1

μ –

TPC

time

mCap experimental strategy I

New idea: active targetof ultra-pure H2 gas 10 bar measure t+ and t-S = 1/- - 1/+ , tm to 10-5

  • “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% !

1010events

High precision measurement of the lifetime difference:

e

eSC

mCap


M cap experimental strategy ii

mCap experimental strategy II

  • Physics

  • Unambigous interpretationAt low density (1% LH2) mostly capture from mp(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

  • m+SR: calibrated with transverse field 70 G

100% LH2

10% LH2

1 % LH2

pm

pm

ppmO

ppmO

pm

ppmO

ppmP

ppmP

ppmP

time (ms)

  • Statistics

  • 1010 statistics: Complementary analysis methods

mCap


M cap experimental setup

mCap experimental setup

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

mSC

(t = 0)

mPC1

Muon

Detectors

mPC2

TPC

μ

Electron

Detectors

ePC1

eSC (Hodoscope)

ePC2

mCap

e


M cap experimental setup tpc

mCap experimental setup: TPC

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

m stop

rare impurity capture m+Z  Z’+n+n


Precision muon physics group

2003 run

Assembly:

March → August

Data-Taking:

September → mid-October.

commissioning / first physics

mCap


Time spectra 2003

time spectra 2003


M cap status and plans

mCap status and plans

  • Planned schedule mCap

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

  • commissioning 2003

  • final detector upgrades 2004

  • data run 2003 4% precision

  • data run 2004 1% precision

  • …. mCap II or md project

Steve’s and Tom’s thesis

Contact me if you are interested !

mCap


Experimental facility

Experimental facility

Location

Paul Scherrer Institute (PSI),

Switzerland

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


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