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

- + p + n

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

Cap @ PSI

Supported byPaul Scherrer Institute, Russian Ministry of Science and Technology, US National Science Foundation,US Department of Energy, University of Illinois, Civilian Research Development Foundation and INTAS.

collaborationV.A. Andreev, A.A. Fetisov, V.A. Ganzha, V.I. Jatsoura, A.G. Krivshich, E.M. Maev, O.E. Maev,

G.E. Petrov, S. Sadetsky, G.N. Schapkin, G.G. Semenchuk, M. Soroka, A.A. Vorobyov Petersburg Nuclear Physics Institute (PNPI), Gatchina 188350, Russia

P.U. Dick, A. Dijksman, J. Egger, D. Fahrni, M. Hiltebrandt, A. Hofer, L. Meier, C. Petitjean, R. Schmidt

Paul Scherrer Institute, PSI, CH-5232 Villigen, Switzerland

T.I. Banks, T.A. Case, K.M. Crowe, S.J. Freedman, B. Lauss University of California Berkeley, UCB and LBNL, Berkeley, CA 94720, USA

K.D. Chitwood, S. Clayton, P. Debevec, F. E. Gray , D. W. Hertzog, P. Kammel, B. Kiburg, C. J. G. Onderwater, C. Ozben, C. C. Polly, A. Sharp

University of Illinois at Urbana-Champaign, Urbana, IL 61801, USA

L. Bonnet, J. Deutsch, J. Govaerts, D. Michotte, R. Prieels Université Catholique de Louvain, B-1348 Louvain-La-Neuve, Belgium

R. M. Carey. J. PaleyBoston University, Boston, MA 02215, USA

T. Gorringe, M. Ojha, P. Zolnierzcuk University of Kentucky, Lexington, KY 40506, USA

F.J. Hartmann Technische Universität München, D-85747 Garching, Germany

Cap

Scientific case: +p capture

capture probes axial structure of nucleon

capture decay

hadronic vertex dressed by QCD q2 dependent form-factors

dual role of

• acts as well defined probe of hadronic structureQCD tests, pseudoscalar form-factor gP, chiral symmetry

• Standard Model symmetries of lepton-quark interaction

pn

e

e-

n

p

-

W W

- + p + n

Cap

Nucleon charged current at q2= - 0.88 m2

J = V - A

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

AgA(q2) + gP(q2) q/m + igT(q2)/2M q

• Vector current in SM determined via CVC gV(0)=1, g(q2)=1+q2 r2/6, rV

2=0.59 fm2

gM(0)=p-n-1=3.70589, rM2=0.80 fm2

q2 dependence from e scatt.

• Axial vector FF from experiment gA(0)=1.2670(35), rA

2=0.42±0.04 fm2 q2 dependence from quasi-elastic scattering, e-production

• 2nd class FF gS, gT forbidden by G symmetry, e.g. gT/gA=-0.15 ±0.15 (exp), -0.0152 ±0.0053(QCD sum rule, up-down mass difference)

• error fromVud = 0.16 %

nucleon weak formfactors gV,gM,gA

• determined by SM symmetries and data

• contribute <0.4% uncertainty to S

gV = 0.9755(5)

gM = 3.5821(25)

gA = 1.245(3)

remains

gP = ?Cap

pseudoscalar form factor gP

PCAC:

gP=8.7

heavy baryon chiral perturbation theory:

gP=(8.74 0.23) – (0.48 0.02) = 8.26 0.23gNN

13.31(34)13.0(1)

13.05(8)

calculations O(p3) show good convergence: 100 % 25 % 3 % delta effect small LO NLO NNLO

author year gP

S

T comment

Primakoff 1959 smaller gA

Opat 1964 smaller gA

Bernard et al 1994 8.44(23)Fearing et al 1997 8.21(9)

Govaerts et al 2000 8.475(76) 688.4(38) 12.01(12)Bernard et al 2000/1 687.4 (711*) 12.9 NNLO, small scaleAndo et al 2001 695 (722*) 11.9 NNLO

n

p

-

gNN

F

*NLO result

fundamental and least known weak nucleon FF solid theoretical prediction at 2-3% levelbasic test of QCD symmetries

Recent reviews:T. Gorringe, H. Fearing, Induced pseudoscalar coupling of the proton weak interaction, nucl-th/0206039, Jun 2002V. Bernard et al., Axial Structure of the Nucleon, Nucl. Part. Phys. 28 (2002), R1

fundamental and least known weak nucleon FF solid theoretical prediction at 2-3% levelbasic test of QCD symmetries

Recent reviews:T. Gorringe, H. Fearing, Induced pseudoscalar coupling of the proton weak interaction, nucl-th/0206039, Jun 2002V. Bernard et al., Axial Structure of the Nucleon, Nucl. Part. Phys. 28 (2002), R1

Cap

Experimental information on gP

Ordinary Muon Capture - + p + n

Radiative Muon Capture - + p + n +

BR~10-3, 8 experiments 1962-82, BC, neutron, electron detection “in principle” most direct gP measurement

BR~10-8, TRIUMF (1998), E>60 MeV, 297 ± 26 eventscloser to pion pole 3x sensitivity of OMC

theory more involved (min substitution, ChPT)

• Muon capture in nuclei

+ 3He + 3H st=1496 ±4 s-1 PSI (1998) gp=gp

th (1.08 ±0.19) error dominated by 3-N theory

correlation measurements

• Neutrino scattering

• electro production at thresholdCap

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

OP

n+

n+

n+

Cap

Muon Capture and gP

20 40 60 80 100 120

2.5

5

7.5

10

12.5

15

17.5

20

ChPT

OP (ms-1)

g P

RMC

Cap proposed

exp theory

OMC Saclay

update from Gorringe & Fearing

Interpretation of observed rate sensitive to pp state, where capture occurs, atomic physics

• OMC not precise, ambiguous interpretation

• RMC 4discrepancy exp/th

• no overlap theory & OMC & RMC

• OMC not precise, ambiguous interpretation

• RMC 4discrepancy exp/th

• no overlap theory & OMC & RMCCap

Cap experimental strategy 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

TPC

ePC1

ePC2

eSCe

Cap

experimental strategy

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 capture on impurity and transfer to deuterium 10-8 sensitivity with gas chromatograph

• +SR: calibrated with tranverse field 70 G

Statistics

• 1010 statistics: Complementary analysis methods

ppP

ppO

p

pp

ppP

ppP

ppO

ppO

time (s)

100% LH2 1 % LH2 10% LH2

Cap

time projection chamber

electron detector

Cap detector

Cap

TPC tracking

muon decay rare impurity capture +Z Z’+n+

Cap

- +

transfer to deuterium, diffusion

p+d d + pRamsauer Townsend minimum in d + p scattering at 1.6 eVdiffusion

catalyzed pd fusion

d + p pd (5.3MeV)+3He(0.2KeV)

Cap

Gas purification and analysis

        

Hydrogen purification and analysis to better than 10-8

• Electrolytic generator purity ~0.3 ppm

• Pd filter cleaning from O2 and N2 to better 10-8 directly verified.

• TPC gas purity deterioration can be reduced by longer conditioning after N2 filling. Continuous purification system under construction.

• Different methods of D2 diagnostic indicate isotopic purity at 1 ppm level, further effort in production and monitoring required for sub ppm level.

Cap

Cap status and plans

Planned schedule Cap I

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

• development final detector components and high purity chambers, 2001-2002

• commissioning fall 2002, spring 2003

• data run 2003, 2004 (S 3%, 1%)

Cap II with muon-on-request beam* (2004, 2005)chopper development and + result from Lan

• goal S to 0.3 %, gP 2-3%

20-30x exp improvementS similar precision as n

exp challenges: statistics, purity, atomic physics

*P.K. et al, PSI letter of intent 1998Cap

Scientific Context

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% with Lan kicker)

muon decay+ e++e+

+ to 1 ppm

muon decay+ e++e+

+ to 1 ppm

Fermi Coupling Constant

Lan, FAST 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

Cap