Peter KammelUniversity of Illinois at Urbana-Champaign

www.npl.uiuc.edu/exp/mucapture

MuCap Collaboration

V.A. Andreev, T.I. Banks, B. Besymjannykh, L. Bonnet, R.M. Carey, T.A. Case, D. Chitwood, S.M. Clayton, K.M. Crowe, P. Debevec, J. Deutsch, P.U. Dick, A. Dijksman, J. Egger, D. Fahrni, O. Fedorchenko,A.A. Fetisov, S.J. Freedman, V.A. Ganzha, T. Gorringe, J. Govaerts, F.E. Gray, F.J. Hartmann, D.W. Hertzog, M. Hildebrandt, A. Hofer, V.I. Jatsoura, P. Kammel, B. Kiburg, S. Knaak, P. Kravtsov, A.G. Krivshich, B. Lauss, M. Levchenko, E.M. Maev, O.E. Maev, R. McNabb, L. Meier, D. Michotte, F. Mulhauser, C.J.G. Onderwater, C.S. Özben, C. Petitjean, G.E. Petrov, R. Prieels, S. Sadetsky, G.N. Schapkin, R. Schmidt, G.G. Semenchuk, M. Soroka, V. Tichenko, V. Trofimov, A. Vasilyev, A.A. Vorobyov, M. Vznuzdaev, D. Webber, P. Winter, P. Zolnierzcuk

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

University of California, Berkeley (UCB and LBNL), USAUniversity of Illinois at Urbana-Champaign (UIUC), USA

Université Catholique de Louvain, BelgiumTU München, Garching, Germany

University of Kentucky, Lexington, USABoston University, USA

Contents

• Physics Context

• Muon Capture on the Proton Theory – Experiment

• Cap and First Results

First Physics Results from the MuCap Experiment at PSI

Topics in Nuclear PhysicsDNP, October 28, 2006

EW current key probe for nucleon structure

Understanding hadrons from fundamental QCD• lattice QCD• chiral effective field theory (ChPT)

Goldstone boson of spontaneously broken symmetry, sys. expansion in q/model independent predictions

fundamental properties and symmetry testsinteresting processes (astrophysics)

interface to lattice calculations…

Nuclear Physics Context

nucleon levelquark level

(1- 5)ud

W

W

relevant degrees of freedom ?

qq

charged current

Muon Capture and Axial Nucleon Structure

- + p + n

rate S

Lorentz, T invariance+ second class currentssuppressed by isospin symm.

Vector form factors q2= -0.88 m2

gV = 0.9755(5) gM = 3.5821(25)

Vector form factors q2= -0.88 m2

gV = 0.9755(5) gM = 3.5821(25)

Conserved Vector Current CVC

strong program JLab, Mainz, ...

Main motivation forCap studies

Axial form factors q2= -0.88 m2

gA = 1.245(4) gP = 8.3 ± 50%

Axial form factors q2= -0.88 m2

gA = 1.245(4) gP = 8.3 ± 50%

Axialvector Form Factor gA

Exp. History Axial radiusLattice QCD

+N scattering

consistent with electroproduction (with ChPT correction)

introduces 0.4% uncertainty to S (theory)

PDG 2006 Edwards et al. LHPC Coll (2006)

Bernard et al. (2002)

gP determined by chiral symmetry of QCD: n

p

-

gNN

F

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

PCAC pole term Adler, Dothan, Wolfenstein

ChPT leading order one loop two-loop <1% N. Kaiser Phys. Rev. C67 (2003) 027002

Lincoln Wolfenstein, Ann. Rev. Nucl. Part. Sci. 2003

… The radiative muon capture in hydrogen was carried out only recently with the result that the derived gP was almost 50% too high. If this result is correct, it would be a sign of new physics that might contribute effectively to V, A or P.

Lincoln Wolfenstein, Ann. Rev. Nucl. Part. Sci. 2003

… The radiative muon capture in hydrogen was carried out only recently with the result that the derived gP was almost 50% too high. If this result is correct, it would be a sign of new physics that might contribute effectively to V, A or P.

• gP basic and experimentally least known weak nucleon form factor

• solid QCD prediction via ChPT (2-3% level)

• basic test of QCD symmetries

• gP basic and experimentally least known weak nucleon form factor

• solid QCD prediction via ChPT (2-3% level)

• basic test of QCD symmetries

Recent reviews:T. Gorringe, H. Fearing, Rev. Mod. Physics 76 (2004) 31V. Bernard et al., Nucl. Part. Phys. 28 (2002), R1

Pseudoscalar Form Factor gP

S Calculations

1%

Processes to Determine gP

- + p + n OMC rate S BR~10-3

8 experiments, typical precision 10-15%, Saclay 4%

- + p + n + RMCBR~10-8, E>60 MeV

- + 3He + 3H

pion electroproduction

…

279±25 eventsBR(k>60MeV)=(2.10±0.21)x10-8

Wright et al. (1998)

authors stat (s-1) comment

theory 1993 Congleton & Fearing 1304 1B

theory 1996 Congleton & Truhlik 1502 ± 32 1B + 2B

exp 1998 Ackerbauer et al 1496.0 ± 4.0 3He TPC

theory 2002 Marcucci et al. 1484 ± 8 1B+2B, T beta constraint

rad. corrections?

Muon capture and muon molecular processes

T = 12 s-1

pμ↑↓

singlet (F=0)

S= 691 s-1

n+

triplet(F=1)

μ

pμ↑↑

ppμ

para (J=0)ortho (J=1)

λop

ortho=506 s-1 para=200 s-1

ppμ ppμ ppμ

• Interpretation requires knowledge of pp population

• Strong dependence on hydrogen density

ppP

ppO

p

100% LH2

p

ppP

ppO

1 % LH2

time (s)

rate proportional to H2 density !

λ pp

• no overlap theory & OMC & RMC

• large uncertainty in OP gP 50% ?

• no overlap theory & OMC & RMC

• large uncertainty in OP gP 50% ?

Precise Theory vs. Controversial Experiments

20 40 60 80 100 120

2.5

5

7.5

10

12.5

15

17.5

20

ChPT

OP (ms-1)

gP

- + p + n + @ TRIUMF

Cap precision goal

exp theory TRIUMF 2005

- + p + n @ Saclay

Lifetime method 1010 →e decays measure to 10ppm,

S = 1/ - 1/to 1% Unambiguous interpretation capture mostly from F=0 p state at 1% LH2 density

Clean stop definition in active target (TPC) to avoid: Z capture, 10 ppm level

Ultra-pure gas system and purity monitoring to avoid: p + Z Z + p, ~10 ppb impurities

Isotopically pure “protium”to avoid:p + d d + p, ~1 ppm deuterium diffusion range ~cm

Cap Experimental Strategy

fulfill all requirements simultaneouslyunique Cap capabilities

e

Cap Detector Design 2001-2Reality 2004

3D tracking w/o material in fiducial volume

Muon Stops in Active Target

p-

10 bar ultra-pure hydrogen, 1.16% LH2

2.0 kV/cm drift field ~5.4 kV on 3.5 mm anode half gapbakeable glass/ceramic materials

Observed muon stopping distribution

E

e-

Operation with pure H2 challenging, R&D @ PNPI, PSI

Time Spectra

-e impact parameter cut

huge background suppression

diffusion (deuterium) monitoring

-

+

SR

in 50G

+ as reference

identical detector systematics

different physics

blinded master clock frequency

TPC fiducial cutsStart time fit

Consistency Studies

Event selection cuts

6 m

m In

sid

e T

PC

Cap Unique Capabilities: Impurities

Results

cN, cO < 7 ppb, cH2O~30 ppb correction based on observed capture yield

Diagnostic in TPC

rare impurity capture Z(Z-1)+n+Z (C, N, O) ~ (40-100) x S

~10 ppb purity required

Hardware Circulating Hydrogen Ultrahigh Purification System

Gas chromatography CRDF 2002, 2005

Imp. Capture

x

zt

Results• Directly from data

cd= 1.49 ± 0.12 ppm

• AMS (2006)

cd= 1.44 ± 0.15 ppm

On-site isotopic purifier 2006 (PNPI, CRDF)

p + d d + p (134 eV)large diffusion range of d

< 1 ppm isotopic purity required

Cap Unique Capabilities: p, d diffusion

Diagnostic:

• vs. -e vertex cut

• AMS, ETH Zurich

e- e-p p d

or to wall

-e impact par cut

World Record

cd < 0.1 ppm

Muon-On-Demand conceptMuon-On-Demand concept

Cap Unique Capabilities: Muon-On-Demand

Beamline

Single muon requirement (to prevent systematics from pile-up)

limits accepted rate to ~ 7 kHz,

while PSI beam can provide ~ 70 kHz

-

+12.5 kV -12.5 kV

Kicker Plates

50 ns switching time

detector

TPC

Fig will be improved

~3 times higher rate

dc

kicked2-Dec-2005

Lan kickerTRIUMF rf design

Corrections & preliminary results data 2004

MuCap PDG

events =1/ (s-1) S(s-1) 1/(s-1)

- 0.16 x 1010 455854 15 73018

+ 0.06 x 1010 455164 28 455160 8.3

internalcorrection

(s-1)uncertainty

(s-1)

statistics 12

Z>1 impurities -14 6

stop definition 2

d diffusion -12 1

p diffusion -3 1

+p scatter -5 2

pileup 1 1

det combination 5

clock 3

total systematics -33 9

total sys & stat -33 15

externalcorrection

(s-1)uncertainty

(s-1)

pp formation 19 4

OP transition 5 2.3

1/ in p system 12

1/PDG 8.3

total external 36 9.5

Cap and S calculations

rad. corrections

• Goldman (1972)

• Czarnecki Marciano Sirlin (2006) private comm. preliminary

MuCap agrees within ~1 with S theory

Thorough theory studies needed for next MuCap 1% stage !

preliminary

• within one sigma of chiral prediction, no dramatic discrepancy

• nearly independent of molecular physics (OP)

• has overlap with old OMC, barely with recent RMC result

• final result (’06 and ’07 data) will reduce error to 7%

• within one sigma of chiral prediction, no dramatic discrepancy

• nearly independent of molecular physics (OP)

• has overlap with old OMC, barely with recent RMC result

• final result (’06 and ’07 data) will reduce error to 7%

Cap and gP preliminary

2006 data and 2007 plans 1010 events - achieved in 2006 1010 events + and suppl. measurements in 2007

S with 1% uncertainty +d proposal planned for 2007

Summary and Plans

Cap theory* S 730 18 707 - 715 gP 6.95 1.09 8.26 0.23

Cap theory* S 730 18 707 - 715 gP 6.95 1.09 8.26 0.23

Preliminary results 2004 data

Ideas for ultrapure H2 TPC welcome

*including Czarnecki et al. rad. corrections

preliminary