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 ?
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