Transcript MuCap - University of Washington

First Physics Results from the MuCap
Experiment at PSI
Peter Kammel
University of Illinois at Urbana-Champaign
www.npl.uiuc.edu/exp/mucapture
MuCap Collaboration
Contents
V.A. Andreev, T.I. Banks, B. Besymjannykh, L. Bonnet,
R.M. Carey, T.A. Case, D. Chitwood, S.M. Clayton, K.M.
Cro we, P. Debe ve c, J . Deut sch, P. U. Dick, A . Dijksman, J. Egger, D. Fahrni, O. Fedorchenko,
• Physics
Context
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,
• Muon
Capture
onD.the
Proton
M. Levchenko, E.M. Maev, O.E. Maev,
R. McNabb,
L. Meier,
Michotte,
F. Mulhauser, C.J.G. Onderwater, C.S.
Özben, C. Petitjean, G.E. Petrov, R.Theory
Prieels, –
S.Experiment
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
mCap and
First
Results
Petersburg•Nuclear
Physics
Institute
(PNPI), Gatchina, Russia
Paul Scherrer Institute (PSI), Villigen, Switzerland
University of California, Berkeley (UCB and LBNL), USA
University of Illinois at Urbana-Champaign (UIUC), USA
Université Catholique de Louvain, Belgium
TU München, Garching, Germany
Topics in Nuclear Physics
University of Kentucky, Lexington, USA
DNP, October 28, 2006
Boston University, USA
Nuclear Physics Context

EW current key probe for nucleon structure
nucleon level
quark level
u
m
gm(1- g5)
q
q
relevant
degrees of
freedom ?
d
W
m
n

charged current
W
n
Understanding hadrons from fundamental QCD
• lattice QCD
• chiral effective field theory (ChPT)
p Goldstone boson of spontaneously broken symmetry, sys. expansion in q/L
model independent predictions
fundamental properties and symmetry tests
interesting processes (astrophysics)
interface to lattice calculations
…
Muon Capture and Axial Nucleon Structure
m- + p  nm+ n
rate LS
+ second
class currents
Lorentz, T invariance
suppressed by
isospin symm.
Conserved Vector
Current CVC
Main motivation for
mCap studies
Vector form factors q2= -0.88 mm2
gV = 0.9755(5)
gM = 3.5821(25)
Axial form factors q2= -0.88 mm2
gA = 1.245(4)
gP = 8.3 ± 50%
strong program
JLab, Mainz, ...
Axialvector Form Factor gA
Exp. History
Lattice QCD
Axial radius
n+N scattering
consistent with p electroproduction
(with ChPT correction)
PDG 2006
Edwards et al. LHPC Coll (2006)
Bernard et al. (2002)
introduces 0.4% uncertainty to LS (theory)
Pseudoscalar Form Factor gP
gpNN
gP determined by chiral symmetry of QCD:
n
p
p
Fp
gP=
(8.74  0.23)
–
(0.48  0.02)
= 8.26  0.23
PCAC pole term
Adler, Dothan, Wolfenstein
ChPT
one loop
leading order
m-
nm
two-loop <1%
N. Kaiser Phys. Rev. C67 (2003) 027002
Lincoln
Wolfenstein,
Ann. Rev. Nucl.
Sci.weak
2003nucleon form factor
•
gP basic
and experimentally
leastPart.
known
…
radiative
muon capture
hydrogen
carried out only recently
• The
solid
QCD prediction
viainChPT
(2-3%was
level)
with the result that the derived gP was almost 50% too high. If this result is
•
basic
test ofbeQCD
symmetries
correct,
it would
a sign
of new physics that might contribute effectively
to V, A or P.
Recent reviews:
T. Gorringe, H. Fearing, Rev. Mod. Physics 76 (2004) 31
V. Bernard et al., Nucl. Part. Phys. 28 (2002), R1
LS Calculations
1%
Processes to Determine gP

m- + p  nm+ n
OMC rate LS
BR~10-3
8 experiments, typical precision 10-15%, Saclay 4%

m- + p  nm+ n + g
RMC
BR~10-8, E>60 MeV
279±25 events
BRg(k>60MeV)=(2.10±0.21)x10-8
…
Wright et al. (1998)

m- + 3He  nm+ 3H
authors
Lstat (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
theory 2002
Marcucci et al.
1484 ± 8
3He
TPC
1B+2B, T beta constraint
rad. corrections?

pion electroproduction
Muon capture and muon molecular processes
LT
= 12 s-1
pμ↑↑
triplet
(F=1)
μ
Lortho=506 s-1
ppμ
λop
ppμ
ortho (J=1)
pμ↑↓
singlet (F=0)
LS= 691 s-1
n+n
Lpara=200 s-1
para (J=0)
• Interpretation requires knowledge of ppm population
• Strong dependence on hydrogen density f
rate proportional
to H2 density f !
100% LH
1 % LH2
2
ppmO
pm
pm
ppmO
ppmP
time (ms)
ppmP
Precise Theory vs. Controversial Experiments
gP
20
17.5
15
12.5
10
7.5
ChPT
mCap precision goal
5
2.5
exp
20
TRIUMF 2005
theory
40
60
80
100
120
lOP (ms-1)
• no overlap theory & OMC & RMC
• large uncertainty in lOP  gP  50% ?
mCap Experimental Strategy

Lifetime method
1010 m→enn decays
measure m- to 10ppm,
fulfill all requirements simultaneously
unique mCap capabilities
 LS = 1/m- - 1/m+ to 1%

Unambiguous interpretation
capture mostly from F=0 mp state at 1% LH2 density

Clean m stop definition in active target (TPC)
to avoid: mZ capture, 10 ppm level

Ultra-pure gas system and purity monitoring
to avoid: mp + Z  mZ + p, ~10 ppb impurities

Isotopically pure “protium”
to avoid: mp + d  md + p, ~1 ppm deuterium
diffusion range ~cm
mCap Detector
e
m
Design
2001-2
Reality
2004
Muon Stops in Active Target
10 bar ultra-pure hydrogen, 1.16% LH2
2.0 kV/cm drift field
~5.4 kV on 3.5 mm anode half gap
bakeable glass/ceramic materials
Operation with pure H2 challenging,
R&D @ PNPI, PSI
Observed muon stopping distribution
E
me-
3D tracking w/o material
in fiducial volume
p
Time Spectra
m-e impact parameter cut
m-
huge background suppression
diffusion (deuterium) monitoring
m+ as reference
identical detector systematics
m+
different physics
mSR
in 50G
blinded master
clock frequency
Consistency Studies
TPC fiducial cuts
6 mm Inside TPC
Start time fit
Event selection cuts
mCap Unique Capabilities: Impurities
rare impurity capture mZ(Z-1)+n+n
LZ (C, N, O) ~ (40-100) x LS
Hardware
Circulating Hydrogen Ultrahigh Purification System
Gas chromatography
~10 ppb purity required
CRDF 2002, 2005
Diagnostic in TPC
Results
x
t
z
Imp. Capture
cN, cO < 7 ppb, cH2O~30 ppb
 correction based on observed
capture yield

mCap Unique Capabilities: mp, md diffusion
mp + d  md + p (134 eV)
m-e impact par cut
large diffusion range of md
mp md
mp
< 1 ppm isotopic purity required
Diagnostic:
• l vs. m-e vertex cut
e-
e-
or to wall
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)
World Record
cd < 0.1 ppm
• AMS, ETH Zurich
mCap Unique Capabilities: Muon-On-Demand
Single muon requirement (to prevent systematics from pile-up)
limits accepted m rate to ~ 7 kHz,
while PSI beam can provide ~ 70 kHz
Muon-On-Demand concept
Kicker Plates
Beamline
m detector
m-
TPC
+12.5 kV
-12.5 kV
50 ns switching time
2-Dec-2005
mLan kicker
TRIUMF rf design
kicked
Fig will be
improved
dc
~3 times
higher rate
Corrections & preliminary results data 2004
internal
correction
(s-1)
statistics
Z>1 impurities
-14
m stop definition
uncertainty
(s-1)
external
uncertainty
(s-1)
12
ppm formation
19
4
6
lOP transition
5
2.3
2
1/ in mp system
12
md diffusion
-12
1
1/ PDG
mp diffusion
-3
1
total external
m+p scatter
-5
2
pileup
1
1
det combination
5
clock
3
total systematics
-33
9
total sys & stat
-33
15
mm+
correction
(s-1)
8.3
events
MuCap
l=1/ (s-1)
LS(s-1)
0.16 x 1010
455854  15
73018
0.06 x 1010
455164  28
36
9.5
PDG
1/(s-1)
455160 8.3
mCap and LS calculations
rad. corrections
• Goldman (1972)
• Czarnecki
Marciano
Sirlin (2006)
private comm.
preliminary
MuCap agrees within ~1s with LS theory
Thorough theory studies needed for next MuCap 1% stage !
mCap and gP
• within one sigma of chiral prediction, no dramatic discrepancy
• nearly independent of molecular physics (lOP)
• has overlap with old OMC, barely with recent RMC result
• final result (’06 and ’07 data) will reduce error to 7%
Summary and Plans

Preliminary results 2004 data
LS
gP

mCap
730  18
6.95  1.09
theory*
707 - 715
8.26 0.23
2006 data and 2007 plans
1010 events m- achieved in 2006
 1010 events m+ and suppl. measurements in 2007
LS with 1% uncertainty
 m+d proposal planned for 2007


Ideas for ultrapure H2 TPC welcome
*including Czarnecki et al. rad. corrections