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New Precision Determination of
gp and GF,
the MuXperiments at PSI
Bernhard LaussUniversity of California @ Berkeley
on behalf of the MuCAP and MuLAN Collaborations
EXA’05
MuLAN Muon Lifetime Analysis
MuLAN makes a precision measurement of the Positive Muon Lifetime
EXA’05
Positive Muon Lifetime is closely connected to the Fermi Coupling Constant GF
e
eW
Standard Model
GF is a fundamental constant of nature
The GF from Fermi Theory successfully describes all weak
processes
ee
n pee
e
e
n
p
e
e
G
2F
L L eH e
5
G
2F
V A L eH p g g n e
1F
F
G
G
EXA’05
muon decay beta decay
additional higher order QED contributions
QED radiative corrections
1
GF2 m
5
192 31
2
25
4 2
e
e
e
e
EXA’05
All weak radiative corrections can be incorporated in the Standard Model
e
e
W
e
e
e
e
W
Z 0g g g Re-normalize g
e
e
e
W
Z 0
2
21
82F
W
G gr
M precision EW physics precision EW physics
via quantum loops.via quantum loops. (probes particle spectrum / top (probes particle spectrum / top prediction)prediction) EXA’05
Dominant theoretical uncertainty in muon Dominant theoretical uncertainty in muon lifetime was reduced from 16 to 0.3 ppmlifetime was reduced from 16 to 0.3 ppm
(2-loop (2-loop ’99) !’99) !
EXA’05
Recent improvement in calculations of
- Hadronic Contributions to the Muon LifetimeTimo van Ritbergen, Robin G. Stuart, Phys.Lett. B437 (1998) 201-208
- Complete 2-loop Quantum Electrodynamic Contributions to the Muon Lifetime in the Fermi Model,Timo van Ritbergen, Robin G. Stuart, Phys.Rev.Lett. 82 (1999) 488-491
- Complete O(N_f alpha2) Weak Contributions to the Muon LifetimeParesh Malde, Robin G. Stuart, Nucl.Phys. B552 (1999) 41-66
- Complete Two Loop Electroweak Contributions to the Muon Lifetime in the Standard ModelM. Awramik, M. Czakon, hep-ph/0305248
- Two Loop Electroweak Bosonic Corrections to the Muon Decay LifetimeM. Awramik, M. Czakon, hep-ph/0211041
etc ........
2 5
3
11
192FG m
EXA’05
Present Experimental Situation
PDG 2004 average: = 2.19703 s (18 ppm)
GF = 1.6637 (1) GeV2 (9ppm)
single best experiment 27 ppm error
e
eW
Duclos BalandinGiovanetti Bardin
Lan 03
1973 1974 1984 1984
EXA’05
Present Experimental Situation
PDG 2004 average: = 2.19703 s (18 ppm)
GF = 1.6637 (1) GeV2 (9ppm)
single best experiment 27 ppm error
e
eW
Duclos BalandinGiovanetti Bardin
Lan
1973 1974 1984 1984 2003
EXA’05
Present Experimental Situation
PDG 2004 average: = 2.19703 s (18 ppm)
GF = 1.6637 (1) GeV2 (9ppm)
single best experiment 27 ppm error
e
eW
Duclos BalandinGiovanetti Bardin
Lan
1973 1974 1984 1984 2003 04ex
pect
ed
EXA’05EXA’05
Duclos BalandinGiovanetti Bardin
Lan
Langoal
10
Lan goal
The MuLAN experimental goal is to no longer limit the GF extraction by experiment
ppm 5.0G ppm 1τ Fμ
Need ~1012 events
5
0
The lifetime is determined by stopping muons in a target and waiting for the decay positrons.
Segmented Scintillator Detector
+
e+
log
coun
ts
time
e+
simple slope measurement
of exponential time distribution !
EXA’05EXA’05
Using a pulsed muon beam will allow faster accumulation of statistics.
+
TimeAccum.Period
in target
20x faster than dc mode
Kicker2x 75 cm plates
E=0kV
EXA’05EXA’05
5s
Using a pulsed muon beam will allow faster accumulation of statistics.
+
Time
in target
Accum.Period
MeasurementPeriod
e+ 20x faster than dc mode
KickerE=25kV
EXA’05EXA’05
5s 22 s 45 ns rise/fall time
new M
uLAN beamline
developed
Kicker
@ TRIUMF
EXA’05
e
eW
Simple slope measurement at 1ppmis not so simple anymore:
The MuLAN experiment has been designed to
reduce systematic errors.
EXA’05
e
eW
The impact of muon spin rotation (SR)
N
SFront
Back
front-back symmetry
muon beam is polarized muon precesses in magnetic field Decay e+’s are preferentially emitted
in the direction of the μ+ spin. Residual polarization effects will
produce direction-dependent distortions in the μ+ lifetime histograms.
fit (F+B)monitor (F-B)
FrontBack
Silver Target
EXA’05
e
eW
The impact of muon spin rotation (SR)
•Silver - preserves muon polarization (100%)
•Sulfur - muon residual polarization (8%)
•Arnokrome-3 (AK3)
• (30% chromium, 10% cobalt, 60% iron)
• Internal Field 1 T.
• No observable precession frequency up to 320 MHz or <B>=2.4 T.
EXA’05
e
eW
Double-Pulse Resolution - Hit Pileup
detector modularity: new electronics: 174 tile pairs 500 MHz wave form digitizers
EXA’05
e
eW
“Sneaky Muons” during beam-off period
lead to time dependent backgroundhigh rate (MHz), thin, fast (30 ns FWHM) wire chamber
beambeam
~100 Gauss magnet ring to avoid influence on systematics
due to muon stops in the chamber
EXA’05
e
eW
Online fit of 10 min of 2004 data
The time scale has a secret offset - blind analysis
all tile pairs
different start times
2004:- Setup and Test of final beam line with kicker - Finalized Detector- Accumulated 1010 decay positrons in both targets, sulfur and AK3 - sensitive systematics comparison - used multi-hit TDCs- analysis goal: 5 ppm error
2005 - finalize and test run with WFD electronics
2006- full 1012 statistics for 1ppm error
MuLAN Achievements and Plans
EXA’05
MuCAPmeasures: μ- capture rate in ultrapure hydrogen
Precision Measurement of the Singlet Muon Capture Rate on the Proton
EXA’05
g
W-
νμd
uμ–
gVud
ee
n pee
e
e
n
p
e
e
G
2F
L L eH e
5
G
2F
V A L eH p g g n e
(1 5) 1, 1.26V Ag g
1F
F
G
G
EXA’05EXA’05
muon decay beta decay
The GF from Fermi Theory successfully describes all weak
processes
Beta Decay (involves nucleons at low
momentum)
(V-A)
gv = 1gA = -1
n pee
n
p
e
e
5
G
2F
V A L eH p g g n e
1, 1.26V Ag g EXA’05
-decay
modified axial coupling
Muon Captureat higher momentum q2 = -0.88
m
p n
p
n
the simple(V-A) formbecomes more complicated
VgV(q2) + igM(q2)/2M q + gS(q2)/m q
AgA(q2) + gP(q2) q/m + igT(q2)/2M q Muon capture involves nucleons rather than isolated quarks. The strongly-interacting substructure of the proton and neutron complicates the weak interaction physics. These complicating effects are encapsulated in the nucleonic charged-current’s four “induced form factors”:
G-symmetry
no second class currents
EXA’05
nucleon charged current
Muon Capture
p n
• Vector current in SM determined via CVC gV(0) = 1, gV(q2)=1+q2 r2/6, rV
2=0.59 fm2
• gM(0) = p-n+1=-3.70589 q2 dependence from e scatt.
• Axial vector FF from n decay experimentgA(0)=-1.2670(35)
q2 dependence from quasi-elastic neutrino- nucleon 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 form factors gV,gM ,gA,gP
• 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 induced pseudo-scalar
gP = ?known at best only to ~ 20%
EXA’05
Pseudoscalar Form Factor gP in
TheoryPCAC: gP=8.7
heavy baryon chiral perturbation theory:
gP=(8.74 0.23) – (0.48 0.02) = 8.26 0.23
n
p
-
gNN
F
EXA’05
- fundamental but least known weak nucleon FF - solid theoretical prediction at few percent level- basic test of chiral QCD symmetriesCalculations NNLO show
good convergence: 100 % 25 % 3 % delta effect small LO NLO NNLO
Calculation by Fearing, Meißner et al.
Ordinary muon capture on the proton can be considered an excellent testing ground for our understanding of spontaneous and explicit chiral symmetry breaking in QCD.
Meißner, nucl-th/0001052
existing precise
calculations
are a
strong motivation
for a precision experim
ent
Experimental Informationon gp comes from nuclear Muon Capture Rate s
EXA’05
p n
Ordinary Muon Capture
Radiative Muon Capture
p n
Yield = 10-3
Yield = 10-8
EPH>60MeV
μ–, muon capture competes with muon decay:
(99.85%)
( ) (0.15%)
ee
p n
1 1
( )' ( )'s
Lifetime method
avoids absolute neutron counting
MuCAP Experimental PrincipleComparison of Lifetimes
log
coun
ts
time
e+
e –
μ+ lifetime = 2.19703 s
+ e+ + e+ ~
Experimental goal: measure + and - to 10-5 Experimental goal: measure + and - to 10-5
EXA’05
EXA’05
Present Experimental Situation
0 20 40 60 80 100 120 1400
2
4
6
8
10
12
14
16
18
20
g p(-0
.88
m2 )
OP
(ms-1)
0 20 40 60 80 100 120 1400
2
4
6
8
10
12
14
16
18
20
0 20 40 60 80 100 120 1400
2
4
6
8
10
12
14
16
18
20update from Gorringe & Fearing
ChPT
EXA’05
g p(-0
.88m
2 )
μ– Kinetics in Hydrogen -> Experimental Challenges
T = 12 s-1
n+
pμ↑↓
singlet(F=0)
S= 664 s-1
n+
triplet(F=1)
μ
pμ↑↑
EXA’05
strong spin dependence of V-A interaction
EXA’05
Present Experimental Situation
0 20 40 60 80 100 120 1400
2
4
6
8
10
12
14
16
18
20
g p(-0
.88
m2 )
OP
(ms-1)
0 20 40 60 80 100 120 1400
2
4
6
8
10
12
14
16
18
20
0 20 40 60 80 100 120 1400
2
4
6
8
10
12
14
16
18
20update from Gorringe & Fearing
ChPT
EXA’05
g p(-0
.88m
2 )
EXA’05
Present Experimental Situation
0 20 40 60 80 100 120 1400
2
4
6
8
10
12
14
16
18
20
OP
g p(-0
.88
m2 )
OP
(ms-1)
0 20 40 60 80 100 120 1400
2
4
6
8
10
12
14
16
18
20
0 20 40 60 80 100 120 1400
2
4
6
8
10
12
14
16
18
20update from Gorringe & Fearing
ChPT
Saclay 1981 Theory
TRIUMF 2004
EXA’05
with recent TRIUMF result
on op
situation even more puzzling !g p(
-0.8
8m2
)
EXA’05
Present Experimental Situation
0 20 40 60 80 100 120 1400
2
4
6
8
10
12
14
16
18
20
OP
g p(-0
.88
m2 )
OP
(ms-1)
0 20 40 60 80 100 120 1400
2
4
6
8
10
12
14
16
18
20
0 20 40 60 80 100 120 1400
2
4
6
8
10
12
14
16
18
20update from Gorringe & Fearing
ChPT
Saclay 1981 Theory
TRIUMF 2004
MuCAP - PSI: precision goal
need for a new,
unambiguous
precision determination
EXA’05
g p(-0
.88m
2 )
Mark & Dimitarplease check calculation
e
eW
negative muons in hydrogen pose additional problems in
comparison to positive stopped muons
EXA’05
μ– Kinetics in Hydrogen -> Experimental Challenges
T = 12 s-1
n+
ZμBackground: Wall stops and diffusion Transfer to impurities p+Z Z +p
pμ↑↓
singlet(F=0)
S= 664 s-1
n+
triplet(F=1)
μ
pμ↑↑
EXA’05
strong spin dependence of V-A interaction
ppμ ppμ
para (J=0)ortho (J=1)
λop
ortho=506 s-1
para=200 s-1
molecular disturbances
experimental strategyPhysics
• 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
(goal: cZ<10-8, cd<10-6 /reached in 2004: cZ=7x10-8, cd= ~2x10-6) hydrogen chambers bakeable to 150º 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 (saddle coil magnet around the TPC vessel)
Statistics
• 1010 statistics
ppP
ppO
p
pp
ppP
ppP
ppO
ppO
time (s)
100% LH2 1 % LH2 10% LH2
Experimental Challenges / MuCAP’s Solutions
EXA’05
The Time Projection Chamber
tracks muon stops in 3D.
- dT
active Target = TPC
- operates in proportional mode (gain ~104) - 5 - 6 kV- bakeable- quartz glass with very low thermal expansion- operates in 10 bar protium
EXA’05
horiz
onta
l
beam
dire
ctio
n
Anodes
Strips
Stop
vertical (drift time)
Anodes
Cathod
es
MuCap Achievements
Fall 2004: - full experiment ran stably for several weeks- collected 2.5 109 statistics => s 2-3%
EXA’05
(ns)
Impact Parameter Cutsno cut60 mm30mm
huge BG reduction
e
eW
Mucap Data 2004
ONLINE:continuous monitoring
of muon stopping
anddetector performance
EXA’05
Drift Time
e
eW
continuous high Z cleaning systemfor hydrogen based on Zeoliteafter filling through Pd filter
EXA’05
obtained 70 pbb
over several weeks
e
eW
We achieved gas impurity levels of 7x10–8, as determined from real-time software analysis of impurity events, and post-run chromatography analysis.
high Z purity monitoring (mainly Nitrogen, H2O)
EXA’05
MuCap Achievements
Fall 2004: - 70 ppb high-Z contamination over 5 weeks maintained- 1-2 ppm deuterium
EXA’05
A trickier impurity: deuterium transfer to deuterium, diffusion, CF
cd = 1ppm -> change in lifetime ~ 1ppm
p+d d + p
Ramsauer Townsend minimum in d + p scattering at 1.6 eV
Check by comparing + and
Diffusion
-catalyzed pd fusion (Alvarez)
monitors deuterium concentration
d + p pd (5.3MeV)+3He(0.2KeV)
EXA’05
MuCAP plans to add components to directly
monitor the deuterium concentration
to ± 0.1ppm in liquid hydrogen,
via fusion ’s and Alvarez muons
MuCap TimetableSummer 2005:
- additional development of the online impurity monitoring system- improvement of high-Z cleaning capacity- TPC overhaul to reach stable 5.4 kV running conditions - FADC implementation on all TPC channels- additional neutron counter for -kinetics control (pd, op)
Fall 2005/Spring 2006: - Planned 18 weeks of production data taking towards the final goal: s 1% - muon on request beamline (using the MuLAN kicker)
EXA’05
muon capture on deuteron
- + d + n +n
to 1 %
muon capture on deuteron
- + d + n +n
to 1 %
Basic EW two nucleon reaction
tests effective theories and serves to
calibrate v-d reactions via L1a (SNO)
Future (<2007)
D project
EXA’05
Paul Scherrer Institute (PSI), Villigen, Switzerland
University of California, Berkeley (UCB and LBNL), USA
University of Illinois at Urbana-Champaign (UIUC), USA,
University of Kentucky, Lexington, USA
Boston University, USA
James Madison University, USA
KVI Groningen, Netherlands
Istanbul Technical University
MuLAN Collaborating Institutions MuCap
EXA’05
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
University of Kentucky, Lexington, USA
Boston University, USA