MuLan– a precision measurement of the positive muon lifetime and ...

MuLan– a precision measurement of the
positive muon lifetime and determination of
the Fermi constant.
Tim Gorringe, Univ. of Kentucky,
on behalf of MuLan Collaboration.
Boston Univ. 5 , Groningen Univ 7 , James Madison Univ 6 ,
TRIUMF 3 , Univ. of California Berkeley 2 , Univ. of Illinois
at Urbana-Champaign 1 , Univ. of Kentucky 4 .

Overview
● remarks on the muon lifetime, the Fermi
constant and electroweak interactions
● MuLan setup
● MuLan systematics
● 2004 run results
● 2006/7 run progress

muon lifetime, Fermi constant and
electroweak interactions

Electroweak interactions ...
α (±0.4ppb), G F (±10ppm),
and M Z (±23ppm).
predictive power of
electroweak interactions
between quarks and leptons
at tree level: SM relations to bare couplings and masses
4 =g g ' / g 2 g' 2 , G F =2 / 2
M Z=g 2 g' 2 , M W =g
beyond tree level: quantum loops dress relations between bare
couplings and masses
heavy qq pairs + Higg's loops + SUSY loops? ...

μ
μ
Electroweak interactions ...
W
G F
1
Δq contains QED, QCD loops
g
g
e
ν e
ν μ
ν μ
ν e
e
= G 2 5
F m
1q
2
192
G F
2
Δr contains electroweak loops
H
g2
= 2
8 M W
1r
+ ...
+ ...

Brief history of the Fermi Constant
1934
Fermi's four-fermion
interaction of β-decay
50's
V-A structure of
weak interactions
Universality of
weak interactions
60's
Unified theory and
electroweak interactions
70-80's
Discovery of neutral currents,
W,Z bosons
LHC era
higher symmetries?

Brief history of muon lifetime
τ = 2.19703(4) µs (PDG2002)
one-by-one exptl limit,
one-loop QED limit
2002PDG world
average

MuLan setup

Paul Scherrer Institute – proton
accelerator complex

Paul Scherrer Institute – proton
accelerator complex
590 MeV, 2.0 mA
proton cyclotron
graphite target
stations, π's, μ's
μLan situated
on πE3 beamline

principle of accumulating µ + 's and measuring e + 's
µ +
kicker
on
off
ball
tgt
e +

µLan method of accumulating µ + 's and
measuring e + 's
beam on beam off
beam monitor
µLan ball
(FAST collaboration use alternative method)

wire chamber
μ
μLAN Setup.
e
scintillator tiles
stopping target

a tile ....
a house ..
μLAN Setup
the ball ...

μLAN Setup

MuLan systematics – pulse pileup
“Minimize by segmentation and digitization
– then measure very carefully.”

digitize
Δt = artifical deadtime
±Δt = coincidence window
fit
Δt
Data
Analysis
histogram
counts counts
time

digitize
Δt = artifical deadtime
±Δt = coincidence window
“Double coincidence” pile-up,
-Re -2t/τ distortion
fit
Δt
histogram
counts
time

i.o
beam
on
shadow
window
counts
true
hits, e -t/τ
time
“Double coincidence” correction,
shadow windowing
beam
on
counts
Δt
measured
hits,e -t/
time
beam
on
= +
τ ­ Re-2t/τ counts
shadow
hits, Re -2t/τ
time

2004 data pile-up correction
uncorrected
spectrum
shadow
spectrum
( τ – τ ) [ppm]
offset
Measured τ vs artifical deadtime
uncorrected
lifetime
corrected
lifetime
artifical deadtime [ns]

MuLan systematics – μSR
“Minimize by dephasing, geometry and target choices
– then measure very carefully.”

ν
π +
parity violating
pion decay
μ +
beamline
μ +
θ
parity violating
muon decay
e +

transverse field μSR longitudinal field μSR
μ μ
TFµSR effect is minimized
by dephasing.
LFµSR effect is minimized
by geometry.

1) dephasing
2) targets
beam on
1 2 3 4
a) μ + in B int =5000G
ferromagnetic Fe-Cr-Ni alloy
3) geometry
μ
μ
B
tgt tgt
FF
TF μSR
3
4
1
2
b) μ + e ­ in B ext =100G
quartz (SiO 2 )
F+B
F-B

Dedicated quartz TF μSR measurement
showing
precession signal.
~500 ppm precession signal in
quartz production data.
Dedicated quartz LF μSR measurement
showing
longitudinal relaxation
±50 ppm lifetime shift in
quartz production data.

MuLan systematics – errant muons
“put the target in the beampipe
– then measure very carefully.”

eam on beam off
~10 -3 beam extinction

plastic scintillator beam profile
at ~1m upstream of target position
beampipe
radius

MuLan systematics –
other systematics include instrumental stabilities
(timing, gain, pedestal, etc) over the measurement period

MuLan results – 2004 run
“First results.”
- in-air ferromagnetic target
- multihit TDC readout
- ~10 10 decays

2004 results - the fit

2004 results – the numbers
source uncertainty
statistical 9.6 ppm
systematic 5.0 ppm
total 11 ppm
time-errant muons 3.5 ppm
space-errant muons 2 ppm
pulse pile-up 2 ppm
instrumental linearites 2.5 ppm
τ μ (MuLan) =
2.197013(21)(11) μs

11ppm
16ppm

MuLan progress – 06,07 runs
“Part-per-million goal.”
- improved beam extinction
- in-vacuum targets
- 500 MHz waveform digitizers

2006
ferromagnetic alloy
2007
quartz crystal

10 12 decays -> ~100 TB raw data -> ~10 5 CPU hours
understanding systematics including ~100 ppm effects of
pile-up and µSR to sub-ppm levels
e.g
+ + ...

Goal 1ppm!

muCap experiment – negative muon lifetime
in 1% LH 2 density, 300 K, ultra-pure hydrogen
−1 −1
p n , . D= − p
g p coupling ,QCD symmetries
muSun experiment – negative muon lifetime
in 5% LD 2 density, 30 K, ultra-pure deuterium
d n n , D= .
−1 − d
−1
astro− phys , neutrino− phys.

muCap experiment – negative muon lifetime
in 1% LH 2 density, 300 K, ultra-pure hydrogen
muSun experiment – negative muon lifetime
in 5% LD 2 density, 30 K, ultra-pure deuterium

muCap experiment – negative muon lifetime
in 1% LH 2 density, 300 K, ultra-pure hydrogen
muSun experiment – negative muon lifetime
in 5% LD 2 density, 30 K, ultra-pure deuterium

muCap experiment – negative muon lifetime
in 1% LH 2 density, 300 K, ultra-pure hydrogen
−1 −1 −1
p n ; . S= − p=725±17
s ; g p=7.3±1.1
muSun experiment – negative muon lifetime
in 5% LD 2 density, 30 K, ultra-pure deuterium
−1 −1 −1
d n n ; . D= − d=?
s ; astro ,neutrino