1. Precision experiments
practical tools
scientific:
test of theoretical models, existing laws of physics
confirm and/or constrain models
potential to discover (interactions, particles, ...)
Electroweak precision experiments
measures in the distant past
precision measurements: what do they provide?
precision experiments part of large facilities
precision experiments with neutrons
proton decay measurements
muon decay measurements
neutron decay measurements
lifetime experiment
correlation parameters between neutron
and decay products
neutron electric dipole moment experiments

2. precision experiments: measurement tools
measures: a practical tool
define a length on the basis of a common feature
~ 3400 BC
1 cubit
Royal cubit stick
Giza pyramids
sides built on the basis of the cubit
to a precision of 0.05%!!!

3. precision experiments: measurements
measurements: to add to academic interests
deduce earth curvature by angle of sunlight
250 BC - Eratosthenes:
In Syene ~5000 stadia south of Alexandria
sunlight shining directly down well shafts
in Alexandria light measured to be at 7 angle
~5000 × 360/7 = 252,000 stadia (of the order of 40,000 km) - (cf 40,030 km)

4. precision experiments: particle physics
Scientific precision experiments: testing the limits of our description
and understanding of nature
particle physics:
masses and lifetimes of particles (quarks, leptons, hadrons, ...)
matrix elements of transitions (CKM, PMNS, nuclear trs, ...)
forces and couplings in reaction processes (GF, , ... )
signals of rare events, breaking of laws and symmetries, ...
proton lifetime
neutron lifetime (Vud)
neutron decay
neutrinoless -decay
Maki-Nakagava-Sakata
goes hand-in-hand with ever more
precision calculations

5. precision experiments: proton decay
Standard Model describes the change of quark colour and flavour
and lepton conversion through gauge bosons g, W±, Z0 d u
decay rate as function of energy T, coupling constant G: s d u νe e- Λ0
( Baryon number B and lepton number L conserved ) p

6. precision experiments: proton decay
GUT mechanisms
in models quarks and leptons incorporated into common families (e.g. e+ with d):
interaction with new gauge bosons (X, Y)
masses MX ~ 1015 GeV, coupling gU ~ 1/42
new allowed processes:
p → π0 + e+
( Baryon number B and lepton number L NOT conserved )
into specific channel:

7.    (100 km < L < 10,000 km)
precision experiments: proton decay
Super kamiokande: neutrino oscillation experiment
11,200 PMTs detecting e and 
50,000 tonnes of ultra-pure water, 1000m
underground in the Kamioka Mine
   (100 km < L < 10,000 km)
neutrino flavour states mix, neutrino’s are massive
Super kamiokande: use data to look for proton decay events

8. precision experiments: proton decay
106 event triggers per day:
background from cosmic rays
flashing PMT’s
radioactivities
analyse all data to look for electron signals:
in the correct energy range
total invariant mass per event determined
in the correct momentum range
from the correct part of detector
18816 surviving events:
precision measurement constraining GUT’s

9. precision experiments: lepton g-2
1927 Dirac intrinsic angular momentum and magnetic moment
of electron quantified
measurements of g factors pushed further development of QED
May and November 1947 electron g factor measurement different
from 2: g factor anomaly ae
Formulation of QED with first order radiative correction
six orders of magnitude improvement in precision expts
and theoretical calculation
testing the Standard Model to its limits, discovery of new
interaction beyond SM

10. precision experiments: lepton g-2
protons
target
pions
muons
detectors
muon decay to electron
Muon g-2 experiment Brookhaven
24 GeV proton focused on nickel target generates pions
pions decay to polarised muons and are injected in storage ring
decay electrons emerge preferentially in direction of muon spin
detect those electrons with high enough energy to be in the direction of the muon motion
detecting a signal of the muon spin in forward direction
signal oscillates with spin precession frequency of muon

11. precision experiments: lepton g-2
Brookhaven National Lab: 3 GeV muons stored in 14 m dia. ring in 1.45 T field
muon has orbital motion in magnetic field
at cyclotron frequency ωC
spin has precession frequency ωS
relative precession of S with respect to velocity
of muon: ωS- ωC
direct relationship between ωD and a

12. precision experiments: lepton g-2

13. precision experiments: lepton g-2SM
Experiment
March 2001 PRL
first signs of deviation from 2.6σ
Standard Model description?
not quite... error in experimental analysis code
six orders of magnitude improvement in precision expts
opening a window to beyond SM physics phenomena

14. precision experiments: neutron decay
neutron beta decay experiment:
Standard Model precision measurements
precision tests on unitarity of the CKM matrix
cosmological significance
neutron decay probability, function of particles momenta, spin, correlation coefficients

15. precision experiments: neutron decay parameters
neutron beta decay experiment:
correlation coefficients between particles spin and momenta
coupling constants
correlation electron and anti-neutrino momentum
correlation electron momentum – neutron spin
ratio axial-vector / vector coupling constant
free neutron decay
from muon decay

16. precision experiments: neutron correlation parameter experiments
measurement of λ
the “A” experiment: correlation electron momentum – neutron spin
polarised neutrons
electron detection with respect to neutron spin direction

17. Spectra for both spin states
2002: result: A = (8)  = (19) 2006: result: A = (5)  = (13)
testing the CKM matrix of Standard Model
B. Maerkisch, PERKEO III : Neutron Decay Measurements

18. precision experiments: neutron correlation parameter experiments
measurement of λ
the “a” experiment: correlation electron-neutrino momentum
proton energy spectrum depends on a p
neutrons (unpolarised)
proton detection, energy measurement p
neutrons energy ~ meV, energy release ~MeV n n e- e-
proton energy depends on angle between electron and anti-neutrino

19. precision experiments: neutron correlation parameter experiments
measurement of proton energy spectrum
Penning trap
proton detection, energy measurement
cold neutrons pass through volume between two electrodes, kept in a magnetic field
decay protons trapped and orbit around magnetic field lines
open trap by lowering voltage on gate electrode
repeat sequence for mirror voltages ranging 0V to 800 V

20. precision experiments: neutron correlation parameter experiments
measurement of decay proton integrated energy spectrum
fit curve to energy spectrum as function of a:
no competition for A measurement but independent method
a = ± , λ = ± 0.018

21. precision experiments: neutron lifetime experiments
the neutron lifetime experiment:
precision tests on unitarity of the CKM matrix
cosmological significance
neutrons (of cold or ultra-cold energy)
detect decay products or detect surviving neutrons
experiment at NIST - USA:
beam of cold neutrons
neutrons pass through penning trap
decay protons recorded

22. precision experiments: neutron lifetime experiments
the neutron lifetime experiment: NIST
superconducting magnet 3T
incoming neutron beam
solid-state
charged particle detector
high voltage (27 kV) cage for
proton acceleration

23. precision experiments: neutron lifetime experiments
need to know neutron flux to very high precision
need to know trap volume to high accuracy
need to know efficiency of detectors to high accuracy
need to collect many events for statistical precision
the neutron lifetime experiment: NIST
neutron flux monitor: n + 6Li→3H + 
ρ = (39.30 ± 0.10) µg/cm2 6Li density
σ = (941.0 ± 1.3) b absorption cross section at 2200 m/s
Ω/4π = ± 0.1% fractional solid angle detector
τn = ± 3.4 s.

24. precision experiments: neutron lifetime experiments
the neutron lifetime experiment: stored ultra-cold neutrons
experiment at ILL:
ultra-cold neutrons guided into storage chambers
seal chamber and store neutrons for a period T
open chamber to neutron detector and count remaining neutrons
repeat cycle for different storage periods T
two storage chamber configurations: different surface exposure
UCN
detector

25. precision experiments: neutron lifetime experiments
the neutron lifetime experiment: stored ultra-cold neutrons
need to know neutron flux stability
need to know neutron loss mechanism during storage
need to collect many events for statistical accuracy
different detection efficiencies for two chamber configurations ± 0.36 s
uncertainty in shape of chamber
statistical uncertainty

26. precision experiments: neutron lifetime experiments
experiment at ILL:
ultra-cold neutrons guided into storage chambers
seal chamber and store neutrons for a period T
open chamber to neutron detector and count remaining neutrons
repeat cycle for different storage periods T and different energies
the neutron lifetime experiment: stored ultra-cold neutrons

27. precision experiments: neutron lifetime experiments

28. precision experiments: neutron lifetime experiments
the neutron lifetime experiment: stored ultra-cold neutrons
latest result too far off to be included in average, now additional measurement:
polarised ultra-cold neutrons guided into storage chambers
seal chamber and store neutrons for a period T
open chamber to neutron detector and count remaining neutrons
repeat cycle for different storage periods T

29. precision experiments: neutron lifetime experiments
measurements / error bars incompatible, to be continued...

30. Vud from neutron and nuclear beta decay
n = (878.5  0.7st  0.3syst) s
“Gravitrap” result
n = (885.7  0.7) s
world average
Perkeo result:
A0 = (7)
 = (19)
=GA/GV

31. precision experiments: neutron electric dipole moment
If average positions of positive and negative charges do not coincide:
EDM dn + -
T reversal dn S
electric dipole moment dn
spin S + - dn S + -
Electric Dipole Moment:
neutron is electrically neutral
P transform. dn S + - dn S - +
P & T violation
CPT conservation  CP violation
CP violation in Standard Model generates very small neutron EDM
Beyond the Standard Model contributions tend to be much bigger
neutron a very good system to look for CP violation beyond the Standard Model

32. nEDM: measurement principle
Compare the precession frequency for parallel fields:
 = E/h = [-2B0n - 2Edn]/h
Experiments:
Measurement of Larmor precession frequency of polarised neutrons in a magnetic & electric field
to the precession frequency for anti-parallel fields
 = E/h = [-2B0n + 2Edn]/h
: polarisation product
E: electric field
T: observation time
N: number of neutrons
The difference is proportional to dn and E:
h( - ) = 4E dn

33. nEDM: measurement principle4. 3. 2. 1.
Free precession...
Apply /2 spin
flip pulse...
“Spin up” neutron...
Second /2 spin
flip pulse.

34. nEDM at ILL: scheme used
Four-layer mu-metal shield
High voltage lead
Quartz insulating cylinder
Coil for 10 mG magnetic field
Upper electrode
Main storage cell
Hg u.v. lamp
PMT to detect Hg u.v. light
Vacuum wall
Mercury prepolarising cell
RF coil to flip spins
Magnet
UCN polarising foil
UCN guide changeover
Ultracold neutrons
(UCN)
UCN detector

35. nEDM at ILL: set-up room temperature experiment

36. nEDM at ILL: normalised frequency measurement

37. nEDM at ILL: performance room temperature experiment

38. nEDM: experiment vs theory
10-19
10-20
10-21
10-22
10-23
10-24
10-25
10-26
10-27
10-28
year of publication
Experiment Theory
10-29
10-30
10-31
10-32
10-33
10-34
10-35
Neutron EDM upper limit [ecm]
nEDM: experiment vs theory
Progress at ~ order of magnitude per decade
Standard Model out of reach
Severe constraints on e.g. Super Symmetry
|dn|< 3 x ecm
dn = 1 ecm

39. precision experiments
we have seen:
precision measurements examples
neutron electric dipole moment experiments
neutron lifetime & correlation experiment
anomalous g-factor (g-2)
decay experiments (p, double beta)
these can:
test of theoretical models, existing laws of physics
confirm and/or constrain models
potential to discover (interactions, particles, ...)
current precision experiments:
mostly indirect measurements
a very powerful tool to probe theories
and their limits
revealing signatures of new physics