Post on 16-Dec-2015
• measures in the distant past• precision measurements: what do they provide?• precision experiments part of large facilities• precision experiments with neutrons
Precision experiments
Electroweak precision experiments
proton decay measurementsmuon decay measurements
neutron decay measurements lifetime experiment correlation parameters between neutron
and decay productsneutron electric dipole moment experiments
practical toolsscientific:
test of theoretical models, existing laws of physics
confirm and/or constrain modelspotential to discover (interactions,
particles, ...)
precision experiments: measurement tools
~ 3400 BC
Giza pyramids
sides built on the basis of the cubitto a precision of 0.05%!!!
Royal cubit stick
measures: a practical tool
define a length on the basis of a common feature
1 cubit
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)
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, ...
goes hand-in-hand with ever moreprecision calculations
• proton lifetime
• neutron lifetime (Vud)
• neutron decay
• neutrinoless -decay
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
sdu
udu
e-
νe
Λ0
p( Baryon number B and lepton number L conserved )
52TKGF
2
2
2 W
WF
M
gG
decay rate as function of energy T, coupling constant G:
precision experiments: proton decay
new allowed processes:p → π0 + e+
GUT mechanismsin 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
4
54
X
pU
M
Mg
d
u
u
u
u-
e+
p
0
{}
X
u
u
u-
u
d
p{0}
e+
Y-
i
iLBLB
yrp291 10 yr
ep
32100
( Baryon number B and lepton number L NOT conserved )
into specific channel:
Super kamiokande: neutrino oscillation experiment
11,200 PMTs detecting e and 50,000 tonnes of ultra-pure water, 1000m underground in the Kamioka Mine
Þ (100 km < L < 10,000 km)
neutrino flavour states mix, neutrino’s are massive
precision experiments: proton decay
Super kamiokande: use data to look for proton decay events
precision experiments: proton decay
)%90(102.8/ 330 CLyrB
ep
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
106 event triggers per day:
• background from cosmic rays• flashing PMT’s• radioactivities
p → π0 + e+
Þ 18816 surviving events:
precision measurement constraining GUT’s
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 differentfrom 2: g factor anomaly ae
• Formulation of QED with first order radiative correction
2,2
2
gS
Sm
gq
)5(00119.02
2
gae
00116.02
six orders of magnitude improvement in precision expts and theoretical calculation
testing the Standard Model to its limits, discovery of newinteractions beyond SM
protons
target
pions muons
detectorsmuon decay to electron
precision experiments: lepton g-2
• 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
Muon g-2 experiment Brookhaven
precision experiments: lepton g-2
Brookhaven National Lab: 3 GeV muons stored in 14 m dia. ring in 1.45 T field
mc
eBc
2
22
2
ga
mc
eBa
gccSD
mc
eB
mc
eBgS
)1(2
• 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
precision experiments: lepton g-2
precision experiments: lepton g-2
first signs of deviation of 2.6σ from Standard Model description?
not quite... error in experimental analysis code
11659100 11659150 11659200 11659250
SM
1010a
Experiment
March 2001 PRL
six orders of magnitude improvement in precision expts opening a window to beyond SM physics phenomena
precision experiments: neutron decay
neutron beta decay experiment:
• Standard Model precision measurements• precision tests on unitarity of the CKM matrix• cosmological significance
1222 ubusud VVV
keVepn e 782
EE
ppD
E
pB
E
pAP
EE
ppa
E
mbdW
e
e
e
en
e
e
e
e
1
neutron decay probability, function of particles momenta, spin, correlation coefficients
precision experiments: neutron decay parameters
correlation electron and anti-neutrino momentum
neutron beta decay experiment:
• correlation coefficients between particles spin and momenta• coupling constants
2
2
31
1
a 231
12
A
correlation electron momentum – neutron spin
V
A
G
G
45
732
cmK
e
FudV GVG 22 31
Vn
n Gf
K
free neutron decay lifetime
from muon decay
ratio axial-vector / vector coupling constant
the “A” experiment: correlation electron momentum – neutron spin
• polarised neutrons• electron detection with respect to
neutron spin direction
precision experiments: neutron correlation parameter experiments
measurement of λ
Spectra for both spin states
B. Maerkisch, PERKEO III : Neutron Decay Measurements
2002: result: A = -0.1189(8) = -1.2739(19)2006: result: A = -0.1198(5) = -1.2762(13)
testing the CKM matrix of Standard Model
precision experiments: neutron correlation parameter experiments
precision experiments: neutron correlation parameter experiments
• neutrons (unpolarised)• proton detection, energy measurement
the “a” experiment: correlation electron-neutrino momentum proton energy spectrum depends on a
n
p
e-e
n
p
e-
eneutrons energy ~ meV, energy release ~MeV
proton energy depends on angle between electron and anti-neutrino
measurement of λ
• 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
measurement of proton energy spectrum
precision experiments: neutron correlation parameter experiments
precision experiments: neutron correlation parameter experiments
a = -0.1054 ± 0.0055, λ = 1.271 ± 0.018
measurement of decay proton integrated energy spectrum
fit curve to energy spectrum as function of a:
no competition for A measurement but independent method
precision experiments: neutron lifetime experiments
• neutrons (of cold or ultra-cold energy)• detect decay products or detect surviving neutrons
the neutron lifetime experiment:• precision tests on unitarity
of the CKM matrix• cosmological significance
experiment at NIST - USA:
• beam of cold neutrons• neutrons pass through penning trap• decay protons recorded
precision experiments: neutron lifetime experiments
superconducting magnet 3T
solid-statecharged particle detector
high voltage (27 kV) cage forproton acceleration
incoming neutron beam
the neutron lifetime experiment: NIST
τn = 885.5 ± 3.4 s.
• 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
precision experiments: neutron lifetime experiments
• ρ = (39.30 ± 0.10) µg/cm2 6Li density• σ = (941.0 ± 1.3) b absorption cross section at 2200 m/s• Ω/4π = 0.004196 ± 0.1% fractional solid angle detector
the neutron lifetime experiment: NIST
neutron flux monitor: n + 6Li→3H +
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
the neutron lifetime experiment: stored ultra-cold neutrons
UCN
detector
two storage chamber configurations: different surface exposure
precision experiments: neutron lifetime experiments
• 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
the neutron lifetime experiment: stored ultra-cold neutrons
precision experiments: neutron lifetime experimentsexperiment 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
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
precision experiments: neutron lifetime experiments
precision experiments: neutron lifetime experiments
measurements / error bars incompatible, to be continued...
the neutron lifetime experiment: stored ultra-cold neutrons
precision experiments: neutron lifetime experiments
Vud from neutron and nuclear beta decay
=GA/GVPerkeo result:A0 = -0.1189(7) = -1.2739(19)
n = (885.7 0.7) sworld average
n = (878.5 0.7st 0.3syst) s“Gravitrap” result
2
2
31
9.17.4908
n
ud
sV
P & T violation
CPT conservation CP violation
Electric Dipole Moment:
neutron is electrically neutral
If average positions of positive and negative charges do not coincide:
EDM dn
+
-
T reversaldn S
electric dipole moment dn
spin S
+
- dn S
+
-
P transform.dn S
+
- dn S-+
precision experiments: neutron electric dipole moment
CP violation in Standard Model generates very small neutron EDMBeyond the Standard Model contributions tend to be much bigger
neutron a very good system to look for CP violation beyond the Standard Model
Compare the precession frequency for parallel fields:
= E/h = [-2B0n - 2Edn]/h
to the precession frequency for anti-parallel fields
= E/h = [-2B0n + 2Edn]/h
The difference is proportional to dn and E:
h( - ) = 4E dn
Experiments: Measurement of Larmor precession frequency of polarised neutrons in a
magnetic & electric field
NETdn
2
)(
: polarisation productE: electric fieldT: observation timeN: number of neutrons
nEDM: measurement principle
4.
3.
2.
1.
Free precession...
Apply /2 spinflip pulse...
“Spin up” neutron...
Second /2 spinflip pulse.
29.7 29.8 29.9 30.0 30.1
10000
12000
14000
16000
18000
20000
22000
24000Ramsey Resonance Curve
working pointsresonance frequency
1/Ts
ne
utr
on s
pin
up
co
un
t
applied frequency [Hz]
nEDM: measurement principle
N S
Four-layer mu-metal shield High voltage lead
Quartz insulating cylinder
Coil for 10 mG magnetic field
Upper electrodeMain storage
cell
Hg u.v. lamp
PMT to detect Hg u.v. lightVacuum wall
Mercury prepolarising
cell
Hg u.v. lampRF coil to flip spins
Magnet
UCN polarising foil
UCN guide changeover
Ultracold neutrons
(UCN)
UCN detector
nEDM at ILL: scheme used
nEDM at ILL: set-up room temperature experiment
0 5 10 15 2029.9260
29.9265
29.9270
29.9275
29.9280
29.9285
29.9290
29.9295
10-10
T
Neu
tron
re
sona
nt fr
eque
ncy
(Hz)
Run duration (hours)
7.7882
7.7884
7.7886
7.7888
7.7890
nEDM at ILL: normalised frequency measurement
1300 1400 1500 1600 1700 1800 1900-60
-40
-20
0
20
40
60
80
100
neut
ron
ED
M [1
0-25 e
cm
]
run number
ecmdn26103
nEDM at ILL: performance room temperature experiment
-e
+e
1 cm
dn = 1 ecm
10-19
10-20
10-21
10-22
10-23
10-24
10-25
10-26
10-27
10-28
1960 1980 2000year of publication
Experiment Theory10-19
10-20
10-21
10-22
10-23
10-24
10-25
10-26
10-27
10-28
10-29
10-30
10-31
10-32
10-33
10-34
10-35
Neu
tron
ED
M u
pper
lim
it [
ecm
]
Progress at ~ order of magnitude per decadeStandard Model out of reachSevere constraints on e.g. Super Symmetry
|dn|< 3 x 10-26 ecm
nEDM: experiment vs theory
precision experiments
test of theoretical models, existing laws of physics
confirm and/or constrain models
potential to discover (interactions, particles, ...)
precision measurements examples neutron electric dipole moment experiments neutron lifetime & correlation experiment anomalous g-factor (g-2) decay experiments (p, double beta)
mostly indirect measurements
a very powerful tool to probe theoriesand their limits
revealing signatures of new physics
we have seen:
these can:
current precision experiments: