measures in the distant past precision measurements: what do they provide?

• 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:


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


Super kamiokande: use data to look for proton decay events


)%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


• 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


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


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

Kfree neutron decay

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


• 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



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


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


• 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 +


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


• 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


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



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



measurements / error bars incompatible, to be continued...

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:

measures in the distant past precision measurements: what do they provide?

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