NEUTRONS, PARTICLES, AND THE UNIVERSE. Dirk Dubbers, U. Heidelberg. A. OVERVIEW. The ultimate aims of PARTICLE Physics :. Maxwell eqs., Schrödinger eq. electroweak eqs., quantumchromodyn., ... (works beautyf. ) gravitation, masses, charges, families,
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NEUTRONS, PARTICLES,
AND THE UNIVERSE
Dirk Dubbers, U. Heidelberg
ESS 17.05.2002 Neutron Particle Physics
A. OVERVIEW
The ultimate aims of PARTICLE Physics:
Maxwell eqs.,
Schrödinger eq. electroweak eqs., quantumchromodyn.,
... (works beautyf.)
gravitation, masses, charges,
families,
...(doesn't work yet)
Derive the basic laws of nature …
e.g. 'gauge invariance' implies
E = /0
E+Bt = 0 B = 0
c2BEt = j/0
… from simple symmetry principle(s)
Link all this to cosmology:
ESS 17.05.2002 Neutron Particle Physics
ESS 17.05.2002 Neutron Particle Physics
The role of the NEUTRON
Beam energy in experiments:
Highenergy particle physics at TeraeV10+12 eV
Studies on 2nd and 3rd particle families
3rd: b, t, , 2nd: s, c, ,
Lowenergy particle physics at NanoeV109 eV
Precision studies on 1st particle family1st: d, u, e,e
ESS 17.05.2002 Neutron Particle Physics
Sensitivity of neutron experiments:
Energy:E ~ 1022 eV
Momentum:p/p = 1011
Polarization:P ~ 107
Neutron exp’t:
EDM: E/ ~ 1/month
ncharge: 1Å on 10m
Pviolation: 0.000010 spinrot.
Neutronparticle physics:
free neutron
provides more than two dozen observables
Neutron Data Booklet 2002
addresses about two dozen
from particle physics and cosmology:
ESS 17.05.2002 Neutron Particle Physics
B. SOME PAST ACHIEVEMENTS
redshifts and microwave background
pre1990: 'soft' qualitative evidencefor Big Bang
1990: 'hard' numeric evidence for Big Bang:
after 1 sec:freezeout of neutron/proton ratio to 1/7:
after 10 min:lightelement abundances:
relative to hydrogen
n
p
ESS 17.05.2002 Neutron Particle Physics
n p+e–+e*
n+e p+e–
is universeopen, closed, or critical (flat) ?
This makes: number of particle familiesN
and density of the universe
accessible to observation! But:
Largest error is due to neutron lifetime
From 4He yield:
N = 13 /
ln/0 = 20 /
. · · . · · . . . · · . . . · .· . UCN
Measurement of in ultracoldneutron bottle Tn 1 mK
Neutron lifetime :1985: (925 11) s
1990: (889 3) s
2002: (885.8 0.9) s
n = noexp(– t/)
ESS 17.05.2002 Neutron Particle Physics
1989: Big Bang result, with new neutron lifetime:
N = 2.6 0.3 i.e. N is limited to 3 families.
Confirmed later by highenergy experiment:
N = 3.00 0.02 now used as input
in Big Bang calculations.
Z0  width at CERN
This leaves the average densityof the universe as the only unknown parameter :
ESS 17.05.2002 Neutron Particle Physics
Answer: Yes, but not with ordinary matter!
Density of ordinary matter
Critical density
Y
/crit
Present status: Neutron lifetime is still largest source of error in 4Heabundance calculation
ESS 17.05.2002 Neutron Particle Physics
Neutrinos oscillate: e ,
'Leptonnumber oscillations'mc2 0.05 eV
's
detection efficiency 1/
'Strangeness oscillations' mc2 1018 eV
Kaons oscillate: K K*
Do neutrons oscillate n n*(neutron antineutron, 'nnbar' )
'Baryonnumber oscillations' B = +1 1
Baryonnumber oscillations are allowed in some GrandUnified Theories.
ESS 17.05.2002 Neutron Particle Physics
The antineutron detector
Experimental limit: nn* > 2.9 years
< nHn*> 1023 eV
(90% c.l.)
Present: limit on neutron oscillations probes 105 GeV range Future: neutronoscillation search with UCN ?
ESS 17.05.2002 Neutron Particle Physics
Within seconds, solarsystem masses are created in SuperNova explosions. The field urgently needs neutronnuclear data.(from neutronfission products 'faroff stability')
SuperNovae do explode, though not on the computer.
n(C)= Cn(R)n(R)·dR
Mathematical 'theories of connections'
are right at the heart of avantguard physics.
1984: Berry's theorems on 'topological phases'
1985: first measurements with polarized neutrons
1995: 'hidden symmetries' detected with microwaves
2000: theory of 'offdiagonal Berry Phases' developed
2001: first measurements with neutron interferometry
ESS 17.05.2002 Neutron Particle Physics
R(3600) = 1 AharonovBohm AharonovCasher squeezed states beat optics dressed neutrons optical pumping ...
This, too, is a neutron:
= I + II 2
Status: Nonclassical states of neutrons and UCN can be produced and used in neutroninterferometry and spinecho systems
ESS 17.05.2002 Neutron Particle Physics
Neutrons are sensitive to all four forces of nature
1. THE 'WEAK' FORCE:
Neutrondecay measurements:
• neutron lifetime = (885.8 0.9) s
• electronneutrino correlation a = 0.102 0.005
• beta asymmetry A = 0.1189 0.0007
• neutrino asymmetry B = 0.983 0.004
• triplecorrelation D = (0.55 0.95)103 . . .
give nucleonlepton weakinteraction couplingconstants:
Vector: gV = (1.1470 0.0016)105 (c)3 GeV2
Axialvector: gA = (1.4602 0.0008)105 (c)3 GeV2
Phase(VA): = 180.070 0.120.
ESS 17.05.2002 Neutron Particle Physics
Example: betaasymmetry in neutron decay
Experiment:
(= e)
neutrons spin up
Detector
Beamtime will start soon
Problem is overdetermined: precision tests beyond the Standard Model (see below)
ESS 17.05.2002 Neutron Particle Physics
2. THE ELECTROMAGNETIC FORCE:
The strength of the electromagnetic force is given by the finestructure constant
= e2/c =(2Rh/mec)½
neutron measurements of:
h/mn = (3.956 033 3 0.000 000 3)107 m2s1
mn/mp = 1.001 378 418 87 0.000 000 000 58
give a modelindependent value:
1 = 137.036 011 0.000 005
nvn = h/m, h = Planck's const.
… plus R plus mp/me
is needed for precision tests of Standard Model
example: magnetic moment of muon
Theory (input ):
g=2.002 331 8320(14)
Experiment: 3 deviation?
g=2.002 331 8404(30)
Status: Neutron data give strengths of 2 of the 4 forces of nature
ESS 17.05.2002 Neutron Particle Physics
Neutron: gravitational force/inertial force: = 1.00011 0.00017
3. THE GRAVITATIONAL FORCE:
Quantization of UCN in the earth's gravitational field: Do neutrons fall in 'steps'? Answer: yes, they do!
•_
_
_
4. THE 'STRONG' FORCE:(see below)
ESS 17.05.2002 Neutron Particle Physics
C. ESSFLAGSHIP EXPERIMENTS
Standard Model: strong interactions of protonproton, protonneutron, and neutronneutron must all be equal.
But: scattering lengthsapp = 23.82(1) fm
anp = 17.1(2) fm
ESS FLAGSHIP: DIRECT MEASUREMENT OF NEUTRON  NEUTRON SCATTERING LENGTH ann
UCN ?
N.B.: nn rate (nflux)2 !
Expected nn scattering rate: several events per minute
ESS 17.05.2002 Neutron Particle Physics
. ..qq*.
Big Bang theory: matter and antimatter should annihilate each other
vs. evidence:we exist
explanation: violation of 'CPsymmetry' ?
(Sacharow 1965)
experimentum crucis:
Electric Dipole Moment (EDM) of the neutron:
if 'CP' explanation is right: EDM = 10271 ecm
= value required to explain our existence
if 'CP' explanation is wrong: EDM = 10321 e cm
= value predicted by the Standard Model
present experimental limit: EDM < 6.31026e cm
CPT=1
Ultracold neutrons !

EDM
+
(90% c.l.)
ESS 17.05.2002 Neutron Particle Physics
ESSFLAGSHIP: NEW TYPE OF ULTRACOLD NEUTRON (UCN) SOURCE
Soliddeuterium UCNsource
Future: Question of dominance of matter over antimatter will be solved in the next twenty years. ESS should be in the game and provide strongest UCN source in the world.
ESS 17.05.2002 Neutron Particle Physics
Standard Model:
Electroweak Interaction is 100% lefthanded
Did Universe start leftright symmetric, i.e. is lefthandedness an 'emergent property' ?
If so, then 'righthanded' heavy brother of Wboson must exist
did parity violation arise as an orderparameter during a phase transition of the vacuum in the early universe
Limits from neutron decay experiments:
mass of righthanded W:mR > 280 GeV/c2
leftright mixing phase: 0.20 < < 0.07
mL=81 GeV/c2
WL=W1cos–W2sinWR=W1sin+W2cos
(90 % c.l.)
Present: neutrons very competitive with highenergy work
ESS 17.05.2002 Neutron Particle Physics
ESSFLAGSHIP: SPONTANEOUS TRANSFORMATION OF A FREE NEUTRON INTO A HYDROGEN ATOM
Experimentum crucis: would isolate effect of righthanded boson
Fasthydrogen recoil detector
n H(2S) + e*mS:+½ +1 +½ (lefthd.) mS:+½ +1 –½ (righthd.)
Decay volume
Cold neutrons
Optical detection of Lyman in fast coincidence
Interesting event signature. Expected n H rate:10 events/minute
Future: sensitive yes/no experiment on origin of Pviolation
ESS 17.05.2002 Neutron Particle Physics
When quarks are subject to electroweak force:
'down' = down + some strangeness + some bottomness
'strange' = strange+ some downness + some bottomness
'down' = down + some strangeness + some downness( with respect to 'mass eigenstates')
quark mixing matrix is 'unitary' (pure rotation in 'flavor' space)
Standard Model of Particle Physics requires:
this 'quarkmixing' should be a zerosum game
From neutron decay experiments:
3.0 standard deviations from zero observed: = 0.0083 0.0028
Present: puzzling deviation from Standard Model ?
ESS 17.05.2002 Neutron Particle Physics
ESSFLAGSHIP: THE ULTIMATE NEUTRONDECAY CORRELATION EXPERIMENT
ESS neutron longpulset = 2 ms
Beam chopper
= 4.5 Å, = 1.5 Å I = 1.2 ·1010/s (peak)
Freeneutron cloud N = 2·108 neutrons
103m/s
Future: neutron decay at rate N/ =2·105/s studied under optimum conditions
107m/s
timeaverage: 104/s present rate: 2 ·102/s
Beam chopper
B
decay products locked to Bfield
e and p+ detector timegated
ESS 17.05.2002 Neutron Particle Physics
D. SUMMARY
ESS 17.05.2002 Neutron Particle Physics
E. CONCLUSION
Neutronparticle and neutronnuclear physics is a successful and growing field of neutron science.
in recent years: + 4 university chairs + 4 associate profs. solely in D
ESS WILL PROVIDE AN OPTIMAL TOOL FOR THEIR WORK.
ESS 17.05.2002 Neutron Particle Physics