Particle Physics with Slow Neutrons II LNGS Summer Institute, September 2005Torsten Soldner Lecture II: Neutrons beyond the SM Motivation Right-handed

Particle Physics with Slow Neutrons II LNGS Summer Institute, September 2005 Torsten Soldner

Lecture II: Neutrons beyond the SM

• Motivation• Right-handed W bosons

– Classical theory of neutron decay

– Search for traces of WR in decay asymmetries

• CP violation beyond the SM– Search for CP violation in neutron decay

– Electric dipole moments

– Measurement of the neutron EDM

• Baryon number violation– Scenarios of Baryon number violation

– Search for neutron-antineutron oscillations


Neutron Decay beyond the Standard Model

eeu

d

LW

F5 5 e1 1

2ud

GV u d e

e

L

L

e

L

L

u

d

L 1

i iR 2

cos sin

e sin e cos

W W

W W

eeu

dRW

(broken) SU(2)LSU(2)R

deviation from maximal parity violation (V+A)

additional phases for CP violation

eeu

d

1X

Exotic (non V,A) couplings

scalar, tensor, or pseudo- tensor interactions

Standard Model

SU(2)L (V-A interaction)

uee

d

1

3S

Leptoquark exchange

additional phases for CP violation

exotic couplings


Neutrons and New Physics

Search for processes which •are unobservably small in the SM

•are not allowed in the SM•deviate observables from the SM values

CP violation

•Electric dipole moment

•Triple correlations D or R of the decay products

Baryon number violation

•Neutron-Antineutron-Oscillations

Right-handed currents

•Neutrino asymmetry B

•CP-violating phases (dn, D, R)

L 1i i

R 2

cos sin

e sin e cos

W W

W W

Unification scenarios Left-right symmetric models

New interactions (SuSy…) new phases

Baryon asymmetry


Why should we search for CP or B violation?

Baryon Asymmetry in the Universe

•Baryon number violation

•C and CP violation

•Thermal non-equilibriumA.D. Sakharov: JETP 5 (1967) 24

Standard Model

•B violation in sphalerons (B–L conserved)

•C violation in weak interaction

•CP violation in Kaons, B mesons

•Thermal non-equilibrium in electroweak phase transition

But

Not enough CP violation for Baryogenesis

Higgs boson too heavy to create first order phase transition

New physics required

10B

γ

6.1(2) 10


Classical Theory of Weak Decay

{S,V,T,A

5,P}

w51 1

2i i ii i

ii

GH p n e pL R n e

O O O O

p nF5 5 e

p

1 122

ud

GH p q n e

mV

• Standard Model:

i

iiiii eCeCnpG

H 5w '2

OOO

S

V

A 5

T

P 5

1 scalarvectoraxial vector

tensor2 2

pseudoscalar

OOO i

iO

O

n

eep

• General Hamiltonian:


Find the Parameters…

e e n e ee e

e e e e n e e

d( ) 1

d d da

Wb A B

mG E

E ED

E E E E E E

p p σ p p p p

e n ee e

e n e

d ( ) 1EE

RW G

σ σ p

w5 5

{S,V,T,A,P}

1 12

i i i ii

i i

GH p n e p n eL R

O O O O

J.D. Jackson et al.: Phys. Rev. 106 (1957) 517

2 2 2 2 2 2 2 2

S T V S T A

* * * *S T S V A T

2 2 2 2* * * *T S T A V A T S T

* * * *S T S T V A

2 2 2 2 2 2 2 2

S T

V A

V A

A V A

V A

V V T AA S

1

2Re 3 3

2Re

2Im

3 3 3 3

a L L R R R R

b L L R R R R

A L L L

L L

L L

L L L

L L

L

R R R R R R

D L L R R R R

RLL L R R R

0b

2

12

1 3A

0D

2

2

1

1 3a

A

V

L

L

Surviving in the SM:


Find the Parameters…

e e n e ee e

e e e e n e e

d( ) 1

d d da

Wb A B

mG E

E ED

E E E E E E

p p σ p p p p

e n ee e

e n e

d ( ) 1EE

RW G

σ σ p

w5 5

{S,V,T,A,P}

1 12

i i i ii

i i

GH p n e p n eL R

O O O O

udVg

g,

V

A

or

T violation beyond SM

Test for righthanded currents


Example: Right-Handed Currents

2

2

1

1 3a

2

12

1 3B

2

12

1 3A

Standard Model (V-A)eeu

dLW

L 1

R 2

cos sin

sin cos

W W

W W

eeu

dRW

+

2

1

2

,M

M

V

A

, 1

V

, 1

A

1

R

R

L

L

SM + (V+A)-contributions2 2 2

V A2 2

V2

A

1

1 3 3

R R

Ra

R

A A V2 2 2

V A3

12

1 3B

R R R

R R

A A V2 2 2

V A

12

1 3 3

R R R

RA

R

and ft(0+0+) and n

B = 0.983(4) [PDG 2004]

Fro

m K

3, K

2

B = 0.983(2) [just for fun]

Fro

m K

3, K

2

and n

B = 0.983(4) [PDG2004]

Fro

m K

3, K

2

Mai

nly

BMainly A


Proton detection: Ep < 750 eV

acceleration prior to detection

special low noise detectors needed

Challenges in Neutron Decay Experiments

Electron detection: Ee < 780 keV

typical energy of gamma background

sophisticated techniques difficult

Life time: =885.7(8) s

Velocity: 1000 m/s

only 10-7 of the passing neutrons decay, low statistics

all others can create background


Neutron Decay and Right-handed Currents

pσn1 B

Neutrino asymmetry

World average: B = 0.983(4)

Effect Error Polarisation analysis 0.26% Energy calibration / resolution Detector solid angle / backscattering Coefficients A and a Other effects

0.20% 0.16% 0.11% 0.07%

Statistics 0.26% Serebrov et al, JETP 86 (1998) 1074B=0.98010.0046


How to Improve?

22 spectrometer

Better statistical sensitivity

Backscattering suppressed

Solid angle:Magnetic field

Detector function:Electron and proton in same detector


First Experiment (2001)

Ep < 750 eV from decay

~20 keV after acceleration)

(4-5)20 keV in detector

B=0.9670.006stat0.010sys

Main limitations•Polarisation•Instable high voltage•Scintillator after pulses•High-voltage related background

Effect Error Polarisation analysis 0.5%

Energy calibration / resolution Detector solid angle / backscattering

Coefficients A and a Other effects Background

0.06% 0.07% 0.07% 0.6%

Statistics 0.8% M. Kreuz et al,PLB 619 (2005) 263

Error 0.26% 0.20% 0.16% 0.11% 0.07% 0.26%

Serebrov et al,JETP 86 (1998) 1074


Neutrons and CP (T) Violation

)(1d en ppσ DW

Triple correlations in the decay

)(1d ene pσσ RW

DSM10-12 DFSI=1.1·10-5 Dexp10-3

RSM10-12 RFSI=1·10-3 Rexp(goal)510-

3

dSM=10-33…10-31 ecm dexp10-25 ecm

r3n d)(rrd

Electric dipole moment


R & D

R coefficientD coefficient

P. Herczeg, Prog. Part. Nucl. Phys. 46 (2001) 413.

•P conserving sensitive to V,A type T violating duee interactions

•P violating sensitive to S,T type T violating duee interactions

EEDW

e

e

n

n1dppσ

en

en

e

e1dE

RW

pσσ

•Limits from P,T violating electron-nucleon interaction more stringent

•EDM more stringent for left-right, exotic fermions

•D more stringent for leptoquark

New T violation may contribute on the tree leveltheoretical uncertainties more reliable than for loop type contributions

Left-right Exotic fermions Leptoquark

Present sensitivity for Dtests MX in TeV range


DDNN

NNPκ

epep

epep

Principle Set-Up

Measurement of D

EEDW

e

e

n

n1dppσ

)(ddd

dee

ee

EGE

W

e

e

e

e1E

mb

EEa

pp

EB

EA

ppσ

e

e

n

n

P violation Asymmetry with spin-flip

BA BA PκPκ 00

11100100

4 DPD

Breaking of detector symmetrySystematic effects

D = 0 in SM


Measurement of D

PWM

D

1

L.J. Lising et al, PRC 62 (2000) 055501.

Optimise for Systematics Optimise for Statistics

D = (–2.86.4stat3.0syst)·10-

4T. Soldner et al, Phys. Let. B 581 (2004) 49.

D = (–612stat5syst)·10-

4


D & dn

Model D dn [ecm] Phase in CKM matrix 10-12 10-33…10-31

QCD parameter 10-16QCD Supersymmetry 10-7…10-6 present limits Left-right symmetric 10-5…10-4 present limits (d199Hg) Exotic fermions 10-5…10-4 present limits (d199Hg) Leptoquark present limits

Experiment -4(6)10-4 <0.6310-25 Final state effects 110-5

Cosmology 610-28…210-25 (via QCD)

P. Herczeg, Prog. Part. Nucl. Phys. 46 (2001) 413.

n e( )σ p p r3n d)(rrd


Electric Dipole Moments

Comparable sensitivity to fundamental CP violation, e.g. superpartner masses and CP-violating phases – complementary observables

Probe flavour-diagonal CP violation (negligible in the SM)

Schiff’s theorem: Electric fields will be shielded by redistribution of electrons – no EDM of atoms

Paramagnetic atoms and molecules

d(205Tl) < 910-25 e cm

Incomplete due to relativistic effects, net enhancement of

atom EDM relative to electron EDM

CP from electron EDM

Diamagnetic atoms(L = 0)

d(199Hg) < 210-28 e cm

Incomplete due to finite size of nucleus; atom EDM still suppressed compared to

nucleus EDM, but not fully

CP from CP-odd nucleon-nucleon interactions

Hadrons, in particularnucleons

dn < 610-26 e cm

CP in quark sector

M. Pospelov & A. Ritz: hep-ph/0504231W. Bernreuther & M. Suzuki: Rev. Mod. Phys. 63 (1991) 313





d(205Tl) < 910-25 e cm

EDM of unpaired electron

Contributions from CP-odd electron-nucleon interactions (e.g. CP violation in Higgs

sector)

Apart from this insensitive to QCD effects

Enhancement of de 500, Even larger for molecules

(e.g. YbF, PbO)


d(199Hg) < 210-28 e cm

CP-odd nuclear moments, caused by CP-odd nucleon-

nucleon interactions or nucleons EDM

In general less important: de, electron-nucleon interaction

Nuclear moment calculations very difficult; suppression of

individual contribution by factor 100 due to

cancellations


dn < 610-26 e cm

dn composed of contributions from quarks

and gluons

No additional atomic or nuclear physics

M. Pospelov & A. Ritz: hep-ph/0504231





d(205Tl) < 910-25 e cm


d(199Hg) < 210-28 e cm


dn < 610-26 e cm

S.M. Barr: Int. Journ. Mod. Phys. A 8 (1993) 209

e electron q quarkG gluonN nucleond EDMdC chromo EDMMQM magnetic

quadrupole moment

At scales up to

103 TeV M. Pospelov & A. Ritz: hep-ph/0504231


Neutron and Electron EDM

EDMs in the SM

Single CP-violating invariant:

JCP = Im(VtbVtd*VcdVcb

*) 310-5

Four electroweak vertices needed

Quark & nucleon EDMs

All EDM vanish on two-loop level

Three-loop for quark EDM

dqCKM 10-34 e cm

Main contribution for dn from four-quark operator, enhanced by long-distance

effects (pion loops)

dnCKM 10-32 e cm

Lepton EDMs

Via diagrams with closed quark loops

Non-vanishing only at four-loop level

deCKM 10-38 e cm

CKM-like phases in lepton sector, Majorana

deSeeSaw < 1.510-43 e cm

(up to 1010 enhancement by fine-tuning)M. Pospelov & A. Ritz: hep-ph/0504231

10-32

10-20

10-22

10-24

10-30

SUSY

10-34

10-36

10-38

Left-Right

MultiHiggs

StandardModel

Electro-magnetic

Neutron

de = (6.9±7.4)10-28 e cm

dn = –(1±3.6)10-26 e cm

Electron


CP Problems

Strong CP Problem SuSy CP Problem

CP violating contribution to QCD Lagrangian suppressed to

< 10-9 – why?

CP violating phases are smallOr

Soft-breaking masses significantly larger than 1TeV

Proposals:

Axions

CP or P exact symmetry at higher energy scale (e.g. some

LR models)

Proposals:

Heavy superpartners

Assume exact CP in soft-breaking sector

Accidental cancellations

2,s

232a ag

G G

L

17n6 10 d

M. Pospelov & A. Ritz: hep-ph/0504231


Measuring the Neutron EDM – Principle

n nH μ B d E

n2h B

B

n n2 2h B d E

EB

n n2 2h B d E

EB

1

2z

1

2z

n4d E

h


Measuring the Neutron EDM – Resonance Method

4.

3.

2.

1.

Free precession...

Apply /2 spinflip pulse...

“Spin up” neutron...

Second /2 spinflip pulse.

B

n 2d

ET N

Sensitivity

Visibility of resonance fringeE Electric field strengthT Time of free precessionN Neutron number


The Rutherford-Sussex-ILL-Experiment

N S

Four-layer mu-metal shield High voltage leadQuartz insulating cylinder

Coil for 10 mG magnetic field

Upper electrodeMain storage cell

Hg u.v. lamp

PMT to detect Hg u.v. lightVacuum

wallMercury

prepolarising cell

Hg u.v. lampRF coil to flip spins

Magnet

UCN polarising foil

UCN guide changeover

Ultracold neutrons

(UCN)

UCN detector

n 2d

ET N

= 0.5E = 4.5 kV/mT = 130 s (time of cycle: 210 s)N = 13000 per bunch

n

256 10 e cm per dayd P.G. Harris et al. : NIM A 440 (2000) 479

n

251.8 10 e cm per dayd

Sensitivity improved steadily, 2003:


Rutherford-Sussex-ILL-Experiment – Hg Magnetometer

0 5 10 15 20 2529.9260

29.9265

29.9270

29.9275

29.9280

29.9285

29.9290

29.9295

B = 10-10

T

Raw neutron frequencyCorrected frequency

Pre

cess

ion

freq

uenc

y (H

z)

Run duration (hours)

In-situ measurement of magnetic field by

observing precession of 199Hg atoms

Precision: 2 nG per cycle

(Neutron counting error: 10 nG per cycle)


Systematic Effects

• Leakage currents– Create additional magnetic field

and precession– Ileak 1nA effect small

• Sparks– Automatically identified and

rejected by magnetometer

• vE effect– Magnetic field in neutron rest

frame due to electric field– Averages out if there is no net

rotational motion of neutrons

Effects estimated to be below 10-26 e cm

2v c

E vB

P.G. Harris et al. : PRL 82 (1999) 904

• Geometric phases– Caused by vE effect in

combination with gradient of B– Works differently on n and Hg

(velocity, distribution)

– On Hg: 110-26 e cm (for 1nT/m)– On n: -110-27 e cm (for 1nT/m)Transfer more dangerous than

direct effect on dn

– Correction possibleBut dangerous for future projects

M. Pendlebury et al. : PRA 70 (2004) 032102


Neutron EDM – Projects

New UCN sources

Superfluid 4He

RAL-Sussex-ILLLANCSE / SNS

Solid D2

Paul Scherrer InstitutFRM II Munich

Gain factors of 103

n 2d

ET N

New n-EDM Projects

RAL-Sussex-ILL: Cryo-EDM

PSI-IN2P3-...

LANSCE / SNS

Attempted final precisions: 10-28 ecm

RAL-Sussex-ILL

Higher fields inside 4He

New magnetometers


An Alternative – CrystalEDM?

Present UCN Laue diffraction E [V/cm] 104 2108 [s] 100 10-3 E [kV s/cm] 1000 200 N [1/s] 100 104 dn [ecm/day] 1.810-25 1.510-25

Not competitive with proposed UCN projects, but with existing oneCompletely different systematics, does not require magnetic field

Idea: Use high electric field inside some crystalsup to 109 V/cm for certain crystalsand higher density of cold neutrons

Prestudies at PNPI:Fedorov, Voronin et al.

n 2d

ET N


Neutrons and Baryon Number Violation

Motivation – needed to create Matter-Antimatter-Asymmetry in Universe– implied by GUTs, SuSy, Left-Right-symmetric models

Classes of B violation

|B| = 1 p leptons, n leptons, p mesons, n mesons

p

0

d u

d u

u

u ed

4

3X

0p e

2X

H uudeM

0

33

15

from 1.6 10 yr

10 GeV

p e

XM

Probes high scales (GUT)

|(B – L)| = 0

|B| = 2 p + n mesons (s) n n

n

n

d

d

u

ud

d

n n

5I

H ddu dduM

8

31nucleons

5

from 10 s,

10 yr

10 GeV

nn

IM

Probes intermediate scales

|(B – L)| = 2


Models with n n

Traditional

Large extradimsSuSy seesaw

“Large class” of seesaw models for masses allow observable n n

Parity and (B – L) breaking close to conventional GUT scale 21016 GeV

Majorana R mass and n n created by same operators

9 1010 10 snn

K.S. Babu & R.N. Mohapatra:Phys. Lett. B 518 (2001) 269

S. Nussinov & R. Shrock:Phys. Rev. Lett. 88 (2002) 171601

Consider 2 large extra dimensions

Fermion wave-functions localised

Effective scale MI for n n:

1

I

9

844TeV

10 snnM

R

c L R

c B-L L R

c L

SU(4) SU(2) SU(2)

SU(3) U(1) SU(2) SU(2)

SU(3) SU(2) U(1)

X

W

M

M

R

2e

W

mm

gM

Interesting for GUT breaking schemes, e.g. (embedded in SO(10)):

Relates (B – L) breaking, parity breaking, and small neutrino masses:

n n observable for scale 100TeV

Today

Neutrinos very light, required mass scale makes n n unobservable in these models

2, 0 : majorana0, 2 :2, 2 : H H

L BL B n nL B

Review: R.N. Mohapatra: NIM A 284 (1989) 1


Phenomenology of n n

m m

m m

H

Free neutrons

5I

H ddu dduM

( ) cos isinmt

i m t m tt e n n

2

2

nn nn

( ) sinn

t tP t

nn m

(0) n ( )t

Numbers

nn

n

t N

N

0.1s free flight (100m at 1000 m/s)Flux 1011 n/sObservation time 1 day

6 22nn 9 10 s m 10 eV

Neutrons in Medium / Field

m m

m m V

H e.g. 2V B

2 2

( ) sinn

m VtP t

V

Vt

B < 10nT (0.1mG)Vacuum < 10-4 mbar

2

nn

( )n

tP t

Vt 2

1

2n

mP

V

Inside nucleus:V 500 MeV

(could also change m)

2

5(0)

I

mM

I 200TeVM 3

3n

1(0) 0.2GeV

R

0.02 0.04 0.06 0.08 0.10 0.12 0.14

1

2

3

4

5

00

t [s]

Pn

[10-1

6 ]

B = 0B = 20nT (2.410-15eV)B = 400nT (4.810-14eV)Earth: 50T (310-12eV)


n n – Experiment

80.86 10 s (90% C.L.)nn M. Baldo-Ceolin et al: Z. Phys. C 63 (1994) 409

1011 n/s600 m/s, 81 m free flightB < 10 nT (Mumetal)p < 10-4 mbar200 m C targetEffective running time 280 days

Analysis by-event visible energy-TOF between SCs-vertex reconstruction


Other Methods

n n in Nuclei

m mH

m m V

Vt 2

1

2n

mP

V

Inside nucleus: V 500 MeVInteraction can change mRequire model-dependent

corrections for nuclear effects

nn

free 80.86 10 s (90% C.L.)

8nn 1.3 10 s (90% C.L.)

Soudan 2 iron tracking calorimeter (5.6 kTyr):

J. Chung et al.: Phys. Rev. D 66 (2002) 032004

TFe > 7.21031yr

Background limited!

2

nn

( )n

tP t

Cold neutrons t 0.1 sUCNs t 800 s

2

freefree

nn

2

storagefree

nn free

free storage2

nn

( )n

tP t N

tt

t

t t

n n with UCNs?

But: n phase is absorbed and reset in wall collision

0.1s free flight (100m at 1000 m/s)Flux 1011 n/sObservation time 1 day

6nn 9 10 s

Very optimistic Numbers

0.2s free flight (1m at 5 m/s)800 s storageDensity 104cm-3, 1m3

Observation time 1 day

7nn 1.3 10 s

Same number of neutrons/s in very opti-mistic UCN scenario, only gain: (tfree/t)1/2


Summary – Neutrons beyond the Standard Model

• Precise absolute measurements of SM observables and consistency checks– Beta asymmetry, Antineutrino asymmetry, Lifetime Search for right-handed currents below 1TeV

• Search for effects unobservably small in the SM (deviations from 0)– CP violation in the decay Search for leptoquarks (up to 10 TeV)

– CP violation in electric dipole moment Search for new phases due to SuSy, LR, exotic fermions (1 to 103TeV)

• Search for processes forbidden in the SM– Neutron-antineutron oscillations

Test of intermediate unification (B-L, LR) scale at 100TeV

Nothing found yet, but this is already something…


The Neutron Guide to the Universe

New Physics Standard ModelT

em

pera

ture

1019 GeV Planck GUTs - -

Inflation Electroweak

Chiral transitionNucleon freeze out

Nuclear freeze out Atomic freeze out

Galactic freeze out

10-43 s 1 sTime

10-11 GeV 10-35 s 10-12 s 105 y 109 y today

Diagram from D. Dubbers

Neutron energies: peV…meVDecay energy: 780 keV

Instead of EE/E0

nd

g

nn

,rWm

nq WMa

udVN

Npp

n PA ,

,,

,,


The Neutron Guide to the Universe

Gravitational/inertial massg Magnetic monopole momentdn Electric dipole momentnn Neutron-antineutron oscillation time CP violating phase in decaymW, WR-WL mixing parametersqn Neutron chargeaWM Strength of weak magnetism Ratio of axial vector to vector couplingN Nucleon-neutrino scattering cross sectionN Number of light neutrino familiesVud Quark mixing elementpp Weak interaction in proton-proton interactionn Electric polarisibility of the neutronA, P Parity violating correlations in n-Nucleon and n-Nucleus interactions Fine structure constant

Documents

Particle Physics with Slow Neutrons II LNGS Summer Institute, September 2005Torsten Soldner Lecture II: Neutrons beyond the SM Motivation Right-handed