Workshop on Exploring the Physics Frontier at the Deep Underground Laboratories

June 24, 2005, INT, University of Washington, Seattle

Yuri Kamyshkov U. of Tennessee

kamyshkov@utk.eduTRIGA reactor

Neutron Neutron →→ antineutron means antineutron means ∆∆B= B= −−22

•• Why it is interesting and important? Why it is interesting and important?

•• Why in underground lab?Why in underground lab?

•• How to do that and what can be expected? How to do that and what can be expected?

What we are learning from ~30 years of proton decay search?What we are learning from ~30 years of proton decay search?

• no nucleon decay is observed

• exp. sensitivities are close to the limits set by the background

• original SU(5) is ruled out (Georgi and Glashow, 1974)

• several other GUT and SUSY-extended models are ruled-out or constrained

• theoretical predictions for certain PDK modes are “improved”

from initial ~ 1029 yr to ≥1034 yr

• gauge couplings in GUT do not unify without SUSY

• even with addition of SUSY the unification is not perfect (S. Raby, PDG 2004)

• conspiracy of GUT and SUSY models (←both not experimentally proven)

• do we believe in “Great Desert”?

• are we diligently exploring all alternative ideas and experimental options?

What is telling us that baryon number is not conserved?What is telling us that baryon number is not conserved?

Observed and yet unexplained Baryon Asymmetry of the Universe (BAU)

Three ingredients needed for BAU explanation ( A. Sakharov, 1967):

(1) Baryon number violation(2) C and CP symmetry violation(3) Departure from thermal equilibrium

BAU does not tell us how baryon number is violated. Violation/decay modes are predictions of theoretical models.How to decide what modes are relevant for BAU explanation?

Two types of baryon instability Two types of baryon instability

In violation of baryon number the conservation of angular momentum requires that spin ½ of nucleon should be transferred to another fermion (lepton or baryon), e.g. ∆B = ± ∆L

That leads to the selection rule:⏐∆(B−L)⏐ = 0 or 2

• In the Standard Model, in SU(5), and common SUSY extensions:∆(B−L) = 0 or ∆B = + ∆L (nucleon → antilepton, e.g. p → e+π 0 )

• Second possibility of ⏐∆(B−L)⏐ = 2 allows transitions with∆B = − ∆L (nucleon → lepton), ⏐∆B⏐ = 2, and ⏐∆L⏐ = 2

Conservation or violation of (B− L) mightdetermine different mechanisms of baryon instability.

Is (BIs (B−−L) conserved?L) conserved?

•• In our laboratory samples (BIn our laboratory samples (B−−L) = #protons + #neutrons L) = #protons + #neutrons −− #electrons#electrons

(B(B−−L)L)≠≠00

•• However, in the Universe most of the leptons exist as, However, in the Universe most of the leptons exist as, yet undetectedyet undetected, , relic neutrino and antineutrino radiation (similar to CMBR) and relic neutrino and antineutrino radiation (similar to CMBR) and conservationconservationof (Bof (B−−L) on the scale of the whole Universe is still an open questionL) on the scale of the whole Universe is still an open question

•• NonNon--conservation of (Bconservation of (B−−L) was discussed theoretically since 1978 by:L) was discussed theoretically since 1978 by:Davidson, Marshak, Mohapatra, Wilczek, Chang, Ramond ...Davidson, Marshak, Mohapatra, Wilczek, Chang, Ramond ...

Important Theoretical DiscoveriesImportant Theoretical Discoveries

•• Anomalous nonperturbative effects in the Standard Model lead tAnomalous nonperturbative effects in the Standard Model lead to o violation of lepton and baryon number violation of lepton and baryon number ((’’t Hooft, 1976)t Hooft, 1976)

thisthis BB and and LL nonconservation in SM is too small to be experimentally nonconservation in SM is too small to be experimentally observable at low temperatures, but was large at T above electroobservable at low temperatures, but was large at T above electroweak scale.weak scale.

•• ““On anomalous electroweak baryonOn anomalous electroweak baryon--number nonnumber non--conservation in the conservation in the early universeearly universe”” (Kuzmin, Rubakov, Shaposhnikov, 1985) (Kuzmin, Rubakov, Shaposhnikov, 1985)

The anomalous SM interactionThe anomalous SM interaction conservesconserves ((BB−−LL) but violate ) but violate ((BB+L+L). ). Rate of anomalous (Rate of anomalous (B+LB+L))--violating electroweak processes at T > TeV violating electroweak processes at T > TeV (sphaleron mechanism) exceeds the Universe expansion rate. If (sphaleron mechanism) exceeds the Universe expansion rate. If B = LB = L would would be set at very high temperature (e.g. at GUT scale) due to some be set at very high temperature (e.g. at GUT scale) due to some ((BB−−LL) conserving ) conserving interaction (e.g. by SU(5) SUSY proton decay), interaction (e.g. by SU(5) SUSY proton decay), all quarks and leptons in the all quarks and leptons in the universe along with BAU will be wiped out by (universe along with BAU will be wiped out by (B+LB+L))--violating electroweak violating electroweak processes. processes. Thus, for the explanation of BAU (Thus, for the explanation of BAU (BB−−LL) violation at the scale above ) violation at the scale above EW (EW ( 1 TeV) is required.1 TeV) is required.

(B(B−−L) needs to be violated at the scale above TeVL) needs to be violated at the scale above TeV

Violation of (BViolation of (B−−L) implies nucleon instability modes:L) implies nucleon instability modes:

( ) 2∆or etc. −=−ννν→νν→→ + LB,n,ep,nn

Rather than conventional pRather than conventional p--decay modes:decay modes:

( ) 0∆or etc. 00 =−µ→ν→π→ +++ LB,Kp,Kp,ep

If conventional (BIf conventional (B−−L)L)--conserving proton decay would be discovered conserving proton decay would be discovered e.g. by Supere.g. by Super--K, it does not help us to understand BAU.K, it does not help us to understand BAU.

“The proton decay is not a prediction of the baryogenesis”“The proton decay is not a prediction of the baryogenesis”Yanagida Yanagida @ @ νν20022002

IIddeeaass ooff 22000055’’ss aarree ddiiffffeerreenntt ffrroomm 11998800’’ss::

1980’s 2005’s

GUT models conserving (B−L) were though to work for BAU explanation [Pati & Salam’73, Georgi & Glashow’74…]

Proton decay is not a prediction of baryogenesis! [Yanagida’02] ∆(B−L)≠0 is needed for BAU [Kuzmin, Rubakov, Shaposhnikov’85…]

No indications for neutrino masses mν ≠ 0 […S-K’98, SNO’02, KamLAND’03] and possible Majorana nature of neutrino

Great Desert [Giorgi & Glashow’74] from SUSY scale to GUT scale

No Desert. Possible unification with gravity at ~ 105 GeV scale [Arkani-Hamed, Dimopoulos, Dvali’98 …]

(B−L) = 0 in SM, SU(5), SUSY SO(10)… (B−L) ≠ 0 in ext. SUSY SO(10), L-R sym, QG

Energy scale: 1015−1016 GeV Effective energy scale: above TeV

. 0 , etcKνp,πep ++ →→ .302 ν, etcν, nβ, , νnn R →→

Spectacular work of SuperSpectacular work of Super--K, SoudanK, Soudan--2, IMB3, Kamiokande, Fr2, IMB3, Kamiokande, Frééjusjus

2003, M. Shiozawa28th International Cosmic Ray Conference

All modes∆(B−L)=0

Some Some ∆∆(B(B−−L)L)≠≠0 nucleon decay modes (PDG0 nucleon decay modes (PDG’’04)04)

(B−L)≠0 modes Limit at 90% CL S/B Experiment’year

>1.7×1031 yr 152/153.7 IMB’99

>2.1×1031 yr 7/11.23 Fréjus’91

>2.57×1032 yr 5/7.5 IMB’99

>7.9×1031 yr 100/145 IMB’99

>1.9×1029 yr 686.8/656 SNO’04

>7.2×1031 yr 4/4.5 Soudan-II’02

> 4.9×1025 yr Borexino’03

+νν→ ep+ννµ→pν→ −+eenνµµ→ −+n

ννν→nnn →

νν→nn

e.g. for with a lifetime >1.7×1031 yr Super-K should detect ~ 430 events/yr

+νν→ ep

limithighest with mode ν→ −+eenlimitlowest with mode 1B −=∆ννν→n

potential futurehighest with mode nn →

limitlowest with mode 2B −=∆νν→nn

∆∆B, B, ∆∆LL≠≠0 s0 searches in particle decays (PDG’2004)earches in particle decays (PDG’2004)

•• All above limits are All above limits are ∆∆(B(B−−L)=0 decay modesL)=0 decay modes

−− π+→τ n•• would be an interesting alternative would be an interesting alternative ∆∆(B(B−−L) = L) = ++22(e.g. for BaBar/Belle; observed branching ~ 10(e.g. for BaBar/Belle; observed branching ~ 10−−99 would indicate scale ~ 10would indicate scale ~ 1055 GeV)GeV)

•• Note, that in other modes (e.g. Note, that in other modes (e.g. p→ e+νν )) ∆∆(B(B−−L) = L) = −−22

KamLAND is searching for KamLAND is searching for ∆∆(B(B−−L)L)≠≠0 0 processes:processes:

) e.g. ( ννν→nNeutron disappearance from Neutron disappearance from 1212C C (small accidental background)(small accidental background)

Expected sensitivity improvementExpected sensitivity improvement to 7to 7××10102929 yryr(current SNO limit is (current SNO limit is ττ > 1.9> 1.9××10102929 yr)yr)

Two neutron disappearance from Two neutron disappearance from 1212C C Expected sensitivity improvementExpected sensitivity improvement to 1.7to 1.7××10103030 yryr(current Borexino limit is (current Borexino limit is ττ > 4.9> 4.9××10102525 yr)yr)

) (e.g. νν→nn

Neutron Neutron →→Antineutron Transitions Antineutron Transitions

( ) 2 and 2 −=∆−=−∆• BLB

in vacuum state mix with can state neutral nn•

free with ons transitiin vacuum searched becan n•

n ngannihilatiofdetection r spectacula •

seenbeen havesearch ons transitiin vacuum background no •

on annihilatiby followedison transitiar intranucle nnn →•

•• has the highest potential in exp. sensitivity improvement has the highest potential in exp. sensitivity improvement for Bfor B--violation searchviolation search

Neutron Neutron →→Antineutron Transition ?Antineutron Transition ?

•• The oscillation of neutral matter into antimatter is well knThe oscillation of neutral matter into antimatter is well known to occur in own to occur in and particle transitions dueand particle transitions due to the nonto the non--conservation of conservation of

strangenessstrangeness and and beautybeauty quantum numbers by electroquantum numbers by electro--weak interactions.weak interactions.

00 KK ↔ 00 BB ↔

•• There are no laws of nature that would forbid the There are no laws of nature that would forbid the transitions transitions except the conservation of "except the conservation of "baryon charge (number)baryon charge (number)":":

M. Gell-Mann and A. Pais, Phys. Rev. 97 (1955) 1387L. Okun, Weak Interaction of Elementary Particles, Moscow, 1963

nn ↔

•• was first suggested as a possible mechanism for explanationwas first suggested as a possible mechanism for explanationof BAU (Baryon Asymmetry of Universe ) by of BAU (Baryon Asymmetry of Universe ) by V. Kuzmin, 1970

nn ↔

•• First considered and developed within the framework of UnifiFirst considered and developed within the framework of Unification cation models by models by R. Mohapatra and R. Marshak, 1979R. Mohapatra and R. Marshak, 1979

For wide class of L-R and super-symmetric models predicted n-nbar upper limit is within a reach of new n-nbar search experiments!If not seen, n-nbar should restrict a wide class of SUSY models.

Quarks and leptons belong to different branes separated by an extra-dimension; proton decay is strongly suppressed, n-nbar is NOT since quarks and anti-quarks belong to the same brane.

Proton decayis strongly suppressed in this model, butn-nbar is not since nR has nogauge charges

Effective D = 7 operators can generate n-nbar transitions

nn→→nbar tnbar transition probability ransition probability

( ) ( )

( ) ( ) ( )level few eaccepatabl down to screened becan field mag.Earth

]measured!not [ CPT from follows as moment magnetic 0 :same theis and for tialgravipoten

ed)not violat is CPT (if 0 whereframe reference a is there

hold) is invariance-T (i.e.

2 ;

2

:operatorsenergy icrelativist-non are and where

system on then Hamiltonia H

state QMnbar -n mixed

22

nTnµnnµ

UU∆Unnmm

pnnnn

UmpmEU

mpmE

EEE

Enn

nn

nn

nn

nnnn

nn

nn

n

n

•µ−=•

=−=•=•

=•α=→α=→α•

++=++=

⎟⎟⎠

⎞⎜⎜⎝

⎛α

α=

⎟⎟⎠

⎞⎜⎜⎝

⎛=Ψ

:sassumption Important

α-mixing amplitude

n→nbar transition probability (for given α)

( )

nn

nnn

n

mm∆mt

V

tmVmV

tPVm

VmH

−=

⎥⎥⎦

⎤

⎢⎢⎣

⎡ ∆++×

∆++=⎟⎟

⎠

⎞⎜⎜⎝

⎛−

+= →

and ,experimentan in n timeobservatio is tial)gravipoten ofpart or field; mag.Earth dcompensate-non todue (e.g.

neutron-anti andneutron for different potential a is where

)2(sin)2(

For 22

222

2

h

αα

αα

α

22

0 and 0 ns"oscillatio vacuum" theofsituation idealIn ⎟⎠

⎞⎜⎝

⎛=⎟⎠⎞

⎜⎝⎛ ×=== →

nnnn τ

ttαP∆mVh

]10[ timeon)(oscillatin transitiosticcharacteri is 23eVnn−<α

α=τh

e)flight tim of square used, neutrons ofnumber (

2

2

tNtN"ySensitivit"

n

n ><⋅∝

Bound n: J. Chung et al., (Soudan II)Phys. Rev. D 66 (2002) 032004 > 7.2⋅1031 years

PDG 2004:Limits for both free reactor neutrons andneutrons bound inside nucleus

123

2

10 where

−

τ⋅=τ

s~R

R freebound

Free n: M. Baldo-Ceolin et al., (ILL/Grenoble) Z. Phys C63 (1994) 409

with P = (t/τfree)2

RR is “nuclear suppression factor”is “nuclear suppression factor”Uncertainty of Uncertainty of RR from nuclearfrom nuclear

models is ~ factor of 2models is ~ factor of 2

Search with free neutrons is squareSearch with free neutrons is squaremore efficient than with bound neutronsmore efficient than with bound neutrons

HFR @ ILL 57 MW

Cold n-source25Κ D2

fast n, γ background

Bended n-guide Ni coated, L ~ 63m, 6 x 12 cm 2

58

H53 n-beam~1.7 10 n/s. 11

(not to scale)

Magnetically shielded

95 m vacuum tube

Annihilation target 1.1m∆E~1.8 GeV

Detector:Tracking&

Calorimetry

Focusing reflector 33.6 m

Schematic layout ofHeidelberg - ILL - Padova - Pavia nn search experiment

at Grenoble 89-91

Beam dump

~1.25 10 n/s11

Flight path 76 m< TOF> ~ 0.109 s

Discovery potential :N tn ⋅ = ⋅2 91 5 10. sec

Measured limit : τnn ≥ ⋅8 6 107. sec

Best reactor measurement at ILL/Grenoble reactor in 89-91 by Heidelberg-ILL-Padova-Pavia Collaboration

Experiment with free neutrons

18106061 measured

1090 and m 90 ~ Lwith

−×<

=

.P

sec.t

nn

Detector of Heidelberg-ILL-Padova-Pavia Experiment @ILL 1991(size typical for HEP experiment)

No background!No candidates observed.Measured limit for a year of running:

sec106.8 7nn ×≥τ

= 1 unit of sensitivity

NN--Nbar in Underground LabNbar in Underground Lab

(B –L) violation physics search at Underground Labs:

in nucleon decay experiments:in double-beta decay ∆L=2most spectacular in n-nbar ∆B=2

νν→ννν→ +ep,n.g.e

• Most important motivation for N-Nbar: sensitivity can be increased

by factor > 1,000 relative to the present level of ILL/Soudan-II

• Magnificent detection signature: ~ 1.8 GeV annihilation star of 5 pions

• No background: one event = discovery!

• P = (t/τfree)2 with t (time of flight) 0.1sec → 1 sec

• Enhance cold neutron flux by neutron focusing

• Vertical layout saves focusing

Scheme of NScheme of N--Nbar search experiment with vertical layoutNbar search experiment with vertical layout

• Dedicated small-power research reactor with cold neutron moderator → Vn ~ 1000 m/s

• Vertical shaft ~1000 m deep with diameter ~ 6 m at DUSEL

• Large vacuum tube, focusing reflector, Earth magnetic field compensation system

• Detector (similar to ILL N-Nbar detector) at the bottom of the shaft (no new technologies)

• Inverse scheme with reactor at the bottom and detector on the top of the mine shaft is also feasible

• Construction ~ 4 years; running time ~ 3 years

1 m

10 m

Annular Core TRIGA Reactor3.4 MW with convective cooling.3E+13 n/cm2/scentral thermal flux

LD2 CM

Focusing ReflectorL~150 m

Vacuum tube

L~1000 mdia ~ 4 m

Annihilation target

dia ~ 2 m

Beam dump

Annihilation detector

Neutrontrajectory

Approximatescales

X

Transition point

Not to scale

Annular core TRIGA reactor (GA) for NAnnular core TRIGA reactor (GA) for N--Nbar search experimentNbar search experiment

• GA built ~ 70 TRIGA reactors 0.01÷14 MW (th)• 19 TRIGA reactors are presently operating in US

(last commissioned in 1992)• 25 TRIGA reactors operating abroad

(last commissioned in 2005)• some have annular core and vertical channel• most steady, some can be pulsed up to 22 GW• safe ~ 20% EU uranium-zirconium hydride fuel

~ 1 ft

Economic solution for n-nbar:annular core TRIGA reactor 3.4 MWwith convective cooling, vertical channel, and large cold LD2 moderator (Tn ~ 35K). Unperturbed thermal flux in the vertical channel ~ 2×1013 n/cm2/s

Courtesy of W. Whittemore (General Atomics)

ySensitivitSearch nn →

Method Present limit Possible future limit Possible sensitivity increase factor

Intranuclear (N-decay expts)

7.2⋅1031 yr = 1unit Soudan II

7.5⋅1032 yr (Super-K) 4.8⋅1032 yr (SNO) × 11

Geo-chemical (ORNL) none 4⋅108÷1⋅109 s

(Tc in Sn ore) × 20 −100

UCN trap (6×107 ucn/sec)

none ~ 1⋅109 s × 100

Cold horizontal beam

8.6⋅107 s = 1unit @ILL/Grenoble

3⋅109 s (HFIR@ORNL) × 1,000

Cold Vertical beam none 3⋅109 – 1⋅1010 s

(Underground Lab) > 1,000

SoudanSoudan--II limit II limit ≈≈ ILL/Grenoble limit = 1 unit of sensitivityILL/Grenoble limit = 1 unit of sensitivity

There is no competition in the world

TRIGA Cold Vertical Beam, 3 years

Col

d B

e am

Science impact of nScience impact of n--nbar searchnbar searchIf discovered:

• n→nbar will establish a new force of nature and a new phenomenon leading to the physics at the energy scale of ~ 105 GeV

• will provide an essential contribution to the understanding of BAU

• might be the first detected manifestation of extra dimensions and low QG scale

• new symmetry principles can be experimentally established: ∆(B−L)≠0

• further experiments with free neutrons will allow high-sensitivity testing

antimatter andmatter baryonic of eequivalenc nalgravitatio 10mm with theorem) (CPT whether 23

−≈∆=− −

nn mm (L. Okun et al, 1984)

(S. Lamoreaux et al, 1991)

If NOT discovered:

• within the reach of improved experimental sensitivity will set a new limit on the stability of matter competitive to X-large nucleon decay experiments

• wide class of SUSY-based models will be removed (K. Babu and R. Mohapatra, 2001)