Yuri Kamyshkov

University of Tennessee

kamyshkov @utk.edu

SLAC Experimental Seminar, Tuesday, May 17, 2005

Searches Searches for Baryon Number Violationfor Baryon Number Violation

PlanPlan

(1) Introduction: (B(1) Introduction: (BL)=0 vs (BL)=0 vs (BL)L)0 0

(2) Search for neutron disappearance in KamLAND(2) Search for neutron disappearance in KamLAND

(3) Future prospects in n(3) Future prospects in nnbar searchnbar search

What can we learn from ~30 years of proton decay search?What can we learn from ~30 years of proton decay search?

• no nucleon decay is observed

• exp. sensitivity is close to the limits set by background

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

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

• theoretical predictions for certain decay modes were “improved”

from initial ~ 1029 yr to 1034 yr

• gauge couplings in GUT do not unify without SUSY

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

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

(experimentalist’s view)

• is nucleon instability search motivated purely by GUT and SUSY?

• do we still believe in Great Desert ?

• are low-energy scale QG models testable with nucleon decay?

• how can we motivate young experimentalists to search for a proton decay?

• are we diligently exploring alternative ideas and experimental options?

More Questions:More Questions:

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.What modes are relevant for BAU explanation?

Two types of baryon instabilityTwo types of baryon instability

Is (BIs (BL) conserved? L) conserved?

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

(B(BL)L)00

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

• • Non-conservation of (BNon-conservation of (BL) 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 to Anomalous nonperturbative effects in the Standard Model lead to nonconservation of lepton and baryon number nonconservation of lepton and baryon number (’t Hooft, 1976)(’t Hooft, 1976) BB and and LL nonconservation in SM is too small to be experimentally observable nonconservation in SM is too small to be experimentally observable at low temperatures, but can be large above TeV scale.at low temperatures, but can be large above TeV scale.

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

Rate of SM nonperturbative (Rate of SM nonperturbative (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 is set in is set in the Universe at some very high temperatures (e.g. at GUT scale) due to some the Universe at some very high temperatures (e.g. at GUT scale) due to some ((BBLL) violating interaction all quarks and leptons along with BAU will be wiped ) violating interaction all quarks and leptons along with BAU will be wiped out by (out by (B+LB+L)-violating electroweak processes. For the explanation of BAU )-violating electroweak processes. For the explanation of BAU ((BBLL) violation is required.) violation is required.

If (BIf (BL) is violated at T above electroweak scale L) is violated at T above electroweak scale

Violation of (BViolation of (BL) implies nucleon instability modes:L) implies nucleon instability modes:

2Δor etc. LB,n,ep,nn

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

0Δor etc. 00 LB,Kp,Kp,ep

If conventional (BIf conventional (BL)-conserving proton decay would be discovered L)-conserving proton decay would be discovered e.g. by Super-K, it does not help us to understand BAU.e.g. by Super-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 @ @ 20022002

II dd ee aa ss oo ff 22 00 00 55 ’’ ss aa rr ee dd ii ff ff ee rr ee nn tt ff rr oo mm 11 99 88 00 ’’ ss ::

1 9 8 0 ’ s 2 0 0 5 ’ s

G U T m o d e l s c o n s e r v i n g ( B L ) w e r e t h o u g h t o w o r k f o r B A U e x p l a n a t i o n [ P a t i & S a l a m ’ 7 3 , G e o r g i & G l a s h o w ’ 7 4 … ]

P r o t o n d e c a y i s n o t a p r e d i c t i o n o f b a r y o g e n e s i s ! [ Y a n a g i d a ’ 0 2 ] ( B L ) 0 i s n e e d e d f o r B A U [ K u z m i n , R u b a k o v , S h a p o s h n i k o v ’ 8 5 … ]

N o i n d i c a t i o n s f o r n e u t r i n o m a s s e s m

0 [ … S - K ’ 9 8 , S N O ’ 0 2 , K a m L A N D ’ 0 3 ] a n d p o s s i b l e M a j o r a n a n a t u r e o f n e u t r i n o

G r e a t D e s e r t [ G i o r g i & G l a s h o w ’ 7 4 ] f r o m S U S Y s c a l e t o G U T s c a l e

N o D e s e r t . P o s s i b l e u n i f i c a t i o n w i t h g r a v i t y a t ~ 1 0 5 G e V s c a l e [ A r k a n i - H a m e d , D i m o p o u l o s , D v a l i ’ 9 8 … ]

( B L ) = 0 i n S M , S U ( 5 ) , S U S Y S O ( 1 0 ) … ( B L ) 0 i n e x t . S U S Y S O ( 1 0 ) , L - R s y m , Q G

E n e r g y s c a l e : 1 0 1 5 1 0 1 6 G e V E f f e c t i v e e n e r g y s c a l e : ~ 1 0 5 G e V

. 0 , etcKνp,πep

.302 ν, etcν, nβ, , νnn R

2003, M. Shiozawa28th International Cosmic Ray Conference

Spectacular work of Super-K, Soudan-2, IMB3, Kamiokande, FrSpectacular work of Super-K, Soudan-2, IMB3, Kamiokande, Fréjuséjus

All modes(BL)=0

Some Some (B(BL)L)0 nucleon decay modes (PDG’04)0 nucleon decay modes (PDG’04)

(BL)0 modes Limit at 90% CL S/B Experiment’year

>1.71031 yr 152/153.7 IMB’99

>2.11031 yr 7/11.23 Fréjus’91

>2.571032 yr 5/7.5 IMB’99

>7.91031 yr 100/145 IMB’99

>1.91029 yr 686.8/656 SNO’04

>7.21031 yr 4/4.5 Soudan-2’02

> 4.91025 yr Borexino’03

epp

een n

n

nn

e.g. for with a lifetime >1.71031 yr Super-K would detect ~ 430 events/yr

ep

limithighest with mode een

limitlowest with mode 1B n

potential futurehighest with mode nn

nn

limitlowest with mode 2B nn

B, B, LL0 searches in particle decays (PDG’2004)0 searches in particle decays (PDG’2004)

• • All these above limits are for All these above limits are for (B(BL)=0 modesL)=0 modes

n• • would be an interesting alternative would be an interesting alternative (B(BL) = L) = ++22

• • Note, that nucleon decay e.g. Note, that nucleon decay e.g. p e+ is is (B(BL) = L) = 22

KamLANDschematic

(2) Searches for Baryon non-conservation in KamLAND(2) Searches for Baryon non-conservation in KamLAND

nn

n.g.e

nnn

:ncedisappeara

and

1 kt ~ CH2

KamLAND CollaborationKamLAND Collaboration

• Tohoku University: K.Eguchi, S.Enomoto, K.Furuno, J.Goldman, H.Hanada, H.Ikeda, K.Ikeda, K.Inoue, K.Ishihara, W.Itoh, T.Iwamoto, T.Kwaguchi, T.Kawashima, H.Kinoshita, Y.Kishimoto, M.Koga, Y.Koseki, T.Maeda, T.Mitsui, M.Motoki, K.Nakajima, M.Nakajima, T.Nakajima, H.Ogawa, K.Owada, T.Sakabe, I.Shimizu, J.Shirai, F.Suekane, A.Suzuki, K.Tada, O.Tajima, T.Takayama, K.Tamae, H.Watanabe

• University of Alabama: J.Busenitz, Z.Djurcic, K.McKinny, D.-M.Mei, A.Piepke, E.Yakushev

• LBNL/UC Berkeley: B.E.Berger, Y.D.Chan, M.P.Decowski, D.A.Dwyer, S.J.Freedman, Y.Fu, B.K.Fujikawa, K.M.Heeger, K.T.Lesko, K.-B.Luk, H.Murayama, D.R.Nygren, C.E.Okada, A.W.P.Poon, H.M.Steiner, L.A.Winslow

• California Institute of Technology: G.A.Horton-Smith, R.D.McKeown, J.Ritter, B.Tipton, P.Vogel

• Drexel University: C.E.Lane, T.Miletic

• University of Hawaii: P.W.Gorham, G.Guillian, J.G.Learned, J.Maricic, S.Matsuno, S.Pakvasa

• Louisiana State University: S.Dazeley, S.Hatakeyama, M.Murakami, R.C.Svoboda

• University of New Mexico: B.D.Dieterle, M.DiMauro

• Stanford University: J.Detwieler, G.Gratta, K.Ishii, N.Tolich, Y.Uchida

• University of Tennessee: M.Batygov, W.Bugg, H.Cohn, Y.Efremenko, Y.Kamyshkov, A.Kozlov, Y.Nakamura

• TUNL/NCSU: L.De Braeckeleer, C.R.Gould, H.J.Karwowski, D.M.Markoff, J.A.Messimore, K.Nakamura, R.M.Rohm, W.Tornow, A.R.Young

• IHEP, Beijing: Y.-F.Wang

Unique features of KamLAND detector:Unique features of KamLAND detector:

Large mass: 1,000 ton of Liquid Scintillator ( ~ CH2)

Low detection threshold: < 1 MeV

Good energy resolution:

Position reconstruction accuracy in x,y,z: ~ 15 cm

Low background: 2700 mwe; buffer shield; veto-shield;

Rn shield; LS purification for U, Th < 1016 g/g

These features allow observation of a sequence of nuclear de-excitation states produces by

a disappearance of nucleon.

)MeV(E%~ 7

Measurement idea:Measurement idea:

excitedCddisappearestatesinnC *1121

12

SIGNATURES OF NUCLEON DISAPPEARANCE IN LARGE UNDERGROUND DETECTORS. Edwin Kolbe and YK Phys.Rev.D67:076007, 2003

2 neutrons out of 6 in 12Care is s½ state

11

nucleusdaughterofdecayβ

particlesexcitationdeC*

Search for the sequence of events (3 hits)correlated in space and time

De-excitation branching of De-excitation branching of JJ==½½++ 1111C* state vs excitation energyC* state vs excitation energy

in statistical code SMOKER: J.J. Cowan, F.-K. Thielemann, J.W. Truran, Phys. Rep. 208 (1991) 267; further code developments by E. Kolbe

n -hole excitation

Neutron Disappearance Modes in KamLANDNeutron Disappearance Modes in KamLAND

12C(n)11C* n +10C* +10C (3.35 MeV )

10B + + (27 sec, QEC = 3.65 MeV, 99%)

one one ss½½ neutron dis.neutron dis.1111C*C* Br % Hits 3-rd hit corr. time

1 n + 10Cgs (+) 3.0 3 27.8 s

2 n + + 10Cgs (+) 2.8 3 27.8 s

two two ss½½ neutrons dis.neutrons dis.1010C*C*

3 n + 9Cgs (+) 6.2 3 182.5 ms

4 n + p + 8Bgs (+,) 6.0 3 1.11 s

Modes favorable for detection in KamLAND (Br calculated in SMOKER)Modes favorable for detection in KamLAND (Br calculated in SMOKER)

30%30%

Expected 90% CL sensitivity (analysis is in progress)Expected 90% CL sensitivity (analysis is in progress)

small accidental backgroundsmall accidental background

For one n-disappearance from For one n-disappearance from 1212CC: : 7710102929 yr yr

current SNO limit is current SNO limit is > 1.9 > 1.910102929 yr yr

For two n-disappearance from For two n-disappearance from 1212CC: : 1.71.710103030 yr yr

current Borexino limit is current Borexino limit is > 4.9 > 4.910102525 yr yr

(3) Neutron (3) Neutron Antineutron TransitionsAntineutron Transitions

2 and 2 BLB

in vacuum state mix with can state nn

potentialt improvemeny sensitivithighest has

free with ons transitiin vacuum searched becan n

on annihilati by followed becan on transitiar intranucle nnn

seenbeen have ons transitimfor vacuu background no

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

•• The oscillation of neutral matter into antimatter is well known to occur in The oscillation of neutral matter into antimatter is well known to occur in and particle transitions due to the non-conservation of and particle transitions due to the non-conservation of strangenessstrangeness and and beautybeauty quantum numbers by electro-weak interactions. quantum numbers by electro-weak interactions.

00 KK 00 BB

•• There are no laws of nature that would forbid the transitions There are no laws of nature that would forbid the 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) 1387 L. 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 explanation of BAU (Baryon Asymmetry of Universe ) by of BAU (Baryon Asymmetry of Universe ) by V. Kuzmin, 1970

nn

Neutron Neutron Antineutron TransitionAntineutron Transition

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!

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

nnnbar transition probability nbar transition 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

nT

nμnnμ

UUΔUnn

mm

p

nnnn

Um

pmEU

m

pmE

EE

E

E

n

n

nn

nn

nn

nnnn

nn

nn

n

n

:sassumption Important

-mixing amplitude

nnbar transition probability (for given )

nn

nnn

n

mmΔmt

V

tmV

mVtP

Vm

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

222

22

2

22

0 and 0 ns"oscillatio vacuum" ofsituation idealIn

nnnn τ

tt

αPΔmV

]10[ timeon)(oscillatin transitiosticcharacteri is 23eVnn

Bound n: J. Chung et al., (Soudan II) Phys. Rev. D 66 (2002) 032004 > 7.21031 years

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

123

2

10 where

s~R

R freebound

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

with P = (t/free)2

Uncertainty of Uncertainty of RR from nuclear from nuclear models is ~ factor models is ~ factor 22

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

544

1027 :limit 2-Soudan 31

./B/S

years.Fe

Since sensitivity of SNO, Super-K, and future large underground detectors will be limited by atmospheric neutrino background (as demonstrated by Soudan-2 experiment), it will be possible to set a new limit, but difficult to make a discovery!

Future nFuture nnbar search limits with bound neutronsnbar search limits with bound neutrons

years.~

years.~

O

D

1057 :K-Super

1084 : SNO

32

32

Future limits expected from SNO and Super-K

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

Free neutron experiment

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

= 1 unit of sensitivity

Future searches with free neutronsFuture searches with free neutrons

• • possible to increase sensitivity by more than possible to increase sensitivity by more than 1,000 1,000 boundbound > 10 > 103535 years; years; freefree > 10 > 101010 sec sec

compete with compete with large Mt detectors large Mt detectors

• • if no background, one event can be a discoveryif no background, one event can be a discovery

• • use existing research reactor facilities? e.g. HFIR at ORNL?use existing research reactor facilities? e.g. HFIR at ORNL?

Not availableNot available

New Scheme of N-Nbar Search Experiment at DUSEL

Dedicated small 3.4 MW power TRIGA research reactor with cold neutron moderator vn ~ 1000 m/s

Vertical shaft ~1000 m deep with diameter ~ 6 m

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

Possible sites ? WIPP, Soudan, Homestake, Sudbury

Annular core TRIGA reactor for N-Nbar search experiment

Annular core TRIGA reactor 3.4 MWwith convective cooling, vertical channel, and large cold moderator. Unperturbed thermal flux in the vertical channel3E+13 n/cm2/s

Courtesy of W. Whittemore (General Atomics)

Example: UT Austin research TRIGA reactor. It is a 1.2-MW core. The last university reactor installed in the country (about 1991). It costs about $3.5 M plus fuel; the cost of the fueldepends on whether you get it from DOE or not.

~ 1 ft

• • A 2 MW 8-GeV Proton Driver could be designed to be a very efficient A 2 MW 8-GeV Proton Driver could be designed to be a very efficient source of cold neutrons with average flux equivalent to that of the ~ 20 MW source of cold neutrons with average flux equivalent to that of the ~ 20 MW research reactorresearch reactor

• • e.g. at SNS ~ 22 neutrons are produced per 1 GeV proton in Hg target e.g. at SNS ~ 22 neutrons are produced per 1 GeV proton in Hg target

• • 2 MW PD spallation target can produce thermal flux ~ 22 MW PD spallation target can produce thermal flux ~ 210101414 n/cm n/cm22/s /s

• • efficient reflector (e.g. Defficient reflector (e.g. D22O) and cryogenic DO) and cryogenic D2 2 moderatormoderator

• • vertical 1000-m deep shaft under the target vertical 1000-m deep shaft under the target

• • no interference with neutrino program no interference with neutrino program

FNAL Proton Driver as a Source of Cold Neutrons?FNAL Proton Driver as a Source of Cold Neutrons?

Target Moderators

Proton Beam

Reflector

(An example) SNS Target-Moderator System

Method Present limit Possible future limit Possible sensitivity

increase factor

Intranuclear (N-decay expts)

7.21031 yr = 1unit Soudan II

7.51032 yr (Super-K) 4.81032 yr (SNO)

16

Geo-chemical (ORNL)

none 41081109 s (Tc in Sn ore)

20 100

UCN trap (6107 ucn/sec)

none ~ 1109 s 100

Cold horizontal beam

8.6107 s = 1unit @ILL/Grenoble

3109 s (HFIR@ORNL)

1,000

Cold Vertical beam

none 3109 – 11010 s

(DUSEL, FNAL PD) 10,000

ySensitivitSearch nn

Soudan-2 limit Soudan-2 limit ILL/Grenoble limit = 1 unit of sensitivity ILL/Grenoble limit = 1 unit of sensitivity

Science impact of n-nbar searchScience impact of n-nbar search

ConclusionsConclusions

• • (B(BL) violating processes are important part of the baryon L) violating processes are important part of the baryon number violation search program number violation search program

• • n-nbar transitions might be most spectacular manifestation n-nbar transitions might be most spectacular manifestation of (Bof (BL) violation due to large possible increase of sensitivity L) violation due to large possible increase of sensitivity and no backgroundand no background

• • new possibilities for the large next step in baryon number new possibilities for the large next step in baryon number violation search can be in connection with DUSEL and FNAL PD violation search can be in connection with DUSEL and FNAL PD

Suppression of nnbar in intranuclear transitions

Δtτ

Δt

τP

ΔtN

τ

Δt

sMeVE

t

nnAA

nn

binding

11 :secondper y probabilit Transition

second.per times1

condition" free ngexperienci" and

y probabilit with goscillatineach

10~10

1~

1~ : timefor the free"" are nuclei inside Neutrons

2

2

22

factor"n suppressionuclear " is 10~t

1~R where

:lifetime al)(exponentiion ar transitIntranucle

122

22

A

s

Rt nnnn

s.τyr nnFe831 1031 toscorrespond 102.7limit 2-Soudan e.g. Thus,

2 ofy uncertaint with factorsn suppressiohigher maginitude oforder an give andconsitent are al.et ich B.Kopeliov al,et W.Alberico al,et Dover C.by ,,,for nscalculatioeory nuclear th Actual 4056216

ArFeDO

t

mV

mVtP nn

222

22

2 )2(sin

)2(

How CPT violation works in nHow CPT violation works in nnbar transitions?nbar transitions?

Following Yu.Abov, F.Djeparov, and L.Okun, Pisma ZhETF 39 (1984) 493

• Transitions for free neutrons V=0 are suppressed when

• Suppression when m >

obstm

eV Δm~eVα -1324 10at 2 offactor by n suppressio 10for E.g.

• In intranuclear transitions where V~10 MeV small provides no additional suppression. Intranuclear transitions are not sensitive to m !

eVΔm~ -1310

reactortm

m vs in nnbar search (if 0)

5

9

8

18

1059/

108

101

10100

nnn

eee

ppp

KKK

mmm

m mm

m mm

mmm

Experimental limits on mass difference

Uncertainty of intranuclear suppression

If nnbar transitionwill be observed this will be a new limit

of CPT m test

TRIGA Cold Vertical Beam, 3 years

Col

d B

eam

Future p-decay Future p-decay sensitivitysensitivity

J. Wilkes, 25 Feb '05at Neutrino Telescopes