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Yuri Kamyshkov
University of Tennessee
kamyshkov @utk.edu
SLAC Experimental Seminar, Tuesday, May 17, 2005
Searches Searches for Baryon Number Violationfor Baryon Number Violation
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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
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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)
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• 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:
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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?
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Two types of baryon instabilityTwo types of baryon instability
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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 ...
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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.
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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
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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
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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
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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
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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
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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
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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
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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
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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
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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
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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%
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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
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(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
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•• 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
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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!
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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.
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Proton decayis strongly suppressed in this model, butn-nbar is not since nR has nogauge charges
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Effective D = 7 operators can generate n-nbar transitions
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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
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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
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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
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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
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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
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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
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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
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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
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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
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• • 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?
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Target Moderators
Proton Beam
Reflector
(An example) SNS Target-Moderator System
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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
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Science impact of n-nbar searchScience impact of n-nbar search
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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
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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
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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
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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
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TRIGA Cold Vertical Beam, 3 years
Col
d B
eam
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Future p-decay Future p-decay sensitivitysensitivity
J. Wilkes, 25 Feb '05at Neutrino Telescopes