Yuri Kamyshkov

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Fermilab Wine and Cheese Seminar, Friday, June 3,
2005
Baryon Number Violating Processes and Proton
Driver
Yuri Kamyshkov University of Tennessee kamyshkov
_at_utk.edu
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Plan
Short status of baryon violation search
(B?L)0 vs (B?L)?0
n?nbar transition search (why, how, where)
n?nbar search with Proton Driver?
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What we learned from 30 years of proton decay
search?
(experimentalists view)
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 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)
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More questions that I hope to find the answers for
is nucleon instability search motivated only
by GUT and SUSY? should we believe in Great
Desert ? are low-energy scale QG models
testable? with nucleon decay? how to
motivate young experimentalists to search for a
proton decay? are we diligently exploring all
alternative ideas and experimental options?
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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)
• Baryon number violation
• 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 instability
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Is (B?L) conserved?
However, in the Universe most of the leptons
exist as, yet undetected, relic neutrino and
antineutrino radiation (similar to CMBR) and
conservation of (B?L) on the scale of the whole
Universe is still an open question
Non-conservation of (B?L) was discussed
theoretically since 1978 by
Davidson, Marshak, Mohapatra, Wilczek, Chang,
Ramond ...
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Important Theoretical Discoveries
Anomalous nonperturbative effects in the
Standard Model lead to violation of lepton and
baryon number (t Hooft, 1976) this B and L
nonconservation in SM is too small to be
experimentally observable at low temperatures,
but can be large above TeV scale.
On anomalous electroweak baryon-number
non-conservation in the early universe (Kuzmin,
Rubakov, Shaposhnikov, 1985)
Anomalous SM interaction conserves (B?L) but
violate (BL). Rate of anomalous (BL)-violating
electroweak processes at T gt TeV (sphaleron
mechanism) exceeds the Universe expansion rate.
If B L was set at very high temperature (e.g.
at GUT scale) due to some (B?L) conserving
interaction (e.g. by SU(5) SUSY), all quarks
and leptons along with BAU will be wiped out by
(BL)-violating electroweak processes. For the
explanation of BAU (B?L) violation at the scale
above EW (?1 TeV) is required.
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If (B?L) is violated at high temperature above
electroweak scale
If conventional (B?L)-conserving proton decay
would be discovered e.g. by Super-K, it does not
help us to understand BAU.
The proton decay is not a prediction of the
baryogenesis Yanagida _at_ ?2002
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Spectacular work of Super-K, Soudan-2, IMB3,
Kamiokande, Fréjus
All modes ?(B?L)0
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Some ?(B?L)?0 nucleon decay modes (PDG04)
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?B, ?L?0 searches in particle decays (PDG2004)
All above limits are ?(B?L)0 decay modes
Note, that in nucleon decay (e.g. p? e??
) ?(B?L) ?2
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KamLAND is searching for ?(B?L)?0 processes
Neutron disappearance from 12C
(small accidental background)
Expected sensitivity improvement to 7?1029
yr (current SNO limit is ? gt 1.9?1029 yr)
Two neutron disappearance from 12C Expected
sensitivity improvement to 1.7?1030 yr (current
Borexino limit is ? gt 4.9?1025 yr)
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Neutron ?Antineutron Transitions
has the highest potential in exp. sensitivity
improvement for B-violation search
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Neutron ?Antineutron Transition ?
First considered and developed within the
framework of Unification models by
R. Mohapatra and R.
Marshak, 1979
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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 decay is strongly suppressed in this
model, but n-nbar is not since nR has no gauge
charges
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Effective D 7 operators can generate n-nbar
transitions
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n?nbar transition probability
?-mixing amplitude
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n?nbar transition probability (for given ?)
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PDG 2004 Limits for both free reactor neutrons
and neutrons bound inside nucleus
Bound n J. Chung et al., (Soudan II) Phys. Rev.
D 66 (2002) 032004 gt 7.2?1031 years ?
Free n M. Baldo-Ceolin et al., ?
(ILL/Grenoble) Z. Phys C63 (1994) 409 with P
(t/?free)2
Search with free neutrons is square more
efficient than with bound neutrons
R is nuclear suppression factor Uncertainty of
R from nuclear models is factor of 2
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Suppression of n?nbar in intranuclear transitions
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Future n?nbar search limits with bound neutrons
Future limits expected from SNO and Super-K
Since sensitivity of SNO, Super-K, and future
large underground detectors will be
limited by atmospheric neutrino background (as
demonstrated by Soudan-II experiment), it
will be possible to set a new limit, but
difficult to make a discovery!
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Experiment with free neutrons
Best reactor measurement at ILL/Grenoble reactor
in 89-91 by Heidelberg-ILL-Padova-Pavia
Collaboration
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Detector of Heidelberg -ILL-Padova-Pavia
Experiment _at_ILL 1991 (size typical for HEP
experiment)
?
?
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Future searches with free neutrons
if no background, one event could be a
discovery
possible to increase sensitivity by more than
? 1,000 ?bound gt 1035 years (?free gt 1010
sec)
use existing research reactor facilities? e.g.
HFIR at ORNL?
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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
DUSEL sites ? WIPP, Soudan, Homestake,
Sudbury
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Annular core TRIGA reactor for N-Nbar search
experiment
Annular core TRIGA reactor 3.4 MW with convective
cooling, vertical channel, and large cold
moderator. Unperturbed thermal flux in the
vertical channel 3E13 n/cm2/s
1 ft
Example UT Austin research TRIGA reactor. It
is a 1.2-MW core. The last university reactor
installed in the country (around 1991). It
costs about 3.5 M plus fuel the cost of the
fuel depends on whether you get it from DOE or
not.
Courtesy of W. Whittemore (General Atomics)
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Why Focusing Reflector?
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Why Vertical ?
Average velocity of cold neutrons 1000 m/s
(Maxwell)
For high sensitivity Nnltt2gt most important are
neutrons with small velocities in the Maxwellian
spectrum
These are mostly affected by gravity
In horizontal layout it leads to the defocusing
of the spectrum. and reduction of Nnltt2gt by
factor ?10
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The conceptual scheme of antineutron detector
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Monte Carlo simulated antineutron annihilation
event in N-Nbar Detector.   Intranuclear
anti-neutron-carbon annihilation model/generator
(1996, E. Golubeva, A. Iljinov, et al.)
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FNAL Proton Driver as a Source of Cold Neutrons
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 research reactor at SNS 22 neutrons are
produced per 1 GeV proton in a liquid Hg target
2 MW PD spallation target can produce
thermal flux ? 2?1014 n/cm2/s efficient
reflector/moderator (e.g. D2O) and cryogenic D2
moderator vertical 1000-m deep shaft under
the target vertical 2 MW PD will have
more discovery potential than 100 MW horizontal
reactor beam.
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SNS Target-Moderator System
Reflector
Target
Moderators
Proton Beam
designed for high yield of neutrons within short
time interval
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PDTarget System Study (N. Mokhov)
designed for high yield of pions
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Conceptual stopping target for Proton Driver
to be designed for high yield of cold neutrons
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Soudan-2 limit ? ILL/Grenoble limit 1 unit of
sensitivity
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Proton Driver
TRIGA Cold Vertical Beam, 3 years
Proton Driver
Cold Beam
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If n?nbar exists one can look for CPT violation
Following Yu.Abov, F.Djeparov, and L.Okun, Pisma
ZhETF 39 (1984) 493
Transitions for free neutrons V0 are
suppressed when Suppression when ?m gt ?
In intranuclear transitions where V10 MeV
small provides no additional suppression.
Intranuclear transitions are not sensitive to
?m !
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?m vs ? in n?nbar search (if ??0)
Experimental limits on mass difference
Uncertainty of intranuclear suppression
If n?nbar transition will be observed this will
be a new limit of CPT ?m test
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Science impact of n-nbar search
If 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
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
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Conclusions
(B?L) violating processes are important part
of the baryon number violation search program
n-nbar transitions might be most spectacular
manifestation of (B?L) violation due to its
clear signature, backgroundless detecton and a
possibility of a large increase of sensitivity
Proton Driver would open new possibilities
for a large next step in baryon number violation
search
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end