Yuri Kamyshkov University of Tennessee

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DUSEL Theory Workshop, OSU April 4, 2008
Experimental Status of NNbar Search and plans for
DUSEL
Yuri Kamyshkov/ University of Tennessee email
kamyshkov_at_utk.edu
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Existing NNbar limits
Sensitivity for free neutron search (observation
probability)
Sensitivity for bound neutron search (in nucleon
decay expts)
known from nuclear theory
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Previous free neutron N-Nbar search experiment
At ILL/Grenoble reactor in 89-91 by
Heidelberg-ILL-Padova-Pavia Collaboration M.
Baldo-Ceolin M. et al., Z. Phys., C63 (1994) 409
No background! No candidates observed. Measured
limit for a year of running
reference unit of sensitivity
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Previous bound neutron N-Nbar search experiments
Preliminary S-K result
Observed improvement weaker than SQRT is due to
irreducible background of atmospheric neutrinos
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Free Neutron and Intranuclear NNbar Limits
Comparison
e.g. intranuclear nn ? pions with presumably
large uncertainty is not accounted
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NNbar unique for DUSEL
Yates
Ross
5 5137?
Shaft 5 might not be usable
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3.4 MW annular core research TRIGA reactor with
Liquid D2 cold neutron moderator
TRIGA Training Research Isotopes from General
Atomics
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Neutron shaft
Schematic of annihilation detector
Detector Hall
Door
Access Tunnel
Control Room Electronics
Neutron Dump
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Why Vertical and TRIGA are needed ?
and not Horizontal and existing high-power
reactors?

• First, one needs RESEARCH not POWER reactor
  since
• by design virtue neutron fluxes are higher in
  former
• Second, most important reason vertical gravity
  produces
• devastating effect on the cold horizontal
  neutron beam
• ? vertical layout doesnt suffer from this
  effect, thus
• 3.5 MW TRIGA is more efficient that largest
  100 MW
• research reactor HFIR at ORNL
• There are no research reactors with the cold
  beam available
• they are all occupied by fundamental
  material research

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DUSEL NNbar Baseline Features
Vertical flight path 1 km Shaft
diameter 15-20 ft Vacuum chamber with
10?5 Pa Active passive magnetic shield 1
nT Annular core TRIGA reactor 3.4 MW LD2
cryogenic cold moderator neutron
temperature 35K Running time 3-5 years Robust
detection signature nA ? several pions 1.8
GeV Annihilation properties are well modeled
LEAR physics Active magnetic shielding allows
effect ON/OFF Sensitivity increase more than
?1000 Expected background at max
sensitivity lt0.01 event
with no background one event can be a discovery!
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NNbar DUSEL Sensitivity Reach
Most exciting for experiment is a possibility of
increasing sensitivity by large factor ? 1,000
(or ?nucl ? 1035 years)
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Other factors that could enhance the sensitivity
(a) Larger shaft length (b) Larger reactor
power (c) New reflector quality (developments at
KEK/Japan)(d) New colder moderator
thermalizing neutrons to lower temperatures
Thermalization of n to the temperatures lower
that 35K is a challenge for CM theory non-suffic
ient RD efforts
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Development of neutron reflectors
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Can NNbar create a background for other DUSEL
experiments?
Neutrinos ? For reactor located at the distance
2 km from the DUSEL main campus reactor
antineutrino flux is not larger (e.g. by scaling
from KamLAND) than solar neutrino flux

• Might be still essential for CC
• antineutrino detection experiments
• at DUSEL (e.g. geo-neutrinos)

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Thermal neutrons? can be easily shielded down
to the environmental level. The environmental
thermal neutron level is not precisely known at
Homestake mine ? ongoing RD to measure it and
then we will have to make sure that TRIGA
reactor will not increase this level.
Attenuation of thermal neutron flux by concrete
shield
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NNbar Collaboration
North Carolina State University A.I. Hawari,
B.W. Wehring, A. Young Indiana University W.M.
Snow, C. M. Lavelle University of Tennessee W.
Bugg, H.L. Dodds, Y. Efremenko,
G. Greene, Y. Kamyshkov,
S. Pfiffner California State University at
Dominguez Hills K. Ganezer, J. Hill Oak Ridge
National Laboratory G. Flanagan, J.O. Johnson,
K. Williams Los Alamos National Laboratory T.
Haines, A. Saunders National Institute of
Standards and Technology Pieter Mumm CNA
Consulting Engineers L. Petersen International
Collaborators KEK, PNPI, Dubna, ILL, Swiss
Neutronics

• The group has experience and
  expertise in
• large projects construction (L3 /LEP Hadron
  Calorimeter, KamLAND)
• participation in large underground experiments
  (UT, CSUDH)
• large scale underground construction (CNA
  Engineering MINOS,S1)
• reactor licensing, commissioning, operations
  (NCSU and ORNL)
• cold neutron sources and cold neutron
  experiments (IU, NCSU, UT)
• neutron technologies like supermirrors and mag.
  shield (IU, UT)
• neutron transport simulations (NCSU, ORNL, UT)
• intranuclear NNbar transition search (CSUDH)
• particle detector design, construction,
  simulations, cost estimate, etc.

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Preliminary Project Development Plan
construction feasibility
2009
2011
2015
2013
conceptual design
prelim design
board approve
construction
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Vertical experiments at DUSEL are non-traditional
other uses. Unique feature of DUSEL among
other underground labs.
? Homestake PAC received in 2005 following
vertical LOIs 7 Search for neutron to
antineutron transitions (Yu. Kamyshkov/UT) 23
Study of diurnal Earth rotation (W. Roggenthen /
SDSMT) 33 Physics of cloud formation (J.
Helsdon / SDSMT)
? New Vertical LOIs (2007) Cold atom
interferometry for detection of gravitational
waves
(M. Kasevich / Stanford U)
Search for transitions to mirror matter (n ? n?)
Mirror matter is an alternative explanation
of the dark matter
(A. Serebrov /
PNPI)