E-mail to NRC CPU: q2c@nas.edu
March 26, 2001
Subject: Connecting Quarks with the Cosmos
I would like to attract the attention of the Committee on the Physics of the
Universe (CPU) to the experimental possibility of performing a new 1000-times more
sensitive search for the neutron to anti-neutron n  n transitions in the reactor-based
experiment at the existing High Flux Isotope Reactor (HFIR) at Oak Ridge National
Laboratory (ORNL). Such an experiment would address several of the CPU’s 11
scientific questions in an exploratory way. Physics motivation of n  n search is shortly
discussed in the attached letter that has been signed by the group of interested physicists
and sent to the High-Energy Physics Advisory Panel (HEPAP) last year.
I think, on behalf of the colleagues who have signed the letter mentioned above, I
can ask assistance and help of CPU in promoting the idea of a new n  n search to the
physics community and to the funding agencies. In remaining of this message are
responses to six questions formulated by CPU.
1.
Contact person: Yuri Kamyshkov, Department of Physics and Astronomy,
University of Tennessee, 401 Nielsen Physics Building, Knoxville, TN 37996-1200; tel.:
(865) 974-6777; e-mail kamyshkov@utk.edu.
2.
Who might be involved: Oak Ridge National Laboratory which operates HFIR
reactor facility with the highest in the world thermal neutron flux; university groups with
experience of research in fundamental physics of cold neutrons; high-energy and
astrophysics groups with experience of operation of moderately large multi-channel
detectors.
3.
Description of the project: reactor-based experiment that uses high-intensity
steady beam of cold neutrons produced by moderation in a volume of liquid hydrogen
placed near the compact core of the reactor. To produce a beam of high intensity a large
focusing reflector of a special optimized shape intercepts neutrons in the wide solid angle
range and concentrates them on the distant anti-neutron target. Low velocities of the cold
neutrons and long time-of-flight base of the experiment will allow to observe up to 1013
neutron flight histories per second with an average duration of ~ 0.3 sec. The 500-m long
neutron flight path should occur in a vacuum better than 104 Pa and with Earth magnetic
field suppressed down to <5nT by passive and active magnetic shielding. Detector of
anti-neutrons is 100-m thick carbon film with diameter 2m surrounded by tracking, an
absorption calorimeter, and cosmic-ray veto systems. Cold neutron production in
cryogenic moderators near the reactor core is a well-established technique. Neutron
reflection from metal surfaces is an industrial technique used in transport neutron guides.
The main challenges here are in the construction of a large (~ 100 m long and 2 m in
diameter) special-focusing-profile reflector and in the compensation of the Earth’s
magnetic field over the large flight-path volume. The detector of anti-neutrons, although
relatively large (overall diameter is ~ 6 m and length ~ 10 m), does not require premium
performance, the main challenge being to build it at low cost. The detector used in the
previous search of n  n transition in the reactor experiment [M. Baldo-Ceolin et al., Z.
Phys. C63 (1994) 409] serves as a prototype proof for the proposed experiment. In the
new HFIR-based experiment the sensitivity of n  n transition search can be increased
by factor of 1000 as compared with the previous search performed at the ILL reactor in
Grenoble [ibid.].
4.
Cost and schedule: The expected cost of the HFIR-based n  n search
experiment should be well below $50M (including ~$15M cost of a new cryogenic
hydrogen moderator). Provided that funding resources exist, the HB-3 beam at
HFIR/ORNL can be available for n  n experiment as was demonstrated by us in a
seed-money study project supported by ORNL. Expected possible schedule scenario after
initiation is: 2 years of Technical Design preparation, 2 years of construction, and 3 years
of operation.
5.
Science questions addressed: The discovery of n  n transition would establish a
new phenomenon leading to new physics at the energy scale of ~ 105 GeV. It will
provide essential contribution to the understanding of baryon asymmetry in the universe
and have major impact on the unification models. New symmetry principles (nonconservation of BL and restoration of L-R symmetry broken in the Standard Model)
might be revealed. In modern theories with the Standard Model fields localized on the
brane that propagates in higher-dimensional space-time [G. Dvali and G. Gabadadze,
hep-ph/9904221], n  n transitions might be a preferred mode to the proton-decay type
of baryon instability. If n  n exists, it will allow further experiments with reactor
neutrons and with intranuclear transitions [L.Okun, hep-ph/9612247] to provide the most
sensitive test of CPT-theorem and the experimental confirmation of the gravitational
equivalence of baryonic matter and antimatter. If n  n transition does not exist within
the proposed improved sensitivity limits, the new HFIR-based experiment will establish a
new limit on the stability of matter (through well-understood connection to the
intranuclear n  n transitions) at the level of 1035 years, beyond the reach of Super-K
and future planned proton-decay experiments.
6.
Multi-agency involvement: Although the physics addressed by an n  n search
belongs to high-energy physics and astrophysics, it does not fall automatically into the
scope of HEPAP, which is primarily concerned with the future of accelerator-based
physics. That motivated the letter (in attachment to this message) written to HEPAP in
support of the development of n  n search in US. The HFIR reactor facility at ORNL
is operated by Basic Energy Science office of DOE that has a different scientific and
operational mission and thus has little expertise in the physics fields related to the
proposed n  n experiment. ORNL/HFIR management has some difficulty with this
divergence of scientific goals and has no good mechanism to support the development of
a new n  n experiment. For these reasons proposed experiment will be probably a
prime candidate for NSF-DOE cooperative effort and due to its relation to the
cosmological matters it might be also of interest to NASA.
With my best regards,
Yuri Kamyshkov
Attachment: Letter to HEPAP from September 8, 2000 :
//web.utk.edu/~kamyshko/hepap.doc, or hepap.ps, or hepap.pdf