CPT test in Neutron-Antineutron transitions

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CPT test in Neutron-Antineutron transitions
Yuri Kamyshkov University of Tennessee and UT
Neutron Science Consortium
III CPT'04 meeting, Indiana University August
4-7, 2004
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Transitions neutron ? anti-neutron are not
discovered yet !

1. if they will be discovered in the future
2. they can be used for CPT test

n?nbar transitions would violate B (Baryon)
and BL (Baryon Lepton) numbers ?B2 and
?(LB)2 these violations are not as
fundamental as CPT and/or LI violations. for
the purpose of this workshop we can assume that
n?nbar occurs.
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What are the reasons why n?nbar might exist in
nature?
observed BAU that proton decay with ?(LB)0
fails to explain neutrino masses (if of
Majorana nature) imply ?(LB)2 arises in
SUSY/GUT L-R symmetric models natural in some
Low Quantum Gravity Scale models where proton
decay is suppressed most important reason
sensitivity of new search can be advanced by
gt3 orders of magnitude with existing reactor
facilities if exists is determined by the
transition (mixing) amplitude ? provided by
some high-energy scale mechanism.
e.g. K.Babu R. Mohapatra PL B518 (2001) 269
G.Dvali G.Gabadadze PL B460 (1999) 47
S. Nussinov, R. Shrock PRL 88 (2002)
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Purpose of this talk
Discussion of importance of ? ?0 search is
beyond the scope of this talk.

(e.g. see YK, hep-ex/0211006) Were the n ?
nbar found CPT test will be a side
application. Purpose of my talk is to discuss
n ? nbar application to CPT test and the
related sensitivities. CPT test for n ? nbar
transitions was first proposed by
Yu.Abov, F.Djeparov, and
L.Okun, Pisma ZhETF 39 (1984) 493
see also L.Okun, hep-ph/9612247
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n?nbar transition probability (if ??0)
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n?nbar transition probability (for given ?)
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Two types of experiments for n?nbar search
with cold neutrons from reactors (free
neutrons) or UCN. Sensitivity neutron flux
? (observation time)2 So far best limit
is obtained at ILL/Grenoble reactor M.
Baldo-Ceolin et al., Z. Phys C63 (1994) 409
inside nuclei
(with bound neutrons) where transitions are
strongly suppressed by nuclear potential
different for neutron and anti-neutron.
Searched in large underground detectors. So
far best limit in Fe is obtained by Soudan-2
Collaboration J. Chung et al., Phys. Rev. D
66 (2002) 032004.
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Free neutron experiment
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)
No background. No candidates observed for a year
of running ? measured limit
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Possible future search
At High-Flux Isotope Reactor HFIR at ORNL the
sensitivity of n-nbar search can be increased
from the present level by factor of gt1,000
With no background one event can be a discovery!
Unfortunately HFIR is not available for n?nbar
search experiment.
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Scheme of N-Nbar search experiment with vertical
layout
? Sensitivity increase by factor 1,000 ?
Dedicated small-power research reactor ?
Vertical shaft 500-1000 m deep with diameter
6 m in Soudan mine (?) ? Large vacuum tube,
focusing reflector, Earth magnetic field
compensation system ? Detector (similar to ILL
N-Nbar detector) at the bottom of the mine
? Availability of underground site is
uncertain. Installation of a new (even small)
research reactor is unlikely.
Ø
Ø
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n?nbar search limit in large underground
detectors
Soudan-2 2002 limit for n?nbar search
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-2 experiment), it
will be possible to set a new limit, but
difficult to make a discovery!
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Suppression of n?nbar in intranuclear transitions
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How CPT violation works in n?nbar transitions?
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 will provide 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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Conclusions
With present intranuclear limits positive
observation of free n?nbar transitions will
test CPT down to ?m/m 1022 (Plank scale
sensitivity) or 4 orders on magnitude better
than from K0. Part of gravipotential
different for neutron and antineutron will be
tested with lt 1022 GeV. If ?m ? 0 n?nbar
might show up first in intranuclear transitions
that are not sensitive to ?m. However, the
intranuclear experiments are limited by
atmospheric neutrino background and can only
improve limits rather than discover the
n?nbar. With free neutrons one measures well
when Note, that suppression depends on
(V?m/2). Once transitions observed one can
try to disentangle effect of ?m by fine tuning of
compensated magnetic field. For polarized
neutron beam ?m effect can be canceled by
magnetic field ? sign of ?m. Lets hope
n?nbar exists.