nnbar cpt

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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 ! if they will be discovered in the future they can be used for CPT test • nnbar transitions would violate B (Baryon) and B–L (Baryon – Lepton) numbers: B=2 and (L–B)=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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• observed BAU that proton decay with (L–B)=0 fails to explain • neutrino masses (if of Majorana nature) imply (L–B)=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 >3 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) What are the reasons why nnbar might exist in nature?

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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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Best reactor measurement at ILL/Grenoble reactor in 89-91 by Heidelberg-ILL-Padova-Pavia Collaboration Free neutron experiment

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Detector of Heidelberg -ILL-Padova-Pavia Experiment @ILL 1991 (size typical for HEP experiment) No background. No candidates observed for a year of running  measured limit:

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At High-Flux Isotope Reactor HFIR at ORNL the sensitivity of n-nbar search can be increased from the present level by factor of >1,000 Unfortunately HFIR is not available for nnbar search experiment. With no background one event can be a discovery! Possible future search

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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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Soudan-2 2002’ limit for nnbar search 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! nnbar search limit in large underground detectors Future limits expected from SNO and Super-K

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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 V=0 are suppressed when • Suppression when m >  • In intranuclear transitions where V~10 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 ~ 10–22 (Plank scale sensitivity) or 4 orders on magnitude better than from K0. Part of gravipotential different for neutron and antineutron will be tested with < 10–22 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. • Let’s hope nnbar exists.