Published on December 17, 2007
Slide1: Yuri Kamyshkov University of Tennessee and UT Neutron Science Consortium III CPT'04 meeting, Indiana University August 4-7, 2004 Slide2: Transitions neutron anti-neutron are not discovered yet ! if they will be discovered in the future they can be used for CPT test • nnbar 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 nnbar occurs. Slide3: • 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 nnbar might exist in nature? Slide4: 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 Slide5: nnbar transition probability (if 0) Slide6: nnbar transition probability (for given ) Slide7: Two types of experiments for nnbar 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. Slide8: Best reactor measurement at ILL/Grenoble reactor in 89-91 by Heidelberg-ILL-Padova-Pavia Collaboration Free neutron experiment Slide9: 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: Slide10: 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 nnbar search experiment. With no background one event can be a discovery! Possible future search Slide11: 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 Slide12: Soudan-2 2002’ limit for nnbar 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! nnbar search limit in large underground detectors Future limits expected from SNO and Super-K Slide13: Suppression of nnbar in intranuclear transitions Slide14: How CPT violation works in nnbar 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 ! Slide15: m vs in nnbar search (if 0) Experimental limits on mass difference Uncertainty of intranuclear suppression If nnbar transition will be observed this will be a new limit of CPT m test Slide16: Conclusions • With present intranuclear limits positive observation of free nnbar 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 nnbar 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 nnbar. • 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 nnbar exists.