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Search for a muon spontaneous emission from heavy nuclei

11 th ICATPP Conference on Astroparticle, Particle, Space Physics, Detectors and Medical Physics Applications Villa Olmo, Como , 5-9 October 2009. Search for a muon spontaneous emission from heavy nuclei. M. Giorgini et al. , Bologna University and INFN. m. m. +. +. n. n. m. m. A. A.

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Search for a muon spontaneous emission from heavy nuclei

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  1. 11th ICATPP Conference onAstroparticle, Particle, Space Physics, Detectors and Medical Physics Applications Villa Olmo, Como, 5-9 October 2009 Search for a muon spontaneous emission from heavy nuclei M. Giorgini et al., Bologna University and INFN

  2. m m + + n n m m A A A 1 A A HC 1 A n A n “Exotic radioactivity” predicted for heavy nuclei Pions or muons could be emitted by heavy nuclei through the decays : (A,Z) → m± + nm (nm) + (A1,Z1) + ……. + (An,Zn) (A,Z) → p± (p0) + (A1,Z1) + ……. + (An,Zn) (a) (b) • Spontaneous m emission : m emitted with nuclear fragments (b)Hyper-Cold approximation : m emitted before nuclear fragments D.B. Ion et al., Spontaneous muon emission as a new natural radioactivity, Rev. Roum. Phys. 31 (1986) 209

  3. Spontaneous fission of heavy nuclei • In the case of spontaneous fission, the emission of the • following particles is energetically allowed : • m± (prompt muons), for Z ≥ 72 • p± → delayed muons, for Z ≥ 76 • 2m± (prompt muon pairs), for Z ≥ 91 • p± → delayed muon pairs, for Z ≥ 100 238U (Z=92) First 3 channels allowed 207Pb (Z=82) First 2 channels allowed The expected branching ratios are very small, so MASSIVE “sources” and LONG measuring times are needed

  4. Kinematical considerations • The fission fragments remain nearly at rest • Most of the kinetic energy would be carried out by the m • As the associated neutrino takes a fraction of the available energy, • the energy spectrum of emitted muons could be similar to the • spectrum of electrons in b decay Available kinetic energy in a decay : 238U 85-90 MeV <Em> 40 ÷ 50 MeV <Em> 10 ÷ 15 MeV 207Pb 25-30 MeV These decays have been searched using small different detectors… but only poor upper limits were obtained [D.B. Ion et al., Rev. Roum. Phys. 32 (1987) 299]

  5. nuclear emulsions for tracking particles large amount of Pb and long exposure time low natural radioactivity background contributions known and estimated ambient neutron flux  1.8.10-6 neutrons/s/cm2 a potential discovery … a good upper limit for these rare processes We propose a search of muon emission from heavy nuclei using some “bricks” of the OPERA detector OPERA + LNGS = GOOD CONDITIONS FOR : ☻ !!!

  6. establish the background contribution validate the analysis procedure reach a good sensitivity level lead (1mm) …..56 base (200 mm) emulsion film (43 mm) First step: use of some OPERA “bricks” 1 OPERA brick (8.23 kg of Pb) exposed at LNGS for 1 year should :

  7. BACKGROUND SOURCES AND REJECTION a and b radioactivity from isotopes present in Lead : a particles can be neglected 8.8 MeV a particles emitted by radioactive nuclides (212Po) present in emulsions: reducible by dE/dx measurements and range (~74 mm) considerations Ambient neutrons ( 1.8.10-6 neutrons/s/cm2) may induce nuclear fissions : flux reduced by the shield; the effects it can be further reduced with “appropriate” candidate definitions Radon induced background : it could be reduced isolating the brick in hermetic bags and could be monitored using radon detectors Background from the CNGS neutrino beam : the induced muon energy is much higher, so the tracks could be easily recognizable Background from cosmic rays : Cosmic ray muons from above : due to their high energy and small energy losses, they can be rejected with geometric considerations Pions produced by atmospheric muon interactions in a lead sheet, decaying into a muon : the rate is 6.10-4 /year for 1 OPERA brick, so can be neglected

  8. Shielding for background reduction 55 cm 10 cm 10 cm 55 cm 15 cm 5 bricks 30 cm 70 cm The background reduction is a crucial point : shields + analysis cuts Copper Lead Shield surrounded by polyethylene/paraffin for neutrons Plastic shields for reduction of radon inside the “cave”

  9. MonteCarlo simulation of events in an OPERA “brick” 20 MeV m- 20 MeV m+ 1500 MC events (microtracks)

  10. Geometricalefficiency eg (%) Nm , Ne = minimum number of emulsion films* crossed by the m-, e- * means a microtrack (43 mm) Next step : reconstruction efficiency

  11. Next step : reconstruction efficiency This search takes advantage of the fast (~20 cm2/h) scanning microscopes used for the OPERA experiment

  12. CONCLUSIONS We propose to perform a search for spontaneous emission of muons from Pb using one or more OPERA bricks A test with few OPERA bricks for 1-few years exposure should be useful for a good background study and for defining appropriate analysis procedures This search would be complementary and superior to other experiments looking for such exotic radioactivity Even in absence of candidate events, we would obtain a significant limit for spontaneous muon radioactivity

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