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Presenters: AGAFONOVA NATALIA BOYARKIN VADIM Corno Grande LVD H=3650 m.w.e. Hmin=3650 m.w.e. <E>=280 GeV Eth = 2.2TeV at sea level -rate (1 tower)~ 120 h-1 Stopping muon rate (1 counter) 0.7510-3 - trigger: ε 40 MeV, 2 sc Data taking trigger: th=4MeV (inner counters) th=7MeV (external counters) Event duration – 1 ms, th=0.6MeV (inner counter) E–resolution: ~30% =1-5MeV ~20% 5 MeV t–resolution: ~70 ns L-shape tracking system 1m 1,5m 1m Module – portatank, 8 sc The Tower The large volume detectors are the underground observatories for: - Neutrino astrophysics - Cosmic Rays physics - Search for point sources of cosmic rays - Study of neutrino oscillations - Search for rare events predicted by the theory (proton decay, monopoles, dark matter...) - Geophysical phenomena General idea How can one detect the neutrino flux from collapsing stars? Until now, Cherenkov (H2O) and scintillation (СnH2n) detectors which are ~ capable of detecting mainly e , have been used in searching for neutrino radiation, This choice is natural and connected with large ~ -p cross-section e ~е p e n ep ~ 9.3Ee2 1044 см2 Ee 0.5 MeV As was shown at the first time by G.T.Zatsepin, O.G.Ryazhskaya, A.E.Chudakov (1973), the proton can be used for a neutron capture with the following production of deuterium (d) with - quantum emission with 180 – 200 µs. n p d EE 2.2 2.2МэВ MeV The specific signature of event How can the neutrino burst be identified ? The detection of the burst of N impulses in short time interval T А t T 1 N~ I ( E i ) ( E i )dE M 2 i 4R i Ethr Сn H 2n H 2O Reactions for scintillation and Cherenkov counters e p e n p ~ 9.3E 10 44 2 e e см 2 cm2 MeV Ee 0.5МэВ Ee E 1.3 МэВ MeV 2 e e e e e ~ 9.4 E2 10 45 см cm2 e e i e i e 2 2 e ~ 1.6 E2 10 45 см cm i i 2 cm2 i e i e e ~ 1.3E2 10 45 см i i C12 C12* 15.1 МэВ ( E 10MeV ) 0.066 10 42 cm 2 С12 (15.1 МэВ) ,е ( Е 20MeV ) 1.23 1042 cm 2 e e e 12C 12N e C e 12 ~e 12C 12B e C e ~ 12 Ethr 17.34 MeV 15.9 ms Ethr 14.4 MeV 29.3 ms Yu.V. Gaponov, S.V. Semenov 1+ GT __________10,589 1+ GT __________ 7,589 1+ GT __________ 4,589 0+ IAS __________ 3,589 1+ __________ 1,72 4+ __________ 56 56 e 26Fe0 27 Co*e + E 56 27 56 56 E 4.056 MeV Co Fe 27 26 E 40 MeV Co Fe e e 56Co Ee Eo E E 1.82MeV 56 e СnH2n E 1.72MeV tot 4.24E 40cm2 So one can expect ~p 550 events from e and more than 700 events from e A & eC in LVD The possibility to observe the neutrino burst depends on background conditions The source of background: 1. Cosmic rays 0<E< а) muons b) secondary particles generated by muons (e,,n and long-living isotopes) с) the products of reactions of nuclear and electromagnetic interactions 2. Natural radioactivity Е<30 MeV, mainly Е<2.65 MeV а) , b) n, (n ), U238, Th232 c) , (n) d) Rn222 Background reduction: 1. Deep underground location 2. Using the low radioactivity materials 3. Anti-coincidence system 4. Using the reactions with good signature 5. The coincidence of signals in several detectors Tower Quarters 4Q C= 1 TOWER 280 scintillation counter (1.2 t/counter) 120 inner counters 3 TOWERS total 840 sc 1kt – scintillator 1kt – Fe L 10.2 m 6.3 m 13.4 m n 56 Fe 57 Fe* 57 Fe (k ), 91.7% nFe-capture nth p , (~7MeV) n54Fe55Fe* 55Fe ( ), 5.8% sc Fe 130 s n35Cl 36 Cl * 36 Cl (k ), 75.8% , n p nth (2.2 MeV) np-capture np D* D 0.334 barn sc 185 s 72294 Neutrons= 5133.7 843.4 dNn dt B N 0 exp( t ) 0-4 MeV 4-12 MeV 23502 N=72294 Neutrons= 5949.6 908.2 0 + n e+e- 19603 Neutrons= 18537 2684 For determining the specific neutron yield number we used the formula: n N tot n l N ev N the number of searched events tot n N N sc n Fe,Cl n l L in the average muon path length total number of muon events both single muons and groups, and electromagnetic and hadronic cascades event N g n 11 10 ( 4 cm 2 ) 1 6 δ=0.07 N. of ev. Nn/ev. muons 0-4 MeV 4-12 MeV Single 1µ 72294 5704 1124 6282 Muon bundle 6611 1211 7822 nFe,sc (cm2/g) nsc 0.155 3.0610-4 1.8410-4 0.547 10.8510-4 6.5110-4 neutron (cm2/g) 23502 1.8410-4 kµ (k=3.54) 83264 cascade 19603 20597 3580 24177 2.03 - - Total 116710 33423 6148 39571 0.557 1110-4 6.610-4 Per 1 (all processes) 4.3810-4 7 LVD En>0MeV 8 dNn dt B N 0 exp( t ) q VFe VPVC VFe VPVC Vsc K=240/146=1.644 sc = 0.9 Fe,Cl = 0.75 q=(VFe+VPVC)/(VFe+VPVC+Vsc) K Nn N 3 V(M pvc=380kg) =0.86 m n 0.5–4 MeV N(<4MeV) 3 =185 µs =7.8 g/cm MFe =9.46 t (np–capture in scintillator) =30081 4 -12 MeV Msc =9.2 t (nFe,Cl - capture) . qN Fe,Cl n /( N сц n 54948 q=0.160 N(>4MeV) 3 =134 µs 10107 =0.78 g/cm =4611 N Fe,Cl n ) 0.155