M. Selvi – SN detection with LVD – NNN‘06 Supernova  detection with LVD Marco Selvi – INFN Bologna, Large Volume LNGS

M. Selvi – SN detection with LVD – NNN‘06 LVD detector 3 identical towers in the detector 35 active modules in a tower 8 counters in one module

M. Selvi – SN detection with LVD – NNN‘06 Construction and data acquisition Start construction and installation: 1990 First tower - Start data acquisition: june, 11 th 1992 Second tower – Start data acquisition : june, 1 st 1994 Third tower – Start data acquisition: december, 13 th LVD is huge: 1000 tons of liquid scintillator and 2000 m 2 of limited streamer tubes. LVD is highly modular: 840 independent counters

M. Selvi – SN detection with LVD – NNN‘06 The detector: basic elements The scintillation counter: External dimensions: 1.5 x 1 x 1 m 3 Scint. composition: C n H 2n+2 = g/l PPO g/l POPOP Scint. density:~ 0.8 g/cm 3 Attenuation lenght:> =420 nm Flash point at:~39 o C PMT:FEU-49B Photocathode diameter:d=15 cm Quantum efficiency:10-15%

M. Selvi – SN detection with LVD – NNN‘06 SN generalities and the role of  oscillations

M. Selvi – SN detection with LVD – NNN‘06 Helium-burning star HeliumBurning HydrogenBurning Main-sequence star Hydrogen Burning Onion structure Degenerate iron core:   10 9 g cm  3   10 9 g cm  3 T  K T  K M Fe  1.5 M sun M Fe  1.5 M sun R Fe  8000 km R Fe  8000 km Collapse (implosion) Stellar Collapse and Supernova Explosion

M. Selvi – SN detection with LVD – NNN‘06 Collapse (implosion) Explosion Newborn Neutron Star ~ 50 km Proto-Neutron Star    nuc  3  g cm  3 T  30 MeV NeutrinoCooling Stellar Collapse and Supernova Explosion

M. Selvi – SN detection with LVD – NNN‘06 Newborn Neutron Star ~ 50 km Proto-Neutron Star    nuc  3  g cm  3 T  30 MeV NeutrinoCooling Gravitational binding energy Gravitational binding energy E b  3  erg  17% M SUN c 2 E b  3  erg  17% M SUN c 2 This shows up as This shows up as 99% Neutrinos 99% Neutrinos 1% Kinetic energy of explosion 1% Kinetic energy of explosion (1% of this into cosmic rays) (1% of this into cosmic rays) 0.01% Photons, outshine host galaxy 0.01% Photons, outshine host galaxy Neutrino luminosity Neutrino luminosity L  3  erg / 3 sec L  3  erg / 3 sec  3  L SUN  3  L SUN While it lasts, outshines the entire While it lasts, outshines the entire visible universe visible universe Stellar Collapse and Supernova Explosion

M. Selvi – SN detection with LVD – NNN‘06 Main goal of the experiment One SN each years is expected in our galaxy. Typical energy  MeV Detection of neutrinos from a gravitational core collapse SN-II. 99% of the available energy (E B ~ erg) is released through the emission of neutrinos of all flavours e    

M. Selvi – SN detection with LVD – NNN‘06 SN fluxes The main features of the flux produced in the star are: 1. Neutrinos   have a Fermi-Dirac energy spectrum, 2. Hierarchy of the temperatures: T e < T e < T x. 3. Approximate equipartition of energy among flavors: L e  L e  L x  E B /6. Typical parameters: distance of D=10 kpc, binding energy E B = 3 x erg, perfect energy equipartition L e = L e = L x = E B /6. assume identical fluxes     (  x ), fix the ratio T x /T e =1.5, T e /T e =0.8 and T e =5 MeV. Warning! Large uncertainties in the astrophysical parameters !!! Second warning ! It’s very difficult to consider rotation, magnetic fields and non spherical geometry in the MC simulations Third warning ! These models are not able to explain the SN explosion

M. Selvi – SN detection with LVD – NNN‘06 Neutrino oscillations in SN We consider the system of 3 active neutrinos f =( e,    ), mixed in vacuum such that f =U m where m =( 1,    ) is the vector of mass eigenstates and U is the mixing matrix. If neutrinos have mass they could oscillate between flavors. The oscillation is resonantly enhanced if a flavor-asymmetric medium is present (MSW matter effect). The medium density  res for the resonance to occur depends on the oscillation parameters. The wide range of density values in the SN matter allows for 2 resonance levels.  (g/cc)MediumOsc. parameters involved HH 10 3 –10 4 He“ATM” (  m 2 atm, U e3 2 ). LL 10–30H“MSW LMA”  m 2 sol, U e2 2 ) The resonance is expected for or depending on the mass hierarchy (=sign of  m 2 atm ) sign of  m 2 atm Resonance in + (normal hierarchy) - (inverted hierarchy)

M. Selvi – SN detection with LVD – NNN‘06 interactions in LS

M. Selvi – SN detection with LVD – NNN‘06 Neutrino interactions in LS interactions in LVD (mass = 1000 tons) Energy threshold (MeV) Detection Efficiency above threshold (%) e + p  n + e x + e -  x + e - // e + 12 C  12 N + e e + 12 C  12 B + e x + 12 C  x +  + 12 C TargetContained inMassNumber of targets Free protonsLiquid Scintillator1000 t9.34 x ElectronsLiquid Scintillator1000 t3.47 x C NucleiLiquid Scintillator1000 t4.23 x (-)

M. Selvi – SN detection with LVD – NNN‘06 Inverse beta decay

M. Selvi – SN detection with LVD – NNN‘06 CC interactions on 12 C nuclei e 12 C, 12 N e -, observed through two signals: the prompt one due to the e - above  h (detectable energy E d  E e MeV) followed by the signal, above  h, from the  decay of 12 N (mean life time  = 15.9 ms). 8  =85% e 12 C, 12 B e +, observed through two signals: the prompt one due to the e + above  h (detectable energy E d  E ne MeV + 2 m e c 2 ), followed by the signal, above  h, from the  - decay of 12 B (mean life time t = 29.4 ms). E th =17.8 MeV E th =13.9 MeV  =70% Detector modularity allows precise event tagging Elastic scattering

M. Selvi – SN detection with LVD – NNN‘06 NC interactions on 12 C nuclei  MeV energy deposit P. Antonioli et al., NIM A309 (1991) 569 The NC carbon reaction allows a bolometric flux measurement, “oscillation” independent. An energy window is selected to look for excess of events due to this reaction  =55% 8 Elastic scattering

M. Selvi – SN detection with LVD – NNN‘06 interactions in Fe

M. Selvi – SN detection with LVD – NNN‘06 Neutrino interactions in iron Fe p Vissani-Strumia astro-ph/ nucl-th/ The considered interaction is: e 56 Fe, 56 Co e -

M. Selvi – SN detection with LVD – NNN‘06 LVD support structure

M. Selvi – SN detection with LVD – NNN‘06 Results -Fe the nb of interaction in iron is 15% of the total number interactions

M. Selvi – SN detection with LVD – NNN‘06 Search for SN in LVD

M. Selvi – SN detection with LVD – NNN‘06 Since:To: LiveTime [days] Duty cycle Mass [ton] Published in: RUN 1Jun 6 th ‘92May 31 st ‘ %31023 rd ICRC 1993 RUN 2Aug 4 th ‘93Mar 11 th ‘ %39024 th ICRC 1995 RUN 3Mar 11 th ‘95Apr 30 th ‘ %40025 th ICRC 1997 RUN 4Apr 30 th ‘97Mar 15 th ‘ %41526 th ICRC 1999 RUN 5Mar 16 th ‘99Dec 11 th ‘ %58027 th ICRC 2001 RUN 6Dec 12 th ‘00Mar 24 th ’ %84228 th ICRC 2003 RUN 7Mar 25 th ‘03Feb 4 th ’05666>99%88129 th ICRC 2005 RUN 8Feb 4 th ‘05Apr 13 th ‘ %940NU 2006  Jun 6 th ’92Apr 13 th ’ %623 LVD data history

M. Selvi – SN detection with LVD – NNN‘06 How can the neutrino burst be identified ? T Detection of a burst of N pulses in a short time interval T А t

M. Selvi – SN detection with LVD – NNN‘06 Most recently analyzed data set: Effective time: days Average trigger mass: 940 t Duty cycle: % Search for SN burst: detector performances

M. Selvi – SN detection with LVD – NNN‘06 Search for SN burst: the method SN selected pulses: Filter noisy counters Energy in the MeV range Then we perform an analysis of the time sequence. We define a cluster as a set of m subsequent events in the time window of duration  t. For each cluster (m,  t) we compute the probability that it is due to poissonian fluctuations of the flat background. We have an alarm if the probability that the event is given by background is below one per century

M. Selvi – SN detection with LVD – NNN‘06 Search for SN burst: results LVD Data since 1992 Upper Limit to SN event in the Milky Way 0.18/year (90% c.l.) m>3 m>6 m>10 m>16 m>30 Galactic SN signal

M. Selvi – SN detection with LVD – NNN‘06 Neutrino burst detection Expected Fermi-Dirac -spectrum from core collapse  10 MeV for e, e ( i ) and  15 MeV for (  x ) T e = 3 MeV a pessimistic assumption

M. Selvi – SN detection with LVD – NNN‘06 SNEWS

M. Selvi – SN detection with LVD – NNN‘06 The SNEWS system SuperNova Early Warning System: working group between experiments looking for SN burst (currently LVD, SK, SNO, Amanda; Borexino, MiniBoone and KamLAND expected to join) Give prompt information to astronomical comunity. Doing online twofold coincidence allows to send a prompt alarm and to reduce to zero fake alarm! SK LVD SNO BROOKHAVEN server Scientific community Every experiment looks for SN burst and send alarm at average rate of 1/month Network as much as possible fault tolerant Interval (yr) Nb of active experiments AMANDA Since July ‘05

M. Selvi – SN detection with LVD – NNN‘06 Gd-doped LVD scintillator

M. Selvi – SN detection with LVD – NNN‘06 Inverse beta decay (double signature) Delay (ms)Energy (MeV) E  = 2.2 MeV  = 200  s Neutron capture efficiency = 60% (from 252 Cf measurement) n + p  d +  e + p  e + + n 1. Positron detection followed by Gamma (2.2 MeV) from neutron capture (  = 200  s)

M. Selvi – SN detection with LVD – NNN‘06 Gd in LVD scintillator Two counters (1.5 m 3 each) have been Gd-doped up to 0.1% in weight (work done at LNGS together with C.Cattadori, Bezrukov et al.): 1 st tankMay st tank doped in May 2005, placed in the Mounting the external LNGS laboratories; 2 nd tankOct nd tank doped in Oct. 2005, inside the LVD experiment in the LNGS Hall A. Gd carboxylate (Gd-CBX):

M. Selvi – SN detection with LVD – NNN‘06 Background at low energy The counting rate in the low energy region is related to the position of the counter inside the apparatus => the bkg sources are external to the detector In the low energy region (E <2 MeV) the main bkg source is natural radioactivity ( 222 Rn). The average rate over the low-threshold is ~230Hz. In order to detect the 2.2 MeV  from neutron capture, the value of the low-energy threshold is ~0.8 MeV.

M. Selvi – SN detection with LVD – NNN‘06 Gd in scintillator three main improvements: increase of the neutron capture cross section (from 0.33 barn to barn) increase of the gamma energy (from 2.2 MeV to about 8 MeV) decrease of the capture mean time (from 180  s to about 30  s) e + p  e + + n

M. Selvi – SN detection with LVD – NNN‘06 Results with Gd Neutron Capture Time Energy spectrum  = ± 1%  = 24.7 ± 1% (Neutron source: 252 Cf) Black: before Gd doping Red: with Gd inside

M. Selvi – SN detection with LVD – NNN‘06 Detector performances with Gd Change the value of the low-energy threshold (0.5÷4.5 MeV) and look at the resulting neutron detection efficiency (signal) Background rate For comparison, requiring the same efficiency of the non-doped case (60%) the bkg rate is about 12 Hz, instead of 230 Hz.

M. Selvi – SN detection with LVD – NNN‘06 Scintillator Stability The stability of the scintillator has been monitored for 170 days measuring neutron capture efficiency mean time Consistent with a flat behaviour Other measurements are done on smaller samples by directly measuring transmittance, light yield, and fluor concentration … result still preliminary The monitoring is going on... Neutron capture efficiency Average capture time