C.Vigorito, University & INFN Torino, Italy 30 th International Cosmic Ray Conference Merida, Mexico Search for neutrino bursts from Gravitational stellar collapses with LVD: update to 2007 C. Vigorito on behalf of the LVD Collaboration University and INFN Torino, Italy

C.Vigorito, University & INFN Torino, Italy 30 th International Cosmic Ray Conference Merida, Mexico LVD: Detector & Performances Searching for SN neutrino Signal: Technique (Off-line, On-line) Data & Results Conclusions Today Topics

C.Vigorito, University & INFN Torino, Italy 30 th International Cosmic Ray Conference Merida, Mexico The LVD Detector A 1 kton scintillator detector for neutrino astronomy in the INFN Gran Sasso National Laboratory

C.Vigorito, University & INFN Torino, Italy 30 th International Cosmic Ray Conference Merida, Mexico Ref. LVD Coll., Nuovo Cimento A105 (1992) 1793 LVD: array of 840 liquid scintillator counters (1.5 m 3 each) arranged in a compact and modular geometry. 3 Towers 35 Modules per tower 8 Tanks per module Total target: 1000 t of Scintillator 900 t of Fe (structure)

C.Vigorito, University & INFN Torino, Italy 30 th International Cosmic Ray Conference Merida, Mexico Each counter is viewed on the top by three 15" PMTs (QE=10-15%) in 3 fold coincidence 1m 1.5m

C.Vigorito, University & INFN Torino, Italy 30 th International Cosmic Ray Conference Merida, Mexico Trigger Mass Uptime

C.Vigorito, University & INFN Torino, Italy 30 th International Cosmic Ray Conference Merida, Mexico The LVD Trigger Optimized to the to Inverse Beta Decay Two detectable signals: the prompt e+ (Evis~ E -0.8 MeV) the delayed ( = 185  s)  (2.2 MeV ). Each PMT is discriminated at two different thresholds resulting in two possible levels of coincidence: High and Low E H ~ 4 MeV and E L <1 MeV active for 1 ms after the trigger

C.Vigorito, University & INFN Torino, Italy 30 th International Cosmic Ray Conference Merida, Mexico Energy calibration: Using the atmospheric muon spectrum (30 days integration) and MC simulation Energy resolution: FWHM/E ~ 30% at 15 MeV. N-capture efficiency: 50% LVD Trigger Efficiency

C.Vigorito, University & INFN Torino, Italy 30 th International Cosmic Ray Conference Merida, Mexico 150 days - Sampling: 2 hours -Variable Detector Configuration (trigger mass) - Basic cuts on muon rejection and noisy counter applied  H =90%  H =95% Background Rate Stability

C.Vigorito, University & INFN Torino, Italy 30 th International Cosmic Ray Conference Merida, Mexico Trigger E>7 MeV sampled every 2 minutes compared with the mean local background over 40 minutes /50 days considered LVD rate is poissonian at level of ~15% sbb

C.Vigorito, University & INFN Torino, Italy 30 th International Cosmic Ray Conference Merida, Mexico Performed by processing the trigger sequence in the range MeV: on-line for prompt alert purpose and off-line to check data. Search for SN Burst Ref. Fulgione, Mengotti & Panaro, NIM A368 (1996) 512 Second step: check of  burst consistency check by: topological distribution in the detector (Uniform) energy spectrum (Fermi-Dirac) time distribution of delayed pulses (N-capture with  T=185  s) For a selected cluster the imitation frequency FIM is calculated taking into account the rate of background events f bk. FIM< 1 y -1 (Alert if FIM< 0.01 y -1 ) First step: statistical analysis of all possible clusters (m≥2,  t<200 s) initiated by each single pulse.

C.Vigorito, University & INFN Torino, Italy 30 th International Cosmic Ray Conference Merida, Mexico Data: 846 days (Feb.2005-May 2007) 14.2 million of events Mean Rate 0.2 Hz Multiplicity and cluster duration have been checked: data (different color markers) compared with expectations (solid color lines) from Poissonian fluctuations of the background is shown. Good agreement for different cluster multiplicities and durations. Results

C.Vigorito, University & INFN Torino, Italy 30 th International Cosmic Ray Conference Merida, Mexico All detected clusters are shown in the Multiplicity (m) vs Duration (  t) scatter plot. The sensitivity of LVD at the alert level of 1 event per 100 years is shown. No alert in the LVD standalone mode is found. 2 candidates are selected at the FIM<1 event/year

C.Vigorito, University & INFN Torino, Italy 30 th International Cosmic Ray Conference Merida, Mexico Candidate 1 Fim=0.46/y N. of Trigger 52 Background rate=6.1 ev/min Duration s Candidate 2 Fim=0.48/y N. of Trigger 65 Background rate=8.9 ev/min Duration s Energy Spectrum Time distribution of delaied pulse Topology (internal & external counter contributions) Fine structure compatible with fluctuation of background events

C.Vigorito, University & INFN Torino, Italy 30 th International Cosmic Ray Conference Merida, Mexico Total 4919 days Upper Limit to SN event in the Milky Way 0.17 /year (90% c.l.) RUNSince:To: Uptime [days] Duty Cycle Mass [tonn] PUBLISHED 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 5 th ‘05May 31 st ‘07846>99%93630 th ICRC 2007

C.Vigorito, University & INFN Torino, Italy 30 th International Cosmic Ray Conference Merida, Mexico The SN On-line Monitor SNM algorithm can generate alarm at fixed selection rate: 1/day SN Monitor Check (active since Jul. 2005) 1/month SNEWS Alert Different approach: study of the cluster multiplicity (m) in fixed time windows  t=20 s starting at t o (and t o +10 s) / fbk rate in the MeV range

C.Vigorito, University & INFN Torino, Italy 30 th International Cosmic Ray Conference Merida, Mexico Cluster selected on-line in 688 days at different threshold Observed rate of alert (fits of the delay distributions) 1.24 day month -1 Ref. On-line recognition of supernova neutrino bursts in the LVD detector submitted to Astroparticle Physics, LVD COLLABORATION

C.Vigorito, University & INFN Torino, Italy 30 th International Cosmic Ray Conference Merida, Mexico Conclusions No SN candidates have been found over 4919 days : the upper limit to to SN event in the Galaxy at 90% c.l. is 0.18 event/year over almost 2 years. The on-line monitor keeps LVD connected to SNEWS: the reliability of the alert selection has been checked on real alert data over almost 2 years. Since 2001 LVD is running in the final configuration: 1 kton and 99.5% of uptime. Monitoring the galaxy since 1992: ~5000 days of data acquisition with an average duty cycle of 93%.

C.Vigorito, University & INFN Torino, Italy 30 th International Cosmic Ray Conference Merida, Mexico

C.Vigorito, University & INFN Torino, Italy 30 th International Cosmic Ray Conference Merida, Mexico INTERNAL COUNTERS (M=475 t) T 1 T 3 T 2 TOP VIEW FRONT VIEW EXTERNAL COUNTERS (M=525 t ) Upper Shield