1 / 20

Search for neutrino bursts from Gravitational stellar collapses with LVD: update to 2007

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. Today Topics. LVD: Detector & Performances Searching fo r SN neutrino Signal: Technique (Off-line, On-line)

ferrol
Télécharger la présentation

Search for neutrino bursts from Gravitational stellar collapses with LVD: update to 2007

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. 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

  2. Today Topics • LVD: Detector & Performances • Searching for SN neutrino Signal: • Technique (Off-line, On-line) • Data & Results • Conclusions

  3. The LVD Detector A 1 kton scintillator detector for neutrino astronomy in the INFN Gran Sasso National Laboratory

  4. LVD: array of 840 liquid scintillator counters (1.5 m3 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) Ref. LVD Coll., Nuovo Cimento A105 (1992) 1793

  5. 7 8 5 6 3 4 1.5m 1 2 1m 1m Each counter is viewed on the top by three 15" PMTs (QE=10-15%) in 3 fold coincidence

  6. Uptime Trigger Mass

  7. The LVD Trigger Optimized to the to Inverse Beta Decay Two detectable signals: the prompt e+ (Evis~ E-0.8 MeV) the delayed (<t> = 185 s)  (2.2 MeV). Each PMT is discriminated at two different thresholds resulting in two possible levels of coincidence: High and Low EH ~ 4 MeV and EL<1 MeV active for 1 ms after the trigger

  8. 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

  9. Background Rate Stability 150 days - Sampling: 2 hours -Variable Detector Configuration (trigger mass) - Basic cuts on muon rejection and noisy counter applied eH=95% eH=90%

  10. Trigger Rate @ E>7 MeV sampled every 2 minutes compared with the mean local background over 40 minutes /50 days considered b s b LVD rate is poissonian at level of ~15%

  11. Search for SN Burst Performed by processing the trigger sequence in the range 7-100 MeV: on-line for prompt alert purpose and off-line to check data. First step: statistical analysis of all possible clusters (m≥2, dt<200 s) initiated by each single pulse. For a selected cluster the imitation frequency FIM is calculated taking into account the rate of background events fbk. FIM< 1 y-1 (Alert if FIM< 0.01 y-1) • Second step: check of n burst consistency check by: • topological distribution in the detector (Uniform) • energy spectrum (Fermi-Dirac) • time distribution of delayed pulses (N-capture with DT=185 ms) Ref. Fulgione, Mengotti & Panaro, NIM A368 (1996) 512

  12. Results 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.

  13. All detected clusters are shown in the Multiplicity (m) vs Duration (Dt) 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

  14. Energy Spectrum Time distribution of delaied pulse Topology (internal & external counter contributions) Candidate 1 Fim=0.46/y N. of Trigger 52 Background rate=6.1 ev/min Duration 194.3 s Candidate 2 Fim=0.48/y N. of Trigger 65 Background rate=8.9 ev/min Duration 183.7 s Fine structure compatible with fluctuation of background events

  15. Total 4919 days Upper Limit to SN event in the Milky Way 0.17 /year (90% c.l.)

  16. The SN On-line Monitor Different approach: study of the cluster multiplicity (m) in fixed time windows Dt=20 s starting at to (and to+10 s) / fbk rate in the 7-100 MeV range • SNM algorithm can generate alarm at fixed selection rate: • 1/day SN Monitor Check (active since Jul. 2005) • 1/month SNEWS Alert

  17. Cluster selected on-line in 688 days at different threshold Observed rate of alert (fits of the delay distributions) 1.24 day-1 1.28 month-1 Ref. On-line recognition of supernova neutrino bursts in the LVD detector submitted to Astroparticle Physics, LVD COLLABORATION

  18. Conclusions 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%. 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 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.

  19. INTERNAL COUNTERS (M=475 t) T 1 TOP VIEW T 2 T 3 EXTERNAL COUNTERS (M=525 t) FRONT VIEW Upper Shield

More Related