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C.Vigorito, University & INFN Torino, Italy30th International Cosmic Ray Conference Merida, Mexico
Search for neutrino bursts from Search for neutrino bursts from Gravitational stellar collapses with Gravitational stellar collapses with
LVD:LVD:update to 2007update to 2007
C. Vigorito C. Vigorito on behalf of the LVD Collaborationon behalf of the LVD Collaboration
University and INFN Torino, ItalyUniversity and INFN Torino, Italy
C.Vigorito, University & INFN Torino, Italy30th 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, Italy30th 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, Italy30th International Cosmic Ray Conference Merida, Mexico
Ref. LVD Coll., Nuovo Cimento A105 (1992) 1793
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)
C.Vigorito, University & INFN Torino, Italy30th 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
1m
1.5m
8765
43
1 2
C.Vigorito, University & INFN Torino, Italy30th International Cosmic Ray Conference Merida, Mexico
Trigger Mass
Uptime
C.Vigorito, University & INFN Torino, Italy30th International Cosmic Ray Conference Merida, Mexico
The LVD Trigger
Optimized to the to Inverse Beta Decay
MeV2.2
e
dγnp
nepν
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
C.Vigorito, University & INFN Torino, Italy30th 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, Italy30th 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, Italy30th International Cosmic Ray Conference Merida, Mexico
Trigger Rate @ E>7 MeV sampled every 2 minutes compared with the mean local background over 40 minutes /50 days considered
20/
/)(2
bb
bsf
LVD rate is poissonian at level of ~15%
s bb
C.Vigorito, University & INFN Torino, Italy30th International Cosmic Ray Conference Merida, Mexico
Performed by processing the trigger sequence in the range 7-100 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 fbk.
)bk
fδt,FIM(m,FIM 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, Italy30th 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, Italy30th 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, Italy30th International Cosmic Ray Conference Merida, Mexico
Candidate 1 Fim=0.46/yN. of Trigger 52 Background rate=6.1 ev/minDuration 194.3 s
Candidate 2 Fim=0.48/yN. of Trigger 65 Background rate=8.9 ev/minDuration 183.7 s
Energy SpectrumTime distribution of delaied pulse Topology (internal & external counter contributions)
Fine structure compatible with fluctuation of background events
C.Vigorito, University & INFN Torino, Italy30th International Cosmic Ray Conference Merida, Mexico
Total 4919 daysTotal 4919 daysUpper Limit to SN event in the Milky Way Upper Limit to SN event in the Milky Way
0.17 /year (90% c.l.)0.17 /year (90% c.l.)
RUN Since: To:Uptime[days]
DutyCycle
Mass [tonn]
PUBLISHED
RUN 1 Jun 6th ‘92 May 31st ’93 285 60% 310 23rd ICRC 1993
RUN 2 Aug 4th ‘93 Mar 11th ’95 397 74% 390 24th ICRC 1995
RUN 3 Mar 11th ‘95 Apr 30th ’97 627 90% 400 25th ICRC 1997
RUN 4 Apr 30th ‘97 Mar 15th ‘99 685 94% 415 26th ICRC 1999
RUN 5 Mar 16th ‘99 Dec 11th ‘00 592 95% 580 27th ICRC 2001
RUN 6 Dec 12th ‘00 Mar 24th ’03 821 98% 842 28th ICRC 2003
RUN 7 Mar 25th ’03 Feb 4th ‘05 666 >99% 881 29th ICRC 2005
RUN 8 Feb 5th ‘05 May 31st ‘07 846 >99% 936 30th ICRC 2007
C.Vigorito, University & INFN Torino, Italy30th 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 to (and to+10 s) / fbk rate in the 7-100 MeV range
1s20T2N
mkbkmkbkim ev/day)f(20P8640)f(m,F
C.Vigorito, University & INFN Torino, Italy30th 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-1
1.28 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, Italy30th 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
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. 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, Italy30th International Cosmic Ray Conference Merida, Mexico
Schema numerazione tank del primo piano
1517 1518 1417 1418 1317 1318 1217 1218 1117 1118
1515 1516 1415 1416 1315 1316 1215 1216 1115 1116
1513 1514 1413 1414 1313 1314 1213 1214 1113 1114
1511 1512 1411 1412 1311 1312 1211 1212 1111 1112
2517 2518 2417 2418 2317 2318 2217 2218 2117 2118
2515 2516 2415 2416 2315 2316 2215 2216 2115 2116
2513 2514 2413 2414 2313 2314 2213 2214 2113 2114
2511 2512 2411 2412 2311 2312 2211 2212 2111 2112
3517 3518 3417 3418 3317 3318 3217 3218 3117 3118
3515 3516 3415 3416 3315 3316 3215 3216 3115 3116
3513 3514 3413 3414 3313 3314 3213 3214 3113 3114
3511 3512 3411 3412 3311 3312 3211 3212 3111 3112
INTERNAL COUNTERS (M=475 t)
T 1
T 3
T 2
TO
P V
IEW
FRONT VIEWEXTERNAL COUNTERS (M=525 t)
Upper Shield