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

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


• LVD: Detector & Performances

• Searching for SN neutrino Signal:

Technique (Off-line, On-line)

Data & Results

• Conclusions

Today Topics


The LVD Detector

A 1 kton scintillator detector for neutrino astronomy in the INFN Gran Sasso National Laboratory


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)


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


Trigger Mass

Uptime


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


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


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


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


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.


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


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


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


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


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


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


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%.



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

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

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