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Carla Distefano for the NEMO Collaboration

Carla Distefano for the NEMO Collaboration. KM3NET ‘Physics and Simulation (WP2)’ Oct 24 – 25, 2006. NEMO sensitivity to point sources. Outline of the talk. Estimate of the NEMO detector sensitivity Simulation of the km 3 neutrino telescope Event selection criteria Results

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Carla Distefano for the NEMO Collaboration

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  1. Carla Distefanofor the NEMO Collaboration KM3NET ‘Physics and Simulation (WP2)’ Oct 24 – 25, 2006 NEMO sensitivity to point sources

  2. Outline of the talk • Estimate of the NEMO detector sensitivity • Simulation of the km3 neutrino telescope • Event selection criteria • Results • Physics cases • Microquasars • SNR RXJ1713.7-3946

  3. Detector sensitivity to muon neutrino fluxes 90% c.l. We compute the detector sensitivity to muon neutrinos from point-like sources: minimum muon neutrino flux detectable with respect to the background. • Calculation of the sensitivity spectrum: • we simulate the expected backgroundb(atm.  and ) and we estimate the 90% c.l. • sensitivity in counts<90(b)>(Feldman & Cousins); • we simulate a reference source spectrum • (d/d)0which producesnscounts; • we calculate the sensitivity spectrum as: • we apply the event selection in order to minimize the sensitivity. Feldman & Cousins define the sensitivity as the average upper limits for no true signal. It is the maximum number of events that can be excluded at a given confidence level.

  4. Simulated NEMO-km3 detector The ANTARES code gentra v1r2 has been used to generate the detector geometry file. DETECTOR LAY-OUT • Simulated Detector Geometry: • square array of 81 NEMO towers • 140 m between each tower • 18 floors for each tower • vertical distance 40 m • storey length 20 m • 4 PMTs for each storey • 5832 PMTs • Depth = 3500 m (Capo Passero site) PMT location and orientation (PMT=10”)

  5. Simulation of point-like neutrino sources We use the ANTARES code genhen v6r2 to simulateNgen=6·109interactingneutrinos in the energy range102÷108 GeVwith a generation spectral indexX=1. Source declination:  = - 60˚ - 24 hours of diurnal visibility - large up-going angular range covered by the source(24 – 84) Code km3 v2r1 is used to simulate the passage of muons inside the detector and to generate the PMT hits using the photon tables with the absorption length profile measured in the Capo Passero site. Code modk40 v4r8 is used to add optical background hits with a rate of 30 kHz on 10” PMTs. Code recov4r4km3 is used to reconstruct the events: Trigger for prefit: at least 3 hits with charge higher than 3.5 p.e. or in concidence Work in progress: test different trigger conditions (charge hit threshold; triple coincidence included in recov4r5km3 ), test reco version recov4r6km3

  6. Simulation of point-like neutrino sources Source declination:  = - 60˚ - 24 hours of diurnal visibility - large up-going angular range covered by the source(24 – 84) detectable (>100 GeV) reconstructed Nrec  5.1·105 reconstructed events The generated neutrino events are weighted to a reference spectrum with a power-law shape

  7. Simulation of atmospheric neutrino background Weighted Events We use the ANTARES event generation codegenhen v6r2(weighted generation); We simulated a power law interacting neutrino spectrum: X=2 for102 GeV<  <108 GeV; Ngen= 7·109 interacting neutrinos 4isotropic angular distribution The atmospheric neutrino events are weighted to the Bartol + RQPM (highest prediction) flux Bartol+RQPM 1 year Nrec  5·105 reconstructed events Events at the detector NBartol+RQPM  4·104 expected events/year

  8. Simulation of atmospheric muon background Weighted Events Weighted Events The events are generated at the detector, applying a weighted generation technique. We simulate a broken power law spectrum (compromise between the requirement of high statistics and CPU time consumption): Okada 1 year X=1 for  < 1 TeV; Ngen= 3·107 events X=3 for  > 1 TeV; Ngen= 2.5·107 events Nrec  3.8·106 reconstructed events Events at the detector The atmospheric muon events are weighted to the Okada parameterization (Okada, 1994), taking into account the depth of the NEMO Capo Passero site (3500 m) and the flux variation inside the detector sensitive height (~ 900 m): Okada 1 year NOkada  4·108 expected events/year tgen  4 days Events at the detector

  9. Atmospheric muon background for a point-like source Weighted Counts • The statistics of generated events corresponds to a few days. • Reconstructed events have a RA flat distribution. • We can project the full sample of reconstructed events in a few degrees bin RA, centered in the source position. • We get statistics of atmospheric muons corresponding to a time of years for each source declination. mis-reconstructed atm. muons

  10. Event selection criteria • quality cut: • The used reconstruction algorithm is a robust track fitting procedure based on a maximization likelihood method. The reconstruction may give more than one possible solutions: • > cut  - log(L)/NDOF+0.1(Ncomp-1) • (see ANTARES documentation) • log(L)/NDOF  log-likelihood per degrees of freedom • Ncomp  number of compatible solutions (within 1) • energy cut: • Nfit>Nfitmin Nfit  number of hits in the reconstructed event • angular cuts: • - rejection of down-going tracks • rec<maxrec reconstructed event direction • - choice of the search bin size • r<rminr  angular distance from source position

  11. Optimization of the event selection Different possible combination of the parameters cut,Nfitmin,maxandrminare tested among: cut= 7.19.0, step=0.1 Nfitmin=6 50, step=1 max< sourcemax (source upper transit), step=1 deg rmin=0.1 1 deg, step=0.1 The optimal values of cut,Nfitmin,maxandrminare chosen optimizing the detector sensitivity:

  12. Sensitivity for a point-like ( = -60˚) neutrino source (3 years) Neutrino energy range: 102 - 108 GeV (d/d)90 is expressed in GeV-1/cm2 s Search bin: NEMO 0.5˚ IceCube 1˚ =2 IceCube sensitivity values from Ahrens et al. Astrop. Phys. 20 (2004) 507

  13. Event detection for a point-like ( = -60˚) neutrino source Energy spectra of detectable, reconstructed and selected neutrino events (3 years) neutrino energy range 102-108 GeV detectable (>100 GeV) reconstructed selected

  14. Sensitivity for a point-like ( = -60˚) neutrino source (3 years) =2.5 =2 =1.5 =1 Detector sensitivity as a function of the search bin radius For all spectra indices the sensitivity doesn’t vary significantly in the range 0.3°<rbin<0.6°

  15. Sensitivity for a point-like ( = -60˚) neutrino source (3 years) Detector sensitivity as a function of the high energy neutrino cut-off max Hard spectrum sources: the detector sensitivity is better and gets better if the spectrum extends to VHE. Soft spectrum sources: the detector sensitivity doesn’t vary much with max.

  16. Sensitivity for a point-like neutrino source (3 years) Detector sensitivity as a function of the source declination The detector sensitivity gets worse with increasing declination due to the decrease of the diurnal visibility. =2 <cut> = -7.3 no selection in Nfit <rbin> = 0.5° max = 90°-101° Diurnal visibility: Time per day spent by the source below the Astronomical Horizon with respect to the latitude of the Capo Passero site. Equatorial coordinates

  17. Galactic Microquasars • Galactic X-ray binary systems which exhibit relativistic radio jets; • persistent or bursting; • about 20 identified microquasars; • not extremely powerful sources but close to the Earth; • good sources to investigate astrophysical relativistic jets (AGN, GRB); • jet composition; • possible TeV neutrino sources.

  18. Detector sensitivity (1 year data taking) Sensitivity vs. declination The sensitivity is calculated for a - neutrino spectrum with  = 2 and  = 1-100 TeV. Average sensitivity: ~510-11 erg/cm2 s search bin radius 0.5°-1°

  19. Microquasar neutrinos: selected events (1 year) Steady microquasars Average number of selected events from source Nµm and of background Nµb in 1 year observation time. Microquasars SS433 and GX339-4: NEMO could detect neutrinos in 1 year of data taking or strongly constrain source physical parameters (acceleration efficiency, energy content …) Neutrino fluxes predicted by Distefano et al., 2002

  20. Microquasar neutrinos: selected events Bursting microquasars We assume that transient sources cause 1 burst per year: Nm calculated for 1 burst, Nb calculated in 1 year. Improvement considering time correlation with source bursts (multi-messenger analysis): Nb~10-3 events per burst Cumulative analysis of considered bursts: Nm=2.55.0 events Nb<0.1 events Improvement integrating over more bursts per microquasar (mandatory knowledge of the duty cycle): GRS 1915+105 and GRO J1655-40 may show more than 1 burst per year; Cir X-1 periodic bursts (T~17 days  ~1.5 evt/year). Neutrino fluxes predicted by Distefano et al., 2002

  21. RXJ1713.7-3946 is a TeV source ! energy spectrum and morphology G=2.1-2.2 with a curvature cutoff (?) at high energies G=2.1-2.2 -evidence of DSA of protons ? no significant spectral variation HESS 2004 data: preliminary ! From F. Aharonian, VLVnT2

  22. SNR: RX J1713.7-3946 Aharonian et al. Nature 432, 75, 2004 Expected neutrino flux: Alvarez-Muñiz & Halzen (ApJ 576, L33, 2002): dn/dn~ 4 ·10-8n-2 cm-2 s-1 GeV-1 nmax = 10 TeV Costantini & Vissani (Astrop. Phys. 23, 477, 2005): dn/dn~ 3 ·10-8n-2.2 cm-2 s-1 GeV-1 n = 50 GeV1 PeV Kappes et al. (ApJ submitted): dn/dn~ nn- exp(-(n/ncut)1/2) =15.52  10-12 cm-2 s-1 TeV-1=1.72cut= 1.35 TeV Kistler & Beacom (Phys. ReV. D74, 063007, 2006): dn/dn~ nn- exp(-n/ncut) =15.0 10-12 cm-2 s-1 TeV-1=2.19cut= 50 TeV

  23. SNR: RX J1713.7-3946 Expected neutrino events in 3 years of data taking: Ns: source events; Nb: bkg events. (d/d)90 is expressed in cm-2 s-1 GeV-1 Simulations were conducted assuming point-like source The source is extended with a diameter of 1.3° The effect of source extension is under study

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