The AMIGA infill detector of the Pierre Auger Observatory: performance and first data

Transcription

1 OBSERVATORY The AMIGA infill detector of the Pierre Auger Observatory: performance and first data Ioana C. Mariş (for the Pierre Auger Collaboration 2 ) Laboratoire de Physique Nucléaire et des Hautes Energies, Paris, France 2 Observatorio Pierre Auger, Malargüe, Argentina (Full author list: html) AMIGA (F.Sanchez, talk 0742) muon counters (B. Wundheiler, poster 034) infill surface detector (this talk)

2 AMIGA (Auger Muons and Infill for the Ground Array) 750 m spacing between detectors, construction began in 2008 all 6 stations deployed (53 completely equipped) data analysis based on methods developed for the regular array y [km] 22 Infill array performance x [km] trigger rate: (55 ± 6) events/day/hexagon good quality events (T5): currently: (28 ± 3) events/day/hexagon (390±70) T5 events/day acceptance (08/ /20): (26±)km 2 sr yr Ioana C. Mariş (Pierre Auger Collaboration) /

3 Trigger efficiency From simulations From data 3ToT Efficiency p infill array Fe infill array / ndof χ p regular array Fe regular array log (E/eV) 3 fold trigger, Time-over-Threshold, lateral trigger probabilities parametrization dependency on zenith angle for < 0% 0% at 3 7 ev for zenith < 55 Pierre Auger Collaboration, submitted to Astropart. Phys., 20) [VEM] S 35 test the hypothesis of a flat distribution in cos 2 θ above a shower size (S 35) value 0% at S 35 20VEM ( 3 7 ev) Ioana C. Mariş (Pierre Auger Collaboration) 2 /

4 Angular resolution Angular resolution o stations 4 stations 5 stations 6 or more stations θ o accidental muons rejection and spherical shower-front assumption adjusted time variance model (flat χ 2 distribution) angular resolution given by the fit uncertainties better than for events with more than 5 stations (E 3 7 ev) Ioana C. Mariş (Pierre Auger Collaboration) 3 /

5 Lateral distribution function (LDF) Signal [VEM] 0 NKG χ 2 /Ndf: 7.8/ 8 candidates not triggered distance to axis [m] Modified Nishimura-Kamata-Greisen (NKG) S(r) = S(r opt) ( ) β r r +700m r opt r opt +700m Log-log parabola (LLP), to infer systematics Parameters β β,γ determine the shape of LDF, parametrized as a function of θ,s(r opt) r opt distance where the shower-to-shower fluctuations and the statistical uncertainties are minimal S(r opt) used to infer the energy estimator ( r S(r) = S(r opt) r opt ) β+2γ log( r r opt ) NKG sec(θ) Ioana C. Mariş (Pierre Auger Collaboration) 4 /

6 Optimum distance (r opt ) Two types of events: with a saturated signal and without saturated signals entries no saturation saturation 50 obtained from varying the LDF shape parameters (D. Newton et al., Astropart. Phys., 2007, 26:44) no saturation: r opt = (442±40)m saturation: r opt = (640±52)m r opt [m] optimum distance: 450 m Ioana C. Mariş (Pierre Auger Collaboration) 5 /

7 Signal uncertainties at r opt = 450m σ S(450) /S(450)[%] total systematic (sh2sh + LDF) r opt, no saturation statistical, no saturation log (S(450)/VEM) VEM 0 VEM 200 VEM r opt, no saturation [%] ±3 ±0. ±0. statistical, no saturation [%] ±9 ±5 ±3 Total: 22% at VEM, 4% at >40VEM Ioana C. Mariş (Pierre Auger Collaboration) 6 /

8 Attenuation in the atmosphere and S 35 S(450) [VEM] θ attenuation correction obtained empirically from data (constant intensity hypothesis) reference angle: 35 (median of the angular distribution of events) Ioana C. Mariş (Pierre Auger Collaboration) 7 /

9 Attenuation in the atmosphere and S 35 S 35 [VEM] dn/ds 35 S < θ < < θ < 4 4 < θ < log (S /VEM) 35 S 35, independent of zenith angle, used as energy estimator Ioana C. Mariş (Pierre Auger Collaboration) 8 /

10 Energy calibration with golden hybrid events (FD+SD) [VEM] S Energy calibration event selection to assure an unbiased energy calibration strong quality cuts and fiducial field of view cuts 44 events with 3 7 ev < E FD < 2 8 ev σ E /E [%] E FD [EeV] E [EeV] E SD = (2.7±2.5) 5 ev S (.0±0.05) 35 Energy uncertainties systematic (fit): 6% at 0.3EeV, 3% at 8EeV statistical (S 35): 6% at 0.3EeV, 4% at 8EeV FD energy systematic: 22% (R. Pesce, poster 60) Ioana C. Mariş (Pierre Auger Collaboration) 9 /

11 Preliminary energy spectrum ev - )) sr - s - -2 ( J /(m log σ (E ) SD σ (E ) FD 8 2 Preliminary Auger Infill (preliminary) E[eV] log (E/eV) extends the energy range down to 3 7 ev (No resolution correction!) very good agreement with the combined spectrum (F.Salamida, talk 0893) slope for E < 3 8 ev: 3.33±0.03(stat)±0.(sys) Ioana C. Mariş (Pierre Auger Collaboration) / 3 2

12 Preliminary energy spectrum ) J/(A E Preliminary Auger Infill (preliminary) Auger E[eV] log (E/eV) extends the energy range down to 3 7 ev (No resolution correction!) very good agreement with the combined spectrum (F.Salamida, talk 0893) slope for E < 3 8 ev: 3.33±0.03(stat)±0.(sys) Ioana C. Mariş (Pierre Auger Collaboration) /

13 Conclusions and outlook Current status Outlook 53 infill stations with a spacing of 750m equipped (6 deployed) trigger efficiency 0% at 3 7 ev (zenith< 55 ) angular resolution better than for events with more than 6 stations preliminary energy spectrum in very good agreement with the Auger energy spectrum energy calibration: HEAT increase statistics at low energies (H.J. Mathes, talk 076) energy spectrum: correct for energy resolution effects deploy stations with a spacing less than 750m Ioana C. Mariş (Pierre Auger Collaboration) /