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UNIVERSITA’ DEL SALENTO Facoltà di Scienze MM.FF.NN

UNIVERSITA’ DEL SALENTO Facoltà di Scienze MM.FF.NN. TIME MEASUREMENTS WITH THE ARGO-YBJ DETECTOR Dott.ssa Anna Karen Calabrese Melcarne. Dottorato di Ricerca in Fisica XIX ciclo Settore scientifico FIS/04. OUTLINE. ARGO-YBJ as a ground-based detector

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UNIVERSITA’ DEL SALENTO Facoltà di Scienze MM.FF.NN

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  1. UNIVERSITA’ DEL SALENTOFacoltà di Scienze MM.FF.NN TIME MEASUREMENTS WITH THE ARGO-YBJ DETECTOR Dott.ssa Anna Karen Calabrese Melcarne Dottorato di Ricerca in Fisica XIX ciclo Settore scientifico FIS/04

  2. OUTLINE • ARGO-YBJ as a ground-based detector • Timing calibration in EAS experiments (Characteristic Plane Method) • Characteristic Plane (CP) correction applied to ARGO-YBJ data • Physics results after calibration

  3. Cosmic Ray Spectrum

  4. Observation of Extensive Air Showers produced in the atmosphere by primary g’s and nuclei

  5. High Altitude Cosmic Ray Laboratory @ YangBaJing Site Altitude: 4300 m a.s.l. , ~ 600 g/cm2 Site Coordinates: longitude 90° 31’ 50” E, latitude 30° 06’ 38” N

  6. Main Physics Goals • Cosmic ray physics • anti-p / p ratio at TeV energy • spectrum and composition (Ethfew TeV) • study of the shower space-time structure • VHE g-Ray Astronomy Search for point-like (and diffuse) galactic and extra-galactic sources at few hundreds GeV energy threshold • Search for GRB’s(full GeV / TeV energy range) • Sun and Heliosphere physics(Eth few GeV)

  7. ARGO-YBJ layout time resolution ~1 ns space resolution = strip 99 m 74 m 10 Pads (56 x 62 cm2) for each RPC 1 CLUSTER = 12 RPC (43 m2) 78 m 111 m BIG PAD Layer (92% active surface) of Resistive Plate Chambers (RPC), covering a large area (5600 m2) + sampling guard ring + 0.5 cm lead converter ADC RPC

  8. RPC is suited to be used as element of a surface detector Resistive Plate Chamber Low cost , high efficiency, high space & time resolution (1 ns), easy access to any part of detector, robust assembling, easy to achieve >90% coverage, mounting without mechanical supports. RPC PAD 2850x1258mm2

  9. Detector performances • good pointing accuracy (less than 0.5°) • detailed space-time image of the shower front • capability of small shower detection(low E threshold) • large FoV (2p) and high “duty-cycle” (100%) • continuous monitoring of the sky (-10°< <70°) Impossible for Atmospheric Cherenkov telescopes

  10. 60 m 150 ns 74 m 50 m 90 m A unique way to study EAS • Full space-time reconstruction • Shower topology • Structure of the shower front

  11. Study of the EAS space-time structure Example 1: Very energetic shower The High space-time granularity of the ARGO-YBJ detector allows a deep study of shower phenomenology with unique performance

  12. Arrival Direction Reconstruction In EAS experiments for an event E the time tEP can be measured on each fired detector unit P, whose position (xP,yP) is well known Primary direction cosines Planar Fit Conical Fit This quantity is not a proper c2 . Indeed the measurement unit is ns2

  13. Timing Calibration Taking into account the time offset DP typical of the detector unit Plane-equation DP= residual correction + systematic correction • Residuals correction reduces the differences between fit time and measured time • Systematic correction guarantees the removal of the complete offset

  14. The systematic offset introduces a quasi-sinusoidal modulation in azimuth distribution The air shower arrival directions have the following distribution: l0=sin0cos0 and m0=sin0cos0 disform the original angular distribution

  15. Characteristic Plane (CP) Definition Real Plane (RP) Fake Plane (FP) On average Assuming uniform azimuth distribution

  16. CP Method Checks (Fast MC simulation) Time offsets introduced in the time measurement CP correction removes the time offsets Azimuth distribution before calibration Azimuth distribution after calibration

  17. CP method works also when a pre-modulation on primary azimuth angle is present The CP method annulls <l> and <m> leaving a sinusoidal modulation on the distribution of the new ’’ azimuth angle

  18. ARGO-YBJ DATA (ARGO-42, ARGO-104, ARGO-130) Residual correction has been applied twice and systematic correction has been applied according to the values: A Gaussian fit is applied in the range ±10 ns around the bin with maximum number of entries

  19. Correction Residuals after correction

  20. FULL SIMULATION Corsika+ARGOG codes Effect of conical shape of the shower front Conical shape planar fit

  21. Planar residual after CP conical correction Conical residual after CP conical correction CP method with conical correction

  22. Geomagnetic field effect In the geomagnetic field, the secondary charged particles generated in EAS are stretched by the Lorentz force Average shift in the shower plane for a secondary electron

  23. H = 45° at ARGO-YBJ q = 55° q = 45° q = 35° q = 15° YBJ - the geomagnetic effect is stronger for showers from North than for showers from South This difference is more evident for larger zenith angles North South

  24. Estimate of South-North asymmetry: MC N events from North (161.5º < Φ < 341.5º ) S events from South (161.5º >Φ and Φ >341.5º) Tibet ASg estimate 2.5% higher rate from South direction with respect to North direction (geomagnetic field effect + slope of the hill where the array is located)

  25. Estimate of South-North asymmetry: Data As expected CP method annulls the mean values of the primary direction cosines but a small sinusoidal modulation is still present in azimuth distribution 1.0% 0.9% The mean values of direction cosines after CP correction are

  26. TDC peaks distribution Before correction After correction

  27. TDC method to update the calibration TDC peak distribution after calibration has a regular concave shape Without hardware change and with the same trigger, the concave surface should remain unvaried On the other hand ….

  28. TDC peak dependence on temperature (night-day difference) A collective shift (~3 ns) is observed. Method odd-even events The main effect of the TDC dependence on temperature is a shift of all TDC peaks, negligible for calibration and a minor effect is present but it is of the order of 0.2 ns

  29. TDC dependence on offline CLUSTERs The effect of offline CLUSTERs is visible only in peculiar conditions, thus this effect on the TDC calibration is negligible

  30. Angular Resolution MC/data Even/Odd Chess board method Y72 parameter : the value in the angular distribution which contains ~72 % of the events The residual correction improves the angular resolution

  31. Moon shadow: absolute pointing Significance map of the Moon shadow selecting events with a number of fired pads > 500 (~ 5 TeV median energy) and with zenith angle of the incident direction < 45°. 558 hours of observation. The systematical correction improves the absolute pointing

  32. Shower curvature Time structure of EAS front • The curvature (Td) of the shower front as the mean of time residuals with respect to a planar fit • The thickness (TS) of the shower front as RMS of time residuals with respect to a conical fit

  33. COMPARISON DATA-simulation Shower thickness SIMULATION COMPARISON proton-photon Shower thickness

  34. Conclusions • Characteristic Plane calibration has been defined and studied • Calibration with planar and conical fit for ARGO-42, ARGO-104, ARGO-130 • Fast TDC calibration • South-North azimuthal asymmetry studied with full simulation • Improvements in the angular resolution and absolute pointing • Study on time structure of the shower front

  35. Papers • G.Aielli et al., Nucl.Instr. And Meth., A562 (2006) 92 • H.H.He, P.Bernardini, A.K.Calabrese Melcarne, S.Z.Chen, ”Detector Time Offset and Off-line Calibration in EAS Experiments”, Astroparticle Physics 27 (2007) 528-531 • Conferences and proceedings • A.K.Calabrese Melcarne, “Time Calibration of the ARGO-YBJ detector”, *Cividale 2005 High Energy Gamma Ray Experiments*, 183-187 • P.Bernardini et al., “Time Calibration of the ARGO-YBJ experiment”, 29th International Cosmic Ray Conference, Pune 2005, 5-147 • A.K.Calabrese Melcarne, “Calibrazione del rivelatore ARGO-YBJ”, XCII Congresso Nazionale Societa’ Italiana di Fisica, atticon3408 III-C-39 • B.Wang et al., “Preliminary results on the Moon shadow with ARGO-YBJ”, 30th International Cosmic Ray Conference, Merida 2007, Mexico • A.K.Calabrese Melcarne, I.De Mitri, G.Marsella, L.Perrone, G.Petronelli,A.Surdo, G.Zizzi , “Study of cosmic ray shower front and time structure with ARGO-YBJ”, 30th International Cosmic Ray Conference, Merida 2007, Mexico

  36. ARGO internal notes • Note 2004/02 • P.Bernardini, A.K.Calabrese Melcarne, C.Pino, “Time calibration of six Cluster” • Note 2005/02 • P.Bernardini, A.K.Calabrese Melcarne, C.Pino, “Time-Calibration of the ARGO-YBJ detector (42 Clusters)” • Note 2006/03 • P.Bernardini, A.K.Calabrese Melcarne, I.De Mitri, G.Mancarella, “Study of the arrival times of cosmic rays” • Note 2006/04 • S.Z.Chen, A.K.Calabrese Melcarne, H.H.He, P.Bernardini, B.G.Sun, F.R.Zhu, • ”Characteristic Plane Method with Conical Correction” • Note 2006/05 • P.Bernardini, A.K.Calabrese Melcarne, G.Mancarella, M.Khakian Ghomi, “Analysis of shower clusters” • Note 2007/03 • A.K.Calabrese Melcarne, S.Z.Chen, P.Bernardini, H.H.He, “Conical Calibration for 130 Clusters and automatic updating”

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