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1 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
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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
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3 Cosmic Ray Spectrum
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4 Observation of Extensive Air Showers produced in the atmosphere by primary ’s and nuclei
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5 High Altitude Cosmic Ray Laboratory @ YangBaJing Site Altitude: 4300 m a.s.l., ~ 600 g/cm 2 Site Coordinates: longitude 90° 31’ 50” E, latitude 30° 06’ 38” N
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6 Cosmic ray physics anti-p / p ratio at TeV energy spectrum and composition (E th few TeV) study of the shower space-time structure VHE -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 (E th few GeV) Main Physics Goals
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7 Layer ( 92% active surface) of Resistive Plate Chambers (RPC), covering a large area (5600 m 2 ) + sampling guard ring + 0.5 cm lead converter time resolution ~1 ns space resolution = strip 10 Pads (56 x 62 cm 2 ) for each RPC 1 CLUSTER = 12 RPC 78 m 111 m 99 m74 m BIG PAD ADC RPC ( 43 m 2 ) ARGO-YBJ layout
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8 RPC is suited to be used as element of a surface detector RPC PAD 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. 2850x1258mm 2
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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 ( 2 ) and high “duty-cycle” ( 100%) continuous monitoring of the sky (-10°< <70°) Impossible for Atmospheric Cherenkov telescopes
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10 Full space-time reconstruction Shower topology Structure of the shower front A unique way to study EAS 74 m 60 m 90 m 150 ns 50 m
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11 Study of the EAS space-time structure The High space-time granularity of the ARGO-YBJ detector allows a deep study of shower phenomenology with unique performance Example 1: Very energetic shower
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12 Arrival Direction Reconstruction Conical Fit Planar Fit In EAS experiments for an event E the time t EP can be measured on each fired detector unit P, whose position (x P, y P ) is well known Primary direction cosines This quantity is not a proper 2. Indeed the measurement unit is ns 2
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13 Timing Calibration P = residual correction + systematic correction Residuals correction reduces the differences between fit time and measured time Systematic correction guarantees the removal of the complete offset Taking into account the time offset P typical of the detector unit Plane-equation
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14 The air shower arrival directions have the following distribution: The systematic offset introduces a quasi-sinusoidal modulation in azimuth distribution l 0 =sin 0 cos 0 and m 0 =sin 0 cos 0 disform the original angular distribution
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15 Characteristic Plane (CP) Definition Fake Plane (FP) Real Plane (RP) On average Assuming uniform azimuth distribution
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16 CP Method Checks (Fast MC simulation) Azimuth distribution before calibrationAzimuth distribution after calibration Time offsets introduced in the time measurement CP correction removes the time offsets
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17 CP method works also when a pre-modulation on primary azimuth angle is present The CP method annulls and leaving a sinusoidal modulation on the distribution of the new ’’ azimuth angle
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18 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 ARGO-YBJ DATA (ARGO-42, ARGO-104, ARGO-130)
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19 Correction Residuals after correction
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20 Effect of conical shape of the shower front planar fit Conical shape FULL SIMULATION Corsika+ARGOG codes
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21 CP method with conical correction Planar residual after CP conical correction Conical residual after CP conical correction
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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
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23 YBJ - the geomagnetic effect is stronger for showers from North than for showers from South This difference is more evident for larger zenith angles H = 45° at ARGO-YBJ 15 ° 35 ° 45 ° 55 ° = North South =
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24 Estimate of South-North asymmetry: MC N events from North (161.5 º < Φ < 341.5 º ) S events from South (161.5 º >Φ and Φ >341.5 º ) Tibet AS 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)
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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 The mean values of direction cosines after CP correction are 1.0%0.9%
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26 TDC peaks distribution Before correction After correction
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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 ….
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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
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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
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30 Angular Resolution MC/data Chess board method 72 parameter : the value in the angular distribution which contains ~72 % of the events The residual correction improves the angular resolution Even/Odd
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31 Moon shadow: absolute pointing The systematical correction improves the 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.
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32 Time structure of EAS front The curvature (T d ) of the shower front as the mean of time residuals with respect to a planar fit The thickness (T S ) of the shower front as RMS of time residuals with respect to a conical fit Shower curvature
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33 COMPARISON DATA-simulation SIMULATION COMPARISON proton-photon Shower thickness
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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
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37 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”, 29 th 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”, 30 th 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”, 30 th International Cosmic Ray Conference, Merida 2007, Mexico
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38 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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