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UNIVERSITA’ DEL SALENTO Facoltà di Scienze MM.FF.NN. TIME MEASUREMENTS WITH THE ARGO-YBJ DETECTOR Dott. 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 SALENTOFacoltà di Scienze MM.FF.NN TIME MEASUREMENTS WITH THE ARGO-YBJ DETECTOR Dott. Anna Karen Calabrese Melcarne Dottorato di Ricerca in Fisica XIX ciclo Settore scientifico FIS/04
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
Observation of Extensive Air Showers produced in the atmosphere by primary g’s and nuclei
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
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)
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 Layer (92% active surface) of Resistive Plate Chambers (RPC), covering a large area (5600 m2) + sampling guard ring + 0.5 cm lead converter BIG PAD ADC RPC
RPC is suited to be used as element of a surface detector Resistive Plate Chamber Low cost , high efficiency, high space & time resolution (<1ns), easy access to any part of detector, robust assembling, easy to achieve >90% coverage, mounting without mechanical supports. RPC PAD 2850x1258mm2
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
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
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
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
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 guarantee the removal of the complete offset
The systematic offset introduces a quasi-sinusoidal modulation in azimuth distribution The air shower arrival direction have the following distribution: sin0cos0 and sin0cos0 were subtracted from the original direction cosines
Characteristic Plane (CP) Definition Real Plane (RP) Fake Plane (FP) On average Assuming uniform azimuth distribution
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
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
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
Correction Residuals after correction
FULL SIMULATION Corsika+ARGOG codes Effect of conical shape of the shower front Conical shape planar fit
Planar residual after CP conical correction Conical residual after CP conical correction CP method with conical correction
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
H = 45° at ARGO-YBJ q = 55° q = 45° q = 35° q = 15° North South YBJ - the geomagnetic effect is stronger for showers from North than for showers from South This difference is more evident for larger zenith angles
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 ASgestimate 2.5% higher rate from South direction with respect to North direction (geomagnetic field effect + slope of the hill where the array is located)
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
TDC peaks distribution Before correction After correction
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 ….
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
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
Angular Resolution MC/data Chess board method Y72 parameter is the range in the angular distribution which contains 72 % of the events The residual correction improves the angular resolution
Moon shadow: absolute pointing Significance of ARGO-130 Moon shadow for showers with <50°. The color scale indicates the significance of the deficit on a 0.9° search window centered on the 0.1°x0.1° The systematical correction improves the absolute pointing
Time structure of EAS front • The curvature (TS) of the shower as deviation from planar fit of the shower front • The shower thickness (Td) as RMS of time residuals (conical fit) at different distance to core
COMPARISON DATA-simulation SIMULATION COMPARISON proton-photon
Conclusions • Characteristic Plane calibration has been defined and studied • Calibration with planar and conical fit for ARGO-42, ARGO-104 and 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