1. 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

2. 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. 3 Cosmic Ray Spectrum

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

5. 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

6. 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

7. 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

8. 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

9. 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

10. 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

11. 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

12. 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

13. 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

14. 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

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

16. 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

17. 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

18. 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)

19. 19 Correction Residuals after correction

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

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

22. 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. 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  =

24. 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)

25. 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%

26. 26 TDC peaks distribution Before correction After correction

27. 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. 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. 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. 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

31. 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.

32. 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

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

34. 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. 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

38. 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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