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UNIVERSITA’ DEL SALENTOUNIVERSITA’ DEL SALENTOFacoltà di Scienze MM.FF.NNFacoltà di Scienze MM.FF.NN

TIME MEASUREMENTS WITH THE ARGO-YBJ DETECTORTIME MEASUREMENTS WITH THE ARGO-YBJ DETECTOR

Dott.ssa Anna Karen Calabrese MelcarneDott.ssa Anna Karen Calabrese Melcarne

Dottorato di Ricerca in Fisica XIX ciclo

Settore scientifico FIS/04

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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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Cosmic Ray SpectrumCosmic Ray Spectrum

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Observation of Extensive Air Showers produced in the atmosphere by primary ’s

and nuclei

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High Altitude Cosmic Ray Laboratory @ YangBaJingSite Altitude: 4300 m a.s.l. , ~ 600 g/cm2

Site Coordinates: longitude 90° 31’ 50” E, latitude 30° 06’ 38” N

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Cosmic ray physics

• anti-p / p ratio at TeV energy• spectrum and composition (Eth 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 (Eth few GeV)

Main Physics GoalsMain Physics Goals

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Layer (92% active surface) of Resistive Plate Chambers (RPC), covering a large area (5600 m2)

+ sampling guard ring+ 0.5 cm lead converter

time resolution ~1 nsspace resolution = strip

10 Pads (56 x 62 cm2)for each RPC

1 CLUSTER = 12 RPC

78 m

111 m

99 m

74 m

BIGPAD

ADC

RPC

(43 m2)

ARGO-YBJ layoutARGO-YBJ layout

88

RPC is suited to be used as element of a surface RPC is suited to be used as element of a surface detectordetector

RPC

PAD

Resistive Plate ChamberLow cost , high efficiency, highspace & time resolution (1 ns),easy access to any part of detector,robust assembling, easy to achieve>90% coverage, mounting withoutmechanical supports.

2850x1258mm2

99

Detector performancesDetector 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

1010

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

1111

Study of the EAS space-time structureStudy 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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Arrival Direction ReconstructionArrival Direction Reconstruction

Conical Fit

2E

PE

PE0

PP

2 )mc

yl

c

xtt(

EEEEEE sinsinm and cossinl

2PE

PE

PE0

PP

2 )c

Rm

c

yl

c

xtt(

Planar Fit

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

angle azimuth

angle zenith

E

E

This quantity is not a proper 2 . Indeed the measurement unit is ns2

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Timing CalibrationTiming 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

PEPEE0PEP ymxl)tΔt(c Plane-equation

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The air shower arrival directions have the following distribution:

.constd

dN

The systematic offset introduces a quasi-sinusoidal modulation in azimuth distribution

l0=sin0cos0 and m0=sin0cos0 disform the original angular distribution

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Characteristic Plane (CP) Definition

Fake Plane (FP)

PEPEE0PEP ymxl)tΔt(c Real Plane (RP)

P'EP

'E

'E0

resPEP ymxl)tt(c

resPE0

PPP c

yb

c

xaΔ On average

E0'

E0E0E'EE

'E tt mmb lla

Assuming uniform azimuth distribution

'E

'E mb and la

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CP Method Checks (Fast MC simulation)

Azimuth distribution before calibration Azimuth distribution after calibration

Time offsets introduced in the time measurement CP correction removes the time offsets

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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

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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)

4'4' 1067m and 10304l

c

ym

c

xlΔ P'

EP'

EresPP

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Correction

Residuals after correction

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Effect of conical shape of the shower front

planar fit

Conical shape

FULL SIMULATION

Corsika+ARGOG codes

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CP method with conical correction

PE0

pE

PEEP

resP R

ct

c

ym

c

xlt

t

Planar residual after CP conical correction

Conical residual after CP conical correction

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Geomagnetic field effect

In the geomagnetic field, the secondary charged particles generated in EAS are stretched by the Lorentz force

2e

2

cosE2

sinBhd Average shift in the shower

plane for a secondary electron

electrons ofenergy average E

North) magnetic 0(shower theof angleazimuth

shower theof anglezenith

ninclinatio cgeomagneti

cos sinsincoscosacos

field cgeomagneti B

rajectoryelectron t theofheight verticalaverage h

e

H

HH

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θcos

χsing

2

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°

cos sinsincoscos acos HH

=

=

North South

=

=

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Estimate of South-North asymmetry: MC

)]4p2cos(3p)2pcos(1p1[0pd

dN

N events from North (161.5º < Φ < 341.5º )

S events from South (161.5º >Φ and Φ >341.5º)

%1NS

NS2

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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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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TDC peaks distribution

Before correction

After correction

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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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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

C4ΔT

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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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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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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.

)TeV(E

Z1.5Δ

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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

Shower curvature

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COMPARISON DATA-simulation

SIMULATION

COMPARISON proton-photon

Shower thickness

Shower thickness

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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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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

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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”