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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. Anna Karen Calabrese MelcarneDott. 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

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RPC is suited to be used as element of a surface detectorRPC is suited to be used as element of a surface detector

RPC

PAD

Resistive Plate Chamber

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

2850x1258mm2

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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

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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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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

P0

PP

2 )mc

yl

c

xtt(

EEEEEE sinsinm and cossinl

2PE

PE

P0

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 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 guarantee 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 direction have the following distribution:

.constd

dN

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

sin0cos0 and sin0cos0 were subtracted from the original direction cosines

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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

resP0

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

2020

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

PE0p

EP

EPEP Rc

tc

ym

c

xlΔt

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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2cos

sing

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 sinsincoscosacos 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 is the range in the angular distribution which contains 72 % of the events

The residual correction improves the angular resolution

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Moon shadow: absolute pointing

The systematical correction improves the 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°

)TeV(E

Z1.7Δ

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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

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COMPARISON DATA-simulation

SIMULATION

COMPARISON proton-photon

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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

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3636

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Another paper in progress on the ARGO-YBJ calibration