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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
66
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 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
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
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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
1414
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
1616
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
2323
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
=
=
2424
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
3232
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
3333
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