EAS Time Structures with ARGO-YBJ experiment 1 - INFN-CNAF, Bologna, Italy 2 - Università del Salento and INFN Lecce, Italy A.K Calabrese Melcarne A.K Calabrese Melcarne 1 , , G.Marsella G.Marsella 2 for the ARGO-YBJ Collaboration for the ARGO-YBJ Collaboration XXIII European Cosmic Ray XXIII European Cosmic Ray Symposium, ECRS 2012 Moscow, Symposium, ECRS 2012 Moscow, Russia, July 3-7, 2012 Russia, July 3-7, 2012 1
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EAS Time Structures with ARGO-YBJ experiment 1 - INFN-CNAF, Bologna, Italy 2 - Università del Salento and INFN Lecce, Italy A.K Calabrese Melcarne 1, G.Marsella.
Strip = space pixel Pad = time pixel Time resolution ~1.8 ns 10 Pads (56 x 62 cm 2 ) for each RPC 8 Strips (6.5 x 62 cm 2 ) for each Pad 78 m 111 m 99 m74 m ( 43 m 2 ) 1 CLUSTER = 12 RPC RPC analog charge read-out dynamical range up to ~ 10 4 TeV 3
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EAS Time Structures with ARGO-YBJ experiment
1 - INFN-CNAF, Bologna, Italy2 - Università del Salento and INFN Lecce, Italy
A.K Calabrese MelcarneA.K Calabrese Melcarne11, , G.MarsellaG.Marsella22 for the ARGO-YBJ Collaborationfor the ARGO-YBJ Collaboration
XXIII European Cosmic Ray Symposium, XXIII European Cosmic Ray Symposium, ECRS 2012 Moscow, Russia, July 3-7, 2012ECRS 2012 Moscow, Russia, July 3-7, 2012
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High Altitude Cosmic Ray Laboratory @ YangBaJing,Tibet, ChinaSite Altitude: 4,300 m a.s.l. , ~ 600 g/cm2
The ARGO-YBJ experimentThe ARGO-YBJ experiment
ARGO-YBJ
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Strip = space pixelPad = time pixelTime resolution ~1.8 ns
10 Pads (56 x 62 cm2)for each RPC
8 Strips (6.5 x 62 cm2) for each Pad
78 m111 m
99 m
74 m
(43 m2)1 CLUSTER = 12 RPC
RPC
analog charge read-out dynamical range up to ~ 104 TeV
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Num
ber o
f Fire
d St
rips
Full coverage, high time and space resolution provide a
detailed view of shower front
Data AnalysisData Analysis
- Quality cut on S2
Reconstruction
Time sequence and position of hit pads used to reconstruct the CR
arrival direction and core position
- Using a plane (α=0)
- Using a conical correction (α0)
- Core reconstructed within the central carpet
contamination of mis-reconstructed events less than 10% at low multiplicity, rapidly decreasing at higher multiplicity
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Average Curvature:Average Curvature: the mean of time residuals Δt(R) with respect to a
plane fit
Time profileTime profile
- larger than 10 ns for particles landing further than 60 m from the core.
- no significant dependence on pad multiplicity observed.
7.9 108 events
zenith < 15°
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Data vs SimulationsData vs Simulations
Very good agreement at the level of time profile
curvaturecurvature Shower generatorShower generator Corsika 6.720 with
SIBYLL+FLUKA as hadronic interaction models at high and low energies
• In order to exploit at maximum space-time information, we started a detailed study on the longitudinal time structures in data
• The idea is to study more in detail the shower structures in order to define selection criteria for particular analysis (gamma/hadron separation, composition, exotic physics)
• In particular we studied showers with large time residual with respect to the shower front
Angular differencebetween the reconstructedsubshower directions
In agreement with CR distribution of consecutiveevents
Multiplicity DistributionMultiplicity Distribution
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Multiplicity distribution of the reconstructedsubshowers Shower 1 is the one whichtriggers the detector!We expect lower multiplicity distribution from shower 2 (triggernot required)
Time DistanceTime Distance
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How to define time distance betweentwo subshowers?
At least 2 variables:•Peak mean value•T0 from the shower plane Fit
Time DistanceTime Distance
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Both variables can be used as indicator
Reconstucted AnglesReconstucted Angles
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Quality requirements on subshowersreconstruction are applied (S2<100ns2)
Applying a planar fit, the directionof both subshowers is reconstructed
AnalysisAnalysisObserved rates
– 7.9 x108 events have been processed
– 700 x103 events selected as double coincidences
– 370 x103 events selected as double coincidences with quality cuts on subshowers
λexp = 2 λ1 λ1 τ η = η (28±1) Hz (η is the event selection efficiency)
η x 0.8% of the events
4.5x10-2 % of the events
(1 order of magnitude less than expected if η=1 )
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AnalysisAnalysisSimulated double events• Artificial double Events have been generated from real data• Merged two consecutive events shifting the time of each hit of the
second event by a randomly extracted ΔT compatible with the 2μs trigger window
• Verified the random double shower distributions (Angle, Multiplicity, relative time distribution)
• Tested the double shower selection and reconstruction efficiency η : The efficiency η is 5% (preliminary selection algorithm) This explains the difference between expected and observed events expected :η x 0.8% = 4.0x10-2 % of the events
observed :4.5x10-2 % of the events
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In this work the shower time profile and distribution have been presented. The curvature of the showers around the core have been studied, illustrating the reconstruction effect on ARGO-YBJ data.Longitudinal time structures have also been investigated selecting events with large time distribution around the shower front. The attention has been focused on double front showers and , in particular, to identify the expected random double coincidences.A new algorithm have been introduced, increasing the detection efficiency. More efforts are on the way. The detailed study of the angular and time distribution of the selected events will be useful in studying possible shower anomalies. In particular narrow Angular difference events will be analyzed on large statistical sample in order detect anomalies in spatial, time and multiplicity distributions as a flag of possible ‘exotic’ physic events in CR.
Conclusions Conclusions
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This is a preliminary step to better investigate the possible “physics of multiple shower fronts”