Observables sensitive to primary mass composition at the Pierre Auger Observatory

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Observables sensitive to primary mass composition
at the Pierre Auger Observatory
Analisa Mariazzi for the Pierre Auger
Collaboration
IFLP - Departamento de Fisica Universidad
Nacional de La Plata
XLIVth - RENCONTRES DE MORIOND February 1-8
2009, La Thuile, Italy
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Pierre Auger Observatory Hybrid instrument
Surface detector array Fluorescence detectors
A unique and powerful design

• Calorimetric energy calibration of the
  fluorescence detector transfered to the event
  gathering power of the surface array
• A complementary set of mass sensitive parameters
• Different measure techniques force understanding
  of the systematics uncertainties

4 Eyes (6 X 4 telescopes) 10 duty cycle
1600 water tanks 1.5 Km spacing 3000 Km2 100
duty cycle
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Mass sensitive SD observables

Three observables based on the time structure of
the shower front as measured with the water
Cherenkov detectors have been studied

• Muon content from the derivative of the signals
• Azimuthal asymmetry in the signal risetime
• Signal risetime in surface detectors to infer
  Xmax

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Muon counting method

• Muon content of the shower is highly sensitive to
  mass composition
• Muons induced peak signals while electromagnetic
  particles induce a continuum
• FADC jump is the ? V over consecutive bins (25
  ns)
• ?V(ti) V(ti1) - V(ti)

Jump distribution
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Muon counting method
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Muon counting MC comparison
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Risetime
Risetime is the time it takes to go from 10 to
50 of the total signal
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Signal asymmetry
Attenuation (em component) across the array
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Asymmetry parameter
t1/2/r vs azimuth in the shower plane for a
given (E, ?) bin Fit with t1/2/r a b
cos ?
a

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Asymmetry and shower development

• Asymmetry (b/a) vs sec? in a bin of energy
• Fit to determine the position of the maximum
  (XAsymMax)

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The asymmetry parameter has maximum which is in
different for different primaries
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Asymmetry parameter as a mass discriminator
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Xmax from Surface Detector

• SD observables with good sensitivity to Xmax
• Improved precision on SD observables is desired
  to improve correlations

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Signal Deconvolution
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Definition and determination of ?i
Larger Xmax
Larger lt?igt
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Slower signals
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Correlation with Xmax - Calibration
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Conclusions

• The mass sensitivity of risetime, azimuthal
  asymmetry in risetime and muon content has been
  established.
• Comparison with data, systematics and
  improvements are on going so us to have public
  results soon.
• A combined analysis will allow to determine the
  primary mass of UHECR and constrain the hadronic
  interaction models

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