Konstantin Belov

1
Measuring p-air Inelastic Cross-Section Using the
HiRes Stereo Data.

• Konstantin Belov
• For High Resolution Flys Eye (HiRes)
  Collaboration

Aspen, April 17, 2007.

• Columbia University
• University of Adelaide
• University of New Mexico
• Rutgers University
• University of Montana
• Los Alamos National Laboratory
• University of Tokyo

2
Outline

• Measuring Cross-Section using Cosmic Rays
• Strong Interaction Model Dependence
• HiRes Stereo Data Reconstruction
• New HiRes p-air Cross-Section Value
• Experimental measurement of the k-factor
• Heavier Component (Fe and He) and Gamma Ray
  Influence
• Conclusion.

3
Observable Shower Profile.
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Measured shower profile.
Measured shower parameters.

• Event by event
• Xmax in g/cm2
• Total energy of the primary particle
• Arrival direction

• Statistically
• p-air inelastic cross-section
• Mass composition.

5
Xmax distribution - what we can measure.

• MC simulated Xmax distribution at E1018.5 eV.
  Corsika 6.003 QGSJET01.

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MC X1 and X separation

• Interaction length distribution. Corsika 6.003
  QGSJET01.

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X distribution

• X distribution. Corsika 6.003 QGSJET01.

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Xmax distribution.

• Xmax distribution is considered as a convolution
  of X1 and X distributions.

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QGSJET01, QGSII, SIBYLL2.1
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X' Fitting parameters.
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Fitting Functions
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Data reconstruction at HiRes

• Adaptive sieve fitting algorithm.
• Propagator method.
• Minuit fitter.
• Time-dependent databases
• Gain
• Ontime
• Atmospherics
• Successfully implemented global fit (HiRes1 and
  HiRes2 combined fit).

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Robust profile reconstruction.
HiRes1 fit
Global fit
HiRes2 fit
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Resolutions with global fit - preliminary.
Minimal quality cuts. Only count events with
global fit. Still work in progress.
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Data Xmax Distribution

• Only events with global fit are used
• Less tight quality cuts due to more stable
  profile reconstruction
• Reduced reconstruction bias
• Work in progress systematic errors are not
  fully evaluated yet.

Preliminary -

• HiRes

16
HiRes 2007 Measurement.
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Experimental measurement of the k-factor

• K-factor was used in previous experiments to
  measure the p-air inelastic cross-section and was
  obtained from MC simulations.

k(exp. Index) / (mean free path)
k 1.21 0.14 - 0.09
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k from the models
Muniz, Engel, Gaisser, Ortis Stanev
arXivastro-ph/0402092 2004
Pryke arXivastro-ph/0003442 (2000) at 1017 eV
Flys Eye used k 1.6
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Heavier component influence.

• Fe is cut off by using the deeper portion of the
  Xmax distribution
• He and gamma has to be taken into account

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Data Xmax Distribution

• Generate MC showers initiated by p and He
  primaries
• Run thru a detector simulator program using pure
  proton contaminated data sets
• Reconstruct the MC data - reconstruction
  efficiency for He and proton is very similar
• Deconvolute the cross-section.

He influence is statistically insignificant for
He flux up to 10.
21
Conclusions

• Preliminary proton-air inelastic cross-section
  value is 460 14 (stat) 39 (sys) 11(sys) mb
• Strong interaction models have minimal influence
  on the proton-air inelastic cross-section
  measurement
• The measurement is very stable
• Experimental value of the k-factor is in good
  agreement with the newer models
• He influence is insignificant for He flux upto
  10
• Gamma effect is more significant and is taken
  into account as a systematic error.