Konstantin Belov

1
Proton-air cross-section measurement at 1018.5
eV.

• Konstantin Belov
• UCLA

New Trends in High Energy Physics, Yalta, Sep.
30, 2008.

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

2
Outline

• The HiRes detector
• Measurement Technique
• Strong Interaction Models at High Energy
• Measured p-air Cross-Section at 1018.5 eV
• Heavier Component (Fe and He) and Gamma Ray
  Influence and systematic errors
• Experimental measurement of the k-factor and
  previous cosmic ray p-air cross-section
  measurements
• Rescaling to pp total
• Conclusion.

3
Observable Shower Profile.
4
HiRes fluorescence detector.
5
Stereo observations.

• HiRes 1 has 20 operational mirrors in one ring.
  S/H electronics. FOV 3-17º in elevation, 322º in
  azimuth
• HiRes 2 has 42 operational mirrors in two rings.
  FADC electronics. FOV 3-31º in elevation, 336º in
  azimuth.
• Stereo fixes shower geometry improving resolution.

An idealistic view of a stereo event
6
An event of the HiRes displays.
HiRes1 one ring detector
HiRes2 two ring detector
7
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.

8
EAS profile reconstruction.
HiRes1 fit
Global fit
HiRes2 fit
9
Resolutions with global fit.
Minimal quality cuts. Only count events with
global fit. Still work in progress.
10
Deconvolution technique.MC simulations.
11
QGSJET01, QGSII, SIBYLL2.1
12
X' Fitting parameters.
13
Fitting Functions
14
Data Xmax Distribution

• Mean energy 1018.5 eV
• Only events with global fit are used
• Without additional systematic errors due to
  heavier and lighter components

• HiRes

15
HiRes 2007 Measurement.
16
Heavier and lighter component influence.

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

17
He flux influence

• 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.
18
HiRes 2007 Measurement.
5 gamma flux and and 10 He flux affect
systematic errors.
19
HiRes 2007 Measurement.
20
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.

21
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
22
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.

23
HiRes 2007 Measurement.
24
pp total cross-section

• Using Glauber theory to rescale fom p-air to pp
  total (Block-Engel 2005)
• Adaptive sieve fitting algorithm and anchoring at
  lowest energies to extrapolate accelerator data
  to UHE

M.Block Aspen 2007
Difractive part is model dependent caution
should be used interpreting the results.
25
Conclusions

• Measured proton-air inelastic cross-section value
  is 460 14 (stat) 39 (sys) 26(sys) mb
• New measurement does not contradict an assumption
  about the Froissart bound saturation
• 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
• Possible gamma ray and He flux effect is taken
  into account as a systematic error.