The distribution of the maxima of high energy cosmic ray induced extensive air showers in the atmosphere was measured as a function of atmospheric depth. From the exponential tail of this distribution, it was determined that the proton-air inelastic cross section at 30 TeV center-of-mass energy to be 540 + or - 40mb

Baltrusaitis, R. M.

Cassiday, G. L.

Cooper, R.

Elbert, J. W.

Gerhardy, P. R.

Ko, S.

Loh, E. C.

Mizumoto, Y.

Sokolsky, P.

Steck, D.

English

NASA Technical Reports Server

5 HE 1.1-2
PROTON-AIRINELASTIC CROSSSECTIONAT Sz/2 = 30 TeV
Baltrusaitis, R.Mo, Cassiday, G.L., Cooper, R., Elbert, J.W.,
Gerhardy, P.R., Ko, S., Lob, E.C., Mizumoto, Y., Sokolsky, P. & Steck, D.
Department of Physics, University of Utah, Salt Lake City, UT 84112
ABSTRACT
We have measured the distribution of the maxima of high
energy cosmic ray induced extensive air showers in the
atmosphere as a function of atmospheric depth. From the
exponential tail of this distribution, we determined the
p-air inelastic cross section at 30 TeV center-of-mass
energy to be 540 + 40mb.
i. Introduction. The technique of extracting the p-air cross section
from tile data ob-tained by the "Fly's Eye" detector has been described
in detail in an earlier paper.(1) We report the results of a recent
analysis from data accumulated through the month of April 1985.
2. Discussion. The "Fly's Eye" detector consists of 67 F/1 mirrors,
Ea-c_"With 12 or 14 photomultiplier tubes mounted at the focus.(2)
These mirrors are arranged so that they cover all but a small portion
of the solid angle near the horizon. The detector records the passage
of distant extensive air showers by means of the light produced by the
shower particles which, depending on the relative geometry between the
track and the detector, is usually an admixture of Cerenkov and
fluorescent light. The shower direction is reconstructed from the
timing information obtained by the photomultiplier tubes. Knowing the
reconstructed geometry and the fluorescence efficiency and taking into
account the Cerenkov intensity, we calculate the number of particles of
each shower as it progresses through the atmosphere. Figure I shows
the number of particles in a shower as a function of atmospheric depth.
_"=,......_ ....... The shower maximum is
' ,_ :,i,3_, C.H;:,UR ES',£'../_ Z.:3_ +/- _.%_._V
.........' .... _ _-"- °_- obtained by fitting a distribu-1.._Y+09 7.c_.+07 o._ I",4ETr= _.6 +1- 5.1 De_
I
_.,_ .......... tion to the shower profile
............................_: _ _.,,, , We ascertained that the shape
_"_........ >l_',._.]_,t of the shower profile can be. I fit d with either a Gaisser-
...... ,+_f-LT_. Hillas (G-H)(3) distribution or
IT+ '\_ a Gaussian distribution. Both" distrib tions yield equally
/ '" ,._ good fits, with the G-H fit._*e9 [ l', x_ \ c nsis ently giving a slightly
" ..TAR-_' I '"'...._ lower value (30 g cm-2) to the
..... __ _, ,, ,-...... depth of maxima. Such consis.-
o. _. o_. _. '_ -_ tent difference does not affect
, the over-all shapes of the
Figure i. An Extensive Air final data distributions
_-h_at Survives All Data obtained from the two fits.
Cuts. The solid curve is a
GH. shower curve. The dotted The error in shower
curve is a Gaussian distribution, maximum, for showers whose
https://ntrs.nasa.gov/search.jsp?R=19850027537 2020-03-20T17:11:32+00:00Z
6 HE 1.1-2
closest distance of approach of exceed one and one half kilometers,
arises almost entirely from the uncertainty in the reconstructed polar
angle. Showers with zenith angle larger than sixty degrees are excluded
in this analysis to avoid bias toward large depths of maxima due to the
exponential behavior of the atmospheric density.
Possible track reconstruction bias has been examined by
using light beams generated by a roving light pulser, and a fixed
position nitrogen pulse laser. Tracks reconstructed from such light
pulses show that, regardless of the angle of the light beams, we can
measure the polar angle to the order of one degree with a sigma of about
1.7 deqrees. Figure 2 shows the result of one of the runs obtained
with the roving flasher.
, _ , _ _ l _ --l Further checks are made with
4o 1 events that are visible from a
partially built second detector
located about 3.5 kilometers
3o from the "ny's Eye". In this
F case, the polar angle is
]-_ determined from the intersection20 - of the two planes which contain
the track. Again, the zenith
° I angles obtained with the
'oFF- - coincidence events are in
kJ agreement within experimental. n uncertainties with the angles
-6 -4 o 2 4 6 calculated with the timing
_8(_,g,,,,) information from one eye alone.
Figure 2. Distribution of differences Figure 3 shows the agreement
between known and fitted zenith angles between the two methods of
for "upward-going" showers of known calculating the zenith angle.
geometry generated by a high intensity
light flacher. The width of the Bias toward large depths
distribution is o=1.7 ° . of maxima could result from
distant showers of very high
energy. Such bias is removed by accepting showers of a narrow band of
energy between i017 eV and 2xi018 eV. Finally, events with shower
maximum uncertainty less than i00 g cm-2 are accepted for analysis
with the average uncertainty of the order of 70 g cm-2.
3. Results and Conclusions. The resulting distribution of the shower
maxlma as a function of the atmospheric depth is shown in Figure 4.
The effect of the finite resolution of 6=70 g cm-2 does not effect the
shape of the exponent behavior of the tail of the distribution
beyond a distance of 62/X where X is the slope of the tail of the
distribution.
A fit of the data based on events beyond a depth of
~ 760 g cm-2 is found to be =70±6 g cm-2 . •
From a paper by Sokolsky et al(4) submitted to this
conference, it seems likely that the primary particles consist of a
considerable amount of light particles, i.e., protons. According to
7
HE 1.1-2
the paper by
THETAD_FFERENCE Ellsworth et al(5),
2B , i , i , _ , those protons
i dominate the tail
of the distribu-
a4- tion. In this
case, the proton-
_- air inelastic
cross-section is
i6- - found to be
I 540_+50g cm-2 .
"' ia-t t T | t t - This result is in
agreement with the
B- _ I - results published
I I I I 1 by Hara et al(6)"
4 m
I I The extrapo-
e , , _ _ ,_: lation of proton-
-_ -le e i_ _ proton inelastic
D_FTH cross-section
from p-air
Figure 3. Difference in Zenith Angle for Events cross-section is
Observed by Both Detectors and With One Detector model dependent.
Alone. The average angular length for the track With the same
is about 40°. assumptions made
in our previous
paper(I), the
p-p inelastic
llYZ.(W_LS= 0 (_ O / O _ [ / O _' (_ (-U_C-_IJY IJ , , , I , , , t , , , _ , , , r ,, , i , ,, f , _ , I , , , / cross-section is
Ie2_ <x>:(_;_;_L_,E-Is=,:(_a_-_I,E-I [ found to be
1 __' __ I 122-+IImb at
sI/2 of 30 TeV
(Figure 5).
° tl
'\
Figure 4. Distributionof Depth of Shower Maxima for Data Whose
" Fitting Errors Are Less Than 6,100 g cm-2 . The slope of the exponential
tail is x = 70 +_6 g cm-2.
8HE 1.1-2
inel
(a) O-p.olr(mb)
' 'LM/ ' ' '7_00 • A
I
600 .i // I_,_
_100 '""
200
IO0
i • I I I I
IoI(b) v pp (rob)
i i I I I140 A L
,,o
80 _'"60
40 ._,-'-_""= .................. cbN's_"=
20
II I I, I I I
Io3 Io4 Io5 io' io7 leo
E,,.(GeV)
Figure 5.
(a) P'airInelastic and (b) p-p Total Cross Section With Our Data.
. Acknowledgements. We gratefully acknowledge the United States
ational Science Foundation for its generous support of this work
under grant PHY8201089.
References.
1. Baltrusaitis, R.M., et al, Phys. Rev. Lett. 52, 1380 (1984).
2. Baltrusaitis, R.M., et al, Nuclear Instrument-sMethods(to be
published).
3. Cassiday, et al, Proceeding of the Workshop on Very High Energy
Interactions, Philadelphia, 1982, pp. 72-82.
4. Baltrusaitis, R.N., et al, paper OG 5;1-7
5. Ellsworth, R.W., Gaisser, T.K., Stanev, T., and Yodh, G.B.,
Phys. Rev. D26, 336 (1982).
6. Hara, T., Hayas-_ida,N., Honda, M., Kamata, K., Kawaguchi, S.,
Kifune, T., Mizumoto, Y., & Nagano, M. Proceedings of
International Symposium on Cosmic Rays and Particle Physics,
March 19-23, 1984, Tokyo. =


Proton-air inelastic cross section at S(1/2) = 30 TeV

Proton-air inelastic cross section at S(1/2) = 30 TeV

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