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Reconstruction of muon height of production in Extensive Air Showers
ELSEVIER
Nuclear Physics B (Proc. Suppl.) 75A (1999) 312-314
PROCEEDINGS SUPPLEMENTS
Reconstruction of muon height of production in Extensive Air Showers M. Ambrosio <* , C. A r a m o b'~, L. Colesanti ~, A. D. Erlykin d. q N F N , Sezione di Napoli, Italy t'INFN, Sezione di Catania, Italy ' D i p a r t i m e n t o di Fisica - Universith di Catania, Italy ~IP.N. Lebedev Physical Institute, Moscow, Russia An attempt has been made to select muons in Extensive Air Showers (EAS) by means of tracking telescopes and reconstruct their apparent height of production along the shower axis. By this way a reconstruction of shower longitudinal development in the Earth atmosphere can be obtained. Results indicate that the only information of muon arrival direction is not enough for the correct reconstruction of shower longitudinal development, mainly because of t.he distorting effect of the Earth geomagnetic field and multiple coulomb scattering by air nuclei.
1. I n t r o d u c t i o n
The reconstruction of EAS longitudinal development in the Earth atmosphere is a very powerful tool for the study of p r i m a r y cosmic rays mass composition, as demonstrated by the Fly's Eye experiment at EeV energies. In the Pev energy region, where the intensity of air fluorescence is low, Cerenkov techniques can be used, unfortunately with a low duty cycle and a narrow solid angle. A complementary technique can be the reconstruction of muon height of production along the shower axis. Muons emitted by parent pions and kaons can be detected by tracking devices. The reconstruction of their apparent height of production can be made by measuring muon arrival direction and core distance. Obviously the effect of geomagnetic field nmst be considered as well as ninon misidentification a m o n g much more abundant electrons in the shower front. 2. E x p e r i m e n t a l
apparatus
Present measurements were made using the G R E X / C O V E R _ P L A S T E X (G/C_P) array located at Haverah Park, near Leeds, UK, at an elevation of 220 m a.s.1. The triple title of experiment originates from the use of three relatively independent parts with *Corresponding autor. Tel.: +39 81 676184; fax 676246; e-mail: ambrosio:¢}na.infn.i t
different kind of detectors, built in different periods of time: • The G R E X array [1] detected EAS in the energy region of 0.25 TeV - 10 PeV and determined the shower axis direction with an accuracy better than 1° and the position of the shower core with an accuracy of ,-~ 6 m. . The P L A S T E X sub-array [2] was made of 4 plastic limited streamer tube (LST) hodoscopes. Two of them, named A&B, were placed side by side at about 4 m from the geometric center of G R E X and the other two, named C & D, were located at the same distance (150 m) from the array center. Each hodoscope was a stack of two identical tracking chambers, one above the other, with a thin layer of high Z absorber between them (Fig. 1). Each chamber consisted of three nearly square ~ 6 m 2 LST planes with X and Y readout strips on each plane. • The C O V E R layer on the top of each LST hodoscope was made of 4 m 2 single gap bakelite R P C [3,4] (Fig. 1) installed with the aim to measure the arrival time of individual particles crossing P L A S T E X hodoscopes. 3. A n a l y s i s o f e x p e r i m e n t a l
data
A pattern recognition program has been built to recognize muon-like particles crossing telescopes. Muons have been defined as particles not scattered by the absorber layer. Then, for each x and y view~ the program analyzes hits in
0920-5632/9915 - see front matter © 1999 Elsevier Science B.V. All rights reserved. PII S0920-5632(99)00276-5
313
M. Ambrosio et al. /Nuclear Physics B (Proc. Suppl.) 75/1 (1999) 312-314
each plane corresponding to fired strips, in order to find straight lines connecting hits. Hits in all 6 planes are required along lines, or in 5 planes provided that missing hit is in the inner planes. Individual single tracks identified in both views define the muon.
angle ~p, are also provided. Then muon track coefficients are translated into a frame in which the shower axis coincides with z axis, obtaining in this frame the coordinates xu, y , and the angles 0~, ~0u for each muon. In such a defined frame the muon slant height of production is : h~ =
T i - e~n,aat~te~
x~,cos~u + y ~ s i n ~ o , tan 9u
(1)
rr
_
tan 8.
In Fig. 2 the 0u, ~ , distributions are presented for all reconstructed muons. The average ninon zenith angle with respect to the shower axis appears to be about 30 , and the azimuth angle distribution is more or less fiat in the 0-360 degree range.
r t ~ k ILI~I a . 9 an Ph t t U k ¢,D: ~ cm Ye * 1,Z ¢aql~ 16000
8O0
14000
.
700
1 2O0O
1
60O
t 0000
/-
1
o
500
8000
4OO
6000
"
5O0
4000
Figure 1. The layout of the COVER_PLASTEX telescope.
2OO G,
2000
1 O0 0
7, ~
0
Pattern recognition conditions have been tested analyzing special autotrigger runs, in which the trigger was provided by the coincidence between the upper and the lower LST plane of each telescope, The analysis has been restricted by only events whose core position was inside the inner part of the array. No cuts have been applied on the shower size or its incidence angles. 4. M u o n h e i g h t o f p r o d u c t i o n The pattern recognition program identifies muon-like particles and provides the angular coefficients of two straight lines: =
( t , ~- Dec " X
zv
=
a v + by • y
with b.,.=tan(O~) and b v = t a n ( O y ). These angular coefficients are combined to obtain the muon zenith angle ®~ and the muon azimuth angle (I)u in the local telescope frame. From the GREX array the gAS axis zenith angle O, and the azimuth
2.5
~,.,m~ 5 7.5 10 ~ (°)
0 0
100
200
500
~ . (°)
Figure 2. Distribution of muon zenith angle 0~, and azimuth angle Cu in the shower frame. It must be taken into account that muons are deviated by the geomagnetic field and multiple coulomb scattering by air nuclei. Due to this reason expression (1) for an apparent height of muon production cannot be used without selection of non-scattered and non-deviated muons. If the muon preserves its direction in the atmosphere, expression (1) corresponds to: h u = R~
z~r
,
tan O,
(2)
with R = muon distance from the shower axis. Then a selection can be applied using the following criteria: rr<0 R-Irr
R
]
<0.1 -
(3)
M. ,4mbrosio et at~Nuclear Physics B (Proc. Suppl.) 7~,4 (1999) 312-314
314
Fig. 3 shows plots obtained using (1) without and with selection criteria (3). The apparent height of production increases quite linearly with core distance and criteria (3) select muons produced higher in the atmosphere.
E 1
-x--"
A
r.-
v
8 I 6
o-0-
-/
-~--"
-C'~-
-K>-
-
2 i ill-,. [ i i
o
•
E 0 c-
100
200
300 R (m)
6
4 [
"--Y_~_ _ ---0~--
0 il
0
- *
.
100
-
~
I
200
300 R
Figure 4. Comparison of experimental average height of production ( h , ) for selected muons (,) with simulated (ha) for showers induced by protons (o) and iron nuclei (A).
(m) 6. Conclusion
Figure 3. C,orrelation between the average apparent height of production ((hu)) and core distance /? tbr all reconstructed rnuons (o) and for selected .mons
(.).
5. Comparison with simulations Preliminary simulations have been developed using the CORSIKA 4.50 Montecarh) code [5]. 1260 proton and 1260 iron induced showers have been generated at 250 zenith angle in the energy range 0.25 TeV - 4 PeV according to a power energy speetrmn with the differential slope index of -2.6 in the 0.25-2.5 PeV energy range and -3.05 at 2.5-4 PeV. By now neither experimental accuracy nor experimental conditions have been taken into accouut.
Muons in simulated showers have been processed by the same way as in the experiment, and their slant height of production according to (1) with the selection (3) has been obtained. Fig. 4 shows comparison between simulations and experimental results for what concerns the apparent muon height of production. Simulations confirm the validity of selection criteria (3), showing that higher energy muons are selected.
The apparent muon height of production has been evaluated using matterless tracking telescopes of G/C_P experiment. Selection criteria have been defined for the selection of muons which azimuth angle is not deflected by the Earth geomagnetic field and multiple scattering in the air. Comparison with simulations indicates that the only information of muon arrival direction is not enough to reproduce the shower longitudinal development in the Earth atmosphere. A complementary timing information is needed to select muons which zenith angle is also uneffected. A detailed account of possible distortions of Or, in the real experimental conditions is absolutely necessary.
REFERENCES 1. Brooke G. et al., 19th ICRC, La Jolla, 3 (19S5), 426 2. Agnetta G. et al., I/ Nuovo Cbnento, 13 C (1990), 391 . Ambrosio M. et al., N.I.M. A 334 (1994) 350 4. Agnetta G. et al., N.I.M. A 381 (1996) 64 5. Capdevielle J.N. et al., Kernforschungszentrum Karlsruhe, K F K 4998 (1992)
Nuclear Physics B (Proc. Suppl.) 75A (1999) 312-314
PROCEEDINGS SUPPLEMENTS
Reconstruction of muon height of production in Extensive Air Showers M. Ambrosio <* , C. A r a m o b'~, L. Colesanti ~, A. D. Erlykin d. q N F N , Sezione di Napoli, Italy t'INFN, Sezione di Catania, Italy ' D i p a r t i m e n t o di Fisica - Universith di Catania, Italy ~IP.N. Lebedev Physical Institute, Moscow, Russia An attempt has been made to select muons in Extensive Air Showers (EAS) by means of tracking telescopes and reconstruct their apparent height of production along the shower axis. By this way a reconstruction of shower longitudinal development in the Earth atmosphere can be obtained. Results indicate that the only information of muon arrival direction is not enough for the correct reconstruction of shower longitudinal development, mainly because of t.he distorting effect of the Earth geomagnetic field and multiple coulomb scattering by air nuclei.
1. I n t r o d u c t i o n
The reconstruction of EAS longitudinal development in the Earth atmosphere is a very powerful tool for the study of p r i m a r y cosmic rays mass composition, as demonstrated by the Fly's Eye experiment at EeV energies. In the Pev energy region, where the intensity of air fluorescence is low, Cerenkov techniques can be used, unfortunately with a low duty cycle and a narrow solid angle. A complementary technique can be the reconstruction of muon height of production along the shower axis. Muons emitted by parent pions and kaons can be detected by tracking devices. The reconstruction of their apparent height of production can be made by measuring muon arrival direction and core distance. Obviously the effect of geomagnetic field nmst be considered as well as ninon misidentification a m o n g much more abundant electrons in the shower front. 2. E x p e r i m e n t a l
apparatus
Present measurements were made using the G R E X / C O V E R _ P L A S T E X (G/C_P) array located at Haverah Park, near Leeds, UK, at an elevation of 220 m a.s.1. The triple title of experiment originates from the use of three relatively independent parts with *Corresponding autor. Tel.: +39 81 676184; fax 676246; e-mail: ambrosio:¢}na.infn.i t
different kind of detectors, built in different periods of time: • The G R E X array [1] detected EAS in the energy region of 0.25 TeV - 10 PeV and determined the shower axis direction with an accuracy better than 1° and the position of the shower core with an accuracy of ,-~ 6 m. . The P L A S T E X sub-array [2] was made of 4 plastic limited streamer tube (LST) hodoscopes. Two of them, named A&B, were placed side by side at about 4 m from the geometric center of G R E X and the other two, named C & D, were located at the same distance (150 m) from the array center. Each hodoscope was a stack of two identical tracking chambers, one above the other, with a thin layer of high Z absorber between them (Fig. 1). Each chamber consisted of three nearly square ~ 6 m 2 LST planes with X and Y readout strips on each plane. • The C O V E R layer on the top of each LST hodoscope was made of 4 m 2 single gap bakelite R P C [3,4] (Fig. 1) installed with the aim to measure the arrival time of individual particles crossing P L A S T E X hodoscopes. 3. A n a l y s i s o f e x p e r i m e n t a l
data
A pattern recognition program has been built to recognize muon-like particles crossing telescopes. Muons have been defined as particles not scattered by the absorber layer. Then, for each x and y view~ the program analyzes hits in
0920-5632/9915 - see front matter © 1999 Elsevier Science B.V. All rights reserved. PII S0920-5632(99)00276-5
313
M. Ambrosio et al. /Nuclear Physics B (Proc. Suppl.) 75/1 (1999) 312-314
each plane corresponding to fired strips, in order to find straight lines connecting hits. Hits in all 6 planes are required along lines, or in 5 planes provided that missing hit is in the inner planes. Individual single tracks identified in both views define the muon.
angle ~p, are also provided. Then muon track coefficients are translated into a frame in which the shower axis coincides with z axis, obtaining in this frame the coordinates xu, y , and the angles 0~, ~0u for each muon. In such a defined frame the muon slant height of production is : h~ =
T i - e~n,aat~te~
x~,cos~u + y ~ s i n ~ o , tan 9u
(1)
rr
_
tan 8.
In Fig. 2 the 0u, ~ , distributions are presented for all reconstructed muons. The average ninon zenith angle with respect to the shower axis appears to be about 30 , and the azimuth angle distribution is more or less fiat in the 0-360 degree range.
r t ~ k ILI~I a . 9 an Ph t t U k ¢,D: ~ cm Ye * 1,Z ¢aql~ 16000
8O0
14000
.
700
1 2O0O
1
60O
t 0000
/-
1
o
500
8000
4OO
6000
"
5O0
4000
Figure 1. The layout of the COVER_PLASTEX telescope.
2OO G,
2000
1 O0 0
7, ~
0
Pattern recognition conditions have been tested analyzing special autotrigger runs, in which the trigger was provided by the coincidence between the upper and the lower LST plane of each telescope, The analysis has been restricted by only events whose core position was inside the inner part of the array. No cuts have been applied on the shower size or its incidence angles. 4. M u o n h e i g h t o f p r o d u c t i o n The pattern recognition program identifies muon-like particles and provides the angular coefficients of two straight lines: =
( t , ~- Dec " X
zv
=
a v + by • y
with b.,.=tan(O~) and b v = t a n ( O y ). These angular coefficients are combined to obtain the muon zenith angle ®~ and the muon azimuth angle (I)u in the local telescope frame. From the GREX array the gAS axis zenith angle O, and the azimuth
2.5
~,.,m~ 5 7.5 10 ~ (°)
0 0
100
200
500
~ . (°)
Figure 2. Distribution of muon zenith angle 0~, and azimuth angle Cu in the shower frame. It must be taken into account that muons are deviated by the geomagnetic field and multiple coulomb scattering by air nuclei. Due to this reason expression (1) for an apparent height of muon production cannot be used without selection of non-scattered and non-deviated muons. If the muon preserves its direction in the atmosphere, expression (1) corresponds to: h u = R~
z~r
,
tan O,
(2)
with R = muon distance from the shower axis. Then a selection can be applied using the following criteria: rr<0 R-Irr
R
]
<0.1 -
(3)
M. ,4mbrosio et at~Nuclear Physics B (Proc. Suppl.) 7~,4 (1999) 312-314
314
Fig. 3 shows plots obtained using (1) without and with selection criteria (3). The apparent height of production increases quite linearly with core distance and criteria (3) select muons produced higher in the atmosphere.
E 1
-x--"
A
r.-
v
8 I 6
o-0-
-/
-~--"
-C'~-
-K>-
-
2 i ill-,. [ i i
o
•
E 0 c-
100
200
300 R (m)
6
4 [
"--Y_~_ _ ---0~--
0 il
0
- *
.
100
-
~
I
200
300 R
Figure 4. Comparison of experimental average height of production ( h , ) for selected muons (,) with simulated (ha) for showers induced by protons (o) and iron nuclei (A).
(m) 6. Conclusion
Figure 3. C,orrelation between the average apparent height of production ((hu)) and core distance /? tbr all reconstructed rnuons (o) and for selected .mons
(.).
5. Comparison with simulations Preliminary simulations have been developed using the CORSIKA 4.50 Montecarh) code [5]. 1260 proton and 1260 iron induced showers have been generated at 250 zenith angle in the energy range 0.25 TeV - 4 PeV according to a power energy speetrmn with the differential slope index of -2.6 in the 0.25-2.5 PeV energy range and -3.05 at 2.5-4 PeV. By now neither experimental accuracy nor experimental conditions have been taken into accouut.
Muons in simulated showers have been processed by the same way as in the experiment, and their slant height of production according to (1) with the selection (3) has been obtained. Fig. 4 shows comparison between simulations and experimental results for what concerns the apparent muon height of production. Simulations confirm the validity of selection criteria (3), showing that higher energy muons are selected.
The apparent muon height of production has been evaluated using matterless tracking telescopes of G/C_P experiment. Selection criteria have been defined for the selection of muons which azimuth angle is not deflected by the Earth geomagnetic field and multiple scattering in the air. Comparison with simulations indicates that the only information of muon arrival direction is not enough to reproduce the shower longitudinal development in the Earth atmosphere. A complementary timing information is needed to select muons which zenith angle is also uneffected. A detailed account of possible distortions of Or, in the real experimental conditions is absolutely necessary.
REFERENCES 1. Brooke G. et al., 19th ICRC, La Jolla, 3 (19S5), 426 2. Agnetta G. et al., I/ Nuovo Cbnento, 13 C (1990), 391 . Ambrosio M. et al., N.I.M. A 334 (1994) 350 4. Agnetta G. et al., N.I.M. A 381 (1996) 64 5. Capdevielle J.N. et al., Kernforschungszentrum Karlsruhe, K F K 4998 (1992)