Muon Component Research Articles

Coupling constants for the cosmic ray muon component

An apparatus employing twin telescopes to study the azimuthal variation of cosmic ray muon intensity was operated at Ahmedabad (geographic 23 degrees N, 37 degrees E; geomagnetic latitude 14 degrees N). Fourteen directions were scanned for long time intervals to give a counting rate accuracy of about 0.4% for each direction. Experimental results are presented. Variation in the coupling constant values in the rigidity range 12-26 GV is rather flat. Some implications of this behaviour are discussed. A theoretical method is described for the estimation of coupling constants applicable to muon telescopes. Correction for the fact that alpha particles and heavy particles have a cut-off (in terms of momentum per nucleon) at half the value for protons is incorporated in the calculation. The method is verified by comparing the theoretical results with experimental data on the latitude effect (namely, for zenith direction) and on the azimuth effect for fixed zenith angles. Theoretically estimated coupling constants for different zenith angles and different atmospheric depths are presented.

Recent measurements of the muon component of large cosmic ray air showers

Measurements are reported for the lateral distribution of muons of energy greater than 1 GeV in large air showers. The measurement which was made with the modified Haverah Park spectrograph extends from core distances of 30-600 m and is in satisfactory agreement with the results of computer simulations. Data on the differential momentum spectra of muons at core distances of 200-600 m in large air showers are reported which are in good agreement with the results of recent computer simulations and do not show the excess of distant energetic muons which featured in earlier measurements.

The electron component of large EAS

A large-area neon flash-tube detector has been used to measure the density of electrons occurring in EAS detected at Haverah Park for shower size 0.29< rho 500<1.7. Comparison of the total charged particle lateral density distribution with that of the muon component is made. The response of the flash tubes is also compared with that from neighbouring 1.2 m deep water Cerenkov tanks.

The lateral distribution of muons in near vertical EAS

A large-area muon detector (12.5 m2) has been used to investigate the muon component of large EAS at Haverah Park of size 0.27< rho 500<2.5 for zenith angle ( theta )<25 degrees . The analysis is based on 821 showers covering core distances of 160 m to 500 m. The results are compared with other observations and with recent model calculations. It is found that only certain models are in reasonable agreement with the experimental data.

Conventional processes and the underground muon component

Conventional processes and the underground muon component

Possible Evidence for Pulsed ∼1012 eV Gamma Rays from NP 0532

I HAVE found experimental and theoretical evidence in studies of extensive air showers (EAS) that suggests that EAS initiated by a primary γ-ray (or electron) may be distinguished with a probability of >70% from those initiated by cosmic rays at energies ∼1012 eV (ref. 1). This distinction is made possible by the identification of a unique feature of the EAS Cerenkov radiation that is attributable to the penetrating muon component in selected EAS and thus only expected for EAS initiated by cosmic rays. The sensitivity of experiments used to search for point sources of primary γ-rays near Eγ ∼1012 eV has also been increased by the improved angular resolution possible with the new methods of Cerenkov detection of EAS.

Periodic solar time variations in the cosmic-ray muon component near sea level

Eight scintillation counters, each about 1.5 m2, have been assembled in a muon telescope array at Winnipeg, Canada. Six telescopes (geometric factor about 750 cm2sr) have their axes approximately in the equatorial plane. For these, the asymptotic cones of acceptance are quite narrow with respect to asymptotic longitude, and they are therefore well suited for time variation studies. Two nearly vertical telescopes (geometric factor about 350 cm2sr) complete the array. Experimental results obtained between 13th November 1966 and 5th May 1968 are presented. It is shown that the phase of the average diurnal anisotropy is consistent with the Parker (1964, 1967) and Axford (1965) theories alone, and its amplitude is dependent on the time in the solar cycle. Further, a semi-diurnal anisotropy is found, extra- terrestrial in origin, with intensity maxima at right angles to the interplanetary magnetic field.

Muons in large extensive air showers

An error in the data on the muon component of extensive air showers presented at the 10th International Conference on Cosmic Rays is corrected. The effect on the explanation of the anomalies in the muon data which involved an abnormally large transverse momentum is considered, and an alternative explanation for the persisting anomalies in the data is suggested.

On the parallel penetrating particles underground as E.A.S. muonic component

A calculation on the nuclear cascade in high energy E.A.S. is performed by using a composite isobaric model, in order to study the muon density functionΔ(N, R, >E μ), whereR is the distance from the axis of the E.A.S.,E μ the muon energy andN the size of the E.A.S. The obtained expression $$\Delta (N,R, > E_\mu ) = \frac{{N^{0.85} R^{ - 0.24} (R + 90)^{ - 2.4} }}{{4.6 \cdot 10^{ - 3} (R + 45)(E_\mu - 10) + 1}}\left( {\frac{{E_\mu + 7}}{{10}}} \right)^{0.002R} (m^{ - 2} ),$$ shows a good agreement with experimental data on the muonic component of the E.A.S. TheΔ(N, R, >E μ) is then used to interpret the results obtained up to now on the parallel penetrating particles underground as resulting from the very penetrating muonic component of the E.A.S. At depths greater than 200 m w.e. a disagreement is found between the calculations and the experimental data. Some discussion is given of the basis for this discrepancy.

Theoretical aspects on the cosmic ray latitude knee

Theoretical calculations are made for the latitude knee of the secondary cosmic rays. It is pointed out that there exist two latitude knees, one for the nucleonic and one for the muon component. The behaviour of the latitude knee is calculated in dependence of the particle's energy, of the atmospheric depth and of the solar activity. The results are compared with known experimental facts.

Trains of diurnal waves in the muonic component at 70 MWE during cosmic-ray decreases

Trains of diurnal waves in the muonic component at 70 MWE have been found during the preliminary phases of some cosmic-ray decreases. A predecrease the day immediately preceding a Forbush decrease has repeatedly been reported from neutron monitor observations. Our analysis indicated that underground data reveal this effect earlier and for a longer period. This is consistent with the interpretation of a Forbush decay as the result of the advance of a shock front.

Lateral distribution of the muon component in the central region of extensive air showers

Using a new device for extensive air shower core localization consisting of four sets of Conversi neon detectors of total area 9 m2 (comprising 36000 neon tubes), cores have been located with high accuracy and the lateral muon distribution and density have been measured for a threshold energy of 0.6 GeV. The interpretation of the shape of this distribution is discussed and compared with theoretical calculations. As the muon lateral distribution is mainly determined by the angles of emission of parent pions, some features of the distribution of transverse momenta pt of pions produced in air can be analysed. For low pt values a discrepancy is found with the Cocconi empirical pt distribution which comes from accelerator data. A flattening of the muons' lateral distribution near the shower axis is interpreted as being due to a lack of small pt values.

A theoretical analysis of extensive air showers. III. Muon showers at large zenith angles

For Pt. II see abstr. A15896 of 1968. A theoretical analysis has been made of the muon component of extensive air showers incident at large angles to the vertical. Using the model described previously, calculations have been made of the expected numbers of muons reaching ground level as a function of threshold energy and zenith angle for primary particles of various energies. The data have been combined with alternative primary spectra of cosmic rays, with and without an enhanced contribution from heavy nuclei, to give the expected muon density spectra. It is found that the density spectrum is sensitive to the distribution of transverse momentum among the parents of the muons and to a lesser extent to the mass composition of the primaries. There is thus the possibility of deriving information about the mean transverse momentum, and perhaps setting limits on the mass composition, from a comparison with experiment.

Coherent Cosmic-Ray Model Based on "Direct" Muon Production

We consider a cosmic-ray muon model in which a directly produced muon component with the same slope as the primary spectrum is added to the conventional pion-derived muons. It is found to be consistent with recent burst measurements, horizontal-air-shower data, atmospheric gamma-ray fluxes, and muon spectrograph measurements. It may also explain the anomalous mu-less air showers. The model requires that the photonuclear cross section increase at very high energies.

A discrepancy between measured and calculated cosmic-ray spectra in the atmosphere

The flux of nucleons, pions, and muons in the energy range 1–1000 GeV and in atmospheric altitudes of 0–48 km has been calculated to a high degree of accuracy and without gross simplifications. Thus a discrepancy indicated already in 1964 byBrooke, Hayman, Kamiya andWolfendale has been firmly established. The discrepancy means, that it has proved impossible to derive the measured nucleon and muon spectra near sea-level from the measured primary nucleon spectrum unless the primary spectrum is reduced by a factor of about 2.5 or the high-energy collision models commonly used are changed. The latter would mean that the fraction of energy lost by the nucleon in a collision is passed over to the muon component to a minor extent than so far accepted, and this may be achieved in two ways: either the ratio of collision energy passed on to the electron-photon component to the energy passed on to the pion-muon component is increased in favour of the former, or about 10–20% of the collision energy are passed on to unspecified particles which do not contribute appreciably to the hard and weak components of cosmic rays. — The possibility is discussed that the missing fraction of 10–20% is spent in production of baryonantibaryon pairs.

Simultaneous observation of air shower cores at sea level and under 800 g/cm2 of shielding

Using a 14-m2 neon hodoscope installed under 800 g/cm2 of concrete and vertically below the 32-m2 neon hodoscope, observations have been made on the strongly interacting and the muon component in air shower cores. A preliminary analysis has yielded the following results: (a) The energy spectrum of strongly interacting particles in air shower cores has been obtained in the energy range from 1 to 10 TeV, yielding an exponent of ~ −1.2 for the integral spectrum. (b) The lateral distribution of muons exhibits a distribution as steep as r−0.9 ± 0.1 down to distances of the order of 1 m from the air shower axis. However, at the present state of evaluation contamination of muon data, due to unrecognized cascades, cannot be ruled out completely.

On the correlation between the primary cosmic radiation and the directional muon flux in the lower atmosphere

The directional muon spectra are reproduced using the diffusion equations, independent measurements of the primary spectrum, the multiplicity in pion production, and the three-dimensional spectrum of pion production in nucleon – light nuclei collisions at accelerator energies extended to high primary energies by a modified CKP model. With an attenuation mean free path L ≈ 140 g cm−2 the calculated muon spectra in the momentum interval 0.2–50 GeV/c at sea level correspond to observations to within ~±10% at 0°, ~±15% at 30°, and ~±20% at 60° to the zenith direction. At the level 700 g cm−2 in the zenith direction the shape of the calculated spectrum falls within the observational error limits. At 300 g cm−2 the intensity of muons falls ~30% below that recorded for the hard component.The atmospheric "multiplicity" (Dorman 1957) for the muon component is evaluated and stored as a five-dimensional matrix on magnetic tape. Some applications of this analysis are proposed.

Lateral distribution of the muon component in the central part of EAS

Using 50 000 recordings of muon densities at distances from the axis established with very high accuracy, the lateral distribution of muons from 2 to 30 m has been obtained. The interpretation of the shape of this distribution is discussed and compared with theoretical calculations. The experimental distribution is flatter than the theoretical one at small distances from the axis. This may be explained by the relative deficiency of small transverse momentum transfer in nucleon – air nucleus collisions.

The muon component of extensive air showers

The lateral distribution of the muon component of extensive air showers, and the variation in the total number of muons with shower size, have been studied for showers of sizes between 3 × 105 and 108 particles. The lateral distribution function is found to be in essential agreement with Griesen's formula, and the total number of muons is found to vary smoothly with shower size, as N0.75.

Calculations of average characteristics of EAS components and Monte Carlo calculations of their fluctuations using different models of nuclear interactions. II. Muons

The results pertaining to the muon component obtained in the calculations described in Part I are presented. The predicted lateral distributions and energy spectra of muons with energies above various thresholds are compared with experimental observations. Also presented are the expected variations of the number of muons with shower size compared with experimental results. None of the models assumed predict in every detail the results obtained experimentally. Modifications that could possibly be made are indicated.