East-west Effect Research Articles

Investigation of the cosmic ray angular distribution and the East–West effect near the top of Etna volcano with the MEV telescope

An experimental investigation of cosmic muons has been carried out with the Muography of Etna Volcano (MEV) tracking telescope, installed at an altitude of about 3100 m a.s.l. in front of the North-East Etna crater. The analysis of a statistically significant data sample ($$\sim 10^7$$ events), taken during a period of approximately 2 months, has been carried out to investigate the angular distribution of cosmic muons originating both from the open sky side and from a large solid rock thickness (Etna side). Due to the geographical orientation of the MEV telescope, anisotropies caused by the East–West effect could also be observed, extracting the asymmetry factor in small steps of the zenithal angle.

Unexpected East-West effect in mesopause region SABER temperatures over El Leoncito

We find that mesopause region temperatures determined by the SABER instrument on the TIMED satellite during nocturnal overpasses at El Leoncito (31.8°S, 69.3°W) are several kelvins higher when SABER observes from the East than when it observes from the West. We distinguish between altitudes corresponding to the nominal emission heights of the OH and O2 airglow layers. The East-West temperature differences of 4.5K obtained for OH-equivalent height, and of 3.5K for O2-equivalent height are surprising, because an effect of the South Atlantic Anomaly on SABER temperature is unexpected. However, the ground-based data obtained with our airglow spectrometer at El Leoncito show that such a SABER artifact can be ruled out. Rather, the phenomenon is explained as a consequence of the temporal sampling of the nocturnal variation, which is mostly due to the semidiurnal tide. The monthly mean tide is strongest from April to September with a mean amplitude of 6.9K for OH, and of 10.5K for O2 rotational temperature, but the contribution to the East-West effect varies strongly from month to month because of differences in the temporal sampling. This mechanism should be active at other sites, as well.

Evidence of a geomagnetic effect on extensive air showers detected with the ARGO-YBJ experiment

The geomagnetic field causes not only the east-west effect on primary cosmic rays but also affects the trajectories of the secondary charged particles in the shower, causing their lateral distribution to be stretched. Thus, both the density of the secondaries near the shower axis and the trigger efficiency of detector arrays decrease. The effect depends on the direction of the showers, thus, introducing a modulation in the measured azimuthal distribution. The azimuthal distribution of the events collected by the ARGO-YBJ detector is deeply investigated for different zenith angles in light of this effect.

Measurement of the deflection of cosmic-ray electrons in the energy range 75–250 GeV by the Earth’s magnetic field with the PAMELA experiment

The deflection of electrons in the Earth’s magnetic field in the energy range 75–250 GeV (the so-called east-west effect) has been measured with the PAMELA satellite-borne experiment. The results are presented for various L-shells. The data obtained can be used to construct mathematical models that describe the structure of the Earth’s magnetic field and to refine the already existing models. These data can also be directly applied to estimate the positron fraction in cosmic-ray electron fluxes both in the PAMELA experiment and in other satellite-borne experiments.

Evidence of geomagnetic effect on the azimuthal distribution of extensive air showers

The geomagnetic field causes not only the East-West effect on the primary cosmic rays but also affects the trajectories of the secondary charged particles in the shower, causing their lateral distribution to be stretched. Thus both the density of the secondaries near the shower axis and the trigger efficiency of detector arrays decrease. The effect depends on the direction of the showers, thus involving the measured azimuthal distribution. The non-uniformity of the azimuthal distribution of the events collected by the ARGO-YBJ detector is deeply investigated for different zenith angles in the light of this effect.

Study of atmospheric muons using a cosmic ray telescope

The charge ratio of cosmic muons holds important information for both the atmospheric neutrino anomaly and hadronic interaction models. In this paper we measured the muon charge ratio () in the cosmic ray flux in the momenta range 0.76–1.60 GeV/c by using a cosmic ray telescope. The delayed coincidence method is used based on the reduced mean lifetime of negative muons due to nuclear capture in matter. The systematic time-dependent effects of the muon charge ratio are considered by grouping the decay data into different time intervals. We compared the experimental data with the predictions of CORSIKA simulations using a high energy interaction model (QGSJET-II) and two low energy interaction models (UrQMD and GHEISHA) in the energy range 1011–1016 eV for primary particles. In addition, by considering the muon flux in different zenithal and azimuthal angles, the muon angular distribution is obtained as I(θ) = I(0)cos nθ with average n = 1.91 ± 0.07. Dependence of the muon flux on the azimuth angle (the East–West effect) is also observed, due to the influence of the geomagnetic field in particular on low energy muons.

Ultra-high energy cosmic rays: Setting the stage

The history of ultra-high energy cosmic ray physics is reviewed from the post-war era of arrays such as Volcano Ranch, Haverah Park and Akeno to the development of air-fluorescence and current hybrid arrays. The aim of this paper is to present the background information needed for a better understanding of the current issues in this field that are discussed in much greater depth in the rest of this conference. a. Pre-history: the discovery of cosmic radiation and the study of its penetrating power. This led to great debates between Millikan and Compton about the kinds of particles that composed it. The discovery of the latitude effect followed by the East-West effect conclusively proved that the majority of the cosmic ray particles were positively charged (protons and nuclei). b. Ancient history: the discovery that high energy cosmic radiation produced extensive air showers and that much of the cosmic radiation on the surface was the result of secondary processes in the atmosphere. This was also the era when the presence of very high energy particles in the primary radiation was clearly demonstrated (by B. Rossi, P. Auger and others). c. Middle Ages: the post-war development of large area surface detectors covering areas up to 10km 2 coming from the pioneering work of B. Rossi., J. Linsley and others. d. Renaissance: the development of fully calorimetric techniques based on air-fluorescence (by the Fly's Eye group, based on earlier work of J. Keuffel, K. Greisen and others) and the extension of ground arrays to 100km 2 (AGASA). e. Modern times: the refinement of air-fluorescence techniques (HiRes) and the construction of hybrid air-fluorescence/surface array detectors of unprecedented scale (Pierre Auger Observatory (PAO), Telescope Array (TA)). 2. POST-WAR DEVELOPMENTS

Effects of longitudinal range-gorge terrain on the eco-geographical pattern in Southwest China

China’s southwestern special terrain pattern as parallel arrangement between longitudinal towering mountains and deep valleys has significant effects on the differentiation of local natural environment and eco-geographical pattern in this region. The 1:50,000 Digital Elevation Model (DEM) data of Longitudinal Range-Gorge Region (LRGR), meteorological observation data from the station establishment to 2010, hydrological observation data, Normalized Difference Vegetation Index (NDVI) and Net Primary Productivity (NPP) products of MOD13 and MOD17 as well as 1:1,000,000 vegetation type data were used. Moisture indices including surface atmospheric vapor content, precipitation, aridity/humidity index, surface runoff, and temperature indices including average temperature, annual accumulated temperature, total solar radiation were selected. Based on ANUSPLIN spline function, GIS spatial analysis, wavelet analysis and landscape pattern analysis, regional differentiation characteristics and main-control factors of hydrothermal pattern, ecosystem structure and function in this region were analyzed to reveal the effects of terrain pattern on regional differentiation of eco-geographical elements. The results show that: influenced by terrain pattern, moisture, temperature and heat in LRGR have shown significant distribution characteristics as intermittent weft differences and continuous warp extension. Longitudinal mountains and valleys not only have a north-south corridor function and diffusion effect on the transfer of major surface materials and energy, but also have east-west barrier function and blocking effect. Special topographic pattern has important influences on vegetation landscape diversity and spatial pattern of ecosystem structure and function, which is the main-control factor on vegetation landscape diversity and spatial distribution of ecosystem. Wavelet variance analysis reflects the spatial anisotropy of environmental factors, NDVI and NPP, while wavelet consistency analysis reveals the control factors on spatial distribution of NDVI and NPP as well as the quantitative relationship with control degree. Special terrain pattern in LRGR is the major influencing factor on eco-geographical regional differentiation in this region. Under the combined effect of zonality and non-zonality laws with “corridor-barrier” function as the main characteristic, special spatial characteristics of eco-geographical regional system in LRGR is formed.

Azimuthal angular dependence study of the atmospheric muon charge ratio at sea level using Geant4

The azimuth dependence of the cosmic muon charge ratio at sea level was estimated using the Geant4 simulation package. Simulations were separately run at 12 azimuth angles ranging from 0° to 330° with 30° increment. Two hundred thousand proton and alpha particles were randomly distributed over the zenith angle range 30° < θ < 40° at each azimuth angle. The kinetic energy spectra of proton and helium nuclei were taken from the balloon-flight measurements. The atmospheric muon charge ratio was calculated at each azimuthal angle for low energy muons with a mean momentum around 0.5 GeV/c. The Geant4 simulation results have been compared with those of the CORSIKA simulation program and with the WILLI measurements. The simulation results reproduce well the measured east–west effect with a non-zero asymmetry AEW = 0.24. This asymmetry in the charge ratio decreases from 0.37 to 0.19 as the momentum increases from 0.22 to 0.70 GeV/c.

Gravity Probe B Data Analysis

This is the first of five connected papers detailing progress on the Gravity Probe B (GP-B) Relativity Mission. GP-B, launched 20 April 2004, is a landmark physics experiment in space to test two fundamental predictions of Einstein’s general relativity theory, the geodetic and frame-dragging effects, by means of cryogenic gyroscopes in Earth orbit. Data collection began 28 August 2004 and science operations were completed 29 September 2005. The data analysis has proven deeper than expected as a result of two mutually reinforcing complications in gyroscope performance: (1) a changing polhode path affecting the calibration of the gyroscope scale factor C g against the aberration of starlight and (2) two larger than expected manifestations of a Newtonian gyro torque due to patch potentials on the rotor and housing. In earlier papers, we reported two methods, ‘geometric’ and ‘algebraic’, for identifying and removing the first Newtonian effect (‘misalignment torque’), and also a preliminary method of treating the second (‘roll-polhode resonance torque’). Central to the progress in both torque modeling and C g determination has been an extended effort on “Trapped Flux Mapping” commenced in November 2006. A turning point came in August 2008 when it became possible to include a detailed history of the resonance torques into the computation. The East-West (frame-dragging) effect is now plainly visible in the processed data. The current statistical uncertainty from an analysis of 155 days of data is 5.4 marc-s/yr (∼14% of the predicted effect), though it must be emphasized that this is a preliminary result requiring rigorous investigation of systematics by methods discussed in the accompanying paper by Muhlfelder et al. A covariance analysis incorporating models of the patch effect torques indicates that a 3–5% determination of frame-dragging is possible with more complete, computationally intensive data analysis.

WILLI – a scintillator detector setup for studies of the zenith and azimuth variation of charge ratio and flux of atmospheric muons

The primary and secondary components of the cosmic radiation are influenced by the geomagnetic field. This leads - in addition to the variation with the zenith angle - to an azimuth dependence, in particular of the ratio of positive and negative muons, pronounced as East-West effect of muon charge ratio for low energy muons. The compact scintillator detector arrangement, WILLI, able to register incident muons with different azimuth and zenith angles ( E 1 G e V ), has been used to study the azimuth dependence of the muon charge ratio. Positive and negative muons are discriminated by observing the different lifetimes when being stopped in matter, in the WILLI case by Al absorbers. We are considering the development of a mini array, installed close to the WILLI detector, for triggering the muon charge ratio measurements in extended air shower events.

Proton Flux Anisotropy in Low Earth Orbit

Proton flux anisotropy as a function of altitude in the South Atlantic Anomaly is investigated using data from the Compact Environment Anomaly Sensor (CEASE) flown onboard the tri-service experiment-5 (TSX-5) satellite from June 2000 to July 2006. In a 410 km times 1710 km, 69 degree inclination orbit, TSX-5 spanned a broad range of the low Earth orbit regime. Using measurements of total dose, integral energy flux >40 MeV and the differential flux at 40 MeV sorted into 3 degree latitude times 3 degree longitude times 50 km altitide bins and averaged over the entire mission, the components arising from eastward and westward traveling protons have been determined in areas of the SAA where CEASE detection efficiency is not compromised. For the first time, ratios of these components have been compared to predictions of east-west effect models above 400 km. There is good agreement in general with the anisotropy becoming apparent at approximately 1200 km (moving down) and increasing rapidly starting at approximately 1000 km, the magnitude and rate depending on location within the anomaly. Measurements of the differential flux at 40 MeV are compared to predictions of standard radiation belt models as a function of altitude and found to be substantially higher in magnitude than AP8, though a comprehensive survey has not yet been performed.

Low energy muons in the cosmic radiation

A review of measurements of the muon energy spectra for different altitudes, height and directions performed with devices placed at various geomagnetic latitudes is presented. The muon spectra and the muon charge ratio, defined as the ratio of positive to negative muon fluxes, are analysed taking into account the geomagnetic field, in view of the East-West effect. Fluxes of both positive and negative muons are analysed.

The East-West effect of the muon charge ratio at energies relevant to the atmospheric neutrino anomaly

The charge ratio of atmospheric muons is rather sensitive to effects of the geomagnetic field and to the hadronic interaction. Experimental information about this quantity is very useful for tuning the ingredients of models used for calculations of atmospheric neutrino fluxes. For experimental observations, and in particular regarding the asymmetry in the charge ratio of muons from the east and West directions (East-West effect) a rotatable device has been installed in NIPNE-HH (National Institute of Physics and Nuclear Engineering — Horia Hulubei) Bucharest (44° 26'N, 26° 04' E, 85 m above sea-level at a vertical cut-off rigidity of 5.6 GV). The detector is mounted in a rotatable frame, consisting of a stack of 16 modules, 90 × 90 cm 2, formed by plastic scintillator layers (3 cm thick) and aluminum support (1.2 cm thick), surrounded by 4 lateral veto counters. The measurements are based on observation of the life time of muons stopped in the absorber layers of the detector. At a mean zenith angle of 35° the East West asymmetry in the ratio has been found to decrease from 0.25 to 0.20, in the momentum range 0.35 – 0.50 GeV/c.

Secondary electrons and positrons in near earth orbit

The secondary e + and e − populations in near earth's orbit have been calculated by simulation. The results are in very good agreement with the recent AMS measurements. The e + over e − flux ratio for particles below the geomagnetic cutoff appears to be due to the geomagnetic East–West effect.

Cosmic ray survey to Antarctica and coupling functions for neutron component near solar minimum (1996–1997): 1. Methodology and data quality assurance

During the 1996–1997 austral summer, a 3NM‐64 neutron monitor was operated on board the ship Italica to record cosmic ray neutron intensities in ocean areas from Italy to Antarctica and back. Two bare BF3 counters also measured the flux of thermalized neutrons. The main purpose of this research was the determination of an accurate latitude curve of cosmic ray nucleonic intensity during solar minimum to be used for obtaining the coupling function appropriate for this phase of solar cycle. Accuracy was achieved through reliable instrumentation and proper control of the experiment and by determining and applying for the first time all corrections, for (1) changes in vertical atmospheric mass column, by taking into account wind effect; (2) oscillations of the ship produced by sea roughness; (3) atmospheric temperature changes; (4) primary cosmic ray temporal variations including north–south asymmetry; and (5) temporal variations in the cosmic ray east–west effect, caused by asymmetric shielding on the ship. In this paper we describe the experiment, present the complex procedure of data reduction which was required for the survey data, evaluate the intensity changes produced by primary cosmic ray temporal variations, correct the data for meteorological effects, and present the “fully corrected” daily values of neutron intensity as a function of threshold rigidity. Several independent tests are applied to evaluate the quality of the “fully corrected” data and to determine their residual statistical uncertainty. In two companion papers, all meteorological effects are investigated in detail, geomagnetic effects are evaluated, and coupling functions are computed.

The east–west effect for atmospheric neutrinos

The atmospheric neutrino fluxes observed by underground detectors are not symmetric under rotations around the vertical axis. The flux is largest (smallest) for the ν's traveling toward east (west). This asymmetry is the result of the effects of the geomagnetic field on the primary cosmic rays and on their showers. The size of the asymmetry is to a good approximation independent of the existence of neutrino oscillations and can, in principle, be predicted without any ambiguity due to the existence of unknown new physics. We show that there is an interesting hint of discrepancy between the experimental measurement of the east–west asymmetry by Super-Kamiokande and the existing theoretical predictions. We argue that the discrepancy is a real effect caused by the neglect, in the existing calculations, of the bending of the charged secondary particles (particularly muons) in the cosmic ray showers. The inclusion of this effect in the calculation gives results in quantitative agreement with the data. We comment on the implications of this result for the study of neutrino oscillations.

Measurements of muons at sea level

We measure muon intensities at sea level by using the OKAYAMA cosmic-ray telescope in detail. Measured muons are also contained in the low-momentum region where they are strongly affected by geomagnetic field effects including the east-west effect. We report the zenith and azimuthal angular dependence of conventional muons in the momentum range 1.5-250 GeV/c in the zenith angular range .

REM measurements aboard Mir during 1995

Measurements of the South Atlantic Anomaly (SAA) made with the Radiation Environment Monitor (REM) aboard Mir from November 1994 to February 1996 are presented. During this period an increase of the SAA radiation by ≈25% is observed, which coincides with a lowering of the radio solar flux. Radio solar flux is one of the parameters controlling the earth's atmospheric distribution and with it the absorption of inner radiation belt protons forming the SAA. Due to the altitude gradient of the atmospheric density, the proton fluxes in the SAA are anisotropic (loss cone, east-west effect). The measured distribution can be accounted for by basic models.

Engineering tool for trapped proton flux anisotropy evaluation

At low altitudes, the high-energy trapped proton fluxes are strongly anisotropic. The proton flux is controlled by the density distribution of the Earth's atmosphere that induces a steep pitch-angle distribution and an East-West effect, the latter caused by the finite size of the proton gyration radius. We have developed a software package, ANISO, to evaluate averaged energy spectra of trapped proton unidirectional fluxes for a given spacecraft orbit and attitude by deducing the angular-dependent proton flux spectra from the AP-8 omnidirectional flux. Included in the model are both the Armstrong et al. (1990) model and a model based on the Badhwar and Konradi (1990) pitch-angle distribution.