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Register a new userStudy of Ultra-High Energy Cosmic Ray Composition Using Telescope Arrays Middle Drum Detector and Surface Array in Hybrid Mode
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Previous measurements of the composition of Ultra-High Energy Cosmic Rays(UHECRs) made by the High Resolution Flys Eye(HiRes) and Pierre Auger Observatory(PAO) are seemingly contradictory, but utilize different detection methods, as HiRes was a stereo detector and PAO is a hybrid detector. The five year Telescope Array(TA) Middle Drum hybrid composition measurement is similar in some, but not all, respects in methodology to PAO, and good agreement is evident between data and a light, largely protonic, composition when comparing the measurements to predictions obtained with the QGSJetII-03 and QGSJet-01c models. These models are also in agreement with previous HiRes stereo measurements, confirming the equivalence of the stereo and hybrid methods. The data is incompatible with a pure iron composition, for all models examined, over the available range of energies. The elongation rate and mean values of Xmax are in good agreement with Pierre Auger Observatory data. This analysis is presented using two methods: data cuts using simple geometrical variables and a new pattern recognition technique.
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In this work we are reporting on the measurement of the proton-air inelastic cross section $sigma^{rm inel}_{rm p-air}$ using the Telescope Array (TA) detector. Based on the measurement of the $sigma^{rm inel}_{rm p-air}$ the proton-proton cross section $sigma_{rm p-p}$ value is also determined at $sqrt{s} = 95_{-8}^{+5}$ TeV. Detecting cosmic ray events at ultra high energies with Telescope Array enables us to study this fundamental parameter that we are otherwise unable to access with particle accelerators. The data used in this report is the hybrid events observed by the Middle Drum fluorescence detector together with the surface array detector collected over five years. The value of the $sigma^{rm inel}_{rm p-air}$ is found to be equal to $567.0 pm 70.5 [{rm Stat.}] ^{+29}_{-25} [{rm Sys.}]$ mb. The total proton-proton cross section is subsequently inferred from Glauber Formalism and Block, Halzen and Stanev QCD inspired fit and is found to be equal to $170_{-44}^{+48} [{rm Stat.}] _{-17}^{+19} [{rm Sys.}] $mb.
The results on ultra-high-energy cosmic rays (UHECR) mass composition obtained with the Telescope Array surface detector are presented. The analysis employs the boosted decision tree (BDT) multivariate analysis built upon 14 observables related to both the properties of the shower front and the lateral distribution function. The multivariate classifier is trained with Monte-Carlo sets of events induced by the primary protons and iron. An average atomic mass of UHECR is presented for energies $10^{18.0}-10^{20.0} mbox{eV}$. The average atomic mass of primary particles shows no significant energy dependence and corresponds to $langle ln A rangle = 2.0 pm 0.1 (stat.) pm 0.44 (syst.)$. The result is compared to the mass composition obtained by the Telescope Array with $mbox{X}_{mbox{max}}$ technique along with the results of other experiments. Possible systematic errors of the method are discussed.
The Telescope Array (TA) experiment is located in the western desert of Utah, USA, and observes ultra high energy cosmic rays (UHECRs) in the Northern hemisphere. At the highest energies, $E>10$~EeV, the shape of cosmic ray energy spectrum may carry an imprint of the source density distribution along the line of sight different in different directions of the sky. In this study, we search for such directional variations in the shape of the energy spectrum using events observed with the Telescope Arrays surface detector. We divide the TA field of view into two nearly equal-exposure regions: the on-source region which we define as $pm 30^circ$ of the supergalactic plane containing mostly nearby structures, and the complementary off-source region where the sources are further away on average. We compare the UHECR spectra in these regions by fitting them to the broken power law and comparing the resulting parameters. We find that the off-source spectrum has an earlier break at highest energies. The chance probability to obtain such or larger difference in statistically equivalent distributions is estimated as $6.2pm1.1times10^{-4}$ ($3.2sigma$) by a Monte-Carlo simulation. The observed difference in spectra is in a reasonable quantitative agreement with a simplified model that assumes that the UHECR sources trace the galaxy distribution from the 2MRS catalogue, primary particles are protons and the magnetic deflections can be neglected.
We present a measurement of the energy spectrum of ultra-high-energy cosmic rays performed by the Telescope Array experiment using monocular observations from its two new FADC-based fluorescence detectors. After a short description of the experiment, we describe the data analysis and event reconstruction procedures. Since the aperture of the experiment must be calculated by Monte Carlo simulation, we describe this calculation and the comparisons of simulated and real data used to verify the validity of the aperture calculation. Finally, we present the energy spectrum calculated from the merged monocular data sets of the two FADC-based detectors, and also the combination of this merged spectrum with an independent, previously published monocular spectrum measurement performed by Telescope Arrays third fluorescence detector (Abu-Zayyad {it et al.}, {Astropart. Phys.} 39 (2012), 109). This combined spectrum corroborates the recently published Telescope Array surface detector spectrum (Abu-Zayyad {it et al.}, {Astrophys. Journ.} 768 (2013), L1) with independent systematic uncertainties.
We measure the spectrum of cosmic rays with energies greater than $10^{18.2}$ eV with the Fluorescence Detectors (FDs) and the Surface Detectors (SDs) of the Telescope Array Experiment using the data taken in our first 2.3-year observation from May 27 2008 to September 7 2010. A hybrid air shower reconstruction technique is employed to improve accuracies in determination of arrival directions and primary energies of cosmic rays using both FD and SD data. The energy spectrum presented here is in agreement with our previously published spectra and the HiRes results.
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