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Browsing Chemistry and Physics publications by Author "Abbasi, R."
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Item Metadata only All-particle cosmic ray energy spectrum measured with 26 IceTop stations(Elsevier Science BV, 2013) Abbasi, R.; Hill, G.We report on a measurement of the cosmic ray energy spectrum with the IceTop air shower array, the surface component of the IceCube Neutrino Observatory at the South Pole. The data used in this analysis were taken between June and October, 2007, with 26 surface stations operational at that time, corresponding to about one third of the final array. The fiducial area used in this analysis was 0.122 km2. The analysis investigated the energy spectrum from 1 to 100 PeV measured for three different zenith angle ranges between 0° and 46°. Because of the isotropy of cosmic rays in this energy range the spectra from all zenith angle intervals have to agree. The cosmic-ray energy spectrum was determined under different assumptions on the primary mass composition. Good agreement of spectra in the three zenith angle ranges was found for the assumption of pure proton and a simple two-component model. For zenith angles θ < 30°, where the mass dependence is smallest, the knee in the cosmic ray energy spectrum was observed at about 4 PeV, with a spectral index above the knee of about -3.1. Moreover, an indication of a flattening of the spectrum above 22 PeV was observed. © 2013 Elsevier B.V. All rights reserved.Item Metadata only An alternative method to finding patterns in HiRes stereo data(Elsevier, 2007) Abbasi, R.; Abu-Zayyad, T.; Amman, J. F.; Archbold, G. C.; Belov, K.; Blake, S. A.; Belz, J. W.; BenZvi, S.; Bergman, D. R.; Boyer, J. H.; Burt, G. W.; Cao, Z.; Connolly, B.M.; Deng, W.; School of Chemistry and PhysicsItem Metadata only An improved method for measuring muon energy using the truncated mean of dE/dx(Elsevier Science BV, 2013) Abbasi, R.; Hill, G.The measurement of muon energy is critical for many analyses in large Cherenkov detectors, particularly those that involve separating extraterrestrial neutrinos from the atmospheric neutrino background. Muon energy has traditionally been determined by measuring the specific energy loss (dE/dx) along the muon's path and relating the dE/dx to the muon energy. Because high-energy muons (Eμ>1TeV) lose energy randomly, the spread in dE/dx values is quite large, leading to a typical energy resolution of 0.29 in log10(Eμ) for a muon observed over a 1 km path length in the IceCube detector. In this paper, we present an improved method that uses a truncated mean and other techniques to determine the muon energy. The muon track is divided into separate segments with individual dE/dx values. The elimination of segments with the highest dE/dx results in an overall dE/dx that is more closely correlated to the muon energy. This method results in an energy resolution of 0.22 in log10(Eμ), which gives a 26% improvement. This technique is applicable to any large water or ice detector and potentially to large scintillator or liquid argon detectors. © 2012 Elsevier B.V.Item Metadata only Background studies for acoustic neutrino detection at the South Pole(Elsevier Science BV, 2012) Abbasi, R.; Hill, G.The detection of acoustic signals from ultra-high energy neutrino interactions is a promising method to measure the flux of cosmogenic neutrinos expected on Earth. The energy threshold for this process depends strongly on the absolute noise level in the target material. The South Pole Acoustic Test Setup (SPATS), deployed in the upper part of four boreholes of the IceCube Neutrino Observatory, has monitored the noise in Antarctic ice at the geographic South Pole for more than two years down to 500 m depth. The noise is very stable and Gaussian distributed. Lacking an in situ calibration up to now, laboratory measurements have been used to estimate the absolute noise level in the 10-50 kHz frequency range to be smaller than 20 mPa. Using a threshold trigger, sensors of the South Pole Acoustic Test Setup registered acoustic events in the IceCube detector volume and its vicinity. Acoustic signals from refreezing IceCube holes and from anthropogenic sources have been used to test the localization of acoustic events. An upper limit on the neutrino flux at energies Eν > 1011 GeV is derived from acoustic data taken over eight months. © 2011 Elsevier B.V. All rights reserved.Item Metadata only Calibration and characterization of the IceCube photomultiplier(Elsevier Science BV, 2010) Abbasi, R.; Hill, G.Over 5000 PMTs are being deployed at the South Pole to compose the IceCube neutrino observatory. Many are placed deep in the ice to detect Cherenkov light emitted by the products of high-energy neutrino interactions, and others are frozen into tanks on the surface to detect particles from atmospheric cosmic ray showers. IceCube is using the 10-in. diameter R7081-02 made by Hamamatsu Photonics. This paper describes the laboratory characterization and calibration of these PMTs before deployment. PMTs were illuminated with pulses ranging from single photons to saturation level. Parameterizations are given for the single photoelectron charge spectrum and the saturation behavior. Time resolution, late pulses and afterpulses are characterized. Because the PMTs are relatively large, the cathode sensitivity uniformity was measured. The absolute photon detection efficiency was calibrated using Rayleigh-scattered photons from a nitrogen laser. Measured characteristics are discussed in the context of their relevance to IceCube event reconstruction and simulation efforts. © 2010 Elsevier B.V.Item Open Access Constraints on the extremely-high energy cosmic neutrino flux with the IceCube 2008-2009 data(American Physical Soc, 2011) Abbasi, R.; Hill, G.We report on a search for extremely-high energy neutrinos with energies greater than 106GeV using the data taken with the IceCube detector at the South Pole. The data was collected between April 2008 and May 2009 with the half-completed IceCube array. The absence of signal candidate events in the sample of 333.5 days of live time significantly improves model-independent limits from previous searches and allows to place a limit on the diffuse flux of cosmic neutrinos with an E-2 spectrum in the energy range 2.0×106-6.3×109GeV to a level of E2φ≤3.6×10 -8GeVcm-2sec-1sr-1. © 2011 American Physical Society.Item Metadata only Cosmic ray composition and energy spectrum from 1-30 PeV using the 40-string configuration of IceTop and IceCube(Elsevier Science BV, 2013) Abbasi, R.; Hill, G.The mass composition of high energy cosmic rays depends on their production, acceleration, and propagation. The study of cosmic ray composition can therefore reveal hints of the origin of these particles. At the South Pole, the IceCube Neutrino Observatory is capable of measuring two components of cosmic ray air showers in coincidence: the electromagnetic component at high altitude (2835 m) using the IceTop surface array, and the muonic component above ∼1 TeV using the IceCube array. This unique detector arrangement provides an opportunity for precision measurements of the cosmic ray energy spectrum and composition in the region of the knee and beyond. We present the results of a neural network analysis technique to study the cosmic ray composition and the energy spectrum from 1 PeV to 30 PeV using data recorded using the 40-string/40-station configuration of the IceCube Neutrino Observatory. © 2012 Published by Elsevier B.V.Item Open Access Determination of the atmospheric neutrino flux and searches for new physics with AMANDA-II(American Physical Soc, 2009) Abbasi, R.; Hill, G.The AMANDA-II detector, operating since 2000 in the deep ice at the geographic South Pole, has accumulated a large sample of atmospheric muon neutrinos in the 100 GeV to 10 TeV energy range. The zenith angle and energy distribution of these events can be used to search for various phenomenological signatures of quantum gravity in the neutrino sector, such as violation of Lorentz invariance or quantum decoherence. Analyzing a set of 5511 candidate neutrino events collected during 1387 days of livetime from 2000 to 2006, we find no evidence for such effects and set upper limits on violation of Lorentz invariance and quantum decoherence parameters using a maximum likelihood method. Given the absence of evidence for new flavor-changing physics, we use the same methodology to determine the conventional atmospheric muon neutrino flux above 100 GeV.Item Metadata only Energy reconstruction methods in the IceCube neutrino telescope(IOP Publishing for Sissa Medialab, 2014) Aartsen, M.; Abbasi, R.; Ackermann, M.; Adams, J.; Aguilar, J.; Ahlers, M.; Altmann, D.; Arguelles, C.; Auffenberg, J.; Bai, X.; Baker, M.; Barwick, S.; Baum, V.; Bay, R.; Beatty, J.; Tjus, J.; Becker, K.; Benzvi, S.; Berghaus, P.; Berley, D.; et al.Accurate measurement of neutrino energies is essential to many of the scientific goals of large-volume neutrino telescopes. The fundamental observable in such detectors is the Cherenkov light produced by the transit through a medium of charged particles created in neutrino interactions. The amount of light emitted is proportional to the deposited energy, which is approximately equal to the neutrino energy for ne and nm charged-current interactions and can be used to set a lower bound on neutrino energies and to measure neutrino spectra statistically in other channels. Here we describe methods and performance of reconstructing charged-particle energies and topologies from the observed Cherenkov light yield, including techniques to measure the energies of uncontained muon tracks, achieving average uncertainties in electromagnetic-equivalent deposited energy of 15% above 10 TeV.Item Open Access Extending the search for neutrino point sources with iceCube above the horizon(American Physical Soc, 2009) Abbasi, R.; Hill, G.Point source searches with the IceCube neutrino telescope have been restricted to one hemisphere, due to the exclusive selection of upward going events as a way of rejecting the atmospheric muon background. We show that the region above the horizon can be included by suppressing the background through energy-sensitive cuts. This improves the sensitivity above PeV energies, previously not accessible for declinations of more than a few degrees below the horizon due to the absorption of neutrinos in Earth. We present results based on data collected with 22 strings of IceCube, extending its field of view and energy reach for point source searches. No significant excess above the atmospheric background is observed in a sky scan and in tests of source candidates. Upper limits are reported, which for the first time cover point sources in the southern sky up to EeV energies.Item Metadata only First neutrino point-source results from the 22 string IceCube detector(Institute of Physics Publishing Ltd., 2009) Abbasi, R.; Hill, G.We present new results of searches for neutrino point sources in the northern sky, using data recorded in 2007–2008 with 22 strings of the IceCube detector (approximately one-fourth of the planned total) and 275.7 days of live time. The final sample of 5114 neutrino candidate events agrees well with the expected background of atmospheric muon neutrinos and a small component of atmospheric muons.No evidence of a point source is found, with themost significant excess of events in the sky at 2.2σ after accounting for all trials. The average upper limit over the northern sky for point sources of muon–neutrinos with E⁻² spectrum is E² Φνμ < 1.4 × 10⁻¹¹ TeV cm⁻² s⁻¹, in the energy range from 3 TeV to 3 PeV, improving the previous best average upper limit by the AMANDA-II detector by a factor of 2.Item Open Access First search for extremely high energy cosmogenic neutrinos with the IceCube neutrino observatory(American Physical Soc, 2010) Abbasi, R.; Hill, G.We report on the results of the search for extremely-high energy neutrinos with energies above 107GeV obtained with the partially (∼30%) constructed IceCube in 2007. From the absence of signal events in the sample of 242.1 days of effective live time, we derive a 90% C.L. model independent differential upper limit based on the number of signal events per energy decade at E2νe+νμ+ντ1. 4×10⊃-6GeVcm⊃-2⊃sec⊃⊃-1sr⊃-1 for neutrinos in the energy range from 3×107 to 3×109GeV. © 2010 The American Physical Society.Item Metadata only IceCube search for dark matter annihilation in nearby galaxies and galaxy clusters(American Physical Society, 2013) Aartsen, M.; Abbasi, R.; Abdou, Y.; Ackermann, M.; Adams, J.; Aguilar, J.; Ahlers, M.; Altmann, D.; Auffenberg, J.; Bai, X.; Baker, M.; Barwick, S.; Baum, V.; Bay, R.; Beatty, J.; Bechet, S.; Becker Tjus, J.; Becker, K.-H.; Benabderrahmane, M.; BenZvi, S.; et al.We present the results of a first search for self-annihilating dark matter in nearby galaxies and galaxy clusters using a sample of high-energy neutrinos acquired in 339.8 days of live time during 2009/10 with the IceCube neutrino observatory in its 59-string configuration. The targets of interest include the Virgo and Coma galaxy clusters, the Andromeda galaxy, and several dwarf galaxies. We obtain upper limits on the cross section as a function of the weakly interacting massive particle mass between 300 GeV and 100 TeV for the annihilation into bb¯, W+W−, τ+τ−, μ+μ−, and νν¯. A limit derived for the Virgo cluster, when assuming a large effect from subhalos, challenges the weakly interacting massive particle interpretation of a recently observed GeV positron excess in cosmic rays.Item Open Access Lateral distribution of muons in IceCube cosmic ray events(American Physical Soc, 2013) Abbasi, R.; Hill, G.In cosmic ray air showers, the muon lateral separation from the center of the shower is a measure of the transverse momentum that the muon parent acquired in the cosmic ray interaction. IceCube has observed cosmic ray interactions that produce muons laterally separated by up to 400 m from the shower core, a factor of 6 larger distance than previous measurements. These muons originate in high p(T) (>2 GeV/c) interactions from the incident cosmic ray, or high-energy secondary interactions. The separation distribution shows a transition to a power law at large values, indicating the presence of a hard p(T) component that can be described by perturbative quantum chromodynamics. However, the rates and the zenith angle distributions of these events are not well reproduced with the cosmic ray models tested here, even those that include charm interactions. This discrepancy may be explained by a larger fraction of kaons and charmed particles than is currently incorporated in the simulations.Item Open Access Limits on a muon flux from neutralino annihilations in the sun with the IceCube 22-string detector(American Physical Soc, 2009) Abbasi, R.; Hill, G.A search for muon neutrinos from neutralino annihilations in the Sun has been performed with the IceCube 22-string neutrino detector using data collected in 104.3 days of live time in 2007. No excess over the expected atmospheric background has been observed. Upper limits have been obtained on the annihilation rate of captured neutralinos in the Sun and converted to limits on the weakly interacting massive particle (WIMP) proton cross sections for WIMP masses in the range 250–5000 GeV. These results are the most stringent limits to date on neutralino annihilation in the Sun.Item Open Access Limits on Neutrino emission from gamma-ray bursts with the 40 string IceCube detector(American Physical Soc, 2011) Abbasi, R.; Hill, G.IceCube has become the first neutrino telescope with a sensitivity below the TeV neutrino flux predicted from gamma-ray bursts if gamma-ray bursts are responsible for the observed cosmic-ray flux above 10¹⁸ eV. Two separate analyses using the half-complete IceCube detector, one a dedicated search for neutrinos from pγ interactions in the prompt phase of the gamma-ray burst fireball and the other a generic search for any neutrino emission from these sources over a wide range of energies and emission times, produced no evidence for neutrino emission, excluding prevailing models at 90% confidence.Item Metadata only Measurement of the anisotropy of cosmic-ray arrival directions with IceCube(Institute of Physics Publishing., 2010) Abbasi, R.; Hill, G.We report the first observation of an anisotropy in the arrival direction of cosmic rays with energies in the multi-TeV region in theSouthern sky using data from the IceCube detector. Between 2007 June and 2008 March, the partially deployed IceCube detector was operated in a configuration with 1320 digital optical sensors distributed over22 strings at depths between 1450 and 2450 m inside the Antarctic ice. IceCube is a neutrino detector, but the data are dominated by a large background of cosmic-ray muons. Therefore, the background data aresuitable for high-statistics studies of cosmic rays in the southern sky. The data include 4.3 billion muons produced by downward-going cosmic-ray interactions in the atmosphere; these events were reconstructed with a median angular resolution of 3° and a median energy of ∼20 TeV. Their arrival direction distribution exhibits an anisotropy in right ascension with a first-harmonic amplitude of (6.4±0.2 stat.±0.8 syst.) × 10-4. © 2010 The American Astronomical Society.Item Open Access Measurement of the atmospheric neutrino energy spectrum from 100 GeV to 400 TeV with IceCube(American Physical Soc, 2011) Abbasi, R.; Hill, G.A measurement of the atmospheric muon neutrino energy spectrum from 100 GeV to 400 TeV was performed using a data sample of about 18 000 up-going atmospheric muon neutrino events in IceCube. Boosted decision trees were used for event selection to reject misreconstructed atmospheric muons and obtain a sample of up-going muon neutrino events. Background contamination in the final event sample is less than 1%. This is the first measurement of atmospheric neutrinos up to 400 TeV, and is fundamental to understanding the impact of this neutrino background on astrophysical neutrino observations with IceCube. The measured spectrum is consistent with predictions for the atmospheric ν(sub)μ+ν̅(sub)μ flux.Item Metadata only Observation of the cosmic-ray shadow of the Moon with IceCube(American Physical Society, 2014) Aartsen, M.; Abbasi, R.; Abdou, Y.; Ackermann, M.; Adams, J.; Aguilar, J.; Ahlers, M.; Altmann, D.; Auffenberg, J.; Bai, X.; Baker, M.; Barwick, S.; Baum, V.; Bay, R.; Beatty, J.; Bechet, S.; Becker Tjus, J.; Becker, K.; Bell, M.; Benabderrahmane, M.; et al.We report on the observation of a significant deficit of cosmic rays from the direction of the Moon with the IceCube detector. The study of this “Moon shadow” is used to characterize the angular resolution and absolute pointing capabilities of the detector. The detection is based on data taken in two periods before the completion of the detector: between April 2008 and May 2009, when IceCube operated in a partial configuration with 40 detector strings deployed in the South Pole ice, and between May 2009 and May 2010 when the detector operated with 59 strings. Using two independent analysis methods, the Moon shadow has been observed to high significance (>6σ) in both detector configurations. The observed location of the shadow center is within 0.2° of its expected position when geomagnetic deflection effects are taken into account. This measurement validates the directional reconstruction capabilities of IceCube.Item Metadata only Probing the origin of cosmic rays with extremely high energy neutrinos using the IceCube Observatory(American Physical Society, 2013) Aartsen, M.; Abbasi, R.; Ackermann, M.; Adams, J.; Aguilar, J.; Ahlers, M.; Altmann, D.; Arguelles, C.; Auffenberg, J.; Bai, X.; Baker, M.; Barwick, S.; Baum, V.; Bay, R.; Beatty, J.; Becker Tjus, J.; Becker, K.; BenZvi, S.; Berghaus, P.; Berley, D.; et al.We have searched for extremely high energy neutrinos using data taken with the IceCube detector between May 2010 and May 2012. Two neutrino-induced particle shower events with energies around 1 PeV were observed, as reported previously. In this work, we investigate whether these events could originate from cosmogenic neutrinos produced in the interactions of ultrahigh energy cosmic rays with ambient photons while propagating through intergalactic space. Exploiting IceCube’s large exposure for extremely high energy neutrinos and the lack of observed events above 100 PeV, we can rule out the corresponding models at more than 90% confidence level. The model-independent quasidifferential 90% C.L. upper limit, which amounts to E2ϕνe+νμ+ντ=1.2×10−7 GeV cm−2 s−1 sr−1 at 1 EeV, provides the most stringent constraint in the energy range from 10 PeV to 10 EeV. Our observation disfavors strong cosmological evolution of the highest energy cosmic-ray sources such as the Fanaroff-Riley type II class of radio galaxies.