arXiv subjects
Publications and source records attributed to Francis Halzen.
We demonstrate that atmospheric neutrino data accumulated with the AMANDA and the partially deployed IceCube experiments constrain the allowed parameter space for a hypothesized fourth sterile neutrino beyond the reach of a combined analysis of all other experiments. We also illustrate the sensitivity of the completed IceCube detector, that is now taking data, to the parameter space of 3+1 model.
Active galactic nuclei (AGN) are believed to be the source of ultra high energy cosmic rays (UHECRs). Particles are assumed to be accelerated in the accretion disk and the plasma jets, produced due to conservation of angular momentum, to the highest energies, where they interact with each other and produce pions, which decay among others in neutrinos. For a known cosmic ray spectral behavior, the main parameters in the calcula- tion of the neutrino flux from proton-proton interactions are the target density nH and the ratio of electrons to protons fe . Using most recent neutrino flux limits from IceCube point source searches, we set limits on the target densities for 33 FR-I galaxies. The densities are shown to be smaller than 30 cm^{-3} to 2000 cm^{-3}, depending on the source and when using a fixed electron to proton ratio of f_{e} = 0.1. This implies that some cosmic ray acceleration sites, espe- cially those close to the core of the AGN, can already be excluded, or else that the ratio of electrons to protons deviates significantly from the commonly used value of 0.1. For Centaurus A (Cen A) and Messier 87 (M 87) we use Fermi observations to model the γ-flux, the neutrino flux and the resulting target density. The detec- tion of these neutrinos will help to find information about acceleration processes in the source.
This Commentary on the paper "Total Hadronic Cross Section Data and the Froissart-Martin Bound", by Fagundes, Menon and Silva, to be published in Braz. J. of Phys., Vol. 42 (2012) (arXiv 1112.4704), was invited by the Editors of the Brazilian Journal of Physics to appear directly after the above authors' printed version, in the same journal issue. We here challenge that paper's conclusions that the Froissart bound was violated. We will show that this conclusion follows from a statistical methodology that we question, and will present compelling supplementary evidence that the latest ultra-high energy experimental $pp$ cross section data are consistent with a $\ln^2 s$ behavior that satisfies the Froissart bound.
The observed flux of ultra-high energy (UHE) cosmic rays (CRs) guarantees the presence of high-energy cosmogenic neutrinos that are produced via photo-hadronic interactions of CRs propagating through intergalactic space. This flux of neutrinos doesn't share the many uncertainties associated with the environment of the yet unknown CR sources. Cosmogenic neutrinos have nevertheless a strong model dependence associated with the chemical composition, source distribution or evolution and maximal injection energy of UHE CRs. We discuss a lower limit on the cosmogenic neutrino spectrum which depends on the observed UHE CR spectrum and composition and relates directly to experimentally observable and model-independent quantities. We show explicit limits for conservative assumptions about the source evolution.
Recently, the Auger group has extracted the proton-air cross section from observations of air showers produced by cosmic ray protons (and nuclei) interacting in the atmosphere and converted it into measurements of the total and inelastic $pp$ cross sections $σ_{\rm tot}$ and $σ_{\rm inel}$ at the super-LHC energy of 57 TeV. Their results reinforce our earlier conclusions that the proton becomes a black disk at asymptotic energies, a prediction reached on the basis of sub-LHC $\pbar p$ and $pp$ measurements of $σ_{\rm tot}$ and $ρ$, the ratio of the real to the imaginary part of the forward scattering amplitude [M. M. Block and F. Halzen, Phys. Rev. Lett. {\bf 107}, 212002 (2011)]. The same black disk description of the proton anticipated the values of $σ_{\rm tot}$ and $σ_{\rm inel}$ measured by the TOTEM experiment at the LHC cms (center of mass) energy of $\sqrt s=7$ TeV, as well as those of $σ_{\rm inel}$ measured by ALICE, ATLAS and CMS, as well as the ALICE measurement at 2.76 TeV. All data are consistent with a proton that is asymptotically a black disk of gluons: (i) both $σ_{\rm tot}$ and $σ_{\rm inel}$ behave as $\ln^2s$, saturating the Froissart bound, (ii) the forward scattering amplitude becomes pure imaginary (iii) the ratio $σ_{\rm inel}/σ_{\rm tot}=0.509 \pm 0.021$, compatible with the black disk value of 1/2, and (iv) proton interactions become flavor blind.
The Large Hadron Collider (LHC) recently started operating at 8 TeV. In this note, we update our earlier LHC forward hadronic scattering predictions \cite{physicsreports,update7, blackdisk}, giving new predictions, including errors, for the $pp$ total and inelastic cross sections, the $ρ$-value, the nuclear slope parameter $B$, $dσ_{\rm el}/dt$, and the large gap survival probability at 8 TeV.
Recent measurements of the inelastic and total proton-proton cross section at the LHC, and at cosmic ray energies by the Auger experiment, have quantitatively confirmed fits to lower energy data constrained by the assumption that the proton is asymptotically a black disk of gluons. We show that data on \bar p(p)p,π^\mp p, and K^\mp p forward scattering support the related expectation that the asymptotic behavior of all cross sections is flavor independent. By using the most recent measurements from ATLAS, CMS, TOTEM and Auger, we predict σ^{pp}_{\rm tot} (\sqrt s=8 {\rm TeV})=100.6 \pm 2.9 mb and σ^{pp}_{\rm tot} (\sqrt s=14 {\rm TeV})=110.8 \pm 3.5 mb, as well as refine the total cross section σ^{pp}_{\rm tot} (\sqrt s=57 {\rm TeV})=139.6 \pm 5.4 mb. Our analysis also predicts the total π^\mp π^+ cross sections as a function of \sqrt s.
High energy measurements of the inelastic proton-proton cross sections, at the LHC at $\sqrt s$=7 TeV and by Auger at 57 TeV, have validated previous evidence from data collected over a wide range of energies that the total and inelastic cross sections for $pp$ and $\bar pp$ interactions saturate the Froissart bound of $\ln^2 s$. Although the data themselves did not cover truly asymptotic energies, our recent analysis of these data obtained the asymptotic ratio $\sigin/\sigtot=0.509\pm 0.021$, consistent with the value of 1/2 required for scattering by a black disk; further, the forward scattering amplitude became purely imaginary for $s\rightarrow \infty$, confirming the black disk interpretation. In addition, the limiting black disk behavior has been independently confirmed by an analysis of Schegelsky and Ryskin including LHC data on the shrinkage of the slope of the forward elastic scattering cross section. Unless one considers these results, emerging from an analytic amplitude analysis of data over an energy range of $6\le \sqrt s\le 57000$ GeV, a complete numerical accident, we rule out any new physics thresholds that contribute higher powers of $\ln s$ or, worse, powers of $s$ to the energy dependence of cross sections {\it at any energy}. This includes theories with additional dimensions of space-time, whose existence is challenged.
Lecture notes for an introductory course in elementary particles.
Identifying the accelerators that produce the Galactic and extragalactic cosmic rays has been a priority mission of several generations of high energy gamma ray and neutrino telescopes; success has been elusive so far. Detecting the gamma-ray and neutrino fluxes associated with cosmic rays reaches a new watershed with the completion of IceCube, the first neutrino detector with sensitivity to the anticipated fluxes, and the construction of CTA, a ground-based gamma ray detector that will map and study candidate sources with unprecedented precision. In this paper, we revisit the prospects for revealing the sources of the cosmic rays by a multiwavelength approach; after reviewing the methods, we discuss supernova remnants, gamma ray bursts, active galaxies and GZK neutrinos in some detail.
Although the framework for oscillations of the three neutrino flavors in the Standard Model has been convincingly established, indications persist that it may be incomplete. Challenges are coming from the LSND and MiniBooNe short-baseline experiments, from the neutrino sources used in the Gallex and Sage solar neutrino experiments and, more recently,from an a-posteriori analysis of reactor neutrino experiments. One way to accommodate the reported "anomalies", if real, is to introduce one or more sterile neutrinos in the mass range $δm^2 \sim 1 eV^2$. TeV atmospheric neutrinos propagating through the Earth undergo resonant oscillations in the presence of sterile neutrinos; a clear signature in a neutrino telescope like IceCube is the the change in shape of the zenith-energy distribution of the atmospheric neutrinos.
Although experimentally accessible energies can not probe `asymptopia', recent measurements of` inelastic $pp$ cross sections at the LHC at 7000 GeV and by Auger at 57000 GeV allow us to conclude that: i) both $\sigin$ and $\sigtot$, the inelastic and total cross sections for $pp$ and $\bar p p$ interactions, saturate the Froissart bound of $\ln^2 s$, ii) when $s\rightarrow \infty$, the ratio $\sigin/\sigtot$ is experimentally determined to be $0.509\pm 0.021$, consistent with the value 0.5 required by black disk at infinite energies, and iii) when $s\rightarrow \infty$, the forward scattering amplitude becomes purely imaginary, another requirement for the proton to become a totally absorbing black disk. Experimental verification of the hypotheses of analyticity and unitarity over the center of mass energy range $6\le \sqrt s\le 57000$ GeV are discussed. In QCD, the black disk is naturally made of gluons; our results suggest that the lowest-lying glueball mass is $2.97\pm 0.03$ GeV.
The LHC has successfully run for a long period at half energy, 7 TeV. In this note, we update earlier full-energy Large Hadron Collider (LHC) forward hadronic scattering predictions \cite{physicsreports}, giving new predictions, including errors, for the $pp$ total and inelastic cross sections, the $ρ$-value, the nuclear slope parameter $B$, $dσ_{\rm el}/dt$, and the large gap survival probability at the current 7 TeV energy.
Despite their discovery potential touching a wide range of science, construction of TeV gamma-ray telescopes, Auger, IceCube and a suite of other particle astrophysics experiments has been largely motivated by the hunt for the sources of cosmic rays. I will assess the status of our search for the still-enigmatic sources of cosmic rays. Although a resolution is decidedly anticipated, the mystery of their origin remains unresolved.
Neutrino astronomy beyond the Sun was first imagined in the late 1950s; by the 1970s, it was realized that kilometer-scale neutrino detectors were required. The first such instrument, IceCube, is near completion and taking data. The IceCube project transforms a cubic kilometer of deep and ultra-transparent Antarctic ice into a particle detector. A total of 5,160 optical sensors are embedded into a gigaton of Antarctic ice to detect the Cherenkov light emitted by secondary particles produced when neutrinos interact with nuclei in the ice. Each optical sensor is a complete data acquisition system, including a phototube, digitization electronics, control and trigger systems and LEDs for calibration. The light patterns reveal the type (flavor) of neutrino interaction and the energy and direction of the neutrino, making neutrino astronomy possible. The scientific missions of IceCube include such varied tasks as the search for sources of cosmic rays, the observation of Galactic supernova explosions, the search for dark matter, and the study of the neutrinos themselves. These reach energies well beyond those produced with accelerator beams. The outline of this review is as follows: Neutrino Astronomy and Kilometer-Scale Detectors. High-Energy Neutrino Telescopes: Methodologies of Neutrino Detection. IceCube Hardware. High-Energy Neutrino Telescopes: Beyond Astronomy. Future Projects
Gamma-ray bursts have the potential to produce the particle energies (up to $10^{21}$\,eV) and the energy budget ($10^{44}\, \rm{erg\, yr^{-1}\, Mpc^{-3}}$) to accommodate the spectrum of the highest energy cosmic rays; on the other hand, there is no observational evidence that they accelerate hadrons. The Fermi GST recently observed two bursts that exhibit a power-law high-energy extension of the typical (Band) photon spectrum that extends to $\sim 30$ GeV. On the basis of fireball phenomenology we argue that they, along with GRB941017 observed by EGRET in 1994, show indirect evidence for considerable baryon loading. Since the detection of neutrinos is the only unambiguous way to establish that GRBs accelerate protons, we use two methods to estimate the neutrino flux produced when they interact with fireball photons to produce charged pions and neutrinos. While the number of events expected from the Fermi bursts detected to date is small, we conclude that an event like GRB941017 will be detected by the IceCube neutrino telescope if gamma-ray bursts are indeed the sources of the observed cosmic rays.
This is a brief report on the status of neutrino "astronomy" at a time when the kilometer-scale neutrino detector IceCube is approaching completion. We revisit the rationale for constructing gigantic neutrino detectors by transforming large volumes of natural ice and water into Cherenkov detectors. With time, the motivation for building such instruments has come into clear focus, and the requirement for their kilometer scale has been rationalized with improved accuracy. We will discuss the performance and some selected results of IceCube based on data taken during construction.
We revisit the prospects for IceCube and similar kilometer-scale telescopes to detect neutrinos produced by the annihilation of weakly interacting massive dark matter particles (WIMPs) in the Sun. We emphasize that the astrophysics of the problem is understood; models can be observed or, alternatively, ruled out. In searching for a WIMP with spin-independent interactions with ordinary matter, IceCube is only competitive with direct detection experiments if the WIMP mass is sufficiently large. For spin-dependent interactions IceCube already has improved the best limits on spin-dependent WIMP cross sections by two orders of magnitude. This is largely due to the fact that models with significant spin-dependent couplings to protons are the least constrained and, at the same time, the most promising because of the efficient capture of WIMPs in the Sun. We identify models where dark matter particles are beyond the reach of any planned direct detection experiments while being within reach of neutrino telescopes. In summary, we find that, even when contemplating recent direct detection results, neutrino telescopes have the opportunity to play an important as well as complementary role in the search for particle dark matter.