arXiv subjects
Publications and source records attributed to F. Halzen.
With an effective telescope area of order 10^4 m^2, a threshold of ~50 GeV and a pointing accuracy of 2.5 degrees, the AMANDA detector represents the first of a new generation of high energy neutrino telescopes, reaching a scale envisaged over 25 years ago. We describe its performance, focussing on the capability to detect halo dark matter particles via their annihilation into neutrinos.
The measurement of the inelastic photoproduction of charmonium at HERA seems to have ignited a new charmonium crisis. The (already discredited) color singlet model fits the data for large charmonium energy fraction z, where the NRQCD model qualitatively fails. We here point out that by the straightforward inclusion of color singlet and octet processes in the soft color (color evaporation) scheme, the HERA data can be accommodated for all z. We anticipate that the color singlet model will fail at low z, as it does in hadroproduction.
In this review we first address two questions: 1. Why do we need kilometer-scale muon and neutrino detectors? 2. What do we learn from the operating Baikal and AMANDA detectors about the construction of kilometer-scale detectors? I will subsequently discuss the challenges for building the next-generation detectors. The main message is that these are different, in fact less ominous, than for commissioning the present, relatively small, detectors which must reconstruct events far outside their instrumented volume in order to achieve large effective telescope area.
Using vector meson dominance we calculate the $γγ$ total cross section from data on $pp$, $p\bar p$ and $γp$ total cross sections. Our result agrees with recent high energy measurements performed by the L3 experiment at the LEP collider, not with the conflicting preliminary data obtained by OPAL.
The sources of $W + n$-jet events in hadron collisions are higher-order QCD processes, but also multiple-parton interactions. A subprocess producing a $W + k$-jet final state, followed by one producing $l$ jets in the same nucleon-nucleon interaction, will result in a $W + n$-jet event if $k + l = n$. In the simplest case a $W + 2$-jet event can be produced by a quark-antiquark annihilation into $W$ and a 2-jet event occurring in the same proton-antiproton interaction. We compute that this happens at the 10% level of the higher-order QCD processes for the type of cuts made by the Tevatron experiments. For jet $p_T$ values of order $5{\sim}10$ GeV, multiple-parton interactions dominate higher-order QCD-processes. The emergence of this new source of $W + n$-jet events towards lower $p_T $ simulates the running of $α_s$; it is imperative to remove these processes from the event sample in order to extract information on the strong coupling constant. Also, BFKL studies of low-$p_T$ jet cross sections are held hostage to a detailed understanding of the multiple-parton interactions. We perform the calculations required to achieve these goals. A detailed experimental analysis of the data may, for the first time, determine the effective areas occupied by quarks and gluons in the nucleon. These are not necessarily identical. We also compute the multiple-parton contribution to $Z + n$-jet events.
It has been argued that the observations of cosmic particles with energies in excess of $10^8$ TeV represent a puzzle. Its solution requires new astrophysics or new particle physics. We show that the latter is unlikely given that the scale associated with a new particle physics threshold must be of order 1 GeV, not TeV and above, in order to resolve the problem. In most cases such new physics should have been revealed by accelerator experiments. We examine the possibility that the highest energy cosmic rays are initiated by non-standard interactions of neutrinos in the atmosphere. We show that proposals in this direction either violate s-wave unitarity or fall short of producing a sizeable effect by several orders of magnitude.
Collider experiments have recently measured the production cross section of hard jets separated by a rapidity gap as a function of transverse momentum and gap size. We show that these measurements reveal the relative frequencies for the production of rapidity gaps in quark-quark, quark-gluon and gluon-gluon interactions. The results are at variance with the idea that the exchange of 2 gluons is a first order approximation for the mechanism producing colorless states, i.e. the hard QCD Pomeron. They do qualitatively support the "soft color" or "color evaporation" scheme developed in the context of bound-state heavy quark production.
Active galaxies and gamma ray bursts are the sources of the highest energy photons detected by astronomical telescopes. We speculate that they may be the sources of the highest energy cosmic rays. This makes them true proton accelerators, where the highest energy photons are the decay products of neutral pions photoproduced when the proton beams interacts with ambient radiation. Neutrinos from the decay of charged pions represent an incontrovertible signature for proton acceleration. A main theme of this talk is that their fluxes can be estimated from the measured gamma ray luminosity by model-independent methods, based on dimensional analysis and textbook particle physics.
This is the summary of a week of very informative presentations on new ways to probe the Universe using gravitational detectors, space and ground based gamma ray telescopes, EeV air shower detectors and neutrino telescopes. Gamma ray bursts and active galaxies were hot theoretical themes in the multi-wavelength discussions.
There are tantalizing hints that jets, powered by supermassive black holes at the center of active galaxies, are true cosmic proton accelerators. They produce photons of TeV energy, possible higher, and may be the enigmatic source of the highest energy cosmic rays. Photoproduction of neutral pions by accelerated protons on UV light is the source of the highest energy photons, in which most of the bolometric luminosity of the galaxy may be emitted. The case that proton beams power active galaxies is, however, far from conclusive. Neutrinos from the decay of charged pions represent an uncontrovertible signature for the proton induced cascades. We show that their flux can be estimated by model-independent methods, based on dimensional analysis and textbook particle physics. Our calculations also demonstrate why different models for the proton blazar yield very similar results for the neutrino flux, consistent with the ones obtained here.
This is a (very) personal attempt to summarize the status of neutrino astronomy: its scientific motivations, our understanding of natural water and ice as particle detectors and, finally, the detector technology.
We review the ideas of renormalizable field theories and the Standard Model at the Born (neutral currents, the Higgs mechanism and unification) and quantum level. We subsequently illustrate how high statistics experiments are producing the first evidence for the validity of the Standard Model as a spontaneously broken gauge theory.
Initial deployment of optical modules near 1 and 2 kilometer depth indicate that deep polar ice is the most transparent known natural solid. Experience with early data has revealed that a detector, conceived to measure muons tracks, can also measure energy of high energy neutrinos as well as bursts of MeV neutrinos, e.g. produced by supernovae and gamma ray bursts. We plan to complete AMANDA this austral summer to form a detector of 11 deep strings instrumented over 400 meters height with 300 optical modules. We will argue that ice is the ideal medium to deploy a future kilometer-scale detector and discuss the first deployment of 10 strings of kilometer length.
The reason why some data on the production of $ψ$- and $Υ$-states disagree with QCD predictions, occasionally by well over one order of magnitude, is that the traditional method for performing the perturbative calculation of the cross section is simply wrong. The key mistake is to require that the heavy quark pair forms a color singlet at short distances, given that there is an infinite time for soft gluons to readjust the color of the $c \bar c$ pair before it appears as an asymptotic $ψ$ or, alternatively, $D \bar D$ state. We suspect that the same mistake is made in the description of rapidity gaps, i.e.\ the production of a color-neutral quark-antiquark pair, in terms of the exchange of a color neutral gluon pair. The $ψ$ is after all a color neutral $c \bar c$ pair and we will show that it is produced by the same dynamics as $D \bar D$ pairs; its color happens to be bleached by soft final-state interactions. This approach to color is suggestive of the unorthodox prescription for the production of rapidity gaps in deep inelastic scattering, proposed by Buchmüller and Hebecker. When applied to the formation of gaps between a pair of high transverse momentum jets in hadron collisions, the soft color approach suggests a formation rate of gaps in gluon-gluon subprocesses which is similar or smaller than in quark-quark induced events. Formation of gaps should increase when increasing transverse momentum or lowering energy, in contrast with 2-gluon exchange Pomeron models.
Although gamma ray showers are muon-poor, they still produce a number of muons sufficient to make the sources observed by GeV and TeV telescopes observable also in muons. For sources with hard gamma ray spectra there is a relative `enhancement' of muons from gamma ray primaries as compared to that from nucleon primaries. All shower gamma rays above the photoproduction threshold contribute to the number of muons $N_μ$, which is thus proportional to the primary gamma ray energy. With gamma ray energy 50 times higher than the muon energy and a probability of muon production by the gammas of about 1\%, muon detectors can match the detection efficiency of a GeV satellite detector if their effective area is larger by $10^4$. The muons must have enough energy for sufficiently accurate reconstruction of their direction for doing astronomy. These conditions are satisfied by relatively shallow neutrino detectors such as AMANDA and Lake Baikal and by gamma ray detectors like MILAGRO. TeV muons from gamma ray primaries, on the other hand, are rare because they are only produced by higher energy gamma rays whose flux is suppressed by the decreasing flux at the source and by absorption on interstellar light. We show that there is a window of opportunity for muon astronomy with the AMANDA, Lake Baikal and MILAGRO detectors.
We present the theoretical arguments and describe the accumulating experimental evidence that jets, powered by supermassive black holes, are true cosmic accelerators. They produce photons of TeV energy, possible higher, and may be the enigmatic source of the highest energy cosmic rays. The features of the multi-wavelength emission spectrum are dictated by the interactions of electrons and protons, accelerated in the vicinity of the black hole, with the ambient light in the galaxy. Photoproduction of neutral pions by protons on UV light is the source of the highest energy photons, in which most of the bolometric luminosity of the galaxy may be emitted. They initiate an electromagnetic cascade which via pair production on the magnetic field and photon-photon interactions determines the emerging gamma-ray spectrum at lower energies. The lower energy photons, observed by conventional astronomical techniques, are, as a result of the cascade process, several generations removed from the primary high energy beams. The case that proton beams power active galaxies is far from conclusive. A three-prong technological assault on the problem will, in the near future, hopefully provide new insights into the structure of active galactic nuclei with the construction of second-generation atmospheric Cherenkov telescopes, large-scale EeV cosmic ray detectors and high energy neutrino telescopes.
The color-evaporation model quantitatively describes all data on photoproduction and hadroproduction of charmonium. Although the model is in part nonperturbative, the associated parameters can for instance be determined from the charmonium photoproduction data. At this point its predictions for the prompt production of $ψ$'s at the $Z$ pole are made with no free parameters. We show here that this approach successfully describes all data on the production of prompt $ψ$'s in $Z$ decays.
The color evaporation model simply states that charmonium production is described by the same dynamics as $D \bar D$ production, {\em i.e.}, by the formation of a colored $c \bar c$ pair. Its color happens to be bleached by soft final-state interactions. We show that the model gives a complete picture of charmonium production including low-energy production by proton, photon and antiproton beams, and high-energy production at the Tevatron and HERA. Our analysis includes the first next-to-leading-order calculation in the color evaporation model.