Neutrino Nucleon Research Articles

Cross section and polarization of neutrino-produced τ's made simple

Practical formulae are derived for the cross section and polarization vector of the τ lepton produced in deep inelastic neutrino–nucleon scattering in the frame of the simple quark–parton model.

Neutrino-induced pion production at energies relevant for the MiniBooNE and K2K experiments

We investigate charged and neutral current neutrino induced incoherent pion production off nuclei at MiniBooNE and K2K energies within the GiBUU model. We assume impulse approximation and treat the nucleus as a local Fermi gas of nucleons bound in a mean-field potential. In-medium spectral functions are also taken into account. The outcome of the initial neutrino nucleon reaction undergoes complex hadronic final state interactions. We present results for neutral current ${\ensuremath{\pi}}^{0}$ and charged current ${\ensuremath{\pi}}^{+}$ production and compare to MiniBooNE and K2K data.

Third-order QCD corrections to the charged-current structure function [formula omitted

We compute the coefficient function for the charge-averaged W ± -exchange structure function F 3 in deep-inelastic scattering (DIS) to the third order in massless perturbative QCD. Our new three-loop contribution to this quantity forms, at not too small values of the Bjorken variable x, the dominant part of the next-to-next-to-next-to-leading order corrections. It thus facilitates improved determinations of the strong coupling α s and of 1 / Q 2 power corrections from scaling violations measured in neutrino–nucleon DIS. The expansion of F 3 in powers of α s is stable at all values of x relevant to measurements at high scales Q 2 . At small x the third-order coefficient function is dominated by diagrams with the colour structure d abc d abc not present at lower orders. At large x the coefficient function for F 3 is identical to that of F 1 up to terms vanishing for x → 1 .

EVALUATION OF CHARGED CURRENT NEUTRINO–NUCLEON INTERACTION CROSS-SECTION

The charged current neutrino–nucleon interaction cross-section is evaluated using Thermodynamical Bag Model (TBM) in the neutrino energy range 1 < Eν < 200 GeV with the value of the four-momentum transfer squared 0.1 < Q2 < 20 GeV 2 and the Bjorken variable 0.1 < x < 0.5. The hadronic current carries the linear moments of the reaction that depend on the Bjorken scaling variable x as well as the four-momentum transfer. The results obtained have been compared with the experimental values.

Eikonal contributions to ultra high energy neutrino–nucleon cross sections in low scale gravity models

We calculate low scale gravity effects on the cross section for neutrino–nucleon scattering at center of mass energies up to the Greisen–Zatsepin–Kuzmin (GZK) scale, in the eikonal approximation. We compare the cases of an infinitely thin brane embedded in n = 5 compactified extra-dimensions, and of a brane with a physical tension M S = 1 TeV and M S = 10 TeV . The extra dimensional Planck scale M D is set at 10 3 GeV and 2 × 10 3 GeV . We also compare our calculations with neutral current standard model calculations in the same energy range, and compare the thin brane eikonal cross section to its saddle point approximation. New physics effects enhance the cross section by orders of magnitude on average. They are quite sensitive to M S and M D choices, though much less sensitive to n.

A precise measurement of the muon neutrino–nucleon inclusive charged current cross section off an isoscalar target in the energy range [formula omitted] by NOMAD

We present a measurement of the muon neutrino–nucleon inclusive charged current cross section, off an isoscalar target, in the neutrino energy range 2.5⩽Eν⩽40 GeV. The significance of this measurement is its precision, ±4% in 2.5⩽Eν⩽10 GeV, and ±2.6% in 10⩽Eν⩽40 GeV regions, where significant uncertainties in previous experiments still exist, and its importance to the current and proposed long baseline neutrino oscillation experiments.

Differences between charged-current coefficient functions

Second- and third-order results are presented for the structure functions of charged-current deep-inelastic scattering in the framework of massless perturbative QCD. We write down the two-loop differences between the corresponding crossing-even and -odd coefficient functions, including those for the longitudinal structure function not covered in the literature so far. At three loops we compute the lowest five moments of these differences for all three structure functions and provide approximate expressions in Bjorken- x space. Also calculated is the related third-order coefficient-function correction to the Gottfried sum rule. We confirm the conjectured suppression of these quantities if the number of colours is large. Finally we derive the second- and third-order QCD contributions to the Paschos–Wolfenstein ratio used for the determination of the weak mixing angle from neutrino–nucleon deep-inelastic scattering. These contributions are found to be small.

Improved analysis of moments of [formula omitted] in neutrino–nucleon scattering using the Bernstein polynomial method

We use recently calculated next-to-next-to-leading order (NNLO) anomalous dimension coefficients for the moments of the x F 3 structure function in νN scattering, together with the corresponding three-loop Wilson coefficients, to obtain improved QCD predictions for both odd and even moments of F 3 . To investigate the issue of renormalization scheme dependence, the Complete Renormalization Group Improvement (CORGI) approach is used, in which all dependence on renormalization and factorization scales is avoided by a complete resummation of RG-predictable scale logarithms. We also consider predictions using the method of effective charges, and compare with the standard ‘physical scale’ choice. The Bernstein polynomial method is used to construct experimental moments (from the x F 3 data of the CCFR Collaboration) that are insensitive to the value of x F 3 in the region of x which is inaccessible experimentally. Direct fits for Λ MS ¯ ( 5 ) ( α s ( M Z ) ) are then performed. The CORGI fits including target mass corrections give a value α s ( M Z ) = 0.1189 −0.0019 +0.0019 , consistent with the world average. The effective charge and physical scale fits give slightly smaller values, which are still consistent within the errors.

Tests of the Standard Model with Low–Energy Neutrino Beams

We discuss the possibility of using future high–intensity low–energy neutrino beams for precision tests of the Standard Model. In particular we consider the determination of the electroweak mixing angle from elastic and quasi–elastic neutrino–nucleon scattering at a superbeam or β –beam.

Event rates vs. cross sections at neutrino telescopes

One of the major goals of neutrino astronomy is to explore the otherwise unknown fluxes and interactions of ultrahigh energy neutrinos. The existing neutrino telescopes look at three types of events: particle showers, muons, and taus. In this paper we discuss the dependence of the event rates on the neutrino nucleon cross-sections as we scale the cross sections, with energy, in different scenarios beyond the standard model. Our focus will be on the IceCube detector.

Ultra high energy neutrino–nucleon cross section from cosmic ray experiments and neutrino telescopes

We deduce the cosmogenic neutrino flux by jointly analysing ultra high energy cosmic ray data from HiRes-I and II, AGASA and the Pierre Auger Observatory. We make two determinations of the neutrino flux by using a model-dependent method and a model-independent method. The former is well-known, and involves the use of a power-law injection spectrum. The latter is a regularized unfolding procedure. We then use neutrino flux bounds obtained by the RICE experiment to constrain the neutrino–nucleon inelastic cross section at energies inaccessible at colliders. The cross section bounds obtained using the cosmogenic fluxes derived by unfolding are the most model-independent bounds to date.

Strangeness in the Nucleon

Strangeness content inside the nucleon has been one of the most important topics for understanding structure of the nucleon. Using electron scattering off nucleon targets, the strangeness component and its electric, magnetic and spin properties have been studied. Neutrino nucleon scattering is ideal to measure the axial structure of the nucleon, so that strange quark spin, Δs, can be directly determined. Expected intensive neutrino beams in the near future will allow determination of Δs with precision of δ ( Δ s ) ∼ 0.03 .

Ultra high energy tau-neutrinos and fluorescence detectors: A phenomenological approach

We investigate the possibility of detecting ultra-high energy cosmic tau-neutrinos by means of a process involving a double extensive air shower, the so-called double-bang phenomenon. In this process a primary tau-neutrino interacts with an atmospheric quark creating a hadronic extensive air shower that contains a tau which subsequently decays creating a second extensive air shower. The number of these events strongly depends on the cross section and on the flux of ultra-high energy tau-neutrinos arriving at the Earth’s atmosphere. We estimate the potential of optical detectors to observe double-bang events induced by tau-neutrinos with energies of about 1 EeV whose detection may confirm the maximal mixing observed in the atmospheric neutrinos also for ultra-high energy neutrinos, and give information on the neutrino flux and cross-section. For neutrino–nucleon standard model extrapolated cross-section and thick source model of flux (MPR), we estimate an event rate of 0.48 y −1 for an observatory with two fluorescence detectors with 90% efficiency in the neutrino energy range 0.5 < E ν < 5 EeV.

Neutrino–nucleus cross section at low energies

The methods of evaluating neutrino–nucleus cross section at low energies (<100 MeV) are reviewed and the most important applications of these processes are discussed. First, the neutrino–nucleon and neutrino–deuteron charged and neutral current reactions are described. These are well studied experimentally, and well understood theoretically. This is contrasted with the situation on complex nuclei where the experimental information is rare, restricted essentially to one target, 12C. The need for more benchmark experiments that should serve as test cases for theoretical evaluation, is stressed.

Exotic neutrino interactions at the Pierre Auger Observatory

The Pierre Auger Observatory for cosmic rays provides a laboratory for studying fundamental interactions at energies well beyond those available at colliders. In addition to hadrons or photons, Auger is sensitive to ultra-high energy neutrinos in the cosmic radiation and models for new physics can be explored by observing neutrino interactions at center-of-mass energies beyond the TeV scale. By comparing the rate for quasi-horizontal, deeply penetrating air showers triggered by all types of neutrinos with the rate for slightly upgoing showers generated by Earth-skimming tau neutrinos, any deviation of the neutrino–nucleon cross-section from the Standard Model expectation can be constrained. We show that this can test models of low-scale quantum gravity (including processes such as Kaluza–Klein graviton exchange, microscopic black hole production and string resonances), as well as non-perturbative electroweak instanton mediated processes. Moreover, the observed ratios of neutrino flavors would severely constrain the possibility of neutrino decay.

Measurement of nucleon structure functions in neutrino scattering

After completion of the data taking for the νμ→ντ oscillation search, the CHORUS lead–scintillator calorimeter was used in the 1998 run as an active target. High-statistics samples of charged-current interactions were collected in the CERN SPS west area neutrino beam. This beam contained predominantly muon (anti-)neutrinos from sign-selected pions and kaons. We measure the flux and energy spectrum of the incident neutrinos and compare them with beam simulations. The neutrino–nucleon and anti-neutrino–nucleon differential cross-sections are measured in the range 0.01<x<0.7, 0.05<y<0.95, 10<Eν<200 GeV. We extract the neutrino–nucleon structure functions F2(x,Q2), xF3(x,Q2), and R(x,Q2) and compare these with results from other experiments.

Cosmic rays at ultra high energies (Neutrinos!)

Resonant photo-pion production with the cosmic microwave background predicts a suppression of extragalactic protons above the famous Greisen–Zatsepin–Kuzmin cutoff at about E GZK ≈ 5 × 10 10 GeV. Current cosmic ray data measured by the AGASA and HiRes Collaborations do not unambiguously confirm the GZK cutoff and leave a window for speculations about the origin and chemical composition of the highest energy cosmic rays. In this work we analyze the possibility of strongly interacting neutrino primaries and derive model-independent quantitative requirements on the neutrino–nucleon inelastic cross section for a viable explanation of the cosmic ray data. Search results on weakly interacting cosmic particles from the AGASA and RICE experiments are taken into account simultaneously. Using a flexible parameterization of the inelastic neutrino–nucleon cross section we find that a combined fit of the data does not favor the Standard Model neutrino–nucleon inelastic cross section, but requires, at 90% confidence level, a steep increase within one energy decade around E GZK by four orders of magnitude. We illustrate such an enhancement within some extensions of the Standard Model. The impact of new cosmic ray data or cosmic neutrino search results on this scenario, notably from the Pierre Auger Observatory soon, can be immediately evaluated within our approach.

The decay of tau leptons produced in neutrino–nucleon scatterings

Energy and angular distributions of the τ decay products in the CERN-to-Gran Sasso ν τ appearance experiments are studied for the decay modes τ → π ν and τ → ℓ ν ¯ ν ( ℓ = e or μ). We find that the decay particle distributions in the laboratory frame are significantly affected by the τ polarization. Rather strong azimuthal asymmetry of π − and ℓ − about the τ momentum axis is predicted, which may have observable consequences even at small statistics experiments.

Propagation of supersymmetric charged sleptons at high energies

The potential for neutrino telescopes to discover charged stau production in neutrino–nucleon interactions in Earth depends in part on the stau lifetime and range. In some supersymmetric scenarios, the next lightest supersymmetric particle is a stau with a decay length on the scale of 10 km. We evaluate the electromagnetic energy loss as a function of energy and stau mass. The energy loss parameter β scales as the inverse stau mass for the dominating electromagnetic processes, photonuclear and e +e − pair production. The range can be parameterized as a function of stau mass, initial energy and minimum final energy. In comparison to earlier estimates of the stau range, our results are as much as a factor of two larger, improving the potential for stau discovery in neutrino telescopes.

Upper bounds on the neutrino–nucleon inelastic cross section

Extraterrestrial neutrinos can initiate deeply developing air showers, and those thattraverse the atmosphere unscathed may produce cascades in the ice or water. Up to now,no such events have been observed. This can be translated into upper limits on the diffuseneutrino flux. On the other hand, the observation of cosmic rays with primary energies>1010 GeV suggests that there is a guaranteed flux of cosmogenic neutrinos, arising from thedecay of charged pions (and their muon daughters) produced in proton interactions withthe cosmic microwave background. In this work, armed with these cosmogenic neutrinosand the increased exposure of neutrino telescopes, we obtain up-to-date model independentupper bounds on the neutrino–nucleon inelastic cross section. Uncertainties in thecosmogenic neutrino flux are discussed and taken into account in our analysis. Theprospects for improving these bounds with the Pierre Auger Observatory are alsoestimated. The unprecedented statistics to be collected by this experiment in 6 yr ofoperation will probe the neutrino–nucleon inelastic cross section at the level of StandardModel predictions.