Narrow Results

We identify a class of perturbatively computable measures of interjet energy flow, which can be associated with well-defined color flow at short distances. As an illustration, we calculate correlations between event shapes and the flow of energy, Q_Ω, into an interjet angular region, Ω, in high-energy two-jet e⁺e^--annihilation events. Laplace transforms with respect to the event shapes suppress states with radiation at intermediate energy scales, so that we may compute systematically logarithms of interjet energy flow. This method provides a set of predictions on energy radiated between jets, as a function of event shape and of the choice of the region Ω in which the energy is measured. Non-global logarithms appear as corrections. We apply our method to a continuous class of event shapes.

Long Gamma-ray bursts (GRBs) are believed to be originated from relativistic jets launched during the core collapses of some massive stars. The two core questions in the contemporary GRB science are the physical composition and the geometric configuration of the jets. Here I review the recent theoretical progress in both directions, and discuss how Swift may address both questions in the near future.

Correlations in the azimuthal angle between the two largest transverse momentum jets have been measured using the DØ detector in collisions at . The analysis is based on an inclusive dijet event sample in the central rapidity region corresponding to an integrated luminosity of 150 pb^-1. Azimuthal correlations are stronger at larger transverse momenta. These are well-described in NLO pQCD, except at large azimuthal differences where soft effects are significant.

We present the results on fragmentation differences of quark and gluon jets obtained by CDF at . We compare the multiplicities and momentum distributions of charged particles in two data samples: dijet data and photon+jet data. These two samples have a different quark/gluon jet content, which allows a measurement of the inclusive properties of gluon and quark jets. The results are compared to the earlier measurements obtained at e+e- collisions and to the re-summed perturbative QCD calculations.

Various aspects of the high-energy emission from relativistic jets associated with compact astrophysical systems are reviewed. The main leptonic and hadronic processes responsible for the production of high-energy γ-rays, very-high-energy neutrinos and ultra-high energy cosmic rays are discussed. Relations between the γγ pair production and photomeson production opacities are derived, and their consequences for the relative emission of γ-rays and neutrinos are examined. The scaling of the size and location of the various emission zones and other quantities with black hole mass and dimensionless luminosity is elucidated. The results are applied to individual classes of objects, including blazars, microquasars and gamma-ray bursts. It is concluded that if baryons are present in the jet at sufficient quantities, then under optimal conditions most systems exhibiting relativistic jets may be detectable by upcoming neutrino telescopes. An exception is the class of TeV blazars, for which γ-ray observations imply neutrino yields well below detection limit.

The analysis is presented for the first moments of collective observable distributions in two-jet events for various interaction types and for wide initial energy range. These observables include sphericity, thrust, components of transverse particle momentum, alignment and planarity. Database of experimental results created in the framework of the paper includes data for all interactions. Energy dependencies of average values for collective observables except components of transverse momentum show universal behavior for various interactions. Particle transverse momentum as well as its components increase faster for e⁺e^- interaction with growth of , than that for other interactions. Empirical analytical functions are suggested for description of energy dependence for all collective observables under study with exception of infrared-stable thrust variable. Energy dependence for average thrust is compared with QCD predictions including perturbative part and analytical phenomenological corrections which account for nonperturbative effects. Dispersive model and single dressed gluon approximation are considered for description of energy dependence of first moment of thrust distribution and estimation of strong coupling constant for various interactions as well as for joint sample. The dispersive model allow to describe average thrust versus initial energy in wide range of down to strongly nonperturbative domain at qualitative level at least. Study of event shape observables allows to obtain estimations of α_S(M_Z) which are in reasonable agreement both with world average value and with results extracted in the framework of other methods. Using suggested analytical fitted functions some estimations of values of collective parameters under study have been obtained for present and future facilities. In TeV energy domain average values of collective observables either depend on weakly or do not depend on initial energy at all within errors. Thus, the TeV scale can be considered as an estimation of the low boundary of asymptotic region for traditional collective parameters. Usually, multiplicity dependence of collective observables under consideration agree with power function in energy domain at qualitative level at least. Behavior of sphericity versus multiplicity and comparison of experimental results with model calculations allow to suggest that the universal estimation of the low energy boundary for experimental appearance of event jet structure in multiparticle production processes is .

Self-similarity of jet production in pp and collisions is studied in the framework of z-scaling. Inclusive jet transverse momentum distributions measured by the STAR Collaboration at RHIC, the CDF and D∅ Collaborations at Tevatron and the CMS and ATLAS Collaborations at LHC are analyzed. The experimental spectra are compared with next-to-leading order QCD calculations in p_T- and z-presentations. It is shown that self-similar features of jet cross-sections manifested by the z-scaling give strong restriction on the scaling function ψ(z) at high z. New results on energy and angular independence and asymptotic behavior of ψ(z) are discussed. The obtained results are considered as confirmation of self-similarity of jet production, fractality of hadron structure and locality of constituent interactions at small scales.

We review three topics on the recent application of the AdS/CFT correspondence to hard processes: deep inelastic scattering, e⁺e^- annihilation and jet quenching at finite temperature.

We explicitly study how jet substructure taggers act on a set of signal and background events. We focus on two-pronged hadronic decay of a boosted Z-boson. The background to this process comes from QCD jets with masses of the order of m_Z. We find a way to compare various taggers within a single framework by applying them to the most relevant splitting in a jet. We develop a tool, TOY-TAG, which allows one to get insight into what happens when a particular tagger is applied to a set of signal or background events. It also provides estimates for significance and purity. We use our tool to analyze differences between various taggers and potential ways to improve the performance by combining several of them.

We review the history of jets in high energy physics, and describe in more detail the developments of the past ten years, discussing new algorithms for jet finding and their main characteristics, and summarising the status of perturbative calculations for jet cross sections in hadroproduction. We also describe the emergence of jet grooming and tagging techniques and their application to boosted jets analyses.

Jets are one of the most prominent physics signatures of high energy proton–proton (p–p) collisions at the Large Hadron Collider (LHC). They are key physics objects for precision measurements and searches for new phenomena. This review provides an overview of the reconstruction and calibration of jets at the LHC during its first Run. ATLAS and CMS developed different approaches for the reconstruction of jets, but use similar methods for the energy calibration. ATLAS reconstructs jets utilizing input signals from their calorimeters and use charged particle tracks to refine their energy measurement and suppress the effects of multiple p–p interactions (pileup). CMS, instead, combines calorimeter and tracking information to build jets from particle flow objects. Jets are calibrated using Monte Carlo (MC) simulations and a residual in situ calibration derived from collision data is applied to correct for the differences in jet response between data and Monte Carlo. Large samples of dijet, $Z$+jets, and $\gamma$+events at the LHC allowed the calibration of jets with high precision, leading to very small systematic uncertainties. Both ATLAS and CMS achieved a jet energy calibration uncertainty of about 1% in the central detector region and for jets with transverse momentum $p_T>100\mathrm{\text{GeV}}$. At low jet $p_T$, the jet energy calibration uncertainty is less than 4%, with dominant contributions from pileup, differences in energy scale between quark and gluon jets, and jet flavor composition.

This review discusses the measurements of the inclusive jet and dijet cross section performed by the experimental collaborations at the LHC during what is now being called LHC Run 1 (2009–2013). It summarises some of the experimental challenges and the techniques used in the measurements of jets cross sections during the LHC Run 1.

Jet observables have been exploited extensively during the LHC Run 1 to search for physics beyond the Standard Model. In this article, the most recent results from the ATLAS and CMS collaborations are summarized. Data from proton–proton collisions at 7 and 8 TeV center-of-mass energy have been analyzed to study monojet, dijet, and multijet final states, searching for a variety of new physics signals that include colored resonances, contact interactions, extra dimensions, and supersymmetric particles. The exhaustive searches with jets in Run 1 did not reveal any signal, and the results were used to put stringent exclusion limits on the new physics models.

We present predictions for the inclusive production of charm jets in proton–proton collisions at 7 TeV. Several CTEQ parton distribution functions (PDFs) of the CTEQ6.6M type are employed, where two of the CTEQ6.6 PDFs have intrinsic charm. At large enough jet transverse momentum and large jet rapidity, the intrinsic charm content can be tested.

The physics potential of the Circular Electron Positron Collider (CEPC) can be significantly strengthened by two detectors with complementary designs. A promising detector approach based on the Silicon Detector (SiD) designed for the International Linear Collider (ILC) is presented. Several simplifications of this detector for the lower energies expected at the CEPC are proposed. A number of cost optimizations of this detector are illustrated using full detector simulations. We show that the proposed changes will enable one to reach the physics goals at the CEPC.

We present predictions for the inclusive production of bottom jets in proton–antiproton collisions at 1.96 TeV and proton–proton collisions at 7 TeV. The bottom quark is considered massless. In this scheme, we find that at small transverse momentum $(p_T)$ the ratio of the next-to-leading order to the leading-order cross-section ($K$ factor) is smaller than one. It increases with increasing $p_T$ and approaches one at larger $p_T$ at a value depending essentially on the choice of the renormalization scale. Adding nonperturbative corrections obtained from PYTHIA Monte Carlo calculations leads to reasonable agreement with experimental $b$-jet cross-sections obtained by the CDF and the CMS collaborations.

Higher collision energies at future colliders may eventually lead to the falsification of standard fixed-order perturbation theory and linear evolutions due to nonlinear structure of QCD at small-$x$. New physics research works that are strictly based on accurate jet measurements will undoubtedly have this observation known as Balitsky–Fadin–Kuraev–Lipatov (BFKL) effect via angular jet decorrelations taking into account the Mueller–Navelet jets. As one of the frontier colliders, FCC-ep, has a great observation potential on parton densities through asymmetrical collisions. We aim to test the observability of azimuthal angular jet decorrelations with the recent event generators (HERWIG, PYTHIA) at the generator and detector level for FCC-ep center of mass energies $\sqrt{s}=3.5$TeV in proton–electron collisions. Jets are reconstructed by the anti-$k_T$ algorithm ($R=0.5$), with $p_T>15$GeV and selected in the range of $|\eta |<6$. Relevant pseudo-rapidity regions have been analyzed with the azimuthal-angle difference between Mueller–Navelet Jets ($\mathrm{\Delta }\mathrm{\Phi }$) in the pseudo-rapidity separation ($\mathrm{\Delta }\eta$) and the distributions of $〈cos(n(\pi -\mathrm{\Delta }\varphi ))〉$ are presented in comparison as the result.

We investigate canonical aspects concerning the relation between symmetries and conservation laws in gauge-natural field theories. In particular, we find that a canonical spinor connection can be selected by the simple requirement of the global existence of canonical superpotentials for the Lagrangian describing the coupling of gravitational and Fermionic fields. In fact, the naturality of a suitably defined variational Lagragian implies the existence of an associated energy-momentum conserved current. Such a current defines a Hamiltonian form in the corresponding phase space; we show that an associated Hamiltonian connection is canonically defined along the kernel of the generalized gauge-natural Jacobi morphism and uniquely characterizes the canonical spinor connection.

We study geometric aspects concerned with symmetries and conserved quantities in gauge-natural invariant variational problems and investigate implications of the existence of a reductive split structure associated with canonical Lagrangian conserved quantities on gauge-natural bundles. In particular, we characterize the existence of covariant conserved quantities in terms of principal Cartan connections on gauge-natural prolongations.

We consider systems of local variational problems defining nonvanishing cohomology classes. Symmetry properties of the Euler–Lagrange expressions play a fundamental role since they introduce a cohomology class which adds up to Noether currents; they are related with invariance properties of the first variation, thus with the vanishing of a second variational derivative. In particular, we prove that the conserved current associated with a generalized symmetry, assumed to be also a symmetry of the variation of the corresponding local inverse problem, is variationally equivalent to the variation of the strong Noether current for the corresponding local system of Lagrangians. This current is conserved and a sufficient condition will be identified in order that such a current be global.