High Energy Jets Research Articles

Level-1 jet trigger hardware for the ALICE electromagnetic calorimeter at LHC

The ALICE experiment at the LHC is equipped with an electromagnetic calorimeter (EMCal) designed to enhance its capabilities for jet measurement. In addition, the EMCal enables triggering on high energy jets. Based on the previous development made for the Photon Spectrometer (PHOS) level-0 trigger, a specific electronic upgrade was designed in order to allow fast triggering on high energy jets (level-1). This development was made possible by using the latest generation of FPGAs which can deal with the instantaneous incoming data rate of 26 Gbit/s and process it in less than 4 μs.

Search for New Fermions (“Quirks”) at the Fermilab Tevatron Collider

We report results of a search for particles with anomalously high ionization in events with a high transverse energy jet and large missing transverse energy in 2.4 fb⁻¹ of integrated luminosity collected by the D0 experiment at the Fermilab Tevatron pp collider. Production of such particles (quirks) is expected in scenarios with extra QCD-like SU(N) sectors, and this study is the first dedicated search for such signatures. We find no evidence of a signal and set a lower mass limit of 107, 119, and 133 GeV for the mass of a charged quirk with strong dynamics scale Λ in the range from 10 keV to 1 MeV and N=2, 3, and 5, respectively.

Jet quenching in hot strongly coupled gauge theories revisited: 3-point correlators with gauge-gravity duality

Previous studies of high-energy jet stopping in strongly-coupled plasmas have lacked a clear gauge-theory specification of the initial state. We show how to set up a well-defined gauge theory problem to study jet stopping in pure \( \mathcal{N} = 4 \) super Yang Mills theory (somewhat analogous to Hofman and Maldacena’s studies at zero temperature) and solve it by using gauge-gravity duality for real-time, finite-temperature 3-point correlators. Previous studies have found that the stopping distance scales with energy as E 1/3 (with disagreement on the gauge coupling dependence). We do find that none of the jet survives beyond this scale, but we find that almost all of our jet stops at a parametrically smaller scale proportional to (EL)1/4, where L is the size of the space-time region where the jet is initially created.

High Energy Description of Processes with Multiple Hard Jets

High Energy Jets (HEJ) is a new framework for approximating the all-order perturbative corrections to multi-jet processes, with a focus on the hard, wide-angle QCD emissions, which underpins the perturbative description of hard jets. In this contribution we review the basic concepts of HEJ, and present some new predictions for observables in dijet-production, and for W-boson production in association with at least 3 jets.

SEARCHES FOR NEW PHYSICS WITH JETS-PLUS-$E\hspace{-6.2pt}/_T$ SIGNATURES USING DATA-DRIVEN BACKGROUND ESTIMATES

Events featuring high energy jets and a large amount of missing transverse energy constitute a key signature for a wide spectrum of new physics models. In this review, the results of two searches with such signatures are presented. The benefits of performing these searches in a model-independent way are discussed and data-driven techniques used to estimate Standard Model backgrounds are described in detail. These data-driven techniques will be an important part of searches for new physics at the LHC, especially in the early data-taking period.

Stopping distance for high energy jets in weakly coupled quark-gluon plasmas

We derive a simple formula for the stopping distance for a high-energy quark traveling through a weakly coupled quark-gluon plasma. The result is given to next-to-leading order in an expansion in inverse logarithms $\mathrm{ln}(E/T)$, where $T$ is the temperature of the plasma. We also define a stopping distance for gluons and give a leading-log result. Discussion of stopping distance has a theoretical advantage over discussion of energy loss rates in that stopping distances can be generalized to the case of strong coupling, where one may not speak of individual partons.

Effect of Y(OH) 3 microparticles on the electrochemical performance of alkaline zinc electrodes

This work focused on the zinc powder coated with Y(OH) 3 microparticles by means of ultrasonic immersion for performance improvement of zinc electrodes in alkaline battery systems. Scanning electron microscopy and other characterization techniques were applied to examine the influence of the ultrasonic power on the sonochemical growth of Y(OH) 3 microparticles in direct contact with zinc powder. Electrochemical properties of zinc electrodes containing Y(OH) 3 microparticles were discussed through the measurements of potentiodynamic polarization and cyclic voltammetry. Simultaneously, the test cells making use of such modified zinc powder were assembled to further evaluate the availability of Y(OH) 3 microparticles in improving the cycle properties of zinc electrodes. It was found that good alkaline environment generated by ultrasonic irradiation of high power led to the formation of Y(OH) 3 microparticles on the surface of modified zinc powder due to high-energy jets of immersion solution. In particular, the Y(OH) 3 microparticles formed with the ultrasonic power of 440 W made the greatest contributions to hinder the corrosion of zinc electrode and the dissolution of zinc oxidation products in alkaline electrolyte as compared with other power parameters. Besides, the detections of assembled cells at a high discharge current density of 250 mA/cm 2 revealed that the Y(OH) 3 microparticles obtained with ultrasonic power of 440 W provided the alkaline zinc electrode with low capacity loss and persistent cycle behavior. The great improvement over the corrosion behavior and cycle properties of zinc electrode is possibly ascribed to the uniform distribution of Y(OH) 3 microparticles on the surface of modified zinc powder.

The ALICE electromagnetic calorimeter

ALICE is the general purpose experiment at the LHC dedicated to the study of heavy-ion collisions. The electromagnetic calorimeter (EMCal) is a late addition to the ALICE suite of detectors with first modules installed in ALICE this year. The EMCal is designed to trigger on high energy gamma-rays and jets, and to enhance the capabilities of ALICE for these measurements. The EMCal is a Pb/scintillator sampling shish-kebab type calorimeter. The EMCal construction, readout, and performance in beam tests at the CERN SPS and PS are described.

Top quark mass measurement in the lepton plus jets channel using a modified matrix element method

We report a measurement of the top quark mass, m_t, obtained from ppbar collisions at sqrt(s) = 1.96 TeV at the Fermilab Tevatron using the CDF II detector. We analyze a sample corresponding to an integrated luminosity of 1.9 fb^-1. We select events with an electron or muon, large missing transverse energy, and exactly four high-energy jets in the central region of the detector, at least one of which is tagged as coming from a b quark. We calculate a signal likelihood using a matrix element integration method, with effective propagators to take into account assumptions on event kinematics. Our event likelihood is a function of m_t and a parameter JES that determines /in situ/ the calibration of the jet energies. We use a neural network discriminant to distinguish signal from background events. We also apply a cut on the peak value of each event likelihood curve to reduce the contribution of background and badly reconstructed events. Using the 318 events that pass all selection criteria, we find m_t = 172.7 +/- 1.8 (stat. + JES) +/- 1.2 (syst.) GeV/c^2.

The CMS-HF quartz fiber calorimeters

Two hadronic forward (HF) calorimeters extend the acceptance of CMS at large rapidities and are built with radiation-hard components (steel absorbers and quartz fibers) to resist the severe radiation levels in the forward regions. Very high energy jets can be measured in HF, by detecting Cherenkov light emitted by shower particles in the quartz fibers. The HF calorimeters are now installed in the underground CMS cavern; after commissioning, the detectors are being prepared for beam. Progress in calibration work and current plans for the HF calorimeters during the initial LHC runs are summarized.

High-energy jet quenching in weakly coupled quark-gluon plasmas

$\stackrel{^}{q}$ is the average squared transverse momentum transfer per unit length to a high-energy particle traversing a QCD medium such as a quark-gluon plasma. We find the (UV-regulated) value of $\stackrel{^}{q}$ to leading order in the weak coupling limit, ${\ensuremath{\alpha}}_{\mathrm{s}}(T)\ensuremath{\ll}1$. We then use this value to generalize previous analytic results on the gluon bremsstrahlung and pair production rates for massless high-energy particles in a weakly coupled quark-gluon plasma, at next-to-leading logarithmic order.

Jets in Photoproduction at HERA

Recent results on the photoproduction of high energy jets at HERA are presented, and their implications for the structure of the photon are discussed.

Jet broadening in unstable non-Abelian plasmas

We perform numerical simulations of the SU(2) Boltzmann-Vlasov equation including both hard elastic particle collisions and soft interactions mediated by classical Yang-Mills fields. Using this technique we calculate the momentum-space broadening of high-energy jets in real time for both locally isotropic and anisotropic plasmas. In both cases we introduce a separation scale that separates hard and soft interactions and demonstrate that our results for jet broadening are independent of the precise separation scale chosen. For an isotropic plasma this allows us to calculate the jet transport coefficient q-circumflex including hard and soft nonequilibrium dynamics. For an anisotropic plasma the jet transport coefficient becomes a tensor with q-circumflex{sub L}{ne}q-circumflex{sub perpendicular}. We find that for weakly coupled anisotropic plasmas the fields develop unstable modes, forming configurations where B{sub perpendicular}>E{sub perpendicular} and E{sub z}>B{sub z}, which lead to q-circumflex{sub L}>q-circumflex{sub perpendicular}. We study whether the effect is strong enough to explain the experimental observation that high-energy jets traversing the plasma perpendicular to the beam axis experience much stronger broadening in rapidity, {delta}{eta}, than in azimuth, {delta}{phi}.

High energy jets in the Earth’s magnetosheath: Implications for plasma dynamics and anomalous transport

High energy density jets in the magnetosheath near the Earth magnetopause were observed by Interball-1 [1]. In this paper, we continue the investigation of this important physical phenomenon. New data provided by Cluster show that the magnetosheath kinetic energy density during more than one hour exhibits an average level and a series of peaks far exceeding the kinetic energy density in the undisturbed solar wind. This is a surprising finding because the kinetic energy of the upstream solar wind in equilibrium should be significantly diminished downstream in the magnetosheath due to plasma braking and thermalization at the bow shock. We suggest resolving the energy conservation problem by the fact that the nonequilibrium jets appear to be locally superimposed on the background equilibrium magnetosheath, and, thus, the energy balance should be settled globally on the spatial scales of the entire dayside magnetosheath. We show that both the Cluster and Interball jets are accompanied by plasma superdiffusion and suggest that they are important for the energy dissipation and plasma transport. The character of the jet-related turbulence strongly differs from that of known standard cascade models. We infer that these jets may represent the phenomenon of the general physical occurrence observed in other natural systems, such as heliosphere, astrophysical, and fusion plasmas [2–10].

Harnessing plant biomass for biofuels and biomaterials

Harnessing plant biomass for biofuels and biomaterials

Collins asymmetry at hadron colliders

We study the Collins effect in the azimuthal asymmetricdistribution of hadrons inside a high energy jet in the single transversepolarized proton proton scattering. From the detailed analysis ofone-gluon and two-gluon exchange diagrams contributions, the Collinsfunction is found the same as that in the semi-inclusive deep inelasticscattering and e+e- annihilations. The eikonal propagators in thesediagrams do not contribute to the phase needed for the Collins-typesingle spin asymmetry, and the universality is derived as a result of theWard identity. We argue that this conclusion depends on the momentum flowof the exchanged gluon and the kinematic constraints in the fragmentationprocess, and is generic and model-independent.

Asymmetric Azimuthal Distribution of Hadrons inside a Jet from Hadron-Hadron Collisions

We study the azimuthal asymmetric distribution of hadrons inside a high energy jet in the single-transverse polarized nucleon-nucleon scattering, coming from the Collins effect multiplied by the quark transversity distribution. We argue that the Collins function in this process is the same as that in the semi-inclusive deep inelastic scattering. The experimental study of this process will provide us with important information on the quark transversity distribution and test the universality of the fragmentation functions.

Holographic Dual of Scattering and Black Hole Formation

The AdS/CFT correspondence [1] has provided a framework for discussing a strongly coupled regime of gauge theories in terms of their gravity dual description. The equilibrium finite temperature problem using a black-hole background was discussed in [2]. This approach has provided a simple explanation for high energy jet quenching at RHIC [3] an issue of considerable experimental interest in the sQGP [4–6]. The purpose of this paper is to address the issues of thermalization in a heavy-ion collision using the gravity dual description of a time dependent black hole formation. In [8], black hole formation in AdS space and its gauge theory dual were discussed by using the setting put forward by Polchinski and Strassler [9], where the gauge theory scattering amplitude is identified as a weighted sum of string amplitudes in AdS. The contribution of each AdS radius is weighted by a radial wave function peaked in the IR region. Because of this, Giddings suggested that the dual of the gauge theory fields live on the IR brane and the black hole should materialize there. More recently, Aharony, Minwalla and Wiseman [13] discussed a scenario leading to a long-lived or quasi-static plasma ball in the same setting. The basic idea of this paper is that if we view the incoming particles as highly excited glueballs, the holographic image of scattering must be at the sky of the AdS space rather than at the bottom (IR region), therefore black holes forms by the debris of scattering which has to fall to the bottom. Such falling will explain the dynamics of the cooling.

Conical Flow from Quenched Jets in sQGP

Starting with a reminder of what is strongly coupled Quark-Gluon Plasma (sQGP), we proceed to recent advances in jet quenching and heavy quark diffusion, with a brief summary of various results based on AdS/CFT correspondence. The conical flow is a hydrodynamical phenomenon created by energy and entropy deposited by high energy jets propagating in matter, similar in nature to well known sonic boom from the supersonic planes. After a brief review, we discuss excitations of two hydro modes – sound and “diffusion” – which can be excited in this way. We also study expanding matter case, with a variable speed of sound, and use adiabatic invariants to show that the parameter v/T ( v velocity in the wave, T temperature) is increasing, up to a factor 3, during expansion. At the end we discuss recent results of the Princeton group which derived conical flow from AdS/CFT.

Single inclusive distribution and two-particle correlations inside one jet at ``modified leading logarithmic approximation'' of quantum chromodynamics II. Steepest descent evaluation at smallx

The MLLA single inclusive distribution inside one high energy (gluon) jet at small x is estimated by the steepest descent method. Its analytical expression is obtained outside the "limiting spectrum". It is then used to evaluate 2-particle correlations at the same level of generality. The dependence of both observables on the ratio between the infrared cutoff Q\_0 and Lambda\_QCD is studied. Fong & Webber's results for correlations are recovered at the limits when this ratio goes to 1 and when one stays close to the peak of the single inclusive distribution.