Transverse Energy Distribution Research Articles

Probe of the anomalous neutral triple gauge couplings in photon-induced collision at future muon colliders

The anomalous ZZγ and Zγγ neutral triple gauge couplings occurred by dimension-eight operators are investigated through the process μ+μ−→μ+γ⁎μ−→μ+Z(νν¯)μ− at the muon collider with s=3, 6, 10 and 14 TeV. The charged lepton pseudo-rapidity, the charged lepton transverse momentum and the transverse missing energy distributions are taken in consideration for the final state of the process in the analysis. The sensitivities of the anomalous couplings are obtained at 95% Confidence Level with integrated luminosity of Lint=1, 4, 10 and 20 ab−1, respectively, according to center-of-mass energies of muon collider taking into account the effects of systematic uncertainties 0%, 3% and 5%. The best limits of anomalous CBB/Λ4, CBW/Λ4, CB˜W/Λ4 and CWW/Λ4 couplings without systematic uncertainty at center-of-mass energy of 14 TeV and integrated luminosity of 20 ab−1 are found to be [-0.01026; 0.00636] TeV−4, [-0.02482; 0.03053] TeV−4, [-0.01830; 0.02510] TeV−4, [-0.06981; 0.07387] TeV−4, respectively.

Multiplicity fluctuations and correlations in 5.02 TeV p+Pb collisions at zero impact parameter

We present a Bayesian method to reconstruct event-by-event multiplicity fluctuations and rapidity correlations in $p+\mathrm{Pb}$ collisions at zero impact parameter from minimum-bias data, without assuming any model of the collision dynamics. We test it on Monte Carlo simulations with the Angantyr model, then apply it to ATLAS data on the distribution of charged multiplicity and transverse energy in $p+\mathrm{Pb}$ collisions at $\sqrt{{s}_{NN}}=5.02$ TeV. Fluctuations in $b=0$ collisions are quantum fluctuations which originate mostly from the proton wave function, and therefore have the potential to constrain the subnucleonic structure of the proton. The Angantyr model is found to overestimate fluctuations. In addition, we find that as the rapidity increases (towards the Pb-going side), not only the multiplicity density increases, but also its relative event-by-event fluctuation. This counterintuitive phenomenon is also observed in simulations with Angantyr, and with the quantum chromodynamics dipole model, where its origin can be traced back to the branching process through which gluons are produced.

Photocathode performance characterisation of ultra-thin MgO films on polycrystalline copper

The performance expected from the next generation of electron accelerators is driving research into photocathode technology as this fundamentally limits the achievable beam quality. The performance characteristics of a photocathode are most notably: normalised emittance, brightness and energy spread. Ultra–thin oxide films on metal substrates have been shown to lower the work function (WF) of the surface, enhancing commonly utilised metal photocathodes, potentially improving lifetime and performance characteristics.We present the characterisation of two MgO/Cu photocathodes grown at Daresbury. The surface properties such as: surface roughness, elemental composition and WF, have been studied using atomic force microscopy (AFM), X-ray photoelectron spectroscopy (XPS) and ultraviolet photoelectron spectroscopy (UPS). The photoemissive properties have been characterised with quantum efficiency (QE) measurements at 266 nm. Additionally, we measure the Transverse Energy Distribution Curves (TEDC) for these photocathodes under illumination at various wavelengths using ASTeC’s Transverse Energy Spread Spectrometer (TESS) and extract the Mean Transverse Energy (MTE).

The measurement of photocathode transverse energy distribution curves (TEDCs) using the transverse energy spread spectrometer (TESS) experimental system.

The minimum achievable particle beam emittance in an electron accelerator depends strongly on the intrinsic emittance of the photocathode electron source. This is measurable as the mean longitudinal and transverse energy spreads in the photoemitted electron beam (MLE and MTE respectively); consequently, MLE and MTE are notable figures of merit for photocathodes used as electron sources in particle accelerators. The overall energy spread is defined by the sum of the MTE and the MLE, and the minimization of MTE is crucial to reduce emittance and thus generate a high-brightness electron beam. Reducing the electron beam emittance in an accelerator that drives a Free-Electron Laser (FEL) delivers a significant reduction in the saturation length for an x-ray FEL, thus reducing the machine's construction footprint and operating costs while increasing the x-ray beam brightness. The ability to measure the transverse energy distribution curve of photoelectrons emitted from a photocathode is a key enabler in photocathode research and development that has prompted the Accelerator Science and Technology Centre (ASTeC) at the STFC Daresbury Laboratory to develop the Transverse Energy Spread Spectrometer to make these crucial measurements. We present details of the design for the upgraded TESS instrument with measured data for copper (100), (110), and (111) single-crystal photocathodes illuminated at UV wavelengths around 266nm.

Higher-order non-global logarithms from jet calculus

Non-global QCD observables are characterised by a sensitivity to the full angular distribution of soft radiation emitted coherently in hard scattering processes. This complexity poses a challenge to their all-order resummation, that was formulated at the leading-logarithmic order about two decades ago. In this article we present a solution to the long-standing problem of their resummation beyond this order, and carry out the first complete next-to-leading logarithmic calculation for non-global observables. This is achieved by solving numerically the recently derived set of non-linear differential equations which describe the evolution of soft radiation in the planar, large-Nc limit. As a case study we address the calculation of the transverse energy distribution in the interjet rapidity region in e+e−→ dijet production. The calculation is performed by means of an algorithm that we formulate in the language of jet-calculus generating functionals, which also makes the resummation technique applicable to more general non-global problems, such as those that arise in hadronic collisions. We find that NLL corrections are substantial and their inclusion leads to a significant reduction of the perturbative scale uncertainties for these observables. The computer code used in the calculations is made publicly available.

Bayesian approach to long-range correlations and multiplicity fluctuations in nucleus-nucleus collisions

The number of particles detected in a nucleus-nucleus collision strongly depends on the impact parameter of the collision. Therefore, multiplicity fluctuations, as well as rapidity correlations of multiplicities, are dominated by impact parameter fluctuations. We present a method based on Bayesian inference which allows for a robust reconstruction of fluctuations and correlations at fixed impact parameter. We apply the method to ATLAS data on the distribution of charged multiplicity and transverse energy. We argue that multiplicity fluctuations are smaller at large rapidity than around central rapidity. We suggest simple, new analyses, in order to confirm this effect.

Next-to-leading non-global logarithms in QCD

Non-global logarithms arise from the sensitivity of collider observables to soft radiation in limited angular regions of phase space. Their resummation to next-to-leading logarithmic (NLL) order has been a long standing problem and its solution is relevant in the context of precision all-order calculations in a wide variety of collider processes and observables. In this article, we consider observables sensitive only to soft radiation, characterised by the absence of Sudakov double logarithms, and we derive a set of integro-differential equations that describes the resummation of NLL soft corrections in the planar, large-Nc limit. The resulting set of evolution equations is derived in dimensional regularisation and we additionally provide a formulation that is manifestly finite in four space-time dimensions. The latter is suitable for a numerical integration and can be generalised to treat other infrared-safe observables sensitive solely to soft wide-angle radiation. We use the developed formalism to carry out a fixed-order calculation to mathcal{O}left({alpha}_s^2right) in full colour for both the transverse energy and energy distribution in the interjet region between two cone jets in e+e− collisions. We find that the expansion of the resummed cross section correctly reproduces the logarithmic structure of the full QCD result.

Correction to: Calibration of Transverse Energy Distribution Parameters in a Beam of Infrared Radiation Using a Highly Sensitive Measurement Device

Correction to: Calibration of Transverse Energy Distribution Parameters in a Beam of Infrared Radiation Using a Highly Sensitive Measurement Device

Non–monotonic behaviour in the mean transverse energy of electrons emitted from a reflection–mode p-GaAs(Cs,O) photocathode during its QE degradation through oxygen exposure

We present a study on the evolution of both transverse and longitudinal energy distributions due to oxygen–induced quantum efficiency degradation in the electrons emitted from a reflection–mode p-GaAs(Cs,O)-photocathode over an effective electron affinity range of χ *∼ −0.1 eV to χ *∼ +0.3 eV under illumination wavelengths λ = 808, 635 and 532 nm. For λ = 635 and 532 nm, we found that the mean transverse energy of electrons emitted as the photocathode effective electron affinity increased has a non–monotonic character. Our proposed fitting model links the measured response to changes in the relative number of thermalised and non–thermalised electrons in the total emitted photocurrent.

Застосування градієнтних металоплівкових вихідних дзеркал у газорозрядних лазерах терагерцового діапазону

Subject and Purpose. The problem of output beam matching with the waveguide transmission line often arises when using terahertz lasers. The special quasi-optical devices that are used to combat the problem lead to radiation losses and additional material costs. The aim of this work is to develop appropriate output mirrors for THz lasers so as to make the output laser beam match the transmission line of a given diameter. Methods and Methodology. As part of the experimental research into the action of the output mirror configuration on the parameters of THz laser radiation, gradient metal-film mirrors are made like a transparent substrate with a thin metal layer on it. The layer thickness varies over the substrate surface, forming therewith a transparency spot with a given change in the transmittance in the middle of the mirror. The properties of the gradient metal-film output mirrors are examined as applied to a gas-discharge HCN laser at a wavelength of 337 μm. Results. The gradient metal-film mirrors enable obtaining laser beams of a diameter equal to the inner diameter of the relevant transmission line and with a proper transverse energy distribution. The efficiency of the transmission of laser radiation energy into the waveguide line increases, and so does the performance of the laser installation. Another positive point is that the enhanced transparency in the middle of the mirror raises efficiency of the active substance energy utilization and conveys focusing properties to the flat mirror, which reduces diffraction losses. Conclusions. The employment of gradient metal-film output mirrors makes it possible to raise efficiency of laser installations. The features of metal-film mirrors suggest broad potentials for their application and make reasonable their further research.

Probing the structure of the initial state of heavy-ion collisions with pT -dependent flow fluctuations

The connection between initial-state geometry and anisotropic flow can be quantified through a well-established mapping between $p_T$-integrated flow harmonics and cumulants of the initial transverse energy distribution. In this paper we successfully extend this mapping to also include $p_T$-differential flow. In doing so, we find that subleading principal components of anisotropic flow can reveal previously unobserved details of the hydrodynamic response, in both the linear and the nonlinear regimes. Most importantly, we show that they provide novel information on the small-scale structures present in the initial stage of relativistic heavy-ion collisions.

Calibration of Transverse Energy Distribution Parameters in a Beam of Infrared Radiation Using a Highly Sensitive Measurement Device

A highly sensitive device for measuring the parameters of transverse energy distribution in a beam of infrared radiation is described as part of an automated system of the synthesis of dynamic and static infrared images. The system is designed to monitor the characteristics of matrix photoreceivers in the spectrum of 2.5–4.6 μm at irradiation levels in the range of 10–9–10–5 W/сm2. The device is subject to periodic graduation and verification of the movement accuracy of the Foucault knife line at two coordinates. Measurements using the device were performed following the state and industry standards of the Russian Federation. The scan error for each coordinate did not exceed 1 μm. The device measured the function of energy concentration and the energy concentration coefficient in the formed image plane in the working spectral and dynamic ranges of the system.

Calibration of highly sensitive measurement device of transverse energy distributions in a beam of infrared radiation

A highly sensitive device for measuring the parameters of transverse energy distribution in a beam of infrared radiation is described as part of an automated system of synthesis of dynamic and static infrared images. The system is designed to monitor the characteristics of matrix photo-receivers in the spectrum of 2,5–4,6 μm at irradiation levels in the range of 10 –9–10 –5 W/сm2. The device is subject to periodic gradation and verification of the accuracy of movements of the Foucault knife line movements at two coordinates. Measurements with the use of the device are carried out in accordance with state and industry standards of the Russian Federation. The scan error for each coordinate does not exceed 1 micrometer. The device measures the function of energy concentration, the concentration of energy in the plane formed image in the working spectral and dynamic ranges of the system.

Transverse Energy Density in High Energy Heavy Ion Collisions

A phenomenological model describing the transverse energy distribution (ET) of nuclear collisions is first studied in detail by fitting it on ET data for O-Pb collisions at √sNN = 200 GeV per nucleon obtained from the NA35 collaboration. Next, the model is used to fit the ET data for Pb-Pb collisions at LHC energies of √sNN = 2.76 TeV per nucleon obtained from the ATLAS collaboration. From the fits, we determine an upper bound for the energy density for Pb-Pb collisions at LHC energies of √sNN = 2.76 TeV per nucleon.

Asymmetric optical vortex in plasma density gradient

A vortex laser pulse is incident on a plasma with a density gradient along one transverse direction and a homogeneous density along the other one. As the laser pulse propagates in the plasma, the transverse energy distribution becomes asymmetric along the direction with the homogeneous density, which is shown from particle-in-cell simulations. We demonstrate theoretically that the asymmetric energy distribution results from the rate of plasma density change along the transverse energy flow of the vortex beam. Meanwhile, the degree of asymmetry is found to be positively related to the topological charge of the vortex beam as well as the density gradient of the plasma. Our finding provides a new approach for measuring the topological charge of a vortex beam, and also implies an available probe of the inhomogeneity of an optical medium.

Centrality and pseudorapidity dependence of the transverse energy density inpPbcollisions atsNN=5.02TeV

The almost hermetic coverage of the CMS detector is used to measure the distribution of transverse energy, $E_\mathrm{T}$, over 13.2 units of pseudorapidity, $\eta$, for pPb collisions at a center-of-mass energy per nucleon pair of $\sqrt{s_\mathrm{NN}} =$ 5.02 TeV. The huge angular acceptance exploits the fact that the CASTOR calorimeter at $-6.6$ $<$ $\eta$ $<$ $-5.2$ is effectively present on both sides of the colliding system because of a switch in the proton-going and lead-going beam directions. This wide acceptance enables the study of correlations between well-separated angular regions and makes the measurement a particularly powerful test of event generators. For minimum bias pPb collisions the maximum value of d$E_\mathrm{T}/$d$\eta$ is 22 GeV, which implies an $E_\mathrm{T}$ per participant nucleon pair comparable to that of peripheral PbPb collisions at $\sqrt{s_\mathrm{NN}} =$ 2.76 TeV. The increase of d$E_\mathrm{T}/$d$\eta$ with centrality is much stronger for the lead-going side than for the proton-going side. The $\eta$ dependence of d$E_\mathrm{T}/$d$\eta$ is sensitive to the $\eta$ range in which the centrality variable is defined. Several modern generators are compared to these results but none is able to capture all aspects of the $\eta$ and centrality dependence of the data and the correlations observed between different $\eta$ regions.

Charged-particle multiplicity and transverse-energy distribution using the Weibull-Glauber approach in heavy-ion collisions

The charged-particle multiplicity distribution and the transverse-energy distribution measured in heavy-ion collisions at top RHIC and LHC energies are described using the two-component model approach based on a convolution of the Monte Carlo Glauber model with the Weibull model for particle production. The model successfully describes the multiplicity and transverse-energy distribution of minimum-bias collision data for a wide range of energies. The Weibull-Glauber model can be used to determine the centrality classes in heavy-ion collisions as an alternative to the conventional negative binomial distribution (NBD)-Glauber approach.

Evolution of the transverse and longitudinal energy distributions of electrons emitted from a GaAsP photocathode as a function of its degradation state

We present measurements of the transverse and longitudinal energy spread of photoelectrons emitted from a GaAsP photocathode as a function of its degradation state. The cathode was initially activated to a state of negative electron affinity in our photocathode preparation facility, achieving a quantum efficiency of 3% at a wavelength of 532 nm. It was then transferred under XHV conditions to our transverse energy spread spectrometer, where energy spread measurements were made while the photocathode was progressively degraded through a controlled exposure to oxygen. Data have been collected under photocathode illumination at 532 nm, and the changing photoelectron energy distribution associated with the changes in the level of electron affinity due to quantum efficiency degradation through an exposure to 0.25 L of oxygen has been demonstrated. Our experiments have shown that GaAsP boasts a significantly higher resilience to degradation under exposure to oxygen than a GaAs photocathode, though it does exhibit a higher level of mean transverse energy. Coupled with the favourable published data on GaAsP photoemission response times, we conclude that GaAsP is a viable candidate material as a particle accelerator electron source.

Flow performance in MPD at NICA

The Nuclotron-based Ion Collider facility (NICA) in Dubna, Russia is currently under construction at the Joint Institute for Nuclear Research (JINR). A Multi Purpose Detector (MPD) at NICA is designed to study properties of baryonic dense matter in the range of center of mass collision energy from 4 to 11 GeV. We present a performance study for anisotropic transverse flow measurement in Au+Au collisions using the UrQMD event generator and Geant4 simulation of the MPD response. The collision symmetry plane is estimated from event-by-event transverse energy distribution in Forward Hadron Calorimeters (FHCal’s). Performance of the MPD for a measurement of the directed (v1) and elliptic (v2) flow of identified charged hadrons is evaluated based on comparison between reconstructed v1 and v2 values and the input one from the UrQMD model.

Transverse Energy Measurements from the Beam Energy Scan in PHENIX

Transverse energy distributions at midrapidity have been measured by the PHENIX experiment at the BNL Relativistic Heavy Ion Collider (RHIC) for Au+Au, U+U, Cu+Au, Cu+Cu, 3He+Au, d+Au, and p+p collisions over a wide energy range from sNN=7.7 GeV to sNN=200 GeV as a function of centrality. For central Au+Au collisions, it is observed that the midrapidity Bjorken energy density demonstrates a power law behavior from sNN=7.7 GeV to sNN=2.76 TeV. At a given collision energy, the data presented as a function of Npart are independent of the size of the collision system. For Au+Au, Cu+Au, and Cu+Cu collisions, the centrality-dependent data are better described by scaling with the number of constituent quark participants than scaling with the number of nucleon participants.