Final-state Spectrum Research Articles

Dark sector studies with the PADME experiment

The Positron Annihilation to Dark Matter Experiment (PADME) uses the positron beam of the DA\PhiΦNE Beam-Test Facility, at the Laboratori Nazionali di Frascati (LNF) to search for a Dark Photon A’. The search technique studies the missing mass spectrum of single-photon final states in e^+e^-\rightarrow A'\gammae+e−→A′γ annihilation in a positron-on-thin-target experiment. This approach facilitates searches for new particles such as long lived Axion-Like-Parti-cles, protophobic X bosons and Dark Higgs. This talk illustrated the scientific program of the experiment and its first physics results. In particular, the measurement of the cross-section of the SM process e^+e^-\rightarrow \gamma\gammae+e−→γγ at \sqrt{s}s=21 MeV was shown.

Identifying the nature of the QCD transition in relativistic collision of heavy nuclei with deep learning

Using deep convolutional neural network (CNN), the nature of the QCD transition can be identified from the final-state pion spectra from hybrid model simulations of heavy-ion collisions that combines a viscous hydrodynamic model with a hadronic cascade “after-burner”. Two different types of equations of state (EoS) of the medium are used in the hydrodynamic evolution. The resulting spectra in transverse momentum and azimuthal angle are used as the input data to train the neural network to distinguish different EoS. Different scenarios for the input data are studied and compared in a systematic way. A clear hierarchy is observed in the prediction accuracy when using the event-by-event, cascade-coarse-grained and event-fine-averaged spectra as input for the network, which are about 80%, 90% and 99%, respectively. A comparison with the prediction performance by deep neural network (DNN) with only the normalized pion transverse momentum spectra is also made. High-level features of pion spectra captured by a carefully-trained neural network were found to be able to distinguish the nature of the QCD transition even in a simulation scenario which is close to the experiments.

Simulación de la reacción de captura neutrónica por gadolinio por medio de GEANT4

El uso de nucleidos de gadolinio como agentes de captura de neutrones en la terapia de cáncer por captura neutrónica es de gran interés debido principalmente a su alta sección eficaz de 225.000 barns. El espectro del estado final de la reacción contiene 158-gadolinio (158Gd), emisión de fotones (rayos X y rayos gamma) y electrones (conversión interna y Auger). Este espectro ofrece una física muy rica y de enorme potencial para la eliminación de células tumorales debido a su alta transferencia lineal de energía. En este trabajo presentamos simulaciones de este proceso, realizadas en las últimas seis versiones de Geant4 (10.00.p04, 10.01.p03, 10.02.p03, 10.03.p03, 10.04.p03 y 10.05.p01). Tomando en cuenta que para este trabajo nos interesan particularmente los neutrones de baja energía (energías < 20 MeV), usaremos el paquete G4NeutronHP. Finalmente obtenemos el conteo de eventos, la energía promedio y las distribuciones angulares (theta y phi) de las partículas en el estado final, encontrando, de esta manera, que para neutrones de baja energía, el estudio de la reacción de captura neutrónica por 158Gd es viable con Geant4.

Pseudo-rapidity distribution from a perturbative solution of viscous hydrodynamics for heavy ion collisions at RHIC and LHC**Supported by National Natural Science Foundation of China (11435004), the Chinese-Hungarian bilateral cooperation program (Te’T 12CN-1-2012-0016) and the CCNU PhD Fund 2016YBZZ100 of China

The charged-particle final state spectrum is derived from an analytic perturbative solution for relativistic viscous hydrodynamics. By taking into account the longitudinal acceleration effect in relativistic viscous hydrodynamics, the pseudorapidity spectrum describes the nucleus-nucleus colliding systems at RHIC and the LHC well. Based on both the extracted longitudinal acceleration parameter and a phenomenological description of , the charged-particle pseudorapidity distributions for Xe+Xe collisions are computed from the final state expression in a limited space-time rapidity region.

Revised neutrino-gallium cross section and prospects of BEST in resolving the gallium anomaly

O(1) eV sterile neutrino can be responsible for a number of anomalous results of neutrino oscillation experiments. This hypothesis may be tested at short base-line neutrino oscillation experiments, several of which are either ongoing or under construction. Here we concentrate on the so-called Gallium anomaly, found by SAGE and GALLEX experiments, and its foreseeable future tests with BEST experiment at Baksan Neutrino Observatory. We start with a revision of the neutrino-gallium cross section, that is performed by utilizing the recent measurements of the nuclear final state spectra. We accordingly correct the parameters of Gallium anomaly and refine the BEST prospects in testing it and searching for sterile neutrinos. We further evolve the previously proposed idea to investigate the anomaly with Zn-65 artificial neutrino source as a next option available at BEST, and estimate its sensitivity to the sterile neutrino model parameters following the Bayesian approach. We show that after the two stages of operation BEST will make 5$\sigma$-discovery of the sterile neutrinos, if they are behind the Gallium anomaly.

Identifying QCD Transition Using Deep Learning

In this proceeding we review our recent work using supervised learning with a deep convolutional neural network (CNN) to identify the QCD equation of state (EoS) employed in hydrodynamic modeling of heavy-ion collisions given only final-state particle spectra ρ(pT, Ф). We showed that there is a traceable encoder of the dynamical information from phase structure (EoS) that survives the evolution and exists in the final snapshot, which enables the trained CNN to act as an effective “EoS-meter” in detecting the nature of the QCD transition.

Thermal conductivity of type-I, type-II, and type-VIII pristine silicon clathrates: A first-principles study

By applying first-principles Peierls-Boltzmann transport calculations, the lattice thermal conductivities of type-I, type-II, and type-VIII silicon clathrates are investigated. The lattice thermal conductivity, spectral lattice thermal conductivity, and lattice thermal conductivity versus mean-free path (MFP) of phonons, relaxation times, and the anharmonicity of selected Si clathrates are calculated and compared. The microscopic origin of the slight difference in the lattice thermal conductivity of Si-I/II/VIII clathrates is discussed extensively. Our calculations uncover that the impact of phonon group velocity on the lattice thermal conductivity is far from enough to explain the discrepancies in ${\ensuremath{\kappa}}_{\text{lat}}$ of studied Si clathrates and it mainly is a consequence of the shorter lifetimes of the acoustic modes in type-VIII structure. Similarity between phase space for three-phonon anharmonic scattering processes of studied silicon clathrates highlights the influence of three-phonon coupling strength and the further calculation of the frequency-resolved final state spectra re-emphasizes that the subtle differences arise from the stronger three-phonon interaction coefficients.

News on collectivity in Pb-Pb collisions from the ALICE experiment

The collective expansion of the color-deconfined fireball created in ultra-relativistic heavy-ion collisions maps the initial state of the quark-gluon plasma (QGP) to the final-state particle spectrum. The ALICE experiment has been leading important roles for completing the individual flow harmonic measurements at the highest energies to date as well as improving flow harmonic correlation techniques to understand the properties of the QGP and the full evolution of the heavy-ion collisions. In this article, a brief summary of the individual flow harmonic measurements, the details of the new observables developed in recent years from ALICE collaboration and their implications to future studies are discussed.

Laser angle-resolved photoemission as a probe of initial statekzdispersion, final-state band gaps, and spin texture of Dirac states in theBi2Te3topological insulator

Angle-resolved photoemission spectroscopy (ARPES) is widely used to investigate topological states and their spin textures in topological materials. Here, the authors examine the role of the ARPES matrix element in laser-ARPES spectra, and delineate how imprints of the Dirac states and their spin textures are encoded in these spectra in terms of the character and symmetry of the underlying initial and final states. For this purpose, they collect laser-ARPES spectra from the exemplar topological insulator material Bi${}_{2}$Te${}_{3}$ over a wide range of momenta in the ${k}_{x}$-k${}_{y}$ plane at energies ranging from 5.57--6.70 eV for two different linear polarizations of the incident light. The experimental results are analyzed via first-principles fully relativistic calculations of ARPES intensities within the framework of the one-step model of photoemission. These include effects of the ARPES matrix element from a semi-infinite solid surface. The authors obtain new insight into the nature of the laser-ARPES spectra from topological materials, and show how these spectra contain fingerprints of the initial state ${k}_{z}$ dispersions and spin textures of the Dirac-cone states, and how laser-ARPES could open a previously unrecognized window on the presence of delicate gaps in the final-state spectra.

Non-exponential Auger decay

We discuss the possibility of non-exponential Auger decay of atoms irradiated by X-ray photons. This effect can occur at times, which are greater than the lifetime of a system under consideration. The mechanism for non-exponential depletion of an initial quasi-stationary state is the cutting of the electron energy spectrum of final continuous states at small energies. Then the Auger decay amplitude obeys t−1/2 power-law dependence on long observation times.

Non-exponential tunneling ionization of atoms by an intense laser field

We discuss the possibility of non-exponential tunneling ionization of atoms irradiated by intense laser field. This effect can occur at times which are greater than the lifetime of a system under consideration. The mechanism for non-exponential depletion of an initial quasi-stationary state is the cutting of the energy spectrum of final continuous states at long times. We first consider the known examples of cold emission of electrons from metal, tunneling alpha-decay of atomic nuclei, spontaneous decay in two-level systems, and the single-photon atomic ionization by a weak electromagnetic field. The new physical situation discussed is tunneling ionization of atoms by a strong low-frequency electromagnetic field. In this case the decay obeys ∼1/t power-law dependence on the (long) interaction times.

Model and parameter dependence of heavy quark energy loss in a hot and dense medium

Within the framework of the Langevin equation, we study the energy loss of heavy quarks due to quasi-elastic multiple scatterings in a quark–gluon plasma created by relativistic heavy-ion collisions. We investigate how the initial configuration of the quark–gluon plasma as well as its properties affect the final state spectra and elliptic flow of D-mesons and non-photonic electrons. We find that both the geometric anisotropy of the initial quark–gluon plasma and the flow profiles of the hydrodynamic medium play important roles in the heavy quark energy loss process and the development of elliptic flow. The relative contribution from charm and bottom quarks is found to affect the transverse momentum dependence of the quenching and flow patterns of heavy flavor decay electron; such influence depends on the interaction strength between heavy quarks and the medium.

Resonant photoemission at the O1s threshold to characterize In2O3 single crystals

We report on spectroscopic investigations on In2O3 single crystals. We focus on the detailed analysis of the O1s resonance profile by resonant photoelectron spectroscopy. We analyze the electronic structure and assign the O2p to build the valence band and both, O2p and In5s5p states to contribute to the conduction band (CB). We determine the partial density of states for the valence and CBs and find a strong hybridization of O2p and In5s states. This is deduced from constant final state spectra on the O-KLL-Auger over the O K-edge and In M4,5-edge and a comparison to the corresponding X-ray absorption spectroscopy data. We also identify several types of defects. A broad band of oxygen derived defects is identified that extends throughout the gap. These are attributed to small polarons which cause an anti-resonance in the valence states around the O1s threshold. In addition, a separate Auger decay at resonance indicates the existence of localized charge transfer states which involves localized In5s5p states.

Heavy quark energy loss and thermalization in hot and dense nuclear matter

We study heavy quark energy loss and thermalization in hot and dense nuclear medium. The diffusion of heavy quarks is calculated via a Langevin equation, both for a static medium as well as for a quark-gluon plasma (QGP) medium generated by a (3+1)-dimensional hydrodynamic model. We investigate how the initial configuration of the QGP and its properties affect the final state spectra and elliptic flow of heavy flavor mesons and non-photonic electrons. It is observed that both the geometric anisotropy of the initial profile and the flow profile of the hydrodynamic medium play important roles in the heavy quark energy loss process and the development of elliptic flow. Within our definition of the thermalization criterion and for reasonable values of the diffusion constant, we observe thermalization times that are longer than the lifetime of the QGP phase.

Formation and decay of core-orbital vacancies in the water molecule

Primary steps in the interaction of high energy photons with water creating multiply ionised products are examined experimentally and theoretically. Double Auger decay from a 1s-hole state populates triply ionised states between 80 and 140eV binding energy. Ejection of one 1s electron and one valence electron gives states around 570eV which decay to triply ionised states between 75 and 110eV. Nuclear motion in these states competes with Auger decay and substantially modifies the final state spectra. The double core–hole state from ionisation of both 1s electrons is found at 1171±1eV and calculated at 1170.85eV.

Direct probe of the variability of Coulomb correlation in iron pnictide superconductors

We use core-valence-valence Auger spectra to probe the Coulomb repulsion between holes in the valence band of Fe pnictide superconductors. By comparing the two-hole final-state spectra to density functional theory calculations of the single-particle density of states, we extract a measure of the electron correlations that exist in these systems. Our results show that the Coulomb repulsion is highly screened and can definitively be considered as weak. We also find that there are differences between the 1111 and 122 families and even a small variation as a function of the doping $x$ in Ba(Fe${}_{1\ensuremath{-}x}$Co${}_{x}$)${}_{2}$As${}_{2}$. We discuss how the values of the hole-hole Coulomb repulsion obtained from our study relate to the onsite Coulomb parameter $U$ used in model and first-principles calculations based on dynamical mean field theory and establish an upper bound for its effective value. Our results impose stringent constraints on model-based phase diagrams that vary with the quantity $U$ or $U$/$W$ by restricting the latter to a rather small range of values.

Collider signatures of goldstini in gauge mediation

We investigate the collider signatures of the multiple goldstini scenario in the framework of gauge mediation. This class of models is characterized by a visible sector (e.g. the MSSM or any extension) coupled by gauge interactions to more than one SUSY breaking sector. The spectrum consists of a light gravitino LSP, behaving as a goldstino, and a number of neutral fermions (the pseudo-goldstini) with a mass between that of the LSP and that of the lightest particle of the observable sector (LOSP). We consider the two situations where the LOSP is either a gaugino-like neutralino or a stau and we assume only one pseudo-goldstino of a mass of O(100) GeV. The coupling of the LOSP to the pseudo-goldstino can be enhanced with respect to those of the gravitino giving rise to characteristic signatures. We show that the decay modes of the LOSP into a SM particle and a pseudo-goldstino can be significant. For both LOSP scenarios we analyze (pseudo)-goldstini production at colliders. Compared to standard gauge mediation the final state spectrum is softer and more structured.

Observation of UV-induced Auger features in catechol adsorbed on anatase TiO2 (101) single crystal surface

We have investigated the electronic structure of catechol adsorbed on the anatase TiO2 (101) surface under illumination with ultraviolet (UV) light (4.75 eV) using resonant photoemission spectroscopy. UV illumination results in the appearance of a strong Ti MVV (M refers to photoionization of 3p level and VV the Auger decay process via the valence levels) feature at a kinetic energy of 26.2 eV. This is attributed to the creation of localised states following catechol to Ti-3d excitation by the UV source. A sharp resonance attributed to excitation from Ti 3p states into these localised states is observed in constant final state spectra.

Resonant Photoemission at the O1s threshold to characterize β-Ga2O3 single crystals

We report on spectroscopic investigations on β-Ga2O3 single crystals. We focus on the detailed analysis of the O1s resonance profile by resonant photoelectron spectroscopy. We analyze the electronic structure and assign the O2p to build the valence band and both, O2p and Ga4s4p states to contribute to the conduction band. We determine the partial density of states for the valence and conduction bands and find a strong hybridization of O2p and Ga4s states. This is deduced from constant final state spectra on the O-KLL-Auger over the O K-edge and Ga L2,3-edge and a comparison to the corresponding X-ray absorption spectroscopy data. We also identify several types of defects. A broad band of oxygen derived defects is identified that extends throughout the gap. Small polarons are attributed to cause an anti-resonance in the valence states around the O1s threshold. In addition, a separate Auger decay at resonance indicates the existence of localized charge transfer states which involves localized Ga4sp states.

Dark matter detection with hard X-ray telescopes

We analyze the impact of future hard X-ray observations on the search for indirect signatures of particle dark matter in large extragalactic systems such as nearby clusters or groups of galaxies. We argue that the hard X-ray energy band falls squarely at the peak of the inverse Compton emission from electrons and positrons produced by dark matter annihilation or decay for a large class of dark matter models. Specifically, the most promising are low-mass models with a hard electron-positron annihilation final state spectrum and intermediate-mass models with a soft electron-positron spectrum. We find that constraints on dark matter models similar to the current constraints from the Fermi Gamma-Ray Space Telescope will be close to the sensitivity limit of the near-term hard X-ray telescopes NuSTAR and ASTRO-H for relatively long observations. An instrument like the Wide Field Imager (WFI) proposed for ATHENA would instead give a significant gain in sensitivity to dark matter if placed in a low background orbit similar to NuSTAR's; however, given the higher expected background level for ATHENA's proposed orbit at L2, its sensitivity will be similar to that of NuSTAR.