Femtosecond Laser Fabrication of Anisotropic Structures in Phosphorus- and Boron-Doped Amorphous Silicon Films

Femtosecond laser-modified amorphous silicon (a-Si) films with optical and electrical anisotropy have perspective polarization-sensitive applications in optics, photovoltaics, and sensors. We demonstrate the formation of one-dimensional femtosecond laser-induced periodic surface structures (LIPSS) on the surface of phosphorus- (n-a-Si) and boron-doped (p-a-Si) amorphous silicon films. The LIPSS are orthogonal to the laser polarization, and their period decreases from 1.1 ± 0.1 µm to 0.84 ± 0.07 µm for p-a-Si and from 1.06 ± 0.03 to 0.98 ± 0.01 for n-a-Si when the number of laser pulses per unit area increases from 30 to 120. Raman spectra analysis indicates nonuniform nanocrystallization of the irradiated films, with the nanocrystalline Si phase volume fraction decreasing with depth from ~80 to ~40% for p-a-Si and from ~20 to ~10% for n-a-Si. LIPSS’ depolarizing effect, excessive ablation of the film between LIPSS ridges, as well as anisotropic crystalline phase distribution within the film lead to the emergence of conductivity anisotropy of up to 1 order for irradiated films. Current–voltage characteristic nonlinearity observed for modified p-a-Si samples may be associated with the presence of both the crystalline and amorphous phases, resulting in the formation of potential barriers for the in-plane carrier transport and Schottky barriers at the electric contacts

Peculiarities of electronic structure of silicon-on-insulator structures and their interaction with synchrotron radiation

SOI (silicon-on-insulator) structures with strained and unstrained silicon layers were studied by ultrasoft X-ray emission spectroscopy and X-ray absorption near edge structure spectroscopy with the use of synchrotron radiation techniques. Analysis of X-ray data has shown a noticeable transformation of the electron energy spectrum and local partial density of states distribution in valence and conduction bands in the strained silicon layer of the SOI structure. USXES Si L2,3 spectra analysis revealed a decrease of the distance between the L2v′ и L1v points in the valence band of the strained silicon layer as well as a shift of the first two maxima of the XANES first derivation spectra to the higher energies with respect to conduction band bottom Ec. At the same time the X-ray standing waves of synchrotron radiation (λ~12–20 nm) are formed in the silicon-on-insulator structure with and without strains of the silicon layer. Moreover changing the synchrotron radiation grazing angle θ by 2° leads to a change of the electromagnetic field phase to the opposite

Pseudorapidity densities of charged particles with transverse momentum thresholds in pp collisions at √ s = 5.02 and 13 TeV

The pseudorapidity density of charged particles with minimum transverse momentum (pT) thresholds of 0.15, 0.5, 1, and 2 GeV/c is measured in pp collisions at the center of mass energies of √s=5.02 and 13 TeV with the ALICE detector. The study is carried out for inelastic collisions with at least one primary charged particle having a pseudorapidity (η) within 0.8pT larger than the corresponding threshold. In addition, measurements without pT-thresholds are performed for inelastic and nonsingle-diffractive events as well as for inelastic events with at least one charged particle having |η|2GeV/c), highlighting the importance of such measurements for tuning event generators. The new measurements agree within uncertainties with results from the ATLAS and CMS experiments obtained at √s=13TeV.

Production of Λ\Lambda and KS0{\rm K}^{0}_{\rm S} in jets in p-Pb collisions at sNN=5\sqrt{s_{\rm NN}} = 5 TeV and pp collisions at s=7\sqrt{s} = 7 TeV

The production of $\Lambda$ baryons and ${\rm K}^{0}_{\rm S}$ mesons (${\rm V}^{0}$ particles) was measured in p-Pb collisions at $\sqrt{s_{\rm NN}} = 5$ TeV and pp collisions at $\sqrt{s} = 7$ TeV with ALICE at the LHC. The production of these strange particles is studied separately for particles associated with hard scatterings and the underlying event to shed light on the baryon-to-meson ratio enhancement observed at intermediate transverse momentum ($p_{\rm T}$) in high multiplicity pp and p-Pb collisions. Hard scatterings are selected on an event-by-event basis with jets reconstructed with the anti-$k_{\rm T}$ algorithm using charged particles. The production of strange particles associated with jets $p_{\rm T,\;jet}^{\rm ch}>10$ GeV/$c$ is reported as a function of $p_{\rm T}$ in both systems; and its dependence on $p_{\rm T}$ with jets $p_{\rm T,\;jet}^{\rm ch}>20$ GeV/$c$ and on angular distance from the jet axis, $R({\rm V}^{0},\;{\rm jet})$, for jets with $p_{\rm T,\;jet}^{\rm ch} > 10$ GeV/$c$ are reported in p-Pb collisions. The results are compared with the strange particle production in the underlying event. The $\Lambda/{\rm K}^{0}_{\rm S}$ ratio associated with jets in p-Pb collisions for $R({\rm V}^{0},\;{\rm jet})<0.4$ is consistent with the ratio measured in pp collisions and with the expectation of jets fragmenting in vacuum given by the PYTHIA event generator

Inclusive J/ψ\psi production at midrapidity in pp collisions at s = 13\sqrt{s}~=~13 TeV

We report on the inclusive J/$\psi$ production cross section measured at the CERN Large Hadron Collider in proton-proton collisions at a centre-of-mass energy $\sqrt{s}~=~13$ TeV. The J/$\psi$ mesons are reconstructed in the $\rm e^{+} e^{-}$ decay channel and the measurements are performed at midrapidity ($|y|<0.9$) in the transverse-momentum interval $0< p_{\rm T} <40$ GeV/$c$, using a minimum bias data sample corresponding to an integrated luminosity $L_{\text{int}} = 32.2~\text{nb}^{-1}$ and an Electromagnetic Calorimeter triggered data sample with $L_{\text{int}} = 8.3~\mathrm{pb}^{-1}$. The $p_{\rm T}$-integrated J/$\psi$ production cross section at midrapidity, computed using the minimum bias data sample, is $\text{d}\sigma/\text{d}y|_{y=0} = 8.97\pm0.24~(\text{stat})\pm0.48~(\text{syst})\pm0.15~(\text{lumi})~\mu\text{b}$. An approximate logarithmic dependence with the collision energy is suggested by these results and available world data, in agreement with model predictions. The integrated and $p_{\rm T}$-differential measurements are compared with measurements in pp collisions at lower energies and with several recent phenomenological calculations based on the non-relativistic QCD and Color Evaporation models

Azimuthal correlations of prompt D mesons with charged particles in pp and p–Pb collisions at sNN\sqrt{s_{NN}} = 5.02 TeV

International audienceThe measurement of the azimuthal-correlation function of prompt D mesons with charged particles in pp collisions at $\sqrt{s} =5.02\ \hbox {TeV}$ and p–Pb collisions at $\sqrt{s_{\mathrm{NN}}} = 5.02\ \hbox {TeV}$ with the ALICE detector at the LHC is reported. The $\mathrm{D}^{0}$, $\mathrm{D}^{+}$, and $\mathrm{D}^{*+}$ mesons, together with their charge conjugates, were reconstructed at midrapidity in the transverse momentum interval $3 0.3\ \hbox {GeV}/c$ and pseudorapidity $|\eta | < 0.8$. The properties of the correlation peaks appearing in the near- and away-side regions (for $\Delta \varphi \approx 0$ and $\Delta \varphi \approx \pi$, respectively) were extracted via a fit to the azimuthal correlation functions. The shape of the correlation functions and the near- and away-side peak features are found to be consistent in pp and p–Pb collisions, showing no modifications due to nuclear effects within uncertainties. The results are compared with predictions from Monte Carlo simulations performed with the PYTHIA, POWHEG+PYTHIA, HERWIG, and EPOS 3 event generators

Λc+\Lambda^+_c production in pppp and in pp-Pb collisions at sNN\sqrt {s_{NN}}=5.02 TeV

International audienceThe production cross section of prompt $\mathrm{\Lambda_{c}^{+}}$ charm baryons was measured with the ALICE detector at the LHC at midrapidity in proton-proton (pp) and proton-lead (p-Pb) collisions at a centre-of-mass energy per nucleon pair of $\sqrt{s_\mathrm{NN}} = 5.02$ TeV. The $\mathrm{\Lambda_{c}^{+}}$ and $\rm {\overline{\Lambda}{}_c^-}$ baryons were reconstructed in the hadronic decay channels $\rm \Lambda_{c}^{+} \rightarrow p K^{-}\pi^{+}$ and $\rm \Lambda_{c}^{+}\to p K^{0}_{S}$ and respective charge conjugates. The measured differential cross sections as a function of transverse momentum ($p_{\rm T}$) and the $p_{\rm T}$-integrated $\mathrm{\Lambda_{c}^{+}}$ production cross section in pp and in p-Pb collisions are presented. The $\mathrm{\Lambda_{c}^{+}}$ nuclear modification factor ($R_\mathrm{pPb}$), calculated from the cross sections in pp and in p-Pb collisions, is presented and compared with the $R_\mathrm{pPb}$ of D mesons. The $\mathrm {\Lambda_{c}^{+}}/\mathrm {D^0}$ ratio is also presented and compared with the light-flavour baryon-to-meson ratios p$/\pi$ and $\Lambda /\mathrm {K^0_S}$, and measurements from other LHC experiments. The results are compared to predictions from model calculations and Monte Carlo event generators

Measurement of Prompt D0^{0}, Λc+\Lambda_{c}^{+}, and Σc0,++\Sigma_{c}^{0,++}(2455) Production in Proton–Proton Collisions at s\sqrt s = 13 TeV

International audienceThe pT-differential production cross sections of prompt D0, Λc+, and Σc0,++(2455) charmed hadrons are measured at midrapidity (|y|&lt;0.5) in pp collisions at s=13  TeV. This is the first measurement of Σc0,++ production in hadronic collisions. Assuming the same production yield for the three Σc0,+,++ isospin states, the baryon-to-meson cross section ratios Σc0,+,++/D0 and Λc+/D0 are calculated in the transverse momentum (pT) intervals 2&lt;pT&lt;12 and 1&lt;pT&lt;24  GeV/c. Values significantly larger than in e+e- collisions are observed, indicating for the first time that baryon enhancement in hadronic collisions also extends to the Σc. The feed-down contribution to Λc+ production from Σc0,+,++ is also reported and is found to be larger than in e+e- collisions. The data are compared with predictions from event generators and other phenomenological models, providing a sensitive test of the different charm-hadronization mechanisms implemented in the models

First measurement of antideuteron number fluctuations at energies available at the Large Hadron Collider

The first measurement of event-by-event antideuteron number fluctuations in high energy heavy-ion collisions is presented. The measurements are carried out at midrapidity (|\eta| |η|<0.8) as a function of collision centrality in Pb-Pb collisions at sNN=5.02  TeV using the ALICE detector. A significant negative correlation between the produced antiprotons and antideuterons is observed in all collision centralities. The results are compared with a state-of-the-art coalescence calculation. While it describes the ratio of higher order cumulants of the antideuteron multiplicity distribution, it fails to describe quantitatively the magnitude of the correlation between antiproton and antideuteron production. On the other hand, thermal-statistical model calculations describe all the measured observables within uncertainties only for correlation volumes that are different with respect to those describing proton yields and a similar measurement of net-proton number fluctuations.The first measurement of event-by-event antideuteron number fluctuations in high energy heavy-ion collisions is presented. The measurements are carried out at midrapidity (|\eta| < 0.8$) as a function of collision centrality in Pb$-$Pb collisions at$\sqrt{s_{\rm NN}} = 5.02$ TeV using the ALICE detector. A significant negative correlation between the produced antiprotons and antideuterons is observed in all collision centralities. The results are compared with a state-of-the-art coalescence calculation. While it describes the ratio of higher order cumulants of the antideuteron multiplicity distribution, it fails to describe quantitatively the magnitude of the correlation between antiproton and antideuteron production. On the other hand, thermal-statistical model calculations describe all the measured observables within uncertainties only for correlation volumes that are different with respect to those describing proton yields and a similar measurement of net-proton number fluctuations