arXiv subjects

Mark Sutton

Publications and source records attributed to Mark Sutton.

At least 19 recordsLinked to original sources

arXiv2024

Precise Determination of the Strong Coupling Constant from Dijet Cross Sections up to the Multi-TeV Range

We determine the value of the strong coupling $\alpha_\text{s}$ and study its running over a wide range of scales as probed by the dijet production process at hadron colliders, based on an NNLO QCD analysis of LHC dijet data. From a large subset of these data a value of $\alpha_\text{s} (m_\text{Z}) = 0.1178 \pm 0.0022$ is obtained for the strong coupling at the scale of the Z-boson mass $m_\text{Z}$, using the invariant mass of the dijet system to select the scale where $\alpha_\text{s}$ is probed. The combination of different data sets enhances the reach and precision of the analysis in the mutli-TeV range and allows for the first determination of $\alpha_\text{s}$ up to scales of 7 TeV. Complementing the LHC data with dijet cross sections measured at the HERA electron-proton collider, the kinematic range is extended to test the running of the strong coupling towards smaller scales. Our results exhibit excellent agreement with predictions based on the renormalization group equation of QCD, and represent a comprehensive test of the asymptotic behavior of QCD, spanning more than three orders of magnitude in energy scale.

hep-ph↗

arXiv2024

Dynamics of Nanoscale Phase Decomposition in Laser Ablation

Femtosecond laser ablation is a process that bears both fundamental physics interest and has wide industrial applications. For decades, the lack of probes on the relevant time and length scales has prevented access to the highly nonequilibrium phase decomposition processes triggered by laser excitation. Enabled by the unprecedented intense femtosecond X-ray pulses delivered by an X-ray free electron laser, we report here results of time-resolved small angle scattering measurements on the dynamics of nanoscale phase decomposition in thin gold films upon femtosecond laser-induced ablation. By analyzing the features imprinted onto the small angle diffraction patterns, the transient heterogeneous density distributions within the ablation plume as obtained from molecular dynamics simulations get direct experimental confirmation.

cond-mat.mtrl-sci↗

arXiv2022

Ultrafast Photo-induced Phase Change in SnSe

Time-resolved multi-terahertz (THz) spectroscopy is used to observe an ultrafast, non-thermal electronic phase change in SnSe driven by interband photoexcitation with 1.55 eV pump photons. The transient THz photoconductivity spectrum is found to be Lorentzian-like, indicating charge localization and phase segregation. The rise of photoconductivity is bimodal in nature, with both a fast and slow component due to excitation into multiple bands and subsequent intervalley scattering. The THz conductivity magnitude, dynamics, and spectra show a drastic change in character at a critical excitation fluence of approximately 6 mJ/cm^2 due to a photo-induced phase segregation and a macroscopic collapse of the band gap.

cond-mat.mtrl-sci↗

arXiv2021

Generation of highly mutually coherent hard x-ray pulse pairs with an amplitude-splitting delay line

Beam splitters and delay lines are among the key building blocks of modern-day optical laser technologies. Progress in x-ray free electron laser source development and applications over the past decade is calling for their counter part operating in the Angstrom wavelength regime. Recent efforts in x-ray optics development have demonstrated relatively stable delay lines that most often adopted the division of wavefront approach for the beam splitting and recombination configuration. However, the two recombined beams have yet to achieve sufficient mutual coherence to enable applications such as interferometry, correlation spectroscopy, and nonlinear spectroscopy. We present the first experimental realization of the generation of highly mutually coherent pulse pairs using an amplitude-split delay line design based on transmission grating beam splitters and channel-cut crystal optic delay lines. The performance of the prototype system was analyzed in the context of x-ray coherent scattering and correlation spectroscopy, where we obtained nearly identical high-contrast speckle patterns from both branches. We show in addition the high level of dynamical stability during continuous delay scans, a capability essential for high sensitivity ultra-fast measurements.

physics.optics↗

arXiv2021

Nanoscale heterogeneous dynamics probed by nanosecond x-ray speckle visibility spectroscopy

We report observations of nanosecond nanometer scale heterogeneous dynamics in a free flowing colloidal jet revealed by ultrafast x-ray speckle visibility spectroscopy. The nanosecond double-bunch mode of the Linac Coherent Light Source free electron laser enabled the production of pairs of femtosecond coherent hard x-ray pulses. By exploring the anisotropic summed speckle visibility which relates to the correlation functions, we are able to evaluate not only the average particle flow rate in a colloidal nanoparticle jet, but also the heterogeneous flow field within. The reported methodology presented here establishes the foundation for the study of nano- and atomic-scale heterogeneous fluctuations in complex matter using x-ray free electron laser sources.

cond-mat.soft↗

arXiv2020

High resolution strain measurements in highly disordered materials

The ability to measure small deformations or strains is useful for understanding many aspects of materials. Here, a new analysis of speckle diffraction peaks is presented in which the systematic shifts of the speckles are analyzed allowing for strain (or flow) patterns to be inferred. This speckle tracking technique measures strain patterns with a accuracy similar to x-ray single crystal measurements but in amorphous or highly disordered materials.

cond-mat.mtrl-sci↗

arXiv2020

Parton Distribution Functions of the Charged Pion Within The xFitter Framework

We present the first open-source analysis of parton distribution functions (PDFs) of charged pions using xFitter, an open-source QCD fit framework to facilitate PDF extraction and analyses. Our calculations are implemented at next-to-leading order (NLO) using APPLgrids generated by MCFM generator. Using currently available Drell-Yan and photon production data, we find the valence distribution is well constrained; however, the considered data are not sensitive enough to unambiguously determine sea and gluon distributions. Fractions of momentum carried by the valence, sea and gluon components are discussed, and we compare with the results of JAM collaboration and the GRV group.

hep-ph↗

arXiv2020

Realizing split-pulse x-ray photon correlation spectroscopy to measure ultrafast dynamics in complex matter

Split-pulse x-ray photon correlation spectroscopy has been proposed as one of the unique capabilities made possible with the x-ray free electron lasers. It enables characterization of atomic scale structural dynamics that dictates the macroscopic properties of various disordered material systems. Central to the experimental concept are x-ray optics that are capable of splitting individual coherent femtosecond x-ray pulse into two distinct pulses, introduce an adjustable time delay between them, and then recombine the two pulses at the sample position such that they generate two coherent scattering patterns in rapid succession. Recent developments in such optics showed that, while true 'amplitude splitting' optics at hard x-ray wavelengths remains a technical challenge, wavefront and wavelength splitting are both feasible, able to deliver two micron sized focused beams to the sample with sufficient relative stability. Here, we however show that the conventional approach to speckle visibility spectroscopy using these beam splitting techniques can be problematic, even leading to a decoupling of speckle visibility and material dynamics. In response, we discuss the details of the experimental approaches and data analysis protocols for addressing issues caused by subtle beam dissimilarities for both wavefront and wavelength splitting setups. We also show that in some scattering geometries, the Q-space mismatch can be resolved by using two beams of slightly different incidence angle and slightly different wavelengths at the same time. Instead of measuring the visibility of weak speckle patterns, the time correlation in sample structure is encoded in the 'side band' of the spatial autocorrelation of the summed speckle patterns, and can be retrieved straightforwardly from the experimental data. We demonstrate this with a numerical simulation.

physics.ins-det↗

arXiv2019

Speckle correlation as a monitor of X-ray free electron laser induced crystal lattice deformation

X-ray free electron lasers (X-FELs) present new opportunities to study ultrafast lattice dynamics in complex materials. While the unprecedented source brilliance enables high fidelity measurement of structural dynamics, it also raises experimental challenges related to the understanding and control of beam-induced irreversible structural changes in samples that can ultimately impact the interpretation of experimental results. This is also important for designing reliable high performance X-ray optical components. In this work, we investigate X-FEL beam-induced lattice alterations by measuring the shot-to-shot evolution of near-Bragg coherent scattering from a single crystalline germanium sample. We show that X-ray photon correlation analysis of sequential speckle patterns measurements can be used to monitor the nature and extent of lattice rearrangements. Abrupt, irreversible changes are observed following intermittent high-fluence monochromatic X-ray pulses, thus revealing the existence of a threshold response to X-FEL pulse intensity.

physics.app-ph↗

arXiv2019

Mechanisms of electron-phonon coupling unraveled in momentum and time: The case of soft-phonons in TiSe$_2$

The complex coupling between charge carriers and phonons is responsible for diverse phenomena in condensed matter. We apply ultrafast electron diffuse scattering to unravel electron-phonon coupling phenomena in 1T-TiSe$_2$ in both momentum and time. We are able to distinguish effects due to the real part of the many-body bare electronic susceptibility, $\Re\left[\chi_0(\mathbf{q})\right]$, from those due to the electron-phonon coupling vertex, $g_{\mathbf{q}}$, by following the response of semi-metallic (normal phase) 1T-TiSe$_2$ to the selective photo-doping of carriers into the electron pocket at the Fermi level. Quasi-impulsive and wavevector-specific renormalization of soft zone-boundary phonon frequencies (stiffening) is observed, followed by wavevector-independent electron-phonon equilibration. These results unravel the underlying mechanisms driving the phonon softening that is associated with the charge density wave transition at lower temperatures.

cond-mat.str-el↗

arXiv2019

Time- and momentum-resolved phonon population dynamics with ultrafast electron diffuse scattering

Interactions between the lattice and charge carriers can drive the formation of phases and ordering phenomena that give rise to conventional superconductivity, insulator-to-metal transitions, and charge-density waves. These couplings also play a determining role in properties that include electric and thermal conductivity. Ultrafast electron diffuse scattering (UEDS) has recently become a viable laboratory-scale tool to track energy flow into and within the lattice system across the entire Brillouin zone, and deconvolves interactions in the time domain. Here, we present a detailed quantitative framework for the interpretation of UEDS signals, ultimately extracting the phonon mode occupancies across the entire Brillouin zone. These transient populations are then used to extract momentum- and mode-dependent electron-phonon and phonon-phonon coupling constants. Results of this analysis are presented for graphite, which provides complete information on the phonon-branch occupations and a determination of the $A_1'$ phonon mode-projected electron-phonon coupling strength $\langle g_{e,A_1'}^2 \rangle = 0.035 \pm 0.001$ eV$^2$ that is in agreement with other measurement techniques and simulations.

cond-mat.mtrl-sci↗

arXiv2019

Scientific Opportunities with an X-ray Free-Electron Laser Oscillator

An X-ray free-electron laser oscillator (XFELO) is a new type of hard X-ray source that would produce fully coherent pulses with meV bandwidth and stable intensity. The XFELO complements existing sources based on self-amplified spontaneous emission (SASE) from high-gain X-ray free-electron lasers (XFEL) that produce ultra-short pulses with broad-band chaotic spectra. This report is based on discussions of scientific opportunities enabled by an XFELO during a workshop held at SLAC on June 29 - July 1, 2016

physics.ins-det↗

arXiv2018

Ultrafast correlated charge and lattice motion in a hybrid metal halide perovskite

Hybrid organic-inorganic halide perovskites have shown remarkable optoelectronic properties (1-3), believed to originate from correlated motion of charge carriers and the polar lattice forming large polarons (4-7). Few experimental techniques are capable of probing these correlations directly, requiring simultaneous sub-meV energy and femtosecond temporal resolution after absorption of a photon (8). Here we use transient multi-THz spectroscopy, sensitive to the internal motions of charges within the polaron, to temporally and energetically resolve the coherent coupling of charges to longitudinal optical phonons in single crystal CH3NH3PbI3 (MAPI). We observe room temperature quantum beats arising from the coherent displacement of charge from the coupled phonon cloud. Our measurements provide unambiguous evidence of the existence of polarons in MAPI.

cond-mat.mtrl-sci↗

arXiv2017

Mapping momentum-dependent electron-phonon coupling and non-equilibrium phonon dynamics with ultrafast electron diffuse scattering

Despite their fundamental role in determining material properties, detailed momentum-dependent information on the strength of electron-phonon and phonon-phonon coupling (EPC and PPC, respectively) across the entire Brillouin zone (BZ) has proved difficult to obtain. Here we demonstrate that ultrafast electron diffuse scattering (UEDS) directly provides such information. By exploiting symmetry-based selection rules and time-resolution, scattering from different phonon branches can be distinguished even without energy resolution. Using graphite as a model system, we show that UEDS patterns map the relative EPC and PPC strength through their profound sensitivity to photoinduced changes in phonon populations. We measure strong EPC to the $K$-point transverse optical phonon of $A_1'$ symmetry ($K-A_1'$) and along the entire longitudinal optical branch between $\Gamma-K$, not only to the $\Gamma-E_{2g}$ phonon as previously emphasized. We also determine that the subsequent phonon relaxation pathway involves three stages; decay via several identifiable channels to transverse acoustic (TA) and longitudinal acoustic (LA) phonons (1-2 ps), intraband thermalization of the non-equilibrium TA/LA phonon populations (30-40 ps) and interband relaxation of the LA/TA modes (115 ps). Combining UEDS with ultrafast angle-resolved photoelectron spectroscopy will yield a complete picture of the dynamics within and between electron and phonon subsystems, helping to unravel complex phases in which the intertwined nature of these systems have a strong influence on emergent properties.

cond-mat.mtrl-sci↗

arXiv2014

aMCfast: automation of fast NLO computations for PDF fits

We present the interface between MadGraph5_aMC@NLO, a self-contained program that calculates cross sections up to next-to-leading order accuracy in an automated manner, and APPLgrid, a code that parametrises such cross sections in the form of look-up tables which can be used for the fast computations needed in the context of PDF fits. The main characteristic of this interface, which we dub aMCfast, is its being fully automated as well, which removes the need to extract manually the process-specific information for additional physics processes, as is the case with other matrix element calculators, and renders it straightforward to include any new process in the PDF fits. We demonstrate this by studying several cases which are easily measured at the LHC, have a good constraining power on PDFs, and some of which were previously unavailable in the form of a fast interface.

hep-ph↗

arXiv2014

Recent constraints on the parton distributions in the proton and the measurement of $\alpha_S$ from ATLAS and CMS

Recent results on cross sections sensitive to the parton distribution functions (PDFs) within the proton from the ATLAS and CMS Collaborations are presented. The potential impact on the inclusion of these data in fits to the PDFs is discussed. Recent results from fits including the data from jet, or vector boson production from the ATLAS and CMS experiments are discussed.

hep-ex↗

arXiv2010

A search for heavy Kaluza-Klein electroweak gauge bosons at the LHC

The feasibility for the observation of a certain leptonic Kaluza-Klein (KK) hard process in {\em pp} interactions at the LHC is presented. Within the $S^1/Z_2$ TeV$^{-1}$ extra dimensional theoretical framework with the focus on the KK excitations of the Standard Model $\gamma$ and $Z^0$ gauge bosons, the hard-process, $f\bar f \to \sum_n\left(\gamma^*/Z^*\right)_n \to F \bar F$, has been used where $f$ is the initial state parton, $F$ the final state lepton and $\left(\gamma^*/Z^*\right)_{n}$ is the $n^{\rm th}$ KK excitation of the $\gamma/Z^0$ boson. For this study the analytic form for the hard process cross section has been independently calculated by the authors and has been implemented using the {\sc Moses} framework. The Moses framework itself, that has been written by the authors, was used as an external process within the {\sc Pythia} Monte Carlo generator which provides the phase space generation for the final state leptons and partons from the initial state hadrons, and the simulation of initial and final state radiation and hadronization. A brief discussion of the possibility for observing and identifying the unique signature of the KK signal given the current LHC program is also presented.

hep-ex↗

arXiv2010

Introduction to the MCnet Moses project and Heavy gauge bosons search at the LHC

This is a technical document that provides supporting information and details of the publicly available code used for the preparation of the analysis for preprint "{\it A search for heavy Kaluza-Klein electroweak gauge bosons at the LHC}" (submitted to JHEP). The {\sc Moses} C++ framework is a project written for probing and developing new models for High Energy Physics processes which allows complete events to be simulated by interface with the standard simulation program Pythia8. This paper demonstrates the usage of {\sc Moses} in a study of the nature of Kaluza-Klein (KK) excitations in a specific model where the SU(2) \times U(1) gauge fields can exist in a single Extra Dimension (ED) compactified on a $S^1/Z_2$ orbifold, while the matter fermions and SU(3) gauge fields are localized in the 3d-brane. Using this framework, the events have been fully simulated at hadron level including initial and final state radiation. The study of particle decays was used to develop a method to distinguish between this Kaluza-Klein model and processes with similar final states. As a consequence, the possibility of observing and identifying a signal of the first excited KK state of the $γ/Z^0$ bosons in the LHC is also discussed.

hep-ex↗