Matteo Bonanomi

Abstract The light-induced ultrafast switching between molecular isomers norbornadiene and quadricyclane can reversibly store and release a substantial amount of chemical energy. Prior work observed signatures of ultrafast molecular dynamics in both isomers upon ultraviolet excitation but could not follow the electronic relaxation all the way back to the ground state experimentally. Here we study the electronic relaxation of quadricyclane after exciting in the ultraviolet (201 nanometres) using time-resolved gas-phase extreme ultraviolet photoelectron spectroscopy combined with non-adiabatic molecular dynamics simulations. We identify two competing pathways by which electronically excited quadricyclane molecules relax to the electronic ground state. The fast pathway (<100 femtoseconds) is distinguished by effective coupling to valence electronic states, while the slow pathway involves initial motions across Rydberg states and takes several hundred femtoseconds. Both pathways facilitate interconversion between the two isomers, albeit on different timescales, and we predict that the branching ratio of norbornadiene/quadricyclane products immediately after returning to the electronic ground state is approximately 3:2.

The absolute photoabsorption cross sections of norbornadiene (NBD) and quadricyclane (QC), two isomers with chemical formula C7H8 that are attracting much interest for solar energy storage applications, have been measured from threshold up to 10.8 eV using the Fourier transform spectrometer at the SOLEIL synchrotron radiation facility. The absorption spectrum of NBD exhibits some sharp structure associated with transitions into Rydberg states, superimposed on several broad bands attributable to valence excitations. Sharp structure, although less pronounced, also appears in the absorption spectrum of QC. Assignments have been proposed for some of the absorption bands using calculated vertical transition energies and oscillator strengths for the electronically excited states of NBD and QC. Natural transition orbitals indicate that some of the electronically excited states in NBD have a mixed Rydberg/valence character, whereas the first ten excited singlet states in QC are all predominantly Rydberg in the vertical region. In NBD, a comparison between the vibrational structure observed in the experimental 11B1–11A1 (3sa1 ← 5b1) band and that predicted by Franck–Condon and Herzberg–Teller modeling has necessitated a revision of the band origin and of the vibrational assignments proposed previously. Similar comparisons have encouraged a revision of the adiabatic first ionization energy of NBD. Simulations of the vibrational structure due to excitation from the 5b2 orbital in QC into 3p and 3d Rydberg states have allowed tentative assignments to be proposed for the complex structure observed in the absorption bands between ∼5.4 and 7.0 eV.

We demonstrate the generation of extreme-ultraviolet (XUV) free-electron laser (FEL) pulses with time-dependent polarization. To achieve polarization modulation on a femtosecond timescale, we combine two mutually delayed counterrotating circularly polarized subpulses from two cross-polarized undulators. The polarization profile of the pulses is probed by angle-resolved photoemission and above-threshold ionization of helium; the results agree with solutions of the time-dependent Schrödinger equation. The stability limit of the scheme is mainly set by electron-beam energy fluctuations, however, at a level that will not compromise experiments in the XUV. Our results demonstrate the potential to improve the resolution and element selectivity of methods based on polarization shaping and may lead to the development of new coherent control schemes for probing and manipulating core electrons in matter.

Improving the durability of polymer electrolyte membrane fuel cells with low platinum loading is a crucial step in the development of next generation electric vehicles. In this work a simplified model of nanoparticle growth is spatially solved across the catalyst layer and combined with a PEMFC model to analyze the heterogeneity of degradation that is induced by accelerated stress test for electrocatalyst durability, which mimics the degradation due to load cycling. The model is calibrated and later validated by analyzing experimental data collected on cathode catalyst layers with 0.1 mg cm−2 platinum loading and average particle size ranging from 2 nm to 5 nm. Non-uniform degradation is observed in the catalyst layer consequently to the formation of a platinum depleted region next to the membrane, which, according to the model, results from diffusion and precipitation of dissolved platinum into the membrane. Performance of catalyst layers with gradient structure is simulated to get insight into the degradation of non-uniform catalyst layers and results are compared to experimental data. It is concluded that gradient catalyst layers mitigate performance degradation because evolve towards more uniform distribution of active surface and improve transport loss due to low-roughness factor and Ohm loss in the catalyst layer.

Abstract As part of its HL-LHC upgrade program, the CMS collaboration is developing a High Granularity Calorimeter (CE) to replace the existing endcap calorimeters. The CE is a sampling calorimeter with unprecedented transverse and longitudinal readout for both electromagnetic (CE-E) and hadronic (CE-H) compartments. The calorimeter will be built with ∼30,000 hexagonal silicon modules. Prototype modules have been constructed with 6-inch hexagonal silicon sensors with cell areas of 1.1 cm 2 , and the SKIROC2-CMS readout ASIC. Beam tests of different sampling configurations were conducted with the prototype modules at DESY and CERN in 2017 and 2018. This paper describes the construction and commissioning of the CE calorimeter prototype, the silicon modules used in the construction, their basic performance, and the methods used for their calibration.

Abstract The upgrade of the CMS experiment for the high luminosity operation of the LHC comprises the replacement of the current endcap calorimeter by a high granularity sampling calorimeter (HGCAL). The electromagnetic section of the HGCAL is based on silicon sensors interspersed between lead and copper (or copper tungsten) absorbers. The hadronic section uses layers of stainless steel as an absorbing medium and silicon sensors as an active medium in the regions of high radiation exposure, and scintillator tiles directly read out by silicon photomultipliers in the remaining regions. As part of the development of the detector and its readout electronic components, a section of a silicon-based HGCAL prototype detector along with a section of the CALICE AHCAL prototype was exposed to muons, electrons and charged pions in beam test experiments at the H2 beamline at the CERN SPS in October 2018. The AHCAL uses the same technology as foreseen for the HGCAL but with much finer longitudinal segmentation. The performance of the calorimeters in terms of energy response and resolution, longitudinal and transverse shower profiles is studied using negatively charged pions, and is compared to GEANT4 predictions. This is the first report summarizing results of hadronic showers measured by the HGCAL prototype using beam test data.

Abstract The Compact Muon Solenoid collaboration is designing a new high-granularity endcap calorimeter, HGCAL, to be installed later this decade. As part of this development work, a prototype system was built, with an electromagnetic section consisting of 14 double-sided structures, providing 28 sampling layers. Each sampling layer has an hexagonal module, where a multipad large-area silicon sensor is glued between an electronics circuit board and a metal baseplate. The sensor pads of approximately 1.1 cm 2 are wire-bonded to the circuit board and are readout by custom integrated circuits. The prototype was extensively tested with beams at CERN's Super Proton Synchrotron in 2018. Based on the data collected with beams of positrons, with energies ranging from 20 to 300 GeV, measurements of the energy resolution and linearity, the position and angular resolutions, and the shower shapes are presented and compared to a detailed Geant4 simulation.

Multiple scattering effects of 12 and 20 GeV electrons on 8 and 20 mm thickness carbon targets have been studied with high-resolution silicon microstrip detectors of the UA9 apparatus at the H8 line at CERN . Comparison of the scattering angle between data and GEANT4 simulation shows excellent agreement in the core of the distributions leaving some residual disagreement in the tails.

In 2018, a test run with muons in the North Area at CERN was performed, running parasitically downstream of the COMPASS spectrometer. The aim of the test was to investigate the elastic interactions of muons on atomic electrons, in an experimental configuration similar to the one proposed by the project MUonE, which plans to perform a very precise measurement of the differential cross-section of the elastic interactions. COMPASS was taking data with a 190 GeV pion beam, stopped in a tungsten beam dump: the muons from these pions decays passed through a setup including a graphite target followed by 10 planes of Si tracker and a BGO crystal electromagnetic calorimeter placed at the end of the tracker. The elastic scattering events were analysed, and compared to expectations from MonteCarlo simulation.

Abstract The CMS experiment at the CERN LHC will be upgraded to accommodate the 5-fold increase in the instantaneous luminosity expected at the High-Luminosity LHC (HL-LHC) [1]. Concomitant with this increase will be an increase in the number of interactions in each bunch crossing and a significant increase in the total ionising dose and fluence. One part of this upgrade is the replacement of the current endcap calorimeters with a high granularity sampling calorimeter equipped with silicon sensors, designed to manage the high collision rates [2]. As part of the development of this calorimeter, a series of beam tests have been conducted with different sampling configurations using prototype segmented silicon detectors. In the most recent of these tests, conducted in late 2018 at the CERN SPS, the performance of a prototype calorimeter equipped with ≈12,000 channels of silicon sensors was studied with beams of high-energy electrons, pions and muons. This paper describes the custom-built scalable data acquisition system that was built with readily available FPGA mezzanines and low-cost Raspberry Pi computers.

The 3.4 σ discrepancy between the experimental value of the muon anomalous magnetic moment g-2 and the Standard Model prediction is one of the most intriguing indications of physics beyond the Standard Model. The MUonE project plans to measure the leading hadronic corrections to the muon g-2 by scattering high energy (∼150 GeV) muons off the atomic electrons of a low-Z target through the elastic process μ+e → μ+e. The angles of the incoming muons and the outcoming muons and electrons have to be measured precisely, to exploit the kinematical correlation of the μ-e collision. To reach this goal a modular target is foreseen, consisting of 60 low-Z (Be or C) elements, 1 cm thick, each sandwiched in layers of Si-microstrip detectors, organized in XY, XU and VY planes (±45 °, to disentangle double tracks). In 2018, a feasibility test at the CERN North Area is foreseen, running parasitically on the beamline behind COMPASS. The setup consist of 16 layers with an area of 9.5×9.5 cm2, 410μm thick, single side AGILE silicon detectors, which have a readout pitch of 242μm and a floating strip scheme, resulting in a position resolution of the order of 40μm. The DAQ rate is of the order of a few kHz. The contribution will describe the setup, the DAQ system and the first data collected during the commissioning phase in April/May.

Superfluid helium nanodroplets are often considered as transparent and chemically inert nanometer-sized cryo-matrices for high-resolution or time-resolved spectroscopy of embedded molecules and clusters. On the other hand, when the helium nanodroplets are resonantly excited with XUV radiation, a multitude of ultrafast processes are initiated, such as relaxation into metastable states, formation of nanoscopic bubbles or excimers, and autoionization channels generating low-energy free electrons. Here, we discuss the full spectrum of ultrafast relaxation processes observed when helium nanodroplets are electronically excited. In particular, we perform an in-depth study of the relaxation dynamics occurring in the lowest 1s2s and 1s2p droplet bands using high resolution, time-resolved photoelectron spectroscopy. The simplified excitation scheme and improved resolution allow us to identify the relaxation into metastable triplet and excimer states even when exciting below the droplets' autoionization threshold, unobserved in previous studies.

Theoretical and semi-empirical methods to calculate electron impact ionization cross sections for atomic shells are subject to validation tests with respect to a wide collection of experimental measurements to identify the state of the art for Monte Carlo particle transport. The validation process applies rigorous statistical analysis methods. Cross sections based on the EEDL Evaluated Electron Data Library, widely used by Monte Carlo codes, and on calculations by Bote and Salvat, used in the Penelope code, are generally equivalent in compatibility with experiment. Results are also reported for various formulations of the Binary-Encounter-Bethe and Deutsch-Märk models.

Evaluated data libraries for electron-photon transport are most important components in Monte Carlo simulation and have been used in general-purpose Monte Carlo codes for decades. A new version of evaluated atomic data libraries, called EPICS2017, was released in early 2018. This paper reports an extensive assessment of EPICS2017, focused on what has changed, and evaluates the impact of using the new libraries in a Monte Carlo simulation environment. The results provide guidelines for developers and users of Monte Carlo codes wishing to use the new libraries. In addition, they also highlight opportunities for improving the data libraries in future releases.

The Standard Model of particle physics (SM) [1] is the pillar on which the current understanding of the subatomic world is based. It describes the elementary particles and their fundamental interactions in the context of a Lorentz-invariant and renormalizable quantum field theory. The theoretical framework of the SM is corroborated by an extensive set of experimental measurements, of which the last is the discovery of a particle compatible with the Higgs boson by the ATLAS and CMS Collaborations at the CERN LHC in June 2012 [2, 3, 4]. A brief theoretical introduction to the SM is given in Sect. 1.1, emphasizing the electroweak symmetry breaking mechanism (EWSB) in Sect. 1.1.2. This process ensures that elementary particles acquire mass while respecting the gauge symmetries of the SM by introducing an additional scalar field to the SM Lagrangian: the Higgs boson, a long-sought particle originally postulated in the second half of the XX century, but experimentally detected only 50 years later. More details about the properties and the phenomenology of this particle at hadron colliders are given in Sect. 1.2. The chapter closes in Sect. 1.3, with the description of the Higgs boson decay into four leptons, being it the channel studied in this work.

The $$\text {H} \rightarrow \text {Z} \text {Z} \rightarrow 4\ell $$ decay channel ( $$\ell = e,\mu $$ ) is often referred to as the golden channel due to its many virtues. Two of its golden properties are the large signal-to-background ratio, with an essentially flat background under the resonant H boson peak, and the completely resolved final state, with an optimal reconstruction of the four-leptons system, made possible by the good lepton resolution of the CMS detector. Figure 4.1 shows a candidate $$\text {H} \rightarrow \text {Z} \text {Z} \rightarrow 4\ell $$ event, comprising of a muon-antimuon pair (red lines) and an electron-positron pair (green lines). One can see the relatively clean environment, where the $$\text {H} \rightarrow \text {Z} \text {Z} \rightarrow 4\ell $$ signature can be identified and reconstructed.

This “golden journey” comes to an end in this chapter, where the results of the analysis are presented. However, before unveiling the outcome of the measurements of the H boson properties in the $$\text {H} \rightarrow 4\ell$$ channel, it is worth taking a step back to have a global overview of the picture assembled throughout the previous chapters.

The High-Luminosity LHC (HL-LHC) is expected to start its operations by the end of 2027. It is designed to deliver a peak instantaneous luminosity of $$5\times 10^{34}$$ cm $$^{-2}$$ s $$^{-1}$$ , thus giving access to a total integrated luminosity of 3000 fb $$^{-1}$$ and therefore increasing the discovery potential of the LHC. The HL-LHC will allow more precise measurements of the SM properties and enhance its sensitivity to rare processes, possibly unveiling the presence of previously unknown particles and BSM scenarios.

This book highlights the most complete characterization of the Higgs boson properties and presents the results of the analysis of the test beam data

The “golden roadmap” that guides the analysis workflow and strategy is the Monte Carlo simulation of the phenomenology of the physical processes studied and their interaction with the CMS detector. It is fundamental to exploit the most precise generators and use the state-of-art calculations to accurately model the physics considered in the analysis and represent the experimental data properly.

In June 2012 the ATLAS and CMS Collaborations at CERN announced the discovery of a scalar particle compatible with the Higgs boson predicted by the Standard Model (SM) of particle physics.

The “golden journey” towards the characterization of the H boson properties in the $$4\ell $$ decay channel continues in this chapter, where the events selection and their subsequent categorization are presented.

Founded in 1954 and located near the Franco-Swiss border west of Geneva, the Conseil Européen pour la Recherche Nucléaire (CERN), or European Council for Nuclear Research, is nowadays the largest particle physics laboratory worldwide. Counting more than 10000 researchers from over 100 nationalities, CERN is at the forefront of fundamental research, innovation, and knowledge transfer.

As part of its HL-LHC upgrade program, the CMS collaboration is replacing its existing endcap calorimeters with a high-granularity calorimeter (CE). The new calorimeter is a sampling calorimeter with unprecedented transverse and longitudinal readout for both electromagnetic and hadronic compartments. Due to its compactness, intrinsic time resolution, and radiation hardness, silicon has been chosen as active material for the regions exposed to higher radiation levels. The silicon sensors are fabricated as 20 cm (8") wide hexagonal wafers and are segmented into several hundred pads which are read out individually. As part of the sensor qualification strategy, 8" sensor irradiation with neutrons has been conducted at the Rhode Island Nuclear Science Center (RINSC) and followed by their electrical characterisation in 2020-21. The completion of this important milestone in the CE's R&D program is documented in this paper and it provides detailed account of the associated infrastructure and procedures. The results on the electrical properties of the irradiated CE silicon sensors are presented.

In this work, we use attosecond time-resolved techniques to investigate photoionization dynamics on its natural timescale, employing both high harmonic generation and seeded free-electron lasers to generate extreme ultraviolet attosecond pulse trains for our studies. With the former approach, we examine the role of nuclear motion in molecular photoionization dynamics, while with the latter we introduce a novel attosecond timing tool for single-shot characterization of the relative phase between the XUV and the infrared field.

Chirality is widespread in nature, playing a fundamental role in bio-chemical processes and in the origin of life itself [1]. The mechanisms controlling the chiral selectivity of chemical reactions have been extensively studied over many decades. However, the ultrafast mechanisms governing chiral behavior at its electronic level are still mostly unexplored and our ability to track the evolving chirality of reacting molecules remains limited. Photoelectron Circular Dichroism spectroscopy (PECD) is a highly electronic and structure sensitive technique [2]–[5] and an established tool to probe chirality on the time scale of chemical reactions [6], [7].

We report preliminary results of an extensive investigation of theoretical and semi-empirical calculations of electron impact ionization cross sections, detailed by individual shells: they encompass the well known tabulations of the EEDL data library (also distributed within ENDF/B-VII) used by Geant4, MCNP and other codes, recent calculations used in Penelope, as well as other models not yet used in general-purpose Monte Carlo transport codes. All models have been subject to a rigorous validation test against a wide collection of experimental measurements. Special attention has been devoted to possible sources of systematics affecting the validation process, both of physical and mathematical origin. As most of the data reported in the literature as experimental measurements of ionization cross sections actually derive from X-ray production measurements, the systematic effect of different compilations of fluorescence yields has been quantitatively assessed. The compatibility of calculated and experimental cross sections has been further examined with categorical analysis methods to determine whether the observed differences across the various models are statistically significant. The results of this validation process identify objectively and quantitatively the state of the art in modeling electron impact ionization; they are relevant for the improvement of ionization modeling in Monte Carlo codes.

As part of the HL-LHC detector upgrade programme, the CMS experiment is developing a High Granularity Calorimeter (HGCAL) to replace the existing endcap calorimeters. The HGCAL will be realised as a sampling calorimeter, including 36 layers of silicon pads and 14 layers combining silicon and scintillator detectors interspersed with metal absorber plates. Prototype modules based on 6-inch hexagonal silicon pad sensors with pad areas of 1.0 cm2 have been constructed. Beam tests of different sampling configurations made from these modules have been conducted at the CERN SPS using beams of charged hadrons and electrons with momenta ranging from 20 to 300 GeV/c. The setup was complemented with a CALICE AHCAL prototype: a scintillator-based sampling calorimeter, mimicking the proposed design of the HGCAL scintillator part. These proceedings summarise the test beam measurements performed at CERN in 2018, including the calibration of the detector with minimum ionizing particles and energy reconstruction performance of electron- and hadron-induced showers. We also show measurements of the timing capabilities of this prototype system and the steps being taken towards electron and hadron identification.

New cross section calculations are usually advertised as improvements over previous ones. Nevertheless these claims are not always supported by rigorous statistical tests. A set of electron impact ionization cross sections for inner shells, suitable for Monte Carlo particle transport, has been evaluated in a large scale validation test with respect to an extensive collection of experimental data retrieved from the literature. It includes the cross sections tabulated in EEDL (Evaluated Electron Data Library), recent calculations by Bote and Salvat, the Binary-Encounter-Bethe (BEB) model and the Deutsch-Mrk (DM) model. The cross sections were compared to experimental data by means of goodness-of-fit tests. The picture that emerges from the validation test does not fully support the expectations of improvement. The complete and final results of the validation process are reported in detail and critically discussed.

The Evaluated Atomic, Electron and Photon Data Libraries (EADL, EEDL and EPDL, respectively) provide the grounds for the simulation of electromagnetic interactions in several Monte Carlo particle transport codes. The most recent of them, EPDL97, was released by the Livermore National Laboratory, USA twenty years ago; although they have been in use for a long time, they have been only partially validated through comparisons with experimental data. This presentation reviews the status of the validation of these data libraries; it summarizes the results reported in the literature and illustrates a few recent ones, which have not been published yet. It identifies the current gaps in the validation of the various components of the three data libraries and the shortage of experimental data in some areas, which hinders the validation. Furthermore, it highlights their position with respect to other calculations in view of determining the state of the art of electromagnetic cross sections and other atomic parameters. These results are relevant to most major Monte Carlo codes and provide guidelines for the next generation of data libraries currently in preparation.

We present an extensive assessment of the systematics associated with fluorescence yields; it involves a large number of compilations of these parameters, which were published over almost 50 years.

The HEPData Database has been built up over the past four decades as a unique open-access repository for scattering data from experimental particle physics; it currently comprises data derived from several thousand publications. HEPData is the main source of experimental data for tuning and validating models of high-energy physics processes that are implemented in Monte Carlo event generators. R&D is currently in progress to extend HEPData, with the intent to make it an open-access reference also for the validation of physics models implemented in Monte Carlo particle transport codes.

With the data collected in Run-2, the Higgs boson can be studied in several production processes using a wide range of decay modes.Combining data in these different channels provides a broad picture of the Higgs boson coupling strengths to SM particles.This contribution outlines the latest combination of Higgs boson production and decay modes at CMS to measure the Higgs boson couplings and production cross sections.

In the excel sheets, data corresponding to the attosecond coherent control experiment has been provided. A word file is included to explain the data in the different excel sheets.

In the excel sheets, data corresponding to the attosecond coherent control experiment has been provided. A word file is included to explain the data in the different excel sheets.

Evaluated data libraries are the foundation of physics modeling in Monte Carlo particle transport codes, such as Geant4, FLUKA and MCNP, which are used in high energy and nuclear physics experiments, accelerator studies and detector development. They encompass recommended cross sections, nuclear and atomic parameters, which may derive from theoretical calculations, evaluations of experimental data or a combination of both. New versions of major, widely used evaluated data libraries were released in early 2018 by the IAEA (International Atomic Energy Agency) and the NNDC (National Nuclear Data Center, BNL); among them, the new data libraries for electron-photon transport represent substantial evolutions with respect to those currently in use, which date back to more than 20 years ago. The changes concern both the physics content and the data structure, which in turn affect the physical the reliability and the computational performance of simulations. The main features of the new data libraries are summarized, with emphasis on what has changed, along a first assessment of their physics quality and of their effects on computational performance in the Geant4 environment. These results provide quantitative and objective elements for developers and users of Monte Carlo codes to evaluate the impact of migrating simulations to new data libraries on sound grounds. The assessment also highlights opportunities for improvement in future releases.

We report on the implementation of time-domain spectroscopy through broadband Four-Wave Mixing in the study of roto-vibrational excitation of hydrocarbons by resonant high-energy mid-IR pulses.

As part of its HL-LHC upgrade program, the CMS Collaboration is developing a High Granularity Calorimeter (CE) to replace the existing endcap calorimeters. The CE is a sampling calorimeter with unprecedented transverse and longitudinal readout for both electromagnetic (CE-E) and hadronic (CE-H) compartments. The calorimeter will be built with $\sim$30,000 hexagonal silicon modules. Prototype modules have been constructed with 6-inch hexagonal silicon sensors with cell areas of 1.1~$cm^2$, and the SKIROC2-CMS readout ASIC. Beam tests of different sampling configurations were conducted with the prototype modules at DESY and CERN in 2017 and 2018. This paper describes the construction and commissioning of the CE calorimeter prototype, the silicon modules used in the construction, their basic performance, and the methods used for their calibration.

We report on the efficient excitation of high-lying rovibrational states in methane by a high-energy mid-IR source and on the time-domain study of the induced dynamics.

This contribution outlines the most recent measurements of the Higgs boson properties in the $H\rightarrow WW$ and $H\rightarrow ZZ$ decay channels performed with the CMS experiment at the CERN LHC.

Abstract We describe the implementation of nonlinear time-domain spectroscopy of rotovibrational IR-active modes in methane through broadband Four-Wave Mixing driven by resonant high-energy mid infrared laser pulses. At high driving pulse intensities we observe an efficient vibrational ladder climbing triggered in the molecules. This study opens the possibility to impulsively and selectively excite molecules of biological interest to high-lying vibrational states and to characterize their dynamics.