Significant progress has been made in the calculation and evaluation of multi-loop QCD (and EW) scattering amplitudes, as well as the development of effective subtraction methods in (N)NNLO QCD. As a result, the level of precision of theoretical predictions for many relevant processes at the Large Hadron Collider has been significantly improved. In this review, we will discuss the latest...
In this talk, I will present the results of the first
calculation of open bottom production at hadron colliders at NNLO+NNLL,
i.e. a next-to-next-to-leading-order calculation that resums collinear
logarithms at next-to-next-to-leading-logarithmic accuracy. This new
computation achieves significantly reduced theory errors compared to
previous calculations, with errors of just a few percent...
Heavy quarks are produced in the early stages of heavy ion collisions due to their large mass, and subsequently traverse the entire QCD medium evolution.
The open heavy flavor hadron ratio provides profound insights into the heavy quark hadronization mechanisms . By comparing these ratios in different collision systems, which reveal the contribution of the coalescence mechanism in...
Recent results from ATLAS on heavy flavours are presented. They include measurement of $B^0$ lifetime, effective lifetime in $B^0_s\to\mu^+\mu^-$ decay, measurement of prompt and non-prompt charmonium production and studies of exotic contributions in low-mass four-muon final state.
Heavy quarks are predominantly produced in the initial hard partonic scatterings, and thus their production cross-section can be calculated by pQCD.
Quarkonia and heavy-flavor hadrons can also be employed as tools for investigating heavy-quark dynamics in Quark-Gluon Plasma created in heavy-ion collisions. The changes in the production rate of quarkonia in the QGP are indicative of the...
The transverse momentum (pT) differential production cross section of the promptly-produced charm-strange baryon Ξ0c is measured at midrapidity via its hadronic decay into π+Ξ− in p–Pb collisions at sqr(sNN) = 5.02 TeV with the ALICE detector at the LHC. The Ξ0c nuclear modification factor (RpPb), calculated from the cross sections in pp and p–Pb collisions, is presented and compared with the...
The usage of charm cross sections from hadron-hadron collisions for
the extraction of perturbative QCD parameters has recently been hampered by
evidence that charm quark fragmentation into charm hadrons is nonuniversal,
i.e. may depend on the collision initial and final state and its energy.
Fragmentation effects can be eliminated from the theory by considering the
total ccbar pair...
Many next-to-leading order QCD predictions are available through Monte Carlo (MC) simulations. Usually multiple CPU-hours are needed to calculate the physical predictions at a feasible precision and are therefore impractical for global PDF analyses. This problem is solved by a process known as "gridding": The values of the hard-scattering cross-section are calculated only once with the MC...
Strange hadron production is an important probe of hadronization in hadron collisions. With its precise vertex reconstruction and particle identification capabilities, the LHCb detector is ideally suited to study strangeness production. LHCb's forward geometry provides access to strange hadrons in an unexplored kinematic regime, and the SMOG system allows LHCb to study strangeness production...
Vacuum-like e+e- collisions provide outstanding opportunities to characterize the properties of Quantum chromodynamics across different energy scales. At high pT, they can be used to study the parton-shower evolution in the cleanest experimental conditions, including modern jet-substructure techniques. At low pT, measurements of two-particle long-range correlations can constrain the possible...
Abstract 210:
Flavour-tagging is a critical component of the ATLAS experiment physics programme. Existing flavour tagging algorithms rely on several low-level taggers, which are a combination of physically informed algorithms and machine learning models. A novel approach presented here instead uses a single machine learning model based on reconstructed tracks, avoiding the need for low-level...
We report progress on the determination and study of quarkonium formation within the fragmentation approximation. Our analyses address the moderate and large transverse-momentum regime, where the production mechanism based on the collinear fragmentation from a single parton is expected to prevail over the short-distance emission, directly from the hard-scattering subprocess, of the constituent...
We perform the first complete one-loop study of exclusive photoproduction of vector quarkonia off a proton, including full generalised parton distribution (GPD) evolution. We confirm the perturbative instability of the cross section at high photon-proton-collision energies at Next-to-Leading Order (NLO) using a Collinear-Factorisation (CF) framework. This issue can be tackled by a scale-fixing...
The impact of Next-to-Leading Order (NLO) QCD corrections to the differential distributions of $J/\psi$ and $\Upsilon$ mesons produced inclusively in $\gamma\gamma$ collisions is revisited for the kinematical conditions of LEPII DELPHI, the Circular Electron-Positron Collider (CEPC) and the Future Circular (Lepton) Collider (FCC-ee). We take into account all sizeable LO in $v^2$ contributions...
The possibility to reanalyse data taken by the HERA experiments offers the chance to study modern QCD jet and event-shape observables in deep-inelastic scattering. In this talk I will present resummed and matched predictions for the event shapes 1-jettinesss [1] and invariant mass including the effect of grooming the hadronic final state using the soft-drop technique. Non-perturbative...
The H1 Collaboration at HERA reports the first measurement of groomed event shapes in deep inelastic e−p and e+p scattering (DIS) at $\sqrt{s} = 319$ GeV, using data recorded between 2003 and 2007 with an integrated luminosity of $351.1\pm 9.5$ pb$^{−1}$. Event shapes in DIS collisions provide incisive probes of perturbative and non-perturbative QCD, and recently developed grooming techniques...
The Lund jet plane is a jet substructure tool introduced to understand the radiation pattern of jets by organizing hadrons into a hierarchical tree of emissions using the Cambridge/Aachen clustering algorithm. The primary LJP, the first triangular leaf of Lund diagrams, is well understood analytically, and measurements at the LHC show how it can be used to constrain parton showers and...
The internal structure of jets allows us to bridge our description and understanding of short-distance physics and color confinement. In this talk, we discuss recent measurements of jet substructure performed using data collected by the CMS experiment. Measurements of various jet substructure observables, with and without jet grooming, are presented. The measurements are corrected for detector...
Abstract 244:
Jets, the collimated streams of hadrons resulting from the fragmentation of highly energetic quarks and gluons, are some of the most commonly observed radiation patterns in hadron collider experiments. The distribution of quantum chromodynamic (QCD) radiation within jets is determined by complex processes, the production of showers of quarks and gluons and their subsequent...
In this talk, we present our results for the azimuthal decorrelation of a vector boson and jet in proton-proton collisions. We show that using a recoil-free jet definition reduces the sensitivity to contamination from soft radiation on the measurement and simplifies our theoretical calculation by eliminating complications associated with non-global logarithms. Specifically, we consider the...
We present theoretical calculations of higher-order QCD and electroweak corrections for the associated production of a top-antitop quark pair and a $W$ boson ($t{\bar t}W$ production) at LHC energies. We show predictions for cross sections at approximate N$^3$LO (aN$^3$LO) which include second-order and third-order soft-gluon corrections added to the exact NLO QCD+electroweak result. We...
We discuss the linear power corrections in $\Lambda_{\text{QCD}}$ to top quark production processes in hadron collisions using renormalon calculus. We show how such non-perturbative corrections can be obtained using the Low-Burnett-Kroll theorem, which provides the first subleading term to the expansion of the real-emission amplitudes around the soft limit. We demonstrate that there are no...
We evaluate the top-bottom interference contribution to the fully-inclusive Higgs production cross section at next-to-next-to-leading order in QCD. Although bottom-quark-mass effects are power-suppressed, the accuracy of state-of-the-art theory predictions makes an exact determination of this effect indispensable. With this result, we address one of the leading theory uncertainties of the...
The only source of matter-antimatter asymmetry in the Standard Model (SM) of particle physics occur through the complex phase of the Cabibbo-Kobayashi-Maskawa (CKM) quark mixing matrix. This complex phase is the origin of the violation of both the charge (C) and parity (P) symmetries. Violation of CP symmetry can be studied by measuring the angles of the CKM unitarity triangle. One of these...
The production of W/Z bosons in association with light or heavy flavor jets or hadrons at the LHC is sensitive to the flavor content of the proton and provides an important test of perturbative QCD. In this talk, measurements by the ATLAS experiment probing the charm and beauty content of the proton are presented. Inclusive and differential cross-sections of Z boson production with at least...
With the growing precision of experimental measurements, combining fixed-order perturbative calculations with parton-shower effects becomes essential for an accurate description of LHC phenomenology. In this talk, we focus on the computation of Higgs production via bottom-quark annihilation ($b \bar{b}H$) at next-to-next-to-leading order (NNLO) in QCD perturbation theory, consistently matched...
Jet vetoes are important tools that are frequently used to cut away backgrounds or separate different hard scattering processes. The most commonly used variable to veto jets is the simple transverse momentum of a jet. However it can be useful to use a jet veto that is tight in transverse momentum at central rapidities, and gradually becomes looser as one goes forward in rapidity - for example,...
High-energy collisions of hadrons (protons and nuclei) at the CERN Large Hadron Collider (LHC) are characterized by multiple interactions of their underlying partonic constituents. The simultaneous production of several particles with large transverse momentum and/or mass ($p_\mathrm{T}, m \gg 3$~GeV) in different independent hard partonic interactions has attracted an increasing interest in...
Abstract 215:
In relativistic heavy ion collisions, the charged ions produce an intense flux of equivalent photons. Thus, photon-induced processes are the dominant interaction mechanism when the colliding nuclei have a transverse separation larger than the nuclear diameter. In these ultra-peripheral collisions (UPCs), the photon provides a clean, energetic probe of the partonic structure...
Inclusive photoproduction of dijets in ultra-peripheral nucleus-nucleus collisions (UPCs) has been suggested as a new probe for studying the nuclear parton distributions (nPDFs). In this talk, we present new NLO pQCD predictions for the photoproduction of dijets in PbPb UPCs at 5.02 TeV with up-to-date nPDFs and realistic impact-parameter dependent photon flux obtained through the nuclear form...
The study of proton-lead events that have gaps in the rapidity distribution of final-state particles provides a unique opportunity to study colorless interactions such as pomeron-lead and photon-lead. The relative contribution of these processes depends on the size of the rapidity gap. The CMS Collaboration has previously studied the cross section of such processes as a function of the...
Two of the questions posed by the 2023 Nuclear Science Long Range Plan are how hadrons produced in deep inelastic scattering of electrons are correlated with one another, and how the nuclear medium modifies the hadronization process. The results we present in this talk on azimuthal correlations in $\pi^+\pi^-$ and $\pi^+p$ pairs measured by the CLAS collaboration at Jefferson Lab seek to...
We propose to study hard processes and bulk nuclear matter on the same footing in heavy-ion collisions using Glauber modelling of heavy nuclei. To exemplify this approach, we calculate the leading-order corrections to azimuthal decorrelation in Drell-Yan and boson-jet processes due to cold nuclear effects. At leading order in both the hard momentum scale and the nuclear size, the...
The DsTau (NA65) experiment at CERN was proposed to measure an inclusive differential cross-section of $D_s$ production, and its decay branching ratios in $p$-$A$ interactions. The DsTau detector is based on the nuclear emulsion technique providing an excellent spatial resolution for detecting short-lived particles like charmed hadrons. The first results of the analysis of the pilot-run...
In this talk, I will present our extensions of MadGraph5_aMC@NLO for two asymmetric systems, photoproduction and proton-nucleus collisions as well as progress towards automation of computations for inclusive-quarkonium production, currently being worked out at leading order.
Indeed, to consolidate the figures of merit of a variety of measurements at the Electron-Ion Collider and...
The azimuthal correlation angle, $\Delta\phi$, between the scattered lepton and the leading jet in deep inelastic $ep$ scattering at HERA has been studied using HERA II data collected with the ZEUS detector. The data set features $e^{\pm}p$ collisions at a centre-of-mass energy of $\sqrt{s} = 318$ GeV, corresponding to an integrated luminosity of 326 pb$^{-1}$. A measurement of jet cross...
In the era of the upcoming Electron-Ion Collider (EIC), the importance of accurate modeling of deep inelastic scattering (DIS) events is ever increasing. We aim to improve the modeling of DIS by implementing multi-jet merging capabilities in Pythia, the most widely-used Monte Carlo (MC) event generator among the LHC experiments. Multi-jet merging allows the combination of parton shower...
The Breit frame provides a natural reference frame to analyze lepton-proton (ep) scattering events when the process of interest is plainly considered as a photon-hadron interaction. In the Breit frame, the photon runs on the z axis into the positive direction, and in the leading order picture the struck quark leaves the interaction on the z axis, too. Higher-order QCD corrections change that...
We present a new event generator for the simulation of both neutral- and charged-current DIS at NLO QCD matched to parton showers using the POWHEG method. Our implementation builds on the existing POWHEG BOX framework originally designed for hadron-hadron collisions, supplemented by considerable extensions to account for the genuinely different kinematics inherent to lepton-hadron collisions....
In this talk, recent measurements of distributions sensitive to the underlying event, the hadronic activity observed in relationship with the hard scattering in the event, by the ATLAS experiment are presented. Underlying event observables like the average particle multiplicity and the transverse momentum sum are measured for Kaons as Lambda baryons as a function of the leading track-jet and...
