The installation of scintillating pad detectors (Herschel), in the LHCb detector along the beamline, have significantly enhanced the LHCb sensitivity to central exclusive production. Additionally, dedicated triggers during the early measurement period of Run 2 produced an extended CEP dataset. A summary of results from Run 1 as well as early results from Run 2 will be shown.
Studies of diffractive events at H1 and ZEUS detectors at HERA are presented.
These studies include: Production of exclusive dijets in diffractive deep
inelastic scattering (DIS); Exclusive ρ 0 meson photoproduction with a leading
neutron; Measurement of D ∗ meson production in diffractive deep inelastic
scattering; Diffractive photoproduction of isolated photons; Measurement of
the...
RHIC can probe low-x partons in nuclei in p/d+A collisions at forward rapidities,
where non-linear QCD effects are expected to set in. So far no clear experimental
observation of the onset of gluon saturation has been made. Di-hadron/jet
correlations and ratios of hadrons yields in p+p and p/d+A collisions at forward
rapidities can be linked to modifications of nuclear parton...
We review the analytical description of Froissart saturation condition in a transverse-momentum-dependent parton distribution function of a self-similarity based proton structure function F_{2}(x,Q^{2}) at small x. Saturating the Froissart bound refers to an energy dependence of the total cross-section rising no more rapidly than ln^{2} s, where s is the square of cms energy. Our...
This talk will describe recent results from CMS on very forward jets in CASTOR, jet gap jets and Mueller Navelet jets as a possible sign of BFKL dynamics.
After recalling briefly the BFKL NLL fits t the HERA forward jet data, we will describe how jet gap jet events at the LHC can be a good observable to look for BFKL resummation effects. We will discuss the full NLL BFKL calculation of such processes
Monte Carlo Tutorial - Part I
Monte Carlo Tutorial - Part II
In hot and dense environments both in heavy ion collisions and high multiplicity proton-proton events, Lund string fragmentation must be modified to take into account effects from the interaction between strings prior to and in the hadronisation. One such modification is colour reconnections, where oppositely directed colour fields may cancel eachother. But there is also a possibility for the...
The core-corona picture implemented in the EPOS~3 model has successfully described the multiplcity dependence of particle production in proton--proton (pp) and proton--nucleus collisions at LHC energies.
The inclusion of viscous hydrodynamics plays a key role in describing the observed features of data. It suggests an interpretation of new phenomena assuming the formation of a small drop of...
New CMS PYTHIA 8 event tunes are presented. The new tunes are obtained using minimum bias and underlying event observables using Monte Carlo configurations with consistent parton distribution functions and strong coupling constant values in the matrix element and the parton shower. Validation and performance studies are presented by comparing the predictions of the new tune to various soft-...
The status of recent studies of modern Monte Carlo generator setups for the pair production of top quarks at the LHC. Samples at a center of mass energy of 13 TeV have been generated for a variety of generators and with different generator configurations. The predictions from these sample are compared to ATLAS data for a variety of kinematic observables.
The predictions of different Monte Carlo generators for QCD jet production, both in multijets and for jets produced in association with other objects, are presented. Recent improvements in showering Monte Carlos provide new tools for assessing systematic uncertainties associated with these jets. Studies of the dependence of physical observables on the choice of shower tune parameters and new...
The beam-energy scan at RHIC aims to discover whether a critical point exists in the phase diagram of QCD. We will report on the most comprehensive measurement of single-particle spectra for a multitude of hadrons from the first run, taken with the STAR experiment. From these measurements we will infer the kinetic and chemical freeze-out temperatures and the baryon chemical potential as...
The measurements of high $p_{T}$ hadron production is an excellent tool to study the parton energy loss in the Quark Gluon Plasma (QGP). The experimental observables of $R_{AA}$ focus on the inclusive suppression, while the high $p_T$ $v_n$ measurements are sensitive to the path-length dependence of the energy loss.
The large suppression ($R_{AA}$ < 1) and the positive $v_2$ were first...
The ALICE collaboration has measured the production of light-flavour hadrons in pp, p--Pb and Pb--Pb collisions at$\sqrt{s\rm{_{NN}}} = $ 5.02 TeV over a wide range of transverse momentum ($p_{\rm T}$). The results on $\pi$, K, p,K$^{*0}$ and $\phi$ $p_{\rm T}$ spectra, ratios of the $p_{\rm T}$-integrated yields and mean transverse momentum will be presented for the three colliding systems at...
The ALICE experiment is dedicated to study the properties of the strongly-interacting matter, usually referred to as the Quark-Gluon Plasma (QGP), created in high-energy heavy-ion collisions. Heavy quarks, i.e. charm and beauty, are produced in the initial stages of the collision via hard scattering processes. Thus they probe the full evolution of the system. Measurements in p-Pb collisions...
We will report on our results for electromagnetic (two-photon) single and double scattering production of two positron-electron and muon pairs in ultraperipheral ultrarelativistic two lead ions collisions. We consider double-scattering contribution obtaining measurable cross section. We take into account realistic cuts on electron/positron or muon (pseudo)rapidities and transverse momenta for...
Large In LHC RUN II, the Large Hadron Collider restarted with a centre-of-mass energy increase of around 60% with respect to the end of the LHC RUN I. At this new energy it is absolutely essential to restudy the general features of the pp interaction, in particular the soft or semi-hard bulk of particles that form the Underlying Event, which is defined to be the complementary activity with...
While the modelling of Minimum Bias (MB) is a crucial ingredient to learn about the description of soft QCD processes, the studies of the Underlying Event (UE) shed light on the description of both soft and hard QCD processes at hadron colliders. The ATLAS collaboration has provided measurements of the inclusive charged-particle multiplicity and its dependence on transverse momentum and...
We present results on the measurement of the underlying event at 13 TeV using leading tracks, jets, and Drell-Yan processes. This presentation also includes recent results from Minimum Bias measurements with CMS experiment.
We study ATLAS results on underlying event in pp collisions at $\sqrt{s}=0.9$, 7 and 13\,TeV. We show that the center-of-mass energy dependences of the charged-particle production sensitive to the underlying event (transverse region) and to the hardest partonic interaction (towards and away regions) in pp collisions can be both understood in terms of the change of the inclusive average...
Calculations of jet substructure observables which are accurate beyond leading-logarithmic accuracy have recently become available. Such observables are significant not only for probing a new regime of QCD at a hadron collider, but also for improving the understanding of jet substructure properties that are used in many studies at the Large Hadron Collider. In this talk, we discuss first...
The production of J/ψ mesons in hadron-hadron collisions occurs at the transition between the perturbative and non-perturbative regimes of quantum chromodynamics, resulting in a rich phenomenology that is yet to be fully understood.
LHCb studied the production of J/ψ mesons in jets in the forward region of proton-proton collisions at a center-of-mass energy of 13 TeV. The fraction of the jet...
Energy and multiplicity dependence of the strangeness enhancement in pp collisions
The ratio of the $p_{\rm T}$-integrated yield of strange and multi-strange particles relative to non-strange hadrons has been measured as a function of the event activity in pp collisions at the LHC, revealing that from low to high multiplicity events, strange hadron production increases smoothly and...
High-energy heavy-ion collisions at RHIC and LHC provide a unique opportunity to study nuclear matter under extreme conditions i.e. at high temperature and/or
energy density. Due to the high multiplicities produced in $p+p$ collisions, one can use the the statistical models to describe the particle production mechanism. As thermodynamically consistent Tsallis statistics has been...
The recently observed phenomenon of enhanced strange particle production in high multiplicity pp collisions at LHC is not yet well understood from a theoretical point of view. While a modelling based on QCD inspired MC models such as PYTHIA, DIPSY or EPOS aims at a microscopic understanding, we present two alternative approaches to study light flavour hadron production as a function of event...
Event shape observables are important tools to get an insight into the physics behind collective phenomena in high multiplicity pp collisions at LHC energies. They can be used to disentangle the contributions from hard and soft processes to particle production. We report measurements with the ALICE detector at the LHC of the production of inclusive and identified charged particles as a...
In high multiplicity p+p collisions, the Underlying Event observable is of great interest to the scientific community. The Multiple Partonic Interaction (MPI) is one of them, where several inelastic interactions at partonic level occur in a single p+p collision. In general, MPI plays an important role to produce light quarks and gluons. But it is observed that it can also contribute to...
Details of charmonium production in hadronic collisions are still under active investigation in the scientific community. The event multiplicity dependence of J/psi production will give insight into the processes at the parton level. Multiple Parton Interactions (MPI) are thought to be a substantial source of hard scattering processes at LHC energies. Here, several inelastic scatterings occur...
In hadronic collisions, interference between different production channels af-
fects momentum distributions of multi-particle final states. As this QCD interference does
not depend on the strong coupling constant
$\alpha_s$, it is part of the no-interaction baseline that
needs to be controlled prior to searching for other manifestations of collective dynamics,
e.g., in the analysis of...
In this contribution, we report on the multiplicity dependence of the pseudorapidity density distribution of charged particles in proton-proton (pp) collisions at $\sqrt{s}$ = 5.02 TeV and at 13 TeV with the ALICE experiment. The measurements rely on track segments reconstructed with the Silicon Pixel Detector in the kinematic region $|\eta| < $ 1.8. Results are presented for three different...
In this talk I will discuss on the latest developments in the theoretical description of small collision systems at the LHC. In particular I will discuss how our understanding of the initial state geometry and momentum space correlations can help explain the origin of collectivity in small collision systems at the LHC.
The total pp cross section is a fundamental property of the strong interaction which can not be calculated in perturbative QCD but only described based on phenomenological models.
The ATLAS collaboration has measured the total inelastic proton-proton cross section and the diffractive part of the inelastic cross section at 13 TeV in special data sets taken with low beam currents and using...
In this talk, we will describe the Electron-Ion Collider project and the physics that can be done.
This talk will discuss recent CT-PPS results concerning exclusive di-lepton production and prospects for future measurements concerning anomalous couplings.
Experimental measurement of observables sensitive to underlying event (UE) has been performed by both ATLAS and CMS experiments at the LHC. However, in the busy LHC environment, these observables receive substantial contribution from extra jets. In this study, we probe if using event shape observables in conjunction with UE observables can help us to disentangle the effect of UE from extra jets.
We present results on measurements of characteristics of events with jets and event shape measurements by CMS using data from pp collisions. The measurements are compared to theoretical predictions from different models of parton shower and hadronization.
This talk provides a review of the latest results on the theory of Double Parton Scattering
We present recent results on Double Parton Scattering (DPS) studies using data collected during Run 1 and Run 2 of the LHC with the CMS experiment. Double parton scattering is investigated in several final states including vector bosons and multi-jets. Measurements of observables designed to highlight the DPS contribution are shown and compared to MC predictions from models based on multiple...
The production cross-section of J/ψ pairs in the forward region is measured using a data sample of pp col-
lisions collected by the LHCb experiment at a centre-of-mass energy of 13 TeV .
Differential cross-sections are presented as functions of several kinematic variables of the J/ψ
pair are measured and compared to theoretical predictions.
LHCb observed the associated production of bottomonia and open charm hadrons in pp collisions at centre of mass energies of 7 and 8 TeV is observed. Production
cross-sections are measured for Υ(1S)D0 and Υ(1S)D+ pairs in the forward region.
Measurements of the production of J/ψ mesons accompanied by open charm, and of pairs of open charm hadrons are shown.
I will review the status of theory studies of Double Parton Scatterings (DPS) using associated production of quarkonia at colliders. This includes $J/\psi+J/\psi$, $\Upsilon+\Upsilon$, $J/\psi+\Upsilon$, $J/\psi+W$, $J/\psi+Z$, $\Upsilon+D$ and $J/\psi+D$. Where relevant, I will discuss the impact of QCD corrections to Single Parton Scatterings which can affect the extraction of the DPS yield....
Phenomena of multiple-parton interaction (MPI) have become very
essential for precise description of high-energy proton-proton
collisions in the ongoing LHC era.
Some time ago we have proposed and discussed double open charm meson
production $pp \to D D \!\; X$ as a potentially one of the best reaction
to study hard double-parton scattering effects at the LHC.
This conclusion was further...
Abstract:. We test the hypothesis that configurations of a proton with a large-$x$ parton, $x_p > 0.1$, have a smaller than average size. The QCD $Q^2$ evolution equations suggest that these small configurations also have a significantly smaller interaction strength, which has observable consequences in collisions with nuclei. We perform a global analysis of jet production data in proton- and...
The aim of the heavy-ion experiments at RHIC is to study the QCD matter at very high temperature and/or at high density by colliding nuclei at ultra-relativistic speeds.
Using the information carried by freely streaming final-state particles as probes, we try to understand the properties of the medium created in these collisions. An extensively studied subject is azimuthal anisotropy or...
We present the review of recent results of femtoscopic studies performed by ALICE experiment at the LHC in heavy ion and pp collisions. The measurements include the correlations between the identical and non-identical pairs of mesons and baryons. These correlations which arise from quantum statistics and final-state interactions among the produced particles, probe the space-time...
In the last years the LHCb experiment has started to provide novel inputs to heavy ion physics by exploiting some of its unique features. Particle production can be studied in p-p, p-Pb and Pb-Pb collisions at LHC energies for pseudorapidity between 2 and 5, providing measurements which are highly complementary to the other LHC experiments.
The excellent vertexing and particle identification...
Ultraperipheral collisions (UPCs) of heavy ions or hadrons involve long range electromagnetic interactions at impact parameters larger than the sum of their radii where hadronic interactions are largely suppressed and they interact electromagnetically via emission of quasi-real photons. Photoproduction of heavy vector mesons (J/psi, Upsilon) provides direct information on the gluon...
Recent measurements in proton-proton (pp) and proton-nucleus (pA) collisions at LHC energies show that the charged particle multiplicity density is comparable to that produced in nuclear collisions at lower energies. The long-range "ridge" structures observed in high multiplicity pp and p-Pb collisions resemble those seen in Pb-Pb collisions. The "ridge" structure in Pb-Pb collisions suggests...
Heavy-flavour production in pp collisions at LHC energies is described by perturbative QCD calculations based on the factorization approach in which the cross-section is obtained as a convolution of a hard process, parton distribution functions and fragmentation functions. The investigation of heavy-flavour production as a function of event properties, like charged-particle multiplicity, can...
In recent years, the ALICE experiment has collected data in proton-proton
collisions at various centre-of-mass energies. In addition to providing a
baseline for heavy-ion collisions, these data provide information on the
particle production in high energy collisions through the study of energy
dependence of various observables. With large statistics data samples
collected in pp at $\sqrt{s}~=$...
The mid-rapidity transverse momentum spectra of hadrons ( p, K+, ks0, lambda, lambda-bar and cascade and the available rapidity distributions of the strange hadrons produced in p-p collisions at LHC energy √sNN = 0.9 TeV have been studied using a Unified Statistical Thermal Freeze-out Model (USTFM). The calculated results are found to be in good agreement with the experimental data.The...
This talk will cover TOTEM results on soft diffraction (total, elastic and inelastic cross sections) as well as the CMS/TOTEM results.
We review the current model for soft interactions which is based on multiperipheral particle kinematics in the Monte Carlo event generator Herwig 7.
Furthermore we investigate the consequences of additional modifications related to
soft physics in pp collisions with respect to hadronic flavour observables.
Angantyr is a new model for collisions involving heavy nuclei in Pythia8. It is inspired by the old Fritiof model, but includes more perturbative physics and a more careful consideration of fluctuations in nucleon-nucleon cross sections, and the related diffractive processes. In the current implementation in Pythia8 parton-level nucleon-nucleon minimum bias events are stacked together and...
Several new double parton scattering (DPS) tunes are constructed in order to investigate the compatibility between the values of the UE parameters determined from fitting UE observables and the values determined from fitting DPS-sensitive observables. In addition, the predictions of the DPS-based tunes are tested against UE observables at 13 TeV.
A study of the latest color-reconnection models in QCD is performed with CMS data. The so called MPI-based, QCD-inspired and gluon-move models are studied within Pythia8, and the tuning parameters for the color reconnection and multiple parton interactions are extracted simultaneously from data. The different tunes are compared with top quark distributions.
