A summary of results on double parton scattering processes from CMS will be presented. The focus of the talk will lie on the latest result on WW production via double parton scattering. The data set in use is from the Run-II data taking periods in 2016 and 2017, corresponding to an integrated luminosity of 77.4 fb-1. The result constitutes the first evidence of this process, with an observed...
The talk is going to include the latest LHCb results on searches of double parton scattering (DPS) effects in the data, taken by the experiment in proton-proton collisions during Run1 and Run2 of the LHC operation. The measurements are performed for the different final states and mainly focused on the processes involving heavy quarks, which provide the most precise probing of factorization...
A composite nature of hadrons leads to a complicated structure of the underlying event in hadronic collisions. In particular it give rise to a possibility to have two hard interactions per one hadron-hadron collision, so called double parton scattering (DPS) phenomenon. Among different possible DPS production processes the four-jet DPS production is of particular interest due to a high...
We examine currently available data for Double Parton Scattering and discuss the energy behaviour of the extracted effective cross-section. A variety of models is compared with different data sets. We find that processes dominated by gluons initiated DPS, such as 4 jet production, exhibit a rising behaviour as the energy increases. Eikonal models as well as models based on empirical fits...
In this talk we review current developments regarding small-x and diffractive physics from the viewpoint of Monte Carlo Event Generators. Besides highlighting advances in describing diffractive events we also point out where further work is necessary.
Understanding the properties of nuclear matter and its emergence through the underlying partonic structure and dynamics of quarks and gluons requires a new experimental facility in hadronic physics known as the Electron-Ion Collider (EIC). The EIC will address some of the most profound questions concerning the emergence of nuclear properties by precisely imaging gluons and quarks inside...
Production of heavy photons (Drell-Yan), gauge bosons, Higgs bosons, heavy flavors and dijets, which is treated within the QCD parton model as a result of hard parton-parton collision, can be considered as a bremsstrahlung process in the target rest frame. In this talk, I will discuss the recent progress and the basic features of the diffractive channels of these processes in the framework of...
This talk focuses on the recent implementation of the Mueller dipole formalism in Pythia 8. We show how the dipole formalism can be used to assign spatial vertices to the MPIs in Pythia 8. This allows us to study geometric quantities such as initial state eccentricities, connected to flow coefficients measured at the LHC. In this work we show comparisons to pp, pPb and PbPb data from the LHC...
New measurements on particle production as a function of the charged-particle multiplicity in pp collisions have been reported by the ALICE Collaboration. The novelty of the results relies on the use of transverse spherocity for event classification in either pencil-like or isotropic events, which turn out to be sensitive to the main hard scattering or underlying event, respectively. Results...
The talk will present the results obtained by the CMS collaboration on minimum bias processes and the so-called underlying event. An overview of what we learned during the whole Run 2 of the LHC will be provided.
The interaction force between Lund strings contributes to the flow effects in high-multiplicity pp and AA collisions. Hence, it is important to know how much push can this force exert on the strings, whose effects might be observed in the system as a whole. In this talk, we present our shoving mechanism implemented in the Lund string model. This mechanism, along with rope hadronization and...
Results from LHCb measuring bulk properties of minimum bias events, as well the inelastic cross-section will be summarized. Using these results, a tuning campaign for Pythia 8, specific to the LHCb fiducial volume, is underway and explores some of the newly available colour reconnection models. Some highlights from this tuning campaign will be presented.
The comparison of experimental data and theoretical predictions is crucial for our understanding of the mechanisms for particle production and interactions in hadron collisions at the LHC. The Rivet (Robust Independent Validation of Experiment and Theory) framework was developed for this purpose and is used as a generator-independent system for event generator validation and tuning. It...
Heavy quarks are sensitive probes to test the properties of the Quark-Gluon Plasma (QGP) state formed in heavy-ion collisions since, due to their large masses, they are formed on timescales shorter than the QGP formation time.
In particular, the measurement of the azimuthal anisotropy of hadrons containing heavy quarks gives insight into the participation of low-momentum heavy quarks in the...
Studies of hot and dense QCD matter created in high energy heavy-ion collisions at the Relativistic Heavy Ion Collider (RHIC) revealed that the matter resembles properties of strongly coupled liquid with very low viscosity. High statistics data and major upgrades of the STAR experiment opened recently a new era of tomography of the QCD matter at RHIC using hard probes. In particular, the Heavy...
Results on hadron production in high-multiplicity proton-proton (pp) and proton-lead (p--Pb) collisions at the LHC energies have revealed the presence of collective phenomena reminiscent to those observed in lead-lead (Pb--Pb) collisions. The bulk particle production in Pb--Pb collisions cannot be calculated from first principles of QCD and instead relies on thermodynamic and hydrodynamic...
We present a phenomenological study of the number of Multiple Parton Interactions (MPI) as a function of mid-rapidity charged-particle multiplicity and leading transverse momentum ($\it{p_{\rm T}^{\rm {leading}}}$) in proton-proton collisions at $\sqrt{s}$ = 13 TeV using the event generator PYTHIA 8.240. We observe important correlations between leading charged particle $\it{p_{\rm T}}$ and...
The underlying mechanisms of light flavour production are currently not well understood, although they can be described in the framework of different phenomenological models. pQCD models based on hard scatterings,
such as PYTHIA, describe light flavour production via string-breakings and rope-hadronization.
Statistical thermal models predict that the production of light flavour particles is...
Strangeness enhancement reported from the ALICE Collaboration [1] is referred to as an indication of the existence of quark-gluon plasma (QGP) in small colliding systems such as p+p and p+Pb collisions. Yield ratios of strange hadron show continuous increase as a function of multiplicity and saturation in averaged Pb+Pb events when the QGP is supposed to be formed. Motivated by this data, we...
The associated production of vector boson with quarkonia is a key observable for understanding the quarkonium production mechanisms, including the separation of single and double parton scattering components.
This talk will present the latest measurements from ATLAS on quarkonium production, including the associated production of W+J/psi.
I will discuss a novel channel for phenomenological studies of the double-parton scattering (DPS) based upon associated production of charm and bottom quark-antiquark pairs in well-separated rapidity intervals in ultra-peripheral high-energy proton-nucleus collisions. This process provides a direct access to the double-gluon distribution in the proton at small-x and enables one to test the...
I will review the status and prospects of studies of Double Parton Scatterings with associated and pair production of quarkonia. This includes J/psi pairs, Upsilon pairs, Upsilon+J/psi, J/Psi+D, Upsilon+D, J/psi+Z and J/psi+W at the LHC and the Tevatron.
We consider a new mechanism for prompt simultaneous production of $J/\psi$ and $\Upsilon$ mesons in high energy hadronic collisions. The process is considered as a perturbative production of $B_c^{(*)}$ mesons $g{+}g\to B_c^{(*)} {+}\bar{B_c}^{\!\!(*)}$ followed by a long-distance final state interaction that rearranges the quarks to form $J/\psi$ and $\Upsilon$ mesons. Passing from...
Double parton distributions (DPDs) are an essentialingredient in the computation of the full DPS cross sections. Their numerical handling is complicated by their structure, which depends on more than twice the number of parameters with respect to regular PDFs. Furthermore, in order to make phenomenological predictions for DPS, it is necessary to also include heavy-quark contributions in the...
Bose-Einstein correlations of charged hadrons provide a tool to investigate the space-time structure of the hadron emitting source. In CMS we measure charged hadrons over a broad multiplicity range, from a few particles up to about 250 reconstructed charged hadrons in proton-proton collisions 13 TeV. Different analysis techniques were used to investigate the dependence on simulations when...
A new set of CMS underlying-event tunes is presented for the PYTHIA 8 event generator. The tunes use the NNPDF3.1 parton distribution functions at leading (LO), next-to-leading (NLO), or next-to-next-to-leading (NNLO) order in perturbative QCD, and the strong coupling amd PDF evolution at LO or NLO. Comparisons of the predictions of the new tunes are provided for observables sensitive to the...
We present a model for generating spacetime coordinates in the Monte Carlo event generator Herwig 7, and perform colour reconnection by minimizing a boost-invariant distance measure of the system. We compare the model to a series of soft physics observables. We find reasonable agreement with the data, suggesting that pp-collider colour reconnection may be able to be applied in larger systems.
Inclusive single diffractive dissociation (pp->pX) is studied using data collected by the
ATLAS experiment at the LHC. The intact proton is reconstructed and measured in the
ALFA forward spectrometer, while charged particles from the dissociative system (X)
are reconstructed and measured using the ATLAS inner tracking detector and
calorimeters. Differential cross sections are presented as...
We present an update of the Miettinen-Pumplim (MP) model for diffractive excitation for proton-proton ($pp$) and antiproton-proton ($\bar{p}p$) scattering considering recent LHC data. The energy dependence of the total, elastic, and diffractive cross sections are analyzed and compared to data. The implications of the diffractive excitation in proton-nucleus ($pA$) collisions are also discussed...
An overview of recent diffractive and exclusive measurements with CMS is given. Results on jet-gap-jet event topologies are shown, together with central exclusive p-p production. Diffractive dijet production is measured with proton tagging in pp collisions. In addition, recent results on exclusive rho0 and upsilon production in pPb collisions at 5.02 TeV are presented.
In this talk we present results of a new calculation and Monte Carlo implementation of photon-initiated production in LHC proton-proton collisions. This includes a precise, differential evaluation of both inclusive and semi-exclusive channels, that is with and without rapidity gaps in the final state. Details of the underlying formalism as well as phenomenological results will be presented.
The LHC-forward (LHCf) experiment is dedicated to the measurement of the very forward neutral particle production cross section in proton-proton and proton-lead collisions at the Large Hadron Collider at CERN. The experiment employs two independent detectors, named Arm1 and Arm2, which are placed on opposite sides along the beam line approximately 140 meters away from the interaction point of...
Collectivity in small systems with the CMS experiment
Particle interferometry has proven to be an indispensable tool in probing the space-time evolution of femtoscopic collision systems. In this talk, I show how hydrodynamic predictions for the space-time evolution of high-multiplicity $pp$ and $p+$Pb collisions can be tested against interferometric observables designed to probe their size and shape. In particular, I consider how the dependence...
Measurements of distributions of two weighted angular moments derived from jet
constituents are presented. The jet-pull angle and the jet-pull magnitude, both of
which are derived from the jet-pull angular moment, encode the colour connections between
partons that seed the jets.
The measurements are performed in top-quark-antiquark events with one leptonically
decaying W boson and one...
We have developed a framework for hadronic rescattering in Pythia. Our goal is to study how rescattering can account for observed phenomena such as flow, jet quenching, etc. In this presentation I will outline our algorithm and present some preliminary results.
High multiplicity events in heavy-ion collisions are still under debate whether they produce an extremely hot and dense matter similar to the QGP formed on heavy atomic nuclei collisions. One of the main characteristics of the formation of this state is that it behaves like a near-perfect fluid, with very tiny shear viscosity. We present an estimate of the shear and bulk viscosity properties...
Exploration of the rich structure of the QCD phase diagram is an important topic in the RHIC heavy ion program whose ultimate goal is to discover the critical endpoint. Investigation of the space-time structure of hadron emissions at various phase transition points using Bose-Einstein correlation of identical bosons will provide insight on the location of the critical endpoint. PHENIX has...
Relativistic heavy-ion collisions produce extremely hot dense matter.
Heavy flavor and electromagnetic particles are promising probes to
investigate the properties of the hot dense matter. The
parton-hadron-string dynamics (PHSD) is a Boltzmann-type transport code,
but it further includes the off-shellness of particles based on
Kadanoff-Baym equations. The equation-of-state and shear...
Open discussion.
With current large cosmic ray observatories, precise data of extensive air shower cascades is recorded up to primary particle energies of 10^{20}eV. While there is significant progress in understanding cosmic rays in general, and also particle physics in the air shower cascades, there are also tantalizing open questions. The most interesting one is the "muon mystery", which is a strong hint...
Various recent measurements of high-multiplicity pp and p-A collisions at LHC energies have revealed, surprisingly, that these small collision systems exhibit some features of the quark-gluon-plasma, e.g. collective behaviour and strangeness enhancement, formerly thought to be achievable only in heavy-ion collisions. A promising method to narrow down the origin of this behaviour is to study...
Recent progress in the development of the general purpose Monte Carlo generator Herwig 7 will be presented. A focus will be given to progress in modeling underlying event and minimum bias.
The correlation between the near side and transverse side has been studied with Pythia. Strong correlations between the two regions occur at high multiplicities of above dN/deta of 50 charged particles. The changes occurring in the spectra obtained subtracting the transverse side spectra are reported. We conclude that the results indicate the possibility of parton energy loss in pp collisions.
Up to now, searches for saturation have concentrated in the the small-x behaviour of QCD. Here we add the transverse dimension to this type of studies. We present a model of hadrons with an energy-dependent structure in the transverse plane made of hot spot, regions of high gluonic density. Using this model and the colour-dipole formalism we compute the diffractive photoproduction of vector...
We present fits to determine parton distribution functions (PDFs) using top-antitop,
inclusive W/Z-boson, as well as W+ and W− boson production measurements in
association with jets from ATLAS, in combination with deep-inelastic scattering data
from HERA. The ATLAS W and Z boson data exhibit sensitivity to the valence quark
distributions and the light quark sea composition, whereas the...
We present results of calculations of cross sections for production of $\eta_c$(1S)
and $\eta_c$(2S) for the LHC for $\sqrt{s}$ = 7, 8, 13 TeV.
The calculations are performed within $k_t$-factorization approach
for different unintegrated gluon distributions from the literature.
Some of UGDFs include saturation effects.
We discuss effect of the transition $g^* g^* \to \eta_c$ form factors...
Here we present our studies on the so called double parton distribution functions (dPDFs) and transverse proton structure. Double PDFs appear in the double parton scattering (DPS) cross section in high energy proton-proton and proton nucleus collisions. These new distributions represent a novel and promising complementary tool, w.r.t. TMDs and GPDs, to access the 3D partonic structure of the...
Double parton distributions (DPDs) are an important piece in the descriptions of double hard interactions. On the lattice we calculate correlation functions of two local quark currents, which can be related to Mellin moments of DPDs. For the first moment we calculate all contributing Wick contractions for the nucleon (proton), considering several channels corresponding to the quark...
W boson creation associated with dijet production is a promising channel to study double parton interactions at the LHC. In this talk we review and update predictions for the W+jets signal in proton lead collisions and discuss a new method which could give access to longitudinal and/or transverse structure of the proton.
I will present results of my investigations on the topics enumerated in the title based on my joint work with my collaborators.
In this talk, a new Monte-Carlo simulation of double parton scattering (DPS) at parton level is presented. In this simulation, the dynamics of the 1→2 perturbative splittings is consistently included, with the impact-parameter dependence taken into account. The evolution is performed using an angular-ordered parton shower which is combined with a set of double parton distributions that depend...
The hadronization of the deconfined matter arising in high-energy particle collisions is considered in terms of the first kind phase transition in the multiple flux tube approach. Based on the compactification of the standard (3+1) chromodynamics into $ QCD_{xy} + QCD_{zt}$, the rate of hadron production in particle collisions with respect to both the rapidity and $p_T$ distributions ...
Recently, an interesting faster than linear dependence of quarkonium production on charged particle multiplicity in p+p collisions has been observed. This can be used to study basic particle production mechanism and relation between soft and hard QCD processes. Such a strong increase of normalized particle yield from hard processes with respect to normalized charged particle multiplicity may...
At the LHC energies Multiple Parton Interactions (MPI) are expected to affect not only processes involving soft particle production, but also the hard momentum scales relevant for the production of heavy quarks, such as charm and beauty. Quarkonium measurements in high-multiplicity proton-proton (pp) collisions can shed light on the role of MPI at such hard momentum scales, as well as on the...
Measurements of the production of light- and heavy-flavor hadrons are of great importance for studies of the matter produced in high-energy collisions. The ALICE experiment has excellent tracking and particle identification capabilities, which have been used to measure a wide variety of hadrons as a function of multiplicity in pp collisions. Studies of light- and heavy-flavor hadrons in...
Certain data features that were attributed to quark-gluon plasma (QGP) formation in more-central A-A collisions -- evidence for radial flow and jet quenching in pt spectra, v2, v3, etc. in azimuth correlations, one or two "ridge" structures in long-range angular correlations -- have more recently been observed in high-multiplicity p-A and even p-p collisions. Arguing by analogy with A-A...
A measurement of charged-particle distributions sensitive to the properties of the
underlying event is presented for an inclusive sample of events containing a Z-boson,
decaying to a muon pair. The measurement is done using proton-proton collision data
collected by the ATLAS experiment at √s=13 TeV. Unfolded differential cross sections
are presented for charged particle multiplicity and...
Measurements of double parton scattering in proton-proton collisions provide insight
into the structure and long-range low-momentum scale interactions of the proton. In this
talk we present a measurement of the double-parton scattering contribution to
four-lepton events at √s=8 TeV. An artificial neural net is used to optimise the analysis
and an upper limit on the double-parton scattering...
In this talk, we present four measurements that probe the internal structure of jets using
data collected by the ATLAS experiment. First, a measurement of the properties of jet
fragmentation using charged particle tracks is presented, including charged particle
multiplicity, jet charge, the summed fragmentation function, the momentum transverse
to the jet axis, and the radial profile of...
