### Regular Series

#### Cracow Epiphany Conference Particle Theory Meets the First Data from LHC Run 2

Effect of Emission of Extra Lepton Pair for Precise Measurement of $W$-boson Mass

Acta Phys. Pol. B 48, 891 (2017)

page 891 •

abstract

In the paper, we present results for the final state emissions of lepton pairs in decays of heavy-intermediate states, principally of $Z$ boson, but of some importance for the $W$ decays as well. The presented semi-analytical calculation and PHOTOS MC program are in a numerical agreement to better than $5\%$ of pair effects. Suggestions for the future works are given.

Challenges of EFT at the LHC

Acta Phys. Pol. B 48, 897 (2017)

page 897 •

abstract

I will discuss the difficulties of putting constraints on the Effective Field Theories (EFT) at the Large Hadron Collider (LHC). In particular, I will analyse the generic properties of the $2\to 2$ scattering in the presence of the higher dimensional operators indicating that some of the beyond Standard Model effects are parametrically smaller than naive expectations.

Systematic of TauSpinner for $\tau$ Pairs With Two Hard Jets and Its Recent Development

Acta Phys. Pol. B 48, 903 (2017)

page 903 •

abstract

In this paper, we review results obtained by using the TauSpinner package. A sample of $pp\rightarrow \tau \tau +jj$ events, where spin effects are not included, is supplemented with weight, then helicities of the $\tau$ leptons are attributed. The systematic uncertainties of TauSpinner due to variation of its input parameters as well as its recent development on implementation of non-Standard Model matrix elements are presented.

Version corrected according to Erratum Acta Phys. Pol. B 48, 1455 (2017)

Measurement of the Phase $\phi _{s}$ at the LHCb

Acta Phys. Pol. B 48, 913 (2017)

page 913 •

abstract

One of the key goals of the LHCb experiment is the determination of the CP-violating phase $\phi _{s}$ in $\bar {b}\rightarrow \bar {c}c\bar {s}$ decays. Its value is predicted to be very small in the Standard Model. The measurements in the $B^{0}_{s}\rightarrow J/\psi \phi$, $B^{0}_{s}\rightarrow J/\psi \pi ^{+}\pi ^{-}$ and $B^{0}_{s}\rightarrow \psi (2S) \phi$ channels are reviewed. The first observation of the $B^{0}_{s}\rightarrow \eta _{c} \phi$ and $B^{0}_{s}\rightarrow \eta _{c} \pi ^{+}\pi ^{-}$ decay modes is presented. These channels can be used to measure $\phi _{s}$ with larger data statistics that will be collected during Run 2 by the LHCb experiment.

Differential $t\bar {t}$ Cross-section Measurements in the Lepton+Jets Channel at $\sqrt {s}=13$ TeV Using the ATLAS Detector

Acta Phys. Pol. B 48, 921 (2017)

page 921 •

abstract

Measurements of differential cross sections of top-quark pair production are presented as a function of the top quark and $t \bar {t}$ system kinematic observables in proton–proton collisions at a centre-of-mass energy of $\sqrt {s}=13$ TeV. The dataset corresponds to an integrated luminosity of 3.2 fb$^{-1}$, recorded in 2015 with the ATLAS detector at the CERN Large Hadron Collider. Events with one lepton and jets in the final state are used for the measurement. Two separate selections are applied that each focus on different top-quark momentum phase-spaces, denoted as resolved and boosted topologies of the $t \bar {t}$ final state. The measured spectra are corrected for detector effects and are compared to several Monte Carlo simulations. The results are in a fair agreement with the predictions over a wide kinematic range. Nevertheless, most event generators predict a harder top-quark transverse momentum distribution at high values than what is observed in the data.

Hollowness in $pp$ Scattering

Acta Phys. Pol. B 48, 927 (2017)

page 927 •

abstract

It is argued that the hollowness effect (depletion in the absorptive part of the scattering cross section at small values of the impact parameter) in the proton–proton scattering at the LHC energies finds its origin in the quantum nature of the process, resulting in large values of the real part of the eikonal phase. The effect cannot be reconciled with an incoherent superposition of the absorption from the proton constituents, thus suggests the change of this basic paradigm of high-energy scattering.

Inclusive Forward-jet and Dijet Production at the LHC

Acta Phys. Pol. B 48, 939 (2017)

page 939 •

abstract

We present a study of inclusive forward-jet and dijet production in the high-energy factorization framework. We examine several physical effects not included in previous analyses i.e. contributions coming from off-shell quarks, double-parton scattering and final-state radiation. We compare our results with the available LHC data at $\sqrt {s}= 7$ and 13 TeV and with collinear factorization.

Modeling NNLO Jet Corrections with Neural Networks

Acta Phys. Pol. B 48, 947 (2017)

page 947 •

abstract

We present a preliminary strategy for modeling multidimensional distributions through neural networks. We study the efficiency of the proposed strategy by considering as input data the two-dimensional next-to-next leading order (NNLO) jet $k$-factors distribution for the ATLAS 7 TeV 2011 data. We then validate the neural network model in terms of interpolation and prediction quality by comparing its results to alternative models.

full authors' list

J. Currie, E.W.N. Glover, T. Gehrmann, A. Gehrmann-de Ridder, A. Huss, J. Pires

Single Jet Inclusive Production for the Individual Jet $p_{\rm T}$ Scale Choice at the LHC

Acta Phys. Pol. B 48, 955 (2017)

page 955 •

abstract

We study the single jet inclusive cross section up to next-to-next-to leading order in perturbative QCD, implemented in the parton-level event generator NNLOJET. Our results are fully differential in the jet transverse momentum and rapidity, and we apply fiducial cuts for comparison with the available ATLAS 7 TeV 4.5 fb$^{-1}$ data for jet radius $R=0.4$. For the theoretical calculation, we employ the antenna subtraction method to reliably cancel all infrared divergences present at intermediate stages of the calculation. We present all results using the individual jet transverse momentum $\mu _{\rm R}=\mu _{\rm F}\sim p_{\rm T}$ as the renormalization and factorization scale for each jet’s contribution to the single jet inclusive cross section. Finally, we consider the differences between our predictions using this scale choice to those for the leading jet transverse momentum scale choice, with reference to the ATLAS data.

Long-lived Light Scalars at the LHC

Acta Phys. Pol. B 48, 969 (2017)

page 969 •

abstract

In the minimal left–right realization of TeV scale seesaw for neutrino masses, there is a phenomenologically allowed range of parameters where one of the neutral scalar particles from the right-handed symmetry breaking sector could have a mass at the GeV scale. We discuss the constraints on this particle from low-energy flavor observables, and find that such a light particle is necessarily long-lived, and can be searched for at the LHC via displaced signals of a collimated photon jet. This decay mode provides a new test of TeV scale left–right seesaw model since this is in sharp contrast with any generic beyond the Standard Model light scalar, which would decay to leptons and jets as well.

Elastic Hadron Scattering in Various Pomeron Models

Acta Phys. Pol. B 48, 981 (2017)

page 981 •

abstract

In this work, the process of elastic hadron scattering is discussed. In particular, scattering amplitudes for the various Pomeron models are compared. In addition, differential elastic cross section as a function of the scattered proton transverse momentum for unpolarised and polarised protons is presented. Finally, an implementation of the elastic scattering amplitudes into the GenEx Monte Carlo generator is discussed.

MINLO for Multi-jet Processes

Acta Phys. Pol. B 48, 987 (2017)

page 987 •

abstract

In this paper, the recent progress in improving the Minlo procedure for generating inclusive event samples that are (N)NLO accurate in various jet multiplicities is discussed. As a proof of principle, a selection of the predictions for Higgs boson production in association with up to two jets is shown. The predictions are simultaneously accurate at NNLO for observables inclusive in $H$ production, NLO accurate in $H$+jet production and NLO accurate in $H$+2 jets production.

New Prospects for the Numerical Calculation of Mellin–Barnes Integrals in Minkowskian Kinematics

Acta Phys. Pol. B 48, 995 (2017)

page 995 •

abstract

During the last several years, remarkable progress has been made in numerical calculations of dimensionally regulated multi-loop Feynman diagrams using Mellin–Barnes (MB) representations. The bottlenecks were non-planar diagrams and Minkowskian kinematics. The method has been proved to work in a highly non-trivial physical application (two-loop electroweak bosonic corrections to the $Z \to b \bar {b}$ decay), and cross-checked with the sector decomposition (SD) approach. In fact, both approaches have their pros and cons. For multidimensional integrals, depending on masses and scales involved, they are complementary. A powerful top–bottom approach to the numerical integration of multidimensional MB integrals is automatized in the MB-suite AMBRE/PlanarityTest/MBtools/MBnumerics/ CUBA. New key elements are: a dedicated use of the Cheng–Wu theorem for non-planar topologies and of shifts and deformations of the integration contours. An alternative bottom–up approach starting with complex 1-dimensional MB integrals, based on the exploration of steepest descent integration contours in Minkowskian kinematics, is also discussed. Short- and long-term prospects of the MB method for multi-loop applications to LHC- and LC-physics are discussed.

Acta Phys. Pol. B 48, 1011 (2017)

page 1011 •

abstract

We present the latest results of studies within the MMHT PDF framework. We discuss the impact of the most recent ATLAS 7 TeV jet data, demonstrating that while a good fit can be achieved for individual jet rapidity bins, it is not possible to achieve a good description of the data when all bins are fitted. We examine the role that the experimental correlated systematic uncertainties play in this, and demonstrate that by simply decorrelating no more than two sources of error between rapidity bins, a remarkably improved description of the data can be achieved. We then study the impact of NNLO corrections, showing that a mild decrease in the fit quality is produced. We also present the results of including new LHC $W$, $Z$, $W+c$ and $t\bar {t}$ data on the MMHT14 PDF set, showing that a marked decrease in the $s+\bar {s}$ uncertainty is in particular achieved. Finally, some discussion of the latest work towards the inclusion of the photon PDF within the MMHT framework is presented.

A New Model for Soft Interactions in Herwig

Acta Phys. Pol. B 48, 1025 (2017)

page 1025 •

abstract

We present a new model for soft interactions in the Monte Carlo event generator Herwig. The soft diffractive final states are modelled on the basis of the cluster hadronization model and interactions between soft particles are modelled as multiple particle production with multiperipheral kinematics. We further present much improved results of mininum-bias measurements at different energies.

full authors' list

A. Kusina, F. Lyonnet, D.B. Clark, E. Godat, T. Ježo, K. Kovařík, F.I. Olness, I. Schienbein, J.Y. Yu

LHC Lead Data and Nuclear PDFs

Acta Phys. Pol. B 48, 1035 (2017)

page 1035 •

abstract

We compare predictions of nCTEQ15 nuclear parton distribution functions with proton–lead vector boson production data from the LHC. We select data sets that are most sensitive to nuclear PDFs and have potential to constrain them. We identify the kinematic regions and flavors where these data can bring new information and will have largest impact on the nuclear PDFs. Finally, we estimate the effect of including these data in a global analysis using a reweighting method.

Optimizing Higgs Boson CP Measurement in $H\to \tau \tau$ Decay With ML Techniques

Acta Phys. Pol. B 48, 1049 (2017)

page 1049 •

abstract

Current measurements of the CP state of the Higgs boson have favoured a scalar Higgs boson but are not able to exclude a mixing of scalar and pseudoscalar Higgs boson states. A measurement of possible mixed CP states of the Higgs boson is best done through the $H\to \tau \tau$ decay mode. The decay products of $\tau$ leptons, produced in $H\to \tau \tau$ decays, encode the CP information of the Higgs. This presents a challenge as a large proportion of $\tau$ decays involve cascade decays to three pions. This results in increased complexity in defining a CP sensitive observable. Deep learning tools (through neural networks) have been employed to extract as much sensitivity as possible. This neural network approach has been shown to effectively separate scalar and pseudoscalar hypothesis with decays of $\tau$ to three pions. Assessing the effectiveness of this approach involves studies into detector resolution and $\tau$-decay modelling. Improvements to the approach are sought through the use of $E_{\rm T}^{\rm miss}$.

Development of the LHCb VELO Monitoring Software Platform

Acta Phys. Pol. B 48, 1061 (2017)

page 1061 •

abstract

One of the most important parts of the LHCb spectrometer is the VErtex LOcator (VELO), dedicated to the precise tracking close to the proton–proton interaction point. The quality of data produced by the VELO depends on the calibration process, which must be monitored to ensure its correctness. This work presents details on how the calibration monitoring is conducted and how it could be improved. It also includes information on monitoring software and data flow in the LHCb software framework.

Version corrected according to Erratum Acta Phys. Pol. B 49, 195 (2018)

Two-particle Correlations in $p$–Pb Collisions at the LHCb

Acta Phys. Pol. B 48, 1067 (2017)

page 1067 •

abstract

This paper describes the analysis of two-particle angular correlations in proton–lead collisions at $\sqrt {s_{NN}}=5$ TeV nucleon–nucleon center-of-mass energy performed by the LHCb experiment. Correlations in function of relative pseudorapidity $\Delta \eta$ and relative azimuthal angle $\Delta \phi$ are measured in different event activity classes and bins of particle transverse momentum. The analysis is done separately for the two beam configurations corresponding to the two proton beam directions. Long-range near-side correlations are observed in high-activity events, thus extending previous analyses of this effect to the forward region ($2.0 \lt \eta \lt 4.9$). The near-side effect becomes stronger with increasing event activity and seems to be more prominent in the lead–proton mode. However, when comparing both beam configurations for events with similar absolute activity, the results are compatible with each other.

Heavy Flavour Highlights from the LHCb

Acta Phys. Pol. B 48, 1073 (2017)

page 1073 •

abstract

This document presents an overview of the flavour anomalies observed by the LHCb experiment. All results are based on the dataset collected during the full LHC Run 1 by the LHCb Collaboration. Measurements of branching fractions of several $b \rightarrow s l l$ decays are presented together with the angular analysis of $B^0 \rightarrow K^* \mu ^+ \mu ^-$ decays and the lepton flavour universality tests $R(K)$ and $R(D^*)$. In addition, a direct search for a new light scalar particle in the $B^+ \rightarrow K^+ \chi$ decay, with $\chi \rightarrow \mu ^+ \mu ^-$, is presented.

$B$ Physics: Phenomenology and Sample Calculations

Acta Phys. Pol. B 48, 1083 (2017)

page 1083 •

abstract

Decays of the $B$ mesons provide us with information on fundamental couplings of the Standard Model, especially those responsible for CP violation. Rare loop-mediated decays are known as sensitive probes of new physics. At present, no deviations from the Standard Model predictions are observed in the radiative ($\bar B \to X_q \gamma$) and leptonic ($B_q^{(0)} \to \ell ^+ \ell ^-$) decays, which imposes constraints on some of the relevant Wilson coefficients. On the other hand, sizeable deviations show up in the rare semileptonic decays ($B \to K^{(*)} \ell ^+ \ell ^-$) and in the semitauonic decays ($B \to D^{(*)} \tau \nu$). Their statistical significance is strongly dependent on our estimation of the theoretical uncertainties.

High-energy Resummation of Higgs $p_{\mathrm {T}}$ Distribution

Acta Phys. Pol. B 48, 1105 (2017)

page 1105 •

abstract

We discuss the generalization of high-energy resummation to transverse momentum distributions to leading-logarithmic accuracy. We check our procedure by reproducing the high-energy limit of the Feynman diagram calculations up to NLO to the Higgs production in gluon–gluon fusion. Then, we estimate finite top mass corrections to the NLO Higgs $p_{\scriptscriptstyle {\mathrm {T}}}$ distribution.

full authors' list

S. Jadach, G. Nail, W. Płaczek, S. Sapeta, A. Siódmok, M. Skrzypek

KrkNLO in Herwig 7

Acta Phys. Pol. B 48, 1121 (2017)

page 1121 •

abstract

We validate and present new results from the first implementation of the KrkNLO method within the Herwig 7 event generator. In this work, we present numerical results for the Drell–Yan process, and Higgs-boson production via gluon fusion. The Drell–Yan process is used to validate this new implementation against the previous version in Sherpa, as well as to compare the recently introduced complete MC-scheme parton distribution functions to previous results. We present the first results of the KrkNLO method for Higgs production via gluon fusion at the LHC, and compare them to MC@NLO and POWHEG predictions from Herwig 7, as well as results from HNNLO and HqT.

Multi-Higgs Boson Production and Self-coupling Measurements at Hadron Colliders

Acta Phys. Pol. B 48, 1133 (2017)

page 1133 •

abstract

The Higgs boson is the first fundamental scalar to be discovered. A crucial task following this discovery is to directly measure its couplings to the Standard Model content. These include the self-couplings that can be probed via production of multiple Higgs bosons at hadron colliders. I will be discussing recent phenomenological advancements in this direction, focussing on Higgs boson pair and triple production at the Large Hadron Collider and a Future Circular hadron Collider (FCC).

Selected Measurements of Rare Decays at the LHCb

Acta Phys. Pol. B 48, 1143 (2017)

page 1143 •

abstract

The LHCb spectrometer is specifically designed to study heavy-flavour physics. These proceedings present a selection of rare decays analyses performed with 1 fb$^{-1}$ and 2 fb$^{-1}$ of proton–proton collision data collected at the center-of-mass energies of 7 and 8 TeV, respectively. Rare decays are highly suppressed (or forbidden) in the Standard Model, thus could provide indirect evidence of New Physics. Results of the angular analyses of the $B^0 \to K^{* 0}\mu ^+\mu ^-$, $B^0 \to K^{* 0}e^+e^-$, ${\mit \Lambda }^0_b \to {\mit \Lambda }\mu ^+\mu ^-$, and $B^0_s \to \phi \mu ^+\mu ^-$ decays, along with branching fraction measurements for the latter two channels, are summarized. In addition, a test of lepton flavour universality in $B^+\to K^+\ell \ell$ decays and searches for the lepton flavour violating decays are presented.

Searches for the Standard Model Higgs Boson Decay to $\tau$ Lepton Pairs at the CMS Experiment

Acta Phys. Pol. B 48, 1151 (2017)

page 1151 •

abstract

We present results of searches for the Standard Model Higgs boson decaying to tau lepton pairs at the CMS experiment with data collected during the LHC Run 1. We also present some insight into the analysis with Run 2 data. CP sensitive variables are described and an experimental method of probing CP of the Higgs boson is presented.

Production Measurements at the LHCb

Acta Phys. Pol. B 48, 1157 (2017)

page 1157 •

abstract

The LHCb detector, with its excellent momentum resolution and flexible trigger strategy, is ideally suited for measuring heavy-quark and quarkonia production properties. In addition, the new system of forward shower counters installed upstream and downstream has begun to be used, therefore the experiment is being suited to measure central exclusive production. The LHCb measurements of inclusive and differential cross sections of the production of $J/\psi$ resonance and $J/\psi$ pairs, as well as bottom quarks and $Z^0$ boson, based on Run 2 datasets are summarized. Finally, results on the prompt production of open charm hadrons and the exclusive production of charmonium are discussed.

Version corrected according to Erratum Acta Phys. Pol. B 49, 197 (2018)

Colour Reconnections in Quark and Gluon Jets in Herwig 7

Acta Phys. Pol. B 48, 1167 (2017)

page 1167 •

abstract

Major event generators deviate significantly in their description of quark and gluon initiated jets. The modelling of these is particularly sensitive to the colour reconnection model used in the cluster hadronization model in the event generator Herwig. However, up to now, observables sensitive to the light flavour of jets have not been widely used in the construction and tuning of event generators. The scheme used in Herwig and changes within it are investigated using observables in $e^+e^-$ and $pp$ collisions, which are expected to discriminate quark and gluon jets.

Four-jet Production with High-energy Factorization Plus Parton Showers

Acta Phys. Pol. B 48, 1175 (2017)

page 1175 •

abstract

We report on the preliminary results of the ongoing update of our study of 4-jet production at the LHC in High-energy Factorization (HEF), which is being supplemented by parton showers. We focus on a specific angular variable introduced in two papers by the CMS Collaboration on 4-jet production with and without two $b$-tagged jets. The variable is, by construction, sensitive to contributions from Multi Parton Interactions (MPIs), specifically hard Double Parton Scattering (DPS). We preliminarily find that, adding parton showers to the single parton scattering channel, the evidence for the need for MPIs is compatible with the one reported by the CMS Collaboration after a comparison of the data with simulations based on collinear Monte Carlo event generators.

Colored Particle Production in New Physics at NLO QCD and Its Matching to Parton Showers

Acta Phys. Pol. B 48, 1183 (2017)

page 1183 •

abstract

In this paper, I show the automated Monte Carlo simulations at next-to-leading order in QCD as well as that its matching to parton showers are already feasible within the framework of MadGraph5_aMC@NLO. I briefly overview the recent activities and take the colored particle production at the LHC as an example. The tools and the models are ready for using by both phenomenologists and experimentalists.

Higher Order Corrections in the CoLoRFulNNLO Framework

Acta Phys. Pol. B 48, 1195 (2017)

page 1195 •

abstract

We discuss the CoLorFulNNLO method for computing higher order radiative corrections to jet cross sections in perturbative QCD. We apply our method to the calculation of event shapes and jet rates in three-jet production in electron–positron annihilation. We validate our code by comparing our predictions to previous results in the literature and present the jet cone energy fraction distribution at NNLO accuracy. We also present preliminary NNLO results for the three-jet rate using the Durham jet clustering algorithm matched to resummed predictions at NLL accuracy, and a comparison to LEP data.

Some New Aspects of Quarkonia Production at the LHC

Acta Phys. Pol. B 48, 1207 (2017)

page 1207 •

abstract

We discuss some different new aspects of $J/\psi$ meson production in exclusive, semiexclusive and inclusive processes. We finish with a short discussion of double $J/\psi$ production. We point out some new results obtained recently by our group and discuss some open issues.

Jet Mass Fluctuations and Fragmentation Functions

Acta Phys. Pol. B 48, 1225 (2017)

page 1225 •

abstract

The effect of jet mass fluctuations on the fragmentation process is examined in the framework of a statistical hadronisation model. In this model, the fragmentation scale $Q^2$ is taken to be the virtuality of the leading parton, and jet mass fluctuations are accounted for through this quantity. The scale evolution of the model is treated in the $\phi ^3$ theory with leading-order splitting function and one-loop coupling.

Ultra-peripheral $J/\psi$ Production in PbPb Collisions in CMS

Acta Phys. Pol. B 48, 1231 (2017)

page 1231 •

abstract

I briefly introduce the Ultra-Peripheral Collisions (UPCs) and explain what is the benefit of studying these events. I also show the current status of an ongoing analysis, which concerns the UPC $J/\psi$ production in PbPb 2015 data from the CMS experiment at CERN. This analysis forms the basis of my Ph.D. Thesis and its results have not been yet approved by the CMS Collaboration.

Highlights from CMS

Acta Phys. Pol. B 48, 1237 (2017)

page 1237 •

abstract

We report on highlights for recent physics results from the CMS experiment. All results are based on proton–proton collision data at $\sqrt {s}=8$ or 13 TeV collected by the CMS detector. This report contains various interesting topics and their latest results at the CMS: Standard Model (SM) physics including Quantum Chromodynamics (QCD), Electroweak (EWK), and top and bottom quarks, Higgs physics, and beyond SM (BSM) searches such as Supersymmetry (SUSY) and non-SUSY exotic searches.

TAUOLA — Hadronic Currents, Systematical Errors and Fits

Acta Phys. Pol. B 48, 1253 (2017)

page 1253 •

abstract

TAUOLA — Monte Carlo event generator for $\tau$-lepton decays, has recently undergone some updates. Summary on those recent developments and plans for future will be discussed. The main point of recent updates is initialization mirroring the one used by the BaBar Collaboration. Apart from that, tools to introduce modeling of chosen decays were introduced. Future plans include preparation for user framework of fitting theoretical models to experimental data. It is planned to be divided into two steps. First, environment allowing the fit of invariant masses of different combination of outgoing particles. This type of fits is most commonly used. Secondly, this fitting framework will be enriched by tools for fitting angular distributions. Such a tool should help to explore medium-energy QCD (0.5–2.0 GeV). In this energy region, the phenomenological description of processes is far less precise than experimental measurements.

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