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H. Jung

Publications and source records attributed to H. Jung.

At least 37 records · Page 2Linked to original sources
arXiv2021

TMDs from Monte Carlo event generators

Transverse Momentum Dependent (TMD) parton distributions are a very powerful concept for the description of low and high transverse momentum effects in high energy collisions. The Parton Branching (PB) method provides TMD distributions which can be used in parton shower simulations, as already implemented in \cascade\ Monte Carlo event generator. This report gives a description of the work done during the DESY summer student program 2021, young scientists from very different time zones connecting from remote twice a day for 8 weeks, to develop a method, PS2TMD, that allows to determine effective TMDs from the standard Monte Carlo parton showers. This method is validated and implemented to successfully reconstruct the PB-TMDs with different configuration settings. We also discuss kinematic shifts in longitudinal momentum distributions from initial state showering and point out the sizable influence of different reconstruction definitions on both collinear and transverse momentum PDFs. %the nonperturbative dependence on longitudinal and transverse degrees of freedom is fully coupled.

hep-ph↗
arXiv2021

Rivet, RivetHZTool and HERA -- A validation effort for coding HERA measurements for Rivet

During the DESY summer student program 2021, young scientists from more than 13 different countries worked together, connecting from remote, to provide computer codes within the Rivet framework for 19 HERA measurements. Most of these measurements were originally available within the HZTool package, but no longer accessible for modern analysis packages such as Rivet. The temporary RivetHZTool interface was used to validate most of the new Rivet plugins.

hep-ph↗
arXiv2021

Azimuthal correlations of high transverse momentum jets at next-to-leading order in the parton branching method

The azimuthal correlation, $Δϕ_{12}$, of high transverse momentum jets in pp collisions at $\sqrt{s}=13$ TeV is studied by applying PB-TMD distributions to NLO calculations via MCatNLO together with the PB-TMD parton shower. A very good description of the cross section as a function of $Δϕ_{12}$ is observed. In the back-to-back region of $Δϕ_{12} \to π$, a very good agreement is observed with the PB-TMD Set 2 distributions while significant deviations are obtained with the PB-TMD Set 1 distributions. Set 1 uses the evolution scale while Set 2 uses transverse momentum as an argument in $α_s$, and the above observation therefore confirms the importance of an appropriate soft-gluon coupling in angular ordered parton evolution. The total uncertainties of the predictions are dominated by the scale uncertainties of the matrix element, while the uncertainties coming from the PB-TMDs and the corresponding PB-TMD shower are very small. The $Δϕ_{12}$ measurements are also compared with predictions using MCatNLO together PYTHIA8, illustrating the importance of details of the parton shower evolution.

hep-ph↗
arXiv2021

Impact of jet-production data on the next-to-next-to-leading-order determination of HERAPDF2.0 parton distributions

The HERAPDF2.0 ensemble of parton distribution functions (PDFs) was introduced in 2015. The final stage is presented, a next-to-next-to-leading-order (NNLO) analysis of the HERA data on inclusive deep inelastic $ep$ scattering together with jet data as published by the H1 and ZEUS collaborations. A perturbative QCD fit, simultaneously of $α_s(M_Z^2)$ and and the PDFs, was performed with the result $α_s(M_Z^2) = 0.1156 \pm 0.0011~{\rm (exp)}~ ^{+0.0001}_{-0.0002}~ {\rm (model}$ ${\rm +~parameterisation)}~ \pm 0.0029~{\rm (scale)}$. The PDF sets of HERAPDF2.0Jets NNLO were determined with separate fits using two fixed values of $α_s(M_Z^2)$, $α_s(M_Z^2)=0.1155$ and $0.118$, since the latter value was already chosen for the published HERAPDF2.0 NNLO analysis based on HERA inclusive DIS data only. The different sets of PDFs are presented, evaluated and compared. The consistency of the PDFs determined with and without the jet data demonstrates the consistency of HERA inclusive and jet-production cross-section data. The inclusion of the jet data reduced the uncertainty on the gluon PDF. Predictions based on the PDFs of HERAPDF2.0Jets NNLO give an excellent description of the jet-production data used as input.

hep-ex↗
arXiv2021

Aspects of BFKL physics at HERA

Aspects of small x physics at HERA are discussed in honor of the work of Lev Lipatov, who influenced and motivated a whole generation of physicists to investigate this new region of phase space. The introduction of transverse momentum dependent parton densities is one of the essential aspects of small x and BFKL physics, and its extension to all flavors with application to various processes marks a new milestone.

hep-ph↗
arXiv2021

Discriminating the heavy jet production mechanisms in associated $Z$ + heavy flavor events at the LHC

We reconsider the associated $Z$ boson and charm or beauty jet production at the LHC with paying special attention to the formation dynamics of heavy jets. Two different approaches are studied: first one, where heavy quarks are produced in the hard scattering subprocesses, implemented in the Monte-Carlo generator PEGASUS, and another scenario, where the hard scattering is calculated at NLO with MadGraph5_aMC@NLO and TMD parton shower is included (implemented in the Monte-Carlo generator CASCADE3). We compare the predictions obtained in both schemes with latest experimental data for associated $Z + b$ production cross sections and the relative production rate $σ(Z + c)/σ(Z + b)$ collected by the ATLAS and CMS Collaborations at $\sqrt s = 13$~TeV. We introduce two kinematic observables (denoted as $z_b$ and $p_T^{\rm rel}$) which can be used to discriminate the heavy jet production mechanisms. Using these variables we trace the shape of the simulated $b$-jet events and recommend that these observables be taken into consideration in the forthcoming experimental analyses.

hep-ph↗
arXiv2021

TMDlib2 and TMDplotter: a platform for 3D hadron structure studies

A common library, TMDlib2, for Transverse-Momentum-Dependent distributions (TMDs) and unintegrated parton distributions (uPDFs) is described, which allows for easy access of commonly used TMDs and uPDFs, providing a three-dimensional (3D) picture of the partonic structure of hadrons. The tool TMDplotter allows for web-based plotting of distributions implemented in TMDlib2, together with collinear pdfs as available in LHAPDF.

hep-ph↗
arXiv2021

CASCADE3 A Monte Carlo event generator based on TMDs

The CASCADE3 Monte Carlo event generator based on Transverse Momentum Dependent (TMD) parton densities is described. Hard processes which are generated in collinear factorization with LO multileg or NLO parton level generators are extended by adding transverse momenta to the initial partons according to TMD densities and applying dedicated TMD parton showers and hadronization. Processes with off-shell kinematics within $k_t$-factorization, either internally implemented or from external packages via LHE files, can be processed for parton showering and hadronization. The initial state parton shower is tied to the TMD parton distribution, with all parameters fixed by the TMD distribution.

hep-ph↗
arXiv2021

TMD parton densities and corresponding parton showers: the advantage of four- and five-flavour schemes

The calculations of $Z + b{\bar b}$ tagged jet production performed in the four- and five-flavour schemes allow for detailed comparison of the heavy flavour structure of collinear and transverse momentum dependent (TMD) parton distributions as well as for detailed investigations of heavy quarks radiated during the initial state parton shower cascade. We have determined the first set of collinear and TMD parton distributions in the four-flavour scheme with NLO DGLAP splitting functions within the Parton-Branching (PB) approach. The four- and five-flavour PB-TMD distributions were used to calculate $Z + b{\bar b}$ tagged jet production at LHC energies and very good agreement with measurements obtained at $\sqrt{s} = 8, 13 $ TeV by the CMS and ATLAS collaborations is observed. The different configurations of the hard process in the four- and five-flavour schemes allow for a detailed investigation of the performance of heavy flavor collinear and TMD parton distributions and the corresponding initial TMD parton shower, giving confidence in the evolution of the PB-TMD parton densities as well as in the PB-TMD parton shower.

hep-ph↗
arXiv2021

Determination of the strong coupling constant $α_s(M_Z)$ in next-to-next-to-leading order QCD using H1 jet cross section measurements

The strong coupling constant $α_s(M_Z)$ is determined from inclusive jet and dijet cross sections in neutral-current deep-inelastic $ep$ scattering (DIS) measured at HERA by the H1 collaboration using next-to-next-to-leading order (NNLO) QCD predictions. The dependence of the NNLO predictions and of the resulting value of $α_s(M_Z)$ at the $Z$-boson mass $m_Z$ are studied as a function of the choice of the renormalisation and factorisation scales. Using inclusive jet and dijet data together, the strong coupling constant is determined to be $α_s(M_Z)=0.1166\,(19)_{\rm exp}\,(24)_{\rm th}$. Complementary, $α_s(M_Z)$ is determined together with parton distribution functions of the proton (PDFs) from jet and inclusive DIS data measured by the H1 experiment. The value $α_s(M_Z)=0.1147\,(25)_{\rm tot}$ obtained is consistent with the determination from jet data alone. The impact of the jet data on the PDFs is studied. The running of the strong coupling is tested at different values of the renormalisation scale and the results are found to be in agreement with expectations.

hep-ex↗
arXiv2021

Photon TMD

We present a complete set of transverse momentum dependent and collinear parton densities including the photon over a wide phase space. The photon density appears when evolving parton distributions with QED corrections. The photons are produced by perturbative radiation using the Parton Branching method. The QCD partons are constrained by a fit to HERA data. The lepton pair production at high masses is described within the extracted TMD densities.

hep-ph↗
arXiv2021

Determination of collinear and TMD photon densities using the Parton Branching method

We present the first determination of transverse momentum dependent (TMD) photon densities with the Parton Branching method. The photon distribution is generated perturbatively without intrinsic photon component. The input parameters for quarks and gluons are determined from fits to precision measurements of deep inelastic scattering cross sections at HERA. The TMD densities are used to predict the mass and transverse momentum spectra of very high mass lepton pairs from both Drell-Yan production and Photon-Initiated lepton processes at the LHC.

hep-ph↗
arXiv2020

Energy Efficiency and Hover Time Optimization in UAV-based HetNets

In this paper, we investigate the downlink performance of a three-tier heterogeneous network (HetNet). The objective is to enhance the edge capacity of a macro cell by deploying unmanned aerial vehicles (UAVs) as flying base stations and small cells (SCs) for improving the capacity of indoor users in scenarios such as temporary hotspot regions or during disaster situations where the terrestrial network is either insufficient or out of service. UAVs are energy-constrained devices with a limited flight time, therefore, we formulate a two layer optimization scheme, where we first optimize the power consumption of each tier for enhancing the system energy efficiency (EE) under a minimum quality-of-service (QoS) requirement, which is followed by optimizing the average hover time of UAVs. We obtain the solution to these nonlinear constrained optimization problems by first utilizing the Lagrange multipliers method and then implementing a sub-gradient approach for obtaining convergence. The results show that through optimal power allocation, the system EE improves significantly in comparison to when maximum power is allocated to users (ground cellular users or connected vehicles). The hover time optimization results in increased flight time of UAVs thus providing service for longer durations.

eess.SP↗
arXiv2020

The transverse momentum spectrum of low mass Drell-Yan production at next-to-leading order in the parton branching method

It has been observed in the literature that measurements of low-mass Drell-Yan (DY) transverse momentum spectra at low center-of-mass energies $\sqrt{s}$ are not well described by perturbative QCD calculations in collinear factorization in the region where transverse momenta are comparable with the DY mass. We examine this issue from the standpoint of the Parton Branching (PB) method, combining next-to-leading-order (NLO) calculations of the hard process with the evolution of transverse momentum dependent (TMD) parton distributions. We compare our predictions with experimental measurements at low DY mass, and find very good agreement.In addition we use the low mass DY measurements at low $\sqrt{s}$ to determine the width $q_s$ of the intrinsic Gauss distribution of the PB-TMDs at low evolution scales. We find values close to what has earlier been used in applications of PB -TMDs to high-energy processes at the Large Hadron Collider (LHC) and HERA. We find that at low DY mass and low $\sqrt{s}$ even in the region of $p_t/m_{DY} \sim 1$ the contribution of multiple soft gluon emissions (included in the PB-TMDs) is essential to describe themeasurements, while at larger masses ($m_{DY} \sim m_{Z}$) and LHC energies the contribution from soft gluons in the region of $p_t/m_{DY}\sim 1$ is small.

hep-ph↗
arXiv2019

Z boson production in proton-lead collisions at the LHC accounting for transverse momenta of initial partons

We perform a calculation of inclusive $Z$ boson production in proton-lead collisions at the LHC taking into account the transverse momenta of the initial partons. We use the framework of $k_T$-factorization combining transverse momentum dependent parton distributions (TMDs) with off-shell matrix elements. In order to do it we need to construct appropriate TMDs for lead nuclei which is done using the parton branching method. Our computations are compared with data from CMS taken at $\sqrt{s}=5.02$ TeV. The results are in good agreement with the measurements especially the transverse momentum distribution of the $Z$ boson.

hep-ph↗
arXiv2019

Production of Z-bosons in the parton branching method

Transverse Momentum Dependent (TMD) parton distributions obtained from the Parton Branching (PB) method are combined with next-to-leading-order (NLO) calculations of Drell-Yan (DY) production. We apply the MCatNLO method for the hard process calculation and matching with the PB TMDs. We compute predictions for the transverse momentum, rapidity and $ϕ^*$ spectra of Z-bosons. We find that the theoretical uncertainties of the predictions are dominated by the renormalization and factorization scale dependence, while the impact of TMD uncertainties is moderate. The theoretical predictions agree well, within uncertainties, with measurements at the Large Hadron Collider (LHC). In particular, we study the region of lowest transverse momenta at the LHC, and comment on its sensitivity to nonperturbative TMD contributions.

hep-ph↗
arXiv2019

On relation between Parton Branching Approach and CCFM evolution

We consider the associated production of electroweak gauge bosons and charm or beauty quark jets at the LHC using the $k_T$-factorization framework. We apply the transverse momentum dependent (TMD) parton distributions in a proton obtained from the Parton Branching (PB) method as well as from the Catani-Ciafaloni-Fiorani-Marchesini (CCFM) evolution equation. For the PB approach, our prescription merges the standard leading order ${\cal O}(αα_s)$ $k_T$-factorization calculations with several tree-level next-to-leading order ${\cal O}(αα_s^2)$ off-shell production amplitudes. For the CCFM scenario, our consideration is based on the ${\cal O}(αα_s^2)$ off-shell gluon-gluon fusion subprocess $g^* g^* \to Z/W + Q\bar Q$ and some subleading ${\cal O}(αα_s^2)$ subprocesses involving quark interactions, taken into account in conventional (collinear) QCD factorization. We find that the $W + c$ and $Z + b$ cross sections, calculated within the PB and CCFM-based schemes with the proper choice of leading and next-to-leading subprocesses, are in good agreement with each other, thus establishing a correspondence between these two scenarios. A comparison with the latest LHC experimental data is given and the necessity for the proper off-shell treatment of the production amplitudes in determination of the parameters of the TMD parton density is demonstrated.

hep-ph↗