The 23rd meeting of the MCnet network is also the ninth meeting of the MCnetITN3 consortium, funded by the European Union’s Horizon 2020 research and innovation programme under the Marie Skłodowska-Curie grant agreement No 722104. Hosted by CERN and The University of Manchester this meeting will be held in person at Manchester.
Participants who are cannot attend in person will be able to join remotely. When you register please indicate if you will attend in person or join remotely.
Zoom link: https://zoom.us/j/96863365397
Meeting ID: 968 6336 5397
Passcode: 546028
Find your local number: https://zoom.us/u/acmGTwXrDz
In this talk I will give a brief introduction about myself as a new PhD student starting to work with Monte Carlo event generators, more specifically, SHERPA. I will also present the main results obtained during my masters' when I studied the K/K ratio in heavy ion collisions. The goal of this project was to understand the supression of this ratio during the hadron gas phase that the collision system undergoes after the hadronization of the quark gluon plasma. Given that the lifetime of the K meson is shorter than that of the hadron gas itself, it's expected that the daughter particles of the K decay will rescatter during this phase and, as a result, the observed K/K ratio will be supressed when compared with predictions by statistical hadronization models. To take into account these hadronic interactions, we solve a system of differential equations for the abundances of K and K mesons and compute the value of the K/K ratio at the moment of thermal freeze-out, i.e., when the hadronic interactions cease. We explored how this solution was affected by different factors: the temperature evolution of the system, the kinetic freeze-out temperature and the interaction mechanisms for the K and K mesons with the constituents of the gas. This analysis showed that the experimental data observed for the K/K ratio in different collision systems can be described using a Bjorken-like temperature evolution and considering that the thermal freeze-out temperature decreases with the size of the post-collision system. We also showed that the most relevant interaction mechanisms in the hadron gas are $K^* \rightarrow{} K \pi$ and $K \pi \rightarrow{} K^*$.
Several important processes and analyses at the LHC are sensitive to higher-order perturbative corrections beyond what can currently be calculated at fixed order. One important class of large logarithmic corrections are so-called high-energy logarithms which appear when the centre-of-mass energy of a QCD collision is much larger than the transverse momenta of the observed jets.
In this talk I will describe the High Energy Jets (HEJ) framework, which includes the dominant high-energy logarithms to provide all-order predictions for several relevant LHC processes. I will summarise the results of a recent study of W boson production in association with at least two jets (arXiv:2012.10310), where we introduced a class of next-to-leading logarithmic improvements to the HEJ description of this process, and we performed the first bin-by-bin matching of HEJ to NLO accuracy.
If dark mesons exist, their evolution and hadronization procedure are currently little constrained. They could decay promptly and result in a very SM QCD like jet structure, even though the original decaying particles are dark sector ones; they could behave as semi-visible jets; or they could behave as completely detector-stable hadrons, in which case the final state is just the missing transverse momentum. Apart from the last case, which is more like a conventional BSM MET signature, the modelling of these scenarios is somewhat an unexplored area, other than the range of phenomenological predictions as implemented in Pythia8's HV module. In this talk I will discuss the prospect of using jet substructure methods for designing observable/s to distinguish between dark jets, semi-visible jets and light q/g jets, by comparing different observables in a IRC-safe linear basis, with some preliminary results, as well as the proposed idea of having a Herwig hidden valley dark shower and hadronisation module. Both these topics are part of my recent MCnet short-term studentship.
I will review recent efforts to extend Sherpa to include photon PDFs in Sherpa and to describe photoproduction events.
Review of the most recent changes to the LHAPDF PDF interpolator.
Status report on Sherpa summing up developments in the closing MCnet period
Status report on developments in Pythia8 in the closing MCnet-funded period.
Status report on Herwig 7
Summary of the research done in Pythia8/Anagntyr as an MCnetITN3 PhD student.
The first project was to develop a string "shoving" model to describe collective effects in heavy-ion collisions in terms of string interactions within the Lund model. This is done by constructing the Lorentz transformation to a symmetric frame where two string pieces are in parallel planes to calculate the resulting pairwise force due to the space-time overlap. Considering all such pairs of string pieces in a collision, the resulting total momentum change on a string piece is calculated. There is ongoing work to implement this along with the rope hadronization model in PYTHIA8.
The model is now further expanded using rope hadronization in heavy-ion collisions. Analysis involving the effects of string interactions on jets, known as jet quenching and the production yields of different hadron species in leading jets is also to be discussed.
Summary of my PhD thesis.
In the hypothesis that the scale of new physics is considerably higher than the energies probed at colliders, we can parametrise modified interactions induced by BSM effects among SM particles in a model-independent framework, the Standard Model Effective Field Theory (SMEFT).
In the thesis, several phenomenological aspects of the SMEFT are discussed, both at present and future colliders.
A characteristic feature of modified interactions is that they can induce unitarity violating effects which can be exploited to gain sensitivity. In this direction, a thorough study of the top quark electroweak sector will be presented, focusing on $2\to2$ scatterings and their embeddings in physical processes at colliders. This analysis allows us to identify several final states that have a good potential to explore the SMEFT parameter space and that could be particularly relevant in a global analysis.
One of the key features of the SMEFT is indeed that deviations from the SM interactions are correlated and global interpretations are therefore of fundamental importance. A combined interpretation of the Higgs, top and diboson data from the LHC is here presented and the interplay between the various datasets discussed.
Finally, the physics potential of a futuristic muon collider will be analysed, focusing in particular on the prospects to determine the Higgs self-interactions, a task that is arduous even in proposed $100$ TeV proton colliders.
Matching of logarithms of high-energy and of the parton shower have previously been reported for the (high energy) leading logarithmic component of the cross section, and only up to the first emission from PYTHIA.
We discuss a method for both extending this matching both to all orders, and to include the non-resummable component of the cross section through standard CKKW-L merging.
First results are presented from a flexible implementation using HEJ2 and PYTHIA, which also allows for matching of the recently calculated leading-logarithmic resummation of the first sub-leading processes.
In this talk I will present my work implementing QED real corrections in the Sherpa event generator. Using the Catani-Seymour dipole formalism, a kT-ordered QED parton shower was constructed. The correct radiation pattern was obtained by applying negative weights to same-charge dipoles using the existing framework for applying analytic weights in the veto algorithm.
I will also present a supplement to the YFS resummation for Z decay to leptons which allows photons to split into fermion-antifermion pairs. This is motivated by the experimental practice of correcting to Born leptons informed by Monte Carlo simulations. Photon splittings appear at NNLO but are logarithmically enhanced with the fermion mass; this work quantifies their contribution.
Status report on Rivet summing up developments in the closing MCnet period.
Status report on Contur summing up developments in the closing MCnet period
Summary of the research done as an MCnetITN3 PhD student.
Di-boson production processes play an important role in many Standard Model studies, including Higgs-boson and electroweak precision measurements. They also form an important background in searches for phenomena beyond the Standard Model. In this talk I will present a recent study on the inclusion of electroweak corrections to $pp→e^+e^-\mu^+\mu^-$ and $pp→e^+e^-\mu^+\mu^-j$, both at exact NLO and using two approximations: the EW virtual and EW Sudakov approach. We also consider for the first time the all-order NLL Sudakov corrections to the fixed-order prediction. Finally, I am going to present prediction for $pp→e^+e^-\mu^+\mu^-$+jets production based on merged NLO QCD matrix-element plus parton-shower simulations in the framework of the Sherpa event generator including electroweak corrections through the aforementioned approximations.
In this talk, which will follow a somewhat unconventional format, I will share with you a few things I learned during my PhD that I found particularly interesting. The specific topics I will touch on are hadronic rescattering, exotic hadrons and cosmic rays.
In this talk we introduce the still-developing color_ordering branch of MadGraph5_amc@NLO. This branch uses Berends-Giele recursions to calculate the matrix element, leading to more compact kinematics calculations. Additionally, this branch allows one to calculate matrix elements to a given order in the 1/Nc colour expansion in the trace basis. In this talk, we give an overview of the status of the branch, describe the physics of the colour expansion, show the results of this approximation, and show some speed comparisons with standard MadGraph.
For the MCnet shortterm studentship program, my task was to construct the interface that connects MadGraph to Rivet and in the end, Contur to do reinterpretation studies. The interface construction was successfully done, with actual working examples (physics results). The talk will be about latest updates to MadGraph interfaced to Rivet/Contur and reinterpretation results on several heavy neutrino mass models with Contur.
Network Dinner
I will present Sherpa's ongoing development for future lepton colliders.
Summary of the work done during my PhD studies in Lund.
Status report on HEJ summing up developments in the closing MCnet period.
Quarkonia production has been a long-standing puzzle in particle physics. The polarisation measurement of $J/\psi$ is expected to have significant transverse polarisation at large $p_{T}$, but has been experimentally observed to be consistent with zero. Hard production of onia processes using NRQCD formalism are available in the Pythia8 framework. However, these processes alone cannot fully describe the data; LHCb and CMS have shown with normalised cross section measurements of $z$ = $p_{T}(J/\psi)/p_{T}(jet)$ that $J/\psi$'s are produced softer than expected. Hence the need to incorporate onia production within the parton shower. A status report for incorporating quarkonia showers into Pythia8 will be presented.
After the discovery of Higgs boson by CMS and ATLAS experiment in 2012 the current mandate of the LHC is to search for the Higgs Boson self coupling along, which is yet to be measured. CMS and ATLAS are performing the search in different channels of non -resonant Higgs boson production using full Run-2 data taken by LHC. In this context one of the most clear channels is di-Higgs to bb-gamma-gamma final state due to less background and better calorimetric resolution. But it's difficult to estimate the di photon background spectrum along with some jets in Monte Carlo. My talk will cover the basic strategy of di Higgs to bb-gamma-gamma searches in CMS and recent work on the di photon background modelling in Herwig interface under MC-Net project.
After the discovery of the Higgs boson at 2012, there is no direct evidence for new physics. It is thus a good time to explore a new phase space. We perform a search for new physics inside a jet using non-isolated leptons related with the muon g-2 and LHCb's lepton universality violation results. There is no proper shower generator to generate the signal sample for this search, we implement BSM parton showers in Herwig 7. This presentation informs a preliminary result of a non-isolated dimuon production using the CMS dataset and BSM parton radiations.