The LHC excess of four-lepton events interpreted as Higgs-boson signal : background from double Drell-Yan process?

We construct a simple model of the Double Drell–Yan Process (DDYP) for proton–proton collisions and investigate its possible contribution to the background for the Higgs-boson searches at the LHC. We demonstrate that under the assumption of the predominance of short range, O(0.1) fm, transverse-plane correlations of quark–antiquark pairs within the proton, this contribution becomes important and may even explain the observed excess of the four-lepton events at the LHC — the events interpreted as originating from the Higgs-boson decays: $H \rightarrow ZZ^{*} \rightarrow 4l$ and $H\rightarrow WW^{*} \rightarrow 2/2\nu$

Exponentiation in QED and quasi-stable charged particles

In this note we present a new exponentiation scheme of soft photon radiation from charged quasi-stable resonances. It generalizes the well established scheme of Yennie, Frautschi and Suura. While keeping the same functional form of an exponent, the new scheme is both exact in its soft limit and accounts properly for the kinematical shift in resonant propagators. We present the scheme on an example of two processes: a toy model of single W production in $e\nu$ scattering and the W pair production and decay in $e^{+}e^{-}$ annihilation. The latter process is of relevance for the planned FCCee collider where high precision of Monte Carlo simulations is a primary goal. The proposed scheme is a step in this directio

Numerical solution of the integral form of the resummed Balitsky-Kovchegov equation

The Balitsky–Kovchegov (BK) evolution equation in its resummed integral form is considered. We solve it numerically and compare to the unresummed BK equation formulated as an integral equation and to the solution obtained by the BKsolver package. Sensitivity of the solution to an introduced resolution parameter and initial conditions is investigated

The Gamma Factory path to high-luminosity LHC with isoscalar beams

There are two main ways to increase LHC luminosity without upgrading CERN injectors: (1) modification of beam-collision optics and (2) reduction of beam transverse emittance. The former is followed in the ongoing high-luminosity upgrade of the LHC (HL-LHC), while the latter, applicable only to ion beams, is described in this contribution. The reduction of the beam emittance can be achieved by employing a laser-cooling technique to bunches of partially stripped ions at the SPS flat-top energy. In the case the isoscalar calcium beams fulfilling the presentbeam-operation constrains, the transverse beam emittance can be reduced in this way by a factor of 5 during the 8 second long cooling phase. This would allow to reach the nucleon–nucleon luminosity L_NN = 4.2 x 10^34 s^(-1)cm^(-2), which is comparable to the levelled luminosity for the HL-LHC proton–proton collisions, but with reduced pile-up background. The calcium–calcium collisions have several advantages over the proton–proton collisions for the electroweak physics, such as precision measurements of the W-boson mass and sin^2_W, clean observation of the Higgs boson decay into bbar in its photoproduction channel or BSM phenomena. If this scheme is confirmed by the future Gamma Factory proof-of-principle experiment, it could be implemented at CERN with minor infrastructure investments. This contribution is based on Ref. [1

How QCD evolution kernels depend on the type of evolution variable

We show that by changing the upper phase space limit in calculation of an evolution kernel, one can change its functional form. This happens already at the NLO level, e.g. when the upper phase space limit is defined in terms of maximum of transverse momenta. The upper phase space limit of the evolution kernel corresponds to the evolution variable used in a Parton Shower, and this dependence means that the different kernels need to be used depending on the ordering of the Parton Shower

Overview of theoretical precision of the luminosity at future electron-positron colliders

For both the FCC-ee and the ILC, to exploit properly the respective precision physics program, the theoretical precision tag on the respective luminosity will need to be improved from the analogs of the 0.054%(0.061%) results at LEP at $M_{Z}$, where the former (latter) LEP result has (does not have) the pairs correction. At the FCC-ee at $M_{Z}$ one needs improvement to 0.01%, for example. We present an overview of the roads one may take to reach the required 0.01% precision tag at the FCC-ee and of what the corresponding precision expectations would be for the FCC-ee$_{350}$, ILC$_{500}$, ILC$_{1000}$ and CLIC$_{3000}$ setups

NLO corrections to hard process in QCD shower : proof of concept

The concept of new methodology of adding QCD NLO corrections in the initial state Monte Carlo parton shower (hard process part) is tested numerically using, as an example, the process of the heavy boson production at hadron–hadron colliders such as LHC. In spite of the use of a simplified model of the process, all presented numerical results prove convincingly that the basic concept of the new methodology works correctly in practice, that is, in the numerical environment of the Monte Carlo parton shower event generator. The differences with the other well established methods, like MC@NLO and POWHEG, are briefly discussed and future refinements of the implementation of the new method are also outlined

Medium induced QCD cascades : broadening and rescattering during branching

We study evolution equations describing jet propagation through quark-gluon plasma (QGP). In particular we investigate the contribution of momentum transfer during branching and find that such a contribution is sizeable. Furthermore, we study various approximations, such as the Gaussian approximation and the diffusive approximation to the jet-broadening term. We notice that in order to reproduce the BDIM equation (without the momentum transfer in the branching) the diffusive approximation requires a very large value of the jet-quenching parameter q

In-medium transverse momentum broadening effects on di-jet observables

Heavy ion collisions at high energies can be used as an interesting way to recreate and study the medium of the quark-gluon plasma (QGP). We particularly investigate the jets produced in hard binary collisions and their interactions with a tentative medium. These jets were obtained numerically from the Monte-Carlo simulations of hard collisions using the Katie-algorithm, where parton momenta within the colliding nucleons were describe by means of unintegrated parton distribution functions (uPDF). We evolved these jets within a medium that contains both, transverse kicks (yielding a broadening in momentum transvers to the jet-axis) as well as medium induced radiation within the Mincas-algorithm following the works. We produce qualitative results for the decorrelation of dijets. In particular, we study deviations from a transverse momentum broadening that follows a Gaussian distribution

In-medium transverse momentum broadening effects on di-jet observables

Heavy ion collisions at high energies can be used as an interesting way to recreate and study the medium of the quark-gluon plasma (QGP). We particularly investigate the jets produced in hard binary collisions and their interactions with a tentative medium. These jets were obtained numerically from the Monte-Carlo simulations of hard collisions using the KATIE-algorithm [1], where parton momenta within the colliding nucleons were describe by means of unintegrated parton distribution functions (uPDF). We evolved these jets within a medium that contains both, transverse kicks (yielding a broadening in momentum transvers to the jet-axis) as well as medium induced radiation within the MINCAS-algorithm [2] following the works of [3,4]. We produce qualitative results for the decorrelation of dijets. In particular, we study deviations from a transverse momentum broadening that follows a Gaussian distribution. [1] A. van Hameren, Comput.Phys.Commun. 224 (2018) 371-380 [2] K. Kutak, W. P{\l}aczek, R. Straka, Eur.Phys.J. C79 (2019) no.4, 317 [3] J.-P. Blaizot, F. Dominguez, E. Iancu, Y. Mehtar-Tani, JHEP 1301 (2013) 143 [4] J.-P. Blaizot, F. Dominguez, E. Iancu, Y. Mehtar-Tani, JHEP 1406 (2014) 07