Condensed Krypton Source and inter-spectrometer Penning trap at the KATRIN experiment @ Aula 500
Giu 26@3:00 pm–4:00 pm

M. Fedkevych, University of Münster, the KATRIN collaboration

The KArlsruhe TRItium Neutrino experiment (KATRIN) is a direct low-background measurement of the neutrino
mass from the kinematics of tritium -decay with an intended sensitivity of 0.2 eV=c2 (90 % C.L.). It uses
a tandem of two electrostatic spectrometers of MAC-E filter type, called pre- and main spectrometers, to analyze
energies of -electrons generated in WGTS (windowless gaseous tritium source). To achieve the sensitivity
goal, background minimization, as well as accurate energy calibration, monitoring and precise determination of
transmission function of the main spectrometer are required.
After an introduction of the current status of the KATRIN experiment I will present two topics of my own
work in more details.
In the first part of my talk, I will report about elimination of one of the important background sources, the
inter-spectrometer Penning trap. The trap is created by the negative retarding potentials of the spectrometers
combined with the magnetic field produced by a common superconducting magnet. Even at the ultra-high
vacuum conditions of KATRIN electrons may get trapped in this Penning trap creating additional background.
They could even produce discharges which may interrupt the data-taking process and damage parts of the
spectrometer and detector section of KATRIN. As a countermeasure, electron catchers were implemented in the
beamline part between the two spectrometers to remove trapped electrons. The system was tested at various
pressure conditions and showed its effectiveness for suppression of the Penning trap effects. In this talk I will
explain details of the measurements and experimental results.
In the second part, I will present the Condensed Krypton calibration Source (CKrS) developed in Münster,
one of the several calibration sources used in KATRIN, which utilizes the nearly monoenergetic conversion
electrons from cryo-adsorbed 83mKr. The CKrS can be used for frequent measurements due to its relative
simplicity; moreover, as a point-like source it allows for per-pixel calibration of KATRIN focal plane detector
(FPD), with comparatively high rates. The cleanliness of the substrate together with quality of frozen radioactive
films being crucial for the stability and reproducibility of the conversion electron spectrum are monitored by
means of laser ellipsometry. The CKrS was installed in 2017 at the KATRIN cryogenic pumping section (CPS).
Here, I will present the characterization measurements with the CKrS at different vacuum conditions (before
and after bake-out of the system) and will discuss analysis and interpretation of the stability, spectroscopy and
ellipsometry data with different krypton films.

Search for light dark matter and new physics with NA64: new results and prospects @ Aula 500
Set 3@3:00 pm–4:00 pm

Dr. Sergei Gninenko (CERN)
What makes up most of the Universe mass? – is the central question of modern science. A possible answer to this question is: It is thermal dark matter (DM) with mass below the electroweak scale, m_DM << 100 GeV. The NA64 experiment is a fixed-target experiment designed to search for light dark matter and sub-GeV New Physics in missing energy events from high-energy electron, muon and hadron interactions in an active target at the CERN SPS. In this talk, I will discuss the motivation for light dark matter, describe in details the NA64 concept and performance. I will also present the latest NA64 results and discuss projections of the expected sensitivities
from running after LHC long shutdown 2 and beyond.

Jets, TMDs and resummation @ Aula 501
Ott 9@2:30 pm–3:30 pm

Seminario di Fenomenologia
Prof. Wouter Waalewijn (University of Amsterdam)
I will discuss (i) my recent calculation of the jet shape, which describes the angular distribution of energy in a jet, comparing to data from the Large Hadron Collider (ii) a new method I proposed to extract the transverse momentum distribution of quarks and gluons in the proton, using jets in semi-inclusive deep-inelastic scattering (iii) the resummation of multiple logarithms, considering the simultaneous measurement of beam thrust and the transverse momentum of the Z boson in the Drell-Yan process as a concrete example.

The quantum effective action, external sources and a new exact RG equation @ Aula 603
Ott 16@2:30 pm–3:30 pm

seminario di fisica teorica
Peter Millington (University of Nottingham)

The effective action is a powerful tool for studying the non-perturbative behaviour of quantum field theories. In this talk, we will revisit the derivation of the so-called two-particle-irreducible effective action, paying particular attention to the role of the sources that appear in its definition. Working in the context of zero-dimensional quantum field theory, we will be able to accompany this derivation with a graphical and pedagogical exposition of the behaviour of the effective action, and its various ingredients. With this intuitive understanding, we will then be able to show that we have much greater control over the effective action than has perhaps previously been realised, and we will be able to use the sources to map between different realisations of the effective action and to preserve symmetry properties in its truncations. Finally, by associating the two-point source of the effective action with the regulator of the renormalisation group evolution, we will arrive at an exact flow equation that differs fundamentally from the well-known Wetterich-Morris-Ellwanger equation. We will conclude by commenting on the potential implications of our results and highlighting possible future directions.

Phases of 3d gauge theories @ Aula 603
Ott 23@2:30 pm–3:30 pm

Seminario di Fisica Teorica
Phases of 3d gauge theories (Riccardo Argurio Univ. Bruxelles)
We will consider gauge theories in 3d with fermionic matter and explore their low-energy phases as some parameters are varied, such as masses for the matter fields and the Chern-Simons level of the gauge group. We will discuss when the transitions between the various phases are first or second order, or go beyond the Landau-Ginzburg paradigm. We will
employ a variety of approaches: consistency conditions based on symmetries, a dual picture involving bosonization, large N limits and holography.

The Holographic QCD Axion @ Aula 603
Ott 30@2:30 pm–3:30 pm

Seminario di Fisica Teorica
Dr. Francesco Bigazzi (INFN Firenze)
A holographic model of QCD axion is presented. It describes a
composite axion in the KSVZ class. Having a gravity dual, based on the
Witten-Sakai-Sugimoto model, it is calculable in the strongly coupled
regime and its UV completion is under control. Its basic properties are
derived, including the low energy Lagrangian, from which the axion
couplings to nucleons can be derived. Basic features in the deconfined
phase are studied as well. In particular, the temperature dependence of
the axion mass is extracted from the topological susceptibility.

Double parton scattering in jet production processes at the LHC @ Aula 501
Nov 6@2:00 pm–3:00 pm

Seminario di Fenomenologia
Dr. Oleh Fedkevych (Università di Genova & INFN Genova)

In spite of the recent progress in both theoretical and experimental studies of QCD, many aspects of multiple parton interactions (MPI) still require a detail investigation. In particular, double parton scattering (DPS) processes can play a dominant role for some specific kinematic regions of multi-jet production, especially in proton-nucleus (pA) collisions where the total DPS cross section is approximately ∌3A times bigger than the corresponding total DPS cross section in proton-proton (pp) collisions.
In this talk, I will provide a general overview of the state-of-the-art of the “first principles” and Monte Carlo description of DPS (MPI) processes
with a special emphasize on the four-jet DPS production in pp and pA collisions and
different approaches to model double parton distribution functions.

Higgsstrahlung at NNLL’+NNLO matched to parton shower in GENEVA @ Aula 501
Nov 20@2:30 pm–3:30 pm

Seminario di Fenomenologia Dr. Matthew Lim (Milano Bicocca)

The GENEVA framework allows fully differential, fixed order calculations at NNLO to be matched to parton shower programs while also achieving NNLL’ accuracy in the distribution of a jet resolution variable. To date, it has been successfully applied to jet production in e+e- collisions and also the Drell-Yan process at the LHC. In this talk I will discuss the methodology and present its application to VH production at the LHC, which has recently been measured for the first time. I will present comparisons with dedicated fixed order programs as well as showered distributions and discuss future avenues to be explored.

Non-Hermitian Holography @ Aula 603
Nov 27@2:30 pm–3:30 pm

Seminario di Fisica Teorica Daniel Arean Fraga (Universidad Autonoma de Madrid)

In this talk I will review the topic of non-Hermitian PT-Symmetric quantum theories and present a proposal for a gravity dual of a non-Hermitian QFT.

Multi-differential resummation for the LHC @ Aula 501
Dic 4@2:00 pm–3:00 pm

Seminario di Fenomenologia Dr. Johannes Michel (DESY, Hamburg)

Differential measurements at the LHC involve many physical scales set by the hard production process and soft or collinear QCD dynamics. When these scales are widely separated, the perturbative series becomes dominated by logarithms of their ratios. Precise (or sometimes even just physical) theory predictions require the resummation of these large logarithms to all orders. In this talk I will provide an overview of the challenges encountered when extending the resummation program to multi-differential observables, and of the new insights one gains into the infrared structure of QCD. I will first briefly review single-differential resummation methods, focusing on TMD factorization and the inclusive transverse momentum spectrum of electroweak gauge bosons at the LHC as a key application. I will then discuss how additional measurements on the decay products of the Z or W affect the resummation (e.g. fiducial acceptance cuts, the lepton pT, or the phi* observable), and present ongoing work to incorporate these effects at the level of precision required for determinations of key electroweak parameters such as the W mass at the LHC.
In the second half of the talk I will show how treating a very basic QCD quantity (the Drell-Yan rapidity spectrum) in a multi-differential spirit leads to surprising new insight into its all-order perturbative structure, and generalizes the classic QCD result of threshold (or soft-gluon) resummation.