Physics analysis

Hyperons serve as powerful probes for investigating various aspects of quantum chromodynamics (QCD). As part of the FAIR Phase-0 program, the HADES (High-Acceptance Di-Electron Spectrometer) at GSI collected high-statistics proton-proton data using a proton beam with a kinetic energy of 4.5 GeV. The beam energy enables the production of hyperons close to threshold, facilitating studies of hyperon-hyperon interactions and searches for intermediate resonances. Currently, the ΛΛ reaction is being analyzed to extract crucial information on hyperon interactions, which is expected to be essential to understand the interiors of neutron stars. Furthermore, the first-time measurements of the Dalitz decay of the Σ0 will provide insights into transition form factors and thereby the electromagnetic structure of the Σ0. The study of Ξ- production in proton-proton collisions is valuable to address the observed excess yields observed in Ar+KCl and p+Nb reactions at HADES. This talk will highlight the ongoing hyperon physics analyses at HADES within the FAIR Phase-0 program and present selected results.

PANDA Annual Report 2023

The abundant production of hyperons in antiproton-proton annihilations open new avenues in the investigations of strong interactions and fundamental symmetries. In recent years, the BESIII experiment has demonstrated the merits of studying spin polarised and correlated hyperon-antihyperon pairs with several pioneering measurements of hyperon structure and precise tests of CP conservation.
With a beam of stored antiprotons, the PANDA experiment can take hyperon physics to a new level, benefitting from the expected huge samples of hyperon-antihyperon pairs. In this talk, I will discuss the potential of hyperon physics with PANDA in particular but also with antiproton beams in general.

The hadron spectroscopy and structure are currently very active fields of research to study the non-perturbative regime of quantum chronodynamics. The first one studies the complex structure of excited hadrons by looking at their decay products, while the latter uses lepton scattering on nucleons. Both methods require reconstruction algorithms with great efficiency and good particle identification and background rejection rates. This work aims to provide these by either improving the existing methods or developing new ones.

The first part of this document presents a feasibility study of a predicted hybrid charmonium state for the $\mathrm{\overline{P}}$ANDA experiment. Lattice QCD calculations predict the ground state hybrid charmonium to be a spin exotic with quantum numbers of $J^{PC}=1^{-+}$ at a mass of around 4.3 GeV with a width to be around 20 MeV. A machine learning based data analysis scheme is proposed to further improve the signal efficiency and the background reduction, alongside with improvements of the analysis software (PandaRoot), that are vital for this study. These improvements include a reworked clustering algorithm for the electromagnetic calorimeter (EMC) and an optimized monte carlo matching for neutral particles.

The second part of this document is about studying the proton structure. A multidimensional study of the structure function ratio $\mathrm{F_{LU}^{sin(\phi)}/F_{UU}}$ has been performed for K$^\mathrm{\pm}$, based on the measurement of beam-spin asymmetries. It uses the high statistics data recorded with the CLAS12 spectrometer at Jefferson Laboratory. $\mathrm{F_{LU}^{sin(\phi)}}$ is a twist-3 quantity that provides information about the quark gluon correlations in the proton. This document will present for the first time a simultaneous analysis of two kaon channels over a large kinematic range of $z$, $x_B$, $P_T$ and $Q^2$ with virtualities $Q^2$ ranging from 1 GeV$^2$ up to 8 GeV$^2$ using machine learning techniques for improved particle identification.

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The PANDA experiment at FAIR offers unique possibilities for performing hyperon physics.
The detector will enable the reconstruction of both hyperon and antihyperon, which will
be created together in proton-antiproton collisions. This enables investigations of the strong
interaction in the non-perturbative regime. Due to their relatively long-lived nature, the hyperons
impose a particular challenge on the track reconstruction and event building. In order to
exploit the large expected reaction rates to the fullest, PANDA will utilize a fully software-based
event filtering. Therefore, reconstructing hyperons for such a filter requires online track
reconstruction that can handle particles created a measurable distance away from the interaction
point and, at the same time, operate on free streaming data is needed. Until antiprotons are
available at PANDA, a part of the hyperon program can be carried out with the predecessor,
PANDA@HADES using a proton beam.
In this thesis, investigations of the detector signatures from the decay channels Λ → pπ-, Ξ- →
Λπ- and Ω- → Λ K- produced in YbarY reactions are presented. The detector signatures guide
the subsequent track reconstruction algorithms. A candidate for online track reconstruction
algorithms on free streaming data based on a 4D Cellular Automaton has been developed and is
benchmarked. It utilizes information from the PANDA straw tube tracker and is agnostic to the
point of origin of the particle. The track reconstruction quality assurance procedure and results
from the tracking at different event rates are also presented. Finally, extrapolation algorithms
for including hit information from additional detectors in the tracks are outlined.
In order to maximize the potential of the predecessor experiment PANDA@HADES, a
kinematic fitting procedure has been developed for HADES that combines geometric the decay
vertex information of neutral particles and track parameters such as momentum. Benchmark
studies on simulated data from the channel p(3.5 GeV)p → ΛK+p are presented as well as tests
of the kinematic fit on experimental data from 2007.

PANDA Management Quarterly Report 21Q3

PANDA Management Quarterly Report 21Q2