Bergamo Days

Sep 19, 2023, 12:00 PM → Sep 22, 2023, 1:30 PM Europe/Berlin

Sala di Sant’Agata

Laura Fabbietti (TUM)

The Bergamo Days have been an annual workshop to discuss current advancements in the fields of particle physics and particle detector development. 

We are proud to bring this tradition back to its first iteration after Covid 19, and this year it will be held in Bergamo, Italy.

 

The workshop will focus on two topics: chiral symmetry breaking/restoration and nuclei formation. 

Chiral symmetry breaking/restoration: Chiral Symmetry Breaking is one of the fundamental effects within the realm of strong interaction and it is responsible for the large mass of hadrons, in comparison to the light quark masses. From a theoretical point of view, there is a spontenous chiral symmetry breaking and explicit ones. The first effect provides the largest contribution to the hadron mass and is due to specific properties of the ground state of QCD. The second effect is due to the finite mass of the quarks. Experimentally, people look for a clear signature of chiral symmetry restoration, meaning an evidence that a transition from the broken symmetry to a partially restored symmetry can be obtained in the laboratory, if conditions of high temperature or baryonic densities are realized. These searches have been carried out for decades, since a detailed understadning of the mechanism responsible for the hadron masses is key in nuclear physics. The intro will introduce the topic and provide some examples of experimental searches. More details will be discussed in the discussions during the meeting. 

Nuclei formation: The creation mechanism of nuclei in hadron collisions is a complex problem governed by the collisions properties but also by the final state interaction of nucleons composing the nuclei of interest. A detailed understanding of these processes is not only interesting from the point of view of nuclear physics but also to infer on astrophysics processes such as the production of nuclei and antinuclei in cosmic rays interaction within the interstellar medium but also the conversion of dark matter into nuclei and antinuclei . In this introduction we will lay out the open physics questions and sketch the tools that are currently employed in modern nuclear physics to quantitatively understand nuclei production.

For summaries of individual topics, please see the timetable. Sessions will be structured as 1.5h blocks, with a presentation covering ca. 40 minutes and a subsequent discussion. 

 

ChiralIntro.pdf

Tuesday, September 19

2:00 PM → 5:00 PM Tour of Bergamo

7:30 PM → 10:00 PM Dinner

Wednesday, September 20

9:00 AM → 10:30 AM Introductory talks: Chiral Symmetry Breaking

Chiral Symmetry Breaking: Chiral Symmetry Breaking is one of the fundamental effects within the realm of strong interaction and it is responsible for the large mass of hadrons, in comparison to the light quark masses. From a theoretical point of view, there is a spontenous chiral symmetry breaking and explicit ones. The first effect provides the largest contribution to the hadron mass and is due to specific properties of the ground state of QCD. The second effect is due to the finite mass of the quarks. Experimentally, people look for a clear signature of chiral symmetry restoration, meaning an evidence that a transition from the broken symmetry to a partially restored symmetry can be obtained in the laboratory, if conditions of high temperature or baryonic densities are realized. These searches have been carried out for decades, since a detailed understadning of the mechanism responsible for the hadron masses is key in nuclear physics. The intro will introduce the topic and provide some examples of experimental searches. More details will be discussed in the discussions during the meeting.

Nuclei formation: The creation mechanism of nuclei in hadron collisions is a complex problem governed by the collisions properties but also by the final state interaction of nucleons composing the nuclei of interest. A detailed understanding of these processes is not only interesting from the point of view of nuclear physics but also to infer on astrophysics processes such as the production of nuclei and antinuclei in cosmic rays interaction within the interstellar medium but also the conversion of dark matter into nuclei and antinuclei . In this introduction we will lay out the open physics questions and sketch the tools that are currently employed in modern nuclear physics to quantitatively understand nuclei production.

Convener: Laura Fabbietti (TUM)

Intro_NucleiProduction.pdf

10:30 AM → 11:00 AM coffe break

11:00 AM → 12:30 PM Introductory talks: Nuclei formation

Chiral Symmetry Breaking: Chiral Symmetry Breaking is one of the fundamental effects within the realm of strong interaction and it is responsible for the large mass of hadrons, in comparison to the light quark masses. From a theoretical point of view, there is a spontenous chiral symmetry breaking and explicit ones. The first effect provides the largest contribution to the hadron mass and is due to specific properties of the ground state of QCD. The second effect is due to the finite mass of the quarks. Experimentally, people look for a clear signature of chiral symmetry restoration, meaning an evidence that a transition from the broken symmetry to a partially restored symmetry can be obtained in the laboratory, if conditions of high temperature or baryonic densities are realized. These searches have been carried out for decades, since a detailed understadning of the mechanism responsible for the hadron masses is key in nuclear physics. The intro will introduce the topic and provide some examples of experimental searches. More details will be discussed in the discussions during the meeting.

Nuclei formation: The creation mechanism of nuclei in hadron collisions is a complex problem governed by the collisions properties but also by the final state interaction of nucleons composing the nuclei of interest. A detailed understanding of these processes is not only interesting from the point of view of nuclear physics but also to infer on astrophysics processes such as the production of nuclei and antinuclei in cosmic rays interaction within the interstellar medium but also the conversion of dark matter into nuclei and antinuclei . In this introduction we will lay out the open physics questions and sketch the tools that are currently employed in modern nuclear physics to quantitatively understand nuclei production.

Convener: Chiara Pinto (TUM)

Intro_NucleiProduction.pdf

12:30 PM → 2:00 PM Lunch break

2:00 PM → 3:30 PM Chiral symmetry restoration: Theory

The idea of this group is to understand the theoretical basics of chiral symmetry in QCD, how its spontaneous and explicit breaking occurs in nature and with which theoretical tools we are able to investigate the restoration of this symmetry at finite density/temperature.

Convener: Valentina Mantovani Sarti (TUM)

ChiralABD_1.pdf

ChiralABD_2.pdf

3:30 PM → 4:00 PM Coffee break

4:00 PM → 5:30 PM Chiral symmetry restoration - Dileptons

Dileptons are one of the promising probes of the restoration of chiral symmetry in heavy-ion collisions since a virtual photon can propagate in a medium without disturbance.
The light vector mesons (ρ,ω and φ resonances) directly couple to the electromagnetic current correlator, which is the central ingredient in dilepton production,
and modify their properties in the medium that may produce multiple bumps and peaks around their vacuum masses.
These modifications could be revealed with various observables, such as invariant-mass spectra and azimuthal asymmetries.
Such measurements at LHC energies are nevertheless quite challenging due to a large combinatorial and physical backgrounds.
In this session, we will focus on the status of experimental studies of dilepton spectra in heavy-ion experiments,
as well as on the current understanding and interpretation of the results.

Convener: Igor Altsybeev (TUM)

Dileptons_Exp_Bergamo_2023-2.pdf

5:30 PM → 5:50 PM Coffe break

5:50 PM → 6:30 PM Wrap up

7:30 PM → 8:30 PM Dinner

Thursday, September 21

9:00 AM → 10:30 AM Nuclei formation: Source

When hadron hadron collisions occur, many news particle are produced. The particle production is characterized by an space-time evolution that is parametrized with a Source function. One can imagine this source function as a hypergeometrical function expanding as a function of time. A data driven method is normally applied to study the source properties for different hadron hadron collisions and this source is an essential element to understand the nuclei formation probablitiy. In this section, we will discuss the different source models.

Convener: Seyed Farid Taghavi (school of particles and accelerators, institute for research in fundamental sciences, Tehran, Iran)

Sources size in small systems and hydrodynamic evolution.pdf

10:30 AM → 11:00 AM Coffee break

11:00 AM → 12:30 PM Nuclei formation: Coalescence

The process by which nuclei are formed is a very complex and interesting question. The coalescence model tries to answer it by assigning a probability for two or more nucleons to get together to form nuclei depending on their relative positions and momenta, resulting in a microscopic description of nuclei formation. This process can be studied in detail, considering both the spacial and momentum correlations between the produced constituents and the quantum mechanical probability to enter the bound state. Thus, both the interactions between the nucleons and the multi nucleon source play an important role in coalescence. The aim of the talk in this workshop is to discuss the effects impacting coalescence in detail.

Convener: Stephan Koenigstorfer (TUM)

Coalescence presentation.pdf

12:30 PM → 2:00 PM Lunch break

2:00 PM → 3:30 PM Chiral symmetry restoration: pionic atoms

Physicists have been hunting for evidence of chiral symmetry restoration for decades. While the QCD Lagrangian is invariant under the chiral symmetry (assuming massless quark), its ground state is not which results in spontaneous chiral symmetry breaking. Indeed, the vacuum state of QCD is not an empty space but filled with quark-antiquark pairs. The expectation value of such chiral condensate is an order parameter of the chiral symmetry, which is expected to decrease at high temperatures or high matter densities where the chiral symmetry is partially restored. One way to look for chiral symmetry restoration is the spectroscopy of meson–nucleus bound systems such as pionic atoms. The pion-nucleus interaction is modified due to the medium effects in nuclear matter. Such interaction can be described by employing optical potential and fitting it to binding energies and widths of the measured pionic atom states. The level of chiral symmetry restoration can then be obtained by comparing the resulting optical potential isovector parameter b1 to the one estimated in vacuum. The talks in this section aim to discuss the underlying theoretical motivation and experimental design of such pionic atom experiments; and to present available measurements, including the new publication on Sn pionic atoms.

Convener: Laura Serksnyte

PionicAtomsSlides.pdf

3:30 PM → 4:00 PM Coffee break

4:00 PM → 5:30 PM Chiral symmetry restoration: future of femto

With the currently ongoing Run 3 data taking campaign, an unprecedented amount of data of high energy nuclear collisions are being collected at the LHC. With these high statistics, a window of opportunity opens up to probe some of the most looked-for effects in nuclear and particle physics, e.g. chiral symmetry restoration.
In this session we dive into the future of femtoscopy at the LHC. We’ll discuss the technical challenges at hand and the physics we can probe with future femtoscopic studies such as axion properties and solving the puzzle of chiral symmetry restoration.

Convener: Marcel Lesch (TUM)

Bergamo_Future_of_Femto.pdf

5:30 PM → 5:50 PM Coffee break

5:50 PM → 6:30 PM Wrap up

7:30 PM → 10:00 PM Dinner

Friday, September 22

9:00 AM → 10:30 AM Nuclei formation: Thermal models

Thermal models are grounded in the principles of statistical mechanics and thermodynamics, applying these concepts to the behavior of particles and their interactions in extreme environments like heavy-ion collisions (HIC). HIC are characterized by high temperatures and energy densities, found in the aftermath of high-energy nuclear collisions. The central idea behind thermal models is that, under certain conditions, the particles produced in these collisions reach a state of approximate thermal equilibrium. In this state, the distribution of particle types and momenta follows well-established statistical patterns.
One of the key aspects of thermal models is their ability to predict particle yields and other observables based on a small set of parameters that describe the system's temperature, volume, and particle species. This simplicity is especially valuable in situations where detailed understanding of the microscopic dynamics is limited due to the complexity of the interactions involved. Thermal models bridge this gap by providing a macroscopic description that encapsulates the collective behavior of particles. The performance of the model is remarkable as the yields of the lightest hadron up to the lightest atomic nuclei are accurately described spanning 9 orders of magnitude.

Convener: Maximilian Korwieser (TUM)

10:30 AM → 11:00 AM Coffee break

11:00 AM → 12:30 PM Nuclei formation: Hydrodynamics in small systems

The emitted particles from a source produced by colliding large and small systems show a common feature known as mT scaling. Particles with larger transverse mass are emitted from smaller system sizes. In large systems such as those produced in Pb-Pb collisions, this effect has been attributed to the collective expansion of the medium. In recent years, collective-like signatures in small systems, namely p-p collision, have been observed, although the origin of such observation is still under debate. The "Hydrodynamics and the source size in small systems" aims to review the physics behind the effect of collectivity in observing mT scaling and discuss its connection to so-called collective expansion in small systems.