News

In the week leading up to Quark Matter 2025, a dedicated satellite workshop held at CERN titled High Energy Probes of the Initial Stages set the stage for pivotal discussions on how the early stages of heavy-ion collisions influence the analysis of high-energy probes. The workshop centered on addressing key questions such as:

• How are jets modified during the early stages: virtuality cascade, medium-induced modifications, conceptual and technical challenges.
• What class of jet (high-pt) observables do we need to explore the early stages?
• Common aspects with other problems: small systems, thermalization dynamics, polarization effects, and heavy flavors.

INDICO page: https://indico.cern.ch/event/1487879/

The pheno group leader, Liliana Apolinário, opened the workshop with her talk on “Jets as Probes of the Initial Stages”. Additionally, Andrey Sadofyev delivered a well-received colloquium at CERN on “High-energy Probes of the Initial Stages in Heavy-Ion Collisions”, and João M. Silva presented his latest research on “Exploring Anisotropic QCD Matter with Jets”. Liliana was also invited to convene the final discussion session on Experimental and Phenomenological Opportunities.

Join us on Wednesday, March 26, at 4:00 PM for a special colloquium featuring Professor David Rousseau (University of Oxford, UK), who will discuss the transformative impact of Artificial Intelligence in LHC Physics.

Prof. Rousseau is a leading figure in the application of AI to Particle Physics. He has played a pivotal role in numerous initiatives—both within the ATLAS collaboration and across the broader LHC community—harnessing Machine Learning to enhance the discovery potential of LHC data. The talk will be held in Room PA1 at 4:00 PM, followed by refreshments.

Particle physics has a long history of developing sophisticated simulators, from modeling proton collisions to creating virtual detectors. Now, we’re integrating Artificial Intelligence through “Neural Simulation Based Inference,” which helps analyze complex phenomena that cannot be to computed analytically from first principles. This approach is highlighted by recent work from the ATLAS experiment at the Large Hadron Collider at CERN, which has provided new insights into quantum interference in a rare Higgs boson decay. We also touch on how biases (“known unknowns”) are modeled, as showcased in the recent Fair Universe HiggsML uncertainty challenge at NeurIPS 2024. Separately, advances in AI generative models, which allow to generate fake images, can be harnessed to emulate particle physics simulators, albeit with specific challenges which will be presented.

On Wednesday 19th February at 4pm we will have the privilege to hear Professor Gavin Salam (University of Oxford, UK) discussing the future of high-energy collider Physics. Prof. Salam is one of the most cited living particle theorists. He was awarded the IOP 2023 Paul Dirac Medal Prize for ‘his for profound, wide-ranging and impactful contributions to particle physics, especially those concerning the identification and structure of hadronic jets.’ His insights are of particular relevance at the time when the European Strategy of Particle Physics is being revised and the future of the field widely discussed. The colloquium will take place in Room PA1 starting at 4pm. Refreshments will be served afterwards. 

The discovery of the Higgs boson opened the door to the investigation of new fundamental interactions of nature unlike any studied before. After a reminder about how certain essential features of the Higgs mechanism matter for the world around us, this talk will examine (a) what we actually know about the Higgs sector of the Standard Model (much more than we expected to, much less than is written in textbooks); (b) some key questions that could be investigated in the near and more distant futures and (c) how we might view the wider landscape of high-energy particle physics.

Afonso Guerreiro, a Physics Master’s student at IST and a member of the Phenomenology Group at LIP, successfully defended his master’s thesis on Tuesday, December 3rd. The thesis, titled “In-medium Gluon Radiation in General Kinematics,” was supervised by Guilherme Milhano (LIP/IST). The defense jury included Mário Pimenta (LIP/IST, President), Liliana Apolinário (LIP/IST, Opponent), and Konrad Tywoniuk (Bergen University, Opponent).

Afonso’s research advanced the theoretical understanding of medium-induced gluon radiation, a key phenomenon in the study of the Quark-Gluon Plasma formed in heavy-ion collisions. Building on the BDMPS-Z formalism, his work extended previous results by deriving a generalized expression for the gluon emission spectrum without relying on commonly used approximations. This comprehensive approach not only verified established results in limiting cases but also introduced a computational routine to solve the resulting integro-differential equations.

Congratulations to Afonso for this achievement and his valuable contribution to theoretical QCD and heavy-ion physics!

Diogo Costa, a Physics Master’s student at IST and member of the Pheno Group at LIP, successfully defended his master’s thesis on Wednesday, November 27th. The thesis, titled “Improving the vacuum baseline for in-medium jet physics studies”, was supervised by Liliana Apolinário (LIP/IST) and Alba Soto-Ontoso (University of Granada). The defense jury included Mário Pimenta (LIP/IST, President), Armesto Pérez (Santiago de Compostela, Opponent), Guilherme Milhano (LIP/IST, Opponent), and Alba Soto-Ontoso (Supervisor Representative).

Diogo’s research tackled the importance of precision in theoretical models for heavy-ion collisions. By incorporating next-to-leading order (NLO) calculations into baseline proton-proton collision simulations, he investigated their impact on jet substructure observables. The results suggest that while the corrections from NLO calculations are small, they could become critical for precision measurements of the Quark-Gluon Plasma as experimental uncertainties decrease in future studies.

Congratulations to Diogo on this achievement and for contributing to advancing our understanding of QCD and heavy-ion physics!

Machine learning has become a hot topic in particle physics over the past several years. In particular, there has been a lot of progress in the areas of particle and event identification, reconstruction, generative models, anomaly detection and more. In this conference, we will discuss current progress in these areas, focusing on new breakthrough ideas and existing challenges.

The ML4Jets workshop will be open to the full community and will include LHC experiments as well as theorists and phenomenologists interested in this topic. We explicitly welcome contributions and participation from method scientists as well as adjacent scientific fields such as astronomy, astrophysics, astroparticle physics, hadron and nuclear physics and other domains facing similar challenges.

The program will cover the following topics:

• Tagging (Classification)
• Reconstruction
• Detector simulation & event generation
• Theory
• Astrophysics
• Unfolding
• Uncertainties
• Anomaly detection
• Interpretability

This year’s conference is organised jointly by LPNHE, LPTHE and IJCLab and hosted by LPNHE on the Paris Sorbonne Campus. Registration for both in-person and Zoom-participation is open and free of charge. It will take place from the 4th to 8th of November.

INDICO page: https://indico.cern.ch/event/1386125/

One of our PhD students, João Gonçalves, will attend and deliver a talk.

Quark Matter 2025 is the XXXI International Conference on Ultra-relativistic Nucleus-Nucleus Collisions, which will be held in Frankfurt, Hesse, Germany. This conference brings together theoretical and experimental physicists from around the world to discuss new developments in high-energy heavy-ion physics. The focus of the discussions is on the fundamental understanding of strongly-interacting matter at extreme conditions, as formed in ultra-relativistic nucleus-nucleus collisions, as well as on emergent QCD phenomena in high-multiplicity proton-proton and proton-nucleus collisions. The scientific program will cover the following topics:

• Chirality
• Collective dynamics & small systems
• Correlations & fluctuations
• Detectors & future experiments
• Electromagnetic probes
• Heavy flavor & quarkonia
• Initial state of hadronic and electron-ion collisions
• Jets
• Light and strange flavor physics & nuclei
• New theoretical developments
• Physics of ultraperipheral collisions
• QCD matter in astrophysics
• QCD phase diagram & critical point

Quark Matter 2025 consists of six days of scientific program, starting on Sunday, April 6th and ending on Saturday, September 12th. Support of early-career researchers (students and young postdocs) will be provided in the form of a reduction of the registration fee.

The deadline for early-bird registration is December 31st, 2024. For regular registration, it is January 31st, 2025.

INDICO page: https://indico.cern.ch/event/1334113/overview

The work by our group members was selected to be presented in several parallel and poster sessions: André Cordeiro, João M. Silva, João A. Gonçalves, Marco Leitão, Nuno Olavo Madureira and Liliana Apolinário. Click on their names to see their respective contributions!

Yesterday, Guilherme Crispim, master’s student at the Instituto Superior Técnico of Lisbon and member of the Pheno group at LIP, successfully defended his master thesis, entitled “Pre-equilibrium of the Quark-Gluon Plasma”.

This study was focused on the pre-thermal equilibrium stage of the Quark-Gluon Plasma (QGP) formed in ultra-relativistic heavy ion collisions at LHC and RHIC. Guilherme investigated the sensitivity of jets to this extremely short-lived phase by simulating various QGP models and analysing the response of particle angular distributions to quenching effects. The findings presented in this thesis suggest that, with sufficient data, it will be possible to discriminate between different pre-equilibrium models at future high-energy colliders like FCC-hh.

Guilherme’s work was supervised by Liliana Apolinário and Ruben Conceição. The jury for the thesis defense comprised Mário Pimenta (president), Pablo Guerrero (main arguer), and Liliana Apolinário (as the supervisor representative).

Congratulations to Guilherme!

Last week marked a significant achievement for Guilherme Calé, a student at the Faculty of Sciences of the University of Lisbon and member of the Pheno group at LIP. Guilherme successfully defended his master thesis, titled “Particle-Particle and Jet-Jet Angular Correlations at the Parton Level”.

Guilherme’s research, guided by supervisors Grigorios Chachamis and João Pires, was an in-depth exploration of partonic correlations and their manifestation at parton jet level. The study was based on simulations of high-energy collisions for multiple systems (proton-proton, proton-nucleus and nucleus-nucleus), whose angular correlations were analyzed and compared for two Monte Carlo codes (Pythia and BFKLex). In all of the examined cases, no connection was found between the high-energy QCD dynamics considered (i.e. BFKL evolution) and the enigmatic near-side, long-range correlations observed in data.

The jury for the thesis defense comprised Margarida Cruz (president), Liliana Apolinário (main arguer), and Grigorios Chachamis (as the supervisor representative).

Congratulations to Guilherme!

ISMD 2024 will be held from September 23 to 27, 2024, in Malargüe, Argentina. This event will bring together physicists from across particle, nuclear, and astrophysics for talks and discussions focused on all aspects and consequences of the strong nuclear force, as well as its complex final states. In order to encourage cross-talk between areas, all presentations at ISMD will be programmed in plenary sessions, organized into the following scientific tracks:

    •  Cosmic ray and astroparticle physics
    •  Multiparticle correlations and fluctuations
    •  Forward physics: Diffraction, Odderon and Pomeron
    •  Hadronic final states in high pT interactions
    •  Collectivity in high energy collisions: jets, flows, and other mechanisms
    •  Proton structure, small-x and large-x physics
    •  Hadronic issues in heavy-flavour physics
    •  Beyond Standard Model Physics and new developments in HEP

Registration deadline: Aug 30th, 2024. Abstract submission deadline: July 15th, 2024.

INDICO page: https://indico.cern.ch/event/1371434/