From June 2 to 6, 2025, the city of Valencia hosted the XV Workshop of the Long-Lived Particles (LLP) Community, an international event that brought together the global community of experts in this field of particle physics. The event took place at the ADEIT building, right in the city center, and was organized by the Instituto de Física Corpuscular (IFIC), a joint center of the Spanish National Research Council (CSIC) and the University of Valencia.

The search for long-lived particles is fundamental to expanding our understanding of the universe beyond the Standard Model of particle physics. These particles, which could exist for long enough to leave distinctive signals in detectors, are candidates to explain yet unresolved phenomena such as dark matter or the matter-antimatter asymmetry. Their detection would mean a revolution in modern physics, opening new avenues in quantum theory and cosmology, and potentially redefining our knowledge about the composition and evolution of the universe and the fundamental laws that govern it.

During the workshop, new ideas and results were presented, setting very significant exclusion limits that expand our knowledge about the possibilities of new physics. Notably, the first results obtained with the MilliQan experiment—one of the dedicated detectors for charged LLPs proposed in 2014 and which began data taking in 2023—were announced. The evolution of the field was also discussed, with proposals to improve crucial aspects of such searches, such as data filtering (trigger), displaced object reconstruction, or background identification, which could be key for future discoveries during the new LHC Run.

This workshop, with an eight-year tradition, brings together the international LLP community, comprising multiple institutions and experiments worldwide. With growing interest in recent years attracting both theoretical and experimental branches, this edition (the first to be held in Spain) gathered 111 attendees from 54 institutions across 20 countries in Europe, the Americas, Asia, and Africa, and the participation of numerous experiments such as ATLAS, CMS, LHCb, Moedal, Mathusla, and NA64, among many others. The workshop was inaugurated by Nuria Rius, Director of IFIC, and Rafael Sebastián, Director General of Science and Research of the Valencian Community. Both highlighted the fundamental role of basic science as a means for the advancement of knowledge and the development of society.

The workshop was organized by an international committee of 12 members and a Local Organizing Committee coordinated by Emma Torró and José Zurita, which included IFIC researchers Chandan Hati, Martin Hirsch, Jacobo López-Pavón, Vasiliki A. Mitsou, Laura Molina, Arantza Oyanguren, Óscar Vives, and Bryan Zaldívar, all of whom are heavily involved in the search for LLPs.

The event had the institutional support of IFIC as a Severo Ochoa Center, the University of Valencia through its Departments of Atomic, Molecular and Nuclear Physics and Theoretical Physics, the Ministry of Science, Innovation and Universities of Spain, the Generalitat Valenciana through its ASFAE, GenT and Prometeo programs, and the COMCHA network.