# Mini-workshop on opportunities to reveal New Physics with feebly-interacting particles and ultra-rare decays in experiments with extracted SPS beams at the CERN North Area

Europe/Rome
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Description

Aim of the meeting:

The aim of the mini-workshop is to present a proposal for a new experiment (SHADOWS) to search for feebly interacting particles at the CERN North Area.
The interplay with current and future experimental activities by the NA62 experiment is also discussed.

Program

Thursday June 10

14:30
"Introduction"

14:40   Gaia Lanfranchi (LNF INFN)
The search for Feebly-Interacting Particles within the Physics Beyond Colliders activity at CERN

15:05   Matthew Moulson (LNF INFN) & Tommaso Spadaro (LNF INFN)
"Physics at a high-intensity kaon beam facility at the CERN SPS"

15:50 Gaia Lanfranchi (LNF INFN)

"The SHADOWS project to search for Feebly-Interacting Particles at CERN"

16:20 General Discussion

17:00 Conclusion

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Meeting number (access code): 163 444 8331

• 2:30 PM 2:40 PM
Introduction 10m
• 2:40 PM 3:05 PM
The search for Feebly-Interacting Particles within the Physics Beyond Colliders activity at CERN 25m

The absence so far of unambiguous signals of New Physics from direct searches at the LHC, indirect searches in flavour physics and direct Dark Matter detection experiments invigorates the need for broadening the experimental effort in the quest for New Physics and in exploring ranges of interaction strengths and masses different from those already covered by existing or planned projects.

Feebly-interacting particles (FIPs) represent an alternative paradigm with respect to the traditional BSM physics explored at the LHC and their search has been recognized by the European Strategy for Particle Physics update as one of the essential activities in particle physics to be pursued in the next decade.

The investigation of this paradigm over a large range of couplings and masses
requires a great variety of experimental facilities. I will present the current plans for searching for FIPs at CERN within the new Physics Beyond Colliders activity and the newly established FIP Physics Centre.

Speaker: Gaia Lanfranchi (LNF)
• 3:05 PM 3:50 PM
Physics at a high-intensity kaon beam facility at the CERN SPS 45m

Precision measurements of the branching ratios (BRs) for rare kaon decays can provide unique constraints on CKM unitarity and may reveal the existence of new physics. Building upon a CERN tradition of groundbreaking experiments in kaon physics, including, most recently, NA62's successful application of the in-flight technique to measure BR($K^+ \to \pi^+\nu\bar{\nu}$), we envision a comprehensive program for the study of the rare decay modes of both $K^+$ and $K_L$ mesons, to be carried out with high-intensity kaon beams from the CERN SPS in multiple phases starting in LHC Run 3 (2026), including both an experiment to measure BR($K^+ \to \pi^+\nu\bar{\nu}$) at the 5% level and an experiment to measure BR($K_L \to\pi^0\nu\bar{\nu}$) at the 20% level. The detectors could also be reconfigured to allow measurements of $K_L$ decays with charged particles, such as $K_L\to\pi^0\ell^+\ell^-$. In addition, the availability of high-intensity proton and kaon beams and detectors with redundant PID systems and precise timing will allow for a wide range of searches for rare phenomena beyond the kaon sector, including dark sector particles produced in kaon and pion decays or in interactions in the experiment’s target or beam dump.

Speakers: Matthew David Moulson (LNF) , Tommaso Spadaro (LNF)
• 3:50 PM 4:15 PM
The SHADOWS project to search for Feebly-Interacting Particles at CERN 25m

SHADOWS is a new experiment proposed at CERN within the Physics Beyond Colliders activity to search for a large variety of Feebly-Interacting Particles (FIPs) produced in the interactions of a proton beam with a dump.

It will use the 400 GeV primary proton beam extracted from the CERN SPS currently serving the NA62 experiment in the CERN North area and will take data running concurrently to NA62 when NA62 is operated in beam-dump mode.

SHADOWS can expand the exploration for a large variety of FIPs well beyond the state of the art in the MeV-GeV mass range which is allowed by cosmological and astrophysical observations and become one of the main players in the search for FIPs at accelerators in the next decade.
I will describe the proposal and its physics reach put into a worldwide context.

Speaker: Gaia Lanfranchi (LNF)