LHC Working Group on Forward Physics and Diffraction

29 Sept 2025, 09:00 → 2 Oct 2025, 18:20 Europe/Zurich

Madrid

Agustin Sabio Vera, Christophe Royon (The University of Kansas), Grigorios Chachamis (LIP, Lisbon), Jesse Liu (New York University), Josep Rubi, Karel Cerny (Palacky University (CZ)), Murilo Santana Rangel (Federal University of Rio de Janeiro (BR))

The September 29-October 2  2025 four-day workshop in Madrid of the LHC Physics Centre at CERN (LPCC) Forward Physics Working Group provides a forum at CERN for experimental collaborations and theorists to meet and exchange latest results across all topics of forward physics at the LHC. 

The workshop will take place at the Institute of Theoretical Physics (Campus de Cantoblanco 28049 Madrid Spain) and we will be hosted by Prof. Agustin Sabio Vera. To come to IFT, you can take Line C-4 (Colmenar Viejo or Alcobendas/San Sebastián de los Reyes), that takes you to the University (Cantoblanco-Universidad Station). You can pick it up in Atocha (main station in the Centre/South of Madrid), Nuevos Ministerios (Paseo de la Castellana) and Chamartín (main station in the North). After Chamartín, the second station is Cantoblanco-Universidad, where you should exit.

Forward physics is a diverse program at the LHC that requires innovative instrumentation and unique techniques to measure high-rapidity particles missed by standard central detectors. Special instrumentation ranges from near-beam spectrometers to zero degree calorimeters. Recent results have witnessed a remarkable breadth of advances underscoring the creativity of this community:

• definitive elastic scattering measurements, 
• nonperturbative dynamics of the strong force,
• forward proton and neutron scattering,
• photon fusion production,
• collider neutrino measurements,
• searches for prompt and long-lived particles beyond the Standard Model,
• synergies with cosmic-ray observatories.

These developments open future opportunities to develop in exciting new directions.

This series of inter-experiment workshops provides a regular exchange of latest LHC results, ideas and techniques between experimentalists and theorists, sharpening open questions to chart future developments. We are a vibrant international community drawn to the richness of forward physics, where newcomers and early-career researchers are especially welcome to showcase their science.

The zoom connection is: https://cern.zoom.us/j/65303234188?pwd=36kOs1CYYabLdMgFu6efgpU3Mcb1S4.1 (password: 20252025)

 

Monday 29 September

1 Welcome

Speakers: Agustin Sabio Vera, Prof. Agustin Sabio Vera, Christophe Royon (The University of Kansas (US)), Jesse Liu (New York University), Karel Cerny (Palacky University (CZ)), Murilo Santana Rangel (Federal University of Rio de Janeiro (BR))

2 TMD extractions from global fits

Speakers: Alexey Vladimirov, Alexey Vladimirov (Universidad Complutense de Madrid)

Vladimirov.pdf

3 Exploring fragmentation into $T_{4Q}$ tetraquarks: Insights from the TQ4Q1.1 functions

We present a phenomenological study of exotic fully heavy tetraquark production based on the TQ4Q1.1 set of collinear, variable-flavor-number-scheme fragmentation functions. Our analysis covers scalar ($0^{++}$), axial-vector ($1^{+-}$), and tensor ($2^{++}$) configurations, incorporating single-parton fragmentation at leading power within a nonrelativistic QCD factorization framework. Short-distance inputs for both gluon- and heavy-quark-initiated channels are updated, and a threshold-consistent DGLAP evolution is implemented via HF-NRevo. Particular attention is given to the propagation of uncertainties from the color-composite long-distance matrix elements driving hadronization. We discuss phenomenological implications for LHC kinematics, with emphasis on high-energy resummed observables and their interplay with precision QCD and exotic-hadron searches.

Speaker: Dr Francesco Giovanni Celiberto (UAH Madrid)

talk_LHC_FP_meeting_2025_Celiberto_TQ4Q11.pdf

11:15 Coffee break

4 Energy-Energy correlators in back-to-back scattering

We study the possibilities of obtaining information on the non-perturbative part of the evolution of transverse momentum distributions from the back-to-back limit of energy-energy correlators.

The analysis is performed through a global fit to all available experimental data from $e^+e^-$ collisions, for which the highest order result ever achieved in perturbation theory can be used as input.

Speaker: Alejandro Bris Cuerpo (Universidad Complutense Madrid - IPARCOS)

LHC_2025_IFT.pdf

5 Formalism of power corrections with soft modes

Speakers: IGNAZIO Scimemi (Universidad Complutense madrid), Ignazio Scimemi (Universidad Complutense (ES)), Ignazio Scimemi (Universidad Complutense (ES)), ignazio scimemi (Universidad Complutense Madrid)

MadridUAM2025.pdf

6 Discussion

13:10 Lunch

7 Inelastic production in ultraperipheral collisions

I will discuss the case of inelastic production in ultraperipheral collisions, namely photon-initiated production where one of the interacting ions emits a photon incoherently, leading to ion dissociation. I will present comparisons to data and discuss the background contribution to light-by-light scattering.

Speaker: Dr Lucian Alexander Harland-Lang (University College London)

lhl_lhcfpwg_sep25.pdf

8 Measurements from the ALICE ZDC, in pp, pA and A-A collisions

Speaker: Chiara Oppedisano (INFN Torino (IT))

ALICEZDC-Madrid_compressed.pdf

15:30 Coffee break

9 UPC results from CMS

Speaker: Luis Alcerro Alcerro (The University of Kansas (US))

Overview of the latest UPC results from CMS.pdf

10 Have we seen saturation in UPC data?

Speaker: Christophe Royon (The University of Kansas (US))

madrid2025.pdf

11 The energy dependence of exclusive heavy vector meson photoproduction cross-sections and NLO BFKL evolution

Speaker: Martin Hentschinski (Universidad de las Americas, Puebla)

hentschinski_lhcfwd_madrid25.pdf

12 Discussion

Tuesday 30 September

13 Entanglement and entropy production in e-P and P-P collisions

Speakers: Krzysztof Kutak (Instytut Fizyki Jadrowej Polskiej Akademii Nauk), Krzysztof Marek Kutak (Polish Academy of Sciences (PL))

14 From Multiperipheral Models to BFKL Dynamics in Mueller–Navelet Jets

Speaker: Dario Vaccaro (EPFL)

11:00 Coffee break

15 Forward proton detectors in HIN runs

Speaker: Michael Pitt (CERN)

HI_with_ProtonTag.pdf

16 Overview of ATLAS forward proton detectors: status, performance and new physics results

A key focus of the physics program at the LHC is the study of head-on proton-proton collisions. However, an important class of physics can be studied for cases where the protons narrowly miss one another and remain intact. In such cases, the electromagnetic fields surrounding the protons can interact producing high-energy photon-photon collisions. Alternatively, interactions mediated by the strong force can also result in intact forward scattered protons, providing probes of quantum chromodynamics (QCD). In order to aid identification and provide unique information about these rare interactions, instrumentation to detect and measure protons scattered through very small angles is installed in the beam pipe far downstream of the interaction point.
We describe the ATLAS Forward Proton AFP Detectors, including their performance to date, covering Tracking and Time-of-Flight Detectors as well as the associated electronics, trigger, readout, detector control and data quality monitoring. Finally, a glimpse on the newest results will be given.

Speaker: Sergio Javier Arbiol Val (Polish Academy of Sciences (PL))

LHCForward_Workshop_Madrid.pdf

17 Discussion

13:00 Lunch

18 Extracting the gluon density at the Electron-Ion Collider from F_L measurements

Speaker: Javier Jiménez-López (University of Alcalá)

LHCWG_JJL_2025.pdf

19 Leading qt/Q corrections in correction for Drell-Yan process in TMD factorization

Speaker: Arturo Arroyo Castro (UCM)

Slides_LHC_2025.pdf

15:30 Coffee break

20 Recent results from pO, OO, Ne Ne runs at the LHC

Speaker: Dr Georgios Krintiras (The University of Kansas (US))

LHC_LightIon_2025.pdf

Light ions.pdf

21 CMS ZDC status

Speaker: Hannah Bossi (Massachusetts Inst. of Technology (US))

HBossi_ForwardPhysicsWorkshop_Sept2025.pdf

22 Performance of AFP/ToF detector in Run 3

Speaker: Karel Cerny (Palacky University (CZ))

ATL-COM-FWD-2025-027.pdf

23 Discussion

Wednesday 1 October

24 ATLAS–TOTEM tension and low-mass diffraction

Speaker: Rafał Staszewski (IFJ PAN Cracow (PL))

2025.10.01_staszewski.pdf

25 CMS-PPS Operation with Rotated Roman Pots

The Roman Pot detector geometry of the CMS Precision Proton Spectrometer, PPS, was designed to cover the leading proton hit distribution for horizontal beam crossing in the CMS interaction point, IP5. This default beam crossing scheme was used throughout Runs 1 - 3 until 2024. In 2025, however, the beam crossing plane in IP5 was changed to vertical, which led to a vertically shifted and wider proton hit distribution, only very insufficiently covered by the detectors, in particular, the diamond timing detectors having a vertical extent of only 4 mm.

To mitigate the almost total acceptance loss, an extensive hardware modification and beamline intervention campaign has been carried out during the winter Technical Stop 2024/2025, rotating all previously horizontal Roman Pots by 27 degrees around the beam axis. This optimal rotation angle was calculated on the basis of the beam optics to maximise the acceptance. Operationally, the insertion of movable devices at a skew angle represented an unprecedented challenge, not foreseen in the collimation hierarchy offering protective shadows in the horizontal and vertical directions.

This presentation shows the adapted Roman Pot insertion scheme and beam-based alignment strategy, optimised with analytical calculations. The proton acceptance in terms of the kinematic variables of the scattering processes is derived for the new Roman Pot insertion positions.

Speaker: Mario Deile (CERN)

fw-ws_202509.pdf

11:00 Coffee break

26 Hard diffraction and photon exchanges at the LHC

Speaker: Christophe Royon (The University of Kansas (US))

madrid2025_diff.pdf

27 Hadron Collider Measurements for IACT Background Modeling

Speaker: Clara Elisabeth Leitgeb (Humboldt University of Berlin (DE))

CosmicRaysLHC_cleitgeb_011025.pdf

28 Discussion

13:00 Lunch

29 PREFACE Update

Speakers: Suat Ozkorucuklu (Istanbul University (TR)), Suat Ozkorucuklu (Bogazici Univ/ Suleyman Demirel Univ.)

PREFACE-Update_01-10-2025 .pdf

30 Space and time structure of luminosity at a collider with crab cavities

The impact of the crab cavity on the space and time structure of luminosity will be presented. For a given set of collider operational parameters the single bunch crossing luminosity and the vertex space-time distributions are computed, based on the ILUMI4d algorithm.

Speaker: Dr Joachim Baechler (CERN)

ILUMI4d_Madrid30.9.2025_pdf.pdf

15:30 Coffee break

31 Rapidity Gaps with FSC: Legacy and Prospects

Speaker: Aldo Penzo (University of Iowa (US))

FSC-AP_01-10-2025.pdf

32 Hadron Forward Calorimeters: Timing optimization and consequences

Speakers: Caglar Zorbilmez (Istanbul University (TR)), Ilknur Hos (Istanbul University - Cerrahpasa (TR))

New-HF-LLP_01-10-2025.pdf

33 Neutrinos in PREFACE

Speakers: Michael Albrow (Fermi National Accelerator Lab. (US)), Michael Albrow, Mike Albrow (Fermi National Accelerator Laboratory)

34 Discussion

35 Workshop conclusion

Speakers: Agustin Sabio Vera (CERN), Agustin Sabio Vera, Prof. Agustin Sabio Vera, Christophe Royon (The University of Kansas (US)), Jesse Liu (New York University), Karel Cerny (Palacky University (CZ)), Murilo Santana Rangel (Federal University of Rio de Janeiro (BR))

Thursday 2 October

36 Discussion: yellow report, long term projects