The Forward Physics Facility (FPF) is a proposed extension of the HL-LHC program designed to exploit the unique scientific opportunities offered by the intense flux of high energy neutrinos, and possibly new particles, in the far-forward direction. Located in a well-shielded cavern 627 m downstream of one of the LHC interaction points, the facility will support a broad and ambitious physics program that significantly expands the discovery potential of the HL-LHC. Equipped with four complementary detectors—FLArE, FASER <italic>&#957;</italic>2, FASER2, and FORMOSA&#8212;the FPF will enable breakthrough measurements that will advance our understanding of neutrino physics, quantum chromodynamics, and astroparticle physics, and will search for dark matter and other new particles. With this Letter of Intent, we propose the construction of the FPF cavern and the construction, integration, and installation of its experiments. We summarize the physics case, the facility design, the layout and components of the detectors, as well as the envisioned collaboration structure, cost estimate, and implementation timeline.

United States

Luis A. Anchordoqui

United Kingdom

John Kenneth Anders

Switzerland

Japan

Akitaka Ariga

Tomoko Ariga

Canada

David Asner

Jeremy Atkinson

Alan J. Barr

Larry Bartoszek

Brian Batell

Hans Peter Beck

Germany

Florian U. Bernlochner

India

Bipul Bhuyan

Jianming Bian

Aleksey Bolotnikov

Silas Bosco

Jamie Boyd

Nick Callaghan

Gabriella Carini

Michael Carrigan

Kohei Chinone

Matthew Citron

Isabella Coronado

Peter Denton

Albert De Roeck

Milind V. Diwan

Sergey Dmitrievsky

Romania

Radu Dobre

Monica D’Onofrio

Jonathan L. Feng

Max Fieg

Elena Firu

Brazil

Netherlands

Reinaldo Francener

Haruhi Fujimori

Frank Golf

Yury Gornushkin

Kranti Gunthoti

Claire Gwenlan

Carl Gwilliam

Andrew Haas

Elie Hammou

Daiki Hayakawa

Christopher S. Hill

Dariush Imani

Tomohiro Inada

Sune Jakobsen

South Korea

Yu Seon Jeong

Kevin J. Kelly

Samantha Kelly

Luke Kennedy

Felix Kling

Umut Kose

Peter Krack

China

Jinmian Li

Yichen Li

Steven Linden

Ming Liu

Kristin Lohwasser

Adam Lowe

Belgium

Steven Lowette

Toni Mäkelä

Roshan Mammen Abraham

Christopher Mauger

Konstantinos Mavrokoridis

Josh Mcfayden

Hiroaki Menjo

Connor Miraval

Keiko Moriyama

Toshiyuki Nakano

Ken Ohashi

Toranosuke Okumura

Hidetoshi Otono

Vittorio Paolone

Saba Parsa

Junle Pei

Michaela Queitsch-Maitland

Mary Hall Reno

Sergio Rescia

Filippo Resnati

Adam Roberts

Juan Rojo

Hiroki Rokujo

France

Olivier Salin

Jack Sander

Sai Neha Santpur

Osamu Sato

Italy

Paola Scampoli

Ryan Schmitz

Matthias Schott

Anna Sfyrla

Dennis Soldin

Albert Sotnikov

Anna Stasto

George Stavrakis

Jacob Steenis

David Stuart

Juan Salvador Tafoya Vargas

Yosuke Takubo

Simon Thor

Poland

Sebastian Trojanowski

Yu Dai Tsai

The forward physics facility: Physics opportunities and conceptual design

<p>This Letter presents the measurement of the energy-dependent neutrino-nucleon cross section in tungsten and the differential flux of muon neutrinos and antineutrinos. The analysis is performed using proton-proton collision data at a center-of-mass energy of 13.6 TeV and corresponding to an integrated luminosity of <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mrow><mo stretchy="false">(</mo><mn>65.6</mn><mo>±</mo><mn>1.4</mn><mo stretchy="false">)</mo><mtext> </mtext><mtext> </mtext><msup><mrow><mi>fb</mi></mrow><mrow><mo>−</mo><mn>1</mn></mrow></msup></mrow></math>. Using the active electronic components of the FASER detector, <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mn>338.1</mn><mo>±</mo><mn>21.0</mn></math> charged current muon neutrino interaction events are identified, with backgrounds from other processes subtracted. We unfold the neutrino events into a fiducial volume corresponding to the sensitive regions of the FASER detector and interpret the results in two ways: (i) we use the expected neutrino flux to measure the cross section, and (ii) we use the predicted cross section to measure the neutrino flux. Both results are presented in six bins of neutrino energy, achieving the first differential measurement in the TeV range. The observed distributions align with standard model predictions. Using this differential data, we extract the contributions of neutrinos from pion and kaon decays.</p>

Xiaocong Ai

CERN

John Anders

Claire Antel

Tobias Boeckh

Lydia Brenner

Angela Burger

Franck Cadoux

Roberto Cardella

David W. Casper

Charlotte Cavanagh

Xin Chen

Dhruv Chouhan

Andrea Coccaro

Stephane Débieux

Ansh Desai

Sinead Eley

Yannick Favre

Deion Fellers

Carlo Alberto Fenoglio

Didier Ferrere

Wissal Filali

Edward Galantay

Ali Garabaglu

Stephen Gibson

Sergio Gonzalez-Sevilla

Yuri Gornushkin

Michael Holzbock

Shih-Chieh Hsu

Zhen Hu

Giuseppe Iacobucci

Luca Iodice

Hans Joos

Israel

Enrique Kajomovitz

Hiroaki Kawahara

Alex Keyken

Daniela Köck

Pantelis Kontaxakis

Rafaella Kotitsa

Susanne Kuehn

Thanushan Kugathasan

Lorne Levinson

Ke Li

Jinfeng Liu

Yi Liu

Margaret S. Lutz

Jack MacDonald

Chiara Magliocca

Lawson McCoy

Josh McFayden

Andrea Pizarro Medina

Matteo Milanesio

Théo Moretti

Mitsuhiro Nakamura

Laurie Nevay

Hao Pang

Lorenzo Paolozzi

Pawan Pawan

Brian Petersen

Titi Preda

Markus Prim

André Rubbia

Jorge Sabater-Iglesias

Kristof Schmieden

Davide Sgalaberna

Mansoora Shamim

Savannah Shively

Noshin Tarannum

Ondrej Theiner

Eric Torrence

Oscar Ivan Valdes Martinez

Svetlana Vasina

First Measurement of the Muon Neutrino Interaction Cross Section and Flux as a Function of Energy at the LHC with FASER

We analyse relevant signals expected at the LHC, assuming that the gluino is the lightest supersymmetric particle (LSP) in the framework of the $$\mu \nu $$ SSM. In this $\textit{R}$-parity violating model, the presence of couplings involving right-handed neutrinos solves simultaneously the $$\mu $$ problem and the accommodations of neutrino masses and mixing angles. We study gluino pair production in quark-antiquark and gluon-gluon collisions. The main decay channels for the gluino LSP are the three-body decays to two quarks and a lepton or a neutrino. In both cases, the leading channels occur for the third family of quarks. We compare the predictions of this scenario with LHC searches for prompt and long-lived particles. To analyse the parameter space we sample the $$\mu \nu $$ SSM for a gluino LSP, paying special attention to reproduce the current experimental data on neutrino and Higgs physics, as well as flavour observables. Our results imply a lower limit on the mass of the gluino LSP of about 2600 GeV, and an upper limit for the decay length of about 6 cm.