The FASER experiment @ the LHC
https://faser.web.cern.ch
Andrea Coccaro on behalf of the FASER collaboration
Lomonosov Conference - https://lomcon.ru/
22 Aug 2021

Physics prospects
Experiments at the LHC focus on heavy, strongly interacting particles by looking at the transverse plane.
In absence of signals of new physics at the TeV scale, the initial paradigm broadened● Using existing experiments / with new triggers, or new reconstruction techniques, with displaced
objects, with analysis with trigger-level quantities, etc.
● Proposing new experiments / to complement the coverage of existing experiments, mainly towards
longer lifetimes and lower masses
FASER aims at searching for light and weakly-interacting particles● By looking at the very-forward region at a distance where known background is highly suppressed● With a dedicated, low-budget detector placed in the TI12 side tunnel at the LHC● Supported by the Simons and Heising-Simons foundations

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The idea behind FASER

New physics at the LHC focus at high pT

σNP ⁓ pb/fb ⇒ NNP ⁓ 1.5 · 102/105 with ℒ=150/fb

If new physics is light and weakly-interacting

σInelastic ⁓ 75 mb ⇒ NInelastic ⁓ 1016 with ℒ=150/fb

That implies extraordinary rates for low-mass SM particles in the very-forward region
N(π0) ⁓ 1017 ⇒ ⁓ 1% within the FASER acceptance (and decay products also highly collimated)

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FASER location4

Detector Layout
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1.5-meter magnetized decay volume
2-meter spectrometer with three tracking stations
electromagnetic calorimeter
three scintillator stations for triggering, veto andprecise timing
20cm aperture (η>9.1)

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Sensitivity to dark photons● two high-energetic, oppositely-charged tracks
originating from common vertex in the decay volumeand pointing back to the IP● no signal in the scintillator station● energy deposit in the calorimeter
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Discovery potential
FASER (fully funded)● L=1.5m, R=10cm, ℒ=150/fb
FASER2 (projection for HL-LHC)● L=5m, R=1m, ℒ=3/ab

More details on the FASER physics inPhys. Rev. D 99, 095011

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Tracker
Using spare silicon strip modules (SCT) from ATLAS● 72 modules with O(105) channels arranged in 3 stations with each 3 layers of 8 modules● 25um resolution and <0.1% defects with extensive testing on surface and cosmic ray runs

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Scintillators
Trigger capabilities in 3 scintillator stations● For vetoing charged particles● Efficiency measured in cosmic data to be >99.9% for a single layer

9Calorimeter
Using spare modules from LHCb outer calorimeter● Readout using PMTs with custom voltage divider base● 66 layers of lead and scintillators corresponding to 25 radiation lengths● 1% energy resolution at 1 TeV

10FASERnu
Neutrino program with dedicated emulsion-based detector● Study of neutrino production, propagation and interaction at the TeV scale● First neutrino interaction candidate events at the LHC with pilot run in arXiv 2105.06197● Dedicated talk by Tomohiro Inada at tomorrow's neutrino session

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FASER evolution in photos

08/2018

08/2019

11/2020

04/2020

04/2021
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FASER schedule
Detector fully and successfully installed into TI12 tunnel in March 2021
● Cosmic ray data since then plus test-beam data in August 2021
● Extensive studies of taken data is ongoing● On track for physics runs in LHC Run-3

13FASER commissioning
Detector running almost continuously since the start of cosmic data taking●●●●

Monitoring, prompt reconstruction being exercised
10-15 Hz trigger rate requiring 2-scintillator coincidence
Per-station tracks triggered by nearby scintillator and reconstructed with a rate of 1/minuteDetector simulation, reconstruction being developed

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Summary
FASER is a new experiment at the LHC● Designed for detecting light and weakly-interacting particles● Complemented by a dedicated detector for neutrino physics
FASER is installed in the TI12 LHC tunnel●●●●Large amount of cosmic and test-beam data being analysed
Commissioning thus far proceeding smoothly
Ongoing work on reconstruction, calibration, dataﬂow
First neutrino interaction candidate observed and related paper submitted for publication

FASER is looking forward to ﬁrst LHC Run-3 collisions in 2022!

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The Collaboration
78 collaborators, 21 institutions, 9 countries

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