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Brainstorming for a future FCC-hh detector

Initial thoughts by M. Citron, M. Low, D. Curtin, A. Haas, J. Beacham

LLP9

28 May 2021

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Detector overview

Timing layer

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General topics

Triggering: should effectively use full event information (tracking, timing, etc.)?

what area is most important? ID vertices? calo objects? other?

Precision timing is a potential game changer for LLP

where is it most important? ID? muon system?

Trackers will be more capable?

short tracks? triggering on IP displacement? other?

Calorimeters will be (much?) more granular

how is this useful for LLP? background rejection?

Muon systems will be ~the same?

But what would we like in terms of new capabilities? Background suppression?

Forward regions / other caverns can be designed instead of parasitically used

what would be ideal for these?

Other ideas …

Subdetector ideas that can help help BIB, cosmics, ?

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Trigger desires for LLPs

Triggering should effectively use full event information (tracking, timing, etc.)
Primarily computing problem, should be tractable by ~2040
Default track reconstruction should consider vertices from anywhere
Loose selections or good bandwidth reduction more important?

Scouting is also key and lives in between
How can we be confident enough in saving only reco quantities?

Are DV's in the trackers still the main improvement possible?

How far in IP can we push the track trigger reco?
L1 reco of charm/b/tau decays / displaced photons

Combinations of triggers from many detectors (at L1!)

e.g. calo jet + dv at L1

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Timing desires for LLPs

Each system should have some level of timing

Multiple layers for confirmation and tail removal
Separation of pi/K up to ~10 GeV?
Mass measurement of tracks

Calo timing

Separation of jets from different interactions
Delayed jets? Dark shower decays?
How good timing do we want?

Example: muon system has 0.5 ns resolution. Would it benefit from a dedicated O(30) ps timing layer?

Neutral decays in the MS?
Pileup rejection?
Reconstruction of complicated decays in the MS / EJs

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Tracker desires for LLPs

Layers close to the beam? (for disappearing tracks)
Pixels everywhere?

dE/dx (including triggering, and ability to combine with pT, other layers, etc. at L1)

Ability to see fractional charged particles?
...

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Calorimeter desires for LLPs

More granular calorimeters (useful for emerging jets?)
Can beam-induced backgrounds be vetoed?
Non-pointing photons (including triggering)

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Muon system desires for LLPs

Idea: wrap the muon system in a thin calorimeter?
Idea: improve shielding from main collision? (may conflict with prompt muons)
...�

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Forward region desires for LLPs

FCC-hh version of FASER (minimal extra cost)?
Best location? Closer with shielding?
Proton tagging / exclusive production (Higgs?)

gamma-gamma collisions, other clean states

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Idea: Separate shielded LLP detector subsystem

If MS can’t be arbitrarily shielded to eliminate QCD backgrounds, could have a dedicated LLP detector subsystem to avoid having to retrofit a MATHUSLA/CODEX.
Could be some caverns in the forward region instrumented like MATHUSLA/CODEX (see 1606.06298), easy to put in when constructing tunnel.
Fully integrated into main detector: reconstruction, triggering, etc.
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1606.06298v1