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v3.3.6-pre
Discussion regarding the physics and detector design for the Forward Physics Facility at the LHC.
Update from last few weeks.
Snowmass related
1) neutrino frontier NF10 has requested a section for FPF detectors. MVD will draft a summary which has to cover all of FPF detectors.
2) Snowmass FPF whitepaper has laid out an excellent science case for the FPF. Energy frontier workshop had
very good representation and talks from Jonathan, and Mary Hall Reno.
https://indico.fnal.gov/event/52465/timetable/
There appears to be a general agreement that this science is worthwhile and should be done. For the energy frontier the key science driver appears to be access to the very low and high x proton structure. These measurements are important for astrophysics and for planning for a new collider.
Several EF topical groups are likely to contain language about the FPF.
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Experimental organization progress
1) J. Boyd has started a new monthly meeting of experimental projects.
The focus is on settling the experimental requirements on space and infrastructure.
https://indico.cern.ch/event/1135125/
Key issues:
A. CERN has approved a new plan for a safety gallery. A connection to the LHC tunnel is no longer needed, greatly simplifying radiation and construction issues.
B. Sweeper magnet location is tentatively found to be feasible.
bad news: Muon rate might be significantly higher than simple extrapolation from FASER. But work is in progress. The reason is changes from the LHC to HL-LHC lattice.
C. CERN machine advisory body wants FPF to remain flexible about the detector locations.
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2) F. Lanni will be the new Neutrino Platform leader. Lanni is included in this meeting.
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Some homework as a result of Wenjie's talk.
1) Can you make the plots separating out tau decays to 1 prong, 3 prong, versus n>3-prong hadronic tau decays ?
2) Also it might be instructive to consider plots versus number of Pi0's from tau decay
3) A flat distribution was assumed within the fiducial volume of the detector for nutau, numu, and nue events.
Is it important to have a detailed simulation for this purpose including the neutrino angular dependence ?
-- MVD contends that this angular dependence is very uncertain and it is best not to fine tune the detector to that.
-- The numu in particular come from pion decay and have great uncertainty due to modeling of the CERN IP region.
-- second remark that happened after the meeting closed: the CERN machine advisory board has asked the experiments to remain flexible in the location of the detector because they want to remain open about the crossing angle at the IP throughout the HL-LHC running. This means the LOS could change by ~15 cm during the running. This could be more if drastic changes in the IP happen.
4) Resnati had a number of questions --
i) What is the science goal in terms of energy resolution of the neutrino spectrum ? What feature would be useful to measure in the spectrum ?
--- This is obviously a key question for which we do not have an answer yet. For tau neutrinos there is a feature due to direct (D_s) decays versus indirect (tau decays) decays.
--- For numu and nue, the resolution is mainly needed to measure the cross section.
--- For nue the spectrum measurement above ~300 GeV is important since it also comes from heavy decays.
ii) If some part of the showering neutrino events is missing can it not be recovered by a fit. Is it necessary to have excellent containment for all events ?
--- MVD stated that it would be a conservative approach to start with good containment for events in the fiducial. The statistics of these showers is probably not Gaussian and is subject to big fluctuations due to losses of pions from the main interaction.
--- However, given that a 2 meter detector appears to have good containment, we might be able to get away with a 1.8 meter wide (high) detector.
--- It will be good to have some more detailed studies that focus now only on 1.8 meters.
iii) With 1.8 meter detector, the protodune style cryostat might be reasonable. We do not yet know what space is needed above the detector. If the design calls for insertion of the TPC from above, then we do not yet have enough understanding of the crane height.
5) Wenjie and Jianming suggested a strategy for tau reconstruction with the muon channel.
-- We need to understand the HADCAL and the muon tagger better.
-- for events in the fiducial as a function of vertex logitudinal location, what is the punch through rate as
a function of HADCAL depth ? How deep does the hadcal have to be to have a pure muon tag ?
-- What is the strategy for determining muon momentum.
a. can we use the TPC with counting of delta rays to measure the muon ?
b. is there any benefit to muon charge determination ?
c. can we calculate the acceptance of muons into the FASER magnet ?
6) MVD and Fillipo will find out what the plans are for the top space of the cavern.
7) What other issues do we need to settle before a nominal configuration of the detector ?