Physics

DELPHES

The muon collider Delphes detector card can be found in DELPHES releases (starting from v3.4.3pre05) [1]. 

The Muon collider Delphes detector description represents a target, based on the current knowledge of what can be probably achieved in the future. It should by no means be intended as the final performance of a Muon Collider detector. Rather, it is aimed to be used for phenomenological explorations, to help assess the reach and determine the physics goal of a muon collider at various center of mass energies. To this end, users are highly encouraged to explore variations around the baseline specifications provided in this delphes card. 

The physics case for a muon collider should be assessed at the highest possible energies (sqrt(s)=10, 14, 30 TeV). Therefore the requirements for central high pT physics are very similar to the FCC-hh [2] and CLICdet [3]. Moreover, the existing muon collider concepts [4] for the muon collider are largely inspired from the CLIC detector. 

The resulting Muon collider Delphes detector card is therefore a hybrid between these two detector concepts. The parameterisation of the reconstruction efficiencies and resolutions for high pT charged particles tracks (including muons) is inspired from the FCC-hh [5,6]. 

The Muon collider detector card does not include any simulation of the beam induced background (BIB), which is assumed to be subtracted by means of specific detector choices and advanced reconstruction techniques. Calorimeters have the same performance as in CLICdet [7,8], and Delphes particle-flow combines the track and calorimeter information to form particle-flow candidates, which in turn are used as input to jet clustering algorithms and missing energy. Jet clustering is largely inspired from CLIC [7,8], and uses the Valencia algorithm [9] in both inclusive and exclusive modes. Electron and photon reconstruction and identification efficiencies has been parameterised after CLIC full simulation results, as well as BTagging efficiencies for various working points  [7,8]. Tau reconstruction efficiency is instead taken from CMSPhase II/ FCC-hh [5,6]. 

A specific and separate muon collection called ForwardMuon has been added for neutral vector boson scattering studies.

A selection of performance plots of the target Muon Collider delphes detector card can be found in Ref. [10].

Users are highly encouraged to vary detector parameters in the Delphes card in order to assess the physics potential of the Muon collider at various center of mass energies. The baseline object resolutions kinematic/geometrical acceptance assumes no BIB. 

Its effect can be studied a posteriori by varying the detector performance. 

A non-inclusive list of suggested detector performance variations to be studied in order to assess the physics requirement of the Muon Collider detector are:

  • pT acceptance of final state objects (pt = [10-50])
  • angular detector acceptance. The baseline detector card assumes a maximum rapidity of eta=2.5. Ranges between [1.5, 3.0] can be studied. This simulates various assumptions on the dead cone introduced by the nozzle shielding. 
  • forward muon performance: no detector concept currently exists for reconstructing muons in the challenging BIB environment at small angles. Both the acceptance and the resolution for reconstructing such muons can be explored. This can studied in the context of neutral vector boson scattering. 
  • Track and Calorimeter resolutions can be degraded by factor 2-4 in physics studies that involve resonant signals. Alternatively, the jet energy resolution can also be degraded by similar factors. This can be studied for instance in the context of double and triple Higgs production in fully hadronic final states.
  • Identification efficiencies, in particular lepton, photons ID, and heavy flavour tagging. This can be also be studied for instance in the context of double and triple Higgs production where b/c/light flavour discrimination can be important. 

References:

[1] Delphes muon collider card - https://github.com/delphes/delphes/blob/master/cards/delphes_card_MuonColliderDet.tcl

[2] FCC-hh CDR - https://fcc-cdr.web.cern.ch/#FCCHH

[3] CLIC CDR - https://project-clic-cdr.web.cern.ch/

[4] Detector and Physics performance at a muon collider - https://arxiv.org/pdf/2001.04431.pdf

[5] Requirements from physics for the FCC-hh - https://cds.cern.ch/record/2717785

[6] Delphes parameterisation of the FCC-hh detector - https://cds.cern.ch/record/2717698

[7] Delphes CLIC validation - https://indico.cern.ch/event/953063/contributions/4079881/attachments/2129466/3585854/UlrikeSchnoor_2020-08-20-DelphesMuColl.pdf

[8] A Delphes card for the CLIC detector - https://arxiv.org/pdf/1909.12728.pdf

[9] Jet reconstruction at high-energy ee colliders - https://arxiv.org/pdf/1607.05039.pdf

[10] Muon collider card performance - https://indico.cern.ch/event/953063/contributions/4004535/attachments/2101907/3533828/delphes_card_mucol.pdf