Muon Reconstruction and Vertex Constraint Giovanni Abbiendi Bologna CMS meeting, 20 November 2007

Momentum Resolution

L1 Muon Trigger Rates

Muon Trigger Rates (L1 - L2 - L3) Improving the Pt resolution the trigger rate decreases

Study of the vertex constraint in StandAlone Muon Reconstruction (G.A.+A.Perrotta) From CMSSW 1_3_0 StandAloneMuons are constrained to the vertex in transverse 2D (i.e. to the beam axis) as the last step in reconstruction, as it was done in ORCA. Both the collections (unconstrained and refitted) are presently kept in the Event. The uncertainty in the constraint was initially set to the default inherited from ORCA, i.e. 15 μm on x,y. We considered alternate values of 1mm or 1cm to allow a lower weight to the vertex constraint (this would take into account a reduced resolution at the HLT-trigger level and possible misalignments). Our goals:  Check the pT resolution obtained on selected signal samples as a function of the uncertainty of the constraint  Check the effects of the constraint on the background, in particular the dominant one from pion and kaon decays in flight: Are there systematic biases on the reconstructed pT for non-prompt muons ? Is the background rate potentially increased ?

Muon samples used in the study The following definitions will be adopted in this presentation: PROMPT MUONS = either particle-gun generated muons or muons from direct W or Z decays NON PROMPT MUONS = muons from in-flight π or K decays MUONS FROM HF = muons from   or from c- and b- hadrons decays We used recent MC samples Re-reconstructed with CMSSW 1_3_1 Wmunu : mc-onsel-120_PU_Wmunu-DIGI-RECO-NoPU Single MuPlus: mc-physval-120-SingleMuPlus-Pt5To200 Enriched (inclusive) muons Type 1: mc-onsel-121-MuEnrichType1-DIGI-RECO-NoPU

1/P T resolutions Black: no constraint Blue: vtx constraint, 1mm Green: vtx constraint, 1 cm Single μ + 5<P T <200 GeV/c W → μ PROMPT Enriched μ NON PROMPT Enriched μ HF

η(rec) – η(gen) Black: no constraint Blue: vtx constraint, 1mm Green: vtx constraint, 1 cm Single μ + 5<P T <200 GeV/c W → μ PROMPT Enriched μ NON PROMPT Enriched μ HF

φ(rec) – φ(gen) Black: no constraint Blue: vtx constraint, 1mm Green: vtx constraint, 1 cm Single μ + 5<P T <200 GeV/c W → μ PROMPT Enriched μ NON PROMPT Enriched μ HF

 2 of the refit at vtx Blue: vtx constraint, 1mm Green: vtx constraint, 1 cm Single μ + 5<P T <200 GeV/c W → μ PROMPT Enriched μ NON PROMPT Enriched μ HF (NB: overflow in the last bin)

Vertex constraint: when do apply? The vertex constraint improves the fit of the StandAlone muon if the muon comes directly from the vertex, or close by (not really a surprise…) Muons originating from around the main interaction vertex profit of the refit with a 2D vertex constraint. At the contrary, non prompt muons originating far away from that vertex get worsened by such a vertex constraint. In particular, non prompt muons are biased towards lower P T : Good for DAQ and trigger rates, if you want to kill them at HLT; Bad for the search for muon-like new physics objects, if originating from late decays of new particles. Try to identify muons originating far from the main interaction vertex, in order to decide whether to use the refitted StandAlone muon or the unconstrained STA:

dxy and dxyError (in cm) Black: single muons Red: W→μ (only prompt muons) Blue: enriched muon sample, type 1 (only non prompt muons) Green: enriched muon sample, type 1 (only [extra-low p T ] muons from taus and heavy quarks)

Best option: refit the StandAlone muon with the vertex constraint only if the muon comes from nearby the main interaction vertex; otherwise, keep the unconstrained StandAlone muon. dxy() and dxyError() methods of reconstructed unconstrained StandAloneMuon tracks can be used to flag muons originating from the beam spot. From our previous plots, a possible prescription could be: Reconstruct unconstrained StandAlone muons Substitute them with a vertex constrained StandAlone muon (with ~1 mm weight) if the dxy significance of the unconstrained muon is below 5 AND |dxy| is below ~25 cm dxy threshold These were our conclusions: after that the default weight used in standard StandAlone Muon Reconstruction has been set to 1 mm. This is used both for Offline and for HLT.

Simulation improvements going on… Better study of backgrounds (mainly decay in flight of pions and kaons, hadron punchthrough) Improving the association between tracker tracks and muon chambers standalone tracks Improve reconstruction validation on complex events (like ordinary minimum-bias events) or for specific difficult cases like very high energy muons To do this, we need to develop a Hit-based associator which links each RecHit to a SimHit, to know which particle made it. This is currently not possible particularly on DT (it was somewhat done at ORCA times). Si-Tracker has already a set of tools to this purpose. CSC has already something, RPC have probably to start. G.A. committed for DT. Need to study a bit the simulated digitization, probably introduce a new SimDataFormat, write a tool associator class to match Reco to Sim and viceversa, and integrate with other muon detectors and Si- Tracker

Proposed by Alessandro and Marco at the Barrel Muon workshop (Oct 07) And previously at SLHC meeting (July 07) Ideas for a Muon Trigger Upgrade at SLHC New CMS Internal Note CMS IN-2007/058