Preliminary Muon Punchthrough Studies D. Hedin 5/2/00

A. Overview

  • Punchthroughs: a hadron which enters thecalorimeter and produces hits in the muon system.
  • Most punchthroughs are due to tertiary pions orkaons within the hadron shower which decay to muons.
  • Energy of exiting muon typically .05-.10 that of entering hadron.
  • Punchthrough rates and exiting muon momentum distributions have been measured. GEANT produces rates and distributions in agreement with data.
  • See Green and Hedin, NIM A297, 111 (1990) and Green, Fenker, Haggerty, Martin, Takasaki, Yamada, Kunori, Rapp, Owen, Grannis, Hedin, NIM A244, 356 (1986) which contains the punchthrough probability vs p.
  • The detector thickness is such that punchthroughs through the iron are nota major problem (and so were not for Run I). But for a-layer muons, punchthroughs will be a substantial background.
  • Can reduce punchthrough rates by correlating exit muon momentum, position, and direction with that determined in the inner tracker.

    B. Estimates of single muon rates

  • use 200,000 ISAJET jets with ET from 5-40 GeV
  • simple parameterization of detector thickness, punchhtrough probability, exiting momentum
  • the eta distribution and pt distribution of particles with |eta|<2 which exit the back end of the calorimeter- .028 of events have at least one with a split of about .05:.51:.44 between prompt (b/c decays), pi/K decays, and punchthroughs. The pt distribution of the punchthroughs depends on whether one uses the entering or exiting momentum (the plot showing the sum utilizes the exiting).
  • A simple cut requiring the inner tracking pt to be less than 3.5 can reduce the punchthrough fraction by about 2: punchthrough fraction vs eta
  • The eta distribution of those that exit the iron shows that punchthroughs mostly occur in the thin region, with .002 of events have at least one particle from any source with a split of about .23:.73:.04 between prompt (b/c decays), pi/K decays, and punchthroughs.

    C. Estimates of dimuon rates

  • use same 200,000 ISAJET jets with ET from 5-40 GeV
  • 97 events with 2 muons |eta|<2; 85 both a-layer (only 1 where both are prompt)
  • 75% of a-layer dimuons have 1 or more punchthroughs
  • Reduce a-layer dimuon from 85 to 32 if require pt < 3.8 GeV/c