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
