Henri Videau

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Calorimetry optimised for jets
Henri Videau Jean- Claude Brient Laboratoire
Leprince-Ringuet Ecole polytechnique - IN2P3/CNRS
Contribution to the session on jet
calorimetry CALOR2002
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The physics programme for a coming electron
linear collider is dominated by events with final
states containing many jets, dijets from H, W, Z
. We contend that, in the energy range under
consideration, the best approach is to optimise
the independent measurement of the tracks in the
tracker, the photons in the electromagnetic
calorimeter and the neutral hadrons in the
calorimetry, together with a good lepton
identification. This can be achieved with a good
tracker and a high granularity calorimetry
providing particle separation, through an
efficient energy flow algorithm.
But we do not contend that this is a universal
panacea
Studying that program from the calorimetric side
on hardware and software issues is the goal of
the CALICE collaboration
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Jets at the linear collider
_
radiative qq at 500 GeV
WW at 800 GeV

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The analytical energy flow approach has been
widely used at LEP
and the energy ditributions are quite similar
ALEPH
but LEP detectors had some
draw- backs
coil in the middle
projective cracks
poor longitudinal segmentation
2d digital read- out in the HCAL
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Impact of the jet resolution on the physics
programme
Parametrising
a 0.3 Þ 6s
6 jets L1 ab-1
a 0.6 Þ 3s
work in progress
a 0.3 Þ 0.6 loosing 45 of L
in the separation ZZ / WW
a 0.3 Þ 0.6 loosing 40 of L
a lot more work to assess the effect on all the
programme
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separation ZZ / WW
0.6
0.3
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Reminder on the analytical energy flow basics
The energy flow of a jet is written as the sum of
its components
the charged particles make about 60 of the
energy and, being of rather low energy, are
much better measured by the tracker
Isolate the 10 neutral hadron energy
Argument Þ
Such a method relies more on separation of
particles than on intrinsic energy
resolution
Þ
far enough from the interaction point small
radiation length small interaction
length matched granularity
Inside coil
Compactness
seeing the mips
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To profit from that we need
a good tracker, not so much on momentum
resolution but good track efficiency,
small rate of fake energetic tracks good
V0 identification small rate of
reinteraction
a good electromagnetic calorimeter, not so
much on resolution but good photon
efficiency, even close to tracks small rate
of fakes from hadronic debris good electron
identification (prompt)
a good hadron calorimeter to identify muons to
disentangle neutral hadronic showers from charged
ones to measure their energy
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Elements for a solution concerning the calorimetry
Density, good separation electromagnetic/hadron
sandwich tungsten / silicium
24 X0
40 layers
no projective cracks
thickness lt 20 cm
ECAL
cells matched to the Moli?re radius 1 cm2
good efficiency to mips. noise 1/10 mips
Radiator adapted to separation/resolution
HCAL
small cells read digitally
A solution with scintillating tiles is also
studied within CALICE
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Aspect of the detector
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Effect of going
from iron
Resolution
to expanded tungsten
Separation
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Old results
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(No Transcript)
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All the studies presented here have been done
using Mokka an application on Geant4
http//polywww.in2p3.fr/tesla/calice_software.html
Are these performances kept at high energies?
The jet energies have been obtained in a multi
step process
knowing the extrapolation of the charged
tracks reconstruct the photons in the Ecal
subtract the cells of these photons identify
the hadrons estimate the energy of the neutral
hadrons
through a neural net
Different other approaches thermodynamical or
neural net
This is the cornerstone of jet calorimetry
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Seeing a W dijet impact on the first 4 X0 of the
calorimeter in q f projection
The square is 100 mrad wide
X generated g's 8 charged 4
neutral had. 1 O reconstructed g's
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Some results at 800 GeV on photons
number of reconstructed g's versus number of
generated g's
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Energy distribution for true photons and
reconstructed ones including fakes
GeV
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Energy distribution of generated true
photons and reconstructed true photons
A reconstructed photon is associated to a true
one if more than 75 of its energy comes from it.
GeV
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Difference between the true photon energy and
the reconstructed one per event.
The fit is done with 2 gaussians.
Norm1 101.88 Mean1 0.23
GeV s1 7.01 GeV Norm2
35.84 Mean2 - 0.02 GeV s2
18.49 GeV c2/dof 1.1
GeV
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Photon reconstruction efficiency at low energy
GeV
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Photon reconstructed energy versus true energy
GeV
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Energy photons/evt kin versus rec.
Distribution of event photonic true energy and
reconstructed
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Distribution of event photonic true
multiplicity and reconstructed
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Neutral hadron energy distribution
GeV
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A more complete reconstruction of the jets at
high energy is under way.
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Few more informations about the digital HCAL
solution.
The sensitive detector
A gas detector, compact, efficient to mip, high
signal and cheap!
Streamer or Geiger wire detector
information from DHCAL subcollaboration IHEP,
Interphysica, LLR, MEPhI, Seoul U.
RPC's
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1x1 cm2
Pads outside
Gap 1.2 mm
Glass plates 1 mm
TFE/N2/IB 80/10/10
Pads inside
Efficiency to mip gt 98
Signal on 50 W 3 V
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Scheme for a digital HCAL signal detection
Fe or ..
Chip
PCB
Pad
Glass
insulating layer
Spacers
resistive layer
Fe
conductive layer
insulating layer
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Read out scheme for a 64 channel chip
64 million channels
Cost 0.2 Euros/ch
Reading the chips through a token ring
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Conclusions
To extract the physics produced in an electron
linear collider below 1 TeV, a measurement of the
jet energies with a stochastic term at a level of
0.3 or below seems mandatory.
Such a precision does not seem out of reach
with an adequate calorimetric hardware
and a proper software.
We have a roadmap with hardware developments
and prototypes
(2004) and with software
imagination
Join the worldwide effort of the CALICE
collaboration
http//polywww.in2p3.fr/tesla/calice.html