Cerenkov Calorimeter Studies for NLC

1
Cerenkov Calorimeter Studies for NLC
Oleksiy Atramentov
2
NLC requirements on performance

• The NLC design luminosity places rather tight
  constraints on the performance of NLC detectors

bunch-to-bunch time interval of 1.4ns suggests
almost speed-of-light response
large background of low energy e,? suggests a
detector with a 10-20 MeV energy threshold
large IR radiation dose will radioactivate the
detector mass, suggesting an energy threshold
above 8 MeV
GRad will damage detector components, requiring
radiation-hard detector
3
Cerenkov light is produced by EM shower charged
particles that pass gas gaps in absorbing
material.
10 GeV EM shower in Pb absorber with 2mm
reflective gas conduits
4
Gas Cerenkov calorimeter satisfies these
requirements.

• The Cerenkov photon signal exits the calorimeter
  volume at the velocity of light

• Gas has index of refraction n 1?, (? ?10-3),
  therefore energy threshold for electrons is high

• Decay products from radioactivation of the
  calorimeter mass are below Eth and therefore
  invisible

• A calorimeter made wholly of gas and metal cannot
  be damaged by any dose of radiation.

5
Lasagna (accordion) geometry
6
Cylindrical Lasagna geometry
Y
Z
X
7
Honeycomb geometry
8
Honeycomb geometry
Side view
9
Simulation I reflectivity
Change of reflectivity from 100 to 90 reduces
of photons by a factor of two, resolution
decreases due to depth fluctuation.
Therefore it is important to have reflectivity as
close as possible to 100
Rohit Nambyar
10
Optical Surfaces
Not only do we need reflectivity 100 but also
area should be large.
It is a notoriously difficult problem.
However high reflectivity (gt95) can be achieved
with a very smooth surfaces coated with Al.
11
Optical Surfaces

• Technique for obtaining optical quality of the
  metallic surfaces is well underway polishing
  machine is built surface roughness 30nm
  reflectivity measurements at grazing angles down
  to 200nm is coming (being fine tuned).

commercial glassAlMgF mirror (100/inch2)
Polished stainless steel shim (Ukraine).
scratch
12
Simulation II choice of gas
We would like to have gas with the highest
possible n.
gas n-1
CH4 0.00081
C2H6 0.00140
C3H8 0.00200
C4H8 0.00258
Watch, however, for resident light from
scintillation!
ß-butylene( n1.00131 NTP ) might be a better
candidate (than alkanes) scintillation/Cherenkov
10-5
13
Simulation III
Conversion from number of photons to energy seems
to be independent on the energy of incoming
electron.
Time spread 11ps!
14
DAQ new High Speed MPC
15
DAQ
16
(No Transcript)
17
Summary
Satisfies NLC luminosity monitor requirements

• Even more applications
• Beam Stabilization
• Veto SUSY gamma-gamma

• Very fast emptied every ns, resolution 10ps!
• RadiationHard
• low energy e silent
• robust