Detector WG
Francesco Forti
SuperB Workshop
LNF, 16-18 March, 2006
A SuperB Detector
• Basic conclusion from December
Workshop:
– It is possible to reuse large parts of Babar and
Belle with relatively minor technology changes
• Detector components
– Silicon vertex, with small radius pixels,
essential for reduced boost.
– Drift chamber
– DIRC style PID, with improved readout
– CsI(Tl) calorimeter in barrel, something faster
(LYSO) in endcap
– Existing coil
– LST style muon detectors
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Issue number 0
• Beam parameters
– Current and Collision frequency vary
wildly in different designs
• Was mA and 1MHz in december
• Raimondi – Round with extraction: 100 mA
and 10 MHz
• Raimondi – Flat(3) uncompressed: 1600mA
and 500 MHz
• Seeman – 4500 mA and 68 MHz
– Different options have very large impact
on technology choices and on the
reusability of Babar and Belle
components.
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Collision frequency
• With 0.1-1MHz fc one could exploit the
beam crossing time structure to relax
detector constraints
–
–
–
–
Drift time
Electronics shaping time
Crystal decay time
One the other hand a low fc implies overlapping
events (mainly Bhabha)
• The 10-50MHz regime is the LHC
electronics area
– It might be possible to exploit the bx time
structure, but is it useful ?
• At high fc (>100MHz) back to current
BFactories operation mode
– Continuous beam, no bx information
– no pileup
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Current
• Two consequences of higher
currents:
– higher background in the detector
• occupancy
• radiation damage
– power dissipation in the beampipe
requires water cooling
• more material
• larger radius
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Types and level of backgrounds
• Beam gas
• Synchroton radiation
•  Both proportional to current
– Should not be a problem at Superb
• They become a problem at higher currents
• Luminosity sources (eg radiative Bhabhas)
– Careful IR design. Bhabhas into the detector are there.
• Beam-beam interactions
– Potentially important
• Touschek background
– 1/E2. Improves with smaller asymmetry. But, much higher beam
density
• Thermal outgassing
– Due to HOM losses. Not an issue with small currents
• Injection background
– Not an issue because of damping rings scheme
• Maybe not true anymore with the 1 collision/turn scheme
• Bursts
– Due to dust. No real cure. Need robustness of detector
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Background bottom line
• Probably reasonable to assume
background is not larger than what with
have today
• Cannot claim a large background
reduction with present schemes
– Need to design a robust detector with the
enough segmentation and radiation hardness
to withstand surprises (x5 safety margin)
• IR design is critical
– Radiative Bhabhas
– Syncrotron radiation shielding
– Shielding from beam-beam blow up
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Issue number 1
• Boost
– lower boost advantegeous for machine
design
• Babar: 9 + 3.1 βγ=0.56
• Belle: 8 + 3.5 βγ=0.45
• SuperB?: 7 + 4 βγ=0.28
– we can afford to have a lower boost only
if the vertexing resolution is good:
• small radius beam pipe
• very little material in b.p. and first layer
– if not, then we should stay with higher
boost (0.45)
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Separation significance
• <Dz>/s(Dz) vs bg
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Detector components
• Vertexing
– Thin pixel layer glued on beam pipe
• Good aspect ratio for small radius (compared to
strips)
• Improves patter recognition robustness
• needs R&D
• Intermediate tracking
– Strip detectors
• More or less like the current detectors
• Reduction in thickness would be desirable, but not
essential
• Central tracking
– Drift chamber
• Solid state tracking not performant at low momentum
• Need to optimize cell size against occupancy
• Belle has developed a fast gas small cell DCH, but
with a degraded resolutions
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Detector components
• PID
– Čerenkov based PID – like DIRC
– Need development on readout
• Fast focusing DIRC
• TOP
– Endcap region requires special study
• Calorimeter
– Barrel part could be reused (see other talks)
– In the endcaps require smaller Moliere radius and faster
crystals  LYSO
• Higher currents and smaller Bhabha pileup may change
this conclusion
• Muon
– It doesn’t seem to be a problem
• Trigger/DAQ
– Calorimeter and/or tracking information
– Not substantially different from current schemes.
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