Linear Collider Vertex
Detector R&D
Natalie Roe
UCSC Linear Collider Workshop
June 27-29, 2002
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R&D: General Goals
& Strategy
R&D should be undertaken to mitigate risk and
ensure a project will succeed
Technical risk for new, unproven techniques or
significant extensions of existing methods
Schedule risk for long-lead development or
procurements
R&D strategy: identify areas of technical or
schedule risk with biggest physics impact
Focus on most critical areas needing early R&D
investment to ensure the project’s success and to
maximize the physics reach
N. Roe LBNL LC Workshop 6/28/02
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What type of R&D is required
for LC Detectors?
Hard to argue schedule risk at this stage…
There is time for new technical developments
with significant physics impact
First step is to write down machine constraints
and physics-driven requirements
Next, devise a focused R&D plan to address the
technical issues associated with the
requirements that:
• a) have biggest physics impact, and
• b) are most challenging
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Requirements for an
LC Vertex Detector
Accelerator-related requirements, such as
Beam-pipe radius, thickness, machine
stayclear
Radiation levels & background rates
Event rate and time structure of collisions
etc.
Physics requirements, eg vertex flavor
tagging, driven by:
Impact parameter resolution
Two-track/two-hit separation
Efficiency, fake track rate
Solid angle N.coverage
Roe LBNL LC Workshop 6/28/02
etc.
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Quantifying Requirements:
Accelerator constraints
Machine design is not yet finalized
Detailed design studies exist for several machines consider worst case parameters
Experience suggests conservative assumptions
eg, radiation levels generally get worse with
more realistic machine studies, bkgds go up etc.
Critical design areas may require iteration with
accelerator experts, additional efforts on
machine simulations
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Quantifying Requirements:
Accelerator constraints I
 Beam pipe radius: determined by beamstrahlung and
synchrotron radiation backgrounds. Present thinking:
NLC: r = 1 cm for z = ± 2.5 cm, then increases to 2.2 cm
Tesla: r = 1.4 cm
 Radiation & background rates:
Tesla:
beam-beam e+e- pairs produce 0.03 hits/mm2/BX, resulting in
~20kRad/yr ionizing radiation for B= 4T and r = 1.5 cm
Neutron fluence ~ 109 1 MeV neutrons/cm2/yr
NLC:
beam-beam e+e- pairs produce 3 hits/mm2/train =0.015 hits/mm/BX
at B=3T and r = 1.2 cm
Neutron fluence estimates vary from 107 to 1011 n/cm2/year
Maruyama - 2.3 x 109 n/cm2/year
What about beam gas backgrounds?
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NLC Bkgds
B=6T, no crossing angle
See talk this morning by MaruyamaB= ?
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Quantifying Requirements:
Accelerator constraints II
 Time Structure & Event Rates
B
C
A
Tesla500
A 200 ms
B
337 ns
C
950 us
C/B 2820
C/BA 14kHz
L(1034) 3.4
Tesla800 NLC
250 ms
8.3ms
176ns
1.4 ns
860us
266 ns
4886
190
19.5kHz 23kHz
5.8
2.0
 Layer 1 hit occupancies (bkgd dominated):
At NLC 190 x 0.015 hits/mm2/BX = 2.85 hits/mm2/train = 1 x 10-3
occupancy for 20x20um pixels => read out between bunch trains
At Tesla 2820 x 0.030 hits/mm2/BX = 84.5 hits/mm2/train = 3.4 % occ
for 20x20 um pixel => readout during train
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Reality Check: NLC vs
Tesla background rates
 Tesla = 0.03 hits/mm2/BX at 4T, r=1.5 mm
 NLC = 0.015 hits/mm2/BX at 3T, r=1.2 mm
 Why are NLC bkgds lower with smaller B field and radius?
 Bkgds/BX should be proportional to lumi/BX
Tesla: 3.4x1034 / 14kHz
NLC:
2x1034 / 23kHz
Factor of 3 lower lumi/BX at NLC => compensated for
by lower B and r
 More detailed comparisons needed, eg compare rates at
same B field and radius.
 Understand beamgas and synchrotron backgrounds and
compare
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Quantifying Requirements:
Accelerator constraints III
 Beam pipe thickness (scale: 100 um of Si ~ 0.1%X0):
Tesla studies assume a beampipe of ~ 0.25 mm Be = 0.07%X0
Matches first detector layer thickness of 0.06% X0
NLC studies: assumptions ranging from 0.160 - 0.180 mm Be (?)
NLC beampipe has stepped radius from 1.2 -> 2.4 cm to avoid
backgrounds - does this create problems with showering?
 Multiple scattering in beampipe sets scale for thickness
of first detector layer and for point resolution at low p
 Radius and thickness of beampipe are critical inputs for
vertex detector; think of beampipe as part of detector
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Physics Requirements I

Flowdown of requirements:
1)
2)
3)
y
Science requirement: Precision on particular physics
quantities, eg error on Br(H-> cc)
Performance requirement: high-level event parameter, eg
specified flavor tag purity at a given efficiency
Detector requirement, eg impact parameter resolution or
tracking efficiency vs fake rate for a given detector subsystem
A number of LC vertex detector studies have
already been performed at all 3 levels.
y
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Selected Previous Vertex
Performance Studies
 Sinev: http://blueox.uoregon.edu/~jimbrau/talks/IEEE-99/ieee99.pdf
 Abe(ghost tracks):
http://www.slac.stanford.edu/~toshi/LCDstudy/toshi_ghost.pdf
 Schumm (vertex parameters):
http://scipp.ucsc.edu/~schumm/talks/fnal2000/fnal2000_ag.ps
 Oregon vertex detector parameters study:
http://blueox.uoregon.edu/~jimbrau/LC/vxd-studies.PDF
 Chou (H->cc): http://wwwsldnt.slac.stanford.edu/nld/meetings/ChicagoJan2002/BRHccJan8.pdf
 Potter et al (Higgs branching ratios ):
http://www.slac.stanford.edu/econf/C010630/forweb/P118_potter.pdf
 Iwasaki - top:
http://www.slac.stanford.edu/~masako/LC_study/Chicago2002/Top.pdf
 Walkowiak:http://www.slac.stanford.edu/~walkowia/lcd/talks/
chicago2002/lcChicago010802-1.pdf
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 LCFI studies : ( http://hep.ph.liv.ac.uk/~green/lcfi/home.html )
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Physics Requirements II
 Impact parameter resolution:
Simplified formula for i.p. resolution in 2 layer device with
measurements at r1,r2 and errors   :
r2   1  r1   2 
 

  
r2  r1  r2  r1 
1,2   ms   pt ;
0.014  r X 0
 ms  3/ 2
sin   cp
Dominated by resolution of first hit
Multiple scattering dominates for low momenta; material in beampipe
and first detector layer must be minimized, along with radius of 1st hit
Intrinsic point resolution dominates at high momenta - includes
misalignment effects N. Roe LBNL LC Workshop 6/28/02
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Impact Parameter Resolution
Studies - Schumm
10 um
Pt resolution
dominated
M.S.
dominated
2-3 um
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Impact parameter study




resolution
ladder thickness
beampipe radius
outer radius
http://scipp.ucsc.edu/
~schumm/talks/fnal2000/
fnal2000_ag.ps
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“Standard L2” = 1.2 cm beampipe, 160 um Be, 5 um resolution
B. Schumm
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How does i.p. resolution
affect flavor tagging?
Compare i.p. resolution to typical impact
parameters at LC
For B decay products, i.p. ~ 300 um>>10 um
B-tagging should not depend strongly on pt resolution,
beampipe radius or thickness
For charm decay products, i.p. ~ 80-100 um
Might see mild dependence
To correctly assign tracks to both b and c vertices to
determine charge or mass will be more challenging
Needs a level 2/level 3 study
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Study of Charm Tagging
 Mild detector dependence: 15%
change going from 10 um, 1.0%X0
to 1 um, 0.03%X0 detector
 Beampipe radius = 1 cm
 What was the beampipe thickness?
 What bkgd levels?
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A. Chou
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Error on Higgs BRs - Oregon Study
MH = 140 GeV/c2 ,
s = 500 GeV,  L = 500 fb-1
RINNER(cm)
1.2
2.4
1.2
2.4
1.2
hit res (mm)
5.0
5.0
3.0
3.0
4.0
H  bb
3.8%
3.8%
3.8%
3,8%
3.8%
H  tt
10%
10%
10%
10%
10%
H  cc
46%
47%
42%
46%
42%
H  gg
23%
22%
22%
22%
22%
H  WW*
3.5%
3.5%
3.5%
3.5%
3.5%
Error on Higgs branching ratios is essentially independent of radius and
resolution, with mild dependence for H-> cc
Potter, Brau, Iwasaki
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http://blueox.uoregon.edu/
~jimbrau/LC/vxd-studies.PDF
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Vertex R&D - paper studies &
simulations
 Write down assumptions for NLC/Tesla/JLC beampipe, backgrounds,
radiation levels; compare/rationalize different results, get improved
estimates if possible (=>run accelerator simulations)
 Consider dependence of i.p. resolution on beampipe thickness as well
as detector thickness; engineering study of beampipe construction?
 Consider effects of material at large radius as well (cryostat can
decouple vertex from outer tracking, reduce effective lever arm for
tracking)
 Consider design where L1 is special: thinner, faster readout, better
resolution. (may want L2 also for backup)
 Document a set of science-driven requirements (goals) for vertex
detector performance, with a clear link from specific measurements to
the required performance parameters.
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R&D: Hands-on studies
Leading candidates: CCDs, hybrid pixels, active
pixels … + time to develop new ideas!
General areas for R&D
Radiation hardness
Readout speed, especially in Tesla context
Minimizing material thickness including mechanical
structures and beampipe
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Summary
There are interesting vertex detector issues to
address both in simulation and in hands-on R&D
To coordinate US efforts, please provide a brief
description, list of participants and proposed
budget
Should aim to cooperate on global level with
international partners
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