Transcript A New Window to Top: Measuring the Top Quark Mass without

SLHC Physics and B tagging
Joe Incandela
University of California, Santa Barbara
10/12/06
Outline
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The SLHC Physics Argument (cf. Eur. Phys. J. C39 (2005) 293)
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Tracking and tagging at high luminosity
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ATLAS B tag study
CMS Heavy Ions:
Lepton track triggers
B tagging in CMS @ LHC.
B tagging in CMS @ SLHC:
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The physics case as from the viewpoint of the tracker
Does it become less important?
What would be needed to make it work as well as at LHC?
Some remarks
SLHC Physics and B-tagging : FNAL Pixel Workshop, October 12, 2006 J. Incandela (UCSB)
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Disclaimer
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This talk was put together on short notice and mostly in an
airplane…
Not intended as a final word on anything…
In the spirit of a workshop – it is meant mostly as a point of
departure for more work and discussion
SLHC Physics and B-tagging : FNAL Pixel Workshop, October 12, 2006 J. Incandela (UCSB)
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SLHC Physics
P.Allport @Hiroshima ‘06
SLHC Physics and B-tagging : FNAL Pixel Workshop, October 12, 2006 J. Incandela (UCSB)
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As viewed from the tracker
If no light higgs seen,
this will be a major
emphasis of SLHC
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Can divide SLHC physics into several relevant categories
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Relies on tracking and/or b tagging
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Requires absence of a track and/or b tag
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Requires both 1 and 2
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E.g. Vector boson resonance
Need to identify high energy leptons
Veto events with b tags to help eliminate tt background
SLHC Physics and B-tagging : FNAL Pixel Workshop, October 12, 2006 J. Incandela (UCSB)
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Leptons are top priority
All new ground.
up to 6 l final states!
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Multi-boson couplings & Higgs pair production
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Both rely upon efficient detection of leptons
Leptons should be the 1st priority of SLHC tracking
Only sensitive if H
above threshold to
decay to VB pairs-
170 ≤ MH ≤ 200
SLHC Physics and B-tagging : FNAL Pixel Workshop, October 12, 2006 J. Incandela (UCSB)
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The case for track triggers @ L1
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From Gianotti et al. Eur. Phys. J. C 39, 293-333(2005)
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Larger event size due to higher occupancy means that 100 kHz L1 rate
will probably need to be maintained…”such a strategy… implies raising
transverse momentum thresholds on candidate electrons, photons,
muons, etc. and using less inclusive triggers…”
SLHC Physics and B-tagging : FNAL Pixel Workshop, October 12, 2006 J. Incandela (UCSB)
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Higgs
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Discovered Higgs at LHC
At SLHC interested in rare
decays, couplings to
fermions and bosons.
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HZ, H  +- …
H and WH  ln
Comparison tells us about Htt
coupling since gg  H
proceeds via top loop
Or if SUSY seen, we would
want to extend our reach for a
2nd and heavier SUSY higgs
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Need b/tau tagging.
SLHC Physics and B-tagging : FNAL Pixel Workshop, October 12, 2006 J. Incandela (UCSB)
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Degradation of b tagging & Electron id
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No studies by CMS yet.
ATLAS has studied current
detector w/full simulations
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Mistagging rises x3 to x8 for
fixed 50% b tag rate
Rate of jets faking electrons
at fixed 80% electron
efficiency nearly doubles.
SLHC Physics and B-tagging : FNAL Pixel Workshop, October 12, 2006 J. Incandela (UCSB)
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B tagging in CMS
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Very similar to Tevatron tagging
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Track tags
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Jet probability
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Number of tracks (2 or 3) above some impact parameter significance
Vertex tagging
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Effectively similar in many ways to CDF SECVTX algorithm but
developed in a much more intelligent way*
* ( I can say this since I was one of the original developers of the CDF algorithm)
SLHC Physics and B-tagging : FNAL Pixel Workshop, October 12, 2006 J. Incandela (UCSB)
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Inputs to Combined B tag Algorithm
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Jet Reconstruction: Iterative Cone Algorithm with cone size = 0.5
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Track Reconstruction: CombinatorialTrackFinder
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Vertex Reconstruction:
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≥ 8 hits in total (pixel + strips) and ≥ 2 pixel hits
pt > 1 GeV/c
χ2/dof < 10
dxy < 2 mm (transverse impact parameter)
Primary Vertex: Global Reconstruction
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PVFPrimaryVertexFinder with reduced pt=0.7 GeV/c for tracks
See CMS AN 2005/043 (C.Piasecki, C.Weiser et al.)
Cone based association of tracks to jets: ΔR < 0.3
SLHC Physics and B-tagging : FNAL Pixel Workshop, October 12, 2006 J. Incandela (UCSB)
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Two Definitions
1) “Physics” Definition:
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Match reconstructed jets to
“initial” partons from the primary
physics process (within ΔR < 0.3
of reconstructed jet cone)
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Try to find the parton that most
likely determines the properties
of the jet and assign that flavour
as true flavour
e.g. For tt the initial partons
are: 2 b jets from top decays
2 non-b jets per hadronic W
decay & no initial gluon jets
jets from radiation are not
matched with full efficiency
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here, the “final state” partons
(after showering, radiation) are
analysed (also within ΔR < 0.3 of
reconstructed jet cone)
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2) “Algorithmic” Definition:
Gluon jets splitting to c- or bquarks are labeled “gluon”
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jets from radiation are matched
with full efficiency
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if there is a b/c within the jet
cone: label it as b/c otherwise:
assign flavour of the hardest
parton
SLHC Physics and B-tagging : FNAL Pixel Workshop, October 12, 2006 J. Incandela (UCSB)
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The Algorithm
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Inclusive vertex reconstruction in jets using the “Trimmed Kalman
Vertex Finder”;
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select secondary vertex candidates:
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100 μm < Lxy > < 2.5 cm
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Significance (Lxy/σ) > 3
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Invariant Mass of tracks in vertex candidate < 6.5 GeV
Reject if vertex has two oppositely charged particles with invariant mass
within 50 MeV of K0 mass
3 Categories: depend on result of inclusive vertex reconstruction:
1.
2.
3.
“RecoVertex”: at least one accepted SV candidate found
“PseudoVertex” : built from tracks incompatible with the primary vertex
(d/s > 2), if at least two such tracks are present
“NoVertex”: the rest
SLHC Physics and B-tagging : FNAL Pixel Workshop, October 12, 2006 J. Incandela (UCSB)
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Vertex Categories
b
c
uds
QCD 50-80
|η| < 2.4
SLHC Physics and B-tagging : FNAL Pixel Workshop, October 12, 2006 J. Incandela (UCSB)
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Input Variables I
Lifetime signed 2D Track Impact Parameter Significances
“RecoVertex”
“PseudoVertex”
Enter for all categories into the final discriminator
Furthermore:
QCD 50-80
-sort tracks in decreasing order of IP significance
|η| < 2.4
-compute mass for tracks
-look at IP significance of track pushing the mass above threshold related to
charm hadron mass (here: 1.5 GeV)
SLHC Physics and B-tagging : FNAL Pixel Workshop, October 12, 2006 J. Incandela (UCSB)
“NoVertex”
b
c
uds
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Input Variables II
Additional secondary vertex related variables for
category 1 (“RecoVertex”)
b
c
inv. mass of charged
particles at SV
uds
multiplicity of charged
particles at SV
PV-SV
σPV-SV
QCD 50-80
|η| < 2.4
C.Weiser
A Combined SV Based B-Tagging Algorithm in CMS
CMS Phys. Meeting 6/12/2005
Input Variables III
Additional secondary vertex related variables for
category 1 (“RecoVertex”)
fractional charged
energy at SV
b
c
uds
rapidities of
charged particles
at SV
C.Weiser
A Combined SV Based B-Tagging Algorithm in CMS
IP sign. of first track
above charm mass
QCD 50-80
|η| < 2.4
CMS Phys. Meeting 6/12/2005
Input Variables IV
Additional secondary vertex related variables for category 2 (“PseudoVertex”)
inv. mass of charged
particles at SV
multiplicity of charged
particles at SV
rapidities of
charged particles
at SV
b
c
uds
C.Weiser
A Combined SV Based B-Tagging Algorithm in CMS
fractional charged
energy at SV
IP sign. of first track
above charm mass
QCD 50-80
|η| < 2.4
CMS Phys. Meeting 6/12/2005
Final Discriminator II
QCD 50-80
|η| < 2.4
b
c
udsg
b
c
udsg
Plots have been obtained by scanning the
cut on the discriminator
SLHC Physics and B-tagging : FNAL Pixel Workshop, October 12, 2006 J. Incandela (UCSB)
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QCD 50-80 GeV
SLHC Physics and B-tagging : FNAL Pixel Workshop, October 12, 2006 J. Incandela (UCSB)
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Dependence On PT and η
non b-jet efficiency
Misidentification efficiencies for fixed b-tagging efficiency of 50%
|η| < 2.4
QCD 50-80
● uds
* g
▲c
pt
loss of tracks in this bin!
SLHC Physics and B-tagging : FNAL Pixel Workshop, October 12, 2006 J. Incandela (UCSB)
η
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Heavy Ions as a proxy for pp@SLHC
SLHC Physics and B-tagging : FNAL Pixel Workshop, October 12, 2006 J. Incandela (UCSB)
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HI Algorithm
Default pp algorithm with following modifications:
1) Trajectory Seed Generation
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Trajectory Building
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3)
Includes all material effects
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multiple scattering
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energy loss
Special error assignment to merged hits
Trajectory cleaning
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Three pixel hit combinations (Pixel triplets)
Primary vertex constraint
Allow only one track per trajectory seed: best 2
Trajectory Smoothing
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Final fit with split stereo layers
SLHC Physics and B-tagging : FNAL Pixel Workshop, October 12, 2006 J. Incandela (UCSB)
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Acceptance
Require
8 strip layersacceptance
(~12 hits) and 3 pixel
layers.
Geometrical
~80%
SLHC Physics and B-tagging : FNAL Pixel Workshop, October 12, 2006 J. Incandela (UCSB)
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Track quality Cuts
Good
reconstruction
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More than 12 hits on track (stereo layer => 2 hits)
Require fit probability > 0.01
(Cut on compatibility with primary vertex)
SLHC Physics and B-tagging : FNAL Pixel Workshop, October 12, 2006 J. Incandela (UCSB)
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Fakes
• Efficiency
o
Fake Rate
nhit > 12
• Efficiency
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Fake Rate
nhit > 12
pchi2 > 0.01
looser
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Fakes substantially higher than at LHC, as seen by ATLAS.
SLHC Physics and B-tagging : FNAL Pixel Workshop, October 12, 2006 J. Incandela (UCSB)
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Trajectory Building
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Number of candidates drops fast as you move to larger
radius even though the occupancy does not fall as quickly.
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Track gets more refined and so road narrows…
SLHC Physics and B-tagging : FNAL Pixel Workshop, October 12, 2006 J. Incandela (UCSB)
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AlgorithmicEfficiency
Efficiency and
vsvs
h h
Algorithmic
andFake
FakeRate
Rate
High efficiency setting
SLHC Physics and B-tagging : FNAL Pixel Workshop, October 12, 2006 J. Incandela (UCSB)
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Algorithmic Efficiency and Fake Rate vs h
Low Fake Rate Setting
SLHC Physics and B-tagging : FNAL Pixel Workshop, October 12, 2006 J. Incandela (UCSB)
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CMS Subtraction
Would all
strips
continue
to need to
be read
out?
SLHC Physics and B-tagging : FNAL Pixel Workshop, October 12, 2006 J. Incandela (UCSB)
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Go back to that occupancy plot…
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Mismatch at system
boundaries
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Layer 4 appears pretty
useless here.
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3 cm strip would cut
occupancy to under 10%
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Pixel layer would likely
ice the cake
Layers 5-13
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Shorter strips but fewer
layers to compensate for
material? A factor of 3
reduction in strip length
would do a lot for this
plot.
SLHC Physics and B-tagging : FNAL Pixel Workshop, October 12, 2006 J. Incandela (UCSB)
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ATLAS Granularity Guide
Using mainly
strips, they’d get
substantially better
granularity than
CMS has now
SLHC Physics and B-tagging : FNAL Pixel Workshop, October 12, 2006 J. Incandela (UCSB)
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But granularity can be wasted…
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Fine Granularity is necessary but not sufficient…
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It is wasted if there is substantial multiple scattering, radiation, and
secondary particles generated in material interactions.
Material can set an effective granularity if one is not careful
Material reduction throughout the tracker would enhance our
effective granularity now, without changing anything else.
SLHC Physics and B-tagging : FNAL Pixel Workshop, October 12, 2006 J. Incandela (UCSB)
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Multiple Scattering Now
Cucciarelli et al. CMS Note 2006/026
SLHC Physics and B-tagging : FNAL Pixel Workshop, October 12, 2006 J. Incandela (UCSB)
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Well this is a workshop…
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I don’t have answers… want to 1st frame the questions correctly
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Some thoughts
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Some technologies could run warm (e.g. n-in-p discussed in Mara Bruzzi’s talk
tuesday) … This might allow us to eliminate much of the cooling related mass in
the tracking volume.
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Super thin is in. We need to think more like e+e- people regarding our material
budgets
Recognizing that material can alter the effective granularity of a tracker, we should
carefully consider the possible benefits of a reduction in the number of layers !
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Main points:
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Leptons 1st displaced tracks 2nd on priority list (just in case push comes to
shove…)
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Granularity can be improved substantially without necessarily using pixels but it will be meaningless if the material budget is not reduced.
We need to do some serious studies of these issues
Triggering was not covered in this talk, but is important, particularly for leptons
SLHC Physics and B-tagging : FNAL Pixel Workshop, October 12, 2006 J. Incandela (UCSB)
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Tangent-Point Reconstruction
α
J.Jones Imperial College London (Perugia Workshop)
SLHC Physics and B-tagging : FNAL Pixel Workshop, October 12, 2006 J. Incandela (UCSB)
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More stuff
construction costs
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Upgrade cost ~ 200MCHF
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Broad brush estimate reported to
CMS MB/CB & DG
~60-70% tracker related
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plus staff costs (significant)
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G. Hall, Imperial College
CMS Tracker Meetings,
CERN - August 2006
Inner Tracker
25-30 MCHF
Outer Tracker
90 MCHF
Level 1 Trigger
15 MCHF
DAQ
10 MCHF
Other Front Ends
5-10 MCHF
extra costs 10ns/15ns
20-30 MCHF
Infrastructure
15 MCHF
SLHC Physics and B-tagging : FNAL Pixel Workshop, October 12, 2006 J. Incandela (UCSB)
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Roadmap from previous workshop
2006
2007
2008
2009
2010
New Layers
C onc ept
N ew RO C /N ew Sens orF abric ate
Full Tracker
M onte C arlo
C onc ept
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2012
2013
2014
2015
I ns tall
N ew RO C /N ew Sens or
Fabric ate
Installation of modest system at t = to + 5y may be possible
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2011
Lower cost and risk
Allows trial of components or devices, which may still evolve
May be possible to react to LHC conditions
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machine, experiment or even discoveries
An evolutionary approach to replacing full tracker?
Ideas are still to gel but must do so soon
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CMS proposes common EoI (2006), and LoI (mid-2007)
R&D proposals to be evaluated by CMS, and approved/encouraged
G. Hall, Imperial College
SLHC Physics and B-tagging : FNAL Pixel Workshop, October 12, 2006 J. Incandela (UCSB)
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You can’t always get what you want…
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But how much increase in granularity is actually needed?
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Present microstrip occupancies are 0.5% - 2.8% in barrel
CMS NOTE 2002/047
G. Hall, Imperial College
SLHC Physics and B-tagging : FNAL Pixel Workshop, October 12, 2006 J. Incandela (UCSB)
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Potential synergy with ATLAS
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ATLAS & CMS have exchanged speakers at several workshops
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Initial phases of LHC R&D were common
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Although many similarities, also important points of divergence
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eg sensor design, electrical & optical interfaces, analogue/digital, DAQ design,..
Possible common efforts
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Sharing ASIC processing runs (in CMS & CERN done well for 0.25µm CMOS)
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Advantageous to share circuits, evaluate technology and adopt common standards
Share development of common SLHC systems
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Optical links and Timing-Trigger-Control system are prominent items
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Common effort on power provision - eg DC-DC conversion?
Dialogue with machine
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Agree clock speed, verify current systems, information about machine operation
Special tooling
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removal and installation of irradiated systems in irradiated environment
Information exchange via regular meetings
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Annual LECC workshops are one common forum for electronic R&D
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Comparison of cooling system performance might be profitable
G. Hall, Imperial College
SLHC Physics and B-tagging : FNAL Pixel Workshop, October 12, 2006 J. Incandela (UCSB)
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Cooling costs
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Using power has heavy
material cost
For present pixel system
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Power in ~4%
Power out ~29%
For microstrips
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Cables ≈ Cooling
Cables + Cooling + Support ≈
2x (Sensors+ Electronics)
SLHC Physics and B-tagging : FNAL Pixel Workshop, October 12, 2006 J. Incandela (UCSB)
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Noise & granularity
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Leakage current shot noise also determines element size
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Noise scales ~ (area, time, fluence, shaping time,...)1/2
How much can be gained by cooling? (ATLAS discuss -35°C)
Ileak will be more significant power burden so must be contained
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thermal runaway is increased danger
Is required lifetime again 10 years?
SLHC Physics and B-tagging : FNAL Pixel Workshop, October 12, 2006 J. Incandela (UCSB)
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Seeds
SLHC Physics and B-tagging : FNAL Pixel Workshop, October 12, 2006 J. Incandela (UCSB)
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Performance of the Track Reconstruction
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Match Reconstructed tracks to MC input on a hit by hit basis.
Momentum Resolution
Transverse Impact
Parameter Resolution
Longitudinal Impact
Parameter Resolution
(Event sample: dn/dy ~3000 + one 100GeV Jet/Event)
SLHC Physics and B-tagging : FNAL Pixel Workshop, October 12, 2006 J. Incandela (UCSB)
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