tracker in the trigger: from cdf experience to s-cms fabrizio palla infn – pisa vertex 2007 lake...
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Tracker in the Trigger: from CDF experience to S-CMS
Fabrizio Palla INFN – Pisa
Vertex 2007Lake Placid, NY, USA
Vertex 2007, 23-28 September 2007
Tracker in the Trigger: from CDF to S-CMSF. Palla INFN Pisa
The Tracker and the Trigger Trigger rates control is extremely challenging in high luminosity
hadron collider experiments As the luminosity increases, physics goals change in response to new
discoveries and the detector ages.
It is thus essential that the trigger system be flexible and robust, and have redundancy and significant operating margin
Providing high quality track reconstruction over the full detector can be an important element in achieving these goals.
This has certainly been the case in the CDF experiment where the Silicon Vertex Trigger (SVT) has significantly extended the experiment’s physics capability
B-physics and Bs oscillations Search for the Higgs boson
Even more challenging will be the trigger for the foreseen upgrade of LHC, the so-called SuperLHC (SLHC)
Luminosity increase of a factor 10 wrt “standard” LHC
Vertex 2007, 23-28 September 2007
Tracker in the Trigger: from CDF to S-CMSF. Palla INFN Pisa
3cm15cm150cm
Outerdrift
chamber
Silicon stripdetector
Siliconclose-up
Impact parameter
Beam spot
1mm
Zoom-inInput (every Level 1 accept):XFT trajectories silicon pulse height for each channel
Output (about 20 s later): trajectories that use silicon pointsr- tracksimpact parameter: (d)=35 m
AMalgo
SVT at CDF Level-2 Trigger
Vertex 2007, 23-28 September 2007
Tracker in the Trigger: from CDF to S-CMSF. Palla INFN Pisa
The Event
...The Pattern
Bank
The pattern bank is flexibleset of pre-calculated patterns:
can account for misalignmentchanging detector conditionsbeam movement …
Pattern matching in CDF (M. Dell’Orso, L. Ristori – 1985)
Vertex 2007, 23-28 September 2007
Tracker in the Trigger: from CDF to S-CMSF. Palla INFN Pisa
The Displaced Track Trigger @ CDF Striking difference wrt D0 thanks to SVT But also vs CDF:
Run II ~2000 BsDs vs 1 in Run I Compare with only 10 times increased
integrated luminosity The trigger had a big impact
Online mass
Phys. Rev. Lett. 97, 242003 (2006).
Vertex 2007, 23-28 September 2007
Tracker in the Trigger: from CDF to S-CMSF. Palla INFN Pisa
On the opposite side: FPGA for the same AMchip
P. Giannetti et al. “A Programmable Associative Memory for Track Finding”, Nucl. Intsr. and Meth., vol. A413/2-3, pp.367-373, (1998).
AM chips from 1992 to 2005
• (90’s) Full custom VLSI chip - 0.7m (INFN-Pisa)
• 128 patterns, 6x12bit words each
• 32k roads / wedgeF. Morsani et al., “The AMchip: a Full-custom MOS VLSI Associative memory for Pattern Recognition”, IEEE Trans. on Nucl. Sci., vol. 39, pp. 795-797, (1992).
In the middle: Standard Cell 0.18 m(INFN-Pisa) 5000 pattern/chip AMchip
L.Sartori, A. Annovi et al., “A VLSI Processor for Fast Track Finding Based on Content Addressable Memories”, IEEE Transactions on Nuclear Science, Volume 53, Issue 4, Part 2, Aug. 2006 Page(s):2428 - 2433NEXT:
NEW VERSIONFor both L1 & L2
Vertex 2007, 23-28 September 2007
Tracker in the Trigger: from CDF to S-CMSF. Palla INFN Pisa
SLHC Level-1 Trigger issues @ 1035
~400 Minimum Bias events/bx (50 ns) [16xLHC]
Occupancy Degraded performance of algorithms
Electrons: reduced rejection at fixed efficiency from isolation Muons: increased background rates from accidental coincidences
Larger event size to be read out New Tracker: higher channel count & occupancy large factor Reduces the max level-1 rate for fixed bandwidth readout
Trigger Rates Try to hold max L1 rate at 100 kHz by increasing readout bandwidth Implies raising ET thresholds on electrons, photons, muons, jets and use
of less inclusive triggers Need to compensate for larger interaction rate & degradation in
algorithm performance due to occupancy
Vertex 2007, 23-28 September 2007
Tracker in the Trigger: from CDF to S-CMSF. Palla INFN Pisa
Needs for a Tracker Trigger at SLHC
Note limited rejection power (slope) without tracker information
Tracker needs to be rebuild due to radiation aging
Move some HLT algorithms into Level-1 or design new algorithms reflecting tracking trigger capabilities
See previous talk by Marcin Konecki
Proposed boundary conditions Rebuild L1 processors Maintain 100kHz limit Increase latency to 6.4µs
ECAL digital pipeline holds 256 samples @ 40MHz
From CMS-DAQ TDR
L =1034 cm-2 s-1
Vertex 2007, 23-28 September 2007
Tracker in the Trigger: from CDF to S-CMSF. Palla INFN Pisa
Main issues for Tracker Trigger Data Rate in Tracker Volume at SLHC
About 12,000 tracks per bunch crossing (50 ns) in the Tracker volume ||<2.5 and ~400 primary vertices/bx
Needs high granularity information
Innermost radii (~<10 cm) needs new technology to cope high radiation doses (>3x1015 neq cm-2)
At 10 cm radius the rate is ~108 cm-2s-1 giving ~6000 links @ 2.5 Gbps link speed– simply impossible to cope with
Push towards larger radii Benefits for momentum measurement
based trigger Ideal to match with muon and
calorimeter triggers ~1 mm pointing resolution for z- larger
than average 2 pileup interactions (~0.4 mm)
Still fairly nice impact parameter resolution in transverse plane (~100 m for 10 GeV muons) to get rid of muons from and decays
Without pixel
With pixel
(z0)
Without pixel
With pixel
(d0)
Vertex 2007, 23-28 September 2007
Tracker in the Trigger: from CDF to S-CMSF. Palla INFN Pisa
Tracking Trigger driving ideas Design considerations:
Main usage for pT reconstruction Need low occupancy and large lever-
arm, rather than brilliant space-point resolution
Need to decrease Tracker material budget by a sizeable amount
multiple scattering will drive the momentum resolution below ~10 GeV
Reduce to a minimum (possibly null) Tracker trigger-only layers
Impact on the Tracker design Two possible approaches
Tracker primitives Full readout for trigger Limited information
Detector level data reduction
Selective readout using Mu or Calo information
Like CDF XFT
Vertex 2007, 23-28 September 2007
Tracker in the Trigger: from CDF to S-CMSF. Palla INFN Pisa
Tracker primitives from CDF SVX approach
1 AM for each enough-small Patterns
Hits: position+time stampAll patterns inside a single chip
N chips for N overlapping events(identified by the time stamp)
Event1AMchip1
Event2AMchip2
Event3AMchip3
EventNAMchipN
Main problem: input Bandwidthdivide the detector in thin sectors. Each AM searches in a small
OFF DETECTOROFF DETECTOR
Data links
Vertex 2007, 23-28 September 2007
Tracker in the Trigger: from CDF to S-CMSF. Palla INFN Pisa
Full readout option Exercise using CMS layout but modified strip pitch:
From 40 to 90 cm radius Conservative approach Barrel coverage up to ||<1.5
R=40 and 50 cm macro-pixel like sensors of 0.2x5 mm2 cell size R>50 cm strip like sensors 50 m x 10 cm cell size
Subdivide the detector in many sectors Keep data volume limited in each sector
Combine information from at least 3 layers out of 4 in each sector
Momentum resolution of ~ few (<10)% at 10 GeV/c Granularity driven by the minimum measurable pT for triggering
purposes, without loosing efficiency 70 sectors at the innermost radius
Well covering the bending of a track of 10 GeV pT and above
Vertex 2007, 23-28 September 2007
Tracker in the Trigger: from CDF to S-CMSF. Palla INFN Pisa
Sensors and signal routing
hybrid
5 cm
6 cm
200x5000 m2
Readout chips
Fiber(s)
Smaller radius sensors
Larger radius sensors
Fiber(s)
32 bits sufficient to locate hit positionin the sector and bx time stamp
hybrid
6 cm
10 cm
50 m x 10 cm
Readout chips
fibers
Vertex 2007, 23-28 September 2007
Tracker in the Trigger: from CDF to S-CMSF. Palla INFN Pisa
Occupancy GEANT4 simulation of tracking layers
Includes material budget and loopersRadius (cm) Hit/module/bxa Rate*/module (Gbps) Rate*/sector (Gbps) No. data links†/layer
40 43.6 28 170 3200
50 33.5 21 130 3100
60 25.5 16 175 5300
70 20.2 13 110 4600
80 16.6 11 80 5300
90 13.9 9 60 3900
ª average number on minimum bias events, 50 ns bx*32 bits/hit † for a data link speed of 5 Gbps Pros: same fiber links for data and trigger
Simple and elegantCons : large number of links needed
Need >=5Gbps laser drivers: 90 nm technology required Allow for fluctuations: increase by ~1.5 ? Laser driver power: commercial range from 330mW/fiber (4Gbps) to 700 mW/fiber (10Gbps)
Current links in CMS Silicon Strip: 1300 @ 60 cm and 2600 @34 cm
Vertex 2007, 23-28 September 2007
Tracker in the Trigger: from CDF to S-CMSF. Palla INFN Pisa
Conceptual design
AM EV0
AM EV1
AM EV50
...
Layer 0: ~35 fibers bringing ~20 Hits/50 ns
1 Hit/5 ns
1 Hit/5 ns
1 Hit/5 ns
From otherlayers
From otherlayers
From otherlayers
Distribute hits into different sets of storage units
depending on EVent #
Parallel INSerial OUT
...Parallel INSerial OUT
Parallel INSerial OUT
1 FPGA
From Detector
Vertex 2007, 23-28 September 2007
Tracker in the Trigger: from CDF to S-CMSF. Palla INFN Pisa
Reducing the data rate Keeping all information
Send only cluster position Need simple ASIC on chip to perform clustering Reduction of a factor ~2
Reducing the number of bits per hit Possible if time stamp not needed
Only strips detectors (larger radii) Reduction of a factor ~1.8 Needs fast readout electronics
Overall a factor ~3.5 reduction feasible Current GBT chip (Marchioro group) 2.56 Gbps for data
Local data reduction for trigger purposes only Coarser granularity joining readout channels for trigger
purposes Exploit high vs low pT tracks patterns
Vertex 2007, 23-28 September 2007
Tracker in the Trigger: from CDF to S-CMSF. Palla INFN Pisa
Board dimensions Current board dimensions
About 30,000 patterns per AM chip required Needed ~ 80 boards with ~40 AM chips each
3200 AM chips The current AM for CDF holds ~5000 patterns/6 planes in 0.18m technology If developed in the 90 nm technology one could accommodate ~4 times more
patterns/AM chip hence 30,000 for 4 planes
In order to evaluate the board dimensions need to define the granularity and the lowest pT threshold
For instance, a 50 m pitch on 4 detector planes and a pT threshold of 10 GeV needs ~90,000 patterns (needs 3 AM chips)
Vertex 2007, 23-28 September 2007
Tracker in the Trigger: from CDF to S-CMSF. Palla INFN Pisa
MIPMIP
Cluster width discrimination
90 cm70 cm50 cm30 cm
Discrimination of low pT tracks made directly on the strip detector by choosing suitable pitch values in the usual range for strip sensors.
Vertex 2007, 23-28 September 2007
Tracker in the Trigger: from CDF to S-CMSF. Palla INFN Pisa
Cluster width results In this region, using 50µm pitch,
about 5% of the total particles leave cluster sizes with ≤2 strips
Huge reduction in trigger links Once reduced to ~100 KHz, it
would only need few fast readout links to readout the entire Tracker
R(cm) Pitch
(m)
Z coverage
(cm)
Data Rate /Layer (Gbps)
40 40 170 350
60 60 200 160
70 90 200 160
90 90 200 95
No. of links (5Gbps) ~ 150 for whole tracker
Data rate per layer could be reduced by more than 1 order of magnitude wrt full readout case
Vertex 2007, 23-28 September 2007
Tracker in the Trigger: from CDF to S-CMSF. Palla INFN Pisa
Coarser granularity Calorimeters and muon system is
=0.087x0.087 Compromise with momentum
resolution Sufficient to use O(500m) at
innermost radius (R~50 cm) for a precision of ~15% at 10 GeV
OR-ed readout of 10 strips – simple logic
Reduction of a factor 10
ButpT/pT pT solve reducing promotion of
low pT tracks and kill photons from , but not brilliant momentum resolution
Loss in precision recovered by adding in AND a electron or a muon directly adding other information in the AM chip “layer”
Natural with AM chips
Silicon sensorOR
OR
OR
OR
AM chip
Muon pT,
Vertex 2007, 23-28 September 2007
Tracker in the Trigger: from CDF to S-CMSF. Palla INFN Pisa
A first idea on selective readout Provide a Muon Track fast Tag
(MTT) to be associated with hits in outermost Tracker layers
Need a new detector for MTT yet to be defined (2 layers of RPC?)
Still very preliminary need more thoughts
Electrons and Jets?
Vertex 2007, 23-28 September 2007
Tracker in the Trigger: from CDF to S-CMSF. Palla INFN Pisa
Stacked readout for Trigger Angle determines pT of track, assuming tracks
coming from origin Smaller a = greater pT
Pair of sensor planes at ~ mm distance for local pT estimate
Needs a correlator ASIC Fast data links
If located at ~20 cm needs 3 Gbps Stacks of 2 sensor planes at ~cm distance to be
correlated (off detector) for pT measurement Tight construction tolerances required for both
sensors and their alignment See M. Mannelli talk
Vertex 2007, 23-28 September 2007
Tracker in the Trigger: from CDF to S-CMSF. Palla INFN Pisa
Conclusions Tracker information helps reducing drastically the rate of
uninteresting events CDF SVT experience has become cornerstone for Tracker Trigger
B physics reach has been boosted after the usage of displaced vertex triggers and now Higgs search uses it
S-CMS will make use of tracking information at SLHC and has started to discuss several options
Triggering at SLHC is challenging due to fantastic data rate Concentrate on momentum resolution, muon and electron matching SVT approach seems feasible, especially if complemented by a data
reduction at the module level The trigger design and the detector layout are completely interleaved
and are influencing each other Next steps will involve simulating trigger with different layouts and are
going to define which strategy will be used, stay tuned!
Vertex 2007, 23-28 September 2007
Tracker in the Trigger: from CDF to S-CMSF. Palla INFN Pisa
BACKUP
Vertex 2007, 23-28 September 2007
Tracker in the Trigger: from CDF to S-CMSF. Palla INFN Pisa
L at end of year
time to halve error
integrated L
radiationdamage limit~700 fb-1
(1) LHC IR quads life expectancy estimated <10 years from radiation dose(2) the statistical error halving time will exceed 5 years by 2011-2012(3) therefore, it is reasonable to plan a machine luminosity upgrade based on new low-
IR magnets by ~2016
design luminosity
ultimate luminosity
courtesy J. StraitModified (start date) by F. Palla
ultimatevs. design
Time Scale of LHC Upgrade
2010 2012 2014 2016 2018 2020
Vertex 2007, 23-28 September 2007
Tracker in the Trigger: from CDF to S-CMSF. Palla INFN Pisa
switch board numbersAll info here TBC with simulation and R&D!
•80 switch boards• 1 / -sector
• 80 fibers / board• assume 5Gbps each
• 40 AMchip / board• now we can fit 32 AMchips in one 4th of a 9U VME board
• 4 FPGA switches (1/layer)•Each receiving ~20 fibers, i.e. ~100Gbps•40 outputs: one per Amchip•Possible with today’s FPGAs
32 AMchips
Vertex 2007, 23-28 September 2007
Tracker in the Trigger: from CDF to S-CMSF. Palla INFN Pisa
•Dedicated device: maximum parallelism•Each pattern with private comparator•Track search during detector readout
• If you can read it out you can track it!
AM: Associative Memory
Bingo scorecard
AM = BINGO PLAYERS
HIT # 1447
PATTERN NPATTERN 1PATTERN 2
PATTERN 3
PATTERN 5
PATTERN 4
Vertex 2007, 23-28 September 2007
Tracker in the Trigger: from CDF to S-CMSF. Palla INFN Pisa
Associative Memory (AM) for pattern matching ~ Bingo game
BINGO PLAYERS
Dedicated device:
Maximum parallelism !
Each pattern with
private comparator
Tracks found during
detector readout !
M. Dell'Orso and L. Ristori, “VLSI structures for track finding”,
Nucl. Instr. and Meth., vol. A278,
pp. 436-440, (1989).
Vertex 2007, 23-28 September 2007
Tracker in the Trigger: from CDF to S-CMSF. Palla INFN Pisa
Level 1 drift chamber trigger (XFT)
1 1.5 2 2.5 3 3.5 4
offline transverse momentum (GeV)
XFT
effi
cien
cy
Finds pT>1.5 GeVtracks in 1.9 s
For every bunchcrossing (132 ns)!
(1/pT) = 1.7%/GeV
(0) = 5 mrad
96% efficiency
Vertex 2007, 23-28 September 2007
Tracker in the Trigger: from CDF to S-CMSF. Palla INFN Pisa
PDPD
TIBTIB
TOBTOB
TOBTOB
TIDTIDTIBTIB
TECTEC
PDPD
• 210m2 micro-strip silicon detectors 15.232 modules• 6136 320m thick and 18.192 500m thick sensors (all from 6” wafers).• 7.136 APV chips• 9.648.128 analog strip channels.• About 25M wire bonding.
The CMS Silicon Tracker at LHC 22
0 cm
270 cm
Vertex 2007, 23-28 September 2007
Tracker in the Trigger: from CDF to S-CMSF. Palla INFN Pisa
SLHC Trigger Requirements
High-pT discovery physics Need high thresholds
Completion of LHC physics program Example: precise measurements of Higgs sector Require low thresholds on leptons/photons/jets
Use more exclusive triggers since final states will be known Still an issue for L1
Control & Calibration triggers W, Z, Top events Low threshold but prescaled
Vertex 2007, 23-28 September 2007
Tracker in the Trigger: from CDF to S-CMSF. Palla INFN Pisa
Too large AM? 2 step approach
Roads1. Find low resolution track candidates called “roads”. Solve most of the pattern recognition
2. Then fit tracks inside roads.Thanks to 1st step it is much easier
Super Bin (SB)
OTHER functions are needed inside SVT: Hit Buffer + Track fitter + Hit Finder
Vertex 2007, 23-28 September 2007
Tracker in the Trigger: from CDF to S-CMSF. Palla INFN Pisa
Latency ~100 m fiber 300 ns [6 bx] Switch + AM ~1s [20 bx] Sensor read-out latency budget should be less than ~20 bx TOTAL ~ <50 bx [2.5 s]
Vertex 2007, 23-28 September 2007
Tracker in the Trigger: from CDF to S-CMSF. Palla INFN Pisa
Muon L1 Trigger Rate at L=1035 cm-2 s-1
1.E+02
1.E+03
1.E+04
1.E+05
1.E+06
1.E+07
0 5 10 15 20 25
pT (GeV/c)
Ra
te (
Hz)
Muons+Tracker
Muons
Vertex 2007, 23-28 September 2007
Tracker in the Trigger: from CDF to S-CMSF. Palla INFN Pisa
Stacked trigger