High-Level Trigger Studies
Darin Acosta
University of Florida
DOE/NSF Report on US CMS
Software and Computing
DOE Germantown
June 29, 2000
June 29, 2000
DOE/NSF USCMS Computing and Software Report. HLT Studies D. Acosta
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CMS DAQ Architecture
CMS has a multi-tiered trigger system:
 L1 reduces rate from 40 MHz to 75 kHz
 Custom
hardware processes calorimeter and muon data to
select electrons, photons, jets, muons, ET above threshold

L2, L3,… (HLT) reduces rate from 75 kHz to 100 Hz
 Commercial
CPU farm runs online programs to select
physics channels
HLT
June 29, 2000
DOE/NSF USCMS Computing and Software Report. HLT Studies D. Acosta
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DAQ / HLT Challenge

HLT selection algorithms must keep only 1 event
out of 1000


Limited by ability to filter a L1 data sample which is already rich
in physics
DAQ bandwidth is finite

Total event size is 1 MB, event rate is 75 kHz
 Bandwidth limited by switch and link technology
First HLT milestone:
Demonstrate that L2 can achieve 10X rate reduction
using only 25% of the event data

Partial event reconstruction using only calorimeter
and muon data
June 29, 2000
DOE/NSF USCMS Computing and Software Report. HLT Studies D. Acosta
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CMS Physics Groups
Physics Reconstruction and Selection (PRS)
groups were established by CMS in 1999:
 Electron/Photon
C. Seez
 Muon
U. Gasparini
 Jet/Missing ET
S. Eno
 b/tau
A. Caner

Overall coordination by P. Sphicas
Charge is to evaluate the physics capability of CMS from L1 to
offline
US-CMS has substantial involvement in the Electron/Photon,
Jet/MET and Muon groups
 Focus of the Calorimeter, Endcap Muon, and
TriDAS construction project communities
June 29, 2000
DOE/NSF USCMS Computing and Software Report. HLT Studies D. Acosta
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Context of Studies
The L1 Trigger TDR is targeted for November, 2000
 Final design efficiencies and rates being
determined
The DAQ TDR is targeted for November, 2001
 Need to understand the rejection capability of the
HLT triggers and the amount of data each step
requires to validate possible hardware solutions
A Physics TDR is targeted for 2003
 It was delayed to allow for the transition to
object-oriented software
In all cases, we need to validate the algorithms for the CMS
physics plan, taking into account all possible backgrounds
June 29, 2000
DOE/NSF USCMS Computing and Software Report. HLT Studies D. Acosta
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HLT History
First HLT milestone was set for November 1999,
6 months after the creation of the PRS groups
Despite rapid progress, milestone was not met:
 Growing pains:


Learning curve:


Many inexperienced users and developers tackling C++
Not enough time:




First wide scale use of ORCA as a tool
More validation needed of reconstruction software
Endcap Muon software not completed
HLT algorithms developed only at the last minute
Insufficient manpower and resources
HLT milestone postponed until July 21, 2000
June 29, 2000
DOE/NSF USCMS Computing and Software Report. HLT Studies D. Acosta
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Recent Developments
Transition from ORCA3 to ORCA4
 Full migration to Objectivity in place of Zebra files
 Additional functionality


Inclusion of endcap muon code (L1 and reconstruction)
Correct handling of out-of-time b.x. in calorimeter

Further validation tests
Production of large simulated event samples
 Why?
inel = 55 mb and L = 1034 ( 17.3 collisions/b.x.)
 GEANT3 production at CERN, Italy, and U.S.
(Caltech, UFlorida, UCDavis)
 OO hit formatting and digitization done at CERN


2 weeks for each on a large Linux PC farm
Users access a User Federation
All file/database details hidden from user
 Standard ntuples produced for physics groups

June 29, 2000
DOE/NSF USCMS Computing and Software Report. HLT Studies D. Acosta
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ORCA Production 2000
CMSIM
HEPEVT
ntuples
MB
MC Prod.
Signal
Zebra files
with HITS
Objectivity
Database
ORCA
Digitization
(merge signal
and MB)
Objectivity
Database
ORCA
ooHit
Formatter
DOE/NSF USCMS Computing and Software Report. HLT Studies D. Acosta
Mirrored Db’s
HLT Grp
Databases
June 29, 2000
Objectivity
Database
Objectivity
Objectivity
Database
ytivitcejbO
Database
esabataD
(US, Russia, Italy..)
Catalog import
HLT Algorithms
New
Reconstructed
Objects
ORCA Prod.
Catalog import
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Data Sets
e/ and Jet/MET groups:
 0.9 Mevt (0.8 TB)
 Supplement 1999 Monte Carlo production


0.6 Mevt QCD dijet (various ET ranges)
H bb, H   , SUSY, min. bias pile-up, single particle
Muon group:
 1.3 Mevt (1.3 TB)
 Production redone in 2000 to update Pythia,
endcap geometry, and event weighting


0.9 Mevt minimum bias events for rate and pile-up
H ZZ  4 , H WW  2 , W  , Z   , single 
CMS operations:
 Expect 1000 TB/year
HLT milestone is a 0.1% Mock Data Challenge!
June 29, 2000
DOE/NSF USCMS Computing and Software Report. HLT Studies D. Acosta
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Muon Physics Plan
Validate L1 trigger decision and use as a seed for muon
reconstruction
Improve PT resolution
 Refit with vertex constraint
using reconstructed hits
 Extrapolate to outer tracker
and refit
Apply isolation requirement
 Extrapolate to calorimeter
and sum energy in cone
Effective PT Threshold
U.S. physicists working on L1 and Reconstruction for EMU
June 29, 2000
DOE/NSF USCMS Computing and Software Report. HLT Studies D. Acosta
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Results: Single  L1 Efficiency
First look with ORCA4
Recoverable
June 29, 2000
DOE/NSF USCMS Computing and Software Report. HLT Studies D. Acosta
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Barrel/Endcap Overlap Region
Must include ME2-ME3
tracks for redundancy,
despite poor PT
resolution
Drift Tubes
Cathode Strip
Chambers
June 29, 2000
We are learning from
the simulation…
DOE/NSF USCMS Computing and Software Report. HLT Studies D. Acosta
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e /  and Jet / MET Physics Plan
Electrons:
 Bremsstrahlung recovery (>½X0 of silicon tracker)
 0 rejection
 Isolation
 Track match and E/p cuts (L3)
Jets:
 Finer tower granularity
 Improved jet axis
 Energy calibration (non-linearity, pile-up)

All this improves the ET resolution
MET:
 Improve the ET resolution
Taus:
 Improve shape cuts
June 29, 2000
DOE/NSF USCMS Computing and Software Report. HLT Studies D. Acosta
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Jet Resol’n before & after Correction
Cone R=0.5 No Pileup
Cone R=0.5 Pileup
Average for || < 3
June 29, 2000
DOE/NSF USCMS Computing and Software Report. HLT Studies D. Acosta
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Conclusions
Closing in on HLT milestone for L2 performance
 Expect results in mid – July
 However, this is just a first pass at the code that will eventually run
online. Will have to optimize, etc.
The task is challenging and work intensive!
 Production is finally complete, analysis is underway
The HLT groups are driving (US)CMS software & computing
Significant work performed by U.S. physicists in Endcap Muon, Jet/MET,
and e/ groups
 Could use even more manpower, since the “users” are often the
code developers as well
User facilities and software/computing support are essential for U.S.
physicists to maintain the prominent role taken so far
June 29, 2000
DOE/NSF USCMS Computing and Software Report. HLT Studies D. Acosta
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