high level trigger of m uon spectrometer
DESCRIPTION
High Level Trigger of M uon Spectrometer. Indranil Das Saha Institute of Nuclear Physics. Description of the problem. Signal. Background. y. L0 Trigger by Muon Trigger. J/ Ψ μ + μ - Y μ + μ - B μ + / μ - + X D μ + / μ - + X. Muons from π and K. Z. - PowerPoint PPT PresentationTRANSCRIPT
High Level Trigger of Muon Spectrometer
Indranil DasSaha Institute of Nuclear
Physics
Description of the problem
Z
y
J/Ψ μ+ μ- Y μ+ μ- B μ+ /μ- + X D μ+ /μ- + X
Signal
Muons from π and K
BackgroundL0 Trigger by Muon Trigger
P2 = (P1 + P2)2 Continue hardware and software trigger…..
(for hadronic background)
Description of the problem• For ALICE Muon Spectrometer L0 (hardware trigger) == Hits in trigger station. + Track pointing to origin + Option for transverse momentum (pT) selection.
• Muons coming from Pions and Kaons decay have low pT .
• Thus to reduce the background two pT cuts of 1 GeV or 2 GeV has been planned to clean invariant mass spectrum of J/Ψ and Y.
px
py
pz
p
pT
Software cut improves the result, so why not online software cut ?
HLT : Thus, on top of the hardware trigger a software trigger is applied, which is called High Level Trigger (HLT). The HLT is an online system that provides the common facilities (i.e. Input/Output Link, PC farm for analysis) and executes the triggering algorithms (full reconstruction) developed for different detectors.
Main motivation of Dimuon HLT : In case of Muon Spectrometer, HLT algorithms are supposed to improve the pT cuts (1 GeV or 2 GeV at most, depending on beam luminosity) as defined by Muon Trigger Station (L0 Trigger), which are important remove the combinatorial background of low momentum particles to clear the J/Ψ and Y signals. A typical processing rate of 1 kHz is the design requirement of muon HLT for heavy ion Pb-Pb collisions.
Description of the problem
How do we deal online data in reality ?
ALICE data flow in online mode
Offline
Detector
Physics Trigger {Level 0 [L0]}
HLT
DAQ
Clusters HLTESD
Tracks
Rawdata (GRID)
Clusters
Tracks
ESD
HLTESD
Event Display
But then it is very straight forward right ?
Description of the problem
• One simulated Pb-Pb event needs few seconds for offline reconstruction (official physics analysis software) and therefore this can not be used for online analysis.
• Thus, a new algorithm has been developed which will perform online analysis of data and satisfies,
– A online processing component has to be robust (24x7)– It is to be fault tolerant against input data stream– It has to provide results of appreciable quality– It has to be fast enough so that the rest of experimental
component does not wait for HLT If any of above conditions are violated dimuon part of HLT is excluded
from the experimental run.Data rate of 500 MB/s for 1 kHz trigger rate with hit multiplicity ~ 300Accuracy as good as offline reconstruction within the time limit of 1 ms
Outline
• Development of the Algorithm– Hit Reconstruction (Thesis work)– Trigger Reconstruction (UCT + Cagliary)– Track Finding (Thesis work)• Cellular Automata• Kalman Filtering
• Validation with the simulated data (Thesis work)• Implementation in HLT PC-Cluster and validation
with cosmic data (Thesis work)• Online display of LHC p-p data (Thesis work) • Ongoing Analysis of p-p data (Thesis work)
At first the Hit Reconstruction algorithm…..
A fast Algorithm The charges are found to spread over 2 or 3 pads along a direction in most of the cases => one cluster.
Each cluster is characterized by one Central Pad (Pad with maximum charge for the given cluster).
Thus, to generate reconstructed hits, it is not essential to make clusters but only identification of Central Pad is sufficient.
Once the central pad is found the reconstructed Y hits in bending plane is calculated using centre of gravity method over three pads around the central pad.
Above method is repeated for non bending plane to find out reconstructed X .
Finally the bending and non bending hits are merged to form reconstructed X and Y.
Comparison with offline…
Comparison of Simulation Results
Fine !!! What about tracking ?
Charged particle track
Z
y
Trigger SeedSt. line track
Kalman χ2 matchCellular Automata
MCS and E.Loss Correction
Trigger Seed
The Trigger chamber issues a Trigger when at least three out of four planes are fired along linear direction
Linear Extrapolation in St4/5
A trigger tracklet can be formed with the trigger seed, which is
extrapolated to find the ROI in St4/5.the hits inside those ROI are
checked for the alignment with the trigger tracks and added to extrapolate
the tracks.
CA in St1 and St2
At First the small tracklets between thetwo chambers of a given station are
formed. Then the tracklets from different stations are collected to make a
track segment in the forward half of the Spectrometer.
Kalman Chi2Test
The tracksegs in the St4/5 are extrapolated through the magnetic fieldusing Kalman filter to meet the trackseg
In St1/2.
Extrapolate
The tracks are then extrapolated to vertex to incorporate energy loss and
MCS (multiple Coulomb Scattering)
in the Muon absorber .
Full Tracker Scheme
What is Cellular Automata ?
Cellular Automaton
Cell Creation
Cell is a small tracklet between thetwo chambers of a given station. The tracklet object contains three
pointers, one corresponds to its rankin the track and the rest two points
towards each other
Connect Tracks
The cells from different stations arecollected into a track from the Muon
Trigger stations towards station1 with certain strict boundary
condition.
How does Kalman Filter Works ?
Kalman Gain
Project to k+1
Update Covariance
Update Estimate
Measurement
Kalman Filtering Process
Projected Estimate
Initial Estimate
Result on simulated data….
Transverse Momentum Reconstruction at a given PT
For other delta PT values…..
Comparison of Different Tracking Approach
0.5 GeV 1.0 GeV 1.5 GeV 2.0 GeV 2.5 GeV
Offline Resolution(MeV)
33.8 +/- 0.7 34.9 +/- 0.2 39.8 +/- 0.2 43.9 +/- 0.2 40.5 +/- 0.1
Efficiency(%) 96.49 +/- 0.912
99.57 +/- 0.533
98.86 +/- 0.473
98.61 +/- 0.458
98.83 +/- 0.457
Full Tracker Resolution(MeV)
44.7 +/- 1.0 47.0 +/- 0.3 61.6 +/- 0.4 74.9 +/- 0.4 78.8 +/- 0.5
Efficiency(%) 95.61 +/- 0.906
97.57 +/- 0.525
97.95 +/- 0.470
98.50 +/- 0.458
97.98 +/- 0.455
How does it fit to the PT efficiency plot ?
PT Cut Efficiency
Offline testing is not same as online implementation….
Pause and discuss….
First Track in Muon Spectrometer of ALICE was detected by SINP group
Run 24841March 3, 2008
And many more…..
Event Snapshots of ALICE Control Room
Run 119842
ALICE Control Room (ACR)First online snapshot of muon track in 7 TeV (highest energy) pp collision beam at record luminosity (~ 6 × 1028 cm-2 s-
1), processing at a rate of 700 Hz
Not Only Display, but Quality Assurance(QA) as well……….
PT Distribution
Cluster D
ist. Attached to
the tra
cks
Real Time Vertexing !!!!!!
Online Inv. Mass Distribution
Bingo!!
Analysis of the quality of the events…..
Number of Clusters per Data Link
Charge Ratio in the Two Planes of the Detectors
Trigger Type as declared by Trigger Chamber
Total ADC Charge per Data Link
Monitoring even deeper…..
Cluster size distribution
Cluster Charge Distribution
Offline Comparison
The performance plots are shown for the Full-Tracker on data from 54 runs from LHC10d:126097 12608 126087 126081 126078 126073 126008 126007 126004 125855 125848 125847 125844 125843 125842 125632 125630 125628 125296 125292 125186 125156 125139 125134 125131 125101 125100 125097 125085 125083 124608 124607 124606 124605 124604124603 124600 124388 124380 124378 124374 124371 124367124364 124362 124360 124359 124358 124355 124187 124186 124183 122375 122374
How does L0, Offline, HLT triggered mass spectrum look like …. ?
Preliminary
Preliminary
Ongoing Analysis of p-p data
Any track passes 1.0 GeV cut
Summary and Future Plan
• Successful development, simulation testing, online implementation, real-time execution and validation by physics analysis of the Hit Reconstruction and Track Reconstruction algorithms
• Histogram incorporation to QA for global run characteristics.
• Continue Validation test with p-p and Pb-Pb collision.