High Level Trigger of Muon Spectrometer Indranil Das Saha 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 Background L0 Trigger by Muon Trigger P 2 = (P 1 + P 2 ) 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 (p T ) selection. Muons coming from Pions and Kaons decay have low p T. Thus to reduce the background two p T cuts of 1 GeV or 2 GeV has been planned to clean invariant mass spectrum of J/Ψ and Y. pxpx pypy pzpz p pTpT 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 p T 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 ClustersHLTESD 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 ~ 300 Accuracy 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 Seed St. line track Kalman χ 2 match Cellular 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 the two 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 field using 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 the two chambers of a given station. The tracklet object contains three pointers, one corresponds to its rank in the track and the rest two points towards each other Connect Tracks The cells from different stations are collected 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 P T For other delta P T values…..

Comparison of Different Tracking Approach 0.5 GeV1.0 GeV1.5 GeV2.0 GeV2.5 GeV OfflineResolution (MeV) / / / / /- 0.1 Efficiency(%) / / / / / Full TrackerResolution (MeV) / / / / /- 0.5 Efficiency(%) / / / / / How does it fit to the P T efficiency plot ?

P T 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 March 3, 2008 And many more…..

Event Snapshots of ALICE Control Room Run ALICE Control Room (ACR) First online snapshot of muon track in 7 TeV (highest energy) pp collision beam at record luminosity (~ 6 × cm -2 s -1 ), processing at a rate of 700 Hz

Not Only Display, but Quality Assurance(QA) as well………. P T Distribution Cluster Dist. Attached to the tracks 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: How does L0, Offline, HLT triggered mass spectrum look like …. ? 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.