The SLHC CMS L1 Pixel Trigger & Detector Layout Wu, Jinyuan Fermilab April 2006

Preference on Detector Layout Pixel planes are expensive in terms of material, cost, data volume, power, cooling etc. (C3: Cost, Cable, Cooling) If N layers of pixel detector planes are affordable, normally spaced configurations like (b) is more preferable for data analysis stage. Pattern recognition for (b) is more difficult . From BTeV works, the pattern recognition for (b) is not as hard as we thought several years ago. (a) (b)

Brief History of Tracking Long time ago, tracking was done by: –Finding 2-point candidates (doublets) and then –Finding the third point. Before BTeV, it was known: –Triplet can be found in one step. During BTeV, we learnt how to do triplet finding in FPGA fast and cheaply. (e. g. Tiny Triplet Finder)

Circular Tracks from Collision Point on Cylindrical Detectors For a given hit on layer 3, the coincident between a layer 2 and a layer 1 hit satisfying coincident map signifies a valid circular track. A track segment has 2 free parameters, i.e., a triplet. The coincident map is invariant of rotation.  1 -  3 )+64  2 -  3 )+64

Tiny Triplet Finder Reuse Coincident Logic via Shifting Hit Patterns C1 C2 C3 One set of coincident logic is implemented. For an arbitrary hit on C3, rotate, i.e., shift the hit patterns for C1 and C2 to search for coincidence.

Tiny Triplet Finder for Circular Tracks *R1/R3 *R2/R3 Triplet Map Output To Decoder Bit Array Shifter Bit Array Shifter Bit-wise Coincident Logic 1.Fill the C1 and C2 bit arrays. (n1 clock cycles) 2.Loop over C3 hits, shift bit arrays and check for coincidence. (n3 clock cycles) Also works with more than 3 layers

Question: How can data from different layers merge together? Total data rates from pixel 10cm are: 3.125, 5 or 12 Gb/s/cm 2. To send full data over large distance is difficult. (The good side of stacked layer ideas is the possibility of doing coincident locally.) Difficult, yes, but there are several possibilities.

Possibility 1 Pre-trigger

From LHC to SLHC The total L1 latency for SLHC has been increased to 6.4 us. Total L1 rate is kept the same (100kHz). Consider a pre-trigger of 3.2 us. Use pre-trigger to dump data from pixel. Data rate: 1/80 or 1/40. BX=40MHz L=10 34 BX=80MHz L=10 35 Latency 3.2  s Current LHC CMS L1: <100 kHz SLHC CMS pre-trigger? <1MHz Latency 6.4  s SLHC CMS L1: <100 kHz

Sending Data to Triplet Finder: The Pre-trigger ECAL (or any other) generates coarse pre-trigger and sends to global L1. The pre-trigger is distributed to all (or 1/2, 1/4 of all) readout chips at 3.2 us. The distribution lines are original L1 trigger signal lines. The ROC output data and the tracker trigger generates trigger primitives. The L1 system makes final global T1. Pre-triggered data stored in Tracker Trigger during the second 3.2 us are sent to HLT/DAQ. ROC has shorter pipeline in this operation mode. Worst case: two round trips. Better if one round trip can be eliminated. ECAL ROC Triplet Finder L1 ECAL Pre-triggerECAL finer trigger CableL1 PTCable L1 triggerCable L1 triggerCable ROC out Triplet Trigger 3.2us HLT DAQ

Some Numbers Assume: ECAL generates up to 1MHz pre-trigger with 3.2us latency. Use the hit rate 4hits/(1.28cm) 2 R=8cm. Total data rate: 4hits x 16 bits/hit x 1MHz = 64 Mb/s. Assume each (1.28cm 2 ) ROC output Cu 160 Mb/s. ECAL ROC L1 ECAL Pre-triggerECAL finer trigger CableL1 PTCable L1 triggerCable L1 triggerCable ROC out 3.2us HLT DAQ R (cm)[hits]/(1.28cm) 2 /BX [Foundas] Data Rate (Mb/s/ROC) (assume 16 bits/hit) # of 160 Mb/s Cu pairs/ROC Output Capacity (Mb/s/ROC) cm]641 or 2160 or cm] [est.] Triplet Finder Triplet Trigger

Possibility 1+ Pre-trigger + Stacked layers for high PT tracks

High PT Doublet Finding, If Needed The system supports both ECAL pre-trigger mode and high PT doublet finding mode. The ROC at 300mm and 295mm communicate to each other. High PT doublets are found in ROC. The doublets point the searching windows on 200 and 100mm layers and hits in the window are enabled to be readout. One set of stack layers, rather than 3. ECAL ROC 300 ROC 295 Triplet Finder & Readout L1 HLT DAQ R=300mm R=295mm R=200mm R=100mm R=50mm ROC 200 ROC 100 ROC 50 Readout Only

Stack Layers: 1mm or 5mm Pixel pitch:  u in ,  v in z. Layer separation: (r 2 -r 1 ). Measurement error: –  =  u / (r 2 -r 1 ) –  =  v / (r 2 -r 1 ) Power Consumption: – P = P 0 A /(  u  u). Therefore: –P   = P 0 A / (r 2 -r 1 ) 2. When the layer separation increases from 1mm to 5mm, P   reduces by factor of 25. 1mm5mm Pixel Pitch 20  m(  ) 200  m(z) 50  m(  ) 200  m(z)   Power P 0 =10  W 2.5KW/m 2 1KW/m 2 Sharing Mech. Support & Cooling ?Yes

Straw Man Stack Layers (r-z view) The two stack layers share same mechanical support and cooling layer. ROC in two layers overlap to each other in z direction. Hits from 1/4 of chip at both end are sent to opposite chips for coincident. Questions: overlapping in phi direction? Sensor Readout Chip Mechanical Support, Cooling, interconnection Readout Chip Sensor Seeding Hits Coincident Range

Straw-Man Readout Chip -- Backend Column Logic & Zero Suppression Pipeline 6.4us3.2us1.0us High PT Segment Correlation CS10HDACS10AHDB From/to Stack Layer ROC DOUT CS64 CS32 T1orPT From L1

Pipeline and CS32/64 Column Logic & Zero Suppression Pipeline 6.4us3.2us1.0us DOUT CS64 CS32 T1orPTFrom L1 The hit data are stored in the pipeline. After 3.2 us, when the pre-trigger comes (signal T1orPT), the ROC sends data out for triplet trigger. After 6.4 us, when the L1 comes, the ROC sends data of the BX out.

High PT Correlation The OR-AND coincident logic accepts high PT doubles. Set the Bit Enable Register to change PT cut and correct offset on pixel alignment. The OR gate is replaced with a priority encoder in real implementation. Bit Enable Register Plane A Plane B

1 Copy, Not 256 Copies in real implementation Some design may use N copies of coincident logic. (N=256 here.) The design here uses 1 copy. Note that Plane A is local in the ROC and Plane B is another ROC. The data from Plane B are column coordinate of hits. The priority encoder output represents track angle. Plane A Plane B Logarithmic Shifter Priority Encoder

About This Work It is extremely interesting since it is still in detector layout stage. There are not so many chances one can work at this stage in ones life time. Simulation, simulation, simulation. Time is tight. (TDR around ’07, ’08)

The End Thanks

Analysis Track reconstruction: –I–Impact parameter. –T–Transverse momentum. Fake track rejection Compare configuration (a) and (c) when silicon strip tracker data are also included. (a) (b) (c)