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Stage-1 L1 calorimeter trigger upgrade for Heavy-Ion physics. Alex Barbieri, Christof Roland, Ivan Cali, Bolek Wyslouch, Gunther Roland (MIT) Krisztián Krajczár, Yen-Jie Lee (CERN) Matthew Nguyen (LLR) Wei Li (Rice) CMS Upgrade Project Office 9 th August 2013. The case….

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stage 1 l1 calorimeter trigger upgrade for heavy ion physics
Upgrade Project Office Meeting Stage-1 L1 calorimeter trigger upgrade for Heavy-Ion physics

Alex Barbieri, Christof Roland, Ivan Cali, Bolek Wyslouch, Gunther Roland(MIT)

Krisztián Krajczár, Yen-Jie Lee (CERN)

Matthew Nguyen (LLR)

Wei Li (Rice)

CMS Upgrade Project Office

9th August 2013

the case
Upgrade Project Office MeetingThe case…
  • The readout rate of the CMS detector in HI collisions is limited by the Pixels and the Tracker to about 3kHz
    • No zero suppression in strips and pixel buffer overruns for large events
    • 2011: Max. Interaction Rate ~4.5kHz  2.7kHz L1A rate
    • The current L1 Calo trigger system is (barely) selective enough for HI run in 2011
    • For jets and photons about 50% of the hadronic interactions need to be accepted due to the large underlying PbPb event
  • 2015: expect at least a factor of 4-6 lumi increase
    • There is strong overlap between the triggersreducing the L1A rate by 2 will require prescaling individual paths by factors of 10-20
    • Need a factor of ~20 rejection factor for 2015
  • The Stage-1 L1 Calorimeter Trigger upgrade (2015) can achieve the desired rejection factor
t rigger rate
Upgrade Project Office MeetingTrigger rate

Rate does not respond much to the threshold. Need change in algorithm

Rate can becontrolled by the threshold.

To be optimized

Energy sum seeds for the single track trigger should be replaced by updated jet triggers

Note: There is strong overlap between the triggers, reducing the L1A rate by 2 will require prescaling individual paths by factors of 10-20

background subtraction algorithm
Upgrade Project Office MeetingBackground Subtraction Algorithm

Region Energy Distributions

PbPb central event

HLT/Offline background subtraction:

  • Process phi rings at const. eta
  • Calculate average and subtract
  • Jet finder runs after BG subtraction

Current L1 Jet Finder:

  • Processes eta strips at const. phi
  • 2 x 11 sectors
  • 1 sector = 4x4 calo towers
  • Sliding window jet finder
  • Current strategy: Jet Finder at L1 and Jet Background subtraction at HLT
    • The high non-uniformity in η of HI events does not permit a useful BG subtraction within a single 2x11 sector
  • Access to the full eta phi map at L1 allows for a efficient underlying event subtraction (phi-rings)
    • Peripheral and central events respond consistently to the thresholds applied to L1 jets
hi stage 1 calo upgrade strategy
Upgrade Project Office MeetingHI Stage-1 calo upgrade strategy
  • Make decision in a central place!!!
  • Trigger “primitives” are available in 18 separate 9U VME crates with custom high-speed backplanes corresponding to φ slices
  • Insert a processing/communication board: optical Regional Summary Card (oRSC) into existing slot in each RCT crate
  • Send regional calorimeter trigger products to L2 calorimeter trigger processor (MP7) boards
  • Program FPGA to do background subtraction in full φ rings using 4x4 tower “regions” to estimate background
  • Find jets at L1 speeds
stage 1 hi algorithm performance
Upgrade Project Office MeetingStage-1 HI algorithm performance

Current System

Accept rate can be controlled by L1 threshold using Stage-1 and Stage-2 system

Stage-1 System

Stage-1 System:

Reasonable trigger turn-on curvefor both central and peripheral collisions

L1 accept rate reduced by a factor of 10-20

heavy ion contribution
Upgrade Project Office MeetingHeavy-Ion Contribution
  • Manpower:
    • MIT provides 1 postdoc and 1 student
    • Rice University provides 1 postdoc and 1 student (starting in September 2013)
  • The HI group responsibility (in collaboration with WU and IC):
    • Establishment of the detailed triggering specifications based on the requirements of heavy ion physics
    • Testing of the boards and firmware at the trigger demonstrator at CERN 904
    • Development of FPGA firmware for MP7 boards with specific heavy-ion triggering algorithms
    • Installation and commissioning of the new trigger in CMS experiment.
    • Purchase and testing of the 3 prototype oRSC boards
    • Purchase and testing of the final 22 oRSC boards
    • Purchase of optical fibers and patch panel
  • All the existing L1 calorimeter trigger electronics has been designed and produced by the University of Wisconsin and Imperial College (oRSC, CTP6/7, MP7)
status and schedule
Upgrade Project Office MeetingStatus and schedule
  • Contributing to the setup of the test system/demonstrator in CERN 904. The system includes 2 RCT crates and 1 MCC crate
  • XDAQ application to allow easy control and pattern test of trigger electronics (JCC, JSC, oRSC)
  • Gained hand on experience with the RCT system and with oRSC and MP7
  • Specific HI algorithm implementation schedule:
    • September 2013: Defined requirements for HI running
    • October 2013: Algorithms performance studies offline completed (it will include also the test of the existing stage-1 pp algorithm)
    • February 2014: Algorithm implemented in MP7
    • June 2014: Basic performance tests completed
    • Fall 2014: System ready for data-taking
  • MIT and Rice groups will collaborate with the Wisconsin and Imperial College groups for the installation and commissioning of the system in the CERN/P5 CMS experimental hall.
summary
Upgrade Project Office MeetingSummary
  • The upgraded Stage-1 system
    • Significantly improve the online jet trigger
    • Sufficient for data taking with heavy-ion collisions in 2015
    • Achieve similar performance for calo-jets as the HL-LHC system
  • Active collaboration with Wisconsin and Imperial college group already started
    • XDAQ application for 904 tests developed
    • Hand on experience with the electronics acquired (RCT, oRSC, MP7)
  • Definition of HI algorithm for the 2015 data-taking is ongoing
    • Schedule/milestones for algorithm implementation is defined
    • A first L1 jet UE background subtraction algorithm for HI already tested offline
track trigger t rigger turn on curves
Upgrade Project Office MeetingTrack trigger: trigger turn-on curves

“Central event”

0-20%

“Peripheral event”

60-100%

For Approval

For Approval

It is feasible to seed high pT track with L1 jet trigger

Provides a factor of 5-10 reduction of the L1 accept rate

current l1 sector wise subtraction
Upgrade Project Office MeetingCurrent L1: Sector wise subtraction

Before

After

  • The high non-uniformity in η does not permit a useful BG subtraction within a single 2x11 sector
current l1 sector wise subtraction1
Upgrade Project Office MeetingCurrent L1: Sector wise subtraction

Before

After

  • Test on 3 data samples
    • Min. Bias, Jets and central events
  • Can’t apply a threshold that keeps full efficiency for jets while rejecting a sufficient fraction of min bias events
trigger turn on 2015 l1 system
Upgrade Project Office MeetingTrigger Turn On: 2015 L1 system
  • Access to the full eta phi map allows for a efficient underlying event subtraction (phi-rings)
    • Peripheral and central events respond consistently to the thresholds applied to L1 Jets

Jet + Central UE

Jet + Peripheral UE

trigger turn on current l1 system
Upgrade Project Office MeetingTrigger Turn On: Current L1 system

High Threshold

  • Lack of UE subtraction does not allow for a consistent threshold for central and peripheral events
  • Poor control over L1 accept rates

Jet + Central UE

Jet + Peripheral UE

Low Threshold

physics performance plots
Upgrade Project Office MeetingPhysics performance plots
  • b jet quenching performance
    • Assuming the same amount of quenching as light jet
  • 3-jet event performance
    • R32 (3-jet / 2-jet ratio), access to gluon jet
  • High pT track RAA and v2 performance
    • Increased the pT reach from 100 to 160 GeV/c
b jet physics performance
Upgrade Project Office Meetingb-jet physics performance

PAS

  • Goal: di-b-jet asymmetry as done for inclusive jets in HIN-10-004 and HIN-11-013
  • Proposed observable:
    • Dijet asymmetry (AJ) & RB (fraction of balanced di-b-jet)
  • Expect similar systematics as light jets + (b tagging uncertainty & light jet contamination)
  • Use 2011 kinematic cuts: pT,1 > 100 GeV/c and pT,2 > 30 GeV/c
physics performance of 3 jet events
Upgrade Project Office MeetingPhysics performance of 3-jet events
  • Access to gluon jets: three jet events
    • R32 may be modified due to jet quenching
  • Similar study as QCD-10-012
    • All jet pT threshold > 100 GeV/c
  • No existing experimental measurements in heavy ion collision
  • Simulated with PYTHIA at 5.5 TeV

PAS

high p t reach of tracks and jets
Upgrade Project Office MeetingHigh pT reach of tracks and jets

High pT Jet (Anti kT R =0.3)

High pT track

Entries

PAS HIG-12-054

Approved

Jet pT (GeV/c)

Track