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Triggering on Diffraction with the CMS Level-1 Trigger: Pushing the Limits

Triggering on Diffraction with the CMS Level-1 Trigger: Pushing the Limits. Monika Grothe U Wisconsin / U Turin Manchester December 2004. Outline: 1. The high luminosity case: L LHC = 10 33 to 10 34 cm -2 s -1 E.g. double diffractive Higgs production

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Triggering on Diffraction with the CMS Level-1 Trigger: Pushing the Limits

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  1. Triggering on Diffraction with the CMS Level-1 Trigger:Pushing the Limits Monika Grothe U Wisconsin / U Turin Manchester December 2004 Outline: 1. The high luminosity case: L LHC = 1033 to 1034 cm-2 s-1 E.g. double diffractive Higgs production 2. The low luminosity case:L= 1028 to 1031cm-2 s-1 E.g. double diffractive b production 3. Squeezing more latency out of the L1 trigger Monika Grothe, Triggering on Diffraction with the CMS L1 Trigger:Pushing the Limits

  2. Muon Calo 40 MHz collision < 100 Hz < 75 kHz Level-1 trigger CMS and its Level-1 trigger Tracking: Si pixel, Si strips Calorimetry: ECAL PbWO4 crystals HCAL Scintillator/copper HF Quartz/copper 4T solenoid Muon detection with instrumented iron Coverage Tracking0 < || < 3 Calorimeters0 < || < 5 no tracking! High-Level Trigger HLT Monika Grothe, Triggering on Diffraction with the CMS L1 Trigger:Pushing the Limits

  3. The high luminosity case:L LHC = 1033 to 1034 cm-2 s-1 • Relevant for double-diffractive production • of a low-mass Higgs (~120 GeV) that • decays preferably into a b-bbar pair • Low cross section, hence need highest achievable LHC luminosities • TOTEM RP (220m) acceptance low for diffractively scattered protons at nominal LHC luminosities and beam-optics • Hence need to trigger with the central CMS detector (disregarding RPs at 400m for the moment) • L1 trigger signature: • 2 jets in the CMS calorimeters, each with ET < 60 GeV H Monika Grothe, Triggering on Diffraction with the CMS L1 Trigger:Pushing the Limits

  4. CMS Level-1 Calorimeter Trigger Iso/non-iso e cands ET per region 4 highest ET iso e + non-iso e 4 highest ET central jets 4 highest ET central tau jets 4 highest ET fw jets Total ET Ht = ET in jets Jet multiplicities Missing ET Monika Grothe, Triggering on Diffraction with the CMS L1 Trigger:Pushing the Limits

  5. Level-1 Jets HCAL Trigger tower ECAL • 4x4 trigger towers = region • Search for jets with a sliding 3x3 regions window • Jet = 3x3 region where the ET in the central region is above some threshold and is bigger than the ET in any of the 8 outer regions • Jet = t if the t veto is off in all 9 regions PbWO4 crystal t veto patterns A jet = 144 trigger towers, with typical tower dimensions Dh x Df = 0.09 x 0.09 Hence typical jet dimensions: Dh x Df = 1 x 1 Monika Grothe, Triggering on Diffraction with the CMS L1 Trigger:Pushing the Limits

  6. Trigger Mapping onto Cal surface Area covered by 1 jet Monika Grothe, Triggering on Diffraction with the CMS L1 Trigger:Pushing the Limits

  7. How low can one cut in L1 jet ET ? L1 2-jet rates ! Calibrated L1 jet ET cut and resulting L1 2-jet rate: 110 GeV -- 1 kHz 60 GeV -- 10 kHz Need additional conditions to trigger a 120 GeV Higgs with L1 Possible L1 condition that comes closest to a rap gap trigger (rap gap > 2): 2 jets in central Cal (|h|<3)with ∑(ET 2 jets) / HT > threshold HT = sum of the scalar ET of all jets in the event with ET(jet)>threshold, i.e.only ET around local energy maxima is included in sum 2 x 1033 cm-2 s-1 jet trigger rates Monika Grothe, Triggering on Diffraction with the CMS L1 Trigger:Pushing the Limits

  8. How low can one cut in L1 jet ET ? Other possibilities and caveats • Resolution for a L1 jet is ~25% - 30% For jets with 60 GeV Et, would want to cut not higher than 40GeV • Rate plots show calibrated L1 jet ET; on average, the ET seen in a L1 jet is only ~60% of the true jet energy (~25 GeV for true 40 GeV) • Noise per trigger tower ~300 MeV • 1 jet consists of 144 trigger towers, of which only those with ET>1 GeV are included in the uncalibrated jet ET A cut on a calib’d jet ET of 40 GeV is already getting close to the limit • Other possibilities: • Back-to-backness of 2 jets: L1 jets come with position information (resolution in h, fof ~ 0.35) • Combine Cal and Muon trigger info for events where one b decays semileptonically Monika Grothe, Triggering on Diffraction with the CMS L1 Trigger:Pushing the Limits

  9. The low luminosity case:L= 1028 to 1031 cm-2 s-1 Case in which one can disregard rate as a problem What are the lowest mass states the CMS L1 can trigger on ? Example: Double-diffractive production of cb Relevant for alignment of RPs L1 trigger signature: 2 muons in the CMS muon chambers, each with mass ~ 4.5 GeV cb cb   (1S)  l+ l- mass ~10 GeV ~9.5 GeV Monika Grothe, Triggering on Diffraction with the CMS L1 Trigger:Pushing the Limits

  10. Digression: Alignment of RPs • Lesson from ZEUS Leading Proton Spectrometer: You cannot rely on the beam position monitors for aligning the RPs. You need to use a physics process. (ZEUS: photoproduction of r0) • This physics process must provide leading particles with a known momentum and high cross section. • Diffractively scattered leading protons ideal because of the size and width of the diffractive peak in the leading particle spectrum. • Any diffractive process (SD, DD) is fine that results in a low mass state in the central CMS detector. • Production of cb implies x1 x2= 10GeV/14TeV, i.e. x ~ 0.1% • “Monochromatic” beam of leading protons in the RPs (with tails, when x1 and x2 are asymmetric) • Caveat: For a t measurement, need to align such that the pT of the central detector state balances that of the leading protons, g is a problem there. Monika Grothe, Triggering on Diffraction with the CMS L1 Trigger:Pushing the Limits

  11. How low can one cut in m pT ? Was investigated for the question of a L1 trigger in heavy-ion runs Shown above: L1 efficiency for triggering one or two of the decay muons of an Upsilon(1S) with |h|<1.5 as a function of the muon pT If you need to trigger on low-mass states in the central CMS detector, muons are your best bet. Monika Grothe, Triggering on Diffraction with the CMS L1 Trigger:Pushing the Limits

  12. CMS L1 Trigger & TOTEM • TOTEM implements its DAQ and trigger system in a CMS-compatible fashion • TOTEM contributes as subtrigger to the CMS L1 within the CMS L1 latency time window of 3.2 ms (i.e. 128 bunch crossings BX) • TOTEM subtrigger is sent to the CMS L1 Global Trigger • The CMS L1 Global Trigger generates the L1 trigger response and sends the L1-Accept decision back to the TOTEM front-end • CMS prefers the TOTEM subtrigger to enter as a physics trigger which allows the L1 Global Trigger to generate its trigger decision by combining the CMS and the TOTEM subtriggers (not possible for technical triggers) • TOTEM/CMS Global Trigger interface has been defined Need to start working out the details beyond this now. Monika Grothe, Triggering on Diffraction with the CMS L1 Trigger:Pushing the Limits

  13. Pushing the limits even harder:Squeezing more latency out of L1 • Normal L1 running mode: • Trigger rate 50 kHz • L1 latency 3.2 ms (128 BX) • Set of “standard” trigger rules derived from minimizing simultaneously L1 dead time and buffer overflows in subsystems: No more than 1 (2) (3) (4) L1A per 75 ns (625 ns) (2.5 ms) (6 ms) • Limits driven by Tracker and Preshower Detector Total deadtime cost at 100 kHz L1A rate of the order 1% CMS assumes that the TOTEM RPs are going to contribute to the L1 trigger in the normal running mode Monika Grothe, Triggering on Diffraction with the CMS L1 Trigger:Pushing the Limits

  14. 129 192 ... ... ... Revolving part of 128 BX depth Storage part can hold 8 L1A à 3 buffer cells each Pushing the limits even harder:Squeezing more latency out of L1 (II) Tracker memory buffer partitioning upon L1A cell 1 pre-L1A storage post-L1A buffer “Long latency” mode: Only option to include RPs at 400m in CMS L1 Uses post-L1A event buffers for pre-L1A storage For trigger rate < 10 kHz, L1 latency 4.8 ms (189 BX) Resulting trigger rule: Each L1A separated by at least 8.75 ms because events has to be read out from Tracker buffer with 8.75 ms latency Total deadtime cost at 10 KHz L1A rate of the order 10% Monika Grothe, Triggering on Diffraction with the CMS L1 Trigger:Pushing the Limits

  15. Conclusions • Triggering diffractive Higgs production on L1 is difficult • Work ongoing to assess possibility of triggering diffractive Higgs production on L1 with CMS Cal only, without using any RPs Not hopeless, but difficult, not ready to give up yet • Including RPs at 400m in L1 trigger requires running of the CMS L1 Trigger in a special long latency mode Is 4.8 ms (instead of 3.2 ms) sufficient ? • Triggering production of low mass states in central CMS detector on L1 (for example for purpose of aligning RPs for which it is essential) is possible but requires using muon trigger Monika Grothe, Triggering on Diffraction with the CMS L1 Trigger:Pushing the Limits

  16. Backup slides Monika Grothe, Triggering on Diffraction with the CMS L1 Trigger:Pushing the Limits

  17. Jet or t ET • 12x12 trig. tower ET sliding in 4x4 steps w/central 4x4 ET > others t: isolated narrow energy deposits • Energy spread outside t veto pattern sets veto • Jet  tif all 9 4x4 region t vetoes off • Electron (Hit Tower + Max) • 2-tower ET + Hit tower H/E • Hit tower 2x5-crystal strips >90% ET in 5x5 (Fine Grain) • Isolated Electron (3x3 Tower) • Quiet neighbors: all towerspass Fine Grain & H/E • One group of 5 EM ET < Thr. Monika Grothe, Triggering on Diffraction with the CMS L1 Trigger:Pushing the Limits

  18. Cal trigger tower segmentation Central CAL FWD CAL (HF) Seg. in f: 5 Seg. in h: 0.09 to 0.15 Monika Grothe, Triggering on Diffraction with the CMS L1 Trigger:Pushing the Limits

  19. Trigger Rates vs Threshold Monika Grothe, Triggering on Diffraction with the CMS L1 Trigger:Pushing the Limits

  20. Cal Trigger Rates: 2 x 1033 cm-2 s-1 Selected Scenario: 5 kHz e/g, 5 kHz t,jets, 1 kHz combined, rest m Monika Grothe, Triggering on Diffraction with the CMS L1 Trigger:Pushing the Limits

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