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LHC News

LHC News. End of June: The LHC is expected to be cooled down End of July: First particles may be injected, and the commissioning with beams and collisions will start. Sept/Oct: First collisions at 10 TeV. Cooldown status 13/5/08. Magnet tests. Sector 4-5 Power Tests

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LHC News

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  1. LHC News • End of June: The LHC is expected to be cooled down • End of July: First particles may be injected, and the commissioning with beams and collisions will start. • Sept/Oct: First collisions at 10 TeV. Cooldown status 13/5/08 Early Physics at the LHC, Sheffield May 08

  2. Magnet tests • Sector 4-5 Power Tests • Several training quenches were observed above 5 TeV equivalent currents • Stable conditions~10 TeVHopefully! • The magnet training for full 14 TeV operation will then be completed over the winter shutdown 2008 - 2009 Ramp of 138 power converters to a current equivalent to 5.3 TeV(including all high current magnets realistic LHC optics ) Early Physics at the LHC, Sheffield May 08

  3. What are minimum bias events? • Minimum bias are inelastic collisions of two protons • Includes very rare high-pt scatters and very common low-pt scatters • Minimum bias is an experimental definition • Defined by experimental trigger and analysis • Relation between experiment and physics is: fi are acceptances for different physics processes determined by the trigger Trigger bias Early Physics at the LHC, Sheffield May 08

  4. Triggering Minimum bias 75ns @ L=1031cm-2s-1 mean # of interactions/crossing ~0.06 Two Triggers implemented: 1. Random+track trigger L1 Filled bunch trigger Bunch crossing rate 13.3MHz Mean no events/crossing=0.06  94:6 empty:interaction Use L2 pixel and SCT spacepoints to reject empty events Use tracks in EF to reject beam-gas 2. L1 using Minimum bias trigger scintillators Early Physics at the LHC, Sheffield May 08

  5. η=2.0 interaction point η=3.8 +η pannel Beam-pipe MBTS MBTS • Trigger scintillation counters mounted on end of LAr calorimeter covering same radii as ID • Cover 2<|h|<4 • Can be used for first data BUT! • Not rad-hard • Uses 1/8th of tilecal readout  Lifetime unknown • At L1 S/N is ‘modest’ • Now in simulation can be tuned to measurement in the summer • Can do better at L2 with precision readout UA5 Early Physics at the LHC, Sheffield May 08

  6. MBTS trigger: Trigger bias • MBTS_1_1 requires hits in both hemispheresThis should be similar to earlier NSD triggers • MBTS_2 requires two paddles to be hit, can be same side • Trigger bias = efficiency of trigger for specific processNot trigger rates! preliminary preliminary Will Bell Early Physics at the LHC, Sheffield May 08

  7. Inner Detector Trigger at L2 L1 random trigger preliminary preliminary Use pixel and SCT spacepoints to reject empty events Empty:Interaction ~ 94:6 Still have large beamgas contribution Early Physics at the LHC, Sheffield May 08 Will Bell and Regina Kwee

  8. Inner Detector Trigger SCT Space Points >= 3 & Pixel Space Points >=12 preliminary |η| < 2.5 & pT > 200 MeV & |Z0| < 200.0 mm Track constraint removes beamgas through vertex constraint Early Physics at the LHC, Sheffield May 08 Will Bell and Regina Kwee

  9. pT~250MeV pT>500MeV MC primary charged particles Tracking in MB events 1000 events dNch/d • Acceptance limited in rapidity and pt • Rapidity coverage • Tracking covers |h|<2.5 • pT problem • Need to extrapolate by ~x2 • Need to understand low pt charge track reconstruction h Early Physics at the LHC, Sheffield May 08

  10. Low pT track reconstruction M.Leyton preliminary preliminary Use tracks pT>150MeV preliminary Track-particle correction Acceptance*efficiency*fake subtraction Technical details: Release 13.0.40 low pT tracking Now improved – see later Early Physics at the LHC, Sheffield May 08

  11. Minimum bias distributions ATLAS has the tools to trigger on and reconstruct minimum bias events preliminary • Minimum bias sample • Selected by MBTS_2 • Corrections for: • track reconstruction • vertex reconstruction • Multi-vertex events not looked at! MB sample PYTHIA preliminary Distributions have pT>150MeV 6% NSD sample Corrected for trigger bias -- change trigger bias NSD sample Early Physics at the LHC, Sheffield May 08

  12. Particle Composition MB particle dominiated by low pT pions and ~10% K • Pions • 150MeV can traverse to edge of SCT but reduced efficiency due to inelastic collisions in ID • Kaons • Much larger inefficiencies due to increased inelastic collisions in ID • Efficiencies depend on relative rates of particle production in MB interactions (Sadly CMS can do PID with analog readout) Ian Dawson Early Physics at the LHC, Sheffield May 08

  13. Coming soon: Improved low pT tracking • Based on two-pass tracking • Find tracks with pT>500 MeV • Find tracks with 100<pT<500MeV from remaining hits, widens track finding roads Improved low pT turn-on 0.1 < PT≤ 0.5 (GeV) Early Physics at the LHC, Sheffield May 08

  14. Coming Soon: Improved low pT tracking 0.1 < PT≤ 0.5 (GeV) Early Physics at the LHC, Sheffield May 08

  15. Track Reconstruction efficiencies by track insertion D.Clements • Insert a track into a minimum bias event by overlapping an RDO-DIGI file of a single track event. • Reconstruct merged event and look for inserted single track to determine efficiency. Muons pT>0.5GeV Muons pT>0.5GeV • Uses InDetOverlay-00-00-02 (by Andrei Gaponenko) Early Physics at the LHC, Sheffield May 08

  16. PHOJET PHOJET implemented in ATHENA Important for systematic cross-checks Early Physics at the LHC, Sheffield May 08

  17. More work to be done • Release 14 • Multi-vertex analysis • Identification of SD, DD, ND? • Alignment study Early Physics at the LHC, Sheffield May 08

  18. Startup Conditions • Current expectations: 2 months single beam running from the end of July • Beam stability poor • Single beam running provides: • ‘Clean’ environment to study beam backgrounds: Beam halo and beam gas • Alignment and commissioning of endcap systems • When to switch-on? • Aim to trigger on beam gas and beam halo events • Beam gas events distributed along Z following gas density • Beam halo events mainly coming from upstream tertiary collimators (TCT) n Early Physics at the LHC, Sheffield May 08

  19. L1 for single-beam running • Make a trigger decision from a loose time coincidence between Beam Pickup (BPTX) and • 2 or more Minimum bias trigger scintillators (MBTS) above threshold (MBTS overlaps EC-SCT) OR • 1 or more BCM above threshold • The HV of the TGCs will be switched on when the beam is stable enough. • The TGCs may be used to trigger on beam halo by faking a hit in the TGC1 station. • This is similar to the current cosmic setup in the barrel. Early Physics at the LHC, Sheffield May 08

  20. Track Reconstruction • Beam halo tracks can be reconstructed by using cosmic style tracking code • First go – beam-halo muons in endcap SCT • Alignment • Rate ~130Hz? A. Salzburger Early Physics at the LHC, Sheffield May 08

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