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Toward the Unknown: First Physics from Atlas

Toward the Unknown: First Physics from Atlas. Outline. Introduction Why the LHC? Atlas Experiment Won’t discuss CMS, LHCB, … 1 st results Summary. Thanks to my Atlas colleagues…. Introduction. The Standard Model (SM) provides an excellent description of experiments and is predictive .

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Toward the Unknown: First Physics from Atlas

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  1. Toward the Unknown: First Physics from Atlas

  2. Outline • Introduction • Why the LHC? • Atlas Experiment • Won’t discuss CMS, LHCB, … • 1st results • Summary Thanks to my Atlas colleagues…. J. Hobbs, SBU Colloquium

  3. Introduction The Standard Model (SM) provides an excellent description of experiments and is predictive a priori “SM” predictions |c| contributions to fits assuming SM J. Hobbs, SBU Colloquium

  4. But there are still issues… • Some pieces of SM to work on • Electroweak symmetry breaking unproven • Precision flavor studies • Stability: fine tuning issues? • SM doesn’t answer some big questions • Fermion mass spectrum? • Dark matter? • Matter/antimatter asymmetry? • Including D0 results described 2 weeks ago • Ultimately EW + strong unification J. Hobbs, SBU Colloquium

  5. EW Symmetry Breaking • Simplest form of (Local) gauge invariance requires massless force carriers • Photon (and gluon), m=0. OK… • MW = 80 and MZ = 91 GeV • SM and the Higgs mechanism • Permits non-zero boson mass & gauge invariance together • Requires a Higgs boson (thus “the Higgs search”) • Is this correct? We don’t know… J. Hobbs, SBU Colloquium

  6. EWSB: Current state Indirect constraints on Higgs from SM consistency… … mW and mt precision are current limiting factors J. Hobbs, SBU Colloquium

  7. Fine Tuning / Dark Matter • SM has far too little dark matter (n’s). • Fine tuning: SM values must be within a part in 1032 for stability. May be unnerving? Supersymmetry (e.g,) is a possible solution to both: Includes a dark matter candidate. Removes fine-tuning by cancellation and leads to mH < 135 GeV? Predicts new particles whose multiplicity is determined by SM particle content But no direct experimental evidence, only bounds if it exists M > 100 – 300 GeV Is it right? J. Hobbs, SBU Colloquium

  8. LHC Motivation • Tests of posited solutions to SM shortcomings have led to lower mass bounds for new physics, but no direct observation • The space of new physics possibilities is large. Won’t discuss specifics further… • How to proceed? • Indirect tests (ala Higgs constraints and CP violation of 2 weeks ago and others) • Direct searches for higher mass. • High mass means higher energy, thus the LHC J. Hobbs, SBU Colloquium

  9. Large Hadron Collider (LHC) • In general, rate for reaction X is • NX = sX* L • LHC: pp collider design • Ecm = 14 TeV(7x FNAL) • L = 1034/cm2/s (30x FNAL) • Beam • Stored energy 360 MJ (!) • Current 0.58 A accelerator nature, ECM Most significant increase in Ecm since 1981 (ISR -> SppS) J. Hobbs, SBU Colloquium

  10. Large Hadron Collider Rate vs. Ecm Jet rate vs. jet ET b quark This is background! unknown Jet ET>100 Z LHC Tevatron t quark H (150) H (500) Other processes, s(LHC)/s(TeV) W ttbargg(400 GeV) Z’(1 TeV) 10x 100x 20000x 300x (but mass dependent) ~~ Jet ET > ECM/4 J. Hobbs, SBU Colloquium

  11. LHC: Is 14 TeV enough? • For WW scattering to remain bounded • Requires *something* with M<1 TeV • MH (including SUSY)… • In SM *something* = Higgs, so MH<O(1 TeV) • In “SUSY”, MH < 135 GeV, and more particles • Alternatives must leave WW OK. Encouraging… (some say “guaranteed”) J. Hobbs, SBU Colloquium

  12. LHC: What’s the situation now? • Restart in Sept. 2009 after year delay for magnet connection induced problems • ECM = 7 TeV. • A safety factor for magnet connections • (Also lower energies during start up) • Beyond ECM, performing very well • Already at design protons/bunch • Long beam lifetimes, good emittance • Stored energy, 5 MJ – 10 MJ (FNAL, 2 MJ) J. Hobbs, SBU Colloquium

  13. LHC Performance 4/pb/day: 400,000 W/day 400 top pairs/day !! Bunch trains commissioned For past two weeks, injecting more bunches While writing this talk, the record instantaneous luminosity increased 4x with possibly another >2x coming this month… J. Hobbs, SBU Colloquium

  14. Atlas Experiment • Higher energies means more particles and particles with more energy. • Drives experimental design: energy containment, particle density “jet” p Hadronic energy g e Beam perp to screen Charged particle trajectories EM energy n m J. Hobbs, SBU Colloquium

  15. Atlas Experiment O(107) read out channels operating efficiency 98% J. Hobbs, SBU Colloquium

  16. (plus others…) Dijet Event: MJJ = 2.55 TeV ETJ1 = 420 GeV ETJ2 = 320 GeV J. Hobbs, SBU Colloquium

  17. J. Hobbs, SBU Colloquium

  18. J. Hobbs, SBU Colloquium

  19. Atlas Experimeters SBU Atlas @ CERN + a few missing SBU Atlas @ SBU Can you find Caputo, McCarthy or Hobbs? 20% of the Atlas collaborators J. Hobbs, SBU Colloquium

  20. 1st Science • Can we see the things we expect? • Reconstruct charged particles • p0, hadronic jets, J/y • W*, Z bosons • Top quark? • Aggregations: multiplicities, W+jets* • Or the unexpected? Early (proto)searches • q* high rate, low S/B • W’ lower rate, excellent S/B • Early SUSY*, LQ* Every measurement at the LHC is new territory… J. Hobbs, SBU Colloquium *SBU involved

  21. Low Masses: p0->gg Pseudorapidity, h (polar angle) Diphoton mass OK at O(1%)… ECM = 900 GeV Mass vs. h Azimuthal angle Are the material and calorimeter understood for the inner “1/2” of the detector? J. Hobbs, SBU Colloquium

  22. Dijet Production High-rate process Differential cross section (pT) for |y| < 2.8 Measures shape, but not absolute rate. NLOJET++ 4.1.2, CTEQ6.6 J. Hobbs, SBU Colloquium

  23. Low Masses: J/y -> mm Do we understand the material in the outer detector? Somewhat different samples and selections J. Hobbs, SBU Colloquium

  24. High Mass: Z and W Bosons Reconstruct Z->ll (l=e,m), This is a critical standard candle. But low rate… Low mass resonances indicated OK understanding of material, but here resolution mismatch indicates better stats for (probably) alignment and channel-to-channel calibration J. Hobbs, SBU Colloquium

  25. W->ln SBU involvement… Loose Selection MT= √2pTlpTv(1-cosdf) Final Selection primarily adds MET requirement Tests understanding of hadroniccalib J. Hobbs, SBU Colloquium

  26. W Cross Section W cross section Why is W+ different than W- J. Hobbs, SBU Colloquium

  27. Correlations: W and Z with jets • Intrinsically interesting because • Hard to calculate rates with precision. • Dominant background to many new physics scenarios More gluons give more jets. (Each gluon is one more factor of as) SBU works on this J. Hobbs, SBU Colloquium

  28. W+Jets Jet multiplicity distribution jet pT distribution Stony Brook group working on this topic. Cross sections in internal review now… J. Hobbs, SBU Colloquium

  29. Top Quarks? Well, maybe Expect a few top pairs in summer data sample Analyses ready, and and a few events… J. Hobbs, SBU Colloquium

  30. 1st Physics Publications Charged particle multiplicities in pp Collisions at ECM = 900 GeV(Phys Lett B 68, Issue 1, 21-42) And updated for 7 TeV data Early bread & butter science which requires low Linst J. Hobbs, SBU Colloquium

  31. Excited quark search • Highest rate visible process is pp -> jet+jet. • Can be enhanced by direct production of new particles or indirect effects (high mass states) Signal e.g. excited quarks, Excluded over region 0.3 TeV < mq* < 1.26 TeV (Prev. excl. mq*<0.76 TeV) Jul. 23 (preliminary) Accepted by Phys. Rev. Lett. J. Hobbs, SBU Colloquium

  32. But it’s already been updated… Sep. 26 Signal e.g. excited quarks, Excluded over region 0.5 TeV < mq* < 1.53 TeV Preliminary, 9/26 J. Hobbs, SBU Colloquium

  33. Near Term: W’ search Heavy vector bosons (W’, Z’) features of many new physics models Clean channel, but yield falls quickly as a function of mass Existing FNAL bounds roughly 1 TeV, so wait < 1 yr. J. Hobbs, SBU Colloquium

  34. And down the road, e.g. SUSY Start with a basic selection and then specific requirements. Early days… J. Hobbs, SBU Colloquium

  35. Future • Continue running at 7 TeV until end 2011 • Accumulate 1 fb-1 data (increase 100x) • Already significant room for discovery • Not Higgs, though… • LHC shutdown for 1 yr. Finish magnet fixes, maybe modest Atlas changes • After restart, move to 14 TeV • Longer term • Atlas upgrades (2 stages at least) • LHC luminosity growth to design J. Hobbs, SBU Colloquium

  36. Summary • After a long wait, the LHC/Atlas program is really underway • LHC & experiments working well • Established 1st signals and initial calibrations • Early search results already new mass range • Will explore significant new territory with the current data. What’s there? • Dark Matter? EWSB explained? It really is unknown territory J. Hobbs, SBU Colloquium

  37. Where to? J. Hobbs, SBU Colloquium

  38. (Simulated) H->ZZ->eejj (Simulated )SUSY event J. Hobbs, SBU Colloquium

  39. BACKUP J. Hobbs, SBU Colloquium

  40. g1 g2 g3 Gauge Unification The SM couplings do not intersect at one point. SUSY does… g1 g3 g2 SM SUSY 40 J. Hobbs, SBU Colloquium

  41. Composition of the Universe (0.4% stars) J. Hobbs, SBU Colloquium

  42. J. Hobbs, SBU Colloquium

  43. Atlas good beam efficiency J. Hobbs, SBU Colloquium

  44. Z cross section J. Hobbs, SBU Colloquium

  45. Trigger rates crossing at 40 MHz -> L1 then at 10 kHz -> L2 then at 1 kHz -> HLT (10 GB/s) then at 100 Hz -> tape (1 GB/s) In a year at 50% duty cycle: 15 PB J. Hobbs, SBU Colloquium

  46. Magnet Problem During ramp tests, a solder joint in the cold region failed with 1 V at 9 kA. 1. current ramp (10 A/s) auto stopped 2. relief circuit automatically turned on to dump magnet current ==> All functioned correctly to this pt 3. An arc developed causing failure of He (1.9K) containment 4. He boiled catastrophically causing high pressure… J. Hobbs, SBU Colloquium

  47. J. Hobbs, SBU Colloquium

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