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The Physics of Run II

The Physics of Run II. John Womersley Fermi National Accelerator Laboratory DØ Software and Analysis Meeting Prague, Czech Republic, September 1999 http://d0server1.fnal.gov/users/womersley/PragueSep99/Run2Physics.ppt. CDF. Tevatron. MI. DØ. Run II redefined. The “Long Run II”

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The Physics of Run II

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  1. The Physics of Run II John Womersley Fermi National Accelerator Laboratory DØ Software and Analysis Meeting Prague, Czech Republic, September 1999 http://d0server1.fnal.gov/users/womersley/PragueSep99/Run2Physics.ppt

  2. CDF Tevatron MI DØ Run II redefined • The “Long Run II” • 2 fb-1 by 2002 • 9 month shutdown • install new silicon layers • ~ 15 fb-1 (or more) by 2006 • Fermilab schedule slippage (always a sore point) • New schedule will be fixed in October • Data taking now seems unlikely before the end of 2000

  3. Run I  Run II • The Tevatron is a broad-band parton-parton collider Huge statistics for precision physics at low mass scales Number of Events Formerly rare processes become high statistics processes Increased reach for discovery physics at highest masses Run II Run I Subprocess s Extend the third orthogonal axis: the breadth of our capabilities

  4. Three ways in which we gain • Statistics • Huge statistics at “low” mass scales • B-physics, QCD, W-mass • Formerly rare processes enter the precision domain • QCD with vector bosons, thousands of top events • lay to rest some “undead” Run I anomalies • the high-ET jet “excess”, the CDF ee event • Increased reach at the highest mass scales • electroweak symmetry breaking • SUSY, Higgs, etc. • New detector capabilities • displaced vertex b-tagging • much improved muon momentum resolution • tracking triggers

  5. Some of our strengths Jets Inclusive jet cross section EM calorimetry Missing ET  + X mW = 80.450  0.093 GeV DØ electrons

  6. New Tools: charged particle tracking

  7. In Run I only one of these three muons would have been found! W   b   W  

  8. New tools: heavy flavor tagging c b ~ 55% at large pT u,d,s

  9. New tools: all new software • Full rewrite of online code,level 3 trigger and offline reconstruction in C++

  10. Physics Goals of Run II • b-physics • Targeted program including CP violation in B  KS • QCD • Nucleon structure (parton distributions, diffraction) • Jets, photons, Drell-Yan, vector bosons+jets, heavy flavour production • Standard-Model Physics • High-statistics study of the top quark (mass, cross section, rare decays, single top production) • Precision measurement of the W mass (< 50 MeV) • Beyond the Standard Model • Supersymmetry • Higgs searches • Technicolor, compositeness, new vector bosons, etc. Take a closer look at the highlighted topics: low, medium and high mass scales

  11. B Physics Slides from Rick Jesik, Indiana University

  12. Run II B Physics Topics • Spectroscopy • Lifetimes • Branching ratios • Rare decays • CKM measurements

  13. QCD measurements • Cross sections vs. pTmin • single leptons (muons and electrons) • dileptons • muons with jets • J/y, y(2s) • Differential cross sections • B J/y + K  • Correlations • dilepton Df • muon + jet • forward - central • Charmonium • color octet model

  14. Exclusive B decays Expected yields in 500 pb-1

  15. B Physics in the 21st Century • Experiments will confront the Standard Model interpretation of CP violation • A and l have been measured to a few percent • unitarity condition:

  16. B  J/ KSReconstruction • J/   + -require two central tracks with pT > 1.5 GeV/c • KS   + -use long lifetime to reject background: Lxy/ > 5 • Perform 4-track fit assuming B J/ KS • constrain   and - to mass of KS and J/ respectively • force KS to point to B vertex and B to point to primary

  17. Sin2b Expectations for 2fb-1 For a time independent analysis: • (S/B ~ 0.75) • eD2~ 6.7 % But, since most of the background is at small t’s, a time dependent analysis gives reduced error: (sin2b) ~ 0.07 And this is just in the first two years - 2 fb-1. We won’t stop there…...

  18. Expectations beyond 2fb-1

  19. 2002 - exciting times • BaBar and BELLE will have results from their first physics runs (not at design luminosity) • 1 - 30 fb-1d(sin2b) ~ 0.12 - 0.18 • We (and CDF) should have 1.0 - 2.0 fb-1 analyzed • d(sin2b) ~ 0.10 - 0.07 • Tevatron could beat the B-factories • everyone combined could signal new physics. • The new detector puts us in a great position to do significant B physics measurements in Run II, but we have a lot of hard work ahead of us • getting the detector and triggers ready and working • reconstruction programs for B0 J/y + Ks 0 • But hey, look what we did in Run I without an inner tracker.

  20. Top quark physicsSlides from Ann Heinson, UC RiversideDØ Workshop, Seattle, June 1999http://www-d0.fnal.gov/~heinson/top500/

  21. Beyond the Standard Model

  22. Where do we stand, circa 2000? • The Standard Model works at the 10-3 level • All observations are consistent with a single light SM Higgs, though no such beast has yet been observed • mH > 95.2 GeV (LEP) and mH < 245 GeV (SM fit, Eidelman & Jegerlehner)

  23. Beyond the Standard Model • General arguments for new physics at the EW scale (250 GeV) • Standard Model fits suggest the new physics is weakly coupled • Indirect pointers to supersymmetry Direct searches all negative so far • LEP2 • squarks (stop, sbottom) > 80-90 GeV • sleptons (selectron, smuon, stau) > 70-90 GeV • charginos > 70-90 GeV • lightest neutralino > 36 GeV • Tevatron Run I • squarks and gluinos • stop, sbottom • charginos and neutralinos

  24. Your mission (should you choose to accept it) At your earliest convenience, please carry out one or more of the following challenges: • Discover the SM Higgs • Discover or exclude lightest SUSY Higgs with masses up to ~ 130 GeV • Discover one or more superpartners • Exclude supersymmetry at the TeV scale by discovering some other new physics • Can any of this be done in the next five years?

  25. SM Higgs: LEP2 prospects • Eilam Gross at EPS99 • mH excluded < 108.5 GeVwith 150 pb-1 per expt at s = 200 GeV

  26. Higgs Production at the Tevatron • gg  H dominates, but huge QCD background • WH and ZH seem to offer the best potential • SUSY enhances associated b production • Run II SUSY/Higgs workshop • http://fnth37.fnal.gov/higgs.html • repeated and extended previous studies, combining all possible channels • simulated “average” of CDF and DØ (SHW parameterized simulation) program

  27. SM Higgs Channels mH < 130-140 GeV • WH  l bb backgrounds Wbb, WZ, tt, single top • factor ~ 1.3 improvement in S/B with neural network • possibility to exploit angular distributions (WH vs. Wbb) Parke and Veseli, hep-ph/9903231 • WH  qq bb overwhelmed by QCD background • ZH  l l bb backgrounds Zbb, ZZ, tt • ZH   bb backgrounds QCD, Zbb, ZZ, tt • requires relatively soft missing ET trigger (35 GeV?) mH > 130-140 GeV • gg  H  WW* backgrounds Drell-Yan, WW, WZ, ZZ, tt, tW,  signal:background ratio ~ 7  10-3 ! • Angular cuts to separate signal from “irreducible” WW background

  28. Combined reach • Bayesian combination of two experiments • 30% improvement in bb mass resolution over Run I • SHW acceptance but no neural network improvement assumed • 10% systematic error on backgrounds 15 fb-1 2 fb-1

  29. SM Higgs: Issues • LEP2 analysis is clear-cut, and the reach is predictable • The Tevatron analysis is an exciting prospect. Is it credible? • In my view, yes: it is an exercise similar in scale to the top discovery, with a similar number of backgrounds and requiring similar level of detector understanding. • but it will be harder: the irreducible signal:background is worse • it has caught the imagination of experimenters • the single biggest problem with the studies so far (in my opinion) is the assumptions about the bb dijet mass resolution • can the assumed resolution really be achieved (and in a high luminosity environment)? • can it be improved (through the use of “smarter” algorithms)? e.g. kT?

  30. DØ simulation for 2fb-1 Higgs simulation for 10fb-1 CDF observation in Run I signal Mass resolution • Directly influences signal significance • Requires corrections for missing ET and muon • Z  bb will be a calibration signal

  31. Minimal Supersymmetric Standard Model i.e. SM particles plus two Higgs doublets and their SUSY partners Even this minimal spectrum can have many faces: • Is R-parity conserved? • Is the LSP (lightest supersymmetric particle) stable? • How is supersymmetry broken? • Supergravity-inspired (mSUGRA): the typical benchmark • parameters m1/2, m0, A0, tan b, sign(m) • radiative EWSB occurs naturally from large top mass • the c01 is the LSP • c01 , c02 , c1 , sleptons and h are “light” • c03 , c04 , c2 , squarks and gluinos are “heavy” • Gauge-mediated (GMSB): LSP can be Gravitino • signatures with photons and/or slow-moving particles which may decay within or outside detector • Anomaly mediated • lightest chargino and neutralino almost degenerate

  32. Hadron collider SUSY signatures • The highest production cross section at a hadron collider is for the pair production of squarks and gluinos • As long as R-parity is conserved, jets + missing transverse energy: Missing ET SUSY backgrounds

  33. estimated background data DØ search for squarks and gluinos Run II limit: gluino mass ~ 400 GeV • Demand • 3 jets, ET > 25 GeV, one jet ET > 115 GeV • HT > 100 GeV • veto electrons, muons • Main Backgrounds: top, QCD jets, W/Z+jets • Cascade decays to charginos can give leptons in final state: complementary analysis requiring • 2 electrons, 2 jets + Missing ET Run I excluded

  34. Chargino/neutralino production • “golden” trilepton signature • Run II reach on  mass ~ 180 GeV (tan  = 2, µ< 0) ~ 150 GeV (large tan ) • this channel becomes increasingly important as squark/gluino production reaches its kinematic limits (masses 400-500 GeV) • Low pT triggering? • Can we include tau modes?

  35. Stop sensitivity ~ 150-200 GeV in Run II Stop and Sbottom • Stop • stop  b + chargino or W (top like signatures) • stop  c + neutralino • top  stop and gluino  stop • Sbottom • 2 acollinear b-jets + ETmiss CDF Run I stop and sbottom limits Sbottom sensitivity ~ 200 GeV in Run II 115 GeV 145 GeV

  36. DØ  Gauge Mediated SUSY • Is this selectron pair production? • All we can say is that searches for related signatures have all been negative • CDF and DØ  + missing ET • DØ  + jets + missing ET • LEP 2 events observed 2.3 ± 0.9 expected LEP

  37. A taxonomy of GMSB signatures • Are event generators available for non-prompt scenarios? • Interface to detector simulation maybe non-trivial • Standard searches pick up taus, multileptons and missing ET. • Prompt photons are “easy” • Challenges: Displaced photons, kinked tracks and cannonballs

  38. EM calorimeter x Preshower Displaced photons • Run II DØ direct reconstruction with z = 2.2 cm, r = 1.4 cm • Non-pointing photon analysis used at LEP: excludes neutralino masses < 85 GeV for c < 1 m

  39. Massive charged particles • Kinked tracks: • c < 1 cm  OK: impact parameter • 1 cm < c < 1 m  difficult: hard to trigger • Cannonballs • LEP limits: stau > 76 GeV, sleptons > 85 GeV • Tools: dE/dx and timing (TOF counter in CDF; muon system in DØ) CDF Run II TOF ~ 180 GeV

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