The Physics of Run II

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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/PragueSe
  p99/Run2Physics.ppt

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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

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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
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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

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Some of our strengths
Jets
Inclusive jet cross section
EM calorimetry
Missing ET
?? X
mW 80.450 ? 0.093 GeV DØ electrons
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New Tools charged particle tracking
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In Run I only one of these three muons would
have been found!
W ? ?
b ? ?
W ? ?
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New tools heavy flavor tagging
?c
?b
55 at large pT
?u,d,s
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New tools all new software

• Full rewrite of online code,level 3 trigger and
  offline reconstruction in C

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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 bosonsjets,
  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 (lt 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

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B Physics

• Slides from Rick Jesik, Indiana University

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Run II B Physics Topics

• Spectroscopy
• Lifetimes
• Branching ratios
• Rare decays
• CKM measurements

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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

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Exclusive B decays
Expected yields in 500 pb-1
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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

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B ? J/? KS Reconstruction

• J/? ? ? ? - require two central tracks with pT
  gt 1.5 GeV/c
• KS ? ? ? - use long lifetime to reject
  background Lxy/? gt 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

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Sin2b Expectations for 2fb-1
For a time independent analysis

• (S/B 0.75)
• e D2 6.7

But, since most of the background is at small
ts, a time dependent analysis gives reduced
error ? (sin2b ) 0.07
And this is just in the first two years - 2 fb-1.
We wont stop there...
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Expectations beyond 2fb-1
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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.

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Top quark physicsSlides from Ann Heinson, UC
Riverside DØ Workshop, Seattle, June 1999
http//www-d0.fnal.gov/heinson/top500/
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Beyond the Standard Model
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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 gt 95.2 GeV (LEP) and mH lt 245 GeV (SM fit,
  Eidelman Jegerlehner)

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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) gt 80-90 GeV
• sleptons (selectron, smuon, stau) gt 70-90 GeV
• charginos gt 70-90 GeV
• lightest neutralino gt 36 GeV
• Tevatron Run I
• squarks and gluinos
• stop, sbottom
• charginos and neutralinos

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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?

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SM Higgs LEP2 prospects

• Eilam Gross at EPS99
• mH excluded lt 108.5 GeV with 150 pb-1 per
  expt at ?s 200 GeV

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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

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SM Higgs Channels

• mH lt 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 gt 130-140 GeV
• gg ? H ? WW backgrounds Drell-Yan, WW, WZ, ZZ,
  tt, tW, ?? signalbackground ratio 7 ? 10-3
  !
• Angular cuts to separate signal from
  irreducible WW background

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Combined reach
15 fb-1
2 fb-1

• 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

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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
  signalbackground 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?

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Mass resolution

• Directly influences signal significance
• Requires corrections for missing ET and muon
• Z ? bb will be a calibration signal

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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

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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
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DØ search for squarks and gluinos

• Demand
• 3 jets, ET gt 25 GeV, one jet ET gt 115 GeV
• HT gt 100 GeV
• veto electrons, muons
• Main Backgrounds top, QCD jets, W/Zjets
• Cascade decays to charginos can give leptons in
  final state complementary analysis requiring
• 2 electrons, 2 jets Missing ET

Run II limit gluino mass 400 GeV
Run I excluded
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Chargino/neutralino production

• golden trilepton signature
• Run II reach on ?? mass 180 GeV (tan ? 2, µlt
  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?

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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
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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
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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

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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 lt 85 GeV for c? lt 1 m

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Massive charged particles

• Kinked tracks
• c? lt 1 cm ? OK impact parameter
• 1 cm lt c? lt 1 m ? difficult hard to trigger
• Cannonballs
• LEP limits stau gt 76 GeV, sleptons gt 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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Anomaly mediated SUSY

• delayed decay of chargino cannonball type
  signatures
• decays may be in detector, soft pion plus missing
  ET
• Do event generators exist?

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Large extra dimensions

• Gravitons propagate into higher dimensional
  space?
• Direct searches for
• ee- ? ? nothing
• pp ? ? nothing, jetnothing
• Indirect effects in ee- ? ??, ??, ??
• Do event generators exist?

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R parity violation

• Usual assumption decay chain as in mSUGRA but
  LSP decays via B or L violating operator (hence
  no missing ET)
• LEP sensitivity comparable to mSUGRA with R
  conserved
• CDF and DØ searches for ee jets again,
  comparable sensitivity
• R violation in production process
• HERA leptoquark searches ep ? squark
• LEP ee- ? sneutrino ? tau pairs

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Supersymmetry Issues

• The basic menu of Run II searches is well-defined
  and we should have no trouble in exploring
• minimal SUGRA
• GMSB with prompt photon signatures
• some subset of R violation
• Concerns what have we forgotten?
• This is especially true at the Tevatron where
  triggering is a crucial issue
• For example, can we cover
• slow moving massive particles
• GMSB with detached photons or taus
• anomaly-mediated (e.g. ? ? ?0 soft)
• extra dimension signatures ...
• Lets look at the DØ straw-man trigger list
• http//www-d0.fnal.gov/lucotte/TRG/trigger_list.h
  tml

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MSSM Higgs at LEP2

• Complementary processes ee- ? (h/H)Z and (h/H)A
• General MSSM scans find a few points that can
  evade limits
• Invisible Higgs decays included in searches

Summer 1999 mh gt 81 GeV mA gt 81
GeV Excludes 0.9 lt tan ? lt 1.6 max mixing 0.6 lt
tan ? lt 2.6 no mixing but no exclusion if mtop
180 GeV
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MSSM Higgs sector at the Tevatron

• Assuming 1 TeV sparticle
• masses, ? lt 0

But not always so straightforward Fixed A (
? 1.5 TeV here) suppresses hbb, h?? couplings
for certain (mA, tan?)
Enhances h ? ?? (branching ratio as high as
10?)
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Strong SUSY Higgs Production

• bb(h/H/A) enhanced at large tan ?
• ? 1 pb for tan? 30 and mh 130 GeV

bb(h/A) ? 4b
CDF Run I 3 b tags
tan ? 30
150 GeV
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Charged Higgs

• Tevatron search in top decays
• Standard tt analysis, rule out competing decay
  mode t ? H?b
• Assumes 2 fb-1, nobs 600, background 50 ? 5
• LEP not really sensitive to MSSM region (expect
  mH gt mW)

LEP summer 99 77 GeV
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Non-Supersymmetric EWSB

• Dynamical schemes like technicolor and topcolor
  predict
• new particles in the mass range 100 GeV - 1 TeV
• with strong couplings and large cross sections
• decaying to vector bosons and (third
  generation?) fermions
• Plus we should always be looking for
• Leptoquarks
• Fourth generation fermions or isosinglet fermions
• W and Z
• contact interactions, etc etc.

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Some final remarks
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Common Features

• To fully explore the broad range of physics in
  Run II we will need to seek out the common
  features in this menu so as to make the most of
  our bandwidth and our personnel
• for example
• isolated, moderate pT leptons (W/Z, SUSY, top . .
  .)
• b-jets
• other examples
• Wjets is QCD, top, single top, SUSY,
  technicolor, Higgs . . .
• Photons are QCD, SUSY, technicolor . . .
• This is why I would like to see a strong,
  continuing role for the physics object ID groups

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Run II Strategy

• play to our strengths
• EM calorimetry
• Jets
• Missing ET
• put in the effort to exploit our new tools
• charged particle tracking
• muon acceptance and resolution
• heavy flavor tagging
• remain grounded
• dont all start searching for the Higgs with 500
  pb-1

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A message to our European colleagues

• DØ wants you!
• Run II offers a broad and compelling physics
  program, but its going to take a lot of work on
  the detector, trigger, infrastructure software,
  calibration . . .
• We need to make sure that all our collaborators
  are full participants in this enterprise we
  cant do it without your help
  

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Conclusions

• The Tevatron is an immensely productive facility
• ?s from 10 GeV to 1 TeV
• Run II offers three ways to gain over Run I
• increased statistics for standard model processes
• increased reach for new particle searches
• increased detector capabilities
• Theres nowhere more
• exciting to do physics!