Search for the Higgs bosons in supersymmetric extensions of the SM

1
Search for the Higgs bosons in supersymmetric
extensions of the SM

• Giorgos Dedes
• Seminar Physik am Large Hadron Collider (LHC)

2
Outlook

• ATLAS - CMS
• SUSY MSSM Higgs sector
• Higgs masses
• Production and Decay
• Benchmark scenarios
• Higgs searches
• Summary

3
ATLAS

• Inner Detector Highly segmented silicon strips,
  determine very accurately charged particles
  trajectories
• Solenoid Magnet Solenoid coil that generates a
  2T magnetic field in the region of the Inner
  Detector
• Electromagnetic Calorimeter Electron and photon
  energies are measured through electromagnetic
  showers
• Hadronic Calorimeter Hadrons interact with dense
  material and produce a shower of charged
  particles
• Toroid Magnets 8 toroidal coils that create a
  0,4T magnetic field in the area of the Muon
  Spectrometer
• Muon Spectrometer Muons traverse the rest of the
  detector and are measured in its outer layers

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CMS

• Tracker Cocentric layers of silicon sensors,
  measure charged particles trajectories
• Electromagnetic Calorimeter Lead-Tungstate
  crystals, electrons positrons photons
  interact there and their energy is measured
• Hadronic Calorimeter Hadrons interact brass
  layers and produce a shower of charged particles
• Solenoid Magnet Largest solenoid ever built,
  creates 4T field that bends the charged particle
  trajectories
• Return Yoke Magnetic field created from the
  solenoid is returned in the iron yoke. Offers
  support structure for the detector
• Muon Chambers Located in the iron yoke, measure
  energy of muons

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SuperSymmetry (motivation from Higgs sector)

• Hierarchy problem in the SM Higgs sector
• Quantum corrections to the H mass have quadratic
  divergencies
• By introducing supersymmetric partners for the SM
  particles
• quadratic divergencies are cancelled

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SuperSymmetry

• By introducing superparticles, the SM particle
  spectrum is doubled.

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MSSM (in a nutshell)

• MSSM is the minimal extension to the standard
  model that realizes supersymmetry.
• It imposes an extra symmetry, R parity
• Sparticles enter interactions in pairs, with
  particles having R parity
• of 1 and sparticles of -1
• Sparticles are produced and annihilated in pairs

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MSSM Higgs sector

• In order to implement electroweak symmetry
  breaking into the MSSM, two Higgs doublets (H1,
  H2) that couple to up and down type particles,
  are needed.

• 2 CP even (h, H),1 CP odd (A) and 2 charged H
• The MSSM Higgs sector (at tree level) is
  determined by 2 free parameters
• MA and tanßv2/v1 (ratio of the vacuum
  expectation values of the 2 Higgs doublets)
• In CP conserving scenarios mass eigenstates are
  equal to CP eigenstates.
• In CP violating scenarios additional free
  parameters appear.
• Non vanishing phases mix the CP eigenstates to 3
  mass eigenstates

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Higgs masses

• At tree level
• and for
• This gives us an upper limit for the h mass
• Modifications to tree level due to top loops
  give additional contributions to Mh
• So Mh lt 133 GeV

• For the decoupling limit MAgtgtMZ
• A and H have similar couplings and are
  degenerate in mass
• while h resembles standard model Higgs

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Higgs production (neutral)

• d

• Main production mechanisms
• gluon fusion and associated production with
  b-quarks which is dominant at high values of tanß
• Vector boson fusion and Higgs-strahlung are
  suppressed for h/H/A (suppressed coupling to W,
  Z)
• With respect to the SM, cross sections are
  enhanced with rising tanß

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Higgs production (charged)

• Three main production processes in LHC, for
  single H
• From tt via gg fusion
• In association with top and b quarks
• In association with t quark

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Higgs decays

• For large tanß, the dominant decay channels for
  h/H/A are bb and tt
• H branching ratios are divided to 2 regions
• dominant decay to t? for MH ltMt
• and decay to tb for MH gtMt

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Benchmark scenarios

• Due to the large number of free parameters, the
  MSSM Higgs search is performed
• in 4 CP conserving (CPC) and 1 CP violating
  (CPV) scenarios
• CPC scenarios
• mh max scenario (MSUSY 1TeV, µ200GeV,
  M2200GeV, Xtv6MSUSY, AbAt, Mgluino0,8MSUSY)
• no - mixing scenario (MSUSY 2TeV, µ200GeV,
  M2200GeV, Xt0, AbAt, Mgluino0,8MSUSY)
• gluophobic scenario (MSUSY 350GeV, µ300GeV,
  M2300GeV, Xt-750GeV, AbAt, Mgluino500GeV)
• small a scenario (MSUSY 800GeV, µ2TeV,
  M2500GeV, Xt-1100GeV, AbAt, Mgluino500GeV)
• CPV scenario
• the CPX scenario (MSUSY 500GeV, µ2TeV,
  M2200GeV, AbAt, Mgluino1000GeV)

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Benchmark scenarios

• mh-max scenario Designed to maximize the h mass.
  Gives a limit for the Mh (133 GeV) that strongly
  depends on Mt
• no-mixing scenario Similar to mh-max but with no
  mixing in the stop sector.
• Designed to explore the effect of no stop
  mixing, results to Mh lt 116 GeV (Difficult for
  LHC)
• gluophobic scenario Coupling of h to gluons
  strongly suppressed. Designed to affect the
  processes gg?h , h??? and h?ZZ ?4l. Yields a Mh lt
  119 GeV
• small a scenario Coupling of h to b and t is
  suppressed. Mh lt 123 GeV. Designed to affect the
  channels h?tt and tth, h?bb
• CPX scenario CP eigenstates do not coincide with
  mass eigenstates. So h, A, H mix to mass
  eigenstates H1, H2, H3. CPX has maximal mixing
  (90 degrees)

Suppressed h-gluon coupling
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Status of previous Higgs searches

• The search for MSSM H bosons has been performed
  at LEP and is an ongoing effort at Tevatron
• LEP 8 scenarios scanned at LEP1 and LEP2
• No discovery but limits for the masses and
  tanß have been set.
• tanß exclusion 0,7 2.0 and Mh , MA gt 90 GeV
• Tevatron Still no discovery,
• a large part of the tanß - MA
• parameter space will be covered
• with 5 fb-1 of data (2007-2008)

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Higgs searches in LHC

• ATLAS and CMS will cover a large variety of
  different final states and a big part of the
• (MA, tanß) plane
• The channels investigated during the last years
  in ATLAS and CMS are
• h/H/A???
• h/H/A?bb
• h/H/A?tt
• h/H/A?µµ
• H?ZZ , tt , hh
• A?Zh
• H?t? , tb
• H/A??o2 ?o2

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h / H / A ? ??

• The expected MSSM rates for h and H decaying to
  ?? are generally suppressed with respect to SM
  case. For this rare decay, A boson is only
  observable in a limited region of the parameter
  space.
• Optimistic scenario Branching ratio is estimated
  assuming that all SUSY particles have a mass
  higher than 1TeV
• (there can be stop-quarks , charginos and
  neutralinos lighter than 1TeV)
• The same kinematic cuts are applied as in the
  case of the SM
• 2 photon candidates ordered in PT
• (starting from PT1 gt 40GeV and PT2 gt 25GeV for h
  and reaching PT1 gt 125GeV and PT2 gt 25GeV for the
  heavy Higgses
• Both photon candidates in nlt2,4 and events with
  more than one ? in transition region in an
  interval ?n 0,15
• are rejected
• Backgrounds ?? pair production, ?-jet, dijet and
  Z?ee

ATLAS
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h / H / A ? bb
ATLAS

• More promising channel is h / H / A ? bb , due to
  the high branching ratio (90) especially for
  high values of tanß
• For the low mass Higgs best sensitivity is
  achieved in the tth, h?bb

• For high mass region bbH/A, H/A?bb
• Quite challenging to trigger a 4 jet final state
• Require 2 hard jets from Higgs decay and 2 softer
  tagging jets
• Enormous QCD background
• Complex final state, 20 combinatoric background

ATLAS
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h / H / A ? bb

• In more recent study performed for the CMS
  detector, this channel is considered as cross
  check after discovery in H / A ? tt

CMS

• At least 4 jets are required
• within the detector acceptance nlt2,4
• with the hardest 2 passing PT thresholds
  dependant on the Higgs mass
• Additional selection in CMS analysis
• the centrality variable
• Discovery possible for tanßgt30 (largely dependant
  on background uncertainties)

CMS
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h / H / A ? tt

• For h main production mechanism is VBF while for
  H/A associated production with b-jets
• All t decay modes have been considered
• (lepton-lepton / lepton hadron / hadron -
  hadron)
• Due to the escaping neutrinos mass
  reconstructions is done by using the collinear
  approximation

ATLAS

• Mass resolution dependant on ?f between the
  visible decay products and sensitive to ETmiss
  resolution

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h / H / A ? tt

• Is considered a discovery channel for heavy
  neutral Higgs, especially in mass range 150 300
  GeV

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h / H / A ? µµ
ATLAS

• Same coupling as for tt channel, but BR scales as
  (mµ/mt)2 1/300
• For high tanß, associated production with b-jets
  is dominant
• Clean signature in the detector
• Excellent mass resolution, can provide the best
  mass and width measurement for H/A

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H?ZZ() ?4l , H?tt

• h/H?ZZ()
• Not thoroughly searched, extrapolated results
  from SM
• For high tanß suppressed HZZ coupling, rise of hh
  tt
• If observed identified from the low rate

ATLAS MH370GeV tanß1,5

• H?tt
• Suppressed coupling with gauge bosons, tt becomes
  interesting
• Observed as peak over the continuous tt
  background
• Mass reconstruction from the decay channel
  bWbW?bl?bj

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H?hh , A?Zh

• Would allow simultaneous observation of 2 Higgs
  bosons
• For H?hh, possible decays are bbbb (largest
  rate-difficult trigger), bbtt (can trigger on
  leptonic tau), bb?? (easy to trigger low rate)
• For A?Zh with final state µµbb or eebb , require
  2 leptons with Z mass constrain and 2 bjets well
  separated from the leptons

Signal Zbb tt Zjets
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H ? t? / tb

• 2 prominent decay modes, t? / tb for MH
  lower/higher than tb production threshold
• MH lt Mt tt?HWbb?(t?)(l?)bb?(h??)(l?)bb ,
  trigger from W leptonic decay
• MH gt Mt gg?tbH ?(bW)b(t?)?(bjj)b(h??) ,
  disentangle t-jet from light jets
• t mass constraint
• tb decay channel opens gg?tbH ?tb(tb)?WWbbbb?qqµ?
  bbbb
• gb?tH ?t(tb)?WWbbb?qqµ?bbb
• has large ttjets background , multivariate
  techniques used

CMS , 30fb-1
3-tags
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A/H ??o2 ?o2

• MSSM Higgs can be also searched in decays to
  supersymmetric particles
• Can give us a handle on the low and intermediate
  tanß region not accessible by A/H?tt
• Promising decay into the next to lightest
  neutralinos , ?o2?ll- ?o1
• Main backgrounds squarks and gluinos cascade
  decays , ZZ(), Zbb
• Apply lepton isolation , jet and Z veto
• No mass peak reconstruction, excess of events

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Overall discovery potential

• In LHC MSSM Higgs could be discovered within the
  first years (30 fb-1)
• At 300 fb-1, the biggest part of the parameter
  space will have been scaned
• A challenge for both theorists and experimentals
  A region where only one Higgs can be seen, is
  it SM or MSSM ?

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Conclusions

• Supersymmetry and MSSM in particular are favorite
  candidates for extension of the SM
• Searches for the MSSM Higgs have been started at
  LEP, continue at Tevatron and will start soon in
  LHC experiments
• A large number of processes provide us the
  capability to scan a large area of the parameter
  space
• Tevatron could surprise us, otherwise LHC can
  give as indications during the first 3 years and
  discovery afterwards

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Backup slides
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Production cs at low tanb
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A BR also in SUSY particles
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MSSM Higgs sector
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h/H/A couplings
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CPV mixing
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SM MSSM discrimination
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Other contributions in cs
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h discovery potential

• .dependence on scenarios

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CPV discovery potential