mSUGRA SUSY Searches at the LHC

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mSUGRA SUSY Searches at the LHC

• Why use mSUGRA and what signals does it give ?
• Detector requirements.
• SUSY discovery (production via strong
  interactions)
• Squarks gluinos.
• Next-to-lightest neutralino.
• SUSY parameter determination
• From Drell-Yan production cross-sections
  (gauginos sleptons)
• Sparticle masses (neutralinos, squarks
  gluinos)
• Conclusions

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Why use mSUGRA ?

• Why not just use the MSSM ?
• Particles SM ones 5 Higgs
• Sparticles Spin 0 partners of SM fermions
  qL,qR,lL,lR,nL Spin 1/2 partners of
  bosons/Higgs c10,c20,c30,c40,c1,c2, g
• Nice theory, but 124 free parameters !

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Why use mSUGRA ?

• mSUGRA (minimal Supergravity)
• Favourite SUSY theory for LHC studies. (Peter
  will discuss alternatives).
• Only 5 parameters ( SM ones)
• m_0 (Scalar mass at GUT scale)
  Squark Slepton masses.
• m_1/2 (Gaugino mass at GUT scale)
  Gaugino gluino masses.
• tan(b) (VEV ratio of 2 Higgs doublets).
• A_0 (Higgs-fermion-antifermion coupling)
• sign(m) (Higgsino mixing parameter)

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mSUGRA Characteristics
m_1/2 (GeV)
lR mass contours N.B. lR mass is
approximately m_0.
m_0 (GeV)
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mSUGRA Signals

• R-parity SUSY particles pair-produced
  c10 is stable (so missing ET).
• Mass (q, g) gt mass (t) gt mass ( l, c)
• SUSY production
• Dominated by q g (strong interaction) - up to
  100M/year.
• Some l c from Drell-Yan (EW interaction)
  10K/year.
• SUSY decays
• Give ET(miss), many (b-)jets, leptons.

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mSUGRA Signals
s(q) gtgt s(g)q q c c20 l l-
s(q) s(g)q q c g t tc20 c10 h/Z
m_1/2 (TeV) mass c g
s(q) ltlt s(g)g t t c20 c10 h/Z
s(q) ltlt s(g)g c10 t tc20 c10 l l-
m_0 (TeV) mass q l
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Detector Requirements

• Calorimeter coverage for h lt 5 (i.e. q gt 10)
• Needed for good ET(miss) resolution.
• Needed to identify Drell-Yan events - with jet
  veto.

• Tracker
• To identify b jets.
• Prove leptons are isolated.
• Measure lepton momenta

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Detector Requirements
Measured Et(miss) in events with no missing
energy.
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SUSY Discovery - Squarks and Gluinos

• Expect up to 100M q and g per year ! Can discover
  in days !
• Signatures ET(miss), many (b-)jets,
  leptonsSelection cuts depend on m_0 and m_1/2
• SM Backgrounds t t, W/Z jets.Huge SUSY
  cross-section means Signal/Background 1.
• By end of LHC life, explore q and g masses up to
  3 TeV.

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SUSY Discovery - Squarks and Gluinos
Signal and background for events with two
like-charge isolated leptons.
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SUSY Discovery - Squarks and Gluinos
Explored region after 1st LHC year. Various
final states help constrain SUSY. Easily cover
region where c10 could be dark matter.
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SUSY DiscoveryNext-To-Lightest Neutralino
q and g often decay to c20. c20 c10 l l-
Mass (ll-) has sharp upper threshold
-- Clear signal for SUSY -- Measures
m_1/2 !! If decay proceeds via slepton, also
measures m_0.
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SUSY DiscoveryNext-To-Lightest Neutralino
Reach after 1 years high luminosity running.
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Constraining SUSY with Cross-Sections

• Measure q g rate to various final states (1, 2,
  3 leptons )(Tend to decrease with increasing
  m_0 and m_1/2.)
• Measure Drell-Yan (EW) production rates of
• c1 c20 (3 lepton final state)
• l l- (2 lepton final state)
• (Must use jet-veto to suppress q g SUSY
  background. Need large luminosity.)

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Constraining SUSY with Sparticle Masses

• Providing c20 c10 l l- then
• Can measure m_1/2 using maximum ll- mass seen
  in c20 c10 l l- .
• Can also measure m_0, if c20 decays via slepton.
• At maximum ll- mass, know c20 momentum
  P(c20) P( ll- ) .M(c20) /M( ll- )
  where M(c20) estimated from m_0.
• If qL qc20 or g qq qqc20 , can then
  determine qL and g mass.

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Conclusions

• Many studies use mSUGRA, as better constrained
  than MSSM.
• Detectors must find ET(miss), (b-)jets and
  isolated leptons.Need excellent solid angle
  coverage.
• SUSY may be discovered within days of LHC
  start-up via production of squarks and gluinos.
• .c20 c10 l l- decays could determine
  sparticle masses. Together with cross-section
  measurements, this helps constrain SUSY.