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mSUGRA SUSY Searches at the LHC


Particles: SM ones 5 Higgs. Sparticles: Spin 0 partners of SM fermions: qL,qR,lL,lR,nL ... Huge SUSY cross-section means Signal/Background ~ 1. ... – PowerPoint PPT presentation

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Title: mSUGRA SUSY Searches at the LHC

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

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 !

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)

mSUGRA Characteristics
m_1/2 (GeV)
lR mass contours N.B. lR mass is
approximately m_0.
m_0 (GeV)
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
  • Some l c from Drell-Yan (EW interaction)
  • SUSY decays
  • Give ET(miss), many (b-)jets, leptons.

mSUGRA Signals
s(q) gtgt s(g) q q c c20 l l-
s(q) s(g) q q c g t t c20 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 t c20 c10 l l-
m_0 (TeV) mass q l
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
  • Tracker
  • To identify b jets.
  • Prove leptons are isolated.
  • Measure lepton momenta

Detector Requirements
Measured Et(miss) in events with no missing
SUSY Discovery - Squarks and Gluinos
  • Expect up to 100M q and g per year ! Can discover
    in days !
  • Signatures ET(miss), many (b-)jets,
    leptons Selection 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.

SUSY Discovery - Squarks and Gluinos
Signal and background for events with two
like-charge isolated leptons.
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.
SUSY Discovery Next-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.
SUSY Discovery Next-To-Lightest Neutralino
Reach after 1 years high luminosity running.
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.)

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.

  • Many studies use mSUGRA, as better constrained
    than MSSM.
  • Detectors must find ET(miss), (b-)jets and
    isolated leptons. Need excellent solid angle
  • 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.