WHY LHC?

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WHY LHC?

• D. P. ROY
• Homi Bhabha Centre for Science Education
• Tata Institute of Fundamental Research
• Mumbai, India

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Contents

• Basic Constituents of Matter and their
  Interactions Matter Fermions and Gauge Bosons
  (Std Model)
• High Energy Colliders
• Discovery of Std Model Particles at Colliders
• Higgs Mechanism Higgs Search at LHC
• Supersymmetry SUSY Search at LHC
• (Natural units h c 1 gt m mc2 , mp ? 1
  GeV)

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Basic Constituents of MatterMass (GeV)

• Fermions (Spin 1/2 h)
  e
• Leptons ?e ?µ ?t 0
• e .0005 µ 0.1 t 1.8 -1
• Quarks u 0.3 c 1.5 t 175 2/3
  d 0.3 s 0.5 b 5 -1/3
• For each Pair ?e 1 gt Weak Int
• Quarks also carry Colour Charge (C)gtStrong Int

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Basic Ints (Gauge Bosons Groups)
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SU(2)xU(1) EW Th (GSW) gtaWa/sin2?W?4agt DAµ
?4a/MW2 gt MW80 GeV, MZ91GeV

• p (uud), n (udd), e gt All the Visible
  Matter
• Heavier Leptons Quarks Decay by Weak Int
• They can be Observed in Accelerator or Cosmic ray
• Cosmic ray Observation of µ and k (su) in 1947
• ?s are stable but very hard to Observe lt Weak
  Int
• ?e Observed in Atomic Reactor Expt in 1956
• ?µ in BNL PS in 1962 ( KGF Cosmic ray in 1965)
• ee- Collider c (1974), t (1975), b (1977), g
  (1979)
• p-p Collider W Z (1983), t (1995), ?t
  (2000) FT

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eBv mv2/R eB mv/R
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ee - ( p - p) Collider
Accleration Mode
Collision Mode
Advantage of Collider over Fixed Target
Accelerator
Tevatron p-p Collider
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PrecissionTune e-e Energy MZ gt Higher Rate
Better Mass Res Z events/yr LEP-I 10 6,
CERN p-p Coll. 10 1-2 Signal
Clean , Dirty (Debris from Spectator q g)
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Past, Present Proposed Colliders
Period Machine Location Beam Energy(GeV) Radius Highlight
70s SPEAR DORIS CESR PEP PETRA Stanford Hamburg Cornell Stanford Hamburg ee- 3 3 5 5 8 8 1818 2222 125 m 300 m charm , t bottom bottom gluon
80s TRISTAN SPPS Japan CERN ee- p p 3030 300300 1 km W,Z boson
90s Tevatron SLC LEP-I (LEP-II) HERA Fermilab Stanford CERN Hamburg p p ee- e p 10001000 5050 5050 100100 30800 5 km Top Z Z W
2009 LHC CERN p p 70007000 5 km Higgs,SUSY
2??? ILC ??? ee- 500500
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3-jets
91 GeV
80 GeV
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Godbole, Pakvasa Roy, Phys. Rev. Lett. 50, 1539
(1983) Gupta Roy, Z. Phys. C39, 417 (1988)
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lt
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g2
Wµ
Wµ
Higgs couplings to Particles is Proportional to
their Mass gtMost Important Channels for Higgs
Search are the Heavy Pairs h ( WW, ZZ, tt, bb,
tt ) H ( tb, t? ) t Polarization Effect lt
Roy, Phys.Lett.B459, 607 (1999)
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Ferromagnetism(Spontaneous Symmetry Breaking)

• T lt TC

• T gt TC

Rotational Symmetry Broken
Rotational Symmetry
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Hierarchy Problem Supersymmetry (SUSY)
Solution
k
Without a protecting symmetry scalar mass gets
quad. div. quantum corr.
GeV
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LSP
Weakly Int Massive Particle (WIMP)
gt LSP escapes detection like ? gt Apparent
imbalance of PT (Missing-PT Signature)
Pair production of Gluinos and Squarks at
LHC gt Multi-jet plus Missing-PT Signature for
SUSY
Reya Roy, Phys. Lett. 141B, 442 (1984) Phys.
Rev. Lett. 53, 881 (1984)
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Conclusion

• Higgs Superparticles are the minimal set of
  missing pieces reqd. complete the picture of
  particle physics (MSSM).
• LHC offers comprehensive Higgs and Superparticle
  search up to MH,SUSY 1000GeV.
• It will either complete the picture a la MSSM or
  provide valuable clue for an alternative picture
  Little Higgs, Extra Dim, ETC...?
• LSP is leading candidate for the cosmic dark
  matter 10 times the baryonic matter of the
  Universe.

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Rotation curve of nearby dwarf spiral galaxy
M33, superimposed on its optical image
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