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

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

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: ħ & c = 1 => m = mc, m p 1 GeV)

Basic Constituents of Matter Mass (GeV) Fermions (Spin = 1/ ħ) Leptons ν e ν μ ν τ 0 e e.0005 μ 0.1 τ 1.8-1 Quarks u 0.3 c 1.5t 175 /3 d 0.3 s 0.5 b 5-1/3 For each Pair : Δe = 1 => Weak Int Quarks also carry Colour Charge (C)=>Strong Int

Basic Ints (Gauge Bosons & Groups) 1. Strong Int (QCD) g Q. E.M. Int (QED) e γ ν μ μ Q 3. Weak Int W Q ν e e : SU() e ν e :SU(3) C α s / Q :U(1) e e e α / Q α W / Q -M W u d p p u SU(3) => C g => ggg Int => Confinement u μ > eν μ ν e : Q «M W => DA μ = α W / M W r d F = Constant => V > r F = α/r => V = α/r => V = (α/r). Exp ( -r M W ) e

SU()xU(1) EW Th (GSW) =>α W =α/sin θ W 4α => DAμ 4α/M W => M W =80 GeV, M Z =91GeV p (uud), n (udd), e => 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 (sū) in 1947 νs are stable but very hard to Observe <= Weak Int ν e Observed in Atomic Reactor Expt in 1956 ν μ in BNL PS in 196 ( KGF Cosmic ray in 1965) e + e - Collider : c (1974), τ (1975), b (1977), g (1979) p - p Collider : W & Z (1983), t (1995), ν τ (000) FT

ebv = mv /R eb = mv/r

e + e - ( p - p) Collider Accleration Mode Collision Mode Advantage of Collider over Fixed Target Accelerator s E E E s = E Tevatron p - p Collider s = me' = 1000 GeV ' s (000GeV ) E = = = 000, GeV 1TeV Euiv mp 1GeV 000

p - p Collider vs e + e - Collider s s s ~ < x > s p - p Same s' 1/6 M 4 4π. e E s' s 6 s + : E pp ee Sync 4 3m ρ Z 100GeV : s pp 600GeV, s = s e e+ e s ee + 100GeV CERN: p - p Coll. (ρ = 1 km), LEP-I (ρ = 5 km) COST: ( 00 + 100) million$, 1 billion$ Precission:Tune e - e + Energy = M Z => Higher Rate & Better Mass Res Z events/yr : LEP-I ~ 10 6, CERN p - p Coll. ~ 10 1- Signal : Clean, Dirty (Debris from Spectator & g)

Past, Present & Proposed Colliders Period Machine Location Beam Energy(GeV) Radius Highlight 70 s SPEAR DORIS CESR PEP PETRA Stanford Hamburg Cornell Stanford Hamburg e + e - 3 + 3 5 + 5 8 + 8 18+18 + 15 m 300 m charm, τ bottom bottom gluon 80 s TRISTAN SPPS Japan CERN e + e - p p 30+30 300+300 1 km W,Z boson 90 s Tevatron SLC LEP-I (LEP-II) HERA Fermilab Stanford CERN Hamburg p p e + e - e p 1000+1000 50+50 50+50 100+100 30+800 5 km Top Z Z W 009 LHC CERN p p 7000+7000 5 km Higgs,SUSY??? ILC??? e + e - 500+500

k T ~ ħ/1fm~0. GeV 3-jets 80 GeV 91 GeV

Hard Isolated e / μ with 3-4 Hard jets 175 GeV 80 GeV Top pair production Godbole, Pakvasa & Roy, Phys. Rev. Lett. 50, 1539 (1983) Gupta & Roy, Z. Phys. C39, 417 (1988)

Mass Problem : Higgs Mechanism How to give mass to the SU() Gauge Bosons w/o breaking Gauge Sym of the L? For simplicity look at the U(1) Gauge Th (EM Int). v + h v + h * * * L EM = ( µ ieaµ ) φ ( µ + ieaµ ) φ [ µ φ φ + λ( φ φ) ] 4 1 F µν F µν F µν = µ A ν ν A µ 1..3 iα ( x) 1 GaugeTr : φ e φ, Aµ Aµ + µ α( x) e E, B 1..3 -M A μ A μ * * V = µ φ φ + λ ( φ φ ) μ <0 μ >0 v = µ / λ vev φ r = v + h( x) M = ev m = y v < m h = µ = λv = λ / e M ~ 10 GeV

φ 0 = v + h 1 φ 0 = v + h 1 φ 0 = v + h 1 W μ g W μ y { g v W W + { g v hw W M W µ µ µ µ gm W y v + y h { { m m / v Higgs couplings to Particles is Proportional to their Mass =>Most Important Channels for Higgs Search are the Heavy Pairs: h ( WW, ZZ, tt, bb, ττ ) & H ± ( tb, τν ) τ Polarization Effect <= Roy, Phys.Lett.B459, 607 (1999)

Ferromagnetism (Spontaneous Symmetry Breaking) T < T C T > T C Rotational Symmetry Broken Rotational Symmetry

H, He p α e νγ α p pne νγ p n uud ddu eνγ W Z h t b e ν γ

Hierarchy Problem: Supersymmetry (SUSY) Solution How to control Higgs Mass m h ~ M W ~ 10 GeV? 1 ( k m h ) λ k λ 3 k dk ( k m ) k Without a protecting symmetry scalar mass gets uad. div. uantum corr. m ( M ; M ) SUSY: fermions<=>bosons s 1/, l ~ ~, l 0 h 10 16 GUT γ, g, W, Z ~ ~ ~ γ, g~, W, Z 10 19 Plank s 1 1/ GeV h ~ h => Superparticles mass ~ 10 GeV 1, 1, s 0 - R h + 1 1/ 1 h ~ = ( 1) 3B + L s R Cons.=> Pair-prod of SP & Stable LSP (Cold dark matter)

LSP γ ~ :Weakly Int Massive Particle (WIMP) M e~, ~ M W => LSP escapes detection like ν => Apparent imbalance of P T (Missing-P T Signature) Pair production of Gluinos and Suarks at LHC => Multi-jet plus Missing-P T Signature for SUSY Reya & Roy, Phys. Lett. 141B, 44 (1984); Phys. Rev. Lett. 53, 881 (1984)

Conclusion Higgs & Superparticles are the minimal set of missing pieces red. complete the picture of particle physics (MSSM). LHC offers comprehensive Higgs and Superparticle search up to M H,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.

Rotation curve of nearby dwarf spiral galaxy M33, superimposed on its optical image v R = G M ( R) R v M ( R) R

H, He p α e νγ α p pne νγ p n uud ddu eνγ W Z h t b e ν γ ~~ γ ~ ~ γ ~~~~~ γ γγ γγ ~ γ WZh ~~~~~~ t b e ~ ν ~ γ