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

Transcription

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

2 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)

3 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 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

4 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

5 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

6 ebv = mv /R eb = mv/r

7 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

8 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: ( ) 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. ~ Signal : Clean, Dirty (Debris from Spectator & g)

9 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 m 300 m charm, τ bottom bottom gluon 80 s TRISTAN SPPS Japan CERN e + e - p p km W,Z boson 90 s Tevatron SLC LEP-I (LEP-II) HERA Fermilab Stanford CERN Hamburg p p e + e - e p km Top Z Z W 009 LHC CERN p p km Higgs,SUSY??? ILC??? e + e

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

11 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)

12 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 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

13 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)

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

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

16 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 GUT γ, g, W, Z ~ ~ ~ γ, g~, W, Z 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)

17 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)

18 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.

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

20 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