The Electro-Weak Sector. Precision Experiments before LEP LEP Physics Probing the Standard Model Beyond the Standard Model

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1 The Electro-Weak Sector Precision Experiments before LEP LEP Physics Probing the Standard Model Beyond the Standard Model P. Langacker CERN, LEP Fest 11 October, 2000

2 The Z, the W, and the Weak Neutral Current Primary prediction and test of electroweak unification WNC discovered 1973 (Gargamelle, HPW) 70 s, 80 s: (few %) weak neutral current experiments Pure weak: νn, νe scattering Weak-elm interference in ed, e + e, atomic parity violation W, Z discovered directly 1983 (UA1, UA2) 90 s: Z pole (LEP, SLD), 0.1%; lineshape, modes, asymmetries LEP 2: M W, Higgs, gauge self-interactions Tevatron: m t, M W Implications SM correct and unique to zeroth approx. (gauge principle, group, representations) SM correct at loop level (renorm gauge theory; m t, α s, M H TeV physics severely constrained (unification vs compositeness) Precise gauge couplings (gauge unification)

3 Results before the LEP era Global Analysis more information than individual experiments caveat: exp./theor. systematics, correlations model-independent fits Unique νq, νe, eq SM correct to first approximation Contrived imitators out QCD evolved structure functions Radiative corrections necessary (sin 2 θ W defns) sin 2 θ W =.230 ±0.007, m t < 200 GeV Unique fermion reps. (wnc + wcc) t exists Grand unification Ordinary SU 5 excluded; consistent with SUSY GUTS and perhaps even the first harbinger of supersymmetry Stringent limits on new physics Z, exotic fermions, exotic Higgs, leptoquarks, 4-F operators

4 The LEP Era Z Pole: e + e Z l + l, q q, ν ν LEP (CERN), Z s, unpolarized; SLC (SLAC), , P e 75 % Z pole observables lineshape: M Z, Γ Z, σ branching ratios e + e, µ + µ, τ + τ q q, c c, b b, s s ν ν N ν = ± if m ν < M Z /2 asymmetries: FB, polarization, P τ, mixed lepton family universality LEP 2 M W, Γ W, B (also hadron colliders) M H limits (hint?) W W production (triple gauge vertex) quartic vertex SUSY/exotics searches Other: atomic parity (Boulder); νe; νn (NuTeV); M W, m t (Tevatron)

5 The Z Lineshape e + e f f (f = e, µ, τ, s, b, c, hadrons); s = E 2 CM sγ 2 Z σ f (s) σ f ( s M 2 ) 2 s Z + 2 Γ 2 Z MZ 2 (plus initial state rad. corrections) σ f = 12π M 2 Z Γ(e + e )Γ(f f) Γ 2 Z Γ(inv) = Γ Z Γ(had) i N ν Γ(ν ν) R qi Γ(q i q i ) Γ(had), q i = b, c, s Γ(l i l i ) R li Γ(had) Γ(l i l i ), l i = e, µ, τ (R e = R µ = R τ R l lepton universality) Γ(f f) C fg F MZ 3 6 [ ḡv f 2 + ḡ Af 2] 2π (plus mass, QED, QCD corrections; C l = 1, C q = 3; ḡ V,Af = effective coupling (includes ew)) M Z, Γ Z, σ had, R l, R b, R c mainly weakly correlated

6 LEP averages of leptonic widths Γ e ± 0.12 MeV Γ µ ± 0.18 MeV Γ τ ± 0.22 MeV Γ l ± 0.09 MeV m H [GeV] m Z = ± 2 MeV m t = ± 5.1 GeV Γ l [MeV]

7 Z-Pole Asymmetries A 0 = Born asymmetry, after removing γ, offpole, box (small), P e forward backward : A 0f F B 3 4 A ea f (A 0e F B = A0µ F B = A 0τ F B A0l F B universality) τ polarization : P 0 τ = A τ + A e 2z 1+z A τ A e 2z 1+z 2 (z = cos θ, θ = scattering angle) e polarization (SLD) : A 0 LR = A e mixed (SLD) : A 0F B LR = 3 4 A f A f 2ḡ V F ḡ Af ḡ 2 V F + ḡ2 AF where s 2 f ḡ Af ḡ V f = ρ f t 3f = ρ f [ t3f 2 s 2 f q f the effective weak angle, s 2 f = κ fs 2 W (on shell) = ˆκ f ŝ 2 Z ŝ2 Z (f = e) (MS ), ρ f, κ f, and ˆκ f are electroweak corrections, q f = electric charge, t 3f = weak isospin ]

8 A 0 FB ALEPH ± DELPHI ± L ± OPAL ± LEP ± χ 2 /dof = 3.8/3 800 m H [GeV] m Z = ± 2 MeV m t = ± 5.1 GeV α -1 = ± A 0 FB

9 Preliminary m H g Vl m t A l (SLD) Combined e + e µ + µ τ + τ 68% CL g Al

10 Γ b /Γ had ALEPH mult DELPHI mult L3 mult OPAL mult SLD vtx mass ± ± ± ± ± ± ± ± ± ± LEP+SLC ± corrected for γ exchange m t [GeV] Γ b /Γ had for Γ c /Γ had = 0.171

11 bb _ A at s m Z FB ALEPH leptons DELPHI leptons L3 leptons OPAL leptons ALEPH jet-ch DELPHI jet-ch L3 jet-ch OPAL jet-ch ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± LEP Summer mt [GeV] ± Include Total Sys With Common Sys m H [GeV] 10 2 m t = ± 5.1 GeV α had = ± ,bb _ A FB

12 The Z Pole Observables: LEP and SLC Quantity Group(s) Value Standard Model pull M Z [GeV] LEP ± ± Γ Z [GeV] LEP ± ± Γ(had) [GeV] LEP ± ± Γ(inv) [MeV] LEP ± ± 0.15 Γ(l + l ) [MeV] LEP ± ± σ had [nb] LEP ± ± R e LEP ± ± R µ LEP ± ± R τ LEP ± ± A F B (e) LEP ± ± A F B (µ) LEP ± A F B (τ ) LEP ± R b LEP + SLD ± ± R c LEP + SLD ± ± R s,d /R (d+u+s) OPAL ± ± A F B (b) LEP ± ± A F B (c) LEP ± ± A F B (s) DELPHI,OPAL ± ± A b SLD ± ± A c SLD ± ± A s SLD 0.82 ± ± A LR (hadrons) SLD ± ± A LR (leptons) SLD ± A µ SLD ± A τ SLD ± A e (Q LR ) SLD ± A τ (P τ ) LEP ± A e (P τ ) LEP ± s 2 l (Q F B) LEP ± ±

13 20 LEP 21/07/2000 Preliminary RacoonWW / YFSWW 1.14 Gentle 2.1 (±0.7%) no ZWW vertex only ν e exchange E cm [GeV]

14 W-Boson Mass [GeV] -colliders ± P ± erage ± χ 2 /DoF: 0.1 / 1 TeV/CCFR ± 0.11 P1/SLD ± m W [GeV]

15 Non-Z Pole Precision Observables: Tevatron, LEP 2, νn, APV Quantity Group(s) Value Standard Model pull m t [GeV] Tevatron ± ± M W [GeV] LEP ± ± M W [GeV] Tevatron,UA ± R NuTeV ± ± ± R ν CCFR ± ± ± R ν CDHS ± ± ± R ν CHARM ± ± R ν CDHS ± ± ± R ν CHARM ± ± R ν CDHS ± ± ± gv νe CHARM II ± ± gv νe all ± ga νe CHARM II ± ± g νe A all ± Q W (Cs) Boulder ± 0.28 ± ± Q W (Tl) Oxford,Seattle ± 1.2 ± ± Γ(b sγ) Γ(b ceν) CLEO

16 LEP remarkably successful (beyond anticipation) Machine Detectors: ALEPH, DELPHI, L3, OPAL (LEP); SLD (SLC) Analysis: tides, water table/lake, trains LEPEWWG critical Theoretical inputs precise QED, EW, QCD, mixed radiative corrections sin 2 θ W definitions α had (running α) Packages: ZFITTER, TOPAZ0, ALIBABA, BHLUMI, GAPP, (LEP2) new physics parametrizations Global analyses: LEPEWWG, PDG, Polarization: SLC advantage; (Blondel scheme) Future: GigaZ?

17 Radiative Corrections Dominant two-loop electroweak (α 2 m 4 t, α2 m 2 t ) Dominant 3 loop QCD (4 loop estimate) Dominant 3 loop mixed QCD-EW (αα s vertex) Definitions of renormalized sin 2 θ W On shell: s 2 W 1 M W 2 MZ 2 Z mass: s 2 ( ) M Z 1 s 2 MZ πα(m Z ) 2GF MZ 2 MS : ŝ 2 Z ĝ 2 (M Z ) ĝ 2 (M Z )+ĝ 2 (M Z ) Effective (Z-pole): s 2 f 1 4 ( πα/ M 2 W = 2GF = (1 r) s 2 W ) 1 ḡ V f ḡ Af ( πα/ 2GF ) ŝ 2 Z (1 ˆr W ) M 2 Z = M 2 W c 2 W = M 2 W ˆρĉ 2 Z s 2 f = κ fs 2 W = ˆκ fŝ 2 Z s 2 e ŝ2 Z (κ f, ˆκ f depend on m t, M H ) ˆρ 1 + 3G F ˆm 2 t 8 2π 2 + ˆr W α

18 Definitions of sin 2 θ W On-shell : s 2 W = 1 M W 2 = (38) MZ 2 + most familiar + simple conceptually large m t, M H dependence from Z-pole observables depends on SSB mechanism awkward for new physics Z-mass : s 2 M Z = (8) + most precise (no m t, M H dependence) + simple conceptually m t, M H reenter when predicting other observables depends on SSB mechanism awkward for new physics MS : ŝ 2 Z = (16) + based on coupling constants + convenient for GUTs + usually insensitive to new physics + Z asymmetries independent of m t, M H theorists definition; not simple conceptually usually determined by global fit some sensitivity to m t, M H variant forms (m t cannot be decoupled in all processes; ŝ 2 ND larger by ) effective : s 2 l = (15) + simple + Z asymmetry independent of m t + Z widths: m t in ρ f only phenomenological; exact definition in computer code different for each f hard to relate to non Z-pole observables

19 Running of α Largest theory uncertainty in M Z ŝ 2 Z α(m 2 Z ) = α 1 α α = α l + α t + α (5) had α (5) had α α 1 (M Z ) ˆα 1 (M Z ) ( ) πα/ 2GF (cf. ahad µ ) M 2 Z = ˆρĉ 2 Zŝ2 Z (1 ˆr W ) Calculation of α (5) had ˆρ 1 + 3G F ˆm 2 t 8 2π 2 + ˆr W α + Data driven: R had up to 40 GeV; PQCD above Theory driven: PQCD + NPQCD (OPE, sum rules) above 2 GeV smaller uncertainties New BES-II data convergence Measurements of running α: TOPAZ (e + e µ + µ ); VENUS, L3 (Bhabha), OPAL (high Q 2 )

20 Recent evaluations of on-shell α (5) had(m Z ) (Adjusted to fixed α s (M Z ) = 0.120) Author(s) Result Comment Martin & Zeppenfeld ± PQCD for s > 3 GeV Eidelman & Jegerlehner ± PQCD for s > 40 GeV Geshkenbein & Morgunov ± Burkhardt & Pietrzyk ± O(α s ) resonance model PQCD for s > 40 GeV Swartz ± use of fitting function Alemany, Davier, Höcker ± includes τ decay data Krasnikov & Rodenberg ± PQCD for s > 2.3 GeV Davier & Höcker ± PQCD for s > 1.8 GeV Kühn & Steinhauser ± complete O(α 2 s ) Erler ± converted from MS scheme Davier & Höcker ± use of QCD sum rules Groote et al ± use of QCD sum rules Jegerlehner ± converted from MOM Martin, Outhwaite, Ryskin ± includes new BES data Pietrzyk ± details not published

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22 Z pole + LEP 2 + WNC + Tevatron SM tested at 0.1% level, including EW loops (gauge principle, group, representations, renorm. field theory) sin 2 θ W ; m t, α s (loops; agree with direct) determined; α had, M H constrained M H < 194 GeV (direct: M H > 112 GeV) SUSY severe constraint on TeV physics unification (decoupling): expect 0.1% TeV compositeness: expect several % precise gauge coupling constants (unification)

23 Global Electroweak Fits much more information than individual experiments caveat: experimental/theoretical systematics, correlations PDG 00 review + summer (J. Erler and PL) Complete Z-pole and WNC (important beyond SM) New radiative correction program (Erler) GAPP: Global Analysis of Particle Properties Fully MS (ZFITTER on-shell) New α had, correlated with α s Good agreement with LEPEWWG up to wellunderstood effects (WNC, HOT, α had ) despite different renormalization schemes erler/electroweak/

24 Fit Results (10/00) (Erler, PL) M H = GeV, m t = ± 4.4 GeV, α s = ± , ŝ 2 Z = ± , s 2 l = ± , s 2 W = ± s 2 M Z = ± α (5) had(m Z ) = ± Gurtu (Osaka): M H = new BES-II data for α (5) α s = ± m t = GeV s 2 l = ± had(m Z )) GeV ( for

25 α (5) had(m Z ) = ± ± from indirect only (theory (Erler): ± ) m t = ± 4.4 GeV GeV from indirect (loops) only (direct: ± 5.1) α s = ± consistent w. other values (PDG: ± w/o lineshape) Higgs mass M H = GeV direct limit (LEP 2): M H > 112 GeV SM: 115 (vac. stab.) < M H < 750 (triviality) MSSM: M H < 130 GeV (150 in extensions) indirect: ln M H but significant fairly robust to new physics M H < 194 GeV at 95%, including direct

26 80.6 direct (1σ) indirect (1σ) all (90% CL) 80.4 M W [GeV] M H [GeV] m t [GeV]

27 Γ Z, σ had, R l, R q asymmetries ν scattering M W m t 200 all data 90% CL M H [GeV] excluded m t [GeV]

28 6 4 theory uncertainty α had = α (5) ± ± χ Excluded Preliminary m H [GeV]

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30 Skeletons in the Closet Standard model (SU 3 SU 2 U 1 + general relativity) correct to cm, but 21 free parameters ( 28 with m ν 0). Gauge Problem complicated gauge group with 3 couplings charge quantization ( q e = q p ) unexplained Fermion problem Fermion masses, mixings, families unexplained Higgs/hierarchy problem Expect M 2 H = O(M 2 W ) higher order corrections: δm 2 H /M 2 W 1034 Strong CP problem Can add θ 32π 2 g 2 s F F to QCD (breaks, P, T, CP) d N θ < 10 9 but δθ weak 10 3 Graviton problem gravity not unified quantum gravity not renormalizable cosmological constant: Λ SSB = 8πG N V > Λ obs

31 The Two Paths: Unification or Compositeness The Bang unification of interactions grand desert to unification (GUT) or Planck scale elementary Higgs, supersymmetry (SUSY), GUTs, strings possibility of probing to M P and very early universe hint from coupling constant unification tests light (< GeV) Higgs (LEP 2, TeV, LHC) absence of deviations in precision tests (usually) supersymmetry (LHC) possible: m b, proton decay, ν mass, rare decays SUSY-safe: Z ; seq/mirror/exotic fermions; singlets The Whimper onion-like layers composite fermions, scalars (dynamical sym. breaking) not like to atom nucleus +e p + n quark at most one more layer accessible (LHC) rare decays (e.g., K µe) severe problem no realistic models effects (typically, few %) expected at LEP & other precision observables (4-f ops; Zb b; ρ 0 ; S, T, U) anomalous V V V, new particles, future W W W W

32 Beyond the standard model ρ 0 ; S, T, U: Higgs triplets, nondegenerate fermions or scalars; chiral families (ETC) S = 0.05 ± 0.11( 0.09) T = 0.03 ± 0.13(+0.10) U = 0.18 ± 0.14(+0.01) for M H = 115 (340) GeV ρ 0 = 1 + αt = (M H = GeV) N fam = 2.84 ± 0.30 (cf. lineshape: N ν = ± 0.008) Fourth family excluded at 99.92%

33 T Γ Z, σ had, R l, R q asymmetries ν scattering M W Q W all: M H = 115 GeV all: M H = 340 GeV all: M H = 1000 GeV S

34 Supersymmetry decoupling limit (M new > GeV): only precision effect is light SM-like Higgs little improvement on SM fit SUSY parameters constrained Heavy Z : GUTs, string theories Typically M Z > GeV (Tevatron, LEP 2, WNC), θ Z Z < few 10 3 (Z-pole) Gauge unification: GUTs, string theories α + ŝ 2 Z α s = ± M G GeV Perturbative string: GeV (10% in ln M G ). Exotics: O(1) corrections.

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37 α 1 (α, sin 2 θ W ) α 2 (G F, M W ) α 3 m e m µ m b M Z M unification

38 α i -1(µ) α 1 SM World Average 40 α α 3 α S (M Z )=0.117±0.005 sin 2 Θ =0.2317± MS µ (GeV) α i -1(µ) % CL α 1 MSSM World Average α 2 20 α U.A. W.d.B H.F µ (GeV)

39 Conclusions WNC, Z, W are primary predictions and test of electroweak unification SM correct and unique to zeroth approx. (gauge principle, group, representations) SM correct at loop level (renorm gauge theory; m t, α s, M H TeV physics severely constrained (unification vs compositeness) Precise gauge couplings (gauge unification) LEP has performed spectacularly well (accelerator, experiments, analysis (LEPEWWG), theoretical support) Watershed in physics: decoupling