X COLLIDER PHYSICS : BASIC CONCEPTS

Transcription

1 COLLIDER PHYSICS : BASIC CONCEPTS 2006 Busstepp Edinburgh 1. INTRODUCTION Physics scenarios and objectives General collider characteristics 2. ELECTRON-PROTON COLLIDER HERA Quark/gluon densities; QCD coupling 3. PROTON-ANTIPROTON COLLIDER TEVATRON Top quark; W ± boson; Higgs; susy particles 4. PROTON COLLIDER LHC Higgs mechanism / elw Symmetry breaking Supersymmetric particles Extra space dimensions 5. e + e LINEAR COLLIDERS High-resolution picture : Higgs/susy/extra dimensions LHC/ILC coherence : ultimate unification

2 COLLIDER PHYSICS : BASIC CONCEPTS 2006 Busstepp Edinburgh 1. INTRODUCTION Physics scenarios and objectives General collider characteristics 2. ELECTRON-PROTON COLLIDER HERA Quark/gluon densities; QCD coupling 3. PROTON-ANTIPROTON COLLIDER TEVATRON Top quark; W ± boson; Higgs; susy particles 4. PROTON COLLIDER LHC Higgs mechanism / elw Symmetry breaking Supersymmetric particles Extra space dimensions 5. e + e LINEAR COLLIDERS High-resolution picture : Higgs/susy/extra dimensions LHC/ILC coherence : ultimate unification

3 1. INTRODUCTION High energy physics : tremendously successful in unravelling structure of matter and forces in microcosm STANDARD MODEL: [1] Matter: three generations of quarks and leptons all l, q particles identified experimentally [2] Forces: interactions of gauge theoretic nature [J = 1] SU(3) SU(2) U(1) : quantum chromodynamics QCD electroweak GSW theory gravity at classical level [J = 2] 2A

4 1. INTRODUCTION High energy physics : tremendously successful in unravelling structure of matter and forces in microcosm STANDARD MODEL: [1] Matter: three generations of quarks and leptons [2] Forces: interactions of gauge theoretic nature [J = 1] SU(3) SU(2) U(1) : quantum chromodynamics QCD electroweak GSW theory gravity at classical level [J = 2] all gauge forces [force quanta g, γ, W ±, Z] established experimentally 2B

5 STANDARD MODEL: cont d 3 [3] Mass: Higgs mechanism interaction energy of particles with non-zero vacuum field mass STANDARD MODEL / DEFICITS: internal: generating mass by Higgs mechanism experimentally not established external: 1. grand unification of three SM forces ultimate unification incldg gravity 2. symmetry pattern / flavor physics 3. structure of space-time at short distances 4. connection with cosmology : baryon asymmetry cold dark matter

6 e + e and HADRON COLLIDERS past and present collider facilities fundamental discoveries in unravelling structure of matter and forces : future hadron and e + e colliders establishing the Standard Model closing SM breakthrough discoveries beyond SM exploring domain of physics beyond SM potentially closing the system PP+G 4

7 5 E + E and HADRON COLLIDERS Collider Energy Discovery / Fund.result / Target SPEAR SLAC e + e 4 GeV charm quark, τ lepton PETRA DESY e + e 38 GeV gluon Sp ps CERN p p 600 GeV W ±, Z bosons LEP CERN e + e 210 GeV SM: elw and QCD / 3 families SLC SLAC e + e 90 GeV elw SM LC prototype Tevatron FNAL p p 2 TeV top quark HERA DESY ep 320 GeV quark/gluon structure of proton BaBar / Belle SLAC / KEK e + e 10 GeV quark mix / CP violation LHC CERN pp 14 TeV elw.sb/susy/extra.dim ILC e + e 1 TeV hi.res of elw.sb/susy/extra.dim CLIC e + e 3 5 TeV ditto VLHC pp 200 TeV discovering multi-tev physics MuC µµ sev. TeV exploring multi-tev physics

8 6 # PHYSICS RATIONAL FOR COLLIDER FACILITIES: A + B M production in 2-particle collisions: M 2 = (k + p) 2 : (a) fixed target: p = (m, 0, 0, 0) k (E, 0, 0, E) M 2mE root E law : large energy loss in E kin dense target : large collision rate / luminosity (b) collider : p (E, 0, 0, E) k (E, 0, 0, E) M 2E linear E law : no energy loss less dense bunches : small collision rates

9 7 # COLLIDER CHARACTERISTICS: (a) Energy :... from a few GeV to 100 GeV [SLC] to TeV [future] (b) Luminosity : measures collision rate of particles in colliding bunches L = N 1N 2 A f N i = number of particles in bunches A = transverse buch area f = bunch collision rate Lσ = observed rate for process with cross section σ ex: LHC : L = cm 2 s 1 ILC : L = cm 2 s fb 1 in 3 years 1ab 1 in 3 years (c) circular vs. linear collider : charged particles in circular motion : permanently accelerated towards center : emitting photons as synchrotron light E = c γ E 4 /ρ large loss of energy [hypothetical TeV collider at LEP: E E per turn] no-more sharp initial state energy

10 2. ep COLLIDER HERA 8A characteristics: asymmetric : E e = 27.5 GeV E p = 920 GeV HERA : cm energy s = 318 GeV tot lumi 1/2 to 1 fb 1 long. polarized lepton beams : e ( & ) and e + ( & ) satellite mode : e ± ( & ) + fixed polar. target p asymm detectors ZEUS, H1:

11 2. ep COLLIDER HERA characteristics: asymmetric : E e = 27.5 GeV E p = 920 GeV HERA : cm energy s = 318 GeV tot lumi 1/2 to 1 fb 1 long. polarized lepton beams : e ( & ) and e + ( & ) satellite mode : e ± ( & ) + fixed polar. target p Target: (1) quark/gluon structure of the proton (2) measurement of the QCD coupling α s (Q 2 ) (3) search and limits for : leptoquarks / R-pv SUSY e + q LQ R-currents, W, Z interactions... 8B

12 DEEP-INELASTIC SCATTERING: e p e γ, (Z) exchange : asymptotic freedom of QCD scattering on individual quarks : incoh superposition of Rutherford scattering : dσ dx dq 2 = 2πα2 x Q 4 [ [1 + (1 y)2 ] F 2 (x, Q 2 ) y 2 F L ] structure function : F 2 (x, Q 2 ) = Σe 2 q x [q(x, Q 2 ) + q(x, Q 2 )] q(x, Q 2 ) dx = # quarks mom.frct [x, x + dx] at resol. Q 1 variables: Q 2 = q 2 momentum transfer [squared] y = pq/pk energy transfer x = Q 2 /2pq Bjorken variable 9

13 STRUCTURE FUNCTION F 2 (x, Q 2 ) [... HERA] F 2 2 i x = (i = 16) x = (i = 13) x = (i = 10) x = (i = 8) x = (i = 6) x = 0.13 (i = 4) H1 ZEUS BCDMS NMC x = 0.25 (i = 2) x = 0.40 (i = 1) NLO QCD Fit x = 0.65 (i = 0) Q 2 / GeV 2 10

14 Systematics of Quark Densities parton process quark densities 1. NC tot eq eq and e q e q 4(u + ū) + (d + d) + (s + s) + 4(c + c) + (b + b) NC heavy c, c, b; b tagging c, c ; b, b 2. CC tot/diff e u νd; e d νū u ; d e + d νu; e + ū ν d d ; ū e s ν c, c tagging s e + s νc, c tagging s 3. Drell-Yan [Tev] u p + d p W + u d d p + ū p W d u complete set of measurements for quark densities decomposition : u = val + sea ū = sea val x α (1 x) β (1 + p x ) d = val + sea d = sea sea x α (1 x) β (1 + p x) s = sea s = sea up-to-date analyses: H1 and ZEUS MRST and CTEQ 11

15 QCD corrections and gluon density F 2 (x, Q 2 ) / quark densities dependent on resolution Q 1 : quark/gluon splitting: q(x, Q 2 ) reduced at large x g(x, Q 2 ) ditto accumulating at small x [cf. F 2 (x, Q 2 )] DGLAP equations : q(x,q 2 ) = α s(q 2 ) log Q 2 2π = α s(q 2 ) 2π 1 0 dx dz δ(x z x )P qq (z )q(x, Q 2 ) + [g] 1 x dx x P qq (x/x )q(x, Q 2 ) + [g] AP splitting : P qq (z ) = 4 3 [(1 + z 2 )/(1 z ) δ(z 1)] etc 12

16 q = α s(q 2 ) P log Q 2 2π qq q + α s(q 2 ) 2π g = α s(q 2 ) P log Q 2 2π gq q + α s(q 2 ) 2π P qg g P gg g analysis generalized to three loops coupled equations solved numerically [N, x] Gluon density change of F 2 (x, Q 2 ) determines g distribution other methods : high p T jets at HERA and Tevatron 13

17 Quark and Gluon densities 14 xf 1.5 ZEUS xu xu v xu xd v xd xd Q = 10 GeV xg x ZEUS-JETS fit tot. uncert. H1 PDF 2000 tot. exp. uncert. model uncert. many gluons at small x : frequent splitting g gg [int color charge; brems-sing ] perturbative picture [?] : xg(x, Q 2 ) exp log Q 2 log 1/x

18 Scheme dependence of parton densities : divergencies developg in higher order corrections, absorbed by renormalization generates scheme dependent densities accdg to prescription; schemes : DIS parton densities: F 2 remains unaltered sum of parton densities MS parton densities: only singular part absorbed finite shift from DIS QCD coupling α s (Q 2 ) in DIS [on low side of WA] world average α s (M 2 Z) = ± A

19 Scheme dependence of parton densities : 15B divergencies developg in higher order corrections, absorbed by renormalization generates scheme dependent densities accdg to prescription; schemes : DIS parton densities: F 2 remains unaltered sum of parton densities MS parton densities: only singular part absorbed finite shift from DIS QCD coupling α s (Q 2 ) world average α s (M 2 Z) = ± 0.001

20 Transition HERA LHC Q 2 / GeV HERA Experiments: H ZEUS Fixed Target Experiments: 10 3 NMC BCDMS y = E665 SLAC y = x Higgs and new particles, e.g. susy, produced at LHC for M 2 x 2 s : x M/ s 10 2 for M 100 GeV region for DGLAP evolution theoretically under good control : reliable predictions 16

21 3. p p COLLIDER TEVATRON characteristics: p p max energy in q q annihilation E p = E p Tevatron : cm energy s = TeV tot lumi 4 to 8 fb 1 [2008/9] Exps : CDF & D0 17A

22 3. p p COLLIDER TEVATRON characteristics: p p max energy in q q annihilation E p = E p Tevatron : cm energy s = TeV tot lumi 4 to 8 fb 1 [2008/9] Exps : CDF & D0 Target : (1) top quark discovery (2) elw precision physics : W mass measurement trilin cplgs : non-abelian gauge theory (3) new physics discovery : Higgs boson(s) susy particles new gauge bosons W, Z extra space dimensions... 17B

23 TOP QUARK 18 Evidence for t quark: SM anomaly free : ΣQ F = A FB (b) at 35GeV = [0 1] + 3[ ] SM PETRA/LEP : e + e b b : I 3 (b) = 1 2 top : missing iso-partner I 3 R 0 A FB (b) at m z 0.5 Γ(Z bb) 0.5 I 3 L top-quark mass prediction : [tb] loop W mass µ decay LEP : G F 2 = 4πα 8 M 2 W sin2 θ w 2πα M 2 Z sin2 2θ w [1+ ρ] ρ t = G F m 2 t 2π log m2 t M 2 W prediction : m t = 166 ± 26 GeV

24 TOP QUARK Discovery of t quark at Tevatron: present value m t = ± 2.1 GeV Agreement between top mass prediction and measurement establishes validity of electroweak GSW theory at the quantum level 19

25 W ± BOSON MASS 20A Drell-Yan production of W ±, Z bosons at Tevatron: decays : W ± l ± ν l vs. : Z l + l Tev : M W = ± GeV WAv: M W = ± GeV crucial input for testing elw sector in Standard Model and, e.g., Super- symmetry Measurement Fit O meas O fit /σ meas α (5) had (m Z ) ± m Z [GeV] ± Γ Z [GeV] ± σ 0 had [nb] ± R l ± A 0,l fb ± A l (P τ ) ± R b ± R c ± A 0,b fb ± A 0,c fb ± A b ± A c ± A l (SLD) ± sin 2 θ lept eff (Q fb ) ± m W [GeV] ± Γ W [GeV] ± m t [GeV] ±

26 W ± BOSON MASS 20B Drell-Yan production of W ±, Z bosons at Tevatron: decays : W ± l ± ν l vs. : Z l + l 80.5 LEP1 and SLD LEP2 and Tevatron (prel.) 68% CL Tev : M W = ± GeV WAv: M W = ± GeV m W [GeV] 80.4 crucial input for testing elw sector in Standard Model and, e.g., Super- symmetry 80.3 α m H [GeV] m t [GeV]

27 HIGGS BOSON(s) 21 # 1. Many SM production channels p p H, W H, ZH, jjh and results from both detectors are needed to either exclude 2 σ or discover 5 σ Higgs boson in Standard Model in low-mass region: Higgs Mass m (GeV/c ) :: non-zero chance before LHC [?] :: l H ) -1 Int. Luminosity per Exp. (fb 10 2 SUSY/Higgs Workshop ( 98-99) Higgs Sensitivity Study ( 03) statistical power only (no systematics) σ Discovery 3σ Evidence 95% CL Exclusion 2 # 2. Production rate of SUSY Higgs bosons Φ in b-quark fusion p p b bφ [Φ = h, H, A] promising in part of susy parameter space [non-decoupling region] with large Higgs mix angle tan β

28 SUSY PARTICLES 22A focus : charginos / neutralinos, susy partners of gauge and Higgs bosons squarks and gluinos, partners of quarks and gluons (1) golden channel: Drell Yan production p p χ ± 1 χ0 2 with χ 0 2 l + l χ 0 1 χ ± 1 l± ν l χ 0 1 p p l ± l + l :: trilepton signal limit [mod.d] m χ ± GeV (2) squarks and gluinos : p p q q g q g g ) BR(3l) (pb) χ 0 2 σ(χ ± ± 0 Search for χ 1 χ 2 3l+ DØ, 320 pb ± 0 0 ~ 0 M( χ1 ) M( χ2 ) 2M( χ1 ); M( l)>m( χ2 ) tanβ=3, µ>0, no slepton mixing 3l-max heavy-squarks Observed Limit Expected Limit LEP 0.1 large-m Chargino Mass (GeV)

29 SUSY PARTICLES 22B focus : charginos / neutralinos, susy partners of gauge and Higgs bosons squarks and gluinos, partners of quarks and gluons (1) golden channel: Drell Yan production p p χ ± 1 χ0 2 with χ 0 2 l + l χ 0 1 χ ± 1 l± ν l χ 0 1 (2) squarks and gluinos : p p q q g q g g exp analysis in msugra : M 0 vs. M 1/2 squark = gluino mass 387 GeV