X 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

X 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

1. INTRODUCTION

X High energy physics : tremendously successful in unravelling

structure of matter and forces in microcosm ⇒

X STANDARD MODEL:

X [1] Matter: three generations of quarks and leptons

X all l, q particles identified experimentally

X [2] Forces: interactions of gauge theoretic nature [J = 1]

X SU(3)×SU(2)×U(1) : quantum chromodynamics QCD

X electroweak GSW theory

X ⊕ gravity at classical level [J = 2] 2A

1. INTRODUCTION

X High energy physics : tremendously successful in unravelling

structure of matter and forces in microcosm ⇒

X STANDARD MODEL:

X [1] Matter: three generations of quarks and leptons

X [2] Forces: interactions of gauge theoretic nature [J = 1]

X SU(3)×SU(2)×U(1) : quantum chromodynamics QCD

X electroweak GSW theory

X ⊕ gravity at classical level [J = 2]

X all gauge forces [force quanta g, γ, W±, Z] established experimentally

X 2B

X STANDARD MODEL: cont’d 3

X [3] Mass: Higgs mechanism

X interaction energy of particles with non-zero vacuum field ∼ mass

X

X STANDARD MODEL / DEFICITS:

X internal: generating mass by Higgs mechanism

X experimentally not established ⇐

X external: 1. grand unification of three SM forces ⇐X ultimate unification incldg gravity ⇐X 2. symmetry pattern / flavor physics

X 3. structure of space-time at short distances ⇐

X 4. connection with cosmology : baryon asymmetry ⇐X cold dark matter ⇐

X

X e+e− and HADRON COLLIDERS

X past and present collider facilities ⇒ fundamental discoveries in unravelling

X structure of matter and forces :

X establishing the Standard Model

X future hadron and e+e− colliders ⇒ closing SM

X breakthrough discoveries beyond SM

X exploring domain of physics beyond SM

X potentially closing the system PP+G

X X 4

X 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

SppS CERN pp 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 pp 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

X 6X# PHYSICS RATIONAL FOR COLLIDER FACILITIES:

X A + B →M production in 2-particle collisions: M 2 = (k + p)2 :

X(a) fixed target: p = (m, 0, 0, 0)

k ' (E, 0, 0, E)

M '√

2mE

X – root E law : large energy loss in Ekin

X – dense target : large collision rate / luminosity

X(b) collider : p ' (E, 0, 0, E)

k ' (E, 0, 0,−E)

M ' 2E

X – linear E law : no energy loss

X – less dense bunches : small collision rates

X 7X# COLLIDER CHARACTERISTICS:

X(a) Energy : ... from a few GeV to 100 GeV [SLC] to TeV [future]

X(b) Luminosity : measures collision rate of particles in colliding bunches

L = N1N2

Af∗ Ni = 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 = 1034 cm−2s−1 ⇒ 300 fb−1 in 3 years

ILC : L = 3× 1034 cm−2s−1 ⇒ 1ab−1 in 3 years

X(c) circular vs. linear collider :

X charged particles in circular motion : permanently accelerated towards center

X : emitting photons as synchrotron light ∆E = cγE4/ρ

X – large loss of energy [hypothetical TeV collider at LEP: ∆E ' E per turn]

X – no-more sharp initial state energy

X 8A

2. ep COLLIDER HERA

Xcharacteristics: asymmetric : Ee = 27.5 GeV

Ep = 920 GeV

HERA : cm energy√

s = 318 GeV

tot lumi ∼ 1/2 to 1 fb−1

Xlong. polarized lepton beams : e−(→ &←) and e+(→ &←)

Xsatellite mode : e±(→ &←) + fixed polar. target p

Xasymm detectors ZEUS, H1:

� � � �� �� � � ��� � �� � �� � � � �� �

� ��� �

�

�

�� �� � �

2. ep COLLIDER HERA

Xcharacteristics: asymmetric : Ee = 27.5 GeV

Ep = 920 GeV

HERA : cm energy√

s = 318 GeV

tot lumi ∼ 1/2 to 1 fb−1

Xlong. polarized lepton beams : e−(→ &←) and e+(→ &←)

Xsatellite mode : e±(→ &←) + fixed polar. target p

XTarget: (1) quark/gluon structure of the proton ⇐

(2) measurement of the QCD coupling αs(Q2)

(3) search and limits for : leptoquarks / R-pv SUSY e + q → LQ

R-currents, W ′, Z′ interactions

...

X 8B

XDEEP-INELASTIC SCATTERING:

X e−p→ e−X γ, (Z) exchange :

Xasymptotic freedom of QCD ⇒ scattering on individual quarks :

⇒ incoh superposition of Rutherford scattering :

Xdσ

dx dQ2=

2πα2

x Q4[ [1 + (1− y)2] F2(x, Q2)− y2FL ]

structure function : F2(x, Q2) = Σe2q x [q(x, Q2) + q(x, Q2)]

q(x, Q2) dx = # quarks mom.frct [x, x + dx] at resol. Q−1

Xvariables: Q2 = −q2 Xmomentum transfer [squared]

y = pq/pk Xenergy transfer

x = Q2/2pq Bjorken variable 9

STRUCTURE FUNCTION F2(x, Q2) [... HERA]

10-3

10-2

10-1

1

10

10 2

10 3

10 4

10 5

10 102

103

104

105

Q2 / GeV2

F 2 ⋅

2i

x = 0.65(i = 0)

x = 0.40(i = 1)

x = 0.25(i = 2)

x = 0.13(i = 4)

x = 0.050(i = 6)

x = 0.020(i = 8)

x = 0.0080(i = 10)

x = 0.0020(i = 13)

x = 0.00050(i = 16)

H1ZEUSBCDMSNMC

NLO QCD Fit

X 10

Systematics of Quark Densities

parton process quark densities

1. NC tot eq → eq and eq → eq 4(u + u) + (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 → νu u ; d

e+d → νu; e+u → νd d ; u

e−s → νc, c tagging s

e+s → νc, c tagging s

3. Drell-Yan [Tev] up + dp → W+ u ⊗ d

dp + up → W− d ⊗ u

X ⇒ complete set of measurements for quark densities

decomposition : u = val + sea u = sea val ∼ x−α(1 − x)β(1 + px)

d = val + sea d = sea sea ∼ x−α′

(1− x)β′

(1 + p′x)

s = sea s = sea

X ⇒ up-to-date analyses: H1 and ZEUS | MRST and CTEQ

X 11

X QCD corrections and gluon density

XF2(x, Q2) / quark densities dependent on resolution Q−1 :

Xquark/gluon splitting: q(x, Q2) reduced at large x

accumulating at small x [cf. F2(x, Q2)]

g(x, Q2) ditto

XDGLAP equations : ∂q(x,Q2)

∂ log Q2 = αs(Q2)2π

∫ 1

0dx′dz′δ(x− z′x′)Pqq(z

′)q(x′, Q2) +∫

[g]

= αs(Q2)2π

∫ 1

xdx′

x′ Pqq(x/x′)q(x′, Q2) +∫

[g]

AP splitting : Pqq(z′) = 43[(1 + z′2)/(1 − z′)+ + 3

2δ(z′

− 1)] etc 12

∂q∂ log Q2 = αs(Q2)

2πPqq ⊗ q + αs(Q2)

2πPqg ⊗ g

∂g∂ log Q2 = αs(Q2)

2πPgq ⊗ q + αs(Q2)

2πPgg ⊗ g

X analysis generalized to three loops

X coupled equations solved numerically [N, x]

X Gluon density

X change of F2(x, Q2) determines g distribution

X other methods : high pT jets at HERA and Tevatron

X 13

X Quark and Gluon densities 14

xU

vxu

Ux

xD

vxd

Dx

xg

2 = 10 GeV2 Q ZEUS-JETS fit tot. uncert. H1 PDF 2000 tot. exp. uncert. model uncert.

-410 -310 -210 -110 1

-410 -310 -210 -110 1

0

5

10

15

0

0.5

1

1.5

0

0.5

1

1.5

x

xf

ZEUS

many gluons at small x : frequent splitting g → gg [int color charge; brems-sing ]

perturbative picture [?] :

xg(x, Q2) ∼ exp√

log Q2 log 1/x

X Scheme dependence of parton densities :

X divergencies developg in higher order corrections, absorbed by renormalization ⇒X generates scheme dependent densities accdg to prescription; schemes :

X DIS parton densities: F2 remains unaltered sum of parton densities

X MS parton densities: only singular part absorbed ⇒ finite shift from DIS

X QCD coupling αs(Q2) in DIS

X [on low side of WA]

X world average αs(M2Z) = 0.119± 0.001 15A

X Scheme dependence of parton densities : 15B

X divergencies developg in higher order corrections, absorbed by renormalization ⇒X generates scheme dependent densities accdg to prescription; schemes :

X DIS parton densities: F2 remains unaltered sum of parton densities

X MS parton densities: only singular part absorbed ⇒ finite shift from DIS

X QCD coupling αs(Q2)

X world average αs(M2Z) = 0.119± 0.001

X Transition HERA → LHC

x

Q2 /

GeV

2

y =

1

y = 0.

004

.

HERA Experiments:

H1 1994-2000

ZEUS 1994-2000

Fixed Target Experiments:

NMC

BCDMS

E665

SLAC

10-1

1

10

10 2

10 3

10 4

10-6

10-5

10-4

10-3

10-2

10-1

1

X Higgs and new particles, e.g. susy, produced at LHC for M 2 ' 〈x2〉s :

〈x〉 ∼M/√

s ≥ 10−2 for M ∼ 100 GeV

X region for DGLAP evolution theoretically under good control : reliable predictions

X 16

3. pp COLLIDER TEVATRON

Xcharacteristics: pp ⇒ max energy in qq annihilation

Ep = Ep

Tevatron : cm energy√

s = 1.8→ 2.0 TeV

tot lumi ∼ 4 to 8 fb−1 [2008/9] Exps : CDF & D0

17A

3. pp COLLIDER TEVATRON

Xcharacteristics: pp ⇒ max energy in qq annihilation

Ep = Ep

Tevatron : cm energy√

s = 1.8→ 2.0 TeV

tot lumi ∼ 4 to 8 fb−1 [2008/9] Exps : CDF & D0

XTarget : (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

X TOP QUARK 18

XEvidence for t quark:

X SM anomaly free : ΣQF = 0

X = [0− 1] + 3[ 23− 1

3]

X PETRA/LEP : e+e− → bb : I3(b) = − 12

top : missing iso-partner

0.5

0

—0.5

0.50—0.5I3L

Γ(Z→bb)

AFB

(b) at35GeV

AFB

(b)at m

z

SM

I3R

X top-quark mass prediction : [tb] loop ⇒ W mass

µ decay ⊕ LEP : GF√2

= 4πα8 M2

Wsin2 θw

→ 2παM2

Zsin2 2θw [1+∆ρ]

∆ρt =GF m2

t

2πlog

m2t

M2W

prediction : mt = 166± 26 GeV

TOP QUARK

Discovery of t quark at Tevatron:

present value mt = 171.4± 2.1 GeV

Agreement between top mass prediction and measurement establishes validity

of electroweak GSW theory at the quantum level

X 19

X W± BOSON MASS 20A

XDrell-Yan production of W±, Z bosons at Tevatron:

Xdecays : W± → `±ν`

Xvs. : Z → `+`−

XTev : MW = 80.452± 0.059 GeV

WAv: MW = 80.392± 0.029 GeV

Xcrucial input for testing elw sector

Xin Standard Model and, e.g., Super-

Xsymmetry

Measurement Fit |Omeas−Ofit|/σmeas

0 1 2 3

0 1 2 3

∆αhad(mZ)∆α(5) 0.02758 ± 0.00035 0.02766

mZ [GeV]mZ [GeV] 91.1875 ± 0.0021 91.1874

ΓZ [GeV]ΓZ [GeV] 2.4952 ± 0.0023 2.4957

σhad [nb]σ0 41.540 ± 0.037 41.477

RlRl 20.767 ± 0.025 20.744

AfbA0,l 0.01714 ± 0.00095 0.01640

Al(Pτ)Al(Pτ) 0.1465 ± 0.0032 0.1479

RbRb 0.21629 ± 0.00066 0.21585

RcRc 0.1721 ± 0.0030 0.1722

AfbA0,b 0.0992 ± 0.0016 0.1037

AfbA0,c 0.0707 ± 0.0035 0.0741

AbAb 0.923 ± 0.020 0.935

AcAc 0.670 ± 0.027 0.668

Al(SLD)Al(SLD) 0.1513 ± 0.0021 0.1479

sin2θeffsin2θlept(Qfb) 0.2324 ± 0.0012 0.2314

mW [GeV]mW [GeV] 80.392 ± 0.029 80.371

ΓW [GeV]ΓW [GeV] 2.147 ± 0.060 2.091

mt [GeV]mt [GeV] 171.4 ± 2.1 171.7

X W± BOSON MASS 20B

XDrell-Yan production of W±, Z bosons at Tevatron:

Xdecays : W± → `±ν`

Xvs. : Z → `+`−

XTev : MW = 80.452± 0.059 GeV

WAv: MW = 80.392± 0.029 GeV

Xcrucial input for testing elw sector

Xin Standard Model and, e.g., Super-

Xsymmetry

80.3

80.4

80.5

150 175 200

mH [GeV]114 300 1000

mt [GeV]

mW

[G

eV]

68% CL

∆α

LEP1 and SLD

LEP2 and Tevatron (prel.)

X HIGGS BOSON(s) 21

X# 1. Many SM production channels

XXX pp→ H, WH, ZH, jjH

Xand results from both detectors are

Xneeded to

XXX– either exclude ∼ 2σ

XXX– or discover ∼ 5σ

XHiggs boson in Standard Model

Xin low-mass region:

X:: non-zero chance before LHC [?] :: l ) 2 (GeV/cHHiggs Mass m

100 110 120 130 140 150 160 170 180 190

)-1

Int.

Lu

min

osi

ty p

er E

xp. (

fb

1

10

102

SUSY/Higgs Workshop(’98-’99)Higgs Sensitivity Study (’03)

statistical power only(no systematics)

Discoveryσ5 Evidenceσ3

95% CL Exclusion

X# 2. Production rate of SUSY Higgs bosons Φ in b-quark fusion

XXX pp→ bbΦ [Φ = h, H, A]

Xpromising in part of susy parameter space [non-decoupling region] with large

XHiggs mix angle tan β

X SUSY PARTICLES 22A

Xfocus : charginos / neutralinos, susy partners of gauge and Higgs bosons

X squarks and gluinos, partners of quarks and gluons

X(1) golden channel: Drell Yan production pp→ χ±1 χ0

2 with χ02 → `+`−χ0

1

χ±1 → `±ν` χ0

1

pp→ `±`+`− :: trilepton signal

limit [mod.d] mχ±

1

≥ 124 GeV

X(2) squarks and gluinos : pp→ qq

gq

gg

X Chargino Mass (GeV)100 105 110 115 120 125 130 135 140

BR

(3l)

(p

b)

×) 20 χ∼1± χ∼ (σ

0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

3l+X→ 02χ∼

±1χ∼Search for

)20

χ∼)>M(l~); M(10

χ∼2M(≈)20

χ∼M(≈)1±

χ∼M(>0, no slepton mixingµ=3, βtan

-1DØ, 320 pb

LEP

3l-max

heavy-squarks

0large-m

Observed LimitExpected Limit

Chargino Mass (GeV)100 105 110 115 120 125 130 135 140

BR

(3l)

(p

b)

×) 20 χ∼1± χ∼ (σ

0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

X SUSY PARTICLES 22B

Xfocus : charginos / neutralinos, susy partners of gauge and Higgs bosons

X squarks and gluinos, partners of quarks and gluons

X(1) golden channel: Drell Yan production pp→ χ±1 χ0

2 with χ02 → `+`−χ0

1

χ±1 → `±ν` χ0

1

X

X(2) squarks and gluinos : pp→ qq

gq

gg

Xexp analysis in msugra : M0 vs. M1/2

X squark = gluino mass ≥ 387 GeV