Recent QCD Generator Developmentshome.thep.lu.se/~torbjorn/talks/uppsala00.pdf · DELPHI week,...

DELPHI week, Uppsala15 September 2000

RecentQCD GeneratorDevelopments

(A Subjective Selection)

Torbjorn SjostrandLund University

IntroductionImproved parton showers

a) Final state showersb) Initial state showers

Hadronizationγ∗γ∗ physicsOther topics

http://www.thep.lu.se/∼torbjorn/talks/uppsala00.ps

Goodbye LEP!

. . . and thanks for making life exciting4 September 1979: my first LEP workshop13 August 1989: first LEP events1 November 2000 (?): closedown of LEP

LEP part of a High Energy Physics Landscape:

e+e−: . . .→ PETRA/PEP → TRISTAN→ LEP 1 → LEP 2→ LC (TESLA/NLC/CLIC)

ep: fixed target → HERA → LEP+LHC?pp: . . .→ SppS → Tevatron → LHCµ+µ−: ?AA: fixed target → RHIC → LHC

+ fixed target, underground detectors, . . .

Complexity:

e+e− < ep < pp < AA< γp < γγ

= ep = e+e−

Building blocks of understanding⇒ unity of observable particle physics

Event physics overview

Structure of the basic generation process:

1) Hard subprocess:dσ/dt, Breit-Wigners.

2) Resonance decays:includes correlations.

3) Final-stateparton showers:(or matrix elements).

4) Initial-stateparton showers:(or matrix elements).

5) Multipleparton–partoninteractions.

q

q Z0 Z0

h0

Z0

µ+

µ−

h0

W−

W+

ντ

τ−s

c

q → qg

g → gg

g → qq

q → qγ

g

q

Z0

6) Beam remnants:colour-connectedto rest of event

7) Hadronization(PYTHIA: string;HERWIG: cluster;ISAJET: independent).

8) Normal decays:hadronic, τ , charm, . . .

p

p

b

b

ud

ud

u

u

�

�

�

�

�

q

g

g

q

hadrons

ρ+

π0

π+

γ

γ

9) QCD interconnection effects:

e−

e+

W−

W+

q3

q4

q2

q1

�

�

π+

π+

�� BE

a) colour rearrangement (⇒ rapidity gaps?);b) Bose-Einstein.

10) The forgotten/unexpected: a chain isnever stronger than its weakest link!

The role of exploration, be it experimental, theoretical,or phenomenological:

• to predict: too late for LEP⇒ LHC/LC/. . .

• to explain/understand: never too late

LEP will provide the reference for

• final-state QCD showers

• hadronization

• γγ physics (?)

• some electroweak parameters: mZ . . .

• limits of non-observation (?)

cf. PETRA: QCD vs. top/SUSY limits

Improved models and new ideas coming along⇒ important to preserve physics data in easily acces-sible formHZTOOL: correct concept

wrong implementation

⇒ need clean, minimal interface

QCD Radiation off Heavy Particles(E. Norrbin & TS, in preparation)

Shower: effective resummation ofmultiple-gluon-emission effects.

Evolution variable Q2:

PYTHIA: m2

HERWIG: E2θ2

ARIADNE: p2⊥z: energy/momentum sharing in branching

Rbl3 (yc) =

Rb3(yc)

Ru+d+s3 (yc)

=σ(bb → 3jets)/σ(bb)

σ(qq → 3jets)/σ(qq)

0.9

0.92

0.94

0.96

0.98

1

1.02

0 0.02 0.04 0.06 0.08 0.1 0.12

R3bl - DURHAM algorithm

Data

NLO, O(αs2)

LO, O(αs)

PYTHIA 6.125 with mass effects

PYTHIA 6.125 without mass effects

PYTHIA 6.131 with mass effects

mb= 3 GeV

mb= 3 GeV

mb= 5 GeV

yc

R3bl

DELPHI

0

1 (q)

i

2 (q)

3 (g)

0

1 (q)

i

2 (q)

3 (g)

xj = 2Ej/ECM ⇒ x1 + x2 + x3 = 2

mq = 0:

1

σ0

dσME

dx1 dx2=

αs

2πCF

≈2︷︸︸︷

x21 + x22(1 − x1)(1 − x2)

1

σ0

dσPS

dQ2 dz=

αs

2πCF

dQ2

Q2

≈2︷︸︸︷

1 + z2

1 − zdz · (Sudakov)

Q21 = m2

i = (p0 − p2)2 = (1 − x2)E

2CM

z1 =p0p1p0pi

=E1

Ei=

x1x1 + x3

=x1

2 − x2,

⇒ dQ21

Q21

dz11 − z1

=dx2

1 − x2

dx1x3

⇒ 1

σ0

dσPS

dx1 dx2∝ 2

(1 − x2)x3+

2

(1 − x1)x3

=2

(1 − x1)(1 − x2)

since (1−x1)+(1−x2)=x3

⇒ ME/PS < 1, i.e. good MC starting point

r = mq/ECM > 0:

1

σ0

dσME

dx1 dx2∝ x21 + x22 − r2(. . .)

(1 − x1)(1 − x2)

Q21 = m2

i = (p0 − p2)2 = (1 − x2 + r2)E2

CM

z more messy but dz/(1 − z) unchanged

⇒ 1

σ0

dσPS

dx1 dx2∝ 2

(1 − x1 + r2)x3+

2

(1 − x2 + r2)x3

restore by

Q21 = m2

i −m2q = (p0 − p2)

2 − p21 = (1 − x2)E2CM

Q2j = m2

j −m2j,onshell is relevant propagator;

generalized for r1 6= r2, rj = mj/ECM:

Q21 = (1 + r22 − r21 − x2)E

2CM

Q22 = (1 + r21 − r22 − x1)E

2CM

1

σ0

dσME

dx1 dx2=

(. . .)

Q21Q

22

− (. . .)

Q41

− (. . .)

Q42

Also radiation from decaying particle:

0 (t)

1 (b)

2 (W+)

i

3 (g)

0 (t)

1 (b)

2 (W+)

i 3 (g)

Q20 = |m2

i −m20| = |(p0 − p3)

2 −m20| = x3E

2CM

ME 1Q2

0Q21

matches PS b → bg

⇒ can match PS to generic a→ bcg ME

• subsequent branchings: also matched to ME,with reduced energy of system

• angular ordering• αs(p2⊥)

• secondary heavy flavours by gluon splitting• widths of unstable particles: for the future

Calculate for 1 → 2 processes in SM + MSSM:1

σ(a → bc)

dσ(a → bcg)

dx1 dx2

Depends on• mass ratios r1 = mb/ma and r2 = mc/ma

• colour and spin structure• vector vs. axial vector etc. (γ5)

when mb,mc 6= 0

colour spin γ5 example

1 → 3 + 3 — — (eikonal)

1 → 3 + 3 1 → 12+ 1

21, γ5,1 ± γ5 Z0 → qq

3 → 3 + 1 12→ 1

2+ 1 1, γ5,1 ± γ5 t → bW+

1 → 3 + 3 0 → 12+ 1

21, γ5,1 ± γ5 H0 → qq

3 → 3 + 1 12→ 1

2+ 0 1, γ5,1 ± γ5 t → bH+

1 → 3 + 3 1 → 0 + 0 1 Z0 → qq

3 → 3 + 1 0 → 0 + 1 1 q → q′W+

1 → 3 + 3 0 → 0 + 0 1 H0 → qq

3 → 3 + 1 0 → 0 + 0 1 q → q′H+

1 → 3 + 3 12→ 1

2+ 0 1, γ5,1 ± γ5 χ→ qq

3 → 3 + 1 0 → 12+ 1

21, γ5,1 ± γ5 q → qχ

3 → 3 + 1 12→ 0 + 1

21, γ5,1 ± γ5 t → tχ

8 → 3 + 3 12→ 1

2+ 0 1, γ5,1 ± γ5 g → qq

3 → 3 + 8 0 → 12+ 1

21, γ5,1 ± γ5 q → qg

3 → 3 + 8 12→ 0 + 1

21, γ5,1 ± γ5 t → tg

Universal gluon radiation patterns (= no spin depen-dence) for small gluon energies . . .

(with textbook dead cone)

. . . but very process-dependent for large gluon ener-gies . . .

(and no dead cone except for spin 0 → 0 + 0)

. . . results in process-dependent jet rates

r1 = r2 = 0.2

colour spin γ5 Eg 3 jet 3 jet’1 → 3 + 3 1 → 1

2+ 1

21 1.000 1.000 1.000γ5 1.056 1.112 1.133

0 → 12+ 1

21 1.134 1.293 1.376γ5 1.093 1.207 1.271

1 → 0 + 0 1 1.073 1.205 1.3100 → 0 + 0 1 0.875 0.758 0.72012→ 1

2+ 0 1 0.953 0.918 0.916

γ5 1.057 1.132 1.1791 → 3 + 3 eikonal – 0.802 0.695 0.659

eikonal +x23 – 1.201 1.518 1.670

3 → 3 + 1 12→ 1

2+ 1 1 0.323 0.306 0.287

γ5 0.356 0.365 0.34912→ 1

2+ 0 1 0.312 0.284 0.258

γ5 0.357 0.363 0.3440 → 0 + 1 1 0.287 0.242 0.2180 → 0 + 0 1 0.279 0.224 0.1940 → 1

2+ 1

21 0.359 0.379 0.375γ5 0.347 0.354 0.346

12→ 0 + 1

21 0.294 0.257 0.239γ5 0.314 0.302 0.298

3 → 3 + 8 0 → 12+ 1

21 1.634 1.833 1.922γ5 1.574 1.712 1.775

12→ 0 + 1

21 1.385 1.320 1.291γ5 1.549 1.664 1.675

8 → 3 + 3 12→ 1

2+ 0 1 0.561 0.493 0.445

γ5 0.621 0.607 0.574

0.9

0.91

0.92

0.93

0.94

0.95

0.96

0.97

0.98

0.99

1

0 0.02 0.04 0.06 0.08 0.1

R3bl

yc

Pythia 6.153Pythia 6.152Pythia 6.129

DELPHIALEPH

Rbl3 (yc)

ECM = 91 GeV

mb = 4.8 GeV

0.94

0.95

0.96

0.97

0.98

0.99

1

0 0.02 0.04 0.06 0.08 0.1

R3bl

yc

VectorZ0 mixture

Axial vectorDELPHIALEPH

0.94

0.95

0.96

0.97

0.98

0.99

1

0 0.02 0.04 0.06 0.08 0.1

R3bl

yc

Default pythia 6.153Modified pT

Minimal change of coherenceNo coherence (unrealistic)

DELPHIALEPH

0.75

0.8

0.85

0.9

0.95

0 0.01 0.02 0.03 0.04 0.05

R4bl

yc

Pythia 6.153Pythia 6.152Pythia 6.129

DELPHI

Rbl4 (yc)

ECM = 91 GeV

mb = 4.8 GeV

0.82

0.84

0.86

0.88

0.9

0.92

0.94

0.96

0.98

0 0.01 0.02 0.03 0.04 0.05

R4bl

yc

VectorZ0 mixture

Axial vectorDELPHI

0.82

0.84

0.86

0.88

0.9

0.92

0.94

0.96

0.98

0 0.01 0.02 0.03 0.04 0.05

R4bl

yc

Default pythia 6.153Modified pT

Minimal change of coherenceNo coherence (unrealistic)

DELPHI

HERWIG shower developments

(B. Webber, http://home.cern.ch/webber/)

Combine ME and PS for multijet production,e.g. e+e− → 2 jet + 3 jet + 4 jet + . . .

Define jet separation e.g. by Durham p⊥yij = 2min(E2

i , E2j )(1 − cos θij)/E

2CM ≈ p2⊥/E

2CM

For yij > yc: exclusive multijet states byME · SudakovSudakov: needs reconstructed shower history, byDurham clustering

For yij < yc: further evolution by vetoed PSVeto: Durham p2⊥ 6= HERWIG Q2

⇒ do evolution from Qmax ∼ ECM

but reject branchings that would giveextra jet by Durham p⊥ definition

Correct to NLL = next-to-leading logarithmbut not to NLO = next-to-leading order⇒ further development

Photon ISR in Z0 production(G. Miu & TS, PLB449 (1999) 313)

By-product of a study on W± production in hadroncolliders, attempting to combine matrix-element (ME)and parton-shower (PS) strengths.

Merging strategy: correct hardest emissions in show-ers so as to reproduce one order higher matrix ele-ments.

2 → 1 process e+(1) + e−(2) → Z0(0) startingpoint for backwards shower evolution:

34

15

6

20

2 → 2 process e+(3) + e−(2) → γ(4) + Z0(0):

s = (p3 + p2)2 =

(p1 + p2)2

z=m2

Z

zt = (p3 − p4)

2 = p21 = −Q2

u = m2Z − s− t = Q2 − 1 − z

zm2

Z

Relate ME and PS rates:

dσ

dt

∣∣∣∣ME

=σ0s

αem

2π

t2 + u2 + 2m2Zs

tu

Q2→0−→ σ0αem

2π

1 + z2

1 − z

1

Q2=

dσ

dQ2

∣∣∣∣∣PS1

dσ

dt

∣∣∣∣PS1

=σ0s

αem

2π

s2 +m4Z

t(t+ u)

Add mirror e+(1) + e−(5) → γ(6) + Z0(0):

dσ

dt

∣∣∣∣PS

=dσ

dt

∣∣∣∣PS1

+dσ

dt

∣∣∣∣PS2

=σ0s

αem

2π

s2 +m4Z

tu

Ree→γZ(s, t) =(dσ/dt)ME

(dσ/dt)PS=t2 + u2 + 2m2

Zs

s2 +m4Z

1

2< Ree→γZ(s, t) ≤ 1

Improve PS:

• Q2max = s, not Q2

max ≈ m2Z (intermediate)

• MC correction by R(s, t) for first (≈ hardest)emission on each side (new)

Now default.

pp → W± at 1.8 TeV:

1e-06

1e-05

0.0001

0.001

0.01

0.1

1

0 10 20 30 40 50 60 70 80 90 100 110

(1/ N

)(d

N/d

pW

)(G

eV-1)

p W (GeV)

PS,k =0.44 GeVPS,k =4 GeV

D0 data

e+e− → Z0 at 500 GeV,80 GeV <

√s < 100 GeV:

Hadronization

Lund string successful . . .

even HERWIG adopts ‘stringy’ description:• large-mass clusters split in two• small-mass clusters decay anisotropicallyalong ‘string’ direction

. . . but many murky issues

• perturbative ⇒ nonperturbative transition

• ambiguities of gluon structure

• origin of flavour composition(hadron vs. quark masses, wave functions)

• baryon production mechanism(diquark, popcorn, ‘curtain’ quark)

• role of higher resonances: tensor etc.(poorly known, nonisotropic decays,duality with string description)

• spin/polarization phenomena

• interconnection(colour rearrangement, Bose–Einstein)

Small-mass string ⇒ ‘cluster’,by g → qq in shower

(E. Norrbin & TS, PLB442 (1998) 407,LUTP 00-16 (hep-ph/0005110)

Improved description of when collapse occurs(mass spectrum ⇐ constituent quark masses)

example:charmstringin πpcollision

2 2.5 3 3.50

0.05

0.1

0.15

0.2

0.25

0.3

0.35

Msinglet

(1/N

)dN

/dM

(a)

1-body

2-body

cluster

2-body

string

3-body

and1-body collapse: energy-momentum shuffling2-body decay: smoother joining to stringpicture (matched anisotropic decay)

A(xF) =

#D−−#D+

#D−+#D+

in π−p

-0.2

0

0.2

0.4

0.6

0.8

1

1.2

0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9

A(x

F)

xF

(a)Pair production

All channelsWA92, 350 GeVWA82, 340 GeVE791, 500 GeVE769, 250 GeV

Virtual photon processes(C. Friberg & TS, Eur. Phys. J. C13 (2000) 151,LUTP 00-29 (hep-ph/0007314), LUTP 00-31 (hep-ph/0009003))

The photon flux

k1

k′1θ1

k2k′2

θ2

q1

q2

X

W2 = (q1 + q2)2

Q2i = −q2i

yi =qikj

kikjj=2(1) for i=1(2)

xi =qi(k1 + k2)

ki(k1 + k2)

yi ≈ xi +Q2i

s

Q2i ≈ x2i

1 − xim2i + (1 − xi)s sin

2(θi/2)

dσ(ee → eeX) =∑

ξ1,ξ2=T,L

∫

dy1 dQ21 dy2 dQ2

2

× fξ1γ/e

(y1, Q21) f

ξ2γ/e

(y2, Q22) dσ(γ∗ξ1γ

∗ξ2

→ X)

with

fTγ/e(y,Q

2) =αem

2π

(

(1 + (1 − y)2

y

1

Q2− 2m2

ey

Q4

)

fLγ/e(y,Q

2) =αem

2π

2(1 − y)

y

1

Q2

Photoproduction / γγ

Direct VMD Anomalous

Direct: point-like Resolved: hadronic state

γγ: 3 × 3 = 9 combinations (+ subdivisions)

Spectrum of fluctuations γ ↔ qq ∝ dk2⊥/k2⊥

alt. m ' 2k⊥; dm2/m2

? k⊥ < k0 ' 0.5 GeV: nonperturbative γ → qq

hadronic physics ⇒ VMD(Vector Meson Dominance)

parameterized couplings to ρ0, ω, φ, J/ψσγ→ρtot = P(γ → ρ) · σρtot

PDF fγ→ρi (x, µ2), σγ→ρ

jet = . . .

beam remnants, multiple interactions, . . .

? k⊥ > k0: perturbative γ → qq

PDF calculable: anomalous part of γbut σqq

tot not ⇒ GVMD (Generalized VMD)

geometric scaling ansatz σqqtot ∝ k2V /k

2⊥,

kV ' mρ/2 for light quarksagain hadronic character: beam remnants, . . .

Photon ‘high-p⊥’ processes

Three main ‘high-p⊥’ jet process classes:1. direct×direct

γ∗Tγ∗T → qq

γ∗Tγ∗L → qq

γ∗Lγ∗L → qq

γ∗

γ∗

2. direct×resolved , resolved = VMD or anomalous

γ∗Tg → qq

γ∗Lg → qq

γ∗Tq → qg

γ∗Lq → qg

γ∗

γ∗

γ∗

γ∗

etc.

3. resolved×resolved

qq′ → qq′

qq → q′q′

qq → gg

qg → qg

gg → gg

gg → qq

γ∗

γ∗

γ∗

γ∗

etc.

dσ(γ∗γ∗ → X) =

(∫

dx1 fγ∗i (x1, µ

2, Q21)

)

×(∫

dx2 fγ∗j (x2, µ

2, Q22)

) ∫

dtdσ

dt(s = x1x2W

2)

Deeply Inelastic Scattering / γ∗γ

Virtual photon: γ∗q → q, e.g. q in (VMD) ρ0

σγ∗ρtot ' 4π2αem

Q2Fρ2(x,Q2) ' 4π2αem

Q2

∑

q,q

e2q xq(x,Q2)

but F2 → 0 for Q2 → 0 by gauge invariance,+ limit doublecounting with photoproduction

σγ∗ρDIS '

(

Q2

Q2 +m2ρ

)24π2αem

Q2

∑

q,q

e2q xq(x,Q2)

where q(x,Q2) frozen for Q2 < Q20;

and prefactor ensures σDIS → 0 for Q2 → 0

O(αs) DIS =

{

QCDC γ∗q → qgBGF γ∗g → qq

}

= dir × res

σγ∗ρLO DIS = σ

γ∗ρDIS − σ

γ∗ρdir×res → σ

γ∗ρDIS exp

−

σγ∗ρdir×res

σγ∗ρDIS

corresponds to Sudakov form factor

γγ: 9 combinations = (dir+VMD+GVMD)2

γ∗γ∗: + 4 combinations = 2 sides×(VMD+GVMD)

13 !!

From Real to Virtual Photons

Direct photon: Q2 in ME expression

Resolved photon:total cross section σγ→i

tot dampened by dipole(

m2

m2 +Q2

)2

(fewer fluctuations, smaller size)

VMD: m = mρ,mω,mφ,mJ/ψ

GVMD: m ' 2k⊥; in total∫

k20

dk2⊥k2⊥

k2Vk2⊥

(

4k2⊥4k2⊥ +Q2

)2

fγ∗Ti (x, µ2, Q2): SaS 1D (also dipole-based)

fγ∗Li (x, µ2, Q2): simple multiplicative factor

or Chyla (hep-ph/0006232)

Putting it all together, res = VMD + GVMD:

σγ∗γ∗

tot (W 2, Q21, Q

22) = σγ

∗γ∗

DIS×res exp

(

−σγ

∗γ∗

dir×res

σγ∗γ∗

DIS×res

)

+ σγ∗γ∗

dir×res

+ σγ∗γ∗

res×DIS exp

(

−σγ

∗γ∗

res×dir

σγ∗γ∗

res×DIS

)

+ σγ∗γ∗

res×dir

+ σγ∗γ∗

dir×dir +

(W 2

Q21 +Q2

2 +W 2

)3

σγ∗γ∗

res×res

(1 − x)3 reduces doublecounting at large x

Process composition

1E-02

1E-01

1E+00

1E+01

1E+02

1E+03

0.01 0.1 1 10 100 1000 10000

σ totγ∗ γ (

nb)

Q12 (GeV2)

Q22 = 0 GeV2

DISDirect1-res2-resTotal r1Total r2

Wγ∗γ∗ = 100 GeV

Direct = dir×dir1-res = dir×res2-res= res×res

fγ∗L

i /fγ∗T

i :

r1 =2m2Q2

(m2 +Q2)2

r2 =2Q2

m2 +Q2

1E-02

1E-01

1E+00

1E+01

1E+02

0.01 0.1 1 10 100 1000 10000

Q12 (GeV2)

Q22 = 10 GeV2

DISDirect1-res2-resTotal r1Total r2

Energy dependence

1E+00

1E+01

1E+02

1E+03

1E+04

1E+05

1E+06

1E+07

1 10 100

σ totγ∗ γ (

nb)

W (GeV)

×2-2

×20

×22

×24

×26

×28

×210

×212

9.90

7.25

5.15

4.04

2.13

1.31

0.71

0.00

σtotγ∗γ×

Q12 / GeV2

Photopr. DataOPALTPC

1E+00

1E+01

1E+02

1E+03

1E+04

1E+05

1E+06

1E+07

1 10 100

σ totγ∗ γ (

nb)

W (GeV)

×2-2

×20

×22

×24

×26

×28

×210

×212

9.90

7.25

5.15

4.04

2.13

1.31

0.71

0.00

σtotγ∗γ×

Q12 / GeV2

PLUTOTOPAZCELLO

1E+00

1E+01

1E+02

1E+03

1E+04

1E+05

1E+06

1E+07

1 10 100

σ totγ∗ γ (

nb)

W (GeV)

×2-2

×20

×22

×24

×26

×28

×210

×212

9.90

7.25

5.15

4.04

2.13

1.31

0.71

0.00

σtotγ∗γ×

Q12 / GeV2

L3ALEPH

1E+00

1E+01

1E+02

1E+03

1E+04

1E+05

1E+06

1E+07

1 10 100

σ totγ∗ γ (

nb)

W (GeV)

×2-2

×20

×22

×24

×26

×28

×210

×212

9.90

7.25

5.15

4.04

2.13

1.31

0.71

0.00

σtotγ∗γ×

Q12 / GeV2

1E+00

1E+01

1E+02

1E+03

1E+04

1E+05

1E+06

1E+07

1 10 100

σ totγ∗ γ (

nb)

W (GeV)

×2-2

×20

×22

×24

×26

×28

×210

×212

9.90

7.25

5.15

4.04

2.13

1.31

0.71

0.00

σtotγ∗γ×

Q12 / GeV2

1E+00

1E+01

1E+02

1E+03

1E+04

1E+05

1E+06

1E+07

1 10 100

σ totγ∗ γ (

nb)

W (GeV)

×2-2

×20

×22

×24

×26

×28

×210

×212

9.90

7.25

5.15

4.04

2.13

1.31

0.71

0.00

σtotγ∗γ×

Q12 / GeV2

1E+00

1E+01

1E+02

1E+03

1E+04

1E+05

1E+06

1E+07

1 10 100

σ totγ∗ γ (

nb)

W (GeV)

×2-2

×20

×22

×24

×26

×28

×210

×212

9.90

7.25

5.15

4.04

2.13

1.31

0.71

0.00

σtotγ∗γ×

Q12 / GeV2

1E+00

1E+01

1E+02

1E+03

1E+04

1E+05

1E+06

1E+07

1 10 100

σ totγ∗ γ (

nb)

W (GeV)

×2-2

×20

×22

×24

×26

×28

×210

×212

9.90

7.25

5.15

4.04

2.13

1.31

0.71

0.00

σtotγ∗γ×

Q12 / GeV2

1E+00

1E+01

1E+02

1E+03

1E+04

1E+05

1E+06

1E+07

1 10 100

σ totγ∗ γ (

nb)

W (GeV)

×2-2

×20

×22

×24

×26

×28

×210

×212

9.90

7.25

5.15

4.04

2.13

1.31

0.71

0.00

σtotγ∗γ×

Q12 / GeV2

1E+00

1E+01

1E+02

1E+03

1E+04

1E+05

1E+06

1E+07

1 10 100

σ totγ∗ γ (

nb)

W (GeV)

×2-2

×20

×22

×24

×26

×28

×210

×212

9.90

7.25

5.15

4.04

2.13

1.31

0.71

0.00

σtotγ∗γ×

Q12 / GeV2

1E+00

1E+01

1E+02

1E+03

1E+04

1E+05

1E+06

1E+07

1 10 100

σ totγ∗ γ (

nb)

W (GeV)

×2-2

×20

×22

×24

×26

×28

×210

×212

9.90

7.25

5.15

4.04

2.13

1.31

0.71

0.00

σtotγ∗γ×

Q12 / GeV2

1E+00

1E+01

1E+02

1E+03

1E+04

1E+05

1E+06

1E+07

1 10 100

σ totγ∗ γ (

nb)

W (GeV)

×2-2

×20

×22

×24

×26

×28

×210

×212

9.90

7.25

5.15

4.04

2.13

1.31

0.71

0.00

σtotγ∗γ×

Q12 / GeV2

1E+00

1E+01

1E+02

1E+03

1E+04

1E+05

1E+06

1E+07

1 10 100

σ totγ∗ γ (

nb)

W (GeV)

×2-2

×20

×22

×24

×26

×28

×210

×212

9.90

7.25

5.15

4.04

2.13

1.31

0.71

0.00

σtotγ∗γ×

Q12 / GeV2

Total Transv.Total r1Total r2

fγ∗L

i /fγ∗T

i :

r1 =2m2Q2

(m2 +Q2)2

r2 =2Q2

m2 +Q2

1E-02

1E-01

1E+00

1E+01

1E+02

10 100W (GeV)

Q12 = 9.90 GeV2

1E-02

1E-01

1E+00

1E+01

1E+02

10 100W (GeV)

Q12 = 9.90 GeV2

DISDirect1-res2-resTotal r1

Event properties

Wγ∗γ∗ = 100 GeV

average charged multiplicity:

0

5

10

15

20

25

0.01 0.1 1 10 100 1000 10000

⟨ nch

⟩

Q12 (GeV2)

Q22 = 1 GeV2

pp

γ∗p

γ∗γ

γ∗γ∗

0

5

10

15

20

25

30

0.01 0.1 1 10 100 1000 10000

⟨ nch

⟩

Q12 (GeV2)

Q22 = 1 GeV2

γ∗γ∗

1-res

2-res

DIS

Direct

probability to have a jet with E⊥ > 5 GeV

inside a cone R =√

(∆η)2 + (∆ϕ)2 < 1:

1E-03

1E-02

1E-01

1E+00

0.01 0.1 1 10 100 1000 10000

P(N

jet >

0)

Q12 (GeV2)

Q22 = 1 GeV2

pp

γ∗p

γ∗γ

γ∗γ∗ 1E-02

1E-01

1E+00

0.01 0.1 1 10 100 1000 10000

P(N

jet >

0)

Q12 (GeV2)

Q22 = 1 GeV2

γ∗γ∗

1-res

2-res

DIS

Direct

Effects of longitudinal photons

0

0.2

0.4

0.6

0.8

1

1.2

1.4

1.6

0.01 0.1 1

f iγ L(x

i, µ2 ,Q

2 ) /

fiγ T

(xi,

µ2 ,Q2 )

xi

uL(xi, µ2=10, Q2=0.5) / uT

uL(xi, µ2=10, Q2=2.0) / uT

gL(xi, µ2=10, Q2=0.5) / gT

gL(xi, µ2=10, Q2=2.0) / gT

γ∗L: Chyla

γ∗T: SaS 1D

0

0.5

1

1.5

2

2.5

-4 -3 -2 -1 0 1 2 3 4

dσ /

dη

(µb)

η

Q2 = 1.0 GeV2 ETjet > 4 GeV Rjet < 1

Transverse Resolvedr1r2RPDFDirect

r1 =2m2Q2

(m2 +Q2)2

r2 =2Q2

m2 +Q2

RPDF =fγ∗L

i (x, µ2, Q2)

fγ∗T

i (x, µ2, Q2)

Program particulars

To access new γ∗ flux convolution:CALL PYINIT(’cms’,’gamma/e-’,’gamma/e+’,200D0)

Also possible to have γ∗γ∗ collisions directly:CALL PYINIT(’five’,’gamma’,’gamma’,100D0)

with P(1,J) and P(2,J) defining momenta and virtu-alities (P(I,5) < 0 for spacelike ones).

Photon character regulated by MSTP(14):= 10 : mix direct/VMD/anomalous for real

photons; d×V = V×d etc. ⇒ 6 classes.= 30 : (new default) mix dir/VMD/GVMD

and DIS for virtual photons; ⇒ 13 classes.= other numbers : individual classes.Warning : γ∗γ∗ → `+`− included in dir×dir if

not switched off (automatic when mixing).

MSEL = 1, CKIN(3) > 2 : jets with p⊥ >CKIN(3)MSEL = 1, CKIN(3) = 0 : jet + low-p⊥MSEL = 2, CKIN(3) = 0 : + diffractive + elastic

Possible to specify cuts on xi, yi, Q2i , θi, W2

in CKIN(61) - CKIN(78).Phase space sampled according to∏

i

(dQ2i /Q

2i ) (dxi/xi) dϕi

⇒ full efficiency for xi and Q2i cuts.

��

��

��

��

��

��

��

��

��

��

��

� � � � ��

ll

��

��

��

��

��

��

��

��

��

��

PYTHIA

lh hh

statusAuthors: TS, P. Eden,C. Friberg, L. Lonnblad,G. Miu, S. Mrenna, E. Norrbin

JETSET 7.4PYTHIA 5.7SPYTHIA

4 March 1997 : PYTHIA 6.1

Currently PYTHIA 6.152 of 17 August 2000∼ 51,900 lines Fortran 77

Code, manuals, sample main programs:http://www.thep.lu.se/∼torbjorn/Pythia.html

PYTHIA 6.1 main news:

• JETSET routines renamed:LUxxxx → PYxxxx + some more

• All real variables in DOUBLE PRECISION

• New SUSY processes and improved SUSY simu-lation; new PDG codes for sparticles

• New processes for Higgs, technicolour, . . .

• Many improved resonance decays

• Several initial- and final-state showers matched tomatrix elements

• New machinery to handle real and virtual photonfluxes and cross sections

• Newer parton distributions (but . . . )

• QED radiation off an incoming muon

• Energy-dependent p⊥min in multiple interactions

• Colour rearrangement options for W+W−

• Expanded Bose-Einstein algorithm

• New baryon production scheme (optional)

• One-dimensional histograms (GBOOK)

2–, 4– and 6–fermion standard interfaces for showersand hadronization:CALL PY2FRM(IRAD,ITAU,ICOM)

CALL PY4FRM(ATOTSQ,A1SQ,A2SQ,ISTRAT,

&IRAD,ITAU,ICOM)CALL PY6FRM(P12,P13,P21,P23,P31,P32,PTOP,

&IRAD,ITAU,ICOM)

qqgg and qqq′q′ QCD 4–jet standard interface forshowers and hadronization:CALL PY4JET(PMAX,IRAD,ICOM)

HERWIG status

Authors: G. Marchesini, B.R. Webber,G. Abbiendi, G. Corcella, I. Knowles,S. Moretti, K. Odagiri, P. Richardson,M. Seymour, L. Stanco.

Currently HERWIG 6.1 of 16 December 1999∼ 32,000 lines Fortran 77

Code, manuals, related programs:http://hepwww.rl.ac.uk/theory/seymour/herwig/

6.1 release notes: hep-ph/9912396

• SUSY production and decay (in hadron collisions)including R-parity violation

• matrix element corrections to top decay(and W/Z production in hadron collisions)

• e+e− → 4 jets matrix element option• new soft underlying event options• new particles and updated particle data• enhanced nonisotropic decay of clusters• beamstrahlung (interface to CIRCE)

HERWIG 6.2 will follow soon, including e.g.full simulation of MSSM Higgs physics.

Subprocess survey

Process PYTH HERW ISAJ

QCD & relatedSoft QCD ? ? ?Hard QCD ? ? ?Heavy flavour ? ? ?Top threshold — — —γγ physics ? ? —DIS ? ? —γ∗γ∗ physics ? (?) —

Electroweak SMSingle γ∗/Z0/W± ? ? ?

(γ/γ∗/Z0/W±/f/g)2 ? ? ?Light SM Higgs ? ? ?Heavy SM Higgs (?) ? ?

SUSY BSMh0/H0/A0/H± ? ? ?SUSY ? ? ?R/ SUSY — ? —

Other BSMTechnicolor ? — ?New gauge bosons ? — —Compositeness ? — —Leptoquarks ? — —H±± (from LR-sym.) ? — —Extra dimensions — (?) (?)

? = yes, (?) = partial/in progress, — = no

On to C++(L. Lonnblad, CPC 118 (1999) 213;

M. Bertini, L. Lonnblad & TS, LUTP 00-23 (hep-ph/0006152);

input to [email protected])

Why Fortran → C++?

• SLAC →, FNAL →, CERN → LHC era.

• Industrial standard.

• Educational and professional continuity for stu-dents.

• Better to program – for experts.

• User-friendy interfaces – for the rest of us.

PYTHIA 7 milestones:

• January 1998: project formally started.

• June 2000: “proof of concept” version, withgeneric event generation machinery, some pro-cesses and string fragmentation.

• 2001–2002: useful version (?), but limited inscope.

• ??: more and better than current PYTHIA.

HERWIG++ progress:PPARC funds 2 dedicated “postdocs”,3-year work recently started.

Summary

? Renewed interest in shower evolution

• mass effects

• process dependence (spin, colour, . . . )

• multijet composition & topologies

Needed for future physics @ LHC/LC⇒ LEP data needed for calibration

? Hadronization

• strings best first approximation

• slow but steady progress

⇒ LEP data needed as inspiration & reference

? γ∗γ∗ physics

• not for the weak of heart

• new ‘complete’ framework . . .

• . . . but still at level of ‘strawman’

⇒ LEP will provide important tests

? Plea:plan for easy comparison with final QCD data⇒ will keep DELPHI alive in the LHC/LC era!

Recent QCD Generator Developmentshome.thep.lu.se/~torbjorn/talks/uppsala00.pdf · DELPHI week,...

Documents

Transcript of Recent QCD Generator Developmentshome.thep.lu.se/~torbjorn/talks/uppsala00.pdf · DELPHI week,...