Soft QCD: Theory P e t e r S k a n d s ( C E R N T h e o r e t i - - PowerPoint PPT Presentation

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Soft QCD: Theory P e t e r S k a n d s ( C E R N T h e o r e t i - - PowerPoint PPT Presentation

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Soft QCD: Theory P e t e r S k a n d s ( C E R N T h e o r e t i c a l P h y s i c s D e p t ) B o s t o n J e t s W o r k s h o p M I T, J a n u a r y 2 1 - 2 3 2 0 1 4 Questions Pileup How much? In central & fwd acceptance?

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SLIDE 1

P e t e r S k a n d s ( C E R N T h e o r e t i c a l P h y s i c s D e p t )

Soft QCD: Theory

B o s t o n J e t s W o r k s h o p M I T, J a n u a r y 2 1 - 2 3 2 0 1 4

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SLIDE 2
  • P. S k a n d s

Questions

Pileup

How much? In central & fwd acceptance? Structure: averages + fluctuations, particle composition, lumpiness, … Scaling to 13 TeV and beyond

Underlying Event ~ “A handful of pileup” ?

Hadronizes with Main Event → “Color reconnections” Additional “minijets” from multiple parton interactions

Hadronization

Models from the 80ies, mainly constrained in 90ies Meanwhile, perturbative models have evolved

Dipole/Antenna showers, ME matching, NLO corrections, … Precision → re-examine non-perturbative models and constraints New clean constraints from LHC (& future colliders)?

Hadronization models ⥂ analytical NP corrections?

Uses and Limits of “Tuning”

2

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SLIDE 3
  • P. S k a n d s

From Hard to Soft

Factorization and IR safety

Main tools for jet calculations Corrections suppressed by powers

  • f ΛQCD/QHard

Soft QCD / Pileup

~ ∞ statistics for min-bias

→ Access tails, limits

Universality: Recycling PU ⬌ MB ⬌ UE

3

NO HARD SCALE

Typical Q scales ~ ΛQCD Extremely sensitive to IR effects → Excellent LAB for studying IR effects

C M S “ R i d g e ” T r a c k m u l t i p l i c i t i e s pT spectra I d e n t i fi e d P a r t i c l e s C

  • r

r e l a t i

  • n

s Rapidity Gaps C

  • l
  • r

C

  • r

r e l a t i

  • n

s Collective Effects? C e n t r a l v s F

  • r

w a r d Baryon Transport HADRONIZATION

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SLIDE 4
  • P. S k a n d s

What is Pileup / Min-Bias?

We use Minimum-Bias (MB) data to test soft-QCD models Pileup = “Zero-bias”

“Minimum-Bias” typically suppresses diffraction by requiring two-armed coincidence, and/or ≥ n particle(s) in central region

→ Pileup contains more diffraction than Min-Bias

Total diffractive cross section ~ 1/3 σinel Most diffraction is low-mass → no contribution in central regions High-mass tails could be relevant in FWD region → direct constraints on diffractive components (→ later)

4 Hit Hit

SD MB

Hit

Veto → NSD

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SLIDE 5
  • P. S k a n d s

7 TeV 8 TeV

ALICE ATL CMS ALICE TOTEM TOTEM TOTEM AUGER AUGER

13 TeV

The Total Cross Section

5

PP CROSS SECTIONS TOTEM, PRL 111 (2013) 1, 012001

σinel(13 TeV) ∼ 80 ± 3.5 mb σtot(13 TeV) ∼ 110 ± 6 mb σtot(8 TeV) = 101 ± 2.9 mb

(2.9%)

σel(8 TeV) = 27.1 ± 1.4 mb

(5.1%)

σinel(8 TeV) = 74.7 ± 1.7 mb

(2.3%)

Pileup rate ∝ σtot(s) = σel(s) + σinel(s) ∝ s0.08 or ln2(s) ?

Donnachie-Landshoff Froissart-Martin Bound

total inelastic elastic

PYTHIA: 100 mb PYTHIA: 78 mb

(PYTHIA versions: 6.4.28 & 8.1.80)

PYTHIA: 73 mb PYTHIA: 20 mb PYTHIA: 93 mb

PYTHIA elastic is too low

PYTHIA PYTHIA
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SLIDE 6
  • P. S k a n d s

What Cross Section?

Total Inelastic

Fraction with one charged particle in |η|<1 ALICE def : SD has MX<200 Ambiguous Theory Definition Ambiguous Theory Definition Ambiguous Theory Definition Observed fraction corrected to total

σINEL @ 30 TeV: ~ 90 mb σINEL @ 100 TeV: ~ 108 mb σSD: a few mb larger than at 7 TeV σDD ~ just over 10 mb σINEL @ 13 TeV ~ 80 mb

σinel(13 TeV) ∼ 80 ± 3.5 mb

The Inelastic Cross Section

First try: decompose

+ Parametrizations of diffractive components: dM2/M2

6

σinel = σsd + σdd + σcd + σnd

dσsd(AX)(s) dt dM 2 = g3I

P

16π β2

AI P βBI P

1 M 2 exp(Bsd(AX)t) Fsd , dσdd(s) dt dM 2

1 dM 2 2

= g2

3I P

16π βAI

P βBI P

1 M 2

1

1 M 2

2

exp(Bddt) Fdd .

+ Integrate and solve for σnd

log10(√s/GeV)

Note problem of principle: Q.M. requires distinguishable final states

PYTHIA:

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  • P. S k a n d s

Models of Soft QCD - Disclaimer

May not always reflect “best” TH understanding

Not just a matter of cranking perturbative orders Harder due to requirement of fully differential dynamical modeling (event generators), not just cross section formulae

May not always reflect “best” EXP constraints

Not just a matter of “tuning” (+ tunnel vision: exp comparisons for searches or EW measurements rarely formulated as QCD constraints)

Modeling: identify “new” physics + build and constrain models (beyond perturbative leading-twist)

Few people working on soft QCD models → long cycles

7

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SLIDE 8
  • P. S k a n d s

Dynamical Models of Soft QCD

8

Regge Theory

E.g., QGSJET, SIBYLL + “Mixed” E.g., PHOJET, EPOS, SHERPA-KMR

See e.g. Reviews by MCnet [arXiv:1101.2599] and KMR [arXiv:1102.2844]

Optical Theorem + Eikonal multi-Pomeron exchanges σtot,inel ∝ log2(s) Cut Pomerons → Flux Tubes (strings) Uncut Pomerons → Elastic (& eikonalization) Cuts unify treatment of all soft processes EL, SD, DD, … , ND (Perturbative contributions added above Q0)

A

Parton Based

dσ2→2 / dp2

⊥

p4

⊥

+ Unitarity & Saturation → Multi-parton interactions (MPI) + Parton Showers & Hadronization Regulate dσ at low pT0 ~ few GeV Screening/Saturation → energy-dependent pT0 Total cross sections from Regge Theory

(e.g., Donnachie-Landshoff + Parametrizations)

E.g., PYTHIA, HERWIG, SHERPA

B

⊗ PDFs

Froissart-Martin Bound

PYTHIA,

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SLIDE 9
  • P. S k a n d s

Parton-Based Models

9

dσ2→2 / dp2

⊥

p4

⊥

⊗ PDFs Main applications:

Central Jets/EWK/top/ Higgs/New Physics Gluon PDF x*f(x) Q2 = 1 GeV2

Warning: NLO PDFs < 0

100 500 1000 5000 1¥104 5¥1041¥105 1 2 3 4 5 6 7

ECM [GeV] pT0 [GeV] pT0 scale vs CM energy Range for Pythia 6 Perugia 2012 tunes

100 TeV 30 TeV 7 TeV 0.9 TeV

Poor Man’s Saturation High Q2 and finite x Extrapolation to soft scales delicate. Impressive successes with MPI-based models but still far from a solved problem

Form of PDFs at small x and Q2 Form and Ecm dependence of pT0 regulator Modeling of the diffractive component Proton transverse mass distribution Colour Reconnections, Collective Effects

Saturation See also Connecting hard to soft: KMR, EPJ C71 (2011) 1617 + PYTHIA “Perugia Tunes”: PS, PRD82 (2010) 074018 + arXiv:1308.2813

See talk on UE by W. Waalewijn

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SLIDE 10
  • P. S k a n d s

η

  • 1
  • 0.5

0.5 1

η dN/d

3 4 5 6 7 8 9

ALICE Pythia 6 (350:P2011) Pythia 6 (370:P2012) Pythia 6 (320:P0) Pythia 6 (327:P2010)

7000 GeV pp

Soft QCD (mb,diff,fwd)

mcplots.cern.ch 4.2M events ≥ Rivet 1.8.2,

Pythia 6.427 ALICE_2010_S8625980 )

T

| < 1.0, all p η > 0, |

ch

Distribution (N η Charged Particle

Minimum-Bias: Averages

10 0% 10% 20% 30% 40% 50% 60% 70%

INEL>0 |η|<1

PHOJET PY 6 DW PY 6 Perugia 0 PY 6 Perugia 2012 PY8 4C (def)

Data from ALICE EPJ C68 (2010) 345, Plot from arXiv:1308.2813 Central Charged-Track Multiplicity Tevatron tunes were ~ 10-20% low

  • n MB and UE

A SENSITIVE E-SCALING PROBE: Relative increase in the central charged-track multiplicity from 0.9 to 2.36 and 7 TeV

See also energy-scaling tuning study, Schulz & PS, EPJ C71 (2011) 1644

Min/Max Range

Discovery at LHC Min-Bias & UE are 10-20% larger than we thought Scale a bit faster with energy → Be sure to use up-to-date (LHC) tunes

PY8 Monash 2013

Pre-LHC Post-LHC

Representative plot. Several MB/UE models/tunes and

  • bservables show

same behavior.

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SLIDE 11
  • P. S k a n d s

Sum(ET)

11

Plots from mcplots.cern.ch

Central |η|<0.8 Forward 4<|η|<4.8

PY8 doing better than PY6

pre-LHC post-LHC

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SLIDE 12
  • P. S k a n d s

> η /d

Ch

<dn

Totem

1/n

1 2 3 4 5 6 |<6.5) η >0.04, 5.3<|

T

1, p ≥

ch

> (n η /d

Ch

<dn

Pythia 8.181 Data from Europhys.Lett. 98 (2012) 31002

TOTEM PY8 (Monash 13) PY8 (4C) PY8 (2C)

bins

/N

2 5%

χ 0.0 ± 0.2 0.0 ± 2.6 0.0 ± 6.1

V I N C I A R O O T

7000 GeV

pp

η

5.5 6 6.5

Theory/Data 0.6 0.8 1 1.2 1.4

The Forward Region

More sensitive to low x & diffraction

12

2C: an older Tevatron tune 4C: the current LHC tune (Default in Pythia 8.1) Monash 2013: a new LEP + LHC tune (Default from Pythia 8.2?)

Forward Energy Flow Charged Multiplicity

> η <dE/d

100 200 300 400 500 |<4.65) η 1 in both 3.23<| ≥

ch

MB Fwd E Flow (n

Pythia 8.181 Data from JHEP 11 (2011) 148

CMS PY8 (Monash 13) PY8 (4C) PY8 (2C)

bins

/N

2 5%

χ 0.0 ± 0.2 0.0 ± 0.4 0.0 ± 2.2

V I N C I A R O O T

7000 GeV

pp

η

3 3.5 4 4.5 5

Theory/Data 0.6 0.8 1 1.2 1.4

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SLIDE 13

H adroni z ati on

c o lo r f lo w, c o l o r r ec o n n e ct i o ns, par ti cl e spect ra

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SLIDE 14
  • P. S k a n d s

Rapidity Multiplicity ∝ NMPI

Color Connections

14

Leading NC: each parton-parton interaction scatters ‘new’ colors → incoherent addition of colors 1 or 2 strings per MPI

Quite clean, factorized picture WRONG!

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SLIDE 15
  • P. S k a n d s

Color Reconnections?

15

Rapidity Multiplicity ∝ NMPI

<

E.g., Generalized Area Law (Rathsman: Phys. Lett. B452 (1999) 364) Color Annealing (P.S., Wicke: Eur. Phys. J. C52 (2007) 133) …

Hydro? Coherence Coherence

NC=3: Colors add coherently + collective effects?

Better theory models needed Study: coherence and/or finite-NC effects String formation at finite NC In context of multi-parton interactions LEP constraints? Additional collectivity? (a la HI? BE?)

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SLIDE 16
  • P. S k a n d s

Signs of collectivity?

16

0.5 1 1.5 |<2.5) η >0.1, |

T

2, p ≥

Ch

) (n

Ch

>(n

T

Soft <p

Pythia 8.181 Data from New J.Phys. 13 (2011) 053033

ATLAS PY8 (Monash 13) PY8 (4C) PY8 (2C)

bins

/N

2 5%

χ 0.0 ± 0.7 0.0 ± 0.8 0.3 ± 4.0

V I N C I A R O O T

7000 GeV

pp 50 100 150 200

Theory/Data 0.6 0.8 1 1.2 1.4

no color reconnections

1) Rise of <pT> with multiplicity

/dy>

Λ

<dn

NSD

1/n

0.1 0.2 0.3 0.4 )/d|y|> (NSD) Λ <dn(

Pythia 8.181 Data from JHEP 1105 (2011) 064

CMS PY8 (Monash 13) PY8 (4C) PY8 (2C)

bins

/N

2 5%

χ 0.0 ± 6.9 0.0 ± 7.6 0.0 ± 14.7

V I N C I A R O O T

7000 GeV

pp

y

0.5 1 1.5 2

Theory/Data 0.6 0.8 1 1.2 1.4

2) Baryons by coalescence? <pT> nCharged

Λ0

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SLIDE 17
  • P. S k a n d s

Gluon Splitting

Less singular than gluon emission: single log

→ Less precise, from parton-shower viewpoint Massive quarks → not even singular

Predictions for g→cc,bb differ greatly between models

Non-singular terms, evolution variable, renormalization scale

Beware: overpredicted if (c,b) treated massless

17

P(g → q¯ q) ∝ 1 m2

q¯ q

Strong interest in constraints from double-tagged heavy-flavor jets At the theory level we will learn more from NLO corrections to gluon- splitting processes

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SLIDE 18

Tuni ng

means di fferent thi ngs to di fferent peopl e

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SLIDE 19
  • P. S k a n d s

Example: Value of Strong Coupling

19

αs(MZ) = 0.12

1/N dN/d(1-T)

  • 3

10

  • 2

10

  • 1

10 1 10 1-Thrust (udsc)

Pythia 8.165 Data from Phys.Rept. 399 (2004) 71

L3 Pythia

V I N C I A R O O T 1-T (udsc)

0.1 0.2 0.3 0.4 0.5

Theory/Data

0.6 0.8 1 1.2 1.4 1/N dN/d(Minor)

  • 3

10

  • 2

10

  • 1

10 1 10 Minor

Pythia 8.165 Data from CERN-PPE-96-120

Delphi Pythia

V I N C I A R O O T Minor

0.1 0.2 0.3 0.4 0.5

Theory/Data

0.6 0.8 1 1.2 1.4

T = max

  • n
  • i |

pi · n|

  • i |

pi|

  • 1 − T → 1

2

1 − T → 0

Major Minor

PYTHIA 8 (hadronization on) vs LEP: Thrust

Minor 1-T

1/N dN/d(1-T)

  • 3

10

  • 2

10

  • 1

10 1 10 1-Thrust (udsc)

Pythia 8.165 Data from Phys.Rept. 399 (2004) 71

L3 Pythia

V I N C I A R O O T 1-T (udsc)

0.1 0.2 0.3 0.4 0.5

Theory/Data

0.6 0.8 1 1.2 1.4 1/N dN/d(Minor)

  • 3

10

  • 2

10

  • 1

10 1 10 Minor

Pythia 8.165 Data from CERN-PPE-96-120

Delphi Pythia

Minor

0.1 0.2 0.3 0.4 0.5

Theory/Data

0.6 0.8 1 1.2 1.4

Minor 1-T

αs(MZ) = 0.14 + IR regularization → Impact on non-perturbative parameters!

1-loop running, MC 1-loop running, MC

slide-20
SLIDE 20
  • P. S k a n d s

Sneak Preview:

VINCIA: Multijet NLO Corrections

20

0.1 0.2 0.3 0.4 0.5

1/N dN/d(1-T)

  • 3

10

  • 2

10

  • 1

10 1 10

2

10 1-Thrust (udsc)

Vincia 1.030 + MadGraph 4.426 + Pythia 8.175 Data from Phys.Rept. 399 (2004) 71

L3 Vincia (NLO) Vincia (NLO off) Vincia (LO tune)

V I N C I A R O O T

1-T (udsc)

0.1 0.2 0.3 0.4 0.5

Theory/Data 0.6 0.8 1 1.2 1.4

0.2 0.4 0.6 0.8 1

1/N dN/dC

  • 3

10

  • 2

10

  • 1

10 1 10

2

10 C Parameter (udsc)

Vincia 1.030 + MadGraph 4.426 + Pythia 8.175 Data from Phys.Rept. 399 (2004) 71

L3 Vincia (NLO) Vincia (NLO off) Vincia (LO tune)

V I N C I A R O O T

C (udsc)

0.2 0.4 0.6 0.8 1

Theory/Data 0.6 0.8 1 1.2 1.4

0.2 0.4 0.6 0.8

1/N dN/dD

  • 3

10

  • 2

10

  • 1

10 1 10 D Parameter (udsc)

Vincia 1.030 + MadGraph 4.426 + Pythia 8.175 Data from Phys.Rept. 399 (2004) 71

L3 Vincia (NLO) Vincia (NLO off) Vincia (LO tune)

V I N C I A R O O T

D (udsc)

0.2 0.4 0.6 0.8

Theory/Data 0.6 0.8 1 1.2 1.4

First LEP tune with NLO 3-jet corrections

LO tune: αs(MZ) = 0.139 (1-loop running, MC) NLO tune: αs(MZ) = 0.122 (2-loop running, MSbar→MC)

Hartgring, Laenen, Skands, arXiv:1303.4974

HADRON COLLISIONS

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SLIDE 21
  • P. S k a n d s

Soft QCD Models: Outlook

HERWIG++ and SHERPA are developing diffractive models + investigating color reconnections EPOS uses collective effects (hydro) also in pp

Impressive successes for identified-particle spectra (→?)

PYTHIA 8 (by now generally superior to PYTHIA 6)

New “Monash 2013” tune (LEP+MB+UE+DY) (from v.8.185) New model of colour reconnections to be developed over next half year (with J.R. Christiansen) → “Monash 2014”? Hard diffraction included in PYTHIA 8 (not 6), but diffraction generally still poorly understood VINCIA for hadron colliders also to be ready in 2014

PHOJET, SIBYLL, QGSJET (pomeron-based)

Personal (biased?) view: Problems with soft-to-hard transition

Tuning: LO vs NLO & universality needs better understanding

21

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SLIDE 22
  • P. S k a n d s

Observable Wishlist

Gluon Splitting: double-tagged (cc and bb) jets

Interplay with boosted H→bb, Z→bb Do double-tagging algorithms exist? How difficult/complicated would they be to develop? Can dependence on mQQ be measured?

Underlying event in top

Charged-track multiplicity in top events

Dependence on pT and m

Underlying event away from boosted tops

22

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SLIDE 23
  • P. S k a n d s

Observable Wihslist

MB and UE tails (more/less central) Rapidity Gaps: CR vs Diffraction

23

slide-24
SLIDE 24

(mcplots.cern.ch)

24

mcplots.cern.ch

  • Explicit tables of data & MC points
  • Run cards for each generator
  • Link to experimental reference paper
  • Steering file for plotting program
  • (Will also add link to RIVET analysis)
slide-25
SLIDE 25
  • P. S k a n d s

Test4Theory - LHC@home

25

New Users/Day

May June July Aug Sep

July 4th 2012

The ¡LHC@home ¡2.0 ¡project ¡Test4Theory ¡allows ¡users ¡to ¡par8cipate ¡in ¡running ¡simula8ons ¡of ¡high-­‑ energy ¡par8cle ¡physics ¡using ¡their ¡home ¡computers. The ¡results ¡are ¡submiJed ¡to ¡a ¡database ¡which ¡is ¡used ¡as ¡a ¡common ¡resource ¡by ¡both ¡ experimental ¡and ¡theore8cal ¡scien8sts ¡working ¡on ¡the ¡Large ¡Hadron ¡Collider ¡at ¡CERN.

New: ¡Ci#zen ¡Cyberlab ¡(funds ¡from ¡EU)

Develop ¡an ¡app ¡that ¡lets ¡ci8zen ¡scien8sts ¡learn ¡ about, ¡interact ¡with, ¡and ¡op4mize ¡high-­‑energy ¡ physics ¡simula4ons, ¡by ¡comparing ¡them ¡to ¡real ¡ data

http://lhcathome.cern.ch/test4theory

slide-26
SLIDE 26

Oct 2014 → Monash University Melbourne, Australia

Come to Australia

p p

Establishing a new group in Melbourne Working on PYTHIA & VINCIA NLO Event Generators Precision LHC phenomenology & soft physics Support LHC experiments, astro-particle community, and future accelerators Outreach and Citizen Science

slide-27
SLIDE 27

P . Skands

Multiple Interactions

27

Bahr, Butterworth, Seymour: arXiv:0806.2949 [hep-ph]

P a r t

  • n

S h

  • w

e r C u t

  • f

f ( f

  • r

c

  • m

p a r i s

  • n

)

Z

p2

⊥,min

dp2

⊥

dσDijet dp2

⊥

Leading-Order pQCD = Allow several parton-parton interactions per hadron-hadron collision. Requires extended factorization ansatz.

hni < 1 hni > 1

Parton-Parton Cross Section Hadron-Hadron Cross Section

σ2→2(p⊥min) = ⌥n(p⊥min) σtot

QF Q2 ×

Lesson from bremsstrahlung in pQCD: divergences → fixed-order breaks down Perturbation theory still ok, with resummation (unitarity)

→ Resum dijets? Yes → MPI!

dσ2→2 / dp2

⊥

p4

⊥

⇠ dp2

⊥

p4

⊥

Earliest MC model (“old” PYTHIA 6 model) Sjöstrand, van Zijl PRD36 (1987) 2019

slide-28
SLIDE 28
  • P. S k a n d s

Naively

Interactions independent (naive factorization) → Poisson

How many?

28

a solution to : m σtot =

∞

  • n=0

σn σint =

∞

  • n=0

n σn σint > σtot ⇐ ⇒ n > 1

  • σint

> σtot ⇐ ⇒ n Pn n = 2 0 1 2 3 4 5 6 7

Pn = nn n! e−n rgy–momentum conser Real Life

Momentum conservation suppresses high-n tail + physical correlations → not simple product

(example)

hn2→2(p⊥min)i = σ2→2(p⊥min) σtot

slide-29
SLIDE 29

P . Skands

1: A Simple Model

29 Parton-Parton Cross Section Hadron-Hadron Cross Section

σ2→2(p⊥min) = ⌥n(p⊥min) σtot

  • 1. Choose pTmin cutoff

= main tuning parameter

  • 2. Interpret <n>(pTmin) as mean of Poisson distribution

Equivalent to assuming all parton-parton interactions equivalent and independent ~ each take an instantaneous “snapshot” of the proton

  • 3. Generate n parton-parton interactions (pQCD 2→2)

Veto if total beam momentum exceeded → overall (E,p) cons

  • 4. Add impact-parameter dependence → <n> = <n>(b)

Assume factorization of transverse and longitudinal d.o.f., → PDFs : f(x,b) = f(x)g(b) b distribution ∝ EM form factor → JIMMY model Constant of proportionality = second main tuning parameter

  • 5. Add separate class of “soft” (zero-pT) interactions representing

interactions with pT < pTmin and require σsoft + σhard = σtot

→ Herwig++ model

The minimal model incorporating single-parton factorization, perturbative unitarity, and energy-and-momentum conservation

Ordinary CTEQ, MSTW, NNPDF, …

Bähr et al, arXiv:0905.4671 Butterworth, Forshaw, Seymour Z.Phys. C72 (1996) 637

slide-30
SLIDE 30

P . Skands

2: Interleaved Evolution

30

 Underlying Event

(note: interactions correllated in colour: hadronization not independent)

multiparton PDFs derived from sum rules Beam remnants Fermi motion / primordial kT Fixed order matrix elements Parton Showers (matched to further Matrix Elements) perturbative “intertwining”?

“New” Pythia model

Sjöstrand & Skands, JHEP 0403 (2004) 053; EPJ C39 (2005) 129

(B)SM 2→2

Also available for Pomeron-Proton collisions since Pythia 8.165

slide-31
SLIDE 31
  • P. S k a n d s

7 TeV 8 TeV

ALICE ATL CMS ALICE TOTEM TOTEM TOTEM AUGER AUGER

13 TeV

PHOJET elastic

31

PP CROSS SECTIONS TOTEM, PRL 111 (2013) 1, 012001

σinel(13 TeV) ∼ 80 ± 3.5 mb σtot(13 TeV) ∼ 110 ± 6 mb σtot(8 TeV) = 101 ± 2.9 mb

(2.9%)

σel(8 TeV) = 27.1 ± 1.4 mb

(5.1%)

σinel(8 TeV) = 74.7 ± 1.7 mb

(2.3%)

Pileup rate ∝ σtot(s) = σel(s) + σinel(s) ∝ s0.08 or ln2(s) ?

Donnachie-Landshoff Froissart-Martin Bound

total inelastic elastic

PYTHIA: 100 mb PYTHIA: 78 mb

(PYTHIA versions: 6.4.28 & 8.1.80)

PYTHIA: 73 mb PYTHIA: 20 mb PYTHIA: 93 mb

PYTHIA elastic is too low

PYTHIA PYTHIA

PHOJET elastic is too large

slide-32
SLIDE 32
  • P. S k a n d s

Scaling of Multiplicities

32 (GeV) s 10

2

10

3

10

4

10

=0 η

| η /d

ch

dN

1 2 3 4 5 6 7 8

SIBYLL 2.1 QGSJET 01 QGSJET II EPOS 1.99

CMS (p-p NSD) ALICE (p-p NSD) MB) p CDF (p- NSD) p UA1 (p- NSD) p UA5 (p-

dNch(s, η) dη

  • η=0

∝ Imf P(s, 0) s σinel

pp (s)

∼ s∆P log2 s ,

  • D. d’Enterria et al. [arXiv:1101.5596],

From soft models based on Regge Theory, expect:

NSD

A

EPOS too low (but there is coming a new version which fits LHC better, worth trying out) QGSJET too agressive? Would predict very high densities Will keep these models in mind but will base main extrapolations

  • n PYTHIA Perugia tunes
slide-33
SLIDE 33
  • P. S k a n d s

Strangeness: Kaons

33

/dy>

K

<dn

NSD

1/n

0.2 0.4 0.6 0.8 )/d|y|> Rapidity (NSD)

S

<dn(K

Pythia 8.181 Data from JHEP 1105 (2011) 064

CMS PY8 (Monash 13) PY8 (4C) PY8 (2C)

bins

/N

2 5%

χ 0.0 ± 0.0 0.0 ± 0.8 0.0 ± 9.4

V I N C I A R O O T

7000 GeV

pp

y

0.5 1 1.5 2

Theory/Data 0.6 0.8 1 1.2 1.4

T

/dp

K

dn

K

1/n

  • 5

10

  • 4

10

  • 3

10

  • 2

10

  • 1

10 1 10 (|y|<2.0, NSD)

T

p

S

K

Pythia 8.181 Data from JHEP 1105 (2011) 064

CMS PY8 (Monash 13) PY8 (4C) PY8 (2C)

bins

/N

2 5%

χ 0.1 ± 7.1 0.0 ± 3.3 0.1 ± 2.2

V I N C I A R O O T

7000 GeV

pp

[GeV]

T

p

2 4 6 8 10

Theory/Data 0.6 0.8 1 1.2 1.4

slide-34
SLIDE 34
  • P. S k a n d s

Strangeness: Λ hyperons

34

/dy>

Λ

<dn

NSD

1/n

0.1 0.2 0.3 0.4 )/d|y|> (NSD) Λ <dn(

Pythia 8.181 Data from JHEP 1105 (2011) 064

CMS PY8 (Monash 13) PY8 (4C) PY8 (2C)

bins

/N

2 5%

χ 0.0 ± 6.9 0.0 ± 7.6 0.0 ± 14.7

V I N C I A R O O T

7000 GeV

pp

y

0.5 1 1.5 2

Theory/Data 0.6 0.8 1 1.2 1.4

T

/dp

Λ

dn

Λ

1/n

  • 5

10

  • 4

10

  • 3

10

  • 2

10

  • 1

10 1 10 (|y|<2.0, NSD)

T

p Λ

Pythia 8.181 Data from JHEP 1105 (2011) 064

CMS PY8 (Monash 13) PY8 (4C) PY8 (2C)

bins

/N

2 5%

χ 0.1 ± 5.8 0.3 ± 6.7 0.5 ± 10.3

V I N C I A R O O T

7000 GeV

pp

[GeV]

T

p

2 4 6 8 10

Theory/Data 0.6 0.8 1 1.2 1.4

slide-35
SLIDE 35

P . Skands + NEW! full MPI + showers for system (→ UE in Diffraction) + NEW! Central Diffraction (→ fully contained gap-X-gap events) + NEW! Alternative Min-Bias Rockefeller (MBR) Model

Diffraction (in PYTHIA 8)

35 0.0001 0.001 0.01 0.1 1 10 100 2 4 6 8 10 pT (GeV) Pythia 8.130 Pythia 6.414 Phojet 1.12

SD

dσsd(AX)(s) dt dM 2 = g3I

P

16π β2

AI P βBI P

1 M 2 exp(Bsd(AX)t) Fsd , dσdd(s) dt dM 2

1 dM 2 2

= g2

3I P

16π βAI

P βBI P

1 M 2

1

1 M 2

2

exp(Bddt) Fdd .

Diffractive Cross Section Formulæ:

4) Choice between 5 Pomeron PDFs. Free parameter needed to fix 4) Choice between 5 Pomeron PDFs. Free parameter σI

Pp needed to fix ninteractions = σjet/σI Pp.

5) Framework needs testing and tuning, e.g. of . 5) Framework needs testing and tuning, e.g. of σI

Pp.

to I Pp ha n showers

Navin, arXiv:1005.3894

PY6 No diffr jets PYTHIA8 & PHOJET include diffr jets

+ Recently Central Diffraction!

pi pj p

  • i

xg x LRG X

Partonic Substructure in Pomeron:

Follows the Ingelman- Schlein approach of Pompyt PYTHIA 8 MX > 10 GeV MX ≤ 10 GeV

Represent MX as longitudinal string → Fragment → Typical string-fragmentation spectrum

(and for all masses in PYTHIA 6)

slide-36
SLIDE 36
  • P. S k a n d s

(Some) Opportunities with ALFA + ATLAS

36

V E T O

Single Diffraction

H I T

ALFA MBTS CALO TRACKING CALO

H I T

MBTS

?

ALFA

Gap

p p pPom = xPom Pp p’

SD DIJETS * Mass Spectrum (how high can you go?) * Underlying Event in SD DIJET events * Dijet Decorrelation ∆φjj * SD FOUR JETS (MPI in diffraction!) SD: Identified Particles * Λ and KS * Other identified particles? * Compare to minimum bias

V

ZDC? n0,γ, …

?

ZDC? n0,γ, … Measure p’

Glueball-Proton Collider with variable ECM

slide-37
SLIDE 37
  • P. S k a n d s

(Some) Opportunities with ALFA + ATLAS

37

V E T O V E T O

Central Diffraction

H I T

ALFA MBTS CALO TRACKING CALO MBTS

H I T

ALFA

Gap Gap CD

CD * Mass Spectrum (how high can you go?) * Mass2 = xPom1 xPom2 s * Rapidity of system → xPom1 / xPom2 CD JETS * Underlying Event * Dijet Decorrelation, ∆φjj

V

ZDC? n0,γ, …

V

ZDC? n0,γ, … Measure p’ Measure p’

Glueball-Glueball Collider with variable ECM

slide-38
SLIDE 38
  • P. S k a n d s

(Some) Opportunities with ALFA + ATLAS

38

V E T O

Multi-Gap Diffraction (= Subset of Single-Gap)

H I T

ALFA MBTS CALO TRACKING CALO

H I T

MBTS

?

ALFA

Gap

p p p’

Gap A B

p p p’

+

Sometimes called “Triple-Pomeron Vertex”

A B A B V

ZDC? n0,γ, …

?

ZDC? n0,γ, … Measure p’

slide-39
SLIDE 39
  • P. S k a n d s

Wait … is this Crazy?

Best tuning result (and default in PYTHIA)

Obtained with αs(MZ) ≈ 0.14 ≠ World Average = 0.1176 ± 0.0020

Value of αs depends on the order and scheme

MC ≈ Leading Order + LL resummation Other LO extractions of αs ≈ 0.13 - 0.14 Effective scheme interpreted as “CMW” → 0.13; 2-loop running → 0.127; NLO → 0.12 ?

Not so crazy

Tune/measure even pQCD parameters with the actual generator. Sanity check = consistency with other determinations at a similar formal order, within the uncertainty at that order

(including a CMW-like scheme redefinition to go to ‘MC scheme’)

39

Improve → Matching at LO and NLO