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Activities of the Monte Carlo Working Group (II). Convenors: P. Bartalini, S.Chekanov, S. Gieseke, F. Krauss. Multiple Parton Interactions, Underlying Events, etc. - Joint Sessions with Multi-jet final states and Energy flows MC Tuning & Validation MC Steering, Comparison & Fitting Tools.

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slide1

Activities of the Monte Carlo Working Group

(II)

Convenors: P. Bartalini, S.Chekanov, S. Gieseke, F. Krauss

  • Multiple Parton Interactions, Underlying Events, etc.

- Joint Sessions with Multi-jet final states and Energy flows

  • MC Tuning & Validation
  • MC Steering, Comparison & Fitting Tools

Paolo Bartalini (NTU)

slide3

UE: measurement plan at the LHC

Jet #1

Direction

Δφ

“Toward”

“Transverse”

“Transverse”

“Away”

“Away”

Region

From charged jet (using MB and jet triggers)

2

“Transverse”

Region

Topological structure of p-p collision

from charged tracks

Charged jet definition:

ICA with mass-less charged tracks as inputThe leading

The Charged jet defines a direction in the f plane

The transverse region is particularly sensitive to the UE

“Toward”

Region

jet1

“Transverse”

Region

“Away”

Region

Main observables:

+ dN/dhdf, charged density

+ d(PTsum)/dhdf, energy density

0

-2 2

From D-Y muon pair production

(using muon triggers)

observables are the same but

defined in all the f plane

(after removing the m pairs everything else is UE)

The PT of the boson may be used to define a direction

Paolo Bartalini (NTU)

slide4

+ Pythia Tune DW (=.125)

OLD MPI, IP CORRELATIONS, ~ TUNE A

+ Pythia Tune DWT (=0.08)

DW with default PT-cut-off evolution

+ Pythia Tune S0 (=0.08)

P.Skands, New MPI, colour-flow

All these Pythia tunes describe

MB & UE at Tevatron.

->

Paolo Bartalini (NTU)

ue in jets ratios in the transverse region

CMS Preliminary

CMS Preliminary

∫ L dt = 100 pb-1

∫ L dt = 100 pb-1

(input to RECO is DWT)

UE in jets: Ratios in the transverse region
  • Ratios between uncorrected UE-observables:
  • UE-density(pT(track) > 0.9 GeV/c) / UE-density(pT(track) > 1.5 GeV/c)
  • No additional track reconstruction corrections needed!
  • track reconstruction performance uniform in pT for pT > 0.9 GeV/c

CMS Physics Analysis Summary QCD-07-003

→ discriminate DW/DWT against S0

Paolo Bartalini (NTU)

slide6

[Z.Rurikova]

Paolo Bartalini (NTU)

slide7

Jimmy Tune:

Charged Multiplicity OK, Softer PT spectrum

Paolo Bartalini (NTU)

slide8

New UE Model in Herwig++ [M.Bähr]

Description of Tevatron UE phenomenology

Similar predictions with respect to the Pythia tunes at the LHC energy

(Energy dependency of the cut-offs)

Paolo Bartalini (NTU)

slide9

The goal is to produce data (corrected to the particle level) that can be used by the theorists to tune and improve the QCD Monte-Carlo models that are used to simulate hadron-hadron collisions.

Paolo Bartalini (NTU)

slide10

Now it would be interesting to compare with reference tunes adopting the new Pythia MPIs.

See [P.Skands, D.Wielke, hep/ph 0703081]

Paolo Bartalini (NTU)

slide11

Observable: track multiplicity as a function of

 and Pt Jet in bins of Xγ.

Paolo Bartalini (NTU)

slide12
“MI long CC”: Default but PARP (85) = 0.33

“MI short CC2NN”: Default but PARP (85) & PARP (86) “changed” (preferred ?)

Paolo Bartalini (NTU)

slide13

Study of hard Multiple Parton Interactions

Cross section:

Preliminary

additional jets

from PS

LHC

Same sign W. Single int.

additional jets

from MI

Same sign W. Double int.

[D.Treleani]

[F.Bechtel]

Where sinel = ssoft + sH

“S” = Single Interactions, “D” = Double Interactions, “H” = Hard

seff(PT) contains the information on the spatial distribution of partons

Count the interactions (e.g. mini-jets), quote the momenta of Nint

Paolo Bartalini (NTU)

slide14

Pythia 8.1

- physics ~ Pythia 6.4 Tune S0

Herwig++ 2.2

- MPI along the lines of Jimmy

Need double-parton

component to

describe the data

Paolo Bartalini (NTU)

bottom line on mpi
Bottom Line on MPI
  • Huge progress seen in the last two years
    • Refinement of the existing models
    • Implementation in most of the new reference MCs: Pythia 8, Herwig++, Sherpa,…
    • New ideas for the future: dynamical structure of the hadrons, connection to diffraction
  • Much More data avaliable to constraint the models
    • CDF UE in Jets, Drell-Yan, MB <PT> vs Nch etc.
    • Converging on HERA results
  • New Tunes
  • Wide spectrum of LHC feasibility studies in both the soft and hard regimes
    • Didn’t mention Today: eff measurement with mini-jets
  • This section of the proceedings looks promising!

Paolo Bartalini (NTU)

slide18

[A. Buckley]

Paolo Bartalini (NTU)

slide19

[A. Buckley]

Paolo Bartalini (NTU)

slide20

Professor: the tuning tool

[A. Buckley]

Paolo Bartalini (NTU)

slide21

PDF4MC [H.Jung]

Paolo Bartalini (NTU)

slide22

PDF4MC [H.Jung]

Paolo Bartalini (NTU)

slide23

PDF4MC [H.Jung]

Paolo Bartalini (NTU)

slide25

Thanks to all the contributorsof WG5Most of you will be approached in the next weeks in order to contribute to the proceedings

Paolo Bartalini (NTU)

backup
Backup

Paolo Bartalini (NTU)

slide27

pQCD Models

The Pythia solution:

[T. Sjöstrand et al. PRD 36 (1987) 2019]

Multiple Parton Interactions (MPI)

(now available in other general purpose MCs: Herwig/Jimmy, Sherpa, etc.)

ISR, FSR, SPECTATORS…

Not enough to account for

the observed multiplicities

& PT spectra

Inspired by observations of

double high PT scatterings

Main Parameter: PT cut-off PT0

(dampening)

  • Cross Section Regularization for PT 0
  • PT0 can be interpreted as inverse of effective colour screening length
  • Controls the number of interactions hence the Multiplicity:

< Nint > = sparton-parton /sproton-proton

Tuning for the LHC:

Emphasis on the Energy-dependence of the parameters.

Paolo Bartalini (NTU)

mb average charged multiplicity central region

Extrapolation to the LHC Energy

2e

æ

ö

s

ç

÷

=

LHC

P

P

ç

÷

0

0

T

T

14

TeV

è

ø

MB: Average Charged Multiplicity (Central Region)
  • UA5 at s = 53, 200, 546, 900 GeV

[Z. Phys. C 33 (1986) 1]

  • CDF at s = 630, 1800 GeV

[PRD 41 (1989) 2330]

  • “post Hera” PDFs have increased color screening at low x ?

x g(x,Q2)  x- for x  0

  • PT cut-off adjusted to reproduce the measured multiplicity for each PDF
  • PT cut-off fitted with exponential function

NSD

CTEQ4L

Paolo Bartalini (NTU)

side note on the energy dependency of the p t cut off
Side Note on the energy dependency of the PT cut-off

G.Gustafson & G.Miu

rather suggest energy independency of the PT cut-off.

Minijets and transverse energy flow in high-energy collisions. [Phys.Rev.D63:034004,2001]

Hadronic collisions in the linked dipole chain model. [Phys.Rev.D67:034020,2003]

Paolo Bartalini (NTU)

quarkonia also prefers dampening

Total

Color octet

Color-singlet

CTEQ6L|y|<0.6

pT0=2.85 GeV nice agreement

Quarkonia also prefers dampening...

Phys. Rev. D71: 032001, 2005

NRQCD

PYTHIA

Total

Color octet

Color-singlet

NRQCD

PYTHIA

CTEQ6L|y|<0.6

CDF data

  • disagreement

at low PT

[M.Bargiotti]

[M.Bargiotti]

Regularization natural: gluon exchange in the t channel d/dPT2 ~ 1/ dPT4

Let’s assume universality: same PT0 of MPI, same energy dependency!

Paolo Bartalini (NTU)

pythia tunes
Pythia Tunes

PT0= PT0(Ecm/E0)PARP(90)

Paolo Bartalini (NTU)