activities of the monte carlo working group (ii)

Paolo Bartalini (NTU)CERN, May 30 2008

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


A lot of emphasis on the reconstruction of soft tracks!


UE: measurement plan at the LHC

Topological structure of p-p collisionfrom charged tracks

Charged jet definition:ICA with mass-less charged tracks as inputThe leading

The Charged jet defines a direction in the planeThe transverse region is particularly sensitive to the UE

From charged jet (using MB and jet triggers)

From D-Y muon pair production(using muon triggers)

observables are the same but defined in all the plane(after removing the pairs everything else is UE)The PT of the boson may be used to define a direction

Main observables:+ dN/dd, charged density+ d(PTsum)/dd, energy density

“Toward”

“Away”

“Transverse”“Transverse”

Jet #1Direction Δφ

“Transverse”

Region

“Toward”

Region

“Transverse”

Region

“Away”Region

“Away”Region

jet1

-2 2

0

2


+ Pythia Tune DW (+ Pythia Tune DW (=.125)=.125)OLD MPI, IP CORRELATIONS, ~ TUNE AOLD MPI, IP CORRELATIONS, ~ TUNE A+ Pythia Tune DWT (+ Pythia Tune DWT (=0.08)=0.08)DW with default PT-cut-off evolution DW with default PT-cut-off evolution + Pythia Tune S0 (+ Pythia Tune S0 (=0.08)=0.08)P.Skands, New MPI, P.Skands, New MPI, colour-flow

All these Pythia tunes describe All these Pythia tunes describe MB & UE at Tevatron.MB & UE at Tevatron.

->


(input to RECO is DWT)

CMS Preliminary CMS Preliminary

∫ L dt = 100 pb-1 ∫ L dt = 100 pb-1

‣ 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

→ discriminate DW/DWT against S0

CMS Physics Analysis Summary

QCD-07-003

UE in jets: Ratios in the transverse region


[Z.Rurikova]


Jimmy Tune: Charged Multiplicity OK, Softer PT spectrum


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)


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.


Now it would be interesting to compare with reference tunes adopting the new Pythia MPIs.See [P.Skands, D.Wielke, hep/ph 0703081]


Observable: track multiplicity as a function of Δφ and Pt Jet in bins of Xγ.


“MI long CC”: Default but PARP (85) = 0.33“MI short CC2NN”: Default but PARP (85) & PARP (86)

“changed” (preferred ?)


Study of hard Multiple Parton Interactions

additional jets

from PS

Cross section:

additional jetsfrom MI

LHC

[F.Bechtel]

QuickTime™ e undecompressore TIFF (LZW)

sono necessari per visualizzare quest'immagine.

[D.Treleani]

Same sign W. Single int.

Same sign W. Double int.

Preliminary

Where inel = soft + H “S” = Single Interactions, “D” = Double Interactions, “H” = Hard

eff

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

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


Need double-parton component to describe the data

Pythia 8.1- physics ~ Pythia 6.4 Tune S0Herwig++ 2.2- MPI along the lines of Jimmy


Bottom Line on MPIBottom Line on MPI Huge progress seen in the last two yearsHuge progress seen in the last two years

Refinement of the existing modelsRefinement of the existing models Implementation in most of the new reference MCs: Implementation in most of the new reference MCs: Pythia 8, Herwig++, Sherpa,…Pythia 8, Herwig++, Sherpa,…

New ideas for the future: dynamical structure of New ideas for the future: dynamical structure of the hadrons, connection to diffractionthe hadrons, connection to diffraction

Much More data avaliable to constraint the modelsMuch More data avaliable to constraint the models CDF UE in Jets, Drell-Yan, MB <PCDF UE in Jets, Drell-Yan, MB <PTT> vs N> vs Nch ch etc.etc. Converging on HERA resultsConverging on HERA results

New TunesNew Tunes Wide spectrum of LHC feasibility studies in both the Wide spectrum of LHC feasibility studies in both the soft and hard regimessoft and hard regimes Didn’t mention Today: Didn’t mention Today: effeff measurement with mini- measurement with mini-jetsjets

This section of the proceedings looks promising!This section of the proceedings looks promising!


MC Steering, Comparison & Fitting Tools


[A. Buckley]


Professor: the tuning tool

[A. Buckley]


PDF4MC [H.Jung]


An approach to fast fits of the uPDF [A.Knutsson]


Thanks to all the Thanks to all the contributorscontributors

of WG5of WG5

Most of you will be Most of you will be approached in the next approached in the next

weeks in order to weeks in order to contribute to the contribute to the

proceedingsproceedings


BackupBackup


ISR, FSR, SPECTATORS…Not enough to account forthe observed multiplicities& PT spectra

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.)

Inspired by observations ofdouble high PT scatterings

pQCD Models

< N< Nintint > = > = parton-partonparton-parton / /proton-protonproton-proton

Main Parameter: PT cut-off PT0

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:

Tuning for the LHC:Emphasis on the Energy-dependence of the parameters.

(dampening)


“post Hera” PDFs have increased color screening at low x ? x g(x,Q2) x- for x 0

PPTT cut-off adjusted to cut-off adjusted to reproduce the measured reproduce the measured multiplicity for each PDFmultiplicity for each PDF

PPTT cut-off fitted with cut-off fitted with exponential functionexponential function

2

TeVs

PP LHCTT 1400

CTEQ4L

Extrapolation to the LHC Energy

UA5 at s = 53, 200, 546, 900 GeV [Z. Phys. C 33 (1986) 1]

CDF at s = 630, 1800 GeV [PRD 41 (1989) 2330]

MB: Average Charged Multiplicity (Central Region)

NSD


Side Note on the energy Side Note on the energy dependency of the 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]


Quarkonia also prefers Quarkonia also prefers dampening...dampening...

Total Color octet Color-singlet

ppT0T0=2.85 GeV=2.85 GeV nice agreement nice agreement

CTEQ6L|y|<0.6

(/

)/

(/

)T

Br

Jd

dpnb

GeV

ψ

→

g[M.Bargiotti]

(/

)/

(/

)T

Br

Jd

dpnb

GeV

ψ

→

g

Phys. Rev. D71: 032001, 2005

CDF data

CTEQ6L|y|<0.6

Total Color octet Color-singlet

disagreementdisagreementat low Pat low PTT

NRQCDPYTHIA

NRQCDPYTHIA

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

4

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

[M.Bargiotti]


Pythia Tunes Pythia Tunes

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

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