Summary of experimental contributions to SMH working group

Craig Buttar

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SMH Topics

• SM benchmarks for LHC startup• PDF uncertainties• MC• Multi-parton and NNLO• Precision Higgs cross-sections• Electroweak corrections for LHC and LC

A brief summary of many topics!!

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SM Benchmarks

• W/Z– W/Z as luminosity monitors– Effect of PDFs on W/Z xsects– W-production impact on PDFs (Cooper-

Sarkar/Tricoli)– Effect of low-x corrections (Ball, Del Duca)– Uncertainties on DY with MC@NLO (Ferrag)– W-mass

The W mass

The W mass measurement is systematically limited,and theoretical errors play an important role:• Pt distribution of W and Z. Difference between W and Z important. Many calculations exist at NLO, but not all public. Uncertainties discussed → scaling variation not enough. Experimenters wish list: Several public calculations!• Influence of PDF uncertainties. Difference between ubar(x) and dbar(x) at x ≈ 10-3 influence W and Z mass – correlation? Method of reweighting to be checked – other methods? Otherwise, impact on W mass: 17 MeV!!!• Effect of ISR and FSR. FSR dominant effect – correlation between W and Z. Photos good for evaluating photons within EM-cluster.

Experimental comment: Energy scale may dominate error!

T. Petersen, Les Houches, 10th May 2005

- and its theoretical uncertainties.

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W+ rapidity

б.B=12.27 ± 0.40 nb

W- rapidity

б.B=9.08 ± 0.30 nb

Uncertainty in total xsect from PDFs

NLO predictions for dб/dy. B(leptonic) for single W production at the LHC

from ZEUS-S 2002 PDFs with uncertainties-( conventional evolution)

PDF uncertainties of ~ ±3% in б.B, but ~±5% at central rapidity

Z rapidity

б.B=2.025 ± 0.062 nb

Tricoli/Cooper-Sarkar

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Study the effect of including the W Rapidity distributions in global PDF Fits by how much can we reduce the PDF errors?

Generate data with CTEQ6.1 PDF, pass through ATLFAST detector simulation and then include this pseudo-data in the global ZEUS PDF fit.Central value of prediction shifts and uncertainty is reduced

W+ to lepton rapidity spectrum data generated with CTEQ6.1 PDF compared to predictions from ZEUS PDF

BEFORE including W data AFTER including W data

W+ to lepton rapidity spectrum data generated with CTEQ6.1 PDF compared to predictions from ZEUS PDF AFTER these data are included in the fit

Specifically the low-x gluon shape parameter λ, xg(x) = x –λ , wasλ = -.187 ± .046 for the ZEUS PDF before including this pseudo-dataIt becomes λ = -.155 ± .03 after including the pseudodata

Tricoli/Cooper-Sarkar

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Reconstructed e-Reconstructed e+

MRST02

MRST03

MRST02

MRST03

Tricoli/Cooper-Sarkar

generated with HERWIG 6.505 + NLO K factors, ATLFAST (200k events->6hrs at low lumi LHC

MRST02 MRST03

Reconstructed e+- e- Asymmetry Reconstructed e- / e+ Ratio

MRST02

MRST03

Y=0 x=5.10-3

Y=2.5 x=5.10-4

Sensitive to low-x effectsR.Ball

Contrast the prediction of MRST2002 PDFs conventional QCD evolution with those of MRST03 which distrusts the conventional secenario for x< 5 10-3

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Benchmark: Drell-Yan (Ferrag)

• Goal: Limits on the SM predictions • Observables: Mll, Pt, boost,

• MC@NLO: computed by 100 GeV bin 200 GeV < invMass< 2500 GeV • Sources of uncertainties: -Factorisation and Renormalisation scales 1/ * m t < < m t -PDFs CTEQ6 40+1 pdf1

Invariant mass(GeV)

40 CTEQ6pdfs

Energy scalevariation

Define threoretical uncertaintiesStudy experimental uncertainies

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MC• MC@NLO

– ggH (Davatz, Drozdetski)– qqWW spin correlations (Drollinger)– ggWW (Duhrssen)

• Underlying event – Energy extrapolation (Godbole)– Effect of UE in CJV and lepton isolation

(Buttar,Clements, Drozdetski)– Tuning PYTHIA 6.2 and 6.3

(Buttar,Moraes,Skands,Sjostrand)

• Tuning – Hbb,tbb fragmentation functions (Drollinger,

Corcella)

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MC@NLO vs LO (Herwig) for MC@NLO vs LO (Herwig) for gg->H->ZZ->4gg->H->ZZ->4 m mHH = 250 GeV: = 250 GeV:

effect of kinematic selections on K factoreffect of kinematic selections on K factor • Normalized to the number of events for 30 fb-1

• NLO: Nevent(selection)=58.7;

• LO: Nevent(selection)=25.7

• KNLO/LO = 2.22 (before selection)

• KNLO/LO = 2.28 (after selection)

• Conclusion: no Conclusion: no

significant differencesignificant difference

Blue: NLO

Red: K*LO

Analysis cuts: 243 < Minv(H) < 257

GeV

A. Drozdetski

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Differences vary over the pT spectrum:

Integrated efficiency over whole pT spectrum and up to a pT Higgs of 80 GeV:

Jet veto in gg-h with MC@NLO, PYTHIA6.3, HERWIG and Jet veto in gg-h with MC@NLO, PYTHIA6.3, HERWIG and

CASCADE. CASCADE. G. DavatzG. Davatz

total up to 80 GeV

PYTHIA 0.61 0.72

HERWIG 0.54 0.68

MCatNLO 0.59 0.69

CASCADE 0.56 0.65

Within MC@NLO uncertainty will be estimated changing the scale

Cut ~30GeV in gg->H->WW

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Lepton correlations in WW Drollinger

Pythia reweighted to NLO according to Pt-distribution of WW-system -- describes all distributions except lepton correlations MC@NLO

qq->WW

See also qq->WWBy Duehrssen,Binoth

Spin correlation Recently added To MC@NLO

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effect of UE on isolation in H->ZZ->4A. Drozdetski

PARP(82) = 2.9 PTcut_off = 2.9 GeV – default scenario PARP(82) = 2.4 PTcut_off = 2.4 GeV – pessimistic scenarioPARP(82) = 3.4 PTcut_off = 3.4 GeV – optimistic scenario

10-15%

Effect on lepton isolation

PYTHIA 6.2

Ptch>0.5

Ptch>2.0

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Dan Clements – Feb 2005 ATLAS Physics week

Effect of multiple interaction models on CJV efficiency (MH 160GeV/c2)

Model Parameter

Simple MSTP(82)=1

PARP(81)=1.9

Complex MSTP(82)=4

PARP(82)=1.9

Tuned MSTP(82)=4

PARP(82)=1.8

PARP(84)=0.5

The Tuned Model is a fit to experimental data, using a double gaussian matter distribution with a large core radius.

Clements,Buttar,Moraes

6% effect PYTHIA6.2

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PYTHIA 6.3

•Pt-ordering of ISRand FSR•New MI modelCorrelated PDFsColour correlationsInterleaved ISR+MI

Sjostrand, Skands

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PYTHIA 6.3 Tuning Moraes/Buttar

PreliminarySmooth ISR cut-offExponential matter density

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Underlying event and minimum bias: extrapolation to LHC

Godbole, Pancheri,Grou and Srivastava

New calculation of total xsectusing mini-jet modelParameterisation of inelasticfor PYTHIA (with error band)Preliminary inel(LHC)=60mb

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Hbb fragmentationCorcella/Drollinger

Fragmentation functiontuned to e+e- data

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Agenda of Top Quark related sessions during the Workshop (first session)(contact/organiser : Jorgen D’Hondt)

General Top Quark session (2):ttbar Frixione/Maltoni (theory), Huston (Tevatron), D’Hondt (LHC)Single-top Dudko (theory), Dudko (Tevatron), Giammanco (LHC)Jets EllisPolarization Tsuno

Specific single-top quark session :Get the optimal ‘Feynman’ observables from D0 and implement them at the LHC, try the Q-distribution to estimate the W+njet background.

Top Quark mass session :Discussion of mass reconstructions.

Jet definition session (2):Definition of variables which can quantify a jet definition to reconstruct the kinematics of the complete final state.

Top quark systematic session :Try to define a procedure to estimate systematic uncertainties due to ISR/FSR radiation and b-quark fragmentation.

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Jet definition sessions (1&2) :Aim to define some variables which can identify the quality of jet definitionsTo reconstruct the kinematics of the full event (several jet densities)

Angles (in space!) : = Σ i(jet-parton)Energy : E = Σ |(Ejet/Eparton)i – 1|Mass : m = Σ |mi(jet-parton)|Selection efficiency : s (having 4-jets in the final state passing some

basic criterion on Et and )Resolution on energy : A B/sqrt(E) C/E

(radian) E (GeV)

First preliminary results (CMS) : Iterative cone R=0.5, Et,minseed=2GeV

A B

= A/(A+B) E = A/(A+B)

A B

Heyninck Heyninck

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First preliminary results (CMS) : comparison jet definitions• IC : R=0.5, Et,min

seed=2GeV (no merging or splitting)• MC : R=0.5, Et,min

seed=2GeV, overlap thres = 50%, only pairs• kT : D=1 (is basically a cone larger than R=0.5)

General : Calorimeter Towers E-threshold of 1 GeV, ET-scheme

Jet definition E m (GeV) s

IC 0.41 0.31 0.45 0.26

MC 0.40 0.30 0.34 0.35

kT 0.30 0.24 1 (no mass) 0.26

ETraw>10GeV, ||<2.5

→ Clearly some differencences between cone-like and kT-like definitions

Aim : compare these variables for several jet definitions (including : input definition, clustering algorithm, recombination, ...)For several jet densities: single-top (2jets), tt (4jets), ttH (6jets), ttH (8jets) → Giammanco, Heyninck, Schmidt

Heyninck

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Skands

pt of ISR jet

factor ~3-4 increase

PY 6.2

PY 6.3

Top quark systematics session :Aim is to define a procedure to estimate the uncertainties at the LHC (from MC!)

1. Radiation uncertainties (ISR/FSR) ISR : tt+1jet is ~40% of inclusive set (best would be MC@NLO PY6.3 and CKKW matching) syst = change PARP(67) ~ pT

max

between 1 and 4 (or higher for LHC) LHC → reweight PY6.2 to CompHEP/MadGraph → check other distributions !! Problem : large weights, ttH still visible ?? Solution : select on pt of tt system

FSR : change LQCD in Parton Shower

2. Colour reconnection Conservative model to be implemented Estimate effect on mt Skands, D’Hondt

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The End or is it the start?

• Topics will continue after the workshop• Many topics collected on SM benchmark

website:http://www.pa.msu.edu/~huston/Les_Houches_2005/Les_Houches_SM.html

Final thoughts

• Experiments moving to ‘next’ level of study using full simulations and reconstruction

• Theory also moving by providing more precise predictions

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More on• A.N. “Zeppenfeld plot” : effect of ETj3 cut ?

(will bring Tuersday evening)

• Grazzini-effect of W-polarisation in WW

• Low-x: Richard Ball

• Single-top

• Top—Jorgen

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Luminosity with W/Z

W-statistical errorPYTHIA

Z-statistical errorPYTHIA

P. Giraud, S.Hassani

this simulation JHEP 0405:056pp -> W+ -> mu nu 11,902+-0,036pp -> W- ->mu nu 8,778+-0,027Total 20,780+-0,045 20,900+-0,013

sigma (nb)

Now working withMC@NLO

Analysis with PYTHIA and ATLFAST

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For acceptance PYTHIA or MC@NLO will work but for absolute xsect must use MC@NLO

Luminosity with W/Z P. Giraud, S.Hassani

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Quayle