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HERA and the LHCReport on the workshop on HERALHC

A. De Roeck/CERN HEP-MAD07 Madagascar September 2007

Overview & Highlights of the Workshop The continuation of the Workshop…

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Next Meetings: 29 Oct- 2 Nov @DESY: working groups May 2008 @CERN : plenary meetings

History of the Workshop

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The LHC Machine and ExperimentsThe LHC Machine and Experiments

pp collisions at 14 TeV

LHCf

totem

(moedal)

LuminosityFirst phase 21033 cm-2s-1

High lumi phase 1034 cm-2s-1

First data expected in summer 2008

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Workshop Goals

~60 from Hera~50 from LHC~50 theory

(>160March 2007 DESY

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Proceedings of the first Workshop

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QCD at the LHC

CMS experimentAt the LHC

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Jets!

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Systematics on Jet Measurements

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Jet Measurements

Contactinteractions

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Prompt Photon Production

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Shape Variables

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The Underlying Event

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Study of the Underlying Event at the LHC

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MC - ToolsS. Gieseke, F. Krauss,T. Kluge, P. Bartalini,P. Robbe, S. Chekanov

Multijets & final statesUnderlying events,un-integrated pdfsL. Lonnblad, G. Zanderighi, C. Gwenlan, N. Tuning, S. Banerjee, Ch. Risler, D. Traynor

Structure functions and parton distributionsS. Forte, S. Moch,M. Dittmar, A. Glazov M. Botje

DiffractionM. Diehl, V. Khoze M. Arneodo, P. Newman,A. Bruni, B. Cox, R. Orava

Heavy quarks: B quark pdfs of the proton, fragmentation fct, u-pdfs M. Cacciari,H. Spiesberger, A. Dainese, A. Geiser, K. Lipka,U. Uwer

Working Groups of the workshop

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Parton Density functions

• Collinear PDFs

Simple spread of existing PDFs givesup to 10% uncertainty on Higgs cross section

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Parton Density functions

• Collinear PDFs

• Unintegrated PDFs

Large kT effects may affect Higgs searches/measurements

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Parton Density functions

• Collinear PDFs

• Unintegrated PDFs

• Diffractive and Generalized PDFs

All these PDFs can be addressed at HERA via inclusive, semi-inclusive, diffractive, vector meson DVCS …measurements

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PDFs & ADD extra dimensions: di-jet final state

Reduction of the sensitivity due toPDF uncertainty (CTEQ6)

Graviton exchange contributions reduce the cross section (interference)

S. Ferrag

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PDFs are important!!

Tevatron: mid 90’s

?

New Physics? …or PDFs?

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LHC Kinematics/QCD evolution

Evolution of PDFs to high Q2 & low x important at the LHCPrecision? Level of approximation? CCFM/BFKL?, non-linear effects? Test it at HERA

Is this a region of “safe –x”???

?

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Example W, Z production

Theoretical uncertainty small but how well do we know the parton distributions?

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• W prod. at LHC without HERA: • W prod. at LHC including HERA

PDFs including HERA:

PDFs without HERA:

~ 3.5 %~ 16 %

0.0001<x<0.10.0001<x<0.1

HERA Impact on the LHC

PDF uncertainty will be the dominant error!

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Impact of Future HERA Data

Improvement in PDFprecision with projected700 fb-1 of data in HERA-II

Includes jets in DIS and p

Note: only HERA (ZEUS) data are used in the fits

GwenlanCooper-SarkarTargett-Adamshep-ph/0509220

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From M. Cooper-Sakar, C. Gwenlan and S. Glazov

Much reduced uncertainties .... Model independent analysis of data desirable

get THE HERA – PDF !!!!!

● Combined PDF fit to H1& ZEUS ● Average H1&ZEUS data sets

Average HERA data

A request from the 2005 workshop…

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PDFs: E.g. MRST/CTEQ differences

YES: FL can referee the gluon distribution! FL is like F2: little theoretical ambiguity (compared to e.g. F2

C)

H. Stenzel R. Thorne

),()(),(])1(1/[ 222

222 QxFyfQxFFyyF LLr

Need to lower the energy of proton or electron beam for this measurement

Can we know more by the time of the LHC startup?

Strong case madeduring HERA-LHCWorkshops 2004/2005

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Prospects for Measuring FL

Detailed study for H1, with 2 lower proton beam energy settings

FL can refereebetween MRSTand CTEQ gluons

FL is gluon driven

FL measurement at HERA in 2007 !2 lower energy settings

CTEQ

MRST

Feltesse/Klein et al

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CTEQ6.1 CTEQ6.5

Parton Distribution “Evolution”

Heavy flavourstreatementin PDFs!

Any claim that we know the W,Z cross sections with a precision of a few % should be taken with care

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Study of the impact of intrinsic charm

Still an open issue

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PDF determination at LHC

•WG1 convenors: Should form a “group” from ATLAS, CMS, LHCb, •ALICE, H1, ZEUS and theoretical PDF experts

Also jets, photons,…See Eg. M. Cooper-Sarkar et al.

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Finally:

Call for a working group/task force/LHC-study group …

Interest from theorists/fitters/HERA/ LHC/…?

The PDF + uncertainties

…Need to call for a meeting

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Proton AntiProton

Multiple Parton Interactions

PT(hard)

Outgoing Parton

Outgoing Parton

Underlying Event Underlying Event

Outgoing Parton

Outgoing Parton

from R. Field

Underlying event/multiple interactions

Studies and tunes made on Tevatron/lower energy data Do the Tevatron tunes work for HERA? Special program to check… New models on the market that should be tested (new Pythia, Jimmy, Sherpa)

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Pythia 6.214ATLFAST 602

Effect of underlying event on central jet veto in VBF HiggsEffect of underlying event on central jet veto in VBF Higgs

Uncertainty of the central jet vetoefficiency due to UE model; ATLAS.

Rapidity of the central jet in Higgs events; CMS; full simulation, L=2x1033cm-2s-1

“bkg. like” behaviour for soft jets; fake jets: pile up+UE+detector

H->WW*->2lH->WW*->2lin qqH prod.in qqH prod.

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Double Parton interactions

Not well know what to expect…

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HERA II analysis (expect factor 10 more), larger kinematic range➔ Understand b-production mechanism (...remember b-puzzle at the

TeVatron...)➔ NOTE: gluon drives heavy quark PDFs

Current H1 (HERA I) analysis From O.Behnke, A. Geiser, A. Meyer, M. Wing

beautycharm

HERA: Heavy Quark PDFs at large Q2

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estimates for ALICE

×

Nonlinear evolution equation for uPDF: (Balitsky-Kovchegov equation)

A. Dainese et al

Bottom suppression due to non-linear effects in BK

●Significant effects...●up to factor of 2 in hot spot scenario ●factorization still ok ?

Non-Linear QCD effects at the LHC

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Hgap gap

b

b -jet

-jet

Exclusive Higgs ProductionExclusive diffractive Higgs production pp p +H+ p : 2-10 fb SMCross section ‘stabelized’ during the previous workshop 10-100fb MSSM

p p

beam

p’

p’roman pots roman pots

dipole

dipole

22 )''( ppppM H

Advantages Exclusive: Jz=0 suppression of ggbb background Mass measurement via missing mass

E.g. V. Khoze et alM. Boonekamp et al.B. Cox et al. …

M = O(1.0 - 2.0) GeV

P. Landshof: Cross sections can be higher!

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Central Exclusive Production

Kaidalov et al.,hep-ph/0307064

100 fb

1fb

MSSM Higgs/high tan: (30fb-1) 100-200 signal events (after cuts)and O(10) background events

Study correlations between the outgoingprotons to analyse the spin-parity structure ofthe produced boson

120 140A way to get informationon the spin of the HiggsADDED VALUE TO LHC

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MC and other Tools

• Parton distribution library:– LHAPDF now official carrier of the PDFs

• Used by LHC experiments in generators• HERA pdfs have been added• Allows error uncertainty estimates• Pion and photon added, particularly for HERA. F2D next?

• NLOLIB framework for NLO QCD programs– Uniform user interface/interface to HZTOOL– e+e-/ep included, pp can be added

• HZTOOL/JetWeb/RunMC/Cedar(?) for tunning – All HERA results to be included, some e+e-. Include more pp?

• RAPGAP, Cascade Monte Carlos for inclusive and diffractive pp• Plenty of exchange on other MC tools, leading to new MC tools

and comparisons with ep where possible • Continuation of the MC4LHC 2003 (and 2006) workshop ,

concerning MC validation

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Nutshell: Results from HERA/LHC I• Parton Distribution Functions

– Dialogue/discussion between PDF fitters and community that delivers the data.

– Combined data (H1/Zeus Datasets for F2, F2D), measurements of FL at HERA.

– Discrepancies between PDFs will be ironed out, eg via to new measurements. Fits with 1- bands available.

– Quantitative estimates for low-x/large-x resummation available – Timescale for the full program 1-2 years, i.e. just in time for the LHC Will lead to more precise PDFs: maybe factor 2? (personal guess/hope)

• Diffraction– Improved understanding on the DPE/Higgs production and cross section

• Final states– Lots of work/progress on underlying events (tuning), gap survival

• Heavy quarks– Saturation effects measurable at low pt– Heavy quark parton distributions eg. for Higgs cross section calculations.

• Tools– Tool & generator developments, preparing for LHC startup

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• PDF determination:– Best possible PDF. Ultmate expected precision? Impact on LHC

measurements? – Uncertainties on the PDF and QCD evolution– Special PDFs? Diffractive, unintegrated, generalized…

• Event topologies:– Multiple Interact./Underlying Events: understanding the physics/uncertainties– Higher Order Corrections/verified on HERA data/Jet studies (algorithms..)

• Reliable Simulations/ Theory/Models– tuning of free parameters to many different measurements– improved calculations/NLO libraries– test alternative approaches (SCET?)

HERA/LHC II: what does LHC need?

Goals for HERA/LHC II

Next Meeting: 29 Oct-2 Nov @ DESY/Hamburg

Keywords: tools, phenomenological progress, and quantitative estimate for the impact of HERA on LHC measurements

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