Claire Gwenlan PPARC Interview - 07/02/06 1 Claire Gwenlan Why New Physics? Preparation for Measurements at the LHC -> Importance of Proton Structure

PPARC Interview - 07/02/06Claire Gwenlan 1

Claire Gwenlan

Why New Physics? Preparation for Measurements at the LHC

-> Importance of Proton Structure (PDFs) -> Understanding the SM Contribution -> Jet and Missing Energy Resolutions

Beyond the SM – New Physics Models Summary

Preparation for and measurement of new physics with ATLAS at the LHC


Why “New Physics” – and How?

I will focus on signatures of Jets and Jets+Missing-Energy-> powerful signals for very wide variety of new physics models

Why? Introducing “New Physics”, beyond the SM, at the TeV scale, can provide solutions to problems such as … - Hierarchy - Cosmology – what’s the nature of dark matter? (- Where does gravity fit in?)

Fundamental physics is entering a new era…

LHC physics @ TeV scale: - Lots of Standard Model (SM) QCD, electroweak, flavour - Much excitement about what’s beyond!! SUperSYmmetry, Extra Dimensions, …

Key To Success:

PREPARATION !!!

Must understand and control major uncerts.:- Proton structure- SM contribution- Jet resolutionsWill require SM jet measurements with early ATLAS data


A Precise Determination of Proton Structure


Valence quarks

“sea” quarks/ anti-quarks

Gluons

The structure of the Proton

PDFs: fi(x,Q2) - parametrised in x at starting scale - QCD predicts change with Q2

All processes at the LHC depend on proton structure !!! ˆa b sub- process

a,b

ff

Q2

x

Proton structure described by parton density functions (PDFs)

Importance of Proton Structure

-> determined from fits to data

-> Precise knowledge essential for reliable predictions of: - new physics (Higgs, SUSY, …) - SM processes (which are also backgrounds to new physics)

My PDF fit

[C. Gwenlan et al.], ZEUS Coll., Eur. Phys. J., C42 (2005) 1

Need to know the PDFs as well as we can !!!!

fi parameterise proton structure


Tevatron reach

LHC reach in 1st yearHigh-x gluon PDF

uncertainty

EG: Single Inclusive Jets

Impact of PDFs on LHC discovery

PDFs will be dominantuncertainty in high-scale (discovery) physics at the LHC

Scale uncertainty PDF uncertainty

“New Physics”

Sensitive to wide variety of new physics e.g. SUSY, extra spatial dimensions, quark compositeness, …-> look for deviations from SM

Could hide signs of new physics !!!

-> mainly from “high-x” gluon


One of the most important aspects of my recent work is the first rigorous inclusion of jet data in a QCD fit-> significantly improved knowledge of high-x gluon

-> Precisely in region required for new physics discovery at the LHC

[C. Gwenlan et al.], ZEUS Coll., Eur. Phys. J., C42 (2005) 1

Constraining the high-x gluon


A.Tricoli, A.Cooper-Sarkar, C.Gwenlan, hep-ex/0509002

ZEUS PDF before including “data”

ZEUS PDF after including “data”

e+ “data”

e+ “data”

Future Direction: LHC data Include ATLAS data in fits -> important new constraints !!!

Candidate data-sets: Drell-Yan (including W/Z) QCD Jets Others (direct-photon, W/Z+Jet, …)

Work started on W/Z -> 35% reduction in low-x gluon uncertainty

Work initiated on investigating impact of (simulated) LHC jet data -> high-x gluon constraints -> further work: experimental systematics, kinematic cuts, …

Ready to input LHC data (including my own SM jet measurements)

Very Preliminary – First Results Last Week Only Statistical Uncertainties Considered So Far


Understanding the Standard Model Contribution


Recognising deviations from SM expectations requires excellentunderstanding of SM processes that contribute in the new physics region

example: SUSY (jets+missing-ET)

SM Contributions to New Physics

pT of leading jet (GeV)

Need to understand and control this!!!

Dominant SM contributions: “Jets”: - QCD Jets “Jets+Missing-Energy”: - QCD Jets (mismeasured), W/Z+Jets, ttbar+Jets

reducible

irreducible

Need to establish best ways of reducing/modelling SM contribution

Rejection/discrimination of reducible SM contributions (for “Jets+Missing-Energy”): -> studies on simulated data Guidance from TEVATRON -> establish independently for LHC


Reliable description of SM at high scales crucial (both “Jets” and “Jets+Missing-Energy”) -> “Tune” models to data at low scales -> extrapolate to high scales -> many jets problematic !!! (no exact calculations) - Rely on ME+PS models -> Many tuneable parameters

EG.: Four-Jets at HERA

Best tuning to HERA four-jets

Untuned model

Tuning to my four-jet data -> best global descriptions

C. Gwenlan, UCL-THESIS, 2003

Tune/validate available models: Now, using existing data -> HERA, TEVATRON Later, using early ATLAS data, including my own measurements of SM jet processes (especially QCD multi-jets)

SM Contributions to New Physics


Evaluation and Improvement of the Jet and Missing-Energy

Resolutions


Experimental uncertainties must be understood and controlled !!!

For Jets and Missing-Energy, dominant exp. uncertainties: - Hadronic energy scale (PDFs improvements will help this) - Jet and Missing-Energy Resolutions Inner

Detector

Calorimeter

Neutral Deposit

Charged Deposit

Isolated track

Jet/Missing Energy Resolutions

Neutral Deposit

Energy-Flow

CALORIMETER only

Implemented in standard software Tested performance in wide range of jet topologies (dijets, multi-jets)-> improved hadronic reconstruction -> reduced systematics

ZEUS “energy flow” algorithm:

How to improve resolutions … - combine track and calorimeter information in the reconstruction -> “energy flow” technique

Imp

roved

resolu

tion

an

d s

cale

C. Gwenlan, UCL-THESIS, 2003

Reconstruction of four-jet events in data (solid) and Monte Carlo (open) using energy flow

First person to use in measurements of multi-jet production


New energy flow algorithm now being developed for ATLAS

Inner Detector

Calorimeter

Neutral Deposit

Charged Deposit

Isolated track

Energy Flow in ATLAS Jets

-> initial tests on low-energy jets promising

Standard reconstruction

Energy-Flow algorithm

Algorithm needs full validation -> prime candidates are the many jet topologies I will measure test now with simulated data later, with my real measurements (inclusive-jet, two-jet, multi-jets, …)

20% improvement in resolution

So far, only for low-energy jets - To what extent can it be used for high energies of interest to new physics ? - Can its performance be improved ?


Beyond the Standard Model:-New Physics Signatures


Constraining the Models … SUperSYmmetry Postulates symmetry between bosons and fermions -> each SM particle has SUSY (s)partner: spin differs by 1/2 Gluinos/squarks copiously produced - Cascade decays end in quarks and/or gluons (Jets) and (in R-Parity) Missing Energy (LSP escapes undetected)

our world (3+1dimensions)

G Large Extra Dimensions (ADD)(N. Arkani-Hamed, S. Dimopoulos, G. Dvali)

SM particles confined to our universe

Gravity propagates in all dimensions Direct graviton emission into extra dimensions gives Jet+Missing-Energy

brane

extra dimensions

PLUS many other new physics scenarios (e.g. other SUSY/extra dimensions models, leptoquarks, …)

RPC RPV


Summary

Much excitement about “New Physics” beyond the SM

I want to focus on processes with high energy “Jets” and “Jets+Missing-Energy” -> sensitive to wide variety of New Physics models

Discovery and future precision measurement relies on controlling major sources of uncertainty: -> proton structure -> SM contribution -> experimental uncertainties (jet resolution)

Have developed plan to understand/control/reduce limiting sources -> much of this work will be of direct benefit to all of ATLAS

Wealth of prospective publications from this work - early SM jets, PDF fits with ATLAS data, New Physics searches

Looking forward to 2007 !!!


Extras


CDF Run 1Standard Model

An Historical Warning: TEVATRON

Direct high-energy new physics: AN HISTORICAL WARNING: Tevatron jet data originally thought to signal new physics BUT taking proton structure uncertainty into account there is no deviation from SM

PDF uncertainty

-> Similar situations likely at the LHC !!!


C. Gwenlan et al., J. Phys. G., 32 (2006) 221I have shown that by the time of LHC start-up, further improvements can be expected-> requires new jet measurements from HERA [work I am performing with a graduate student at UCL]

Constraining the PDFs at HERA

Work started on quantifying impact on LHC discovery

NEXT STEPS: Ensure useful HERA measurements are made !!! Include in QCD fits for improved PDFs


High-Energy Jet

Lower-Energy Jets

IDEA:

Employ momentum balance of high-energy jets against multiple low-energy jets? -> needs investigation


Discovery reach for squarks/gluinos

Time mass reach

1 month at 1033 ~ 1.3 TeV1 year at 1033 ~ 1.8 TeV1 year at 1034 ~ 2.5 TeVultimate (300 fb-1) ~ 2.5 - 3 TeV

~ “1 day” : up to 1.5 TeV

~ “10 days” : up to 2 TeV

~ 100 days : up to 2.3 TeV

ATLAS 5 discovery curves

But : it will take a lot time to understand the detectors and the backgrounds …

band indicates factor 2 variationin background estimate

Discovery Reach with Jets+Missing-Energy

D.

Tovey


• However, loop diagrams lead to self-energy of the Higgs– Mass correction diagrams:

(M)2 2

Where is the cut-off scale of the theory!

Fermion, e.g. top quark

higgsquarkquark

• The higgs gives mass tostandard model fermions:

• In SM m(h2) -> mPl2 ~ (1019 GeV)2

– Require fine tuning over many orders of magnitude• With SUSY bosonic loops cancel fermionic loops

– No quadratic divergence of m(h2)

The fine tuning problem


I will focus on signatures of Jets and Jets+Missing-Energy -> sensitive to large variety of new physics models

SUperSymmetry, Extra Spatial Dimensions, Others,…

Why “New Physics” – and How?

LHC will provide proton-proton collisions @ 14 TeV -> ATLAS experiment will provide wealth of data allowing us to explore far beyond our current understanding New physics can manifest itself through many final state signatures of p-p collisions involving: Large Missing Energy, Jets, Leptons, …

Introducing “New Physics”, beyond the Standard Model (SM), at the TeV scale, can provide solutions to outstanding problems… - hierarchy and fine tuning - cosmology – what’s the nature of dark matter? (- where does gravity fit in?)

Key to Discovery:Understand and control the major uncertainties: Proton structure Contribution from SM Experimental uncertainties

Documents

Claire Gwenlan PPARC Interview - 07/02/06 1 Claire Gwenlan Why New Physics? Preparation for Measurements at the LHC -> Importance of Proton Structure