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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
PPARC Interview - 07/02/06Claire Gwenlan 2
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
PPARC Interview - 07/02/06Claire Gwenlan 3
A Precise Determination of Proton Structure
PPARC Interview - 07/02/06Claire Gwenlan 4
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
PPARC Interview - 07/02/06Claire Gwenlan 5
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
PPARC Interview - 07/02/06Claire Gwenlan 6
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
PPARC Interview - 07/02/06Claire Gwenlan 7
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
PPARC Interview - 07/02/06Claire Gwenlan 8
Understanding the Standard Model Contribution
PPARC Interview - 07/02/06Claire Gwenlan 9
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
PPARC Interview - 07/02/06Claire Gwenlan 10
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
PPARC Interview - 07/02/06Claire Gwenlan 11
Evaluation and Improvement of the Jet and Missing-Energy
Resolutions
PPARC Interview - 07/02/06Claire Gwenlan 12
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
PPARC Interview - 07/02/06Claire Gwenlan 13
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 ?
PPARC Interview - 07/02/06Claire Gwenlan 14
Beyond the Standard Model:-New Physics Signatures
PPARC Interview - 07/02/06Claire Gwenlan 15
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
PPARC Interview - 07/02/06Claire Gwenlan 16
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 !!!
PPARC Interview - 07/02/06Claire Gwenlan 17
Extras
PPARC Interview - 07/02/06Claire Gwenlan 18
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 !!!
PPARC Interview - 07/02/06Claire Gwenlan 19
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
PPARC Interview - 07/02/06Claire Gwenlan 20
High-Energy Jet
Lower-Energy Jets
IDEA:
Employ momentum balance of high-energy jets against multiple low-energy jets? -> needs investigation
PPARC Interview - 07/02/06Claire Gwenlan 21
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
PPARC Interview - 07/02/06Claire Gwenlan 22
• 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
PPARC Interview - 07/02/06Claire Gwenlan 23
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