Transcript UCL ATLAS TALK BARR - University of Oxford

Preparation for and measurement
of new physics with
ATLAS at the LHC
Claire Gwenlan
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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
Claire Gwenlan
PPARC Interview - 07/02/06
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Why “New Physics” – and How?
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, …
Why?
Introducing “New Physics”, beyond
the SM, at the TeV scale, can provide
solutions to problems such as …
- Hierarchy
Key To Success:
PREPARATION !!!
Must understand and
control major uncerts.:
- Proton structure
- SM contribution
- Jet resolutions
Will require SM jet
measurements with early
ATLAS data
- Cosmology – what’s the nature of dark
matter?
(- Where does gravity fit in?)
I will focus on signatures of Jets and Jets+Missing-Energy
-> powerful signals for very wide variety of new physics models
Claire Gwenlan
PPARC Interview - 07/02/06
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A Precise Determination of
Proton Structure
Claire Gwenlan
PPARC Interview - 07/02/06
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Importance of Proton Structure
[C. Gwenlan
et al.], ZEUS Coll., Eur. Phys.“sea”
J., C42
(2005) 1
Valence
 All processes at the LHC
quarks/
quarks
anti-quarks
depend on proton structure !!!
fi parameterise proton structure
   fa fbˆ sub-process
Gluons
a,b
-> Precise knowledge essential
for reliable predictions of:
- new physics (Higgs, SUSY, …)
- SM processes (which are also
backgrounds to new physics)
 Proton structure described by
parton density functions (PDFs)
PDFs: fi(x,Q2)
- parametrised in x
at starting scale
- QCD predicts
change with Q2
The structure of the Proton
Q2
x
-> determined from fits to data
Need to know the PDFs as well as we can !!!!
Claire Gwenlan
PPARC Interview - 07/02/06
My PDF fit
4
Impact of PDFs on LHC discovery
EG: Single Inclusive Jets
 Sensitive to wide variety
of new physics e.g. SUSY,
extra spatial dimensions,
quark compositeness, …
-> look for deviations from
SM
Scale uncertainty
Tevatron reach
PDF uncertainty
LHC reach in 1st year
High-x gluon PDF uncertainty
PDFs will be dominant
uncertainty in high-scale
(discovery) physics at the LHC
-> mainly from “high-x” gluon
Could hide signs of new physics !!!
“New Physics”
Claire Gwenlan
PPARC Interview - 07/02/06
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Constraining the 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
[C. Gwenlan et al.], ZEUS Coll., Eur. Phys. J., C42 (2005) 1
-> significantly improved
knowledge of high-x gluon
-> Precisely in region
required for new physics
discovery at the LHC
Claire Gwenlan
PPARC Interview - 07/02/06
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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
ZEUS PDF before
including “data”
ZEUS PDF after
including “data”
e+ “data”
e+ “data”
A.Tricoli, A.Cooper-Sarkar, C.Gwenlan, hep-ex/0509002
-> high-x gluon constraints
-> further work: experimental
systematics, kinematic cuts, …
Very Preliminary – First Results Last Week
Only Statistical Uncertainties Considered So Far
Ready to input LHC data (including my own SM jet measurements)
Claire Gwenlan
PPARC Interview - 07/02/06
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Understanding the
Standard Model Contribution
Claire Gwenlan
PPARC Interview - 07/02/06
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SM Contributions to New Physics
Recognising deviations from SM expectations requires excellent
understanding of SM processes that contribute in the new physics region
Dominant SM contributions:
 “Jets”:
irreducible
- QCD Jets
 “Jets+Missing-Energy”:
- QCD Jets (mismeasured), reducible
W/Z+Jets, ttbar+Jets
example: SUSY (jets+missing-ET)
Need to understand
and control this!!!
Need to establish best ways of
reducing/modelling SM contribution
 Rejection/discrimination of reducible
SM contributions (for “Jets+Missing-Energy”):
pT of leading jet (GeV)
-> studies on simulated data
 Guidance from TEVATRON
-> establish independently for LHC
Claire Gwenlan
PPARC Interview - 07/02/06
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SM Contributions to New Physics
 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 !!!
EG.: Four-Jets at HERA
Tuning to my four-jet data
-> best global descriptions
(no exact calculations)
- Rely on ME+PS models
-> Many tuneable parameters
Tune/validate available models:
 Now, using existing data
C. Gwenlan, UCL-THESIS, 2003
Best tuning to
HERA four-jets
Untuned model
-> HERA, TEVATRON
 Later, using early ATLAS data,
including my own measurements of SM
jet processes (especially QCD multi-jets)
Claire Gwenlan
PPARC Interview - 07/02/06
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Evaluation and Improvement
of the Jet and Missing-Energy
Resolutions
Claire Gwenlan
PPARC Interview - 07/02/06
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Jet/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
Isolatedoftrack
Reconstruction
only
Inner CALORIMETER
four-jet events in data
(solid) and Monte
Detector
Carlo (open) using
energy flow
ZEUS “energy flow” algorithm:
 Implemented in standard software
 Tested performance in wide range
of jet topologies (dijets, multi-jets)
-> improved hadronic reconstruction
-> reduced systematics
Improved resolution and scale
 How to improve resolutions …
- combine track and calorimeter
information in the reconstruction
-> “energy flow” technique
C. Gwenlan,
UCL-THESIS, 2003
Calorimeter
Charged Deposit
Energy-Flow
Neutral Deposit
Neutral Deposit
 First person to use in measurements
of multi-jet production
Claire Gwenlan
PPARC Interview - 07/02/06
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Energy Flow in ATLAS Jets
New energy flow algorithm now being developed for ATLAS
-> initial tests on low-energy jets promising
 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, …)
 So far, only for low-energy jets
Calorimeter
Standard
reconstruction
Isolated track
Inner
Detector
Charged Deposit
Energy-Flow
- To what extent can it be used for
algorithm
high energies of interest to new physics ?
20%
improvement
- Can its performance be improved ?
Neutral Deposit
in resolution
Claire Gwenlan
PPARC Interview - 07/02/06
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Beyond the Standard Model:New Physics Signatures
Claire Gwenlan
PPARC Interview - 07/02/06
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Constraining the Models …
 SUperSYmmetry
RPC
RPV
 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)
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
extra
dimensions
brane
our world (3+1dimensions)
 PLUS many other new physics scenarios
(e.g. other SUSY/extra dimensions models, leptoquarks, …)
Claire Gwenlan
PPARC Interview - 07/02/06
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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 !!!
Claire Gwenlan
PPARC Interview - 07/02/06
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Extras
Claire Gwenlan
PPARC Interview - 07/02/06
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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
Standard Model
CDF Run 1
-> Similar situations likely
at the LHC !!!
PDF uncertainty
Claire Gwenlan
PPARC Interview - 07/02/06
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Constraining the PDFs at HERA
I have shown that by
the time of LHC start-up,
further improvements can
be expected
C. Gwenlan et al., J. Phys. G., 32 (2006) 221
-> requires new jet
measurements from HERA
[work I am performing with
a graduate student at UCL]
Work started on quantifying
impact on LHC discovery
NEXT STEPS:
 Ensure useful HERA
measurements are made !!!
 Include in QCD fits for
improved PDFs
Claire Gwenlan
PPARC Interview - 07/02/06
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IDEA:
High-Energy Jet
Lower-Energy Jets
Employ momentum balance
of high-energy jets against
multiple low-energy jets?
-> needs investigation
Claire Gwenlan
PPARC Interview - 07/02/06
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D. Tovey
Discovery Reach with Jets+Missing-Energy
ATLAS
5 discovery curves
band indicates factor  2 variation
in background estimate
~ 100 days :
up to 2.3 TeV
~ “10 days” :
up to 2 TeV
~ “1 day” :
up to 1.5 TeV
Discovery reach for squarks/gluinos
Time
1 month at 1033
1 year at 1033
1 year at 1034
ultimate (300 fb-1)
But
: itGwenlan
will take a lot time to understand
Claire
PPARC Interview - 07/02/06
the detectors and the backgrounds …
mass reach
~ 1.3 TeV
~ 1.8 TeV
~ 2.5 TeV
~ 2.5 - 3 TeV
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The fine tuning problem
•
•
The higgs gives mass to
standard model fermions:
quark
higgs
quark
However, loop diagrams lead to self-energy of the Higgs
– Mass correction diagrams:
Fermion, e.g. top quark
(DM)2  2
Where  is the cut-off scale of the theory!
•
•
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)
Claire Gwenlan
PPARC Interview - 07/02/06
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Why “New Physics” – and How?
 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?)
 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, …
 I will focus on signatures of Jets and Jets+Missing-Energy
-> sensitive to large variety of new physics models
 SUperSymmetry, Extra Spatial Dimensions, Others,…
Key to Discovery:
Understand and control the major uncertainties:
 Proton structure  Contribution from SM  Experimental uncertainties
Claire Gwenlan
PPARC Interview - 07/02/06
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