Post on 30-Mar-2015
LARGE HADRON COLLIDER UPDATE
THE ATLAS PERSPECTIVE
Kaushik De
University of Texas at Arlington
September 26, 2012
Introduction to the LHC
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The Large Hadron Collder (LHC) at CERN near Geneva
LHC Underground
The world’s most powerful particle accelerator In a tunnel, 16.8 miles around,
330 feet underground Running spectacularly for the past two years
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Motivation
Why do we need the LHC? We have an excellent description of the
physical world around us Called the Standard Model (SM) of Physics Consistent with experiments and
observations of nature from the smallest to the largest scale
But many unsolved questions about the Standard Model and beyond
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Unsolved Questions
A small ‘biased’ selection:How do particles get mass? Higgs?
○ Maybe solved by ATLAS already!What is Dark Matter?Unification of fundamental forces?How does gravity fit in the SM?Are there extra dimensions?Fine tuning of Higgs mass?…
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Methodology
How will the LHC help in solving the fundamental mysteries of nature?The LHC is a particle accelerator.Protons are accelerated close to the speed
of light -> aim for head-on collision!Collisions occur millions of times/second
We need a massive ‘camera’ to take pictures of these particle collisions.The ATLAS experiment is the ‘camera’
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Why is the LHC Important? The LHC is at the energy frontier – and will
remain there for the next few decades7 TeV → 8 TeV …... 14 TeV center-of-mass
proton-proton collision energyExploration of unknown frontierDiscovery through precision measurements
The ATLAS perspectiveUnprecedented data = Rich program of physics193 publications in arXiv, and growing
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ATLAS Experiment
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ATLAS Detector
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http://atlas.ch/
Unique device to record pp collisions at the LHC
Some ATLAS Facts
ATLAS took ~15 years to build and commission
The detector is 45 meters long, 25 meters high, 7000 ton weight
ATLAS runs 24 hours when in operation We expect to collect and analyze data
from ATLAS for the next 15-20 years The scale of ATLAS is far beyond anything
done before in basic physics research
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People in ATLAS
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Over 3000 collaborators from 174 institutes in 38 countries
U.S. Institutions at the LHC
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Texas on LHC Baylor University: CMS Rice University: CMS Southern Methodist University: ATLAS Texas A&M University: CMS Texas Tech University: CMS University of Houston: ALICE University of Texas, Arlington: ATLAS, WLCG University of Texas, Austin: LHC University of Texas, Dallas: ATLAS
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UTA Involvement in ATLAS UTA contributed to
ATLAS for ~17 years Build and operate the
Intermediate Tile Calorimeter
SouthWest Tier 2 Computing Center for ATLAS at UTA
Many contributions in hardware, computing and physics
15 authors from UTA were on Higgs paper
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Building ATLAS at UTA
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More Pictures from UTA
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UTA in the ATLAS Pit
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It can be Fun…
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Testing in the pit
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Other UTA Contributions PanDA
Distributed computing software used by ATLASDeployed at hundreds of computing centersUsed by thousands of physicists
Computing OperationsBillions of events collected and analyzed from the
LHC to extract physics resultsAll physics results need massive data processingUTA involved from the beginning
PAT, AFP, shift coordination and many more contributions by other UTA faculty
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PanDA Similar to cloud computing engine
But developed 8 years ago, long before cloud computing became a buzzword
Used by ATLAS world-wideMany other experiments interested now
One of the most important U.S. computing contributions to ATLAS
Cited as example of Big Data innovationMajor new initiative announced by Obama in AprilPanDA received $1.7M DoE ASCR Big Data grant
Major focus of research effort at UTA
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ATLAS Jobs/week
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SouthWest SuperComputing Center UTA leads the
SouthWest Tier 2 center for ATLAS
Multi-million dollar NSF funded facility
Contributing to hundreds of physics papers
Helps physicists in the SouthWest region to quickly analyze ATLAS data
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SWT2 in LHC
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ATLAS Status
ATLAS is operating with data taking efficiency > 95% Almost 20 fb-1 delivered by the LHC Highest luminosity so far = 7.73·1033 cm-2s-1
Total Collisions = 1.29·1015
Two Years of LHC Operations
LHC performance has been phenomenal Good start to 7 TeV program in 2010: 45 pb-1 recorded Outstanding in 2011-2012:
ATLAS recorded 5.25 fb-1 in 2011 @ 7 TeV 14 fb-1 so far in 2012 @ 8 TeV
Perspective: In 2011, almost 1 million top pairs produced, over half billion W bosons produced
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What will ATLAS Measure
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According to Bookies
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Some Standard Model Processes
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Start with the Top Quark World's largest sample of top quarks produced Precision SM tests, while looking for new physics Summer results in top quark production and decay
arXiv:1205.3130 - Measurement of the t-channel single top-quark production cross section in pp collisions at sqrt(s) = 7 TeV with the ATLAS detector
arXiv:1205.2067 - Measurement of the top quark pair cross section with ATLAS in pp collisions at sqrt(s) = 7 TeV using final states with an electron or a muon and a hadronically decaying tau lepton
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W Polarization in Top Decays
arXiV 1205.2484
Test of Wtb vertex 1.04 fb-1 of data analyzed
No anomalous couplings
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Search for tb Resonances arXiV 1205.1016 1.04 fb-1 of data analyzed No excess observed Benchmark limit on mass
W'R>1.13 TeV at 95% CL
Single top summary
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Physics with Gauge Bosons
Study of W/Z are important SM measurements used in precision fits, PDG results, MC tuning...
Anomalous results could signal new physics Topics
W/Z production and decays, associated particles Di-boson production – high rates at the LHC
Summer result ArXiv:1204.6720: - Measurement of tau polarization in
W->taunu decays with the ATLAS detector in pp collisions at sqrt(s) = 7 TeV
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Wg and Zg Production arXiV 1205.2531
1.02 fb-1 of data analyzed
Limits on triple gauge couplings
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Why did P. Higgs Visit ATLAS
Higgs is was the last unobserved particle in the SM
Global EW fit: mH = 96+31
-24 GeV
Above plot shows region not excluded by ATLAS at the beginning of the summer
What’s a Higgs Boson?
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How to Look for the Higgs The Higgs boson
has variety of decaysH -> ggH -> ZZH->WWH->bbH->tt
Hunt requires many techniques
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130-180 WW(*) lnln
<130 gg
130-300 ZZ(*) llll 300-600
ZZ llnn
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Limits from Various Channels
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Have we Found the Higgs?
arXiv:1207.7214, Phys. Lett. B 716 (2012) 1-29 H->ZZ->4l, H->WW->emnn, H->gg modes Combining 4.8 fb-1@7TeV, 5.8 fb-1@8TeV
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The Evidence
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5.9 s signal of a new neutral boson with mass 126 +-0.4 +- 0.4 GeV
More details in colloquium by Haleh Hadavand in January, 2013
Future of Higgs Higher precision measurements Next, verify all decay modes
Most important gg, ZZ, ttWW is most challenging
Measurement of Higgs couplingsCouplings to gauge bosons important for EWSBWWH and ZZH processesMany other couplings – global fit strategy
Look for deviations – search for new physics beyond the Standard Model
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Dark Matter
Astronomy tells us: The matter we know is
5% of the universe The rest is dark matter And dark energy 80 year old mystery Maybe we can make
DM at the LHC?
SLA
C/N
icol
e R
ager
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Search for Supersymmetry
Doubling of SM particles, and more Higgs states
None seen yet Most searches assume
R-parity is conserved LSP = dark matter
candidate Expect missing Et from
LSP
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Scalar Top Search
arXiv 1204.6736 NGMSB model 2.05 fb-1 analyzed 2 SFOS leptons,
missing Et, b-tag Consistent with SM
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SUSY Trilepton + Missing Et
arXiv:1204.5638
Chargino+NLSP cascade
2.06 fb-1 analyzed
Consistent with bkground
SUSY Mass Limits
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Prognosis for SUSY
MSSM SUSY models OK since low mass Higgs found mSUGRA models in trouble: Baer et al, arXiV
1202.4038 ATLAS pushing sparticle mass limits near 1 TeV
These searches require high missing Et from LSP Maybe R-parity not strictly conserved – MPV models Maybe large mass splitting for stops and
sbottoms – NMSSM models, focus of recent ATLAS searches
Combined stop results
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Other BSM Searches
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Mystery - why is Gravity so Weak
Electromagnetism is confined to our usual three dimensions of space
Maybe Gravity sees other dimensions of space?
As the force is spread out, it is weakened.
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Black Hole Signature of LED
arXiv:1204.4646
1.04 fb-1: require 3 high PT objects, at least 1 lepton
Consistent with SM bkground
Also sets limit on string balls
Extra Dimensions or Dark Matter Recent result: arXiv
1209.4625 Photon + missing Et LED (ADD), WIMP models 4.6 fb-1 analyzed @ & TeV Consistent with SM
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Conclusion
Successful two years with ATLAS at the LHC Low mass SM Higgs hunt is almost over! Precision measurements of Standard Model
going well – no surprises so far Search for new physics on many fronts