Kaushik De University of Texas at Arlington September 26, 2012

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?…


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’


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


ATLAS Experiment


ATLAS Detector


http://atlas.ch/

Unique device to record pp collisions at the LHC

http://atlas.ch/

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


People in ATLAS


Over 3000 collaborators from 174 institutes in 38 countries

U.S. Institutions at the LHC


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


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


Building ATLAS at UTA


More Pictures from UTA


UTA in the ATLAS Pit


It can be Fun…


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


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


SWT2 in LHC



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


What will ATLAS Measure



According to Bookies



Some Standard Model Processes


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


W Polarization in Top Decays

arXiV 1205.2484

Test of Wtb vertex 1.04 fb-1 of data analyzed

No anomalous couplings


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



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


Wg and Zg Production arXiV 1205.2531

1.02 fb-1 of data analyzed

Limits on triple gauge couplings


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


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


http://www.sciencedirect.com/science/article/pii/S037026931200857X



The Evidence


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


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

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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


Scalar Top Search

arXiv 1204.6736 NGMSB model 2.05 fb-1 analyzed 2 SFOS leptons,

missing Et, b-tag Consistent with SM


SUSY Trilepton + Missing Et

arXiv:1204.5638

Chargino+NLSP cascade

2.06 fb-1 analyzed

Consistent with bkground

SUSY Mass Limits



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


Other BSM Searches


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.



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



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

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Kaushik De University of Texas at Arlington September 26, 2012