11M. Shupe M. Shupe -- ATLAS CollaborationATLAS Collaboration

Detecting Detecting ParticlesParticles

Experimental Elementary Particle Physics Group at the Experimental Elementary Particle Physics Group at the University of Arizona +University of Arizona +

Searching for Quark Compositeness at the LHCSearching for Quark Compositeness at the LHC

Michael ShupeMichael ShupeDepartment of PhysicsDepartment of Physics

22M. Shupe M. Shupe -- ATLAS CollaborationATLAS Collaboration

The Experimental Elementary Particle Group at The Experimental Elementary Particle Group at the University of Arizonathe University of Arizona

Faculty

Research Associates & Staff

Students

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The Large The Large HadronHadron Collider (LHC), near Geneva, Switzerland, is the Collider (LHC), near Geneva, Switzerland, is the ““Hubble TelescopeHubble Telescope”” for High Energy Physicsfor High Energy Physics, and Arizona is there!, and Arizona is there!

The high energy group at The University of Arizona

joined the ATLAS experiment in 1994, and had major impact—from the start—on the design

of the experiment!

(Proton-Proton Collisions at 14 TeV)

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Magnets in the LHC TunnelMagnets in the LHC Tunnel

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ATLAS, In Its Underground CavernATLAS, In Its Underground Cavern

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ATLAS Detector: ~$1.5B ATLAS Detector: ~$1.5B –– ““WorldWorld’’s Largest Experiments Largest Experiment””CalorimetersTracking

Muon: Air Core Toroids

Integrated Forward Calorimeters ($16M)

Forward Muon System

Arizona was the only U.S. group to make a major change in the ATLAS design. We conceived the integrated FCal and shield design, adopted by ATLAS in June,1994.

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ATLAS ATLAS -- 20052005

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ATLAS ATLAS -- 20072007

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Constructing the ATLAS Integrated Forward

Calorimeter in a clean room in the basement of

the PAS building. Arizona conceived,

engineered and supervised this $16M

project for ATLAS.

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Some of our research group, at CERN, Some of our research group, at CERN, during the installation of the during the installation of the ATLAS ATLAS

Integrated Forward CalorimeterIntegrated Forward Calorimeter

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Quarks are the Quarks are the building blocks of building blocks of protons, neutrons, protons, neutrons, and hundreds of and hundreds of

other similar other similar ((shortlivedshortlived) ) particles.particles.

Are quarks Are quarks themselves made themselves made of even smaller of even smaller building blocks?building blocks?

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The only particles needed to build the periodic table of the

elements are protons, neutrons, and electrons!

(Plus photons and gluons!)

Helium The only quarks needed to build up

protons and neutrons are u and d.

u has charge 2e/3, and d has charge minus e/3. What

quarks do neutrons contain?

Who ordered this one?

What else can we make from the six

quarks? Thousands of other not-so-stable

particles!

Why we call quarks and leptons the “building blocks” of nature.From Atoms, to Nucleons, to QuarksFrom Atoms, to Nucleons, to Quarks

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Particle Particle ““multipletsmultiplets””::

““periodic tablesperiodic tables””of the strongly of the strongly

interacting interacting particles.particles.

Spin1/2

Spin 3/2

ProtonNeutron

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The known quarks The known quarks and leptons also and leptons also

look like a periodic look like a periodic table! Are they table! Are they made of smaller made of smaller

particles?particles?

Electromagnetic ForceElectromagnetic Force

Strong (Nuclear) ForceStrong (Nuclear) Force

Weak Force (Changes Weak Force (Changes particle types)particle types)

Gravity (Gravitons?)Gravity (Gravitons?)

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The zoo of The zoo of quarks, quarks,

leptons, and leptons, and force carrying force carrying

particlesparticles

3/31/2011 15

A composite model may A composite model may explain parameters such explain parameters such as particle mass, electric as particle mass, electric charge, and color charge charge, and color charge

-- which the Standard which the Standard Model of particle physics Model of particle physics

does not.does not.

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Direct route to shortest distance scales?Direct route to shortest distance scales?

ItIt’’s all in the s all in the momentum!momentum!

The de Broglie The de Broglie equation:equation:

λ = λ = h/ph/p

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θ∗q1

q2

q1

q2

gBRbar

Ideal for compositeness search: 7 Ideal for compositeness search: 7 TeVTeV Quark ColliderQuark Collider

Quark Beam 1 3.5 TeV

Quark Detector

Quark Detector

Quark Beam 2 3.5 TeV

The momentum of the “force carrying” particle (here a gluon)

determines its wavelength, and the distance scale that can be probed.

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Reality: the LHC 7 Reality: the LHC 7 TeVTeV ProtonProton--Proton ColliderProton Collider

••Each proton is a chaotic mix of 3 Each proton is a chaotic mix of 3 ““valence quarksvalence quarks”” + other quarks + gluons.+ other quarks + gluons.

••The two that collide typically carry a small fraction of the proThe two that collide typically carry a small fraction of the proton momentum: ton momentum: partonparton distribution functions (distribution functions (PDFPDF’’ss).).

••Outgoing quarks, or gluons, barely escape the protons before theOutgoing quarks, or gluons, barely escape the protons before they cascade in y cascade in to more quarks and gluons (a to more quarks and gluons (a partonparton shower). And this is just the start!shower). And this is just the start!

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with design luminosity pile-up

without pile-up

DijetsDijets seen in the detector:seen in the detector:

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Search With Angular Search With Angular DistributionsDistributions

Angular distributions are sensitive to sAngular distributions are sensitive to s--channel channel vs. tvs. t--channel (QCD) production of channel (QCD) production of dijetsdijets

The variable The variable χχ is convenient is convenient –– itit’’s flat for s flat for Rutherford scattering, and almost flat for Rutherford scattering, and almost flat for QCDQCDss--channel exchange peaks at low channel exchange peaks at low χχ..

We require (depending on mass bin)We require (depending on mass bin)ppTT(j(j11) > 80) > 80--150 150 GeVGeV (trigger)(trigger)ppTT(j(j22) > 30 ) > 30 GeVGeV (reconstruction)(reconstruction)|y|y11 + y+ y22| < 1.5| < 1.5|y|y11 –– yy22| < 4.9| < 4.9

No significant deviation from QCD is observedNo significant deviation from QCD is observedExpressed as our benchmark, a contact Expressed as our benchmark, a contact interaction interaction ΛΛ, this works out to, this works out toΛΛ > 3.4 > 3.4 TeVTeV (at 95%), with an expected (at 95%), with an expected

sensitivity of 3.5 sensitivity of 3.5 TeVTeVPrevious best limit is from D0,Previous best limit is from D0,ΛΛ > 2.8 > 2.8 TeVTeV

TeV4.3>Λqqqq

ATLAS Preliminary

ATLAS Preliminary

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ConclusionConclusion

The LHC is rapidly pushing to shorter distance scales. The LHC is rapidly pushing to shorter distance scales. The full dataset from 2010 is ~10 times larger than The full dataset from 2010 is ~10 times larger than the data shown here. Within a few weeks we will the data shown here. Within a few weeks we will publish a result which greatly increases the excluded publish a result which greatly increases the excluded energy range and reduces the distance scale further. energy range and reduces the distance scale further.

If you are interested in this research, If you are interested in this research, this is the perfect this is the perfect time to join.time to join. The 2011 data sample will be another The 2011 data sample will be another huge increase over the existing data, and many Ph.D. huge increase over the existing data, and many Ph.D. theses will be based on studies of these highesttheses will be based on studies of these highest--energy collisions!energy collisions!