11M. Shupe, ATLAS Collaboration, APS M. Shupe, ATLAS Collaboration, APS

Four Corners Section MeetingFour Corners Section Meeting

Detecting Detecting ParticlesParticles

Searching for Quark Compositeness at the LHC

Michael ShupeDepartment of Physics, University of Arizona

APS Four Corners Section Meeting, October 21-22, 2011

M. Shupe, ATLAS Collaboration, APS Four Corners Section MeetingM. Shupe, ATLAS Collaboration, APS Four Corners Section Meeting 22

Are quarks the most fundamental particles, or are Are quarks the most fundamental particles, or are they composed of smaller particles?they composed of smaller particles?

NatureNature’’s known structural hierarchies.s known structural hierarchies.How collisions give access to short distances.How collisions give access to short distances.Fantasy: a quark collider.Fantasy: a quark collider.Fact: the Large Fact: the Large HadronHadron Collider. Collider. The ATLAS Experiment.The ATLAS Experiment.The search for quark compositeness in ATLAS, The search for quark compositeness in ATLAS, and the most recent results that we have and the most recent results that we have published. published.

Organization of this talk:Organization of this talk:

M. Shupe, ATLAS Collaboration, APS Four Corners Section MeetingM. Shupe, ATLAS Collaboration, APS Four Corners Section Meeting 33

The underlying patterns of matterThe underlying patterns of matterIn Chemistry, all the types of molecules we see are made from In Chemistry, all the types of molecules we see are made from just 92 naturally occurring elements (the Periodic Table).just 92 naturally occurring elements (the Periodic Table).

The atoms in this table, are made of protons, neutrons, The atoms in this table, are made of protons, neutrons, electrons + photons, for the coulomb field + electrons + photons, for the coulomb field + ““nuclear gluenuclear glue””..

M. Shupe, ATLAS Collaboration, APS Four Corners Section MeetingM. Shupe, ATLAS Collaboration, APS Four Corners Section Meeting 44

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 fundamental The fundamental building blocks in building blocks in nature, and the nature, and the interactions among interactions among them.them.

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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Easy way to picture particle masses? Easy way to picture particle masses?

10/22/2011 7

A composite model A composite model could potentially could potentially

explain the pattern of explain the pattern of particle charges and particle charges and

generations, the color generations, the color charge, and the charge, and the Standard Model Standard Model

parameters such as parameters such as masses and the masses and the mixing matrices.mixing matrices.

The constituents are The constituents are generically referred to generically referred to

as as ““preonspreons””..

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Composite models date from the late Composite models date from the late 19701970’’s through the early 1980s through the early 1980’’s. I s. I published this one in 1979, based on spin published this one in 1979, based on spin ½½ preonpreon doublets, one with charge e/3, and doublets, one with charge e/3, and the other, neutral. the other, neutral. HaimHaim HarariHarari was was working on a very similar model at the working on a very similar model at the same time, and his article is published in same time, and his article is published in the same journal.the same journal.

Have Have preonpreon models progressed since then? models progressed since then? No. (See next slide.)No. (See next slide.)

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The Status of The Status of PreonPreon ModelsModels

All All preonpreon models get the quantum numbers right within models get the quantum numbers right within their domain of description (or they would not be their domain of description (or they would not be published)published).. Michael Michael PeskinPeskin calls this calls this ““quantum quantum numerologynumerology””..No existing No existing preonpreon model has a plausible description of model has a plausible description of preonpreon--level dynamics. The fundamental problem has to do level dynamics. The fundamental problem has to do with mass scales. Limits on the compositeness scale with mass scales. Limits on the compositeness scale ΛΛhave been in the multihave been in the multi--TeVTeV range for some time, range for some time, corresponding to distance scales of ~10corresponding to distance scales of ~10--1919 m. m. The The Heisenberg uncertainty principlesHeisenberg uncertainty principles tell us that tell us that preonspreonsconfined to these distances will have confined to these distances will have momentamomenta in the in the ~~TeV/cTeV/c range, naively leading to quark masses in the same range, naively leading to quark masses in the same range.range.Since the known quark masses range from a few Since the known quark masses range from a few MeVMeV to to 173 173 GeVGeV, , preonpreon binding energies would need to be in the binding energies would need to be in the TeVTeV range to cancel most of the kinetic energy. Is this a range to cancel most of the kinetic energy. Is this a problem? Without a description of problem? Without a description of preonpreon dynamics, who dynamics, who knows?knows?So how are compositeness limits set? By assuming that So how are compositeness limits set? By assuming that quark substructure would show up initially as a quark substructure would show up initially as a ““contact contact interactioninteraction”” among the among the preonspreons of colliding quarks of colliding quarks –– leading leading to largeto large--angle scatters in excess of QCD. (More below.) angle scatters in excess of QCD. (More below.)

M. Shupe, ATLAS Collaboration, APS Four Corners Section MeetingM. Shupe, ATLAS Collaboration, APS Four Corners Section Meeting 1010

Distances: Atoms, to Nucleons, to QuarksDistances: Atoms, to Nucleons, to Quarks

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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

Fantasy Machine: A 7 Fantasy Machine: A 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.

M. Shupe, ATLAS Collaboration, APS Four Corners Section MeetingM. Shupe, ATLAS Collaboration, APS Four Corners Section Meeting 1313

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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Hard Scattering Process

2P2 2xP

1P

1 1xP

s

qgqg→σ

)(0

zDqπ

X

q(x1)

g(x2)

Factorization makes this calculable.Factorization makes this calculable.

Parton Jets

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WhatWhat’’s in a proton? Parton distribution functions:s in a proton? Parton distribution functions:

For twoFor two--jet (jet (dijetdijet) ) events, the jets do events, the jets do

not emerge from the not emerge from the collision backcollision back--toto--

back in the back in the longitudinal direction!longitudinal direction!

To access the To access the information about the information about the original collision, we original collision, we rely on kinematics to rely on kinematics to ““undoundo”” the effects of the effects of the Lorentz boost, the Lorentz boost,

and study the and study the collision in the 2collision in the 2--parton rest frame.parton rest frame.

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Higher orders are a challenge.Higher orders are a challenge.

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Particles leave tracks Particles leave tracks or particle showers in or particle showers in detectordetector

Incoming quarks Incoming quarks collide.collide.

Particles form as quarks Particles form as quarks coalesce (coalesce (hadronizehadronize).).

PartonsPartons shower (jets).shower (jets).

Encountering the detector.

Near the original interaction!!!

Data Collected HERE.Experimentalists view:Experimentalists view:

M. Shupe, ATLAS Collaboration, APS Four Corners Section MeetingM. Shupe, ATLAS Collaboration, APS Four Corners Section Meeting 1818

The Large The Large HadronHadron Collider (LHC), near Geneva, Switzerland, is the Collider (LHC), near Geneva, Switzerland, is the ““Hubble TelescopeHubble Telescope”” of High Energy Physicsof High Energy Physics

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 7 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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Arizona created the ATLAS Integrated Arizona created the ATLAS Integrated FCalFCal conceptconceptCalorimetersTracking

Muon: Air Core Toroids

Integrated Forward Calorimeters

Massive Forward Radiation Shield (~700 Metric Tonnes)

Forward Muons

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The University of Arizona TeamThe University of Arizona Team

Faculty

Research Associates & Staff

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Our research group Our research group constructed the EM constructed the EM

modules of the modules of the ATLAS Forward ATLAS Forward

Calorimeter (Calorimeter (FCalFCal) in ) in a clean room in the a clean room in the

basement of the basement of the Physics building. The Physics building. The

hadronichadronic modules modules were constructed by were constructed by

Canadian and Canadian and Russian Russian

collaborators.collaborators.

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

ATLAS Forward Calorimeter

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CSC (Cathode Strip Chambers)CSC (Cathode Strip Chambers)

CSCs

The ArizonaThe Arizona group also works in the group also works in the muonmuon systemsystem

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ATLAS ATLAS -- 20052005

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ATLAS ATLAS -- 20072007

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CSC ChambersCSC Chambers

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with design luminosity pile-up

without pile-up

Prelude to analysis: Simulation! (Dijet events.)Prelude to analysis: Simulation! (Dijet events.)

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ANOTHER SIMULATION:

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Data, 2011:A collision with two high-pT jets.

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How are How are dijetdijet events used to search for events used to search for quark compositeness?quark compositeness?

Search for excited quarks appearing as Search for excited quarks appearing as resonances in the resonances in the dijetdijet mass spectrum, mass spectrum, andand……Search for excess events at large angles Search for excess events at large angles resulting from the interaction of quark resulting from the interaction of quark constituents.constituents.

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Search for resonances due to excited quarks in the Search for resonances due to excited quarks in the dijetdijetmass spectrum using a 1.0 fbmass spectrum using a 1.0 fb--11 ATLAS data set from 2011.ATLAS data set from 2011.

““Search for New Physics in the Dijet Mass Distribution using 1 fbSearch for New Physics in the Dijet Mass Distribution using 1 fb--1 of pp Collision Data at 1 of pp Collision Data at sqrt(ssqrt(s) = 7 ) = 7 TeVTeV collected by the ATLAS Detector'', The ATLAS Collaboration, subcollected by the ATLAS Detector'', The ATLAS Collaboration, submitted to mitted to Phys. Phys. LettLett. B (31 August 2011). B (31 August 2011)

QCD background determined from a smooth fit to the data, then seQCD background determined from a smooth fit to the data, then searched for resonances arched for resonances ((BumpHunterBumpHunter). Most discrepant region in agreement with QCD (no bumps). Li). Most discrepant region in agreement with QCD (no bumps). Limits set on mits set on excited quarks (2.99 excited quarks (2.99 TeVTeV),), axigluonsaxigluons (3.32 (3.32 TeVTeV), and color octet scalars (1.92 ), and color octet scalars (1.92 TeVTeV).).

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Relationship to Rutherford scattering Relationship to Rutherford scattering composite atoms.composite atoms.

10/22/2011 34

At small center of mass scattering angles, the dijet angular distribution predicted by the leading order QCD is proportional to the Rutherford cross‐section. 

By convention the angular distribution is  measured in the flattened variable χ.

*where η is the pseudorapidity of the two leading jets

Search for excess events at large anglesSearch for excess events at large angles

The discovery of The discovery of partonspartons inside protons was also signalled by inside protons was also signalled by extra events at large angles in deepextra events at large angles in deep--inelastic electron scattering.inelastic electron scattering.

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DijetsDijets from quark contact interactionsfrom quark contact interactionsContact interaction terms may be used to model the Contact interaction terms may be used to model the onsetonset of of kinematic properties that would characterize quark kinematic properties that would characterize quark compositeness.  The model compositeness.  The model LagrangianLagrangian in this study is the in this study is the 1984/85 EHLQ four1984/85 EHLQ four‐‐fermionfermion contact interaction using the single contact interaction using the single isoscalarisoscalar term:term:

The effects of the contact interaction would be expected to The effects of the contact interaction would be expected to appear at or below the characteristic energy scale appear at or below the characteristic energy scale Λ. Λ. Above this Above this scale this scale this LagrangianLagrangian is unphysical since it does not contain a is unphysical since it does not contain a description of description of preonpreon dynamics.   The coupling strength is assumed dynamics.   The coupling strength is assumed to be to be gg22/4/4ππ = 1. = 1. The parameter The parameter ηη may be set for constructive or may be set for constructive or destructive interference, with light quark QCD terms.  This modedestructive interference, with light quark QCD terms.  This model l is available in the is available in the PythiaPythia event generator.  event generator.  This term by itself This term by itself would be relatively isotropic, but it must be simulated with QCDwould be relatively isotropic, but it must be simulated with QCD..

Lq

Lq

Lq

Lq

qqqqq

gL ΨΨΨΨΛ

=Λ μμ γγη

2

2

2)(

M. Shupe, ATLAS Collaboration, APS Four Corners Section MeetingM. Shupe, ATLAS Collaboration, APS Four Corners Section Meeting 3636

•mjj > 1.0 TeV•Pseudorapidity of leading and next to leading jet plotted•Left: QCD cross-section•Right: QCD + contact interactions (CI) with a Λ of 1.5 TeV(example)

QCD QCD+CI

Simulation study of the Simulation study of the ηη11 vsvs ηη22 dijetdijet distributions: distributions: QCD QCD w/wow/wo contact interactions contact interactions

M. Shupe, ATLAS Collaboration, APS Four Corners Section MeetingM. Shupe, ATLAS Collaboration, APS Four Corners Section Meeting 3737

Simulation of compositeness signal in Simulation of compositeness signal in dijetsdijets

10/22/2011 37

QCD prediction of dijet angular distribution (light pink) compared to angular distributions Considering different compositeness scales in ATLAS. 

χ cut = 2.7

Large angle scattering corresponds to low values of χ

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Search for quark contact interactions in Search for quark contact interactions in dijetdijet angular angular spectra using a 36 pbspectra using a 36 pb--11 ATLAS data set from 2010.ATLAS data set from 2010.

““Search for New Physics in Dijet Mass and Angular Distributions iSearch for New Physics in Dijet Mass and Angular Distributions in pp Collisions at n pp Collisions at sqrt(ssqrt(s) = 7 ) = 7 TeVTeV Measured with the ATLAS DetectorMeasured with the ATLAS Detector””, The ATLAS Collaboration, , The ATLAS Collaboration, New J. Phys. 13 (2011) 053044 (20 Mar 2011)New J. Phys. 13 (2011) 053044 (20 Mar 2011)

QCD prediction determined PYTHIA with NLOJET++ kQCD prediction determined PYTHIA with NLOJET++ k--factors. All distributions in factors. All distributions in agreement with QCD (Bayesian analysis). Exclusion limits at 95%agreement with QCD (Bayesian analysis). Exclusion limits at 95% CL are set for CL are set for quark quark contact interactions below 6.8 contact interactions below 6.8 TeVTeV, using , using newnew FFχχ analysis (at right), and analysis (at right), and 6.6 6.6 TeVTeV using using traditional traditional χχ distributions (at left). (Many other limits set in this paper.distributions (at left). (Many other limits set in this paper.))

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ATLAS has now accumulated 5 fbATLAS has now accumulated 5 fb--11 –– a big jump over the a big jump over the 36 pb36 pb--1 1 in 2010! Why is the analysis taking longer?in 2010! Why is the analysis taking longer?

*** T*** The statistical errors in the angular distributions are he statistical errors in the angular distributions are approaching the level of the experimental and theoretical approaching the level of the experimental and theoretical uncertainties in our analysis. ***uncertainties in our analysis. ***

The dominant experimental systematic, the jet energy The dominant experimental systematic, the jet energy scale uncertainty, is currently in the 3%scale uncertainty, is currently in the 3%--4% range. It will 4% range. It will need to be improved with inneed to be improved with in--situ calibration. Our situ calibration. Our dijetdijetmeasurements use the highest measurements use the highest pTpT jets, where there are jets, where there are few events available for calibration. few events available for calibration.

As noted earlier, the QCD prediction in angular analyses As noted earlier, the QCD prediction in angular analyses involves Monte Carlo event generation using involves Monte Carlo event generation using PythiaPythia with with various choices of various choices of PDFPDF’’ss, and requires correction to NLO. , and requires correction to NLO. In addition to PDF error sets, uncertainties due to In addition to PDF error sets, uncertainties due to renormalization and factorization scales are present. renormalization and factorization scales are present.

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Arizona:Arizona: F. F. RuehrRuehr ((postdocpostdoc, convenor of the ATLAS , convenor of the ATLAS Jet+XJet+X group), M. group), M. ShupeShupe

Toronto:Toronto: P.P.--0. 0. DeviveirosDeviveiros, P. , P. SavardSavard, P. , P. SinervoSinervo, A. , A. Warburton, A. GibsonWarburton, A. Gibson

Oxford:Oxford: N. N. BoehlaertBoehlaert, R. Buckingham, C. , R. Buckingham, C. IsseverIssever

Chicago:Chicago: G. G. ChoudalakisChoudalakis

Joined analyses in progressJoined analyses in progress: T. : T. DietschDietsch, E. , E. ErtelErtel

(Some are now at different institutions.)(Some are now at different institutions.)

Major contributors to these analyses and papersMajor contributors to these analyses and papers

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ATLAS Limits as of LeptonATLAS Limits as of Lepton--Photon 2011:Photon 2011:

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CONCLUSIONCONCLUSION

ATLAS, and CMS, have made great strides in 2010 and ATLAS, and CMS, have made great strides in 2010 and 2011 in pushing to higher energies and shorter distance 2011 in pushing to higher energies and shorter distance scales at the LHC. scales at the LHC.

No new physics has been seen yet, and we are eager to No new physics has been seen yet, and we are eager to analyze the full 2011 data set.analyze the full 2011 data set.

Data in 2011 are beginning to pose the challenge that Data in 2011 are beginning to pose the challenge that experimental and theoretical uncertainties will need to be experimental and theoretical uncertainties will need to be reduced.reduced.

This will continue to be a problem in 2012, but if the This will continue to be a problem in 2012, but if the energy is raised to 8 energy is raised to 8 TeVTeV or 9 or 9 TeVTeV, some theoretical , some theoretical uncertainties may get smaller (further from low x.)uncertainties may get smaller (further from low x.)

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Backup Slides

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Dijet Kinematic AnalysisDijet Kinematic Analysis