DDetectingetecting Searching for Quark Compositeness at the LHC ParticlesParticles

Michael Shupe Department of Physics, University of Arizona

APS Four CornersM. Shupe, Section ATLAS Meeting, Collaboration, October APS 21-22, 2011 Four Corners Section Meeting 1 AreAre quarksquarks thethe mostmost fundamentalfundamental particles,particles, oror areare theythey composedcomposed ofof smallersmaller particles?particles? OrganizationOrganization ofof thisthis talk:talk: ƒ NatureNature’’ss knownknown structuralstructural hierarchies.hierarchies. ƒ HowHow collisionscollisions givegive accessaccess toto shortshort distances.distances. ƒ Fantasy:Fantasy: aa quarkquark collider.collider. ƒ Fact:Fact: thethe LargeLarge HadronHadron Collider.Collider. ƒ TheThe ATLASATLAS Experiment.Experiment. ƒ TheThe searchsearch forfor quarkquark compositenesscompositeness inin ATLAS,ATLAS, andand thethe mostmost recentrecent resultsresults thatthat wewe havehave published.published.

M. Shupe, ATLAS Collaboration, APS Four Corners Section Meeting 2 TheThe underlyingunderlying patternspatterns ofof mattermatter In Chemistry, all the types of molecules we see are made from just 92 naturally occurring elements (the Periodic Table). The atoms in this table, are made of protons, neutrons, electrons + photons, for the coulomb field + “nuclear glue”.

M. Shupe, ATLAS Collaboration, APS Four Corners Section Meeting 3 FromFromWhy we callAtoms,Atoms, quarks and toto leptons Nucleons,Nucleons, the “building blocks”toto QuarksQuarks of nature.

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?

The only particles needed to What else can we build the periodic table of the make from the six elements are protons, quarks? Thousands of neutrons, and electrons! other not-so-stable (Plus photons and gluons!) particles!

M. Shupe, ATLAS Collaboration, APS Four Corners Section Meeting 4 ParticleParticle multipletsmultiplets:: ““periodicperiodic tablestables”” ofof thethe stronglystrongly interactinginteracting Spin1/2 particles.particles. Neutron Proton

Spin 3/2

M. Shupe, ATLAS Collaboration, APS Four Corners Section Meeting 5 TheThe fundamentalfundamental buildingbuilding blocksblocks inin nature,nature, andand thethe interactionsinteractions amongamong them.them.

ElectromagneticElectromagnetic ForceForce StrongStrong (Nuclear)(Nuclear) ForceForce WeakWeak ForceForce (Changes(Changes particleparticle types)types) GravityGravity (Gravitons?)(Gravitons?)

M. Shupe, ATLAS Collaboration, APS Four Corners Section Meeting 6 EasyEasy wayway toto picturepicture particleparticle masses?masses? A composite model could potentially explain the pattern of particle charges and generations, the color charge, and the Standard Model parameters such as masses and the mixing matrices.

The constituents are generically referred to as “preons”.

10/22/2011 M. Shupe, ATLAS Collaboration, APS Four Corners Section Meeting 77 Composite models date from the late 1970’s through the early 1980’s. I published this one in 1979, based on spin ½ preon doublets, one with charge e/3, and the other, neutral. Haim Harari was working on a very similar model at the same time, and his article is published in the same journal. Have preon models progressed since then? No. (See next slide.)

M. Shupe, ATLAS Collaboration, APS Four Corners Section Meeting 8 TheThe StatusStatus ofof PreonPreon ModelsModels

„ All preon models get the quantum numbers right within their domain of description (or they would not be published). Michael Peskin calls this “quantum numerology”. „ No existing preon model has a plausible description of preon-level dynamics. The fundamental problem has to do with mass scales. Limits on the compositeness scale Λ have been in the multi-TeV range for some time, corresponding to distance scales of ~10-19 m. „ The Heisenberg uncertainty principles tell us that preons confined to these distances will have momenta in the ~TeV/c range, naively leading to quark masses in the same range. „ Since the known quark masses range from a few MeV to 173 GeV, preon binding energies would need to be in the TeV range to cancel most of the kinetic energy. Is this a problem? Without a description of preon dynamics, who knows? „ So how are compositeness limits set? By assuming that quark substructure would show up initially as a “contact interaction” among the preons of colliding quarks – leading to large-angle scatters in excess of QCD. (More below.)

M. Shupe, ATLAS Collaboration, APS Four Corners Section Meeting 9 Distances:Distances: Atoms,Atoms, toto Nucleons,Nucleons, toto QuarksQuarks

M. Shupe, ATLAS Collaboration, APS Four Corners Section Meeting 10 DirectDirect routeroute toto shortestshortest distancedistance scales?scales?

ItIt’’ss allall inin thethe momentum!momentum! TheThe dede BroglieBroglie equation:equation: λλ == h/ph/p

M. Shupe, ATLAS Collaboration, APS Four Corners Section Meeting 11 FantasyFantasy Machine:Machine: AA 77 TeVTeV QuarkQuark ColliderCollider

Quark Detector

q1

q θ∗ Quark Beam 1 1 Quark Beam 2 3.5 TeV gBRbar 3.5 TeV

q2

The momentum of the “force

q2 carrying” particle (here a gluon) determines its wavelength, and the distance scale that can be probed. Quark Detector

M. Shupe, ATLAS Collaboration, APS Four Corners Section Meeting 12 Reality:Reality: thethe LHCLHC 77 TeVTeV ProtonProton--ProtonProton ColliderCollider

•Each proton is a chaotic mix of 3 “valence quarks” + other quarks + gluons. •The two that collide typically carry a small fraction of the proton momentum: parton distribution functions (PDF’s). •Outgoing quarks, or gluons, barely escape the protons before they cascade in to more quarksM. and Shupe, gluons ATLAS (a Collaboration, parton shower). APS Four And Corners this Section is just Meeting the start! 13 FactorizationFactorization makesmakes thisthis calculable.calculable.

P 0 1 Dπ (z) q(x1) q xP 11Hard Scattering Process

sˆ Parton Jets

xP22 P qg→qg 2 σˆ X g(x2)

M. Shupe, ATLAS Collaboration, APS Four Corners Section Meeting 14 WhatWhat’’ss inin aa proton?proton? PartonParton distributiondistribution functions:functions:

For two-jet (dijet) events, the jets do not emerge from the collision back-to- back in the longitudinal direction! To access the information about the original collision, we rely on kinematics to “undo” the effects of the Lorentz boost, and study the collision in the 2- parton rest frame.

M. Shupe, ATLAS Collaboration, APS Four Corners Section Meeting 15 HigherHigher ordersorders areare aa challenge.challenge.

M. Shupe, ATLAS Collaboration, APS Four Corners Section Meeting 16 ExperimentalistsExperimentalists view:view: Data Collected HERE. Particles leave tracks or particle showers in detector Encountering the detector.

Particles form as quarks coalesce (hadronize).

Near the original interaction!!!

Partons shower (jets).

Incoming quarks collide.

M. Shupe, ATLAS Collaboration, APS Four Corners Section Meeting 17 The Large Hadron Collider (LHC), near Geneva, Switzerland, is the “Hubble Telescope” of High Energy Physics

(Proton-Proton Collisions at 7 TeV)

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!

M. Shupe, ATLAS Collaboration, APS Four Corners Section Meeting 18 MagnetsMagnets inin thethe LHCLHC TunnelTunnel

M. Shupe, ATLAS Collaboration, APS Four Corners Section Meeting 19 ATLAS,ATLAS, InIn ItsIts UndergroundUnderground CavernCavern

M. Shupe, ATLAS Collaboration, APS Four Corners Section Meeting 20 ArizonaArizona createdcreated thethe ATLASATLAS IntegratedIntegrated FCalFCal conceptconcept

Tracking Calorimeters Muon: Air Core Toroids

Forward Muons

Integrated Forward Calorimeters Massive Forward Radiation Shield (~700 Metric Tonnes)

M. Shupe, ATLAS Collaboration, APS Four Corners Section Meeting 21 TheThe UniversityUniversity ofof ArizonaArizona TeamTeam

Faculty

Research Associates & Staff

M. Shupe, ATLAS Collaboration, APS Four Corners Section Meeting 22 Our research group constructed the EM modules of the ATLAS Forward Calorimeter (FCal) in a clean room in the basement of the Physics building. The hadronic modules were constructed by Canadian and Russian collaborators.

M. Shupe, ATLAS Collaboration, APS Four Corners Section Meeting 23 Some of our research group, at CERN, during the installation of the ATLAS Forward Calorimeter

M. Shupe, ATLAS Collaboration, APS Four Corners Section Meeting 24 TheThe ArizonaArizona groupgroup alsoalso worksworks inin thethe muonmuon systemsystem CSCCSC (Cathode(Cathode StripStrip Chambers)Chambers)

CSCs

M. Shupe, ATLAS Collaboration, APS Four Corners Section Meeting 25 ATLASATLAS -- 20052005

M. Shupe, ATLAS Collaboration, APS Four Corners Section Meeting 26 ATLASATLAS -- 20072007

M. Shupe, ATLAS Collaboration, APS Four Corners Section Meeting 27 CSCCSC ChambersChambers

M. Shupe, ATLAS Collaboration, APS Four Corners Section Meeting 28 PreludePrelude toto analysis:analysis: Simulation!Simulation! (Dijet(Dijet events.)events.)

without pile-up with design luminosity pile-up

M. Shupe, ATLAS Collaboration, APS Four Corners Section Meeting 29 ANOTHER SIMULATION:

M. Shupe, ATLAS Collaboration, APS Four Corners Section Meeting 30 Data, 2011: A collision with two high-pT jets.

M. Shupe, ATLAS Collaboration, APS Four Corners Section Meeting 31 HowHow areare dijetdijet eventsevents usedused toto searchsearch forfor quarkquark compositeness?compositeness?

ƒ SearchSearch forfor excitedexcited quarksquarks appearingappearing asas resonancesresonances inin thethe dijetdijet massmass spectrum,spectrum, andand…… ƒ SearchSearch forfor excessexcess eventsevents atat largelarge anglesangles resultingresulting fromfrom thethe interactioninteraction ofof quarkquark constituents.constituents.

M. Shupe, ATLAS Collaboration, APS Four Corners Section Meeting 32 Search for resonances due to excited quarks in the dijet mass spectrum using a 1.0 fb-1 ATLAS data set from 2011.

“Search for New Physics in the Dijet Mass Distribution using 1 fb-1 of pp Collision Data at sqrt(s) = 7 TeV collected by the ATLAS Detector'', The ATLAS Collaboration, submitted to Phys. Lett. B (31 August 2011) QCD background determined from a smooth fit to the data, then searched for resonances (BumpHunter). Most discrepant region in agreement with QCD (no bumps). Limits set on excited quarks (2.99 TeV), axigluons (3.32 TeV), and color octet scalars (1.92 TeV).

M. Shupe, ATLAS Collaboration, APS Four Corners Section Meeting 33 SearchSearch forfor excessexcess eventsevents atat largelarge anglesangles Relationship to Rutherford scattering Æ composite atoms.

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

10/22/2011 M. Shupe, ATLAS Collaboration, APS Four Corners Section Meeting 3434 DijetsDijets fromfrom quarkquark contactcontact interactionsinteractions Contact interaction terms may be used to model the onset of kinematic properties that would characterize quark compositeness. The model Lagrangianη in this study is the 1984/85 EHLQ four‐fermion contact interaction using the single μ isoscalar term: 2 γ g L L L L Lqqqq (Λ) = 2 Ψq Ψq Ψq γ μ Ψq 2Λ q The effects of the contact interaction would be expected to appear at or below the characteristic energy scale Λ. Above this scale this Lagrangian is unphysical since it does not contain a description of preon dynamics. The coupling strength is assumed to be g2/4ππ = 1. The parameter ηη may be set for constructive or destructive interference, with light quark QCD terms. This model is available in the Pythia event generator. This term by itself would be relatively isotropic, but it must be simulated with QCD. M. Shupe, ATLAS Collaboration, APS Four Corners Section Meeting 35 Simulation study of the ηη1 vs ηη2 dijet distributions: QCD w/wo contact interactions

QCD QCD+CI

•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)

M. Shupe, ATLAS Collaboration, APS Four Corners Section Meeting 36 SimulationSimulation ofof compositenesscompositeness signalsignal inin dijetsdijets

χ cut = 2.7

Large angle scattering corresponds to low values of χ

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

10/22/2011 M. Shupe, ATLAS Collaboration, APS Four Corners Section Meeting 3737 Search for quark contact interactions in dijet angular spectra using a 36 pb-1 ATLAS data set from 2010.

“Search for New Physics in Dijet Mass and Angular Distributions in pp Collisions at sqrt(s) = 7 TeV Measured with the ATLAS Detector”, The ATLAS Collaboration, New J. Phys. 13 (2011) 053044 (20 Mar 2011) QCD prediction determined PYTHIA with NLOJET++ k-factors. All distributions in agreement with QCD (Bayesian analysis). Exclusion limits at 95% CL are set for quark contact interactions below 6.8 TeV, using new Fχ analysis (at right), and 6.6 TeV using traditional χ distributions (at left). (Many other limits set in this paper.)

M. Shupe, ATLAS Collaboration, APS Four Corners Section Meeting 38 ATLAS has now accumulated 5 fb-1 – a big jump over the 36 pb-1 in 2010! Why is the analysis taking longer? *** The statistical errors in the angular distributions are approaching the level of the experimental and theoretical uncertainties in our analysis. *** The dominant experimental systematic, the jet energy scale uncertainty, is currently in the 3%-4% range. It will need to be improved with in-situ calibration. Our dijet measurements use the highest pT jets, where there are few events available for calibration. As noted earlier, the QCD prediction in angular analyses involves Monte Carlo event generation using Pythia with various choices of PDF’s, and requires correction to NLO. In addition to PDF error sets, uncertainties due to renormalization and factorization scales are present.

M. Shupe, ATLAS Collaboration, APS Four Corners Section Meeting 39 Major contributors to these analyses and papers

Arizona: F. Ruehr (postdoc, convenor of the ATLAS Jet+X group), M. Shupe

Toronto: P.-0. Deviveiros, P. Savard, P. Sinervo, A. Warburton, A. Gibson

Oxford: N. Boehlaert, R. Buckingham, C. Issever

Chicago: G. Choudalakis

Joined analyses in progress: T. Dietsch, E. Ertel

(Some are now at different institutions.)

M. Shupe, ATLAS Collaboration, APS Four Corners Section Meeting 40 ATLAS Limits as of Lepton-Photon 2011:

M. Shupe, ATLAS Collaboration, APS Four Corners Section Meeting 41 CONCLUSIONCONCLUSION

Æ ATLAS, and CMS, have made great strides in 2010 and 2011 in pushing to higher energies and shorter distance scales at the LHC. ÆNo new physics has been seen yet, and we are eager to analyze the full 2011 data set. ÆData in 2011 are beginning to pose the challenge that experimental and theoretical uncertainties will need to be reduced. ÆThis will continue to be a problem in 2012, but if the energy is raised to 8 TeV or 9 TeV, some theoretical uncertainties may get smaller (further from low x.)

M. Shupe, ATLAS Collaboration, APS Four Corners Section Meeting 42 Backup Slides

M. Shupe, ATLAS Collaboration, APS Four Corners Section Meeting 43 DijetDijet KinematicKinematic AnalysisAnalysis

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