Detecting Searching for Quark Compositeness at the LHC Particles Michael Shupe Department of Physics, University of Arizona APS Four Corners Section Meeting, October 21-22, 2011 M. Shupe, ATLAS Collaboration, APS Four Corners Section Meeting 1
Are quarks the most fundamental particles, or are they composed of smaller particles? Organization of this talk: Nature s s known structural hierarchies. How collisions give access to short distances. Fantasy: a quark collider. Fact: the Large Hadron Collider. The ATLAS Experiment. The search for quark compositeness in ATLAS, and the most recent results that we have published. M. Shupe, ATLAS Collaboration, APS Four Corners Section Meeting 2
The underlying patterns of matter 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
From Why we call Atoms, quarks and to leptons Nucleons, the building blocks to Quarks 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 build the periodic table of the elements are protons, neutrons, and electrons! (Plus photons and gluons!) What else can we make from the six quarks? Thousands of other not-so-stable particles! M. Shupe, ATLAS Collaboration, APS Four Corners Section Meeting 4
Particle multiplets: periodic tables of the strongly interacting particles. Neutron Proton Spin1/2 Spin 3/2 M. Shupe, ATLAS Collaboration, APS Four Corners Section Meeting 5
The fundamental building blocks in nature, and the interactions among them. Electromagnetic Force Strong (Nuclear) Force Weak Force (Changes particle types) Gravity (Gravitons?) M. Shupe, ATLAS Collaboration, APS Four Corners Section Meeting 6
Easy way to picture particle 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 7
Composite models date from the late 1970 s 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
The Status of Preon Models 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 angle scatters in excess of QCD. (More below.) M. Shupe, ATLAS Collaboration, APS Four Corners Section Meeting 9
Distances: Atoms, to Nucleons, to Quarks M. Shupe, ATLAS Collaboration, APS Four Corners Section Meeting 10
Direct route to shortest distance scales? It s s all in the momentum! The de Broglie equation: λ = h/p M. Shupe, ATLAS Collaboration, APS Four Corners Section Meeting 11
Fantasy Machine: A 7 TeV Quark Collider Quark Detector q 1 Quark Beam 1 3.5 TeV q 1 g BRbar θ Quark Beam 2 3.5 TeV q 2 q 2 Quark Detector 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 Meeting 12
Reality: the LHC 7 TeV Proton-Proton Collider 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( PDF s). Outgoing quarks, or gluons, barely escape the protons before they y cascade in to more quarks and gluons (a parton shower). And this is just the start! M. Shupe, ATLAS Collaboration, APS Four Corners Section Meeting 13
Factorization makes this calculable. 1P q(x 1 ) xp 11 Hard Scattering Process D q π 0 ( z) ŝ Parton Jets 2P g(x 2 ) xp 22 σˆqg qg X M. Shupe, ATLAS Collaboration, APS Four Corners Section Meeting 14
What s s in a proton? Parton distribution functions: For two-jet (dijet( dijet) events, the jets do not emerge from the collision back-to 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 2-2 parton rest frame. M. Shupe, ATLAS Collaboration, APS Four Corners Section Meeting 15
Higher orders are a challenge. M. Shupe, ATLAS Collaboration, APS Four Corners Section Meeting 16
Experimentalists view: Data Collected HERE. Particles leave tracks or particle showers in detector Encountering the detector. Particles form as quarks coalesce (hadronize( 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
Magnets in the LHC Tunnel M. Shupe, ATLAS Collaboration, APS Four Corners Section Meeting 19
ATLAS, In Its Underground Cavern M. Shupe, ATLAS Collaboration, APS Four Corners Section Meeting 20
Arizona created the ATLAS Integrated FCal concept Muon: Air Core Toroids Tracking Calorimeters Integrated Forward Calorimeters Massive Forward Radiation Shield (~700 Metric Tonnes) Forward Muons M. Shupe, ATLAS Collaboration, APS Four Corners Section Meeting 21
The University of Arizona Team 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( 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
The Arizona group also works in the muon system CSC (Cathode Strip Chambers) CSCs M. Shupe, ATLAS Collaboration, APS Four Corners Section Meeting 25
ATLAS - 2005 M. Shupe, ATLAS Collaboration, APS Four Corners Section Meeting 26
ATLAS - 2007 M. Shupe, ATLAS Collaboration, APS Four Corners Section Meeting 27
CSC Chambers M. Shupe, ATLAS Collaboration, APS Four Corners Section Meeting 28
Prelude to analysis: Simulation! (Dijet 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
How are dijet events used to search for quark compositeness? Search for excited quarks appearing as resonances in the dijet mass spectrum, and Search for excess events at large angles resulting from the interaction of quark 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 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
Search for excess events at large angles Relationship to Rutherford scattering 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 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 34
Dijets from quark contact interactions Contact interaction terms may be used to model the onset of kinematic properties that would characterize quark compositeness. The model Lagrangian in this study is the 1984/85 EHLQ four fermion fermion contact interaction using the single isoscalar term: 2 ηg L μ L L L Lqqqq ( Λ) = Ψq γ Ψq Ψq γ μ Ψ 2 q 2Λ 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 g 2 /4π = 1. The parameter η 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. q M. Shupe, ATLAS Collaboration, APS Four Corners Section Meeting 35
Simulation study of the η 1 vs η 2 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
Simulation of compositeness signal in dijets 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 37
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. k 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 T 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
CONCLUSION ATLAS, and CMS, have made great strides in 2010 and 2011 in pushing to higher energies and shorter distance scales at the LHC. No new physics has been seen yet, and we are eager to analyze the full 2011 data set. Data in 2011 are beginning to pose the challenge that experimental and theoretical uncertainties will need to be reduced. This 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
Dijet Kinematic Analysis M. Shupe, ATLAS Collaboration, APS Four Corners Section Meeting 44