02/21/2003Physics at DZERO1 Exploring the Microscopic Structure of the University with DZero??

02/21/2003Physics at DZERO2 Exploring the Microscopic Structure of the Universe with DZero Jerry Blazey Northern Illinois University

02/21/2003Physics at DZERO3 The Standard Model Simple: “Bits of matter stick together by exchanging stuff.” The crowning achievement of particle physics is a model that describes all particles and particle interactions. The model includes: –6 quarks (those little fellows in the nucleus) and their antiparticles. –6 leptons (of which the electron is an example) and their antiparticles –4 force carrier particles More Precise: “All known matter is composed of composites of quarks and leptons which interact by exchanging force carriers.”

02/21/2003Physics at DZERO4 The Quarks* Three pairs of quarks. The up and down are the constituents of protons (= uud) and neutrons (= udd), and make up most matter. The other particles are produced in energetic subatomic collisions from cosmic rays or in accelerators, where they are also studied. *The name comes from James’s Joyce’s Finnegan’s Wake, “Three quarks for Muster Mark!”

02/21/2003Physics at DZERO5 Leptons* Leptons are generally lighter particles and are most commonly observed in radioactive decays. The best example is neutron decay into a proton, an electron, and a neutrino: *Greek for “small mass”

02/21/2003Physics at DZERO6 Periodic Table of Fundamental Particles All point-like (down to m) spin-1/2 Fermions Families reflect increasing mass and a theoretical organization u, d,, e are “normal matter” These all interact by exchanging spin 1 bosons… -1 +2/3 - 1/3 0 Mass 

02/21/2003Physics at DZERO7 SM Interactions Electroweak interaction –Photons, W, and Z: all spin-1 bosons Strong interaction (QCD) –Gluons: all spin-1 bosons Three lepton generations (e, , , ’s) –feel electroweak interaction only Three quark generations (u,d,s,c,t,b) –feel electroweak, strong interactions

02/21/2003Physics at DZERO8 We could stop here but….. Explained by Standard Model weaker than EM, not explained

02/21/2003Physics at DZERO9 Two Compelling Unsolved Questions (there are many others) How do particles get mass? How does gravity fit into all of this?

02/21/2003Physics at DZERO10 The Higgs Particle The electroweak unification postulates the existence of the Higgs field. (Named after a Scottish physicist who first hypothesized its existence.) This field interacts with all other particles to impart mass - think of walking through molasses. The Higgs field is a microscopic property of space-time, but at least one real particle will result. The experimental program at Fermilab, the Large Hadron Collider in Europe, and the next Linear Collider are dedicated, in part, to the search for this particle. It’s discovery would be an achievement of the highest order - an understanding of the origins of mass!

02/21/2003Physics at DZERO11 Beyond That? Even with the Higgs, the Standard Model requires fine tuning of parameters to avoid infinite Higgs masses from quantum corrections – the theory is “ugly.” Leads to strong belief that the SM is merely a low energy or effective theory valid up to some scale, where additional physics will appear. Most popular theoretical option: Supersymmetry or SUSY.

02/21/2003Physics at DZERO12 SUSY In SUSY every particle and force carrier has a massive partner: Squarks, slectrons, gluinos… Since they are massive they’ve not been produced in current machines. The discovery requires more energetic accelerators – something which is being enthusiastically pursued.

02/21/2003Physics at DZERO13 Or…Extra Dimensions!? Amazingly enough an 11 dimensional world (time, 3-D & 7 very small less than 1mm in size) can accommodate a theory with all four forces. Only gravity can communicate with/to other dimensions, it’s “strength” is diluted in ours. That is, the graviton, or gravity carrier can spread it’s influence among all 10 spatial dimensions. Experiments are underway searching for signals of these dimensions. The “other” dimensions “Our World” q graviton

02/21/2003Physics at DZERO14 How do we test these theories?

02/21/2003Physics at DZERO15 The Two Basic Ideas: –Find a source of particles with high kinetic energy. –Study the debris resulting from collisions inside detectors. The Sources: –Cosmic Rays –Accelerators –The higher the energy the more numerous the number and types of particles. The Detectors: –A series of special purpose devices that track and identify collision products p pp

02/21/2003Physics at DZERO16 Fermilab Proton-Antiproton Collider Main Injector & Recycler Tevatron Booster pp p DØ  p source Batavia, Illinois Chicago 1)Hydrogen Bottle 2)Linear Accelerator 3)Booster 4)Main/Injector 5)Tevatron You are here

02/21/2003Physics at DZERO17 Physics Goals of a Detector Precise study of the known quanta of the Standard Model Weak bosons, top quark, QCD, b-quark Search for particles and forces beyond those known Higgs, supersymmetry, extra dimensions, other new phenomena Driven by these goals, A detector emphasizes –Electron, muon and tau identification –Jets (q and g) and missing transverse energy –Flavor tagging through displaced vertices and leptons

02/21/2003Physics at DZERO18 A Schematic detector Hadronic layers Tracking system Magnetized volume Calorimeter Induces shower in dense material Innermost tracking layers use silicon Muon detector Interaction point Absorber material Bend angle  momentum Electron Experimental signature of a quark or gluon Muon Jet: q or g “Missing transverse energy” Signature of a non-interacting (or weakly interacting) particle like a neutrino EM layers fine sampling p pp

02/21/2003Physics at DZERO19 A Real Detector: D0 muon system electronics Proposed 1982 First Data: TeV Upgrade: Run II: TeV

02/21/2003Physics at DZERO20 Any resemblance between DZero and the Borg Home ship is purely a coincidence.

02/21/2003Physics at DZERO21 Calorimeters Tracker Muon System Beamline Shielding Electronics protons antiprotons 20 m

02/21/2003Physics at DZERO22 International 18 countries 77 institutions 650+ physicists

02/21/2003Physics at DZERO23 Run I (1992-6) Results 140+ reviewed articles –Discovery of the top quark –Precision measurements of particle masses and cross sections –Limits on new physics 100/year presentations 100+ Ph.D./Master’s Students each with an separate data stream, topic, and analysis

02/21/2003Physics at DZERO24 About the Detector: Silicon Microstrip Tracker 1M Channels Four barrel layers Axial and stereo layers Disks for Forward/Backward Coverage

02/21/2003Physics at DZERO25 Scintillating Fiber Tracker 100k Channels in eight layers Scintillating Fiber Clear Fiber Solid State Visible Light Photon Counters at 9 Kelvin

02/21/2003Physics at DZERO26 Fiber Tracker Readout Readout under detector Photoelectron peaks 1 pe ~ 7 fC

02/21/2003Physics at DZERO27 Liquid Argon Calorimeter Z y x   p p Highest E T jet event in Run 1 50k Channels Liquid argon sampling with Ur absorber

02/21/2003Physics at DZERO28 Muon System Connect tracks J/  +-J/  +- scintillator Match to CFT tracks  = 83 MeV Resolutions ~ 20% better in MC than data shielding

02/21/2003Physics at DZERO29 Run II: 24/7 Event Collection Proton-antiprotons collide at 7MHz or seven million times per second Tiered electronics pick successively more interesting events –Level 1 10 kHz –Level 2 1 kHz About 100 crates of electronics readout the detectors and send data to a Level 3 farm of 100 CPUs that reconstruct the data Per second: 50 events or 300 Mbytes of data to tape. Per year: 10 million events or 30 Terabytes of data.

02/21/2003Physics at DZERO30 Physics: Event Analysis Events are “reconstructed” offline by farms of ~100 CPUs. Each detector samples position, energy, or momentum, 1M+ channels Then computers build or reconstruct full event characteristics based upon these samples Interesting events or signals are culled from the background usually 100’s out of millions.

02/21/2003Physics at DZERO31 Sample Run II Event: Z  e + e - p p Z q q’ l l

02/21/2003Physics at DZERO32 Sample Distributions: Z  e + e - 1) Collect events 2) Calculate mass for each event 3) Plot distributions 4) Statistically measure mass or production rate as a function of brightness or luminosity (1pb -1 means 1 event of cross section 1 pb will be produced.) 5) Test predictions of Standard Model

02/21/2003Physics at DZERO33 Prospects for W mass and width Current knowledge of m W : DØ: ±.084 GeV World: ±.033 MeV Run II prospects for  m W 2 fb -1 ±27 MeV 15 fb -1 ±15 MeV To improve measurements will require ~ fb -1 datasets or several years of Tevatron running. p p W q q’ e

02/21/2003Physics at DZERO34 Top Mass Measurement Discovered at Tevatron in 1995 Expected top mass accuracy by the end of Run II : ~ 1.4 GeV

02/21/2003Physics at DZERO35 W and Top Measurements Indirectly constrain mass of The Higgs Top quark mass (GeV) W mass (GeV) 2001 m t  2 GeV m W  15 MeV Standard Model Supersymmetry

02/21/2003Physics at DZERO GeV193 GeV Past Searches for the Higgs Over the last decade, experiments at the CERN e + e – collider ( European Laboratory for Particle Physics) have been searching for the Higgs –direct searches for Higgs production exclude m H < 114 GeV. –precision measurements of parameters of the W and Z bosons, combined with Fermilab’s Run I top quark mass measurements, set an upper limit of m H ~ 193 GeV.

02/21/2003Physics at DZERO37 Higgs Hunting at the Tevatron For any given Higgs mass, the production cross section, decays are calculable within the Standard Model Inclusive Higgs cross section ~ 1pb A good search bet below ~ 140 GeV is associated production with W or Z –e or  decays of W/Z help give the needed background rejection –cross section ~ 0.2 pb p p W* q q’ H W

02/21/2003Physics at DZERO38 “The Tevatron’s a Good Bet!” “We find it or eliminate it” 15 fb GeV Combined Channel/Experiments Higgs Mass Reach

02/21/2003Physics at DZERO39 Well actually… there’s at least one Higgs!

02/21/2003Physics at DZERO40 Supersymmetry Postulates a symmetry between bosons and fermions such that all the presently observed particles have new, more massive super-partners (SUSY is a broken symmetry) Theoretically attractive: –additional particles cancel divergences in m H –SUSY closely approximates the standard model at low energies –allows unification of forces at much higher energies –provides a path to the incorporation of gravity and string theory: Local Supersymmetry = Supergravity –lightest stable particle cosmic dark matter candidate masses depend on unknown parameters, but expected to be 100 GeV - 1 TeV

02/21/2003Physics at DZERO41 Supersymmetry signatures Squarks and gluinos are the most copiously produced SUSY particles As long as the associated new quantum number “R-parity” is conserved, cannot decay to normal particles Missing transverse energy from escaping (lightest supersymmetric particle or LSP) Possible decay chains always end in the LSP: Which leaves missing Transverse Energy in the Detector Search region typically > 75 GeV

02/21/2003Physics at DZERO42 Past Searches at the Tevatron In Run I DØ carried out extensive searches for SUSY –Squarks/gluinos  Missing E T + jets (+ lepton(s)) –Charginos/neutralinos  multileptons –GMSB  Missing E T +photon(s) Searches for other new phenomena –leptoquarks, dijet resonances, W’,Z’, massive stable particles, extra dimensions... Now sign of new physics: DØ analysed 32 final states containing electrons, muons, photons, jets, W’s, Z’s and missing E T Find an 89% CL for agreement with the Standard Model (PRD ) Run II prospect: gluino mass ~ 400 GeV Run I excluded

02/21/2003Physics at DZERO43 Searches for Extra Dimensions Standard Model Extra Dimensions DATA Instrumental background (from data) Extra Dimensions Run II limits from  pp  ee, ,  M S (GRW) > 0.92 TeV (ee/  ) M S (GRW) > 0.50 TeV (  ) (first limit from a hadron collider in this channel) less than 1 mm depending on the number of extra dimensions. p G q q   p

02/21/2003Physics at DZERO44 New York Times

02/21/2003Physics at DZERO45 Closing Comments: Prospects Over the next several years DZero and the Tevatron will explore the microscopic universe: –Constrain the SM and place limits on the Higgs mass or –Discover the Higgs, and perhaps –Discover new physics, extra dimensions…. It is an exciting, challenging program that asks two of the most fundamental questions: –What is the structure of the universe? –What is the history of the universe? “To the Microscopic Universe…. and beyond!”

02/21/2003Physics at DZERO46 Now (15 billion yrs) Stars form (1 billion yrs) Atoms form (300,000 yrs) Nuclei form (180 seconds) Protons and neutrons ( s) Quarks differentiate ( s ) Fermilab 4× seconds