Arizona at the Large Hadron Collider: the ATLAS Detector, the Particle Zoo, the Higgs Boson, and the Search for New Phenomena.

OLLI Presentation. October 24, 2014. Michael Shupe, Professor Department of Physics The University of Arizona At least 156 billion light years Physics Lets Us Touch The Universe At All Scales zoom 10,000,000,000 Astrophysics Biophysics zoom 100,000 more Condensed Matter Physics Atomic, Molecular, and Optical (AMO) At least 1000 Nuclear Physics more High Energy Physics

“Inner space” is as “empty” as outer space. But the vacuum is filled with dancing quanta! High Energy Physics Research focused on the fundamental building blocks in nature, and the interactions among them.

Electromagnetic Force Strong (Nuclear) Force Weak Force (Changes particle types) Gravity (Gravitons?) The Higgs Boson How do we “see” new phenomena at this level? By studying the debris from head-on collisions between particles. Shown below are proton-antiproton collisions leading to the production of top (t) quark pairs. This was used at Fermilab, west of Chicago, to discover the top quark in 1995. Arizona was there! -

Arizona’s Impact on the Design and Construction of the ATLAS Detector at the Large Hadron Collider Arizona HEP Faculty Members

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John Rutherfoord Michael Shupe Ken Johns

Elliott Cheu Erich Varnes The University of Arizona Team

Faculty

Research Associates & Staff

Graduate Students 7 This is the Full Experimental High Energy Physics Group at The University of Arizona

Faculty Graduate Students John Rutherfoord ATLAS Jeff Temple D0 Michael Shupe ATLAS Bryan Gmyrek D0 Kenneth Johns D0/ATLAS Susan Burke D0 Elliott Cheu D0/ATLAS Xiaowen Lei ATLAS Erich Varnes D0/ATLAS Caleb Parnel-Lampen ATLAS Research Scientists Walter Freeman ATLAS Peter Loch ATLAS Technical Sasha Savine ATLAS Charlie Armijo D0 Postdoctoral Gabe Facini ATLAS Stefan Anderson D0 Anna Malin D0 Peter Tamburello D0 Robert Walker ATLAS Jessica Leveque D0 Secretary Walter Lampl ATLAS Claudia Miller Engineers Leif Shaver Mech. Joel Steinberg Elect. Dan Tompkins Elect.

The size and breadth of this group has enabled us to make a substantial impact on D0 at the Fermilab Tevatron, and on ATLAS at the Large Hadron Collider.

Now for what we did. A quick virtual tour of CERN and Arizona Large Hadron Collider, CERN, Geneva, CH pp collision @ 7 TeV  14 TeV

- The ATLAS Detector at the LHC

(Proton-Proton Collisions at 14 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!

Collisions began in 2009. First big data set in 2010. Magnets in the LHC Tunnel

27 kilometer tunnel. More than 1600 magnets. ATLAS, In Its Underground Cavern The ATLAS Detector: ~$1.5B – “World’s Largest Experiment”

Tracking Calorimeters Muon: Air Core Toroids

Integrated Forward Calorimeters ($16M) Massive Forward Radiation Shield (~700 Metric Tonnes) 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. Our research group, constructing the ATLAS Integrated Forward Calorimeter in a clean room in the basement of the Physics building. Arizona conceived, engineered and supervised this $16M project for ATLAS. Some of our research group, at CERN, during the installation of the ATLAS Integrated Forward Calorimeter ATLAS - 2005 ATLAS - 2007 ATLAS - 2007 CSC Chambers

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The structure of matter, and the “Zoo” of Particles That We Know About Today 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 electric force + “nuclear glue”.

21 ATOMS  NUCLEI  NUCLEONS  QUARKS

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! not-so-stable particles! (Plus photons and gluons!) 22 Distance Scales: From Atoms, to Nucleons, to Quarks

23 By the late 1970’s, hundreds of new particles had been detected, and more quarks had been Spin1/2 found: u,d,s,c,b. Neutron Proton

Spin 3/2

24 The Fundamental Particles We Know at Present

Six quarks (and antiquarks), six leptons (and antileptons), four force-carrying particles.

Electromagnetic Force Strong (Nuclear) Force Weak Force (Changes particle types) Gravity (Gravitons?)  The Higgs Boson Particle Mass Ratios, With “Zoo” Comparisons

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The Beginnings of Quantum Mechanics (particles  waves), and Why We Talk About “Particles” and “Fields” The Beginnings of Quantum Mechanics 1900: Max Planck discovers that electromagnetic waves deliver their energy in “bundles”, E = hf Planck’s constant: h  6.6260693(11) 1034 J s

1905: Albert Einstein claims that these waves are composed of particles, “photons” (), each of energy E = hf, explaining the photoelectric effect.

1924: Louis de Broglie suggests 1927: that particles, such as the Davisson- electron, are also waves of Germer wavelength  = h/p  p = h/ experiment says yes! Waves are particles, and particles are waves. They are really all “quanta”, with energy E = hf and momentum p = h/ A given type of particle has “additional” properties: spin, mass, electric charge, weak charge, strong charge, parity, etc. (Photons are mass-less particles with spin 1.) “Nature forces us to the conclusion that quanta are real, but offers no additional ‘guidance’ to help us create a mental picture of how quanta act as both waves and particles. The best we can do currently is to label this two-sided behavior as ‘wave particle duality’. Quantum mechanics still fascinates and mystifies the people who work most closely with it.” (Richard Feynman) What is a “Field”?

* Each force has a “carrier” particle,- and these carriers can be emitted or absorbed by particles with the right type of charge.

* We have seen these “charges” in previous slides. Photons carry the electromagnetic force, and interact with particles that have electric charge (+ or -). Gluons carry the strong force and interact with particles with strong charge (R,G,B,or the “anticolors”). The heavy bosons W+, W-, and Z0, carry the weak force and interact with particles that have weak charge.

* Photons are neutral, and cannot interact with other photons, but gluons can interact with other gluons, and the W’s and Z can interact among themselves.

* Electromagnetic force fields can extend to infinity, strong force fields are self containing with the size scale of a proton, and weak interactions are very short ranged. Sketch of an electric field caused by three electric charges.

The lines show the directions- of the field, and the field is strongest where the lines are densely packed together. Feynman Diagrams: the Horizontal Lines are Field Carriers A “simple” strong interaction between a neutron and proton: A u-quark is exchanged, and a d-quark pair pops out of the vacuum. Later, a d-quark pair annihilates. At every step, gluons are holding the proton and neutron together. In the end, the n and p have swapped identities! Just another day at the office… Superficially, strong interaction fields carried by gluons (below), look a bit like electric fields carried by photons (right), especially at short range.

But since gluons interact with each other, as quarks are driven apart, the gluon field pulls together into a “string” (aka “flux tube”). When the energy in the string get high enough, it breaks, and new quarks are created! Particles interact through the exchange of “field quanta” such as photons (if they have electric charge). The interactions can be represented by Feynman diagrams, which are then translated into mathematical expressions (“Lagrangians”)  next slide The Standard Model Lagrangian: Quantum Field Theory quarks, leptons and their strong, quarks & leptons have mass electromagnetic and weak interactions

gauge sector

flavour sector EWSB sector

 mass sector

neutrinos have Higgs bosons … and mass too! beyond? 36 A Summary of the Interactions Among Particles/Fields - How Do We Study Quarks and Leptons, and Search for New Particles, at the LHC?

By Sifting Through the Debris of Proton-Proton Collisions. The higher the proton beam energies, the shorter the distance scale we can explore. The de Broglie equation: h/p The bigger the momentum of colliding particles, the shorter their wavelengths. Shorter quantum wavelengths improve the resolution! 39 Fantasy Machine: A Quark Collider

Quark Detector

q1

q  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

40 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’s). •Outgoing quarks, or gluons, barely escape the protons before they cascade in to more quarks and gluons (a parton shower). And this is just the start! 41 Factorization makes this calculable.

P1 0 D ( z) q(x1) q xP 11Hard Scattering Process

sˆ Parton Jets

xP22 P 2 qgqg X ) 2 g(x ˆ

42 The momentum distributions of quarks and gluons:

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.

43 Using jets to measure the energies and directions of individual quarks and gluons:

quarks jets Collision point here.

muons muons How jets form: A “jet” starts from a single high energy quark or gluon coming from the point where the protons collide.

The jet shown here has come from a gluon at the bottom. The gluon splits into two gluons, then again (on the left side of this jet). On the other side it splits into two quarks, then encounters a virtual quark-antiquark pair in the vacuum, leading to a quark and gluon.

The quarks and antiquarks start to combine into strongly interacting particles (“hadrons”): protons, neutrons, pions, … This picture shows only the beginning of a jet than in the end may produce hundreds of hadrons. 45 A theorist’s model of a realistic collision jet jet

high energy collision: HP “hard process”

the “underlying event” coming from the other quarks and gluons in the original protons 46 How the detector sees it: 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.

47 ATLAS graphics of a proton-proton collision from 2012:

Four muons. Possible Higgs event. CMS graphics of proton-proton collision, 2012, sans detector:

Two muons, two electrons. Possible Higgs event. A collision showing two well-defined jets of particles coming from the interaction point. Each jet started as a single quark or gluon. This could be a Higgs event with two jets and two electrons. A Simulated Collision- Side View:

51 End view of a collision from 2011 data producing two high momentum jets of particles.

52 An alternate way to plot a collision – an angular plot of energy seen in the detector:

without pile-up with design luminosity pile-up

53 E=mc2 determines what we can find.

E = particle energy m = particle mass c = speed of light Einstein’s equation tells us that energy and mass are interchangeable, with c (squared) being the rate of exchange. Consider colliding two protons, each with an energy of 4 TeV, head-on. In principle, all of their energy could be turned into a single particle with a mass of 8 TeV. Very heavy!!! But since most colliding quarks (or gluons) carry only a fraction of the energy of the incoming protons, the mass of X will be much less than 8 TeV. And, the new particles being created will decay to other particles very quickly, so their masses are found by measuring the energies and momenta of their decay products (such at the two e’s above). 54 -

The Discovery of the Higgs Boson by the ATLAS and CMS Experiments at the Large Hadron Collider Peter Higgs at his desk in the 1960’s. Some were skeptical …

… but enthusiasm grew …

By the mid 1990’s the Higgs boson was considered the most important new particle to search for. 57 The discovery of the Higgs boson was announced at CERN on July 24, 2012, and televised world-wide.

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The two winners of the Nobel Prize for the Higgs theory, Francois Englert (left) and Peter Higgs (right), chatting. These are more recent plots of the type shown at the Higgs discovery meeting. The Higgs particle can decay to two photons (“gammas”). But many other, “background”, processes can also produce two photons. When a collision has

enough energy to produce a Higgs particle,- the combined energy of the two photons is close to the Higgs mass. When enough Higgs have been produced, they appear as an excess “signal” (bump), above the background. ATLAS (left) and CMS (right) both see the bump very clearly, near m = 125 GeV! How Do Particles “Get Mass”?

Nothing in the universe Higgs field in the universe

Electron x x m=0.511 MeV/c2 Photon m=0 x x Top Quark x x x x M~172000 MeV/c2

• Higgs field – is present everywhere

–60 slows heavy particles down  gives them mass The Higgs boson and the Higgs field

- One of the most significant scientific discoveries of the early 21st century is surely the Higgs particle (a boson).

But it is the Higgs field that can (1) give the quarks and leptons their masses and (2) be “clumped” together to form Higgs particles.

Don Lincoln outlines an analogy (originally conceived by David Miller) that all of us can appreciate, starring a large dinner party, and a raucous group of physicists.

Ted Talk: http://ed.ted.com/lessons/the-higgs-field-explained-don-lincoln

Technical: http://www.youtube.com/watch?v=JY_F606E268 How the Higgs Field Gives Quarks and Leptons Mass

Cocktail party: Arrival of celebrity: Guests are evenly spread Guests cluster near celebrity

D. Miller / UCL Celebrity will interact with many guests: acquires mass and moves slowly across the room. (guests act like Higgs field) 62

Higgs bosons can be produced in several ways... And then, each Higgs can decay in various ways. For example:

A decay producing two photons

A decay producing an electron, a positron, and two neutrinos These graphs show the theoretical predictions for all the ways that a Higgs of a given mass can decay, and the probability for each decay. Since we now know that the mass is 125 GeV, this mass has been indicated by the vertical lines. ATLAS and CMS have tested these predictions. (Next slide.)

(This graphed is zoomed in to the first three log cycles.) Do the observed Higgs decays agree with theory? Yes!

This graph of “signal strength” compares the signal in each - of the observed decay modes with the theoretical predictions. The measured signals are the green boxes, relative to the theoretical prediction at “1”. All signals are consistent with theory when uncertainties. In the upper left-hand corner, the mass of the Higgs, averaged over the results from ATLAS and CMS, is now 125.36 GeV. Five decimal place accuracy!

Other measurements have established that the Higgs particle has spin = 0, which was also a prediction of the original theory! -

Searching for New Phenomena at the Large Hadron Collider.

Trying to push beyond the “Standard Model” of particle physics. Back to the “Fundamentals”

Six quarks (and antiquarks), six leptons (and antileptons), four force-carrying particles.

Electromagnetic Force Strong (Nuclear) Force Weak Force (Changes particle types) Gravity (Gravitons?)  The Higgs Boson Many Hypotheses are Being Ruled Out Or Pushed to Higher Masses:

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My Favorite Hypothesis for Going Beyond the Standard Model:

Since Quarks and Leptons Fit into a Table of Charges, Masses, and Generations, Are They Made of Smaller Particles? 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 similar model at the same time, and his article is published in the same journal.

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In 2012, Don Lincoln, who works at Fermilab near Chicago, and is a popularizer of physics, wrote a Scientific American cover article that describes my theory for small particles (“preons”) that might be combined to create quarks and leptons. - How are two-jet (“dijet”) events used to search for quark compositeness?

Method 1: Looking for bumps in the mass spectrum:

Search for bumps in the dijet mass spectrum at masses above the mass of the Higgs. These could be “excited quarks”, with preons vibrating and rotating within the quarks and leptons. Our data extend to masses as high as 60 times the Higgs mass! But no new bumps have been seen to date.

75 Do we see any new bumps in the dijet mass distribution? No, not yet. (The blue bumps are simulations.)

76 How are two-jet (“dijet”) events used to search for quark compositeness?

.

Method 2: Angular distributions

We also search for collisions where “excess” dijets appear at large angles, which could resulting from collisions among preons. This angular analysis approach is quite general, and led to the discovery of atomic nuclei, and later, to the discovery of quarks inside protons - as described in the upcoming slides.

77 The Discovery that Atoms Have Nuclei: Ernest Rutherford,1909-1911:

Large-angle scatters Geiger, Rutherford, Marsden 78 The Discovery that Protons Contain Quarks Stanford Linear Accelerator Center: 1967-1973 High energy electrons are directed at protons (in liquid hydrogen), and the electrons scatter at large angles.

79 As electrons passed through the protons, many of them came out at large angles, showing that there were smaller particles inside the proton (similar to Rutherford’s technique).

In this experiment, high energy electrons were needed so that the force-carrying photons (green below) had wavelengths much shorter than the diameter of the proton. The small particles inside the proton were originally called “partons”, and it took several years for physicists to realize that these were quarks!

Large-angle scatters

e + P  e + X

80 Simulation: Using Dijets to Look For Particles Inside Quarks.

If there are lots of jets scattered to large angles, they would appear here. This would indicate that there are small particles inside quarks.

QCD prediction of dijet angular distribution (light pink) compared to angular distributions, considering different compositeness scales in ATLAS. 81 10/22/2014 81 Do we see an excess of large-angle scatters? No, not yet.

82 Do we see an excess of large-angle scatters as a function of dijet mass? No, not yet.

83 The ATLAS Dijet Analysis Team 2009-2011

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

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

84 CONCLUSIONS

 ATLAS and CMS have made great strides, starting in 2010, to push particle physics to higher energies and to explore shorter distance scales. The Higgs boson has been discovered! The last particle predicted by the Standard Model has been found.  From here on, any new discoveries will lead us beyond the Standard Model. ATLAS and CMS have already ruled out the some of the most “popular” theories that predicted new particles appearing within the currently-measured range of masses. The LHC will start up again in June of next year, at roughly double the energy and double the intensity. This may lead us to the realm of new discoveries! 85