Arnold Pompo KCHFO Seminar Prague Czech Republic April

Arnold Pompoš, KCHFO Seminar @ Prague, Czech Republic, April 20, 2004 1/47

Motivation ØCuriosity is the driving force behind our research. ØHumans always asked questions about the structure of matter. ØWhat’s the structure of the ocean, what’s the structure of a dew drop … ? ØDoes the structure ever end? Is there anything structureless ? Arnold Pompoš, KCHFO Seminar @ Prague, Czech Republic, April 20, 2004 2/47

Modern cosmology and particle physics uncovered fundamental connections between finest structure of matter largest structures of the universe time evolution of the universe Arnold Pompoš, KCHFO Seminar @ Prague, Czech Republic, April 20, 2004 3/47

Arnold Pompoš, KCHFO Seminar @ Prague, Czech Republic, April 20, 2004 4/47

Outline ØWhat is HEP Focusing on these Days ØStandard Model of Particles and Interactions ØBeyond the Standard Model ØParticle Acceleration ØParticle Detection ØGeneral Remarks on New Phenomena Searches ØSense of Scales and Probabilities in HEP ØSearch for Supersymmetry ØSearch for Extra Dimensions ØGraduate Studies in USA Arnold Pompoš, KCHFO Seminar @ Prague, Czech Republic, April 20, 2004 5/47

High Energy Physics these Days Focuses on: (4) Search new phenomena (2) (1) Electroweak Physics (3) Neutrino offor the Symmetry Oscillations Standard Breaking Model physics beyond Particles the Standard Model of Elementary and Fields Arnold Pompoš, KCHFO Seminar @ Prague, Czech Republic, April 20, 2004 6/47

The Standard Model of Particles & Interactions Strong EWK ØSM is SU(3)Cx. SU(2)Lx. U(1)Y gauge theory (Glashow, Salam, Weinberg, 1967) • Matter particles are quanta of fields with given transformation properties under gauge group transformations • Interactionν carriers are generators of gauge groups Example: e is a SU(2)L doublet & SU(3)C singlet L ØSM is the most successful theory of particles • Experiments agree with theory in 10 signif. digits! • No deviation of data from theory observed yet! () Arnold Pompoš, KCHFO Seminar @ Prague, Czech Republic, April 20, 2004 7/47

Electroweak Symmetry Breaking I. ØExact EWK symmetry massless SM particles & force carriers ØArnold = 1027 quarks and electron m(Arnold)=80 kg SM has a problem Solution: ØEWK symmetry is broken at our energy scales ØHow? Nobody knows yet! Only educated guesses exist. Arnold Pompoš, KCHFO Seminar @ Prague, Czech Republic, April 20, 2004 8/47

Electroweak Symmetry Breaking II. Ø Higgs mechanism is the most popular EWK breaking mechanism • Introduces a spin 0 Higgs field with non-zero VEV Higgs boson • Higgs field couples to matter and force fields giving rise to their masses Problem ØHiggs particle hasn’t yet been experimentally observed Solution ØWe are searching. Stay tuned! Arnold Pompoš, KCHFO Seminar @ Prague, Czech Republic, April 20, 2004 9/47

Physics Beyond the Standard Model I. ØStandard Model • Does not predict particle masses • Does not include gravity • Breaks down at high energies ØCosmology measures that only 5% of Nature’s matter is in the form of know substance Conclusion: ØBeyond the Standard Model phenomena must exist Arnold Pompoš, KCHFO Seminar @ Prague, Czech Republic, April 20, 2004 10/47

Physics Beyond the Standard Model II. ØAt what energy scale will the new physics exhibit itself? ØWe are working very hard to scan every bit of available experimental data for possible new physics ØExamples of theories of new physics • Supersymmetry • Large Extra Dimensions • Strong Dynamics Arnold Pompoš, KCHFO Seminar @ Prague, Czech Republic, April 20, 2004 11/47

Theory & Experiment Matter & Spacetime Curvature Arnold Pompoš, KCHFO Seminar @ Prague, Czech Republic, April 20, 2004 12/47

Mass [Ge. V/c 2] Standard Model Mass Scales 175 150 91. 2 80. 5 100 50 0 0. 005 1. 5 0. 01 0. 15 Quarks 5 0. 11 >0? 0. 0005 1. 8 0 Leptons 0 Force Carriers Arena of current HEP experiments is 2 Te. V (soon 14 Te. V) Very good chance for discovering the Higgs if it exists Arnold Pompoš, KCHFO Seminar @ Prague, Czech Republic, April 20, 2004 13/47

Particles Do Like to Decay Ø All goods in our stores are made of the lightest quarks (u, d) and electrons (e) Ø If a store manager tries to stock heavier quarks or leptons, W or Z bosons, they will decay away very fast t W+b Br = 100% Lifetime 10 -26 s τ (W)*ντ lνlντ where l = e, μ τ (W)*ντ q. Qντ where q, Q = u, d Br = 34% Br = 66% Lifetime 10 -15 s W lνl W q. Q where l = e, μ, τ where q, Q = u, d, s, c, b Br = 33% Br = 67% Z ll Z qq- where Br = 30% Br = 70% l = e, μ, τ, νe, νμ, ντ q = u, d, s, c, b Arnold Pompoš, KCHFO Seminar @ Prague, Czech Republic, April 20, 2004 14/47

Particle Factory ØIn order to be able to study heavy particles, we have to create them first in labs. ØThis happens by colliding lighter particles at very high energies. ØThe rest is fixed by E= mc 2: • give me enough energy, I will make you anyhing Arnold Pompoš, KCHFO Seminar @ Prague, Czech Republic, April 20, 2004 15/47

Type I. laboratory for HEP Cosmic Rays ØSource • non-reliable • out of human control ØExperiments • non-repeatable • not suited for systematic studies ØEnergy • as high as 104 Te. V Arnold Pompoš, KCHFO Seminar @ Prague, Czech Republic, April 20, 2004 16/47

Type II. laboratory for HEP Human Made Accelerators ØSource • very reliable • fully under human control ØExperiments • repeatable • well suited for systematic studies ØEnergy • currently at a Te. V scale Arnold Pompoš, KCHFO Seminar @ Prague, Czech Republic, April 20, 2004 17/47

ilab m r e F Fermilab, home of the Te. V collider n ro Tevat Ch ica c a Lin go Arnold Pompoš, KCHFO Seminar @ Prague, Czech Republic, April 20, 2004 18/47

Fermilab’s Accelerator Chain ØCockcroft-Walton 0. 000 750 Te. V ØLinac 0. 000 400 Te. V ØBooster 0. 008 Te. V ØMain Injector 0. 150 Te. V p & anti p ØTevatron 0. 980 Te. V p & anti p Arnold Pompoš, KCHFO Seminar @ Prague, Czech Republic, April 20, 2004 19/47

Tevatron Collides Protons with Antiprotons ØCenter of mass energy of the ppsystem is 1. 96 Te. V (Protons this energetic weight as much as 10 atoms of silver!) Ø The total momentum of p is carried by its quarks & gluons longitudinal momentum of q & g is unknown Proton structure - effectively means 4 processes ØColliding p & p 1. ) 2. ) 3. ) 4. ) Very different from colliding elementary leptons (CERN) Arnold Pompoš, KCHFO Seminar @ Prague, Czech Republic, April 20, 2004 20/47

Sense of Likelyness ØThe deep inelasting cross section of pp- collisions at CME = 1. 96 Te. V is 50 mb (5 x 10 -26 cm 2) ØThe cross section for producing a pair of top quarks at pp collisions is 5 pb (5 x 10 -36 cm 2 ) ØProbability to produce a tt pair in a pp- collision is thus of the order 10 -10 ØFortunately, we have about 106 deep inelastic collisions every second ØUnfortunately, we can record only a rate of 50 Hz, i. e. 0. 001% of available collisions ØFortunately, we employ selection triggers to send only events of interest for recording The rate of recording tt- pairs is not as disastrous as it seems at a first glance!! Arnold Pompoš, KCHFO Seminar @ Prague, Czech Republic, April 20, 2004 21/47

Luminosity ØLuminosity L is a measure of the amount of collided particles per time unit ØCollision rate = Cross section x Luminosity, then N = σ x ∫L dt ØCollider experiments at Fermilab collect ∫L dt = 80 pb-1 in a year. This means we collect about 400 = 5 pbx 80 pb -1 tt pairs in a year, which is about 1 each day. Arnold Pompoš, KCHFO Seminar @ Prague, Czech Republic, April 20, 2004 22/47

Collider Experiments at Fermilab Arnold Pompoš, KCHFO Seminar @ Prague, Czech Republic, April 20, 2004 23/47

CDF Experiment’s Detector ØTrackers ØCalorimeters ØMuon Chambers ØMagnet ØTriggering system Wall Had. Calorim. Centr. Had. & Em. Calorim. Central Muon Extension Forward Muon Forward Calorim. Em. Si Vertex Central Outer Tracker Plug Calorimeter (Em, Had) Solenoid Arnold Pompoš, KCHFO Seminar @ Prague, Czech Republic, April 20, 2004 Central Muon 24/47

Physics Objects in the Detector Given the structure of a collider detector, the fundamental physics objects we do physics with are: ØTracks of charged particles • reconstructed from hits in the silicon detector and the outer tracker ØElectrons • objects with EM energy, tracks and small hadronic energy ØPhotons • objects with EM energy, NO tracks and small hadronic ebergy ØMuons • objects with tracks found in muon chambers ØHadronic Jets • narow cone showers of light hadrons ØEnergy imbalance of the detector (called missing ET) • due to weakly interacting particles that escape observation • in the transverse plane to beam, the total momentum before collision is 0 Arnold Pompoš, KCHFO Seminar @ Prague, Czech Republic, April 20, 2004 25/47

Physics Groups With those few objects from the previous slide, we can do a variety of great physics: ØTop quark physics • mass and properties of top. Deals with σ = 5 pb ØBottom quark physics • mass and properties of bottom quark. Deals with σ = 106 pb ØElectroweak Physics • mass and properties of W and Z bosons. Deals with σ = 200 pb ØQCD • properties of strong interaction. Deals with σ = 109 pb ØHiggs Physics • mechanism of EWK symmetry breaking. Deals with σ = 10 pb ØNew Phenomena • searches for physics beyond the Standard Model. Deals with σ < 1 pb Arnold Pompoš, KCHFO Seminar @ Prague, Czech Republic, April 20, 2004 26/47

How to Search for New Physics - Part I. The Overall Philosophy Look for deviations in data from predictions of the SM Step by step procedure ØPick a physics model going beyond the Standard Model ØStudy what kind of signature would this model leave in the detector (Example: 3 energetic leptons) ØStudy available triggers for such signature (Example: dielectron, dimuon trigger) ØSelect data that passes these triggers Arnold Pompoš, KCHFO Seminar @ Prague, Czech Republic, April 20, 2004 27/47

How to Search for New Physics - Part II. ØStudy ALL possible Standard Model processes yielding the signature of interest (Usually done via Monte Carlo simulations) ØCompare the SM simulation results to real data and look for deviation. ØSimulate New Physics signal with Monte Carlo technique ØDefine variables distinguishing SM background from New Physics signal. ØTune selection cuts on these variables using SM and New Physics MC simulated events ØApply selection cuts to real data – THE MOST EXITING MOMENT ØArrange a trip to Stockholm Arnold Pompoš, KCHFO Seminar @ Prague, Czech Republic, April 20, 2004 28/47

Example 1 – Search for the Supersymmetric Partner of the Top Quark in Dilepton Events Phys. Rev. Lett. 90, 251801 (2003) Arnold Pompoš, KCHFO Seminar @ Prague, Czech Republic, April 20, 2004 29/47

Supersymmetry & Top’s Superpartner ØSupersymmetry • proposed new symmetry of Nature. superstring and supergravity theories) (Originated in • predicts that every SM particle has a superpartner with the same quantum numbers but spin. Spin differs by ½. ØNo superelectron with m=0. 5 Me. V & spin 0 has been observed SUSY is broken @ or above EWK scale ØMasses of superpartners are to be determined by experiment ØSUSY predicts top’s superpartner being potentially the lightest among superquarks Arnold Pompoš, KCHFO Seminar @ Prague, Czech Republic, April 20, 2004 30/47

Production of Top’s Superpartner @ Tevatron ØStops are produced via strong interaction ØStop production cross section varies 10 pb -> 1 pb as stop mass 80 -> 140 Ge. V ØData available for search ∫L dt = 100 pb-1 ØNeed a reasonable signal sample to start with (500 events) ØImplies σ > 5 pb region ØImplies m(stop) < 120 Ge. V/c 2 Arnold Pompoš, KCHFO Seminar @ Prague, Czech Republic, April 20, 2004 31/47

Decay of Interest of Top’s Superpartner ØBeing in a hadronic environment, we searched for leptonic decays of the stop quark ØSignature in the detector will therefore be: Input Parameters ØStop mass ØSneutrino mass ØStop decay branching ratio • 2 opposite charge leptons • b-quark jets • significant energy imbalance in the transverse plane of the detector due to escaping SUSY neutrinos ØEvent kinematics will depend on m(stop)-m(sneutrino) Arnold Pompoš, KCHFO Seminar @ Prague, Czech Republic, April 20, 2004 32/47

Triggers and Datasets Available triggers ØLow threshold single electron trigger ØLow threshold single muon trigger ØHigher threshold dilepton triggers Dataset Selection ØAt least 1 high quality lepton with transverse momentum > 10 Ge. V/c ØAt least 1 lower quality lepton with transverse momentum > 6 Ge. V/c ØAt least one hadronic jet with transverse energy >15 Ge. V ØAt least 15 Ge. V energy imbalance in the transverse plane Arnold Pompoš, KCHFO Seminar @ Prague, Czech Republic, April 20, 2004 33/47

Background Processes ØHeavy Flavor - - Øbb, cc σ~3 μb, 60 eve. Øtt σ~6. 8 pb, 10 eve. ØDrell-Yan Øσ. Br~230 pb, 53 eve. ØWW, WZ, WW Ø σ~12 pb, 4 eve. Arnold Pompoš, KCHFO Seminar @ Prague, Czech Republic, April 20, 2004 34/47

Comparing Background Simulation with Data ØNo deviation of data from SM processes ØAt this stage we have 160 signal plus background events but only 25 expected signal events ØNo statistical significance of signal, need signal enhancing cuts Arnold Pompoš, KCHFO Seminar @ Prague, Czech Republic, April 20, 2004 35/47

Example of a Signal Distinguishing Variable Energy Imbalance in the Transverse Plane (MET) ØBackground- Low MET ØSignal – High MET ØIf cut placed at 30 Ge. V • Background decreases by 85%, 155 ev. -> 33 ev. • Signal decreases by 35%, 23 ev. -> 13 ev. Arnold Pompoš, KCHFO Seminar @ Prague, Czech Republic, April 20, 2004 36/47

After Placing All Selection Cuts Low m(stop)-m(sneu) region High m(stop)-m(sneu) region ØExpected Standard Model background 1. 52 ± 0. 5 events ØExpected Standard Model background 2. 1 ± 0. 5 events ØExpected Stop Signal 5. 7 ± 2. 2 events ØExpected Stop Signal 8. 2 ± 3. 1 events The last remaining step of the analysis is to apply the developed selection cuts to data! Arnold Pompoš, KCHFO Seminar @ Prague, Czech Republic, April 20, 2004 37/47

Is any Supersymmetry in our Data? Phys. Rev. Lett. 90, 251801 (2003) Ø After applying all the signal selection cuts, no data events have been observed. Ø Even though this is not a ticket to Stockholm, we can set limits on stop and sneutrino masses. Ø Any stop & sneutrino mass combination predicting more then 4 events in the data is excluded with 95% confidence level. End of search. Give us more data, will explore new regions. Arnold Pompoš, KCHFO Seminar @ Prague, Czech Republic, April 20, 2004 38/47

Example 2 – Search for Large Extra Dimension Publication in preparation Arnold Pompoš, KCHFO Seminar @ Prague, Czech Republic, April 20, 2004 39/47

Extra Dimensions Already Employed? Ø What extra dimensions? Can’t you count? We have only 3+1 dimensions! OR Ø Was it the magician, D. Copperfield, who already experimentally proved the existence of extra dimensions? Extra dim 3+1 dim D. C. freeing himself from a locked box by using extra dimensions Arnold Pompoš, KCHFO Seminar @ Prague, Czech Republic, April 20, 2004 40/47

Motivation for Large Extra Dimensions - I Ø The EWK scale is ~ 1 Te. V (masses of SM particles) Ø The gravity scale is MPL = 1/√GN ~ 1016 Te. V Ø Hierarchy puzzle: Why is gravity so weak? (Need 16 orders of magnitude larger charge to get the EWK strength) Ø Proposed solution: Gravity is not weak. • gravity’s fundamental scale is 1 Te. V • gravity is diluted into many (4+n) dimensions • SM is confined to the usual 3+1 dimensions (SM particles are open strings attached to 3+1 D brane, whereas graviton is a closed string free to propagate in all (4+n) dimensions) Arnold Pompoš, KCHFO Seminar @ Prague, Czech Republic, April 20, 2004 41/47

Motivation for Large Extra Dimensions- II ØGauss’ law in n- extra dim (compactified to radius R) results in M 2 PL(4 D) ~ Rn M 2+n. PL(4+n D) ØIf MPL(4+n D) ~ 1 Te. V then R~ 1032/n-19 meters • If n=1 R~ 1013 m (not good, Newton’s 1/r 2 law excludes this possibility) • It n=2 R~ 10 -3 m (Newton’s law not yet tested at these scales) • It n=3 R~ 10 -9 m Note on Units 1 e. V = 10 -19 Joules SI units ħ*=c*=1, e. V E/2πħ= ν =E*/2πħ* 1015 s-1 = 1 e. V E/c 2 = m = E*/c*2 10 -36 kg = 1 e. V c/ν = λ =c*/ν* 10 -7 m = 1/e. V Arnold Pompoš, KCHFO Seminar @ Prague, Czech Republic, April 20, 2004 42/47

Experimental Consequencies of ED ØGraviton is a spin-2 quantum of gravity ØCompactified ED periodic boundary conditions graviton has Kaluza-Klein (KK) modes in each ED ØCoupling of KK modes to SM particles ~1/MPL (weak) f _ f g g g Gkk V f _ f Gkk g g ØHuge number of KK modes add up and yield to measurable effects Arnold Pompoš, KCHFO Seminar @ Prague, Czech Republic, April 20, 2004 43/47 Gkk

Experimental Search for ED Search for enhanced dilepton production Cross section depends on MPL(4+n dim) ØData agrees with SM prediction ØNo sign of enhanced ll production ØFrom SM+ED signal simulation compared to data a lower limit on MPL in 4+n dim can be set ØThis is then translated into upper limit on compactification radius R Data Signal SM prediction QCD Data vs MC BEST RESULTS YET: DØ ∫Ldt = 200 pb-1 MPL in 4+n dim > 1. 67 Te. V R< 0. 23 mm Arnold Pompoš, KCHFO Seminar @ Prague, Czech Republic, April 20, 2004 44/47

Appendix – Ph. D studies in USA The University Of Oklahoma Arnold Pompoš, KCHFO Seminar @ Prague, Czech Republic, April 20, 2004 45/47

Ph. D studies in USA ØNeed to pass core courses (EMN, QFT, … ) • This takes about 1 or so years • While doing that, teaching undergraduates (labs, recitations, grading, … ) is the source of income. ØPick a professor (group) to work with ØAgree on thesis research topic with him/her ØWork on your thesis research • This takes about 3 or so years • While doing that, typically research assistantship is the source of income (no need to teach) ØWrite & defend thesis Graduate Arnold Pompoš, KCHFO Seminar @ Prague, Czech Republic, April 20, 2004 46/47

Grid C omput in g Come to the University of Oklahoma Fermilab’s D 0 experiment HEP @ OU is involved in CERN’s Atlas experiment Contact: pompos@fnal. gov Arnold Pompoš, KCHFO Seminar @ Prague, Czech Republic, April 20, 2004 47/47