1. Searching for New Matter with the D0 Experiment Todd Adams Department of Physics Florida State University September 19, 2004

2. Outline Introduction to Particle Physics The D0 Experiment Introduction to Leptoquarks Searches for Leptoquarks e+e+j+j e+ +j+j  +  +j+j

3. What is High Energy Physics?  High Energy Physics is the study of the most basic particles and forces of nature  We explore the smallest scales and the highest energies  We want to know what really makes the Universe tick  Also known as HEP or as particle physics

4. What have we done before?  Discovered lots of new particles  quarks, neutrinos, taus, Z bosons, …  Determined what protons and neutrons are made of  Combined two "fundamental" forces of nature:  electromagnetism  the weak force  Created a model which explains MOST of what we have observed...

5. The Standard Model Our best knowledge of everything. All known particles and forces (except gravity). Experiments test our understanding of the universe The Standard Model has worked remarkably well for more than 20 years

7. Four Basic Forces Electromagnetism Strong Force (nucleus) Weak Force (Beta decay) Gravity n  p + e - + e

8. What are the Big Questions to be Answered? What is the origin of mass? Can all of the forces be unified? How do neutrinos oscillate? Why do we see more matter than anti-matter? What is out there that we have never observed? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ?

9. Collaboration Picture The D0 Collaboration 600 physicists 19 countries

10. The D0 Experiment Study proton-anti-proton collisions at very high energy (1.96 TeV) Fermi National Accelerator Laboratory Use a large, multipurpose detector high precision measurements 3+ stories tall 6000 tons

11. Fermilab  Tevatron  Currently, the world's premier accelerator facility  Proton-Anti-Proton collisions at a center of mass energy of 1.9 trillion electron-volts  Two collider experiments  D0 and CDF  Other physics  neutrino physics, CP-violation, astrophysics and more  Located outside of Chicago  Scientists from all around the world come to Fermilab to do high energy physics

13. Fermilab Accelerator Complex

14. The D0 Experiment

15. Silicon Microstrip Tracker Position and vertex measurement with 12 micron resolution Barrel with 4 layers Charged particle tracking

16. Central Fiber Tracker 8 double layers of scintillating fibers Surrounds silicon detector 2 Telsa solenoid field Silicon Tracker Fiber Tracker Solenoid 125 cm 50cm 20c m

17. Calorimeter Uranium/Liquid Argon Calorimeter Multiple interactions stop most particles Total energy measurement

18. Muon System Some particles (muons) go through the calorimeter Scintallator/drift chambers and toroidal field measure particle momentum Outermost detector system

19. Detector in Collision Hall January 2001

20. D0 Data Taking 24 hours/day 7 days/week for the next 5+ years currently recording a few million events/day

21. Luminosity

22. Physics of D0  Higgs Boson  needed to resolve electroweak symmetry breaking and responsible for creating mass. Not yet discovered, but there are many indications that D0 and CDF can find it.  Supersymmetry  theory which predicts each known particle has a partner, none of which have ever been seen.  Top Quark  discovered at D0 and CDF. Now we will explore its properties.  QCD - Quantum ChromoDynamics.  D0 can explore how well it describes proton-anti-proton collisions and study what makes up the proton.  Other new particle searches  Technicolor, Leptoquarks, etc.

23. Searches for New Phenomena The Standard Model is great, but leaves questions New physics necessary to increase our understanding. New phenomena are our clearest window into new physics: SUSY, leptoquarks, string theory, GUTs, mass,… q,g - Y Y X0X0 - - At Tevatron: annihilation  pair production (exotic YY) or intermediate propagator (exotic X 0 )

24. Leptoquarks qNqN LQ N l N, N Couples to Lepton + Quark Carry lepton & baryon number Fractional EM charge Included in many SM extensions: enlarged gauge structure, compositeness, more At Tevatron: Assume: intra-generational coupling only (e.g. 1 st generation LQ (LQ1)  eq, e q, 2 nd generation LQ (LQ2)   q,  q)  =BF(l ± q) Search for excess of events or M(lq) spectrum q,g - LQ g pair production

25. Leptoquark Decays Three generations of leptoquark Assume each generation couples to one generation of particle table First Generation Second Generation Third Generation Therefore, 1 st generation LQ (LQ1)  eq, e q, 2 nd generation LQ (LQ2)   q,  q

26. 1 st Generation LQ in eejj Require: 2 good electrons w/ E T (e)>25 GeV  2 good jets w/ E T (jets)>20 GeV veto Z  ee S T >450 GeV Luminosity = 175 pb -1 M(LQ1) > 238 GeV for  =1 Run II Preliminary Data: 1 events Bkgd: 0.54±0.15

27. 1 st Generation LQ in e jj Require: 1 good electron w/ E T (e) > 35 GeV  2 good jets w/ E T (jet) > 25 GeV missing E T > 30 GeV ST 12 > 330 GeV M T e > 130 GeV M(LQ1) > 194 GeV for  =0.5 Run II Preliminary Luminosity = 175 pb -1 Data: 1 events Bkgd: 3.6±1.2 events

28. LQ1 Combined Limit

29. 2 nd Generation LQ in  jj M(LQ2) > 186 GeV for  =1 Run 2 Preliminary Luminosity = 104 pb -1 Require: 2 good muons w/ E T (  )>15 GeV  2 good jets w/ E T (jet)>25 GeV M(  )>110 GeV S T >280 GeV Data: 1 event Bkgd: 1.59±0.49

30. Summary Florida State University has a long history and a strong program studying particle physics We currently work on the D0 experiment at Fermilab D0 has a wide range of physics to study Leptoquarks are one example We will produce MANY interesting results over the next decade at D0 and beyond… (LHC in Switzerland)