Rishi Patel1 CONNECTING PARTICLE PHYSICS TO COSMOLOGY THROUGH SUPERSYMMETRY by Rishi Patel Mentor: Prof. Dave Toback REU CYCLOTRON PRESENTATION 08/02/07

Rishi Patel2 OVERVIEW 1.What we do in Particle Physics and how we do it? 2.What I have worked on over the summer? 3.What the implications are in the larger story of Physics?

Rishi Patel3 Particle Physics in a nutshell  Just as cosmology is the story of matter on a really BIG SCALE, particle physics is the story of matter on a tiny scale ► One of the major hopes is that they will meet somewhere  But in cosmology we can use telescopes, how can we ‘look’ at particles that are on a very tiny scale  We kind of have to trick them into coming out (they are shy) ► So our idea is to accelerate them as fast as we can and smash them together ► The spray of particles is short lived, so we have to detect them as quickly and precisely as possible

Rishi Patel4

5 QUESTIONS WE HAVE BEEN THINKING ABOUT Recent observations of cosmic microwave fluctuations surprisingly fit the dark matter theory Recent observations of cosmic microwave fluctuations surprisingly fit the dark matter theory So there is a hint that there is dark matter in the universe So there is a hint that there is dark matter in the universe Is Dark Matter due to a new kind of particle? Is Dark Matter due to a new kind of particle? Can we find it in the lab? Can we find it in the lab? They have to exist in the early universe They have to exist in the early universe They do not interact much with matter They do not interact much with matter If we can do this, then Particle Physics can help us understand the early periods of the Big Bang If we can do this, then Particle Physics can help us understand the early periods of the Big Bang Thus, we can investigate a much larger chunk of the constituent mass of the universe Thus, we can investigate a much larger chunk of the constituent mass of the universe

Rishi Patel6 SCOPE OF THE TALK  A description of our SUSY model and why we chose it  A short description of the tools that we use to investigate Supersymmetry  A description of the analysis of the data and what we can conclude from our results

Rishi Patel7 THE STANDARD MODEL (An early model that needs fixing) Major success of the Standard Model is the unification of all the fundamental forces but Gravity. In order to do our experiments with our massive (expensive) machines, we need to know what we are looking for, so we ask (our friends) the theorists...and shop for a model

Rishi Patel8 UNANSWERED QUESTIONS... Why is there so much matter, and not so much antimatter? How do we know there are not more particles? It seems Standard Model is true but not the TRUTH with a capital T, so we need to pay a visit to some other models.

Rishi Patel9 SUSY ( Could be a pretty girl, but is a pretty model) SUSY or Supersymmetry introduces a mirror image of the standard model particles with different masses and spins that allow for every fermion (1/2 spin) to be transformed to a Boson (integer spin) and vice- versa. So every fermion and boson predicted by the Standard model has a supersymmetric partner.

Rishi Patel10 OUR SUSY MODEL AND A LINK TO COSMOLOGY There are many Supersymmetry (SUSY) models, a Gauge Mediated model as opposed to Gravity Mediated, with basically two free parameters Neutralino mass and lifetime SUSY allows us to have a dark matter candidate from the lightest supersymmetric particle, which is predicted by the model to be the Gravitino

Rishi Patel11 We try to test a cosmological model that postulates Gravitinos in the early universe by measuring its mass experimentally. If the Gravitinos are too light ( 1 keV/c 2 ) then, while they are a warm dark matter candidate, their density can cause the universe to overclose if there is no dilution mechanism. COSMOLOGICAL MODELS TESTED IN PARTICLE PHYSICS EXPERIMENT

Rishi Patel12 MY SUMMER PROJECT  This Summer we have concentrated on a specific model that can possibly link large cosmological phenomena to small Particle Physics Phenomena First we choose a model that is sufficiently supported at high energy levels Once we have the data, we want to find our events (The proverbial needle in a haystack) Finally, we explain the results and the possible implications

Rishi Patel13 (why are they are so special) NOTE: Missing Transverse Energy is a sign of special events The Missing Energy is denoted as transverse because we look at the energy of particles emitted in a direction perpendicular to the beam Jet-stream of hadronic particles Beam Missing Transverse Energy

Rishi Patel14 DELAYED PHOTONS

Rishi Patel15 Delayed Photons Gravitino and Neutralino are not detected resulting in Missing Energy

Rishi Patel16 COLLIDER DETECTOR AT FERMILAB Two main calorimeter systems the central calorimeter (along the sides) and plug (along the caps). Inner chamber contains a tracking system for charged particle Track- the path of a charged particle through some material Electrons are tracked in the inner chamber, before they hit the calorimeter, photons are not tracked since they have no charge, so they are detected in the calorimeter.

Rishi Patel17 EMTIMING SYSTEM Scintillators Tower Photomultiplier Tubes Transition Board Time to Digital Converter Time measurement Discriminator

Rishi Patel18 Identifying the Photon From around 570 pb -1 we sift through our events to find our delayed photons: EM Cal. Tower PHOTON RECORDED Make sure it deposits more energy in the EM Calorimeter which detects photons and electrons Make sure it is not from a muon decay in a jet Make sure the photon is from the vertex you think it is coming from

Rishi Patel 19 Main sources of Background beam halo—come from interactions between protons in the beam and other materials in the detector Cosmic rays— random shower of cosmic particles that we are all continuously subject to Separating Photons from Backgrounds Cosmic shower of Particles Beam Halo muons travel parallel to the beam and open interacting with the aperture they scatter in a halo around the beam

Rishi Patel20 STRUCTURE OF THE ANALYSIS Blind the signal region—select events based only on the signal and background, want to get as much signal as possible and minimize background Signal time window determines what photons arrive with a significant delay compared to prompt photons gives us our signal events

Rishi Patel21 Optimizing With background and signal you can now find the optimal region to look for signal eventsWith background and signal you can now find the optimal region to look for signal events The maximal sensitivity is where the expected cross section limit is minimumThe maximal sensitivity is where the expected cross section limit is minimum The graph shows the optimization of the time delay, the curved line shows the expected probability while the straight line shows the actual value, the optimal value is at the min of the expected.

Rishi Patel22 RESULTS The expected signal and the observed data. A total of 508 events have photon candidates shown in the graph. The number of events in each control region is shown in the table. 2 signal events observed in the timing region. There is no evidence of new physics.

Rishi Patel23 RESULTS The figures depict the mass reach of the Neutralino, that is, based on experiment the furthest we can measure the mass of the particle is 101 GeV/c 2 and the highest expected value is 108 GeV/c 2 at a lifetime of 5ns. The lifetime at a simulated mass of 67 GeV/c 2 is 21 ns and an expected lifetime of 25ns.

Rishi Patel24 Exclusion Region The graph shows the exclusion region, that is the region of mass and lifetime that we have ruled out for the Neutralino based on our analysis. The blue region is where the Gravitino mass is 1-1.5keV/c 2, if we can also exclude the region below the blue then we can conclude that the Gravitino mass is above 1keV/c 2

Rishi Patel25 Second Generation Analysis There are TWO signature events  +Missing Energy (the analysis in this presentation) and  +Missing Energy. The single photon event is more sensitive at large decay times, since the Neutralino leaves the detector. The diphoton event is more sensitive at lower Neutralino lifetimes. The next step will be to look at these events. The green region shows the exclusion region we have found in this analysis, while the yellow is a future analysis where two photons decay from a Neutralino.

Rishi Patel26 CONCLUSION In this presentation we have described a means of investigating cosmological models in particle physics We push the extent of the Neutralino mass, thus the Gravitino mass by a few keV/c 2, bringing our experimental reach into a region that can have cosmological implications.

Rishi Patel27 Special thanks to my colleague Paul Geffert, and my mentor Prof. Dave Toback. REFERENCES 1.P. Wagner and D. Toback, Phys. Rev. D 70, (2004). 2.P. Wagner (2007) “Search For Heavy, Long-Lived Particles That Decay To Photons In Collisions At = 1.96 TEV” (Doctoral Dissertation) Texas A&M ACKNOWLEDGEMENTS