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Why is there mass in our universe ?Azeddine Kasmi* *Lightner-Sams Fellow Physics Department Southern Methodist University AZEDDINE KASMI QuarkNet talk 08/06/2008 1 Some History of Physics. Particle Physics and the Standard Model. Coffee Break The Large Hadron Collider (LHC). Potential discoveries using the ATLAS detector. AZEDDINE KASMI QuarkNet talk 08/06/2008 2 Early Elementary particles pioneers • What is the world made of ? • and what holds it together ? In ancient times, people tried the combination of 4 components: Air, Water, fire, Earth The Greek philosopher Democritus (460 BC – 370 BC) introduced the notion of the atom. AZEDDINE KASMI QuarkNet talk 08/06/2008 3 Classical Physics and Relativity Gravitation is a natural phenomenon. allows objects with mass attract each other. Keeps planets in orbits Gravity acts immediately Isaac Newton (1643-1727) Speed of light is the speed limit And God said Light does not travel instantly. James Clerk Maxwell (1866-1870) ...and there was light. AZEDDINE KASMI QuarkNet talk 08/06/2008 4 Classical Physics and Relativity Mass–Energy Equivalence 3D of space and 1D of time as bound together in a single fabric of space time. Albert Einstein (1915) This fabric of space-time is stretched by heavy object. Curving of that space-time is what we feel as gravity. Earth stays in orbit because it follows the curvature in the space-time caused by the sun presence. If Sun disappears Gravitational disturbance forms a wave No change in orbit until the wave reaches Earth AZEDDINE KASMI QuarkNet talk 08/06/2008 5 Quantum Mechanics 1920’s Quantum mechanics : the study of mechanical systems whose dimensions are close to or below the atomic scale. Explains why Classical Mechanics failed to explain • radiation by heated bodies • stable atoms W. Heisenberg ( in 1932) •Heisenberg uncertainty principle It’s impossible to measure simultaneously the position and momentum of a particle. In QM all what we can do is find the probability of finding a particle in a given state. AZEDDINE KASMI Dp Dx QuarkNet talk 08/06/2008 6 The cop says: Do you have any idea how fast you were going back there ? Driver answers: No Cop: Crap ! Me neither No speeding tickets in the quantum world ! AZEDDINE KASMI QuarkNet talk 08/06/2008 7 Special relativity + Quantum Mechanics = Antimatter What made CERN Popular Paul A.M. Dirac (1928) Movie, May 2009 Detective story about a secret society which ... Every particle has its antiparticle with same mass but opposite charge Particle and its antiparticle annihilates ... steals 1 g of antimatter from a place called “CERN” ... to blow up the Vatican, an old “enemy of science and CERN”. AZEDDINE KASMI QuarkNet talk 08/06/2008 8 Reductionism SLAC(1968): Quarks discovery Chadwick(1932): discovers neutron Most of the particles that were taught to be elementary turned out to have constituents Rutherford: Nuclear atom (proton) Thomson (1897): Electron discovery AZEDDINE KASMI QuarkNet talk 08/06/2008 9 The forces in nature Type of Force Strong Nuclear Strength of Force ~1 Binding Particle. Occurs in Gluons Holds atomic Nucleus together (no mass) ElectroMagnetic ~10-3 Weak Nuclear ~10-5 Photons Think of forces as interaction Two particles interact by exchanging a messenger particle. Atomic shell (no mass) Bosons Radioactivity Zo , W+, WMassive Gravity ~10-38 Gravitons (?) Heavy Bodies AZEDDINE KASMI Exchanged particle transfers momentum from one interacting particle to another. QuarkNet talk 08/06/2008 10 The Standard Model (SM) of particle physics The SM describes interactions between the elementary particles that make up all matter. To date, the SM agrees well with experiment. Last confirmation Top quark discovery (1995 Fermi Lab) The building blocks of matter are fermions Force carriers are bosons AZEDDINE KASMI QuarkNet talk 08/06/2008 11 The origin of mass ? The Standard Model proposes: another field not yet observed. indistinguishable from empty space. This is known as the Higgs field. All space is filled with this field, and that by interacting with this field, particles acquire their masses. The Higgs field has at least one new particle associated with it, the Higgs particle (or Higgs boson). The ATLAS detector at the LHC will be able to detect this particle if it exists. This would be one of the greatest scientific discoveries ever! AZEDDINE KASMI QuarkNet talk 08/06/2008 12 The Higgs mechanism ! To understand the Higgs mechanism, imagine that a room full of physicists chatting quietly is like space filled with the Higgs field ... ... a well-known scientist walks in, creating a disturbance as he moves across the room and attracting a cluster of admirers with each step ... ... this increases his resistance to movement, in other words, he acquires mass, just like a particle moving through the Higgs field... It should be probably a Hollywood star as who cares about a scientist ! AZEDDINE KASMI QuarkNet talk 08/06/2008 13 Spontaneous Symmetry Breaking There is symmetry All directions look the same The symmetry is broken here As the birds have chosen one direction AZEDDINE KASMI QuarkNet talk 08/06/2008 14 Ferromagnet analogy •At low temperature, the iron atoms will align themselves •Despite no direction preferred in interaction between atoms •Therefore, atoms acquire certain energy. •i.e. must add heat to break the alignment. •Lowest energy state of universe •Non zero Higgs field •Generates mass for W,Z AZEDDINE KASMI QuarkNet talk 08/06/2008 15 Spontaneous symmetry breaking illustrated by the horse and the carrot 1 2 3 4 AZEDDINE KASMI QuarkNet talk 08/06/2008 16 Conclusion on Spontaneous Symmetry Breaking The Standard Model relies on the process of spontaneous symmetry breaking to generate mass to the elementary particle. Without it, the elementary particle would indeed remain massless. When applied to particle physics, it leads to the production of a scalar particle named the Higgs boson. Mexican hat potential AZEDDINE KASMI QuarkNet talk 08/06/2008 17 What we know so far in the universe The SM is not a complete theory of fundamental interactions for the following reasons. The lack of inclusion of gravity. Incomplete description of why particles have mass. We are surrounded by: Dark Matter or unseen matter. Dark Energy SM •Tends to increase the expansion rate of the universe. AZEDDINE KASMI QuarkNet talk 08/06/2008 18 Evidence of what we do not know yet Rotation curve of a typical spiral galaxy Evidence for Dark Matter B. Observed Rotational speeds of galaxies A. Predicted by Newtonian dynamics Evidence for Dark Energy •Supernovae Redshift tells us how fast it receding Standard candles (object with extreme consistent brightness e.g. Supernova Type la) are used to measure the distance. •Expansion of the universe accelerates. Multiwavelength X-ray image of SN 1572 or Tycho's Nova, the remnant of a Type Ia supernova. (NASA/CXC/Rutgers/J.Warren & J.Hughes et al.) AZEDDINE KASMI QuarkNet talk 08/06/2008 19 Grand Unification theory GUT 1864: J.C.Maxwell Unified Electricity and Magnetism . Electromagnetism 1973: Salam and Weinberg Unification of the electromagnetic and weak interactions. W, Z bosons AZEDDINE KASMI QuarkNet talk 08/06/2008 20 Coffee Break AZEDDINE KASMI QuarkNet talk 08/06/2008 21 To test a theory you need an Accelerator, Detector, and Cafeteria LHC PROTONS: 99.9999991 per cent of the speed of light 11000 times per second circling the 27 km ring AZEDDINE KASMI QuarkNet talk 08/06/2008 22 General view of the LHC and experiments AZEDDINE KASMI QuarkNet talk 08/06/2008 23 The Large Hadron Collider (LHC) One Higgs per Hour 10-4 Hz AZEDDINE KASMI QuarkNet talk 08/06/2008 24 ATLAS collaboration http://atlas.ch PEOPLE 2100 scientists 37 countries (5 continents) 167 universities and labs SIZE Philippe has a good coffee maker ($1.5) 100 747 jets (empty) is weight of ATLAS Detector 0.5 ATLAS is half the size of Notre Dame Cathedral 122 kilometers of superconducting wire in magnets 3000 kilometers of ordinary cable in ATLAS AZEDDINE KASMI QuarkNet talk 08/06/2008 25 ATLAS detector vs. Foundren science building Length Height Overall weight 46 m 25 m 7000 Tons AZEDDINE KASMI QuarkNet talk 08/06/2008 26 General Principle for particle detection Visible particles are measured by the various subdetectors and identified from their characteristic pattern . AZEDDINE KASMI QuarkNet talk 08/06/2008 27 ATLAS: The Technical Challenges ATLAS major components •The Inner Detector 350000 particles/ mm2 s makes the radiation hardness a top priority. Transition Radiation Tracker •The Calorimeters 80 M rectangular pixels •The Muon Spectrometer •Solenoidal and Toroidal Magnets •Data acquisition and Couputing TRT Hundreds of thousands of gas-filled straws at high voltage, each with a wire down its axis Central Selenoid: 5 tons coil contains 9 km of superconducting wire cooled by liquid helium, I = 8000 Amps, B = 2 T AZEDDINE KASMI QuarkNet talk 08/06/2008 28 Electromagnetic Calorimeter (EMC) The calorimeter consists of thin lead plates (about 1.5 mm thick) separated by sensing devices. The lead plates are immersed in a bath of liquid argon. The liquid argon gaps (about 4 mm) between plates are subjected to a large electric field. AZEDDINE KASMI QuarkNet talk 08/06/2008 29 How does the EMC work ? When the electron shower gets into the argon, it makes a trail of electron-ion pairs along its path. The electric field causes the electrons (from the Argon) to drift to the positive side. This produces an electric current in an external circuit connected to the calorimeter. AZEDDINE KASMI When a High energy photons or electrons traverse the lead, they produce an electron shower. QuarkNet talk 08/06/2008 30 Muons detections Muons are the only charged particle that can travel through all of the calorimeter material and reach the outer layer. much less affected by the electric forces of the atomic nuclei that they encounter (200 times more massive than electrons). Do not produce same kind of electromagnetic shower of electrons. Energy loss via electron-ion pairs along their path. in case of steel or copper, 1 MeV per millimeter of path. Example a muon of 5 GeV penetrate about 5 meters of steel. Monitored Drift Tubes Gas-filled 3 cm tube Thus energetic particles seen outside the hadron calorimeter are guaranteed to be muons. AZEDDINE KASMI QuarkNet talk 08/06/2008 31 Selection of events Interaction rate: Can record Trigger System Level1 Trigger decision less than 2ms larger than interaction rate of 25 ns Of 40 M bunch crossings per seconds, less than 100000 pass Level-1 ~ 109 events/s ~ 200 events/s (event size 1 MB) Level2 Analyses in greater detail specific regions of interest identified by Level 1. Less than 1000 events per second pass Level2 Level3 Less than 100 events per second are left after Level3. These events are passed on to a data storage system for offline analysis AZEDDINE KASMI QuarkNet talk 08/06/2008 32 The Grid Balloon (30 km) LHC will be completed in 2008 and run for the next 10-15 years Experiments will produce about 15 Millions Gigabytes per year of data (about 20 million CDs!) CD stack with 1 year LHC data! (~ 20 Km) Concorde (15 Km) LHC data analysis requires a computing power equivalent to around 100000 of today’s fastest PC processors Requires many cooperating computer centers, as CERN can only provide the 20% of the capacity. SMU is part of the grid AZEDDINE KASMI Mont Blanc (4.8 km) QuarkNet talk 08/06/2008 33 What’s an event ? The occasion of two elementary particles colliding (or a single particle decaying) This is NOT Higgs and yet it repeats every 25 ns ! 40M/s Higgs ZZ* 2e + 2m + jet After some cuts It’s just a junk 10-9 of that is a Higgs AZEDDINE KASMI QuarkNet talk 08/06/2008 34 Data Analysis and statistics H1 H1 H1 The situation is similar to searching for a needle in a stack of hay Fortunately, the characteristics of signal (Higgs) event are different from those of a background. AZEDDINE KASMI QuarkNet talk 08/06/2008 35 Missing Energy in case of WZ n No net momentum into reaction e- But summing 3e gives net momentum out Vector Addition Neutrino momentum would the missing Energy e- Conservation of Momentum. WZ 3e + n Thus, a huge missing Energy will characterize the background event. So, the missing Energy can be used as a veto AZEDDINE KASMI e- QuarkNet talk 08/06/2008 36 What’s the plan Understand ZZ, ttbar, (SM) Higgs searches AZEDDINE KASMI QuarkNet talk 08/06/2008 37 Higgs production AZEDDINE KASMI QuarkNet talk 08/06/2008 38 Higgs decay to a 4 leptons channel L+ Z L- Z L+ L- Unfornately, The ATLAS detector is not perfect. Thus, a substantial leptons identification problems will occur in the 4 leptons channel @SMU we have a group that looks at events with 3 identified leptons and try to find the 4th leptons somewhere on the Detector to increase the efficiency AZEDDINE KASMI QuarkNet talk 08/06/2008 39 Higgs 4leptons and background The Standard Model has a limit on the Higgs mass up to 1000 GeV Experiments have ruled out low masses up to 114 GeV. My focus is on Higgs mass within the range 130 GeV -180 GeV The signal (H) will follow a Gaussian distribution and will be seen as a bump. However, the background will be as flat distribution. Note that the discovery of ZZ dibosons was made on July 25th 2008 by Fermi Lab. (only 3 events) AZEDDINE KASMI QuarkNet talk 08/06/2008 40 Higgs in case of a lost electron H 2m1e + X Here the non identified electron was recovered via the jet algorithm AZEDDINE KASMI QuarkNet talk 08/06/2008 41 The complete picture of the standard Model with the Higgs THANK YOU THE END ! AZEDDINE KASMI QuarkNet talk Wanted 08/06/2008 42