Another talk to OSU Society of Physics Students about LHC & SUSY
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LHC I'mClick a Wino myMaster to & edit mom's name is SUSY • • • • • title style Click to edit Master text styles Second level Third level Fourth level Fifth level OUTLINE The Standard Model of Particle Physics Higgs & SUSY & friends The Large Hadron Collider to the rescue Physics Forecast 1 SPS 4/19/2011 Richard Kass 1 What are the forces laws of physics? Click to edit Master title style • • • • • Click to edit Master text styles Second level Third level Fourth level Fifth level things are really small! proton=uud neutron=ddu 2 SPS 4/19/2011 Richard Kass 2 The Standard Model of Particle Physics toModel editofMaster title style The Click Standard particle physics unites Weak + EM + Strong Forces to edit Master text styles It• isClick the most successful physics model, ever! • Second level Explains all of particle physics data for last ~50 yrs ½ particles: •spin Third level quarks, leptons spin 1 particles: photon, Z & W bosons •mesons, Fourth level bound states of quark anti-quark pairs baryons, bound states of 3 quarks (proton…) • Fifth level Lots of predictions that came true… charm particles, Z and W boson, top quark… 32 Nobel Prizes since 1960 including 2008’s BUT……. 3 SPS 4/19/2011 Richard Kass 3 Problems with the Standard Model NoClick gravity to edit Master title style The SM needs many experimental inputs 12 quark and lepton masses •12Click edit Master styles other to numbers (couplingtext constants…..) The SM fundamental particles have zero mass! • Second level but we have mass! • Third level The origin of mass is tied into the Higgs Field Higgs field •The Fourth levelgives particles their mass Peter Higgs (1964) uses ideas • Fifth level from solid state physics & devises a Prof. Peter Higgs, U. of Edinburgh SPS 4/19/2011 theoretical field to make Energy can be stored massless particles massive! in a field, e.g. electric Note: 2 other groups come with Einstein: E=mc2 similar idea at same time! mass energy Higgs particle could have been known as the “Guralnik” or “Hagen” or”Kibble” or “Brout” or “Englert” 4 Richard Kass 4 Problems with the Standard Model to predict edit Master title style The Click SM cannot the mass of the Higgs The SM cannot tell us how many different Higgs • Click exist. to edit Master text styles particles The minimum level is one, but there can be more! • Second Some scattering processes involving a Higgs particle • Third level are infinite! • Fourth level f ► • Fifthhlevel h f A higgs can turn into a virtual fermion anti-fermion pair. The probability for this to happen in the SM is infinite!!!! ► Infinite cross sections violate unitarity! Unitarity: a foundation of quantum mechanics unitarity->sum of probabilities=1 SPS 4/19/2011 5 Richard Kass 5 Even Worser SM Problems Why are all elementary particles either quarks or leptons ? Are there lepto-quarks ? 1MeV=106eV Why do particles have such a wide range of masses? 1GeV=109eV neutrino very light but not massless (<< 1eV) 12eV 1TeV=10 top quark 175,000 MeV/c2 = 175 mp Why is the electric charge of the proton identical to the electron? • Second electron is alevel lepton but a proton is made up of 3 quarks Do quarks and/or leptons have structure like atoms or protons ? level Why• isThird the proton stable? Click to edit Master title style • Click to edit Master text styles • Fourth level • Fifth level 6 6 SPS 4/19/2011 Richard Kass 6 Click to edit Master title style The Standard Model Must be Replaced • Click to edit Master text styles • Second level The Standard Model of particle physics has basically taken the problems that appeared • Third level in HEP in the 1960’s and moved them from one • Fourth area to thelevel next without ever solving the real problem(s)… • Fifth level How do we get out of this mess? 7 SPS 4/19/2011 Richard Kass 7 Supersymmetry-I SUSY is a grand unified theory with symmetry between fermions & bosons. Eliminates “infinities.” Grand Unified=includes gravity SUSY compatible stringtext theory & SM • Click to editwith Master styles For every SM particle there is a SUSY particle with a spin •that Second differs level by ½. • Third level SUSY predicts lots of new particles: Click to edit Master title style bosons squarks sleptons Higgs gluon W, Z photon fermions quarks leptons Higgsinos gluinos Winos+Zinos photino • Fourth level • Fifth level ~ ~ W H ~ charginos ~ ~ ~ ~ Z h 0 H 0 ~ 0 neutralino s SUSY may contain a new quantum number, R=(-1)3(B-L)+2S with B=baryon #, L=lepton #, S=spin, R=1 for SM, -1 for SUSY particles Because of R, SUSY particles must be produced in pairs. Lightest SUSY particle stable and may be dark matter! Richard Kass SPS 4/19/2011 8 8 8 Supersymmetry-II Click to edit Master title style Besides its mathematical elegance the strongest evidence for SUSY is the unification of coupling constants: • • • • • Click to edit Master text styles Second level Third level Fourth level Fifth level reminder… SUSY can also be tied to String Theory May be able to unify gravity with strong + weak + EM 9 9 SPS 4/19/2011 Richard Kass 9 Click to edit Master title style • Click to edit Master text styles • Second level • Third level SUSY particles • Fourth levelhave not yet been observed. If SUSY were a perfect symmetry: mass of selectron = mass of electron. • Fifth Perhaps SUSYlevel particles are too massive to be produced in previous experiments Perhaps they don’t exist. SUSY predicts at least 5 Higgs bosons! Another annoying thing about SUSY: About 100 free parameters in Minimal SUSY (MSSM)!!! 10 10 SPS 4/19/2011 Richard Kass 10 How do we study quarks & leptons? Small distance high energy Click to edit Master title style DeBroglie: wavelength = planck’s constant/momentum Einstein: rest energy=m0c2 c =speed of light in vacuum=3x108m/s Einstein: (momentum)c = (energy2 - rest energy2)½ Click edit (momentum)c Master text=energy styles So,• for high to energy: energylevel particle has small wavelength • high Second What momentum do we need to “see” a nucleus ? Size of nucleus ≈ 10-15 m • Third level p=h/λ=(4.14x10-24 GeV-s)/(10-15 m) = 4.14x10-9 GeV-s/m = 1.2 GeV/c Could do this with an electron with » 1 GeV Energy ! (big battery) • Fourth level Use particle accelerators to make high energy probes • FifthCERN level Fermilab, accelerate protons to > 1000X rest energy Collide the probes into a target probe could be another beam of protons or anti-protons Use detectors to examine the results of the collisions how many particles produced? what types of particles were produced? (pions, kaons, protons, ……) measure energy and/or momentum of particles SPS 4/19/2011 Richard Kass 11 11 What are the requirements to to find the Master Higgs or SUSY? Click edit title style Must have enough energy to produce the particles A detailed analyisis of the SM says that there must Click to edit text be• new physics with Master mass scale lessstyles than ~ 1TeV • Second level What we already know says that the masses must be greater than ~ 100 GeV • Third level Must collect enough data so we have large samples • Fourth level of the new particles or convince ourselves that they Fifth level do• not exist. Use measurements + physics models to estimate the necessary collision rates. Accelerator must have a collision rate much higher than previous accelerators. Only way to do this is to use beams 12 of protons 12 SPS 4/19/2011 Richard Kass 12 How much energy do we need? Click to edit Master title style Protons: 3 valence quarks+sea of gluons + qq pairs Each quark can have momentum between 0 and Ebeam p p Ebeam Ebeam • Click to edit Master text styles • Second level So, if you want to create a particle with mass ~ 1TeV the proton beams must have energy >> 1TeV • Third level • Higgs Fourth level Production • Examples Fifth level Rather than build a new accelerator tunnel CERN is re-using a tunnel from the 1980’s. The radius of the tunnel and the strength of the bending magnets dictates the energy of the beam: Ebeam = 7 TeV and Ecm=14 TeV Upper limit: p=0.3BR, R~4km, B=7.5T gives p~9TeV SPS 4/19/2011 13 Richard Kass 13 Finding interesting events is like looking for a needle in a Haystack Click to edit Master title style • • • • • Interesting cross section: ~10-15 barn Typical cross section for pp collison ~10-3 barn Need to search trillions of events! Click to edit Master text styles Second level Raw event rate will be ~ 40MHz! Third level Interesting rate much much lower! Fourth level Event rate at LHC >100X Fermilab Fifth level # of events=(cross section)(Luminosity) 14 SPS 4/19/2011 Richard Kass 14 The Large Hadron Collider LHC is located at CERN CERN is located near Geneva Part of CERN is in France The LHC collides protons Center of Mass E=14 TeV ~7X Fermilab Very high luminosity ~100X Fermilab Click to edit Master title style • • • • • Goal: discover Higgs+SUSY+??? Click to edit Master text styles Second level Third level Fourth level Fifth level 15 SPS 4/19/2011 Richard Kass 15 The Large Hadron Collider Click to edit Master title style • • • • • ATLAS site Click to edit Master text styles Second ~4.3km level Third level Fourth level Fifth level main lab 16 SPS 4/19/2011 Richard Kass 16 A Toroidal LHC ApparatuS ATLAS is one of the 4 major experiments planned for the LHC Goal is to find Higgs + physics beyond the standard model (SUSY??) Click to edit Master title style The ATLAS detector stresses: good charged particle tracking • Click to edit Master text styles 2 magnets Second level good•calorimetry (EM+Had) electron ID TRT+ECAL • Third level muon ID ATLAS has limited (none?) • Fourth level p/K/p ID • Fifth level pixel+SCT+TRT good momentum resolution ATLAS superimposed on the 5 story building 40 at CERN SPS 4/19/2011 17 Richard Kass 17 ATLAS Under Construction Click to edit Master title style • • • • • Click to edit Master text styles Second level Third level Fourth level Fifth level 18 SPS 4/19/2011 Richard Kass 18 ATLAS Toroid Magnets Click to edit Master title style • • • • • Click to edit Master text styles Second level Third level Fourth level Fifth level 19 SPS 4/19/2011 Richard Kass 19 How can ATLAS find Supersymmetry? SUSYClick particles to decay into toexpected edit Master title“ordinary style particles” + other SUSY particles Some SUSY will not • Click toparticles edit Master textinteract styles with matter These particles are undetectable in ATLAS • Second So, unlike the Higgslevel we will NOT be able to measure the energy and momentum of all the decay products of a SUSY particle • Third level We can detect the presence of • Fourth levelby noticing that SUSY particles there is “missing” energy in an • Fifth level me e ) max m~ 0 m~ 0 2 1 event. BUT must show that the missing energy is NOT due to neutrinos and/or detector resolution. Can learn about mass of SUSY particles by measuring E & p the ordinary particles in its decay. SPS 4/19/2011 20 Richard Kass 20 How can ATLAS find Supersymmetry? to with: edit LookClick for events Master title style quark jets (q) from squarks & gluino decay leptons (l) from Winos, Zinos,text slepton decay • Click to edit Master styles missing transverse momentum • • • • Second level possible decay chain Third level Fourth level Fifth level simulated SUSY event in ATLAS 21 SPS 4/19/2011 Richard Kass 21 • • • • • Click to edit Master style After 15 years of design and title construction the LHC is ready to start! Click to edit Master text styles Second level Third level Fourth level Fifth level 22 SPS 4/19/2011 Richard Kass 22 The Press takes notice Click to edit Master title style • • • • • Click to edit Master text styles Second level Third level Fourth level Fifth level 23 SPS 4/19/2011 Richard Kass 23 Celebrities Come Out.. Jesse Dylan (son of Bob) Click to edit Master title style • • • • • Click to edit Master text styles Second level Will I am Third level Fourth level Peter Higgs Fifth level Steven Hawkings YOUTUBE: http://www.youtube.com/TheATLASExperiment SPS 4/19/2011 Richard Kass 24 24 Hollywood comes to ATLAS/CERN Click to edit Master title style Tom Hanks Ayelet Zurer • • • • • Angels and Demons follows Harvard symbologist Robert Langdon (Hanks) as he uncovers a plan to annihilate the Vatican in an explosion of light, using 0.25 grams of antimatter stolen from CERN. ClickRontoHoward edit Master text styles Second level Third level Fourth level Hanks admitted to scoring a D in Fifth level physics in school, but said that the explanations of CERN antimatter expert, Rolf Landua, who acted as a scientific adviser on the film, had made it seem much easier to digest. Tom Hanks in the ATLAS control room 25 SPS 4/19/2011 Richard Kass 25 September 9, 2008 OSU is there! Click to edit Master title style • • • • • Dear Professor Kass, I just saw that you were in Geneva at the start up of the LHC. I had the privilege of visiting the LHC twice over the past five years due to strong Vanderbilt physics connections. I am so delighted that Ohio State is equally involved. Congratulations! Gordon Click to edit Master text styles Second level Third level Fourth level Fifth level Harris Kagan SPS 4/19/2011 Waruna Fernando Richard Kass 26 26 26 A Brief History of ATLAS Data Taking Click9-10 to 2008 edit Master title style September First beams in the LHC September 2008 • Click to19edit Master text styles Major magnet-system failure • Second level March 30 2010-Nov 4 2010 • First Thirdcollisions level at 7 TeV CM energy passes Fermilab as highest energy collider • LHC Fourth level March 13 2011-through 2012 • Data Fifthtaking level at 7TeV again LHC delivers record luminosity 2013-20??? detector upgrades & lots more data collection schedule goes to 2040! SPS 4/19/2011 Richard Kass 27 27 Searching for SUSY with ATLAS data Click to edit Master title style Although ATLAS has a small data sample the search for SUSY is in full swing… • • • • • Click to edit Master text styles Two Second levelSUSY-like events… Third level Fourth level Fifth level 28 SPS 4/19/2011 Richard Kass 28 Searching for SUSY with ATLAS data Examine the event sample for SUSY like events. Compare the data with expected rates from known processes Click to edit Master title style look at data as a function of number jets & number of leptons Use• a Click SUSY to model show where “signal” would edittoMaster textthe styles be in the data plot (Monte Carlo method) • Events Second with level missing energy & jets • Third level • Fourth level • Fifth level Events with missing energy & jets & leptons No hint of SUSY in the data! SPS 4/19/2011 29 Richard Kass 29 Searching for SUSY with ATLAS data Even though we do not (yet) see evidence of SUSY we can make model dependent statements about masses of SUSY particles. Click to edit Master title style • • • • • Click to edit Master squarks Vstext gluinosstyles Second level Third level Fourth level Fifth level everything below red line is ruled out by the data MANY other exclusions plots have been produced 30 SPS 4/19/2011 Richard Kass 30 Summary High Energy Physics tries to answer the most fundamental questions about the laws of physics. Click to edit Master title style The• SM is attoitsedit breaking point! Click Master text styles The LHC has enough energy & luminosity to: • Second level a) find the Higgs particle(s) (assuming they exist). b) find evidence for SUSY (assuming it exists) • Third level find a candidate for dark matter • Fourth level of extra dimensions (black holes…) c) search for evidence d) something evener better-er • Fifth level The next year is do or die for SUSY! NOTE: Figuring out WHICH SUSY model is the correct one will take many more (>5) years and maybe a new accelerator. 31 SPS 2/24/2009 Richard Kass 31 extra slides Click to edit Master title style • • • • • Click to edit Master text styles Second level Third level Fourth level Fifth level 32 32 SPS 2/24/2009 Richard Kass 32 Detector Systems A typical detector looks something like: Click to edit Master title style BaBar, CDF, STAR, ATLAS, CMS…… • • • • • Click to edit Master text styles Second level Third level Fourth level Fifth level outside detector inside detector Let’s look at the ATLAS Detector as an example of a “real” system 33 33 SPS 2/24/2009 Richard Kass 33 The Large Hadron Collider Click to edit Master title style • • • • • Click to edit Master text styles Second level Third level Fourth level Fifth level 50-175m 34 SPS 4/19/2011 Richard Kass 34 How Do We Get 7 TeV Protons? Click to edit Master title style ~7 TeV final beam energy LINACPSBPSSPSLHC • Click to edit Master text styles • Second level • Third level • Fourth level • 11Fifth level ~10 protons/beam ~450 GeV ~25 GeV ~2 GeV ~1 GeV 35 35 SPS 2/24/2009 Richard Kass 35 LHC: Just the Facts……. Click to edit Master title style http://lhc-machine-outreach.web.cern.ch/lhc-machine-outreach/lhc-interesting-facts.htm List of facts for the PPARC website. Compiled by Hazel Morris April 2004 Fact 3) The combined strands of the superconducting cable being produced for the LHC would go around the equator 6.8 times. If you added all the filaments of the strands together they would stretch to the sun and back 5 times with enough left over for a few trips to the moon. Fact 4) Part of the LHC will be the world's largest fridge. It could hold 150 000 fridge full of sausages at a temperature colder than deep outer space. • • • • • Click to edit Master text styles Second level Third level Fourth level Fifth level Fact 5) The vacuum in the LHC is comparable to outer space, if it were a car tyre with a leak, there are so few gas molecules that it would take 10 000 years to go flat. Fact 6) The ATLAS cavern could hold the nave of Notre Dam cathedral. Fact 7) When the 27km long circular tunnel at CERN was excavated, between lake Geneva and the Jura mountain range, the two ends met up with just one centimetre of error. Fact 8) LEP was sensitive to the departure of the TGV from Geneva train station, DC current feeds the tracks but the ground return is not good. The LEP electrical earthing network is a better conductor and so some of the train current returned back through the LEP vacuum chamber. Fact 10) The Large Hadron Collider at CERN could be the most ambitious scientific undertaking ever. The results of LHC experiments will probably change our fundamental knowledge of the universe. Fact 16) CERN is the world's largest laboratory dedicated to the pursuit of fundamental science. Fact 17) Many of the parts for the ATLAS detector of the LHC were manufactured using the expertise of ex-arms scientists and factories, through collaboration with the International Science and Technology Centre. Fact 21) If the Higgs boson exists the LHC will be able to make this particle detectable. Confirming or contradicting the first evidence of the Higgs particle is an exciting prospect! Fact 22) The Nobel prize in physics has twice been awarded to scientists whose experiments were conducted at CERN. The laboratory also boasts several additional Nobel Laureates among its physicists. Fact 24) On 1st October 2003 CERN and the California Institute of Technology set a new Internet Land Speed Record by transferring 1.1 terabytes of data in less than 30 minutes across 7000km of network. The equivalent of transferring a full length DVD movie in 7 seconds. Fact 25) In 1984 CERN translator, Francois Siohan, entered the French Guinness Book of Records for cycling up hill. Between 6:15am and 7:15pm on 1st July, he climbed 8848m, the equivalent to Mount Everest, by cycling 13 times from Gex to La Faucille in the Jura mountain range. Fact 26) In the 1960's CERN's main data network was the famous bicycle on line. Tapes of data were loaded into a basket on the bike and then rushed over to the computer centre. Fact 29) The Grid is a service for sharing computer power and data storage capability over the Internet. Its ultimate aim is to turn the global network of computers into one vast computational resource. Fact 30) Verification of the theory that explains why the sun shines - the weak force - is one of CERN's biggest achievements. Fact 31) The discovery of the neutral current was announced at CERN in 1973. The theory was finally confirmed in 1983 with the direct observation of W and Z particles. Fact 34) Since 1962, 38 heads of state have visited CERN. Fact 40) The CERN Fire and Rescue remit covers 40km of underground tunnels, radiation and chemical risks as well as the buildings above ground. CERN firemen train in abseiling and rope rescue techniques in preparation for a tunnel emergency. Fact 41) In 2003, 6.1% of traffic at Geneva International Airport was related to CERN, a total of 54 868 passengers. Fact 42) X-ray and radiopharmaceutical techniques in medical imaging were developed by particle physicists, as was radiotherapy for cancer patients. Fact 43) Particle accelerators are used to dry the paint on soft drinks cans. For the replacements (23, 35, 36, 44 and 45) and 7 novel facts There are firemen of 9 different nationalities, Bulgarian, British, Czech, Dutch, Finnish, French, German, Spanish and Italian tackling fires with the CERN fire brigade. When they are called out they only speak in French over the radio. The moon and snow/water load on the Jura mountains flexed the earth's crust a little bit which alters the circumference of the LEP ring, in this way the orbit of the moon was detected by LEP. Understanding all of the different forces of nature within one framework is one of the ultimate goals of physics. Decades of experiments at CERN are working towards this. 99.999999999999% of an atom's volume is empty space. If the proton were a pea, the electron would be in the back of the strands at Old Trafford. When protons arrive in the LHC they are travelling at 0.999997828 times the speed of light. Each proton goes around the 27km ring over 11 000 times a second. A nominal proton beam in the LHC will have an energy equivalent to a person in a Subaru driving at 1700 kph.36 36 SPS 4/19/2011 Richard Kass 36 How Can ATLAS Discover the Higgs? Click to edit Master title In 1style 3years of data Standard Model st makes predictions for the Higgs production cross section. Many process contribute depends on Higgs mass. • Click to edit Master text styles • Second level • Third level • Fourth level What the Higgs decays • Fifth into depends on thelevel value of it mass. Best guess is mH~120GeV taking ATLAS is expected to accumulate 100 fb-1 of data #evts=Ls L=luminosity=100x10-15 barns s= cross section~30 pb@100GeV #evts~3x107 Higgs If mH ~120 GeV then the discovery modes may be HZZ, H HZ 37 SPS 4/19/2011 Richard Kass 37 How Can ATLAS Discover the Higgs? Use energy-momentum conservation to measure mass of Higgs Click to edit Master title style Simulation of H • • • • • Click to edit Master text styles Second level Third level Fourth level Fifth level Simulation of HZZ 38 38 SPS 4/19/2011 Richard Kass 38 How Can ATLAS Discover the Higgs? What is so good about the decay modes HZZ, HZ and H Click to edit Master title style If we measure the energy/momentum of the decay products then we can measure (reconstruct) the mass of the Higgs. For these decay modes it is possible to measure the energy and/or momentum of all of its decay products: • Click to edit Master text styles H measure ’s in EM calorimeter m ( E level E ) ( p p ) 2 p p (1 cos ) • Second HZZ with Ze e or Zm m measure e’s and m’s tracking+calorimeter(+muon) • Third level The HZZ is more complicated, we must reconstruct the 2 Z’s. Need Z decay modes that do not involve neutrinos or jets. Use Z decays to electrons or muons: • Fourth level m ( p p ) (E E ) ( p p ) m ( p p ) (E E ) ( p p ) m ( p p ) ( E E ) ( p p ) • Fifth level 2 H 1 2 2 + - 2 Z1 2 l 1 2 H 2 2 l1 2 l 1 l1 2 Z2 2 Z2 l 1 2 Z1 1 + - 2 l1 1 2 l 2 2 Z1 Z2 l 2 2 l 2 l 2 l 2 2 l 2 2 Z1 Z2 Other Higgs decay modes involve “jets” and or decays with neutrinos: HW+W- or t+t-: Always a neutrino in the decay products as a W or t decay includes n’s and n’s do not interact in ATLAS (not enough material) Hbb or cc or gg: We can not measure the quarks (b, c) or gluons (g) directly. The quarks and gluons turn into many other particles collectively called a “jet”. The jet may contain neutrinos and/or some particles from the jet may not be measured (efficiency and acceptance) 39 39 SPS 4/19/2011 Richard Kass 39 How Can ATLAS Discover the Higgs? Click to edit Master title style Simulation of Hbb • • • • • Click to edit Master text styles Second level a b-quark “jet” Third level Fourth level Fifth level 40 SPS 4/19/2011 Richard Kass 40 How Can ATLAS Discover the Higgs? ATLAS detector simulations: ClickFrom to edit Master title style The statistical significance of Higgs observation as function of Higgs mass and decay mode • • • • • Click to edit Master text styles MC simulation of H with 3 years of data collection Second level Third level Fourth level Fifth level There can be > 1 Higgs…. SPS 4/19/2011 Richard Kass 41 41 41 How well Can ATLAS Determine the Higgs Properties? Click to edit Master title style • • • • • It is not enough to just show that the Higgs particle(s) exist! Must measure their properties too. Click to edit Master textHiggs styles Branching Fraction mH measurement Second level Third level Fourth level Fifth level 42 42 SPS 4/19/2011 Richard Kass 42 How Can ATLAS Discover the Higgs? mode Click edit pixel to SCT TRT Master ECAL HCALtitle muonstyle reconstruct m H veto veto veto yes no • Click to edit Master text styles yes yes yes/eID yes no • Second level yes yes yes no no Hbb + yes yes yes yes • Thirdyes level vertex eID? if e’s • Fourth level HW W Wen yes yes yes/eID yes no • Fifth level HZZ Ze+emm + yes no yes yes yes yes if m’s maybe no yes no no no no - Wmn Wquark n tt no H yes yes yes yes yes yes no no no yes yes + vertex yes yes eID? yes if e’s yes yes if if m’s hadrons no 43 43 SPS 4/19/2011 Richard Kass 43 How Can ATLAS Find Supersymmetry? Several SUSY particles might be stable and not interact with matter Click to edit Master title style Lightest SUSY particle might be responsible for dark matter… Consider the following decay chain (one of many…) assume ~g ~X pp g m~ 0 97 GeV 2 ~ ~ bb g m~ 0 45 GeV ~ 1 0 ~ b b 2 ~0 ~ 0ee 2 1 • Click to edit Master text styles • Second level • Third level We can measure the electrons (or muon) energy and momentum Also look for the presence of two b-quark jets Fourth Key•is the invariant level mass of the lepton pair: m there is a sharp cutoff in m(e e ) that depends on the • Fifth level masses of the neutralinos: ee + - ) max m~ 0 m~ 0 2 1 p ~ 0 p ~ 0 pe pe p ~ 0 p ~ 0 pe pe 2 1 2 1 me2 e ( pe pe ) 2 ( p ~ 0 p ~ 0 ) 2 1 2 Evaluate in the frame where 2 is at rest me2 e ( m~ 0 E ~ 0 ) 2 p 2~0 m 2~0 m 2~0 2m~ 0 E ~ 0 2 m2 1 1 2 1 2 1 will be max when E1 is min.p1=0 so E1=m1 me2 e ) max m 2~0 m 2~0 2m~ 0 m~ 0 ( m~ 0 m~ 0 ) 2 2 SPS 4/19/2011 1 2 1 2 44 44 1 Richard Kass 44 The Large Hadron Collider Click to edit Master title style • • • • • Above Ground Click to edit Master text styles Second level Third level Fourth level Fifth level Below Ground 45 45 SPS 4/19/2011 Richard Kass 45 Toroids, Calorimeters, Muon Chambers Click to edit Master title style • • • • • Click to edit Master text styles Second level Third level Fourth level Fifth level 46 46 SPS 4/19/2011 Richard Kass 46