PPC - Chasing a Dream at the LHC (Lecture 02)

Transcription

1 PPC - Chasing a Dream at the LHC (Lecture 0) PHYS 83 PPC Cube Summary PPC ) Why? Dark Matter and SUSY ) Where? LHC & CMS Detector 3) How? SUSY Searches Prologue It has been 3.8 B years, since the LHC machine was set up. The machine finally started providing proton-proton collisions at a center-of-mass energy of 7 TeV on March 30, 00 and became the energy frontier machine to lead discoveries of new particles. The Standard Model (SM) is currently well tested up to ~00 GeV, but is expected to break down in the TeV domain where new physics should occur. This is precisely the domain that we will study at the LHC. The World's Major Accelerators SLAC: Stanford Linear Accelerator Center, in California, discovered the charm quark (also discovered at Brookhaven) and tau lepton; ran an accelerator producing huge numbers of B mesons. Fermilab: Fermi National Laboratory Accelerator, in Illinois, where the bottom and top quarks and the tau neutrino were discovered. CERN: European Laboratory for Particle Physics, crossing the Swiss- French border, where the W and Z particles were discovered. BNL: Brookhaven National Lab, in New York, simultaneously with SLAC discovered the charm quark. CESR: Cornell Electron-Positron Storage Ring, in New York. CESR performed detailed studies of the bottom quark. DESY: Deutsches Elektronen-Synchrotron, in Germany; gluons were discovered here. KEK: High Energy Accelerator Research Organization, in Japan, is now running an accelerator producing huge numbers of B mesons. IHEP: Institute for High-Energy Physics, in the People's Republic of China, performs detailed studies of the tau lepton and charm quark 3 Livingstone Curve 4 History Center-of-mass energies of beam Center-of-mass energy of elementary components (quarks, electrons) in GeV Hadron (p,p) colliders W/Z top charm tau I Z-factory B-factory Lepton (e+e-) colliders Year to start running 5 6

2 Inside CERN Big Bang, Back to the Future Billion Years Ago Hadron Collisions at the Tevatron and the LHC Upsilon (bb) + Aspen, 00 UA 980 s UA W in 98 Z in 987

3 CERN Courier (July/August 009) ~ Discovery of W s 984 Nobel prize to Carlo Rubbia and Simon van der Meer When I had a problem and couldn t sleep: Pencil and ruler? 985 Kamon-kun, the safety is the number one priority since you are at a foreign country World Wide Web (WWW) 99 Twenty-two years ago an event at CERN changed the world forever. Tim Berners-Lee Tim Berners-Lee handed a document to his supervisor Mike Sendall entitled Information Management : a Proposal. Vague, but exciting is how Mike described it, and he approved it to go forward. The following year, the World Wide Web was born. We learned English from WWW. On Analysis of Top Quark: Kamon-kun, it doesn t make sense to ignore jets in hadron collider experiments. 7 8

4 candidates from 3.4x0 collisions Discovery of Top in 995 Individual, chasing the nature s truth; Big science, providing the answer Years Ago Years Ago : International Video Conference 0 am Maryland 4 pm CERN 9 am FNAL pm Daegu : First 900-GeV pp Collisions Then, Cube with Real Collision Year Ago pp Collision at CMS Dark Matter Sunghyun Chang LHC Feynman Diagram Youngdo Oh & Adil Khan 3 4

5 March 30, 00 7:5 7:46 7:46 7:50 9: 0:08 :33 :46 :48 :58 0:3 5 Time What is happening ==== =================================================================== 3:00 7 TeV Collisons at CMS (6 am in Texas) :56 Collapsing the separation bumps :36 E = 3.5 TeV -- Flat Top (B ~.8E0; B ~.8E0) :9 E = 3 TeV :5 Ramping :46 Prepare for ramp: Fill #005 (B ~ E0; B ~.9E0) :37 Inject both beams... bunches/beam :3 Injection beam probe :3 Global beam permit for B and B -- green : E = 450 GeV :0 Preparing for injection 0:40 Beam expected in 30 min 0:9 Beam expected in one hour 9:5 Preparing to ramp down 9: E = 3.5 TeV 8:53 Beams dumped 8:50 Lost 386 GeV 8:36 Ramp starts up to 3.5 TeV (E = TeV at 8:46) 8:7 Preparing the ramp: Fill #004 (B =.9E0; B =.8E0) 8:6 Injecting with colliding bunch pattern; correcting chromaticity, tune and orbit: E = 450 GeV 8:04 Injection probe beam 7:58 Prepare for injection 6:53 No beam until 8:5 am GVA (:5 am in Texas) x0 Collisions 7 350x0 Collisions 8 0 Luminosity L f N N 4 f N, is collision frequency N are # particles in each beam isbeam size The beam area is products of accelerator properties and of beam properties 700x0 Collisions 9 30

6 Higher Luminosity To reach higher luminosity More beam Higher collision frequency (more bunches) Smaller beam All can be hard to achieve due to instabilities that may develop Want high luminosity to study rare processes Luminosity Cross Section = Event Rate e.g., 0 33 cm - s - pb = 3.6 events/hr Dream, but, not SF Texas-style hunting Fast detector signals & Fast trigger decision 3 3 Supersymmetry (SUSY) SUSY is : a) Supersymmetrized Standard Model ( Democratic solution between Fermions and Bosons); b) An elegant solution to solve the problem associated with the Higgs mass; c) Beautifully connecting the Standard Model with an ultimate unification of the fundamental interactions; + Unification! e.g., QCD Running Couplings n f = 6 (quark flavors); n c = 3 (colors) n ) log( Q s ( Q ) (ncolor flavor The Nobel Prize in Physics 004 s / ) Introduction to High Energy Physics by D. H. Perkins d) Cosmologically consistent with a Dark Matter candidate stable neutralino. SUSY Particle type ~ 0 Neutral Lightest 33 Q (GeV ) 34 Unification Attractive? SM SM+SUSY I think so. We can construct a SUSY model with a stable neutralino to have the grand unification of the forces. 35 Cosmological Connection: DM Astrophysics CDM = Neutralino ( ~ 0 ) SUSY SM Neutral-ino s-leption s-quark SUSY 3% SUSY is an interesting class of models to provide a weakly interacting massive neutral particle (M ~ 00 GeV). 36

7 Number density (n) dn 3Hn v n dt n eq Cross section () ann Co-annihilation (CA) Process (Griest, Seckel 9) Probing Early Universe LHC Now CMB ~ seconds annihilation SUSY Masses (at the LHC) ~ 0 h D (SUSY masses) h H /[00 kms Mpc ] 37 combination Probing 0-7 sec. after Big Bang 38 Minimal Scenario SUSY is : a) Supersymmetrized Standard Model ( Democratic solution between Fermions and Bosons); b) An elegant solution to solve the problem associated with the Higgs mass around TeV; c) Beautifully connecting the Standard Model with an ultimate unification of the fundamental interactions around TeV; + Unification! Many parameters MSSM Minimal Supersymmetric Standard Model (MSSM) more than 00 parameters Impossible to have more than 00 measurements at the LHC It looks like you have 5 conditions for 00 unknowns. How can we solve 00 unknowns? d) Cosmologically consistent with a Dark Matter candidate stable neutralino around TeV Elegant(?) SUSY World SUSY Philosophy Many parameters MSSM more than 00 parameters Impossible to have more than 00 measurements at the LHC consider a way to test a minimal scenario, first. Then, expand to nonminimal scenarios. Minimal scenario = msugra (two Higgs doublets and Universality) Few parameters ~ 0h D (SUSY masses) D ( m0,m/, tan, A0 ) 4 4

8 Probe Metric at the LHC Excess in Inclusive E T miss + Jets We test msugra cases first, followed by a non-universal SUGRA case. E LHC Future Collider Minimal SUGRA ~ 0 h D ( m0, m/, tan, A0 ) Non-Universal SUGRA Data Events/0 GeV Tevatron Precision ~ 0 h D ( m 0, m/, tan, A 0, ) 43 An Excess Not Good Enough H T 44 How Many Giraffes? Shot # Always Statistical Significance Shot # Shot #3 Shot #4 One snap-shot is not good enough! Few assumptions Many assumptions SUSY Mass Techniques Christopher Lester et al., ICHEP00, arxiv: Missing momentum M eff, Razor, H T shat min M TGEN M T / M CT M T (with kinks ) M T / M CT ( parallel / perp ) M T / M CT ( subsystem ) Polynomial constraints Multi-event polynomial constraints Whole dataset variables Max Likelihood / Matrix Element Teruki Kamon Cosmological Connection 47 Minimal Supergravity (msugra) Higgs Doubles + Supersymmetrized Standard Model + Universality <H d > <H u > + tan = <H u >/<H d > at M Z (spin ½) (spin 0) + m / = Common gaugino mass at M GUT m 0 = Common scalar mass at M GUT A 0 = Trilinear couping at M GUT sign()= sign of in H u H d (We choose > 0 and A 0 = 0 for simplicity.) Teruki Kamon Cosmological Connection 48

9 Higgs Slepton ) M Higgs > 4 GeV ) M chargino > 04 GeV 3).x0 4 <Br(bs ) <4.5x0 4 4) (g) : 3 deviation from SM 5) ~ 0h 0. In the SUSY World Neutralino & Chargino Gluino & Squark Universality allows us to simplify the SUSY world in a D plane (m 0 m / ).? Teruki Kamon Cosmological Connection 49 m 0 Mass of Squarks and Sleptons Excluded Allowed Region Mass of Gauginos Higgs Mass (M h ) Branching Ratio b s Magnetic Moment of Muon CDM allowed region? m / Teruki Kamon Cosmological Connection 50 m 0 Mass of Squarks and Sleptons Cosmologically Allowed Region Excluded Higgs Mass (M h ) Branching Ratio b s Magnetic Moment of Muon CDM allowed region Co-annihilation (CA) Process (Griest, Seckel 9) What are the signals Mass of Gauginos from the narrow coannihilation corridor? m / Teruki Kamon Cosmological Connection 5 ~ 0 ~ Cosmologically Consistent Signals Excluded by ) a Rare B decay b s ) b No CDM candidate 3) c Muon magnetic moment Rouzbeh Allahverdi, Bhaskar Dutta, Yudi Santoso arxiv: CDMS II Stau - neutralino co-annihilation scenario (e.g., Arnowitt, Dutta, Gurrola, Kamon, Krislock, Toback, PRL00 (008) 380) 5 LHC at CERN Tevatron 7 km ring A h Small M ~ 0 ~ LHC The LHC at CERN (known as European Organization for Nuclear Research in Geneva, Switzerland) provides the protonproton (pp) collisions. The smashing power is 3.5 times larger than that of the Tevatron at Fermilab (Batavia, IL, USA)

10 Large Hadron Collider (LHC) The LHC is : Accelerator to provide 7-TeV proton beams from a H bottle; Big (7 km circumference); Cool (.9K using 60 tons of Liquid Helium); Hot (synchrotron radiation, in media); Enormous and very sophisticated magnetic system; Powerful (4 TeV (*) collisions, Total magnetic energy stored is that of Aerobus A380 flying at 700 km/h). 55 Discovery Path at the LHC 4,000 x mass of proton (4 TeV) = Collision Energy Protons fly at % of speed of light 808 = Bunches/Beam 00 billion (0 ) = Protons/Bunch Proton Collisions billion (0 9 ) Hz Parton Collisions 4 TeV Proton-Proton Collisions Bunch Crossing 40 million (0 6 ) Hz New Particles Hz to 0 micro (0-5 ) Hz (Higgs, SUSY,...) 7.5 m (5 ns) Cosmologically Consistent Signals One discovery event in 0,000,000,000,000 0 trillion collisions 56 Compact Muon Solenoid Compact? No! Huge Detector But, smaller than ATLAS As of Aug The CMS ( m x 5 m x 5 m,,500 tonnes) is one of two super-fast & super-sensitive detectors, consisting of 5 heavy elements, collecting debris from the collision and converting a visual image for us. Particle Telescope at CERN vs. Hubble Space Telescope in outer space Missing ET(& Jets) at the LHC Example: SUSY g~ g~, g~ q ~, or q ~ q ~ production will be dominant, followed 0 by their decays (e.g., q ~ q ~ ). Jets R parity conservation Stable lightest supersymmetric particle (LSP) 0 If LSP is the lightest neutralino ( ~ ), it will escape the detector MET ( E T ) 0 ~ = Cold Dark Matter candidate Cosmology Thus, the evidence of SUSY-like new physics will appear in the Jets+MET final states. Cosmology LHC = [Exciting Motivation][Right Place&Timing] MET - inferring new physics (e.g., Dark Matter) 59 e b p Hint for DM: Missing E T det ected b p 0 p b b e det ected p p p slash Experimentally, we measure a momentum imbalance in transverse plane and call it missing transverse energy miss ( or ). E T E T 60

11 Particle Flow (PF) Algorithm All physics objects (jets, leptons, HT, MHT etc) are reconstructed with the PF algorithm. Basic idea: Reconstruct and identify all different types of particles Apply corresponding calibrations The list of particles is given to the jet clustering and missing E T (MET) reconstruction algorithm Charged hadrons ~65% of jet energy Use the high resolution tracker ~% at 00 GeV 6 6 Photons ~5% of jet energy Neutral hadrons ~0% of jet energy Use high resolution / good granularity ECAL Granularity: 0.0 () Energy resolution: ~%/E Use HCAL Granularity: 0. () Energy resolution: ~00%/E PF Jet and MET Performance Particles clustered in jets Jet energy response Calorimeter jet PF jet Jet: Charged hadron (solid) Photon (dashed line) Neutral hadron (dotted line) Jet energy resolution PF jet Calorimeter jet PF algorithm improves the performance of jet and missing E T reconstruction significantly

12 3076/files/SUS pas.pdf.5x0 pp Collisions All hadronic inclusive analysis with key variables: HT = scalar sum of Jet p T (selecting large s-hat production) Analysis Strategy MHT = negative vector sum of Jet p T Baseline Event selection: HT Trigger 3 jet with p T > 50 GeV & <.5 (central production) Veto events with isolated electrons & muons (suppress EWK background) (MHT, Jet,,3) > (0.5, 0.5, 0.3) (reduce QCD background) HT > 300 GeV & MHT > 50 GeV baseline selection Final Event Selection: High HT (HT > 500 GeV): High eff. for signals with long cascade decay chains High MHT (MHT > 50 GeV): High background rejection Baseline selection w/o MHT cut Baseline Selection HT > 300 GeV & MHT > 50 GeV An out-of-box comparison of Data vs MC for HT and MHT >50 GeV [ LM] m0 60 GeV, tan 0, A0 m/ 50 0, 0 GeV, Baseline selection >300 GeV Major BGs: Invisible Z() + Jets.. Irreducible background Top / W + Jets QCD Jets For Future Excitement MHT [ LM] m0 60 GeV m/ 50 GeV tan 0, A0 0 0 High MHT High HT Data-driven BG Estimate 69 HT MHT = 693 GeV & HT = 3 GeV M eff = MHT + HT =.83 TeV No b-tagged jet & No isolated lepton Incompatible with W or top mass Invisible Z??? 70 Results HT > 300 GeV & MHT > 50 GeV MHT > 50 GeV HT > 500 GeV Within the msugra/cmssm 4 parameters and a sign: m 0, m /, tan, A 0, sign() m 0 : common mass for spin 0 particles at the GUT scale m / : common mass for spin / particles at the GUT scale tan 0 tan 0 No excess of observed events over expected Standard Model prediction. Setting limits. 7 Gluino masses up to ~700 GeV are excluded. Less sensitive to tan(see Next page) Sensitivity greater than ATLAS at high m 0. High HT search region was effective. Sensitivity lower than ATLAS at high m /. Need to look at jet events (currently only 3 jets) 7

13 SUSY Large tan Case Low tan vs. High tan CHALLENGE: All hadronic inclusive search is complete at the same pace as other searches. From 00 to 0 tan 0 tan 50 ROBUST data-driven techniques for all SUSY searches in 36 pb - in 00 Less sensitive to tan 73 GOOD agreement with the SM predictions HOT: ~ fb - /month. Big excitement in 0 & 0 Cross-section limits pb, excluding m(gluino) < 700 GeV in the msugra/cmssm plane. [ LM] m0 60 GeV, m/ 50 GeV, tan 0, A 0, My Daughter s View Personal Remarks Discovery with 3 rd generation particles I need,, Uh Oh! The hosts are in CSI: Supersymmetry at the LHC Collider Scene Investigation Summary LHC keep going! Trigger The detector generates unmanageably large amounts of raw data, about 5 megabytes per event (raw; zero suppression reduces this to.6 MB) times 40 million beam crossings per second (or 40 MHz) in the center of the detector, for a total of petabyte/second of raw data. The trigger system uses simple information to identify, in real time, the most interesting events to retain for detailed analysis. There are two primary trigger levels, the first based in electronics on the detector and the other running on a large computer cluster near the detector. After the first-level trigger, about 00,000 events per second have been selected. After the nd-level trigger, a few hundred events remain to be stored for further analysis. This amount of data will require over 00 megabytes of disk space per second at least a petabyte each year

14 Simplest Concept Questions Measurement of Muon Lifetime The muon flux (Hz) is of order of a few Hz. S S TDC If the flux were 40 MHz ( muon per 5 ns), what should we do? Fast response detector Fast data readout system Fast data storage system e e S 3 delay start stop But you can store the data at 300 Hz, what should we do? Fast response detector Fast data readout system Fast event-rate reduction system ( trigger ) Fast data storage system Now you have to handle more than 50M channels, what should we do? Fast response detector Fast&parallel readout with zero suppression and powerful processing system Fast&massive parallel event-rate reduction system ( trigger ) Fast&huge data storage system Beam Crossings: LEP, TeV, LHC LHC has ~3600 bunches And same length as LEP (7 km) Distance between bunches: 7km/3600 = 7.5m Distance between bunches in time: 7.5m/c = 5ns LHC Physics & Event Rates At design L = 0 34 cm - s - 3 pp events/5 ns X-ing ~ GHz input rate Good events contain ~ 0 background events khz W events 0 Hz top events < 0 4 detectable Higgs decays/year Can store ~300 Hz events Select in stages Level- Triggers GHz to 00 khz High Level Triggers (HLTs) 00 khz to 300 Hz 8 8 Collisions (pp) at LHC Processing LHC Data Event rate Operating conditions: one good event (e.g., H4 muons ) + ~0 minimum bias events) All charged tracks with p T > GeV Reconstructed tracks with p T > 5 GeV Event size: Processing Power: ~ MByte ~X TFlop 83 84

15 LHC Trigger & DAQ Challenges Challenges: Pile-up 40 MHz COLLISION RATE LEVEL- TRIGGER khz Terabit/s READOUT 50,000 data channels 500 Gigabit/s 300 Hz FILTERED EVENT Gigabit/s SERVICE LAN DETECTOR CHANNELS Charge Time Pattern SWITCH NETWORK Computing Services 6 Million channels 3 Gigacell buffers Energy Tracks MB EVENT DATA 00 GB buffers ~400 Readout memories EVENT BUILDER. A large switching network ( ports) with total throughput ~400 Gbit/s forms the interconnection between the sources (deep buffers) and the destinations (buffers before farm CPUs). ~ 400 CPU farms EVENT FILTER. A set of high performance commercial processors organized into many farms convenient for on-line and off-line applications. 5 Tera IPS Petabyte ARCHIVE Challenges: GHz of Input Interactions Beam-crossing every 5 ns with ~3 interactions produces over MB of data Archival Storage at about 300 Hz of MB events Challenges: Time of Flight Trigger Timing & Control c = 30 cm/ns d = 7.5 m Optical System: Single High-Power Laser per zone Reliability, transmitter upgrades Passive optical coupler fanout 30 nm Operation Negligible chromatic dispersion InGaAs photodiodes Radiation resistance, low bias Recap: Simplest Concept Measurement of Muon Lifetime S S TDC e e start S 3 stop delay Timing Control, here! 89 90