What is Particle Physics -- and why I like doing it (Horst Wahl, October 2001) l Particle physics Goals and issues -- Why do it? l How to do a particle physics experiment Accelerator, detector DØ detector as example l Overview of the Standard Model Symmetry, constituents, interactions Problems of standard model -- look beyond The “Holy Grail” of (present) particle physics l Going beyond the SM – new experiments Upgraded DØ detector Triggering The Silicon Track Trigger l Webpages of interest (has links to many particle physics sites) (Fermilab homepage) (Fermilab particle physics tour) (Lawrence Berkeley Lab.) (CERN -- European Laboratory for Particle Physics)

Goals of particle physics l particle physics or high energy physics is looking for the smallest constituents of matter (the “ultimate building blocks”) and for the fundamental forces between them; aim is to find description in terms of the smallest number of particles and forces (“interactions”) at given length scale, it is useful to describe matter in terms of specific set of constituents which can be treated as fundamental; at shorter length scale, these fundamental constituents may turn out to consist of smaller parts (be “composite”). Smallest constituents:  in 19th century, atoms were considered smallest building blocks,  early 20th century research: electrons, protons, neutrons;  now evidence that nucleons have substructure - quarks;  going down the size ladder: atoms -- nuclei -- nucleons -- quarks – preons, toohoos, voohoos, ???... ???

Issues of High Energy Physics l Basic questions: Are there irreducible building blocks?  Are there few or infinitely many?  What are they?  What are their properties? What is mass? charge? flavor? How do the building blocks interact? Are there 3 forces?  gravity, electroweak, strong  (or are there more?) – or fewer?? l Why bother, why do we care? Curiosity Understanding constituents may help in understanding composites Implications for origin and destiny of Universe

About Units l Energy - electron-volt 1 electron-volt = kinetic energy of an electron when moving through potential difference of 1 Volt;  1 eV = 1.6 × Joules = 2.1 × Ws  1 kWhr = 3.6 × 10 6 Joules = 2.25 × eV l mass - eV/c 2  1 eV/c 2 = 1.78 × kg  electron mass = MeV/c 2  proton mass = 938 MeV/c 2 = GeV/ c 2  professor’s mass (80 kg)  4.5 × eV/c 2 l momentum - eV/c:  1 eV/c = 5.3 × kg m/s  momentum of baseball at 80 mi/hr  5.29 kgm/s  9.9 × eV/c l Most of the time, use units where c = ħ = 1 (“natural units”)

Luminosity and cross section l Luminosity is a measure of the beam intensity (particles per area per second) ( L~10 31 /(cm 2 s) ) l “integrated luminosity” is a measure of the amount of data collected (e.g. ~100 pb -1 ) cross section  is measure of effective interaction area, proportional to the probability that a given process will occur.  1 barn = cm 2  1 pb = b = cm 2 = m 2 l interaction rate:

WHY CAN'T WE SEE ATOMS,.. QUARKS? l “seeing an object” = detecting light that has been emitted (scattered, reflected,..) from the object's surface l light = electromagnetic wave; l “visible light”= those electromagnetic waves that our eyes can detect l “wavelength” of e.m. wave (distance between two successive crests) determines “color” of light l no sharp image if size of object is smaller than wavelength l wavelength of visible light: between 4  m (violet) and 7  m (red); l diameter of atoms: m, nuclei: m, proton: m, quark: < m l generalize meaning of seeing: seeing is to detect effect due to the presence of an object, and the interpretation of these effects l quantum theory  “particle waves”, with wavelength  1/(m v) l use accelerated (charged) particles as probe, can “tune” wavelength by choosing mass m and changing velocity v l this method is used in electron microscope, as well as in “scattering experiments” in nuclear and particle physics

Particle physics experiments l Particle physics experiments: collide particles to  produce new particles  reveal their internal structure and laws of their interactions by observing regularities, measuring cross sections,... colliding particles need to have high energy  to make objects of large mass  to resolve structure at small distances to study structure of small objects:  need probe with short wavelength: use particles with high momentum to get short wavelength  remember de Broglie wavelength of a particle = h/p in particle physics, mass-energy equivalence plays an important role; in collisions, kinetic energy converted into mass energy;  relation between kinetic energy K, total energy E and momentum p: E = K + mc 2 =  (pc) 2 + (mc 2 )c 2 ___________

How to do a particle physics experiment l Outline of experiment: get particles (e.g. protons, antiprotons,…) accelerate them throw them against each other observe and record what happens analyze and interpret the data l ingredients needed: particle source accelerator and aiming device detector trigger (decide what to record) recording device many people to:  design, build, test, operate accelerator  design, build, test, calibrate, operate, and understand detector  analyze data lots of money to pay for all of this

Collisions at the Tevatron l p-antip Collisions  qq(g) Interactions Underlying Event u u d g q q u u d Hard Scatter Fermilab

Fermi National Accelerator Laboratory (near Batavia, Illinois) Main Injector Tevatron DØ CDF Chicago  _ p source Booster

“Old” Fermilab accelerator complex

Detectors use characteristic effects from interaction of particle with matter to detect, identify and/or measure properties of particle; has “transducer” to translate direct effect into observable/recordable (e.g. electrical) signal example: our eye is a photon detector; “seeing” is performing a photon scattering experiment:  light source provides photons  photons hit object of our interest -- absorbed, some reemitted (scattered, reflected)  some of scattered/reflected photons make it into eye; focused onto retina;  photons detected by sensors in retina (photoreceptors -- rods and cones)  transduced into electrical signal (nerve pulse)  amplified when needed  transmitted to brain for processing and interpretation

Bend angle  momentum Muon Experimental signature of a quark or gluon Jet Hadronic layers Magnetized volume Tracking system EM layers fine sampling Calorimeter Induces shower in dense material Innermost tracking layers use silicon Muon detector Interaction point Absorber material “Missing transverse energy” Signature of a non-interacting particle Electron Typical particle physics detector system

500 scientists and engineers 60 institutions 16 countries 110+ Ph.D. dissertations 80+ papers Around the World The DØ Collaboration ? ?

The old DØ detector Calorimeter Uranium-liquid Argon 60,000 channels Muon System 1.9T magnetized Fe, Prop. drift tubes 40,000 channels Central Tracking Drift chambers, TRD

“Typical DØ Event” E T,1 = 475 GeV,  1 = -0.69, x 1 =0.66 E T,2 = 472 GeV,  2 = 0.69, x 2 =0.66 M JJ = 1.18 TeV Q 2 = 2.2x10 5

“Typical DØ Event” E T,1 = 475 GeV,  1 = -0.69, x 1 =0.66 E T,2 = 472 GeV,  2 = 0.69, x 2 =0.66 M JJ = 1.18 TeV Q 2 = 2.2x10 5

The Standard Model l A theoretical model of interactions of elementary particles l Symmetry: SU(3) x SU(2) x U(1) l “Matter particles” Quarks in six “flavors”  up, down, charm,strange, top bottom leptons  electron, muon, tau, neutrinos l “Force particles” Gauge Bosons   (electromagnetic force)  W , Z (weak, electromagnetic)  g gluons (strong force) l Higgs boson spontaneous symmetry breaking of SU(2) Mass

The Standard Model l Fundamental constituent particles leptonsq = 1, 0e   e   l Fundamental forces (mediated by “force particles”) strong interaction between quarks, mediated by gluons (which themselves feel the force)  leads to all sorts of interesting behavior, like the existence of hadrons (proton, neutron) and the failure to find free quarks Electroweak interaction between quarks and leptons, mediated by photons (electromagnetism) and W and Z bosons (weak force) l Role of symmetry: Symmetry (invariance under certain transformations) governs behavior of physical systems:  Invariance  “conservation laws” (Noether)  Invariance under “local gauge transformations”  interactions (forces) l SM has been thoroughly tested in many experiments -- embarrassingly good description of data quarks q = 2 / 3. – 1 / 3

Inclusive Jets - DØ

“anomalous couplings” DØ and LEP Combined <  < CL

W Boson Mass World average M W =  GeV mass of W

W Boson Width Indirect measurements from the ratio of W and Z cross sections: DØ:  (W) =  GeV CDF:  (W) =  GeV Upper limit on non-SM decays of W  (W)  132 MeV SM: W , qq If additional non-SM particles exist which are lighter than and couple to the W boson  additional contribution to the W boson width

Constraints on Higgs Mass From combined analysis of all available data, obtain constraints on Higgs mass Present SM Higgs Mass limits (95% CL): < M H < 188 (GeV)

The SM works great ! Why change it ? l SM, developed in the 1970’s, has been thoroughly tested in many experiments -- embarrassingly good description of data l Why are we not happy with it? has 18 arbitrary parameters (e.g. quark, lepton masses)  Where do they come from ? does not include gravity E.M. symmetry breaking mechanism via Higgs Boson is “put in by hand”  Is the Higgs really what we think it should be ? Higgs mass calculation within SM is not stable – “quadratic divergences;” SM at very high energies inconsistent (violates “unitarity”) l Looking for the “Theory of Everything” (TOE) that contains SM as approximation – many extensions proposed and considered: GUTs, technicolor, SUSY, … superstring theory,… Need guidance from experiment Frantically looking for deviations from SM

Electroweak Symmetry Breaking l One of the big unanswered question in high energy physics: the couplings of the photon and the W/Z to matter are the same (except for mixing angles) and all agree with the Standard Model but: l In the SM, this occurs because the W and Z interact with a new, fundamental scalar particle, the Higgs boson l SM predicts relation between masses of W, top, Higgs W photon mass = 0 mass = 81 GeV

Looking beyond the SM l Strategies look harder -- do more precise tests of SM get a bigger hammer –- more energy, and look for “new phenomena” not compatible with SM l Tools needed for this: Accelerator with higher energy  to make massive particles predicted by some of the SM extensions  to look closer into structure of proton and antiproton Higher beam intensity  new phenomena are rare  to improve precision, need lots of data better detectors  cope with higher collision rates  provide more end more precise information  be more selective in what is recorded l Fermilab upgrade program Accelerator: energy from 1.8 to 2.0TeV, raise luminosity by factor > 5 upgraded detectors DØ and CDF

 TeVatron collider at Fermilab u Peak Luminosity cm -1 s -1 (5X10 32 cm -1 s -1 ) u Energy in c.m.s. 2 TeV u Integrated Luminosity 2fb -1 ( 8[30?]fb -1 ) u Turn-on March 1, 2001 u First collisions April 3, 2001 u Bunch crossing time 396 ns (132ns)

DØ upgrade detector

The DØ detector in the collision hall (March 2001)

D  Upgrade Tracking Silicon Tracker Four layer barrels (double/single sided) Interspersed double sided disks 793,000 channels Fiber Tracker Eight layers sci-fi ribbon doublets (z-u-v, or z) 74,  m fibers w/ VLPC readout Preshower detectors Central Scintillator strips – 6,000 channels Forward – Scintillator strips – 16,000 channels Solenoid – 2T superconducting cryostat

Silicon Tracker 7 barrels 50 cm 12 Disks “F” 8 Disks“H” 3 1/7 of the detector (large-z disks not shown) 387k ch in 4-layer double sided Si barrel (stereo) 405k ch in interspersed disks (double sided stereo) and large-z disks 1/2 of detector

Central Fiber Tracker A S l channels l Read-out: SVX-II chips l Fast enough for L1 l 2.6 m scintillation fibers, VLPC readout + 10m waveguides l Mounted on 8 cylinders 20 < r < 50 cm l 8 alternating axial and stereo doublets (2 o pitch)

Silicon Microstrip Tracker l Provides very high resolution measurements of particle tracks near the beam pipe a) measurement of charged particle momenta b) measurement of secondary vertices for identification of b-jets from top, Higgs, and for b-physics Track reconstruction to  = 3 l Track impact parameter trigger (STT) Point resolution of 10  m l Radiation hard to > 1 Mrad l Maximum silicon temperature < 10 o C 6 barrel sections 12 Disks “F” 8 Disks “H” 240 cm

Tracking with the SMT l charge collected in sensors  Points for Track Fit l Precise Localization of Charge  accurate particle trajectories SMT precision ~ 10  m p=qBR Charged Particle n Si n+n+ p+p+ 300  m VBVB Readout 50  m Si Detector Reverse-Biased Diode

Trigger l Trigger = device making decision on whether to record an event l why not record all of them?  we want to observe “rare” events;  for rare events to happen sufficiently often, need high beam intensities  many collisions take place  e.g. in Tevatron collider, proton and antiproton bunches will encounter each other every 132ns  at high bunch intensities, every beam crossing gives rise to collision  about 7 million collisions per second  we can record about 20 to (maybe) 50 per second l why not pick 50 events randomly?  We would miss those rare events that we are really after: e.g. top production:  1 in collisions Higgs production:  1 in collisions   would have to record 50 events/second for 634 years to get one Higgs event!  Storage needed for these events:  3  Gbytes l Trigger has to decide fast which events not to record, without rejecting the “goodies”

Our Enemy: High Rates l too much is happening, most of which we don’t want to know about Collision Rate 7 MHz Data to Tape 20 to 50 Hz l Trigger: Try to reject “uninteresting” events as quickly as possible, without missing the “interesting” ones l Strategy: 3 Level System: L1, L2, L3 with successively more refined information and more time for decision available

DØ Trigger System L2FW: Combined objects (e, m, j) L2GLB L1FW: towers, tracks, correlations L1CAL L1 CTT L1MUO L1FPD L2STT L2CFT L2CAL L2MUO L2PS CAL FPS + CPS CFT SMT MUO FPD Detector L1 Trigger L2 Trigger 7 MHz5-10 kHz 1000 Hz 4  s 100  s 100ms L3

Run II Trigger Scheme l Bandwidth Allocations: L1 in: 7MHz, out: 5-10kHz ; time: 4.2  s L2 in: 10kHz, out: 1kHz ; time: 100  s L3 in: 1kHz, out: 20Hz ; time: 100 ms/ 100 CPUs l Trigger configuration: L1: Uses Calorimeter, Fiber tracker (CFT), Muon and Preshower objects; trigger on  Cal E T (em and jets),  muon p T (use CFT),  track p T,  track-preshower stubs L2: preprocessors for detectors, global L2 combines L1 objects into electrons, muons, jets, + makes decision L2STT: use of SMT information in trigger:  refine momentum measurement  determine impact parameter

Our Friend: the b-Quark l Many of the phenomena that we would like to study have b-quarks associated with them: Tag Top Decays  t  bW ~ 100% Tag Higgs (H  bb)   (H  ff)  m f 2 new Particles (e.g. SUSY)  b’s new Physics couples to mass CP Violation  Matter / Antimatter Asymmetry  Should be Large in B systems

Silicon Track Trigger l Idea: use SMT information at L2, to improve background rejection l Goals: Sharpen P T Measurement Identify b  events l B Event Properties Impact Parameter / Vertex Triggers Collision B-Hadron: Flight Length ~ mm’s Decay Vertex B Decay Products Impact Parameter

Silicon Track Trigger l STT: Preprocessor, prepares information for decision by L2GLB l Include SMT hits on CFT Track in L2 trigger SMT Detector Cluster Finder CFT Tracks (L1 Trig) Associate Clusters to Tracks Re-Fit Track with SMT Clusters Global L2 Trigger 50  s Time Budget

STT concept and design goals 1. Refit Tracks  P T,  o, b Use CFT A,H + SMT 4(3) Layers 2. Use only r-  information stereo strips are clustered 3. Use only P T >1.5 GeV, b<2 mm L1CTT efficiency o sectors in SMT independent system relies on this geometry loss in efficiency ~ 2% 5. L1CTT roads  search in SMT CFT geometry remapped in L1CTT use SMT hits closest to road center fixed road width = 2 mm t = t(select) + t(fit) + t(bus) ~ 16  s  budget ~ 50  s  t(bus) < 5.8  s  t(select) ~ t(fit)  t(select)  N(hits in road) 6. Queuing Simulation STT Lat. ~ 25  s deadtime ~ negl. 9.5 o L1CTT region SMT sector CFT H- Layer Hit CFT A- Layer Hit L1CTT Road

STT Functionally broadcast Trig/Road data L1CTT Tracks Trigger (SCL) correct & cluster 1 / input SMT Data (2 HDI / fiber) compare clst / rd 1 / road coord transf clusters clusters in roads roads <46 / 60 o coord transf compare clst / rd fit 8 DSP/30 o fit matrix LUT fitted tracks L2CTT Averages 2 / 30 o 14 / 30 o 3.7 at input rate (no buffering) FRC STC TFC

STT Architecture Numbers Crates6 FRC1 / cr60 o trig in1scl road in1fiber  vt m max rd’s46 STC9 / cr smt in4fiber  vt m HDI/fiber2 TFC2 / cr30 o

STT history and status l Project started in 1996 (first feasibility studies, assess physics merit) l 1997 to 1999: proposals to DØ, Fermilab PAC, NSF l Summer 1999: consortium of 4 universities (Boston U., ColumbiaU., FSU, Stony Brook obtains funding (1.8M$ from NSF and DOE) l Dec. 1999: Reginald Perry joins; He and his students (Shweta Lolage, Vindi Lalam, Sean Roper,….) developed the VHDL code for the cluster finder and hitfilter part, probably the most challenging part of the project l Sept. – Nov 2001: system tests with first prototypes, first at BU, now at Fermilab in the DØ environment l Second (final?) prototype tests Nov. – Dec. l Production Jan – March 2002 l March 2002 Installation in DØ

Two b-jets from Higgs decay Missing E T Electron Track EM cluster Calorimeter Towers P  P  pp  WH  bb  e A WH event in the DØ detector

M top vs M W in Run 2 Run 2 scenario  M t  3 GeV  M W  40 MeV l Within SM, M top and M W constrain M Higgs to an accuracy of 80% l The relation between these 3 masses provides a good consistency check of the SM

Summary l DØ has a new detector which promises to be up to the task of incisive testing of the SM, and capable of discovering new physics phenomena; l New trigger, in particular the STT, greatly enhances potential; l We are looking forward to finally seeing something which clearly disagrees with the SM! l Many thanks to Reginald Perry and ECE Dept. l Hope for continued collaboration