What is Particle Physics --and why I like doing it(Horst Wahl, October 2001)

● Particle physicsGoals and issues -- Why do it?

● How to do a particle physics experimentAccelerator, detectorDØ detector as example

● Overview of the Standard ModelSymmetry, constituents, interactionsProblems of standard model -- look beyondThe “Holy Grail” of (present) particle physics

● Going beyond the SM – new experimentsUpgraded DØ detector TriggeringThe Silicon Track Trigger

● Webpages of interest http://www.hep.fsu.edu/~wahl/Quarknet (has links to many particle physics sites)http://www.fnal.gov (Fermilab homepage)http://www.fnal.gov/pub/tour.html (Fermilab particle physics tour)http://ParticleAdventure.org/ (Lawrence Berkeley Lab.)http://www.cern.ch (CERN -- European Laboratory for Particle Physics)

Goals of particle physics

•● 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 turnout 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● 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??

● Why bother, why do we care?CuriosityUnderstanding constituents may help in understanding composites Implications for origin and destiny of Universe

About Units

● Energy - electron-volt1 electron-volt = kinetic energy of an electron when moving through potential difference of 1 Volt;

1 eV = 1.6 × 10-19 Joules = 2.1 × 10-6 W•s1 kW•hr = 3.6 × 106 Joules = 2.25 × 1025 eV

● mass - eV/c2

1 eV/c2 = 1.78 × 10-36 kgelectron mass = 0.511 MeV/c2

proton mass = 938 MeV/c2 = 0.938 GeV/ c2

professor’s mass (80 kg) ≈ 4.5 × 1037 eV/c2

● momentum - eV/c: 1 eV/c = 5.3 × 10-28 kg m/smomentum of baseball at 80 mi/hr ≈ 5.29 kgm/s ≈ 9.9 × 1027 eV/c

● Most of the time, use units where c = ħ = 1 (“natural units”)

Luminosity and cross section

● Luminosity is a measure of the beam intensity (particles per area per second) ( L~1031/(cm2s) )

● “integrated luminosity” is a measure of the amount of data collected (e.g. ~100 pb-1)

● cross section σ is measure of effective interaction area, proportional to the probability that a given process will

occur.1 barn = 10-24 cm2

1 pb = 10-12 b = 10-36 cm2 = 10-40 m2

● interaction rate:

∫=⇒×= LdtnLdtdn σσ /

WHY CAN'T WE SEE ATOMS, .. QUARKS?

● “seeing an object”= detecting light that has been emitted (scattered, reflected,..) from the object's surface

● light = electromagnetic wave;● “visible light”= those electromagnetic waves that our eyes can detect ● “wavelength” of e.m. wave (distance between two successive crests)

determines “color” of light ● no sharp image if size of object is smaller than wavelength● wavelength of visible light: between 4×10-7 m (violet) and 7× 10-7 m (red); ● diameter of atoms: 10-10 m, nuclei: 10-14 m, proton: 10-14 m, quark: < 10-19 m● generalize meaning of seeing:

seeing is to detect effect due to the presence of an object, and the interpretation of these effects

● quantum theory ⇒ “particle waves”, with wavelength ∝ 1/(m v)● use accelerated (charged) particles as probe, can “tune” wavelength by

choosing mass m and changing velocity v ● this method is used in electron microscope, as well as in “scattering

experiments” in nuclear and particle physics

Particle physics experiments● 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 λ = 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 + mc2 = √(pc)2 + (mc2)c2

___________

How to do a particle physics experiment

● Outline of experiment:get particles (e.g. protons, antiprotons,…)accelerate themthrow them against each otherobserve and record what happensanalyze and interpret the data

● ingredients needed:particle sourceaccelerator and aiming devicedetectortrigger (decide what to record)recording devicemany 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

UnderlyingEvent

u

u

d

g q

q u

u

d

Hard Scatter

● p-antip Collisions ⇒ qq(g) Interactions

Fermilab

Fermi National Accelerator Laboratory(near Batavia, Illinois)

Main Injector

Tevatron

DØCDF

Chicago↓

_ p source

Booster

“Old” Fermilab accelerator complex

Detectorsuse 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) signalexample: our eye is a photon detector;“seeing” is performing a photon

scattering experiment:light source provides photonsphotons 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 neededtransmitted to brain for processing and interpretation

Typical particle physics detector system

Bend angle → momentumMuon

Experimental signature of a quark or gluon

Jet

Hadronic layers

Magnetized volumeTracking system

EM layersfine sampling

CalorimeterInduces shower

in dense material

Innermost tracking layers

use silicon Muon detector

Interactionpoint Absorber material

“Missing transverse energy”Signature of a non-interacting particle

Electron

The DØ CollaborationThe DØ Collaboration

Around the World

¿?¿?

500 scientists

and engineers

60 institutions

16 countries

110+ Ph.D.

dissertations

80+ papers

The old DØ detector

CalorimeterUranium-liquid Argon60,000 channels

Muon System1.9T magnetized Fe,Prop. drift tubes40,000 channels

Central Tracking

Drift chambers, TRD

“Typical DØ Event”CAL+TKS R-Z VIEW 25-MAR-1997 12:22 Run 87288 Event 22409 25-DEC-1994 02:20

MUON

ELEC

TAUS

VEES

OTHER

1.<E< 2.

2.<E< 3.

3.<E< 4.

4.<E< 5.

5.<E

MJJ = 1.18 TeVQ2 = 2.2x105

ET,1 = 475 GeV, η1 = -0.69, x1=0.66ET,2 = 472 GeV, η2 = 0.69, x2=0.66

“Typical DØ Event”CAL+TKS END VIEW 25-MAR-1997 12:22 Run 87288 Event 22409 25-DEC-1994 02:20

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MUON

ELEC

TAUS

VEES

OTHER

MUON

ELEC

TAUS

VEES

OTHER

EM

ICD+MG

HAD

MISS ET

Max ET = 344.6 GeV MISS ET(3)= 9.4 GeV ETA(MIN:-13-MAX: 13)

MJJ = 1.18 TeVQ2 = 2.2x105

ET,1 = 475 GeV, η1 = -0.69, x1=0.66ET,2 = 472 GeV, η2 = 0.69, x2=0.66

The Standard Model ● A theoretical model of interactions of elementary particles

● Symmetry: SU(3) x SU(2) x U(1)

● “Matter particles”Quarks in six “flavors”

up, down, charm,strange, top bottom

leptonselectron, muon, tau, neutrinos

● “Force particles”Gauge Bosons

γ (electromagnetic force)W±, Z (weak, electromagnetic)g gluons (strong force)

● Higgs bosonspontaneous symmetry breaking of SU(2)Mass

The Standard Model

● Fundamental constituent particlesleptons q = 1, 0 e µ τ

νe νµ ντ

● 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)

● Role of symmetry:Symmetry (invariance under certain transformations)

governs behavior of physical systems:Invariance ⇒ “conservation laws” (Noether)Invariance under “local gauge transformations” ⇒ interactions

(forces)● SM has been thoroughly tested in many experiments --

embarrassingly good description of data

quarks q = 2/3 . – 1/3

Inclusive Jets - DØ

ET (GeV)

1/(∆

η∆E T)∫∫

d2 σ/(d

E Tdη)d

E Tdη (

fb/G

eV)

DØ Data |ηjet| < 0.5

JETRAD

CTEQ3M, µ = 0.5 ET max

1

10

10 2

10 3

10 4

10 5

10 6

10 7

50 100 150 200 250 300 350 400 450 500

“anomalous couplings”

DØ and LEP Combined

ALEPH 0.05+0.50−0.51

DELPHI −0.07+0.19−0.16

L3 0.01+0.19−0.17

OPAL −0.08+0.13−0.12

LEP −0.05+0.08−0.09

D0 0.00+0.10−0.10

LEP+D0 −0.03+0.07−0.07

preliminary

λγ

-∆ln

L

0

1

2

3

-1 -0.5 0 0.5 1

-0.16 < λγ < 0.10 @95% CL

W Boson Massmass of W

World average MW= 80.394 ± 0.042 GeV

W Boson Width

Indirect measurements fromthe ratio of W and Zcross sections:

SM: W → lν, qqIf additional non-SM particles exist which are lighter than and couple to the W boson⇒ additional contribution to the W boson widthDØ: Γ(W) = 2.107 ± 0.054 GeV

CDF:Γ(W) = 2.179 ± 0.040 GeV

Upper limit on non-SM decays of W∆Γ(W) < 132 MeV

Constraints on Higgs Mass

80.2

80.3

80.4

80.5

80.6

130 150 170 190 210

mH [GeV]107.7300 1000

mt [GeV]

mW

[G

eV]

Preliminary

68% CL

LEP1, SLD, νN Data

LEP2, pp− Data From combined analysis of all

available data, obtain constraints on Higgs massPresent SM Higgs Mass limits (95% CL):

107.7 < MH < 188 (GeV)

The SM works great ! Why change it ?● SM, developed in the 1970’s, has been thoroughly tested in many

experiments -- embarrassingly good description of data● Why are we not happy with it?

has 18 arbitrary parameters(e.g. quark, lepton masses) ⇒ Where do they come from ? does not include gravityE.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”)

● 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 experimentFrantically looking for deviations from SM

Electroweak Symmetry Breaking

Wphoton

mass = 0

mass = 81 GeV

● 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:

● In the SM, this occurs because the W and Z interact with a new, fundamental scalar particle, the Higgs boson

● SM predicts relation between masses of W, top, Higgs

Looking beyond the SM● Strategies

look harder -- do more precise tests of SMget a bigger hammer –- more energy, and look for “new phenomena” not compatible with SM

● Tools needed for this:Accelerator with higher energy

to make massive particles predicted by some of the SM extensionsto look closer into structure of proton and antiproton

Higher beam intensity new phenomena are rareto improve precision, need lots of data

better detectorscope with higher collision ratesprovide more end more precise informationbe more selective in what is recorded

● Fermilab upgrade programAccelerator: energy from 1.8 to 2.0TeV, raise luminosity by factor > 5 upgraded detectors DØ and CDF

TeVatron collider at Fermilab◆ Peak Luminosity 1032 cm-1s-1 (5X1032 cm-1s-1 )◆ Energy in c.m.s. 2 TeV◆ Integrated Luminosity 2fb-1 ( 8[30?]fb-1 )

◆ Turn-on March 1, 2001◆ First collisions April 3, 2001◆ Bunch crossing time 396 ns

(132ns)

DØ upgrade detector

The DØ detector in the collision hall (March 2001)

The DØ detector in the collision hall (March 2001)

D∅ Upgrade TrackingSilicon Tracker

Four layer barrels (double/single sided)Interspersed double sided disks793,000 channels

Fiber Tracker Eight layers sci-fi ribbon doublets (z-u-v, or z)74,000 830 µm fibers w/ VLPC readout

Preshower detectorsCentral

Scintillator strips– 6,000 channels

Forward– Scintillator strips– 16,000 channels

Solenoid–2T superconducting

cryostat1.1

1.7

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

● 16.000 channels● Read-out: SVX-II chips● Fast enough for L1● 2.6 m scintillation fibers, VLPC

readout + 10m waveguides● Mounted on 8 cylinders

20 < r < 50 cm● 8 alternating axial and stereo

doublets (2o pitch)

Silicon Microstrip Tracker● Provides very high resolution measurements of particle tracks near

the beam pipea) measurement of charged particle momentab) measurement of secondary vertices for identification of b-jets from

top, Higgs, and for b-physics● Track reconstruction to η= 3● Track impact parameter trigger (STT)● Point resolution of 10 µm ● Radiation hard to > 1 Mrad● Maximum silicon temperature < 10o C

240 cm

6 barrel sections12 Disks “F”

8 Disks “H”

Tracking with the SMT

p=qBRCharged

Particle

+-+-

+-n Si

n+

p+ 300 µm

VB

Readout

50 µm

Si Detector Reverse-Biased

Diode

● charge collected in sensors ⇒ Points for Track Fit● Precise Localization of Charge ⇒ accurate particle trajectories

SMT precision ~ 10 µm

Trigger● Trigger = device making decision on whether to record an event● 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 placee.g. in Tevatron collider, proton and antiproton bunches will encounter each other every 132nsat high bunch intensities, every beam crossing gives rise to collision ⇒

about 7 million collisions per secondwe can record about 20 to (maybe) 50 per second

● why not pick 50 events randomly?We would miss those rare events that we are really after:

e.g. top production: ≈ 1 in 1010 collisions Higgs production: ≈ 1 in 1012 collisions

⇒ would have to record 50 events/second for 634 years to get one Higgs event!Storage needed for these events: ≈ 3 × 1011 Gbytes

● Trigger has to decide fast which events not to record, without rejecting the “goodies”

Our Enemy: Rates● too much is happening, most of which we don’t want to know about

Collision Rate 7 MHzData to Tape 20 to 50 Hz

● Trigger:Try to reject “uninteresting” events as quickly as possible, without missing the “interesting” ones

132 ns between collisions !● Strategy:

3 Level System: L1, L2, L3 with successively more refined information and more time for decision available

L1 L2 L3 In Rate 10MHz 10kHz 1kHz

Out Rate 10kHz 1kHz 20Hz Decision 4.2µs 100µs 100ms Objects Single

Detector Correla-

tions Simple Event Recon

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 Trigger7 MHz 5-10 kHz 1000 Hz

4 µs 100 µs 100ms

L3

Run II Trigger Scheme● Bandwidth Allocations:

L1 in: 7MHz, out: 5-10kHz ; time: 4.2 µs L2 in: 10kHz, out: 1kHz ; time: 100 µs L3 in: 1kHz, out: 20Hz ; time: 100 ms/ 100 CPUs

● Trigger configuration: L1: Uses Calorimeter, Fiber tracker (CFT), Muon and Preshower objects;

trigger on Cal ET (em and jets),muon pT (use CFT),track pT,

track-preshower stubsL2: preprocessors for detectors, global L2 combines L1 objects into electrons, muons, jets, + makes decisionL2STT: use of SMT information in trigger:

refine momentum measuremntdetermine impact parameter

Our Friend: the b-Quark

● Many of the phenomena that we would like to study have b-quarksassociated with them:

Tag Top Decayst→bW ~ 100%

Tag Higgs (H→bb) Γ(H→ff) ∝ mf

2

new Particles (e.g. SUSY) → b’snew Physics couples to massCP Violation

Matter / Antimatter AsymmetryShould be Large in B systems

Silicon Track Trigger

Collision

B-Hadron:

Flight Length ~ mm’s

Decay Vertex

B Decay Products

Impact Parameter

● Idea: use SMT information at L2, to improve background rejection● Goals:

Sharpen PT MeasurementIdentify b−events

● B Event PropertiesImpact Parameter / Vertex Triggers

Silicon Track Trigger

SMTDetector

Cluster Finder

CFT Tracks(L1 Trig)

Associate Clustersto Tracks

Re-Fit Trackwith SMT Clusters

Global L2 Trigger

50 µ

s T

ime

Bud

get

● STT: Preprocessor, prepares information for decision by L2GLB ● Include SMT hits on CFT Track in L2 trigger

STT concept and design goals1. Refit Tracks ⇒ PT, ϕo, b

Use CFT A,H + SMT 4(3) Layers2. Use only r-ϕ information

stereo strips are clustered3. Use only PT>1.5 GeV, b<2 mm

L1CTT efficiency4. 30o sectors in SMT independent

system relies on this geometryloss in efficiency ~ 2%

5. L1CTT roads ⇒ search in SMTCFT geometry remapped in L1CTTuse SMT hits closest to road centerfixed road width = 2 mmt = t(select) + t(fit) + t(bus) ~ 16 µs

budget ~ 50 µst(bus) < 5.8 µst(select) ~ t(fit)t(select) ∝ N(hits in road)

6. Queuing SimulationSTT Lat. ~ 25 µs deadtime ~ negl.

9.5o

L1CTT region

SMT sector

CFT H-Layer Hit

CFT A-Layer Hit

L1CTT Road

STT Functionally

broadcast Trig/Road

datacorrect

& cluster

correct &

cluster1 / input

SMT Data (2 HDI / fiber)

compare clst / rd

1 / road

coord transf

clusters

clusters in roads

road

s<4

6 / 6

0o

coord transf

compare clst / rd

fit fit8 DSP/30o

fit matrix LUT

fitted tracks

Averages

3.7<clst/trk>

14 / 30o<N(clst)>

2 / 30o<N(trk)>

at input rate (no buffering)

FRC

STC

TFC

L1CTT TracksTrigger (SCL)

L2CTT

CPU

1 2

spa

re

3

VBD

4 5 6 7

STC

8

STC

9

STC

10

STC

11

STC

12

STC

13

FRC

14

STC

15

STC

16

TFC

20

TFC

1918

STC

17 21

spa

re

spa

re

spa

re

termin

ator

spa

re

termin

ator

Sector 1 Sector 2

STT Architecture

Numbers

2HDI/fiber

46max rd’s

fiber→vtm4smt in

fiber→vtm1road in

scl1trig in

30o2 / crTFC

9 / crSTC

60o1 / crFRC

6Crates

AFE MIX DFE- BC- TMCOL-CFT Ax.

CPS Ax.

L2STTL3L2STTL3

L2STTL3L2STTL3L2STTL3L2STTL3

L1CFT /CPSAx.L3

L2CFTL2PSL2CFTL2PSL2CFTL2PSL2CFTL2PS

L3L3L3L3L3L3L3L3 L1 µT

40

4

75

5

CPS Stereo 20

CFT Stereo.75

L2FPS L3L2FPS L3

L2FPS L3L2FPS L3

L1FPSL316FPS

32

•••• 3••••• 3•

CTT Organization showing links to the L1 TM, L2 PreProcessors and L3

LVDS LINK

DAUGHTER CARDS Each filling corresponds to a

different flavor

TRANSITION CARDS Each color corresponds

to a different flavor

LVDS LINKFSC LINK

G LINK

LEGEND

Created by Manuel I. MartinMay. 6, 99

Review October 2001

Created by Manuel I. MartinMay. 6, 99

Review October 2001

L2PSL3

CTOC

CTOC

FPSS

CTOC

CTOCCTOCCTOC

CTOC

CTOC

CTQDCTQDCTQDCTQD

STSX

STSXSTSX

STSX

STSXSTSX

STOV

STOVSTOV

STOV

STOV

STOV

FPSS FPSS

FPSS

CTTT

FPTT

STT history and status● Project started in 1996

(first feasibility studies, assess physics merit)● 1997 to 1999: proposals to DØ, Fermilab PAC, NSF● Summer 1999: consortium of 4 universities (Boston U., ColumbiaU.,

FSU, Stony Brook obtains funding (1.8M$ from NSF and DOE)● 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

● Sept. – Nov 2001: system tests with first prototypes, first at BU, now at Fermilab in the DØ environment

● Second (final?) prototype tests Nov. – Dec.● Production Jan – March 2002● March 2002 Installation in DØ

A WH event in the DØ detector

Two b-jets fromHiggs decay

Missing ET

Electron Track

EM cluster

CalorimeterTowers

P → ← P

pp → WH → bb

→ eν

ØD

Mtop vs MW in Run 2Run 2 scenario∆M t ≈ 3 GeV∆M W ≈ 40 MeV

● Within SM, Mtop and MWconstrain MHiggs to an accuracy of 80%

● The relation between these 3 masses provides a good consistency check of the SM

Summary

● 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;

● New trigger, in particular the STT, greatly enhances potential;

● We are looking forward to finally seeing something which clearly disagrees with the SM!

● Many thanks to Reginald Perry and ECE Dept.

● Hope for continued collaboration