What is Particle Physics --and why I like doing it

(Horst Wahl, October 2001) Particle physics

Goals and issues -- Why do it? How to do a particle physics experiment

Accelerator, detector DØ detector as example

Overview of the Standard Model Symmetry, constituents, interactions Problems of standard model -- look beyond The “Holy Grail” of (present) particle physics

Going beyond the SM – new experiments Upgraded DØ detector Triggering The 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 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 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? Curiosity Understanding constituents may help in

understanding composites Implications for origin and destiny of Universe

About Units

Energy - electron-volt 1 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•s

1 kW•hr = 3.6 × 106 Joules = 2.25 × 1025 eV

mass - eV/c2

1 eV/c2 = 1.78 × 10-36 kg electron 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/s momentum 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 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 /

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 410-7 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 = 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 them throw them against each other observe and record what happens analyze and interpret the data

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 p-antip Collisions qq(g) Interactions

UnderlyingEvent

u

u

d

gq

q u

u

d

Hard Scatter

Fermilab

Fermi National Accelerator Laboratory(near Batavia, Illinois)

Main Injector

Tevatron

DØCDF

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 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 siliconMuon detector

Interactionpoint 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 CollaborationThe DØ Collaboration

??

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”

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

MJJ = 1.18 TeVQ2 = 2.2x105

“Typical DØ Event”

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

MJJ = 1.18 TeVQ2 = 2.2x105

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

leptons electron, muon, tau,

neutrinos “Force particles”

Gauge Bosons (electromagnetic force) W, Z (weak,

electromagnetic) g gluons (strong force)

Higgs boson spontaneous symmetry

breaking of SU(2) Mass

The Standard Model Fundamental constituent particles

leptons q = 1, 0 e e

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

“anomalous

couplings”

DØ and LEP

Combined

-0.16 < < 0.10 @95% CL

W Boson Mass

World average MW= 80.394 0.042 GeV

mass of W

W Boson Width

Indirect measurements from the ratio of W and Z cross sections:

DØ: (W) = 2.107 0.054 GeV

CDF:(W) = 2.179 0.040 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 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 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”) 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 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

Wphoton

mass = 0

mass = 81 GeV

Looking beyond the SM Strategies

look harder -- do more precise tests of SM get 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 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

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 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, 2001First collisions April 3, 2001Bunch 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 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) 74,000 830 m fibers w/ VLPC readout

Preshower detectors

CentralScintillator strips

– 6,000 channels

Forward– Scintillator strips– 16,000 channels

Solenoid–2T superconducting

cryostat

1.1

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 = 3 Track impact parameter trigger (STT) Point resolution of 10 m Radiation hard to > 1 Mrad Maximum silicon temperature < 10o C

6 barrel sections12 Disks “F”

8 Disks “H”

240 cm

Tracking with the SMT

charge collected in sensors Points for Track Fit

Precise Localization of Charge accurate particle trajectories SMT precision ~ 10 m

p=qBRCharged

Particle

+-+-

+-n Si

n+

p+

300

m

VB

Readout

50 m

Si Detector Reverse-Biased

Diode

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 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 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: High Rates 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

Trigger: Try to reject “uninteresting” events as quickly as possible,

without missing the “interesting” ones 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 4.2s 100s 100ms

Objects Single Detector

Correla-tions

Simple Event Recon

DØ Trigger System

L2FW: Combined objects (e, m, j)

L2FW: Combined objects (e, m, j)

L2GLB

L1FW: towers, tracks, correlations 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 MHz 5-10 kHz 1000 Hz

4 s 100 s 100ms

L3

Run II Trigger Scheme 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

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 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

Many of the phenomena that we would like to study have b-quarks associated with them: Tag Top Decays

tbW ~ 100% Tag Higgs (Hbb)

(Hff) mf2

new Particles (e.g. SUSY) b’s new Physics couples to mass CP Violation

Matter / Antimatter AsymmetryShould be Large in B systems

Silicon Track Trigger

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

Goals: Sharpen PT Measurement Identify bevents

B Event Properties Impact Parameter / Vertex Triggers

Collision

B-Hadron:

Flight Length ~ mm’s

Decay Vertex

B Decay Products

Impact Parameter

Silicon Track Trigger STT: Preprocessor, prepares information for decision by

L2GLB Include SMT hits on CFT Track in L2 trigger

SMTDetector

Cluster Finder

CFT Tracks(L1 Trig)

Associate Clustersto Tracks

Re-Fit Trackwith SMT Clusters

Global L2 Trigger

50

s T

ime

Bud

get

STT concept and design goals1. Refit Tracks PT, o, b

Use CFT A,H + SMT 4(3) Layers

2. Use only r- information stereo strips are clustered

3. Use only PT>1.5 GeV, b<2 mm L1CTT efficiency

4. 30o 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.

9.5o

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

correct & cluster1 / input

SMT Data (2 HDI / fiber)

compare clst / rd

1 / road

coord transf

clusters

clusters in roads

road

s<

46 /

60

o

coord transf

compare clst / rd

fit fit8 DSP/30o

fit matrix LUT

fitted tracksL2CTT

Averages

<N(trk)> 2 / 30o

<N(clst)> 14 / 30o

<clst/trk> 3.7

at inp

ut rate

(no

bu

ffering

)

FRC

STC

TFC

STT ArchitectureCPU

1 2

spare

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

spare

spare

spare

terminator

spare

terminator

Sector 1 Sector 2Numbers

Crates 6

FRC 1 / cr 60o

trig in 1 scl

road in 1 fibervtm

max rd’s 46

STC 9 / cr

smt in 4 fibervtm

HDI/fiber 2

TFC 2 / cr 30o

AFE MIX DFE- BC- TMCOL-

CFT Ax.

CPS Ax.

L2STT L3

L2STT L3

L2STT L3L2STT L3

L2STT L3

L2STT L3

L1CFT /CPS Ax.L3

L2CFT L2PSL2CFT L2PSL2CFT L2PSL2CFT L2PS

L3L3L3L3L3L3L3L3 L1 T

40

4

75

5

CPS Stereo 20

CFT Stereo.75

L2FPS L3

L2FPS L3

L2FPS L3

L2FPS 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

L2PS L3

CTOC

CTOC

FPSS

CTOC

CTOC

CTOC

CTOC

CTOC

CTOC

CTQD

CTQDCTQD

CTQD

STSX

STSX

STSX

STSX

STSX

STSX

STOV

STOV

STOV

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

Two b-jets fromHiggs decay

Missing ET

Electron Track

EM cluster

CalorimeterTowers

P P

pp WH bb

e

A WH event in the DØ detector

Mtop vs MW in Run 2 Run 2 scenarioM t 3 GeVM W 40 MeV

Within SM, Mtop and MW constrain 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