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THINGS BIG & SMALL
Dhiman Chakraborty
([email protected])
Northern Illinois University,
Northern Illinois Center
for Accelerator and Detector Development
Dhiman Chakraborty
THINGS BIG AND SMALL
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Know thyself …
– Where did we come from?
– Where are we going?
– What/who else is out there?
These are the most human of questions.
For most part of its history, mankind has
turned to myth and religion for answers
(eventually being told to shut up & listen).
Of late, science is yielding verifiable, factual
explanations that are proving to be far
wilder and more fascinating than the most
fanciful of fictions.
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Did you know?
• We are all STARFOLKS : more than
95% of our body weights are accounted for
by atoms baked inside a star (or stars)?
• We would not exist if some of the constants
of nature were ~1% different from what
they are? Are these special values a mere
coincidence? Do they change over time?
• Of all the sources of gravity that holds the
universe together, only 4% can be seen
(even with the most powerful and sensitive
telescopes)? Most (73%) is not even matter!
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Composition of the Universe
.
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The extremes are connected…
• To understand the structure and phenomena
at the largest scales (cosmology), we must first
know those at the smallest (particle physics).
• The particle physicists, in turn, get their cues
from cosmological observations.
• The two are inextricably coupled.
• Particle astrophysics is a rapidly growing field.
• 96% of what constitutes the Universe is yet
unknown/unobserved.
• A revolution of unparalleled proportions is
around the corner – DRIVERS WANTED!
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Down to the tiniest…
What are the “fundamental”
building blocks of nature?
Can we ever reach a point
where we are confident
that there is no further
substructure?
The question only makes
sense in the context of
the tiniest distances, or,
equivalently, the highest
energies that we are able
to probe (E=hn).
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Matter and interactions
“Matter”: made of Fermions. Spin-(2n+1)/2
particles that do not share a quantum state.
Consequently, their production and decay
must be associated with an “antifermion”.
“Interactions” (not just among Fermions):
mediated by Bosons. Integer-spin particles
that gladly share a quantum state, and can be
radiated or absorbed singly.
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The Four forces:
1. Gravity
–
–
–
–
–
–
–
–
Mediated by “graviton”s (s=2, m=0, qe=0, Y=0, qc=0).
Couples to energy (no known “neutralization” of charge)
Weakest of all: insignificant at single-particle level, but
Infinite range and absence of neutralization combine to
make it the dominant force at large scales. Holds celestial
bodies together. Keeps us on the planet, a planet on orbit
around a star, a star in a galaxy, a galaxy in a cluster, a
cluster in a supercluster, …
Also responsible for stellar structure and collapse
(supernova) leading formation of neutron stars, black holes.
Only a geometrical description: curvature of space described
by (Einstein’s) principles of general relativity.
No fully-developed quantum description yet (weakness at
small distances make experimental measurements very
difficult, but sub-mm measurements are being made).
Important probe to extra spatial dimensions, if they exist.
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The Four forces:
2. Electromagnetism
– Mediated by “photon”s (s=1, m=0, qe=0, Y=0, qc=0).
– Couples to electric (and magnetic) charge (qe).
– No self-coupling.
– Infinite range, but formation of neutral bound states of +ve &
-ve charges (e.g. atoms and molecules) makes it the primary
force mainly in the intermediate scales (but also prevents/
counters gravitational collapse of multiparticle systems)
– Keeps electrons in orbit around atomic neuclei.
– Coupling strength ideal for perturbative calculations.
– Extremely precise and well-tested quantum-mechanical
description: Quantum Electrodynamics (Dirac, Feynman).
– Until recently, our only means for astronomical observations.
– The only force we can control.
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The Four forces:
3. Weak
– Mediated by W’s & Z’s (s=1, m=80 GeV (W) / 91 GeV (Z),
qe=1 (W) / 0 (Z), Y0, qc=0).
– Couples to weak hypercharge (Y).
– Has self-coupling, although not of much significance.
– Much weaker than EM & strong forces down to nuclear scales.
– Because of large mass of mediators, shortest in range of all
forces (lifetime of W, Z ~10-25 s), but
– Unique in two respects:
• The only force, other than gravity, that couples to neutrinos.
• The only way for matter to mutate. No other mediator has qe  0.
– Not a “binding force”, but causes some types of radioactivity.
– The main mechanishm behind solar energy (4H  He + 2ne).
– Unifies with EM at energies >100 GeV: “electroweak”
interactions (Lee, Yang, Glashow, Salam, Weinberg, t’Hooft, …)
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The Four forces:
4. Strong
– Mediated by “gluon”s (s=1, m=0, qe=0, Y=0, qc 0 (8 types)).
– Couples to “color” charge (qc).
– Strongest of all known forces.
– Strong self-coupling of gluons limits range to nuclear scales.
• Screening  fall-off at shorter distances (“asymptotic freedom”)
• Strong neutralization forbids isolation of q/g (“confinement”)
– Binds quarks in protons and neutrons, p’s & n’s in neuclei.
– Described by Quantum Chromodynamcis (Gell-Mann et al.) but
– Strength makes perturbative calculations very challenging.
– Dominant force at hadron colliders.
– (Grand) Unification with Electroweak theory believed possible,
but requisite energies are beyond terrestrial reach.
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The Standard Model
A description of
PARTICLES that make
up matter and the
FORCES of interaction
between them.
Three generations each
of quarks & leptons.
Subjects of forces:
– strong: quarks only
– EM: q’s & charged l’s.
– weak: all fermions
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Unification theories
.
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Particle acceleration & collisions
• To probe small distances, we need high
energies: E  l-1.
• Only EM fields useful for acceleration,
and only charged particles that are not
too short-lived can be accelerated.
–
–
–
–
This limits us to electrons, protons & ions
Photons piggyback on charged particles
Protons and ions are not point-like, but heavy
e’s are light  E loss due to synchrotron
radiation
– High-energy muons have been used in fixedtarget mode, collider mode in development.
• Two options:
– Look to the heavens (high-E Cosmic rays)
– Build your own (earthbound machines)
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Particle acceleration & collisions:
Energy vs. Luminosity
• High energies are necessary, but not
sufficient. Unfortunately, the size of our
detectors (microscopes) is limited, and
God will not focus his beams to them.
• Cosmic rays have little use except for n’s
& g’s created at very high energies.
• We build our own accelerators to get high
luminosities, although Emax is limited.
• Fixed target: higher luminosity, lower E
• Collider (beam-beam): higher E, lower L.
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Particle Colliders
.
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Particle Colliders
.
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Particle Colliders
Hadron colliders:
Higher energies, but
energy of collision of
point-like constitutents
have large variance.
Lepton (ep) colliders:
Lower energies, but wellknown, controllable ECM
of collisions, much
cleaner final states.
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The Tevatron pp
collider at Fermilab
.
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Fermilab
.
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Fermilab
.
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Fermilab
.
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Indentifying particles
.
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Indentifying particles
.
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Calorimetry
.
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Collider Detectors
.
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Collider Detectors
DØ
CDF
.
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The most common events
at hadron colliders
Production of two jets (narrow showers of high-energy particles) to be
read by the detector and reconstructed with sophisticated algorithms
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Finding needles in haystacks
Bump-hunting
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Data acquisition
At the Tevatron detectors,
events pour out
through ~1 million
electronic channels at
rates of ~1 MHz. Only a
small fraction of these
is interesting, and must
be sifted in real time
through multilevel
trigger systems to
record as many of the
interesting ones while
minimizing the volume
of uninetersting events.
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The
top
: a quark apart
.
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A top-antitop event
.
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A top-antitop event
.
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A top-antitop event
.
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The Higgs
.
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Extra Dimnesions?
.
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A high-energy diphoton
event at DØ
We do expect a few
events like this from
known Standard Model
processes. No
siginificant excess
observed so far.
Much effort goes into
estimating signal
efficiency and
background
contamination.
State-of-the art patternrecognition algorithms
and statistical analysis
methods employed.
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Magnetic monopoles?
If they exist, they could
explain the
quantization of
electric charge.
The quantum will be
O(104) stronger than
that of qe.
Thus, magnetic
monopoles should
cause very strong
scattering of light,
resulting in diphoton
final states at
colliders.
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Up to the grandest…
.
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Evolution of the Universe
.
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Detecting the elusive neutrinos
LSND
Neutrinos ghostlike particles
are stable, and
more abundant
than all other
fermions
combined, but
very hard to
detect due to
their lack of
interactions.
Fascinating,
nonetheless
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Sloan Digital Sky Survey (SDSS)
.
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SDSS
.
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SDSS
The M78 nebula – a nursery of stars
It is extremely
important to
know how the
mass and
energy, most of
it dark, is
distributed
throughout the
universe. A
particle theory
that contradicts
cosmological
observations will
not be viable.
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Geometry of the Universe
.
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Peeking into the Universe’s
infancy: the Wilkinson
Microwave Anisotropy Probe
.
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WMAP
talk about thermal resolution!
.
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WMAP
talk about spatial resolution!
.
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Evolution of the Universe
Time
Since the
Big Bang
The state of the Universe
Human
Equivalent
379,000
years
This is a time when the pattern of the Cosmic
Microwave Background light was set. The
Universe was just cool enough for atoms to
form for the first time.
At this stage, the
Universe is the
equivalent of a baby
just 19 hours old.
200 million
years
The matter in the Universe condensed by
gravity until the first stars ignited. WMAP has
detected this event at about 200 million years
after the Big Bang. (WMAP does not see the
light of the first stars directly, but has detected
a polarized signal that is the tell-tale signature
of the energy released by the first stars.)
The Universe is the
equivalent of a baby
of 13 months, just
old enough to begin
taking its first steps.
1 billion
years
The first galaxies began to form at about this
time. Unlike a human child, the Universe has
reached the end of its formative years at this
young age. There are no further notable
cosmic events past this stage.
At this age, the
Universe is
equivalent to a child
just under six years
old.
13.7 billion
years
The present day Universe with its billions
upon billions of stars and galaxies is found to
be 13.7 billion years old, an age with a margin
of error of close to 1 percent.
An adult person at
80.
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NICADD
The Photoinjector
at Farmilab
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The next Linear Collider
A prototype
9-cell
superconducting
RF cavity
capable of
gradiantes
>50 MeV/m
One of two
contenders,
the winner
will be
picked in
2004.
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NICADD: simulations
GEANT4
simulation of
a calorimeter
module for
beam tests.
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NICADD:
scintillator DHCal
10 cm2, 5 mm thick
scintillating plastic
cells produced in
house.
~1 million of these
could be used in
digital mode at the
linear collider
detector.
Novel algorithms for
unprecedented
energy resolution.
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NICADD
Designing a
thin, yet
strong,
end-plate
for a
cylinder to
hold liquid
hydrogen to
focus muon
beams in
energymomentum
space.
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Spin-offs from HEP
WWW
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Spin-offs from HEP
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THANK YOU!
Feel free to contact the speaker
for more information
[email protected]
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