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Methods of Experimental Particle Physics

Alexei Safonov

Lecture #1

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Syllabus etc• Structure of the class:

• 2 lectures per week (50 mins each)• 2 labs per week (1hr long each)

• Labs are really meant to be the place to get things started, ask questions, get help etc. You will typically be doing bulk of the work on weekly projects outside the class time

• You can do it either in the same computing lab or anywhere you want to (home, starbucks, etc.)

• Instructors:• Alexei Safonov (lectures, some of the labs)• Aysen Tatarinov (labs)

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Course Logistics• Best way to get to me is to email:

• safonov@tamu.edu• Phones: 979-845-1479 (office), 630-650-2078

9cell, for emergencies)• Aysen’s email: tatarinov@physics.tamu.edu

• There will be a web-page setup shortly, which will contain course information, instructions where to find your assignments, how to turn them in etc.

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Topics to be Covered• The syllabus gives an idea of what we will

do, but the exact details will likely change• The idea of this course is to give you an

overview of experimental HEP and give you some hands on experience on data analysis if you are:• A future HEP experimentalist who will be

using this as working knowledge• Or a HEP theorist who wants to have a decent

idea of what experimentalists do and how

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What to Expect• Lectures:

• The list of topics is very broad, there is no way I can go in depth on many of the subjects within one semester

• The intent is to give you an overall understanding of topics and their inter-relationship

• Labs (will start 2nd week of classes):• Geared towards data analysis related topics

• Data analysis and necessary tools: data representation, basic programming, computational math, statistics methods

• Requires some knowledge of C/C++

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PARTICLE PHYSICS: WHAT’S IT ALL ABOUT

Scales and Different Physics• Particle Physics studies fundamental particles

and interactions• Fundamental means “there is no structure”

• Most of what you see around you has very distant relation to particles and fields• Most real world objects are collections of an insane

number of fundamental particles interacting with each other all the time

• Hopeless to describe in the language of particle physics quantitatively

7Scale (mm)

Particle Physics

Grey Area

Nuclear Physics

Classical Mechanics

Solid State Physics

Who knows?

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Why Bother Then?• Particle Physics holds answers to the origin of

the Universe and has many cosmological implications

• Allows sometimes quantitative and more often qualitative understanding of processes that are within our reach from the right on the previous page graph• Radioactive decays and nuclear bombs

• Loads of practical applications related to interaction of particles with matter• NASA electronics, cancer proton therapy etc.

• Curiosity: we are scientists, we want to know answers

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Particle Physics in 24 Seconds• Basic questions:

• What is the world made of?• Matter = particles?

• Where it came from?• Big Bang?

• What forces keep things together?• Gravity, electromagnetism,

weak force, strong force, anything else?

• Follow-up ones:• Why particles have their (so different) masses?• Do particles have substructure?• Why strengths of interactions differ by so much?• Any new particles or interactions we don’t know of?

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Particle Physics Jargon• Most of what we can calculate has something to do with

probabilities of one particle interacting with another particle• Particles are QM “fields”• Interactions are described by QM lagrangians and are

transmitted also by fields• Two electrons know about each other because they exchange a

photon• If you believe in symmetries, you will often call them “gauge” fields

b/c interaction transmitters are generators of the corresponding “gauge symmetry groups”

• Once we know some basics and have enough particles, can predict probabilities of particles decaying into each other• Can’t be regular QM because relativistic effects are important

• A W boson weight about 80,000 MeV, electron is 0.5 MeV, W decays to electron and a near-massless neutrino – electron travels at near the speed of light

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Standard Model of Particle Physics• Physical content:

• 12 basic particles• Each has an antiparticle

• Interact via force carriers called gauge bosons

• Higgs boson giving mass to all other particles

• Includes 2.5 forces:• Electroweak=“electromagnetic

+ weak” combined force• All basic particles participate,

transmitted by W/Z/g bosons • Responsible for radioactive

decays and electromagnetic interactions

• Strong force:• Only quarks participate,

transmitted by gluons• Holds proton and other composite

hadrons together

• Dark Matter is unexplained at all

• Discovery of neutrino oscillations makes Standard Model at least “not quite right”

• Gravity is not included

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Particle Physics and the Origin of Universe

time

• One example is the baryon asymmetry• Lots of protons,

very few antiprotons

• Why? Shouldn’t there be equal numbers?

• Something must have happened in the very early Universe at the level of basic interactions that shifted things there