Columbia University Christine Aidala December 2003 Solving the Proton Spin Crisis My Work (and Life!) as a Graduate Student on the Experiment

Columbia University

Christine Aidala

December 2003

Solving the Proton Spin CrisisMy Work (and Life!) as a Graduate Student on the

Experiment

Christine Aidala, Columbia University, December 2003

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Part I: Some Physics

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What is spin?Spin is a quantum mechanical property of fundamental particles or combinations of particles.

It’s called “spin” because it’s a type of angular momentum and is described by equations treating angular momentum.

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In a magnetic field, different spin states have different energies but have the same magnitude of the angular momentum.

The units of angular momentum are the same as Planck's constant, h and can only have values that are integer : 0, 1, 2, 3, . . . or half-integer: 1/2, 3/2, 5/2, . . .


42s+1 Energy Levels

Any particle with spin

0

z

Β

Spin ½ particle (e.g. 107Ag or 1H)

0

z

Β

Spin 1 particle (e.g. 2H)

0

z

Β

Spin 3/2 particle (e.g. 7Li)

0

z

Β

Stern-Gerlach ExperimentA

pply a magnetic field


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• Fermions include most of the familiar matter around us, such as electrons, protons, and neutrons, as well as quarks and neutrinos.

Fermions and BosonsAll particles can be classified into two categories depending on their spin: fermions and bosons.

• Bosons include force-carrier particles such as the photon (electromagnetic force) and gluon (strong force), as well as composite particles made of two fermions.


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The Quark-Parton Model• Similarly to Rutherford’s 1911

experiment in which the scattering of alpha particles at large angles off of gold revealed a hard atomic core (the nucleus), in the late 1960’s at SLAC, scattering of electrons at large angles off of protons revealed “hard” subcomponents in the proton – Protons weren’t solid lumps of positive

charge as previously believed!

– The pointlike constituents that make up the proton are called “quarks,” or slightly more generally, “partons.” Quark

Quarks are fermions with spin 1/2.


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Quark-Parton Model (cont.)

• But these quarks are not completely free in the nucleon!– Bound by force-carrier particles called “gluons.” – “Sea quarks” are also present: short-lived quark-

antiquark pairs from quantum mechanical fluctuations.

• As you hit the proton harder, you resolve shorter-lived fluctuations: gluons and sea quarks.

The simplest model says a proton’s made of three “valence” quarks: 2 up quarks and 1 down quark.


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Proton

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Surprising data from polarized muon-nucleon scattering in late 1980s!

1987: Only 12% +- 16% of proton’s spin carried by quarks!

The proton spin crisis begins!!

Spin zLG 2

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1Quark Spin Gluon

Spin

Orbital Angular Momentum

The Proton Spin Crisis

Say you have a proton with total spin +1/2 along some axis. You’d expect it to contain two quarks with spin +1/2 and one with spin -1/2.1/2 + 1/2 - 1/2 = +1/2

The rest now expected to be from gluon spinand orbital angular momentum of quarks and gluons, but this hasn’t been easy to measure!


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Part II: PHENIX and RHIC


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USA Abilene Christian University, Abilene, TX Brookhaven National Laboratory, Upton, NY University of California - Riverside, Riverside, CA University of Colorado, Boulder, CO Columbia University, Nevis Laboratories, Irvington, NY Florida State University, Tallahassee, FL Georgia State University, Atlanta, GA University of Illinois Urbana Champaign, IL Iowa State University and Ames Laboratory, Ames, IA Los Alamos National Laboratory, Los Alamos, NM Lawrence Livermore National Laboratory, Livermore, CA University of New Mexico, Albuquerque, NM New Mexico State University, Las Cruces, NM Dept. of Chemistry, Stony Brook Univ., Stony Brook, NY Dept. Phys. and Astronomy, Stony Brook Univ., Stony Brook, NY Oak Ridge National Laboratory, Oak Ridge, TN University of Tennessee, Knoxville, TN Vanderbilt University, Nashville, TN

Brazil University of São Paulo, São PauloChina Academia Sinica, Taipei, Taiwan China Institute of Atomic Energy, Beijing Peking University, BeijingFrance LPC, University de Clermont-Ferrand, Clermont-Ferrand Dapnia, CEA Saclay, Gif-sur-Yvette IPN-Orsay, Universite Paris Sud, CNRS-IN2P3, Orsay LLR, Ecòle Polytechnique, CNRS-IN2P3, Palaiseau SUBATECH, Ecòle des Mines at Nantes, NantesGermany University of Münster, MünsterHungary Central Research Institute for Physics (KFKI), Budapest Debrecen University, Debrecen Eötvös Loránd University (ELTE), Budapest India Banaras Hindu University, Banaras Bhabha Atomic Research Centre, BombayIsrael Weizmann Institute, RehovotJapan Center for Nuclear Study, University of Tokyo, Tokyo Hiroshima University, Higashi-Hiroshima KEK, Institute for High Energy Physics, Tsukuba Kyoto University, Kyoto Nagasaki Institute of Applied Science, Nagasaki RIKEN, Institute for Physical and Chemical Research, Wako RIKEN-BNL Research Center, Upton, NY University of Tokyo, Bunkyo-ku, Tokyo Tokyo Institute of Technology, Tokyo University of Tsukuba, Tsukuba Waseda University, Tokyo S. Korea Cyclotron Application Laboratory, KAERI, Seoul Kangnung National University, Kangnung Korea University, Seoul Myong Ji University, Yongin City System Electronics Laboratory, Seoul Nat. University, Seoul Yonsei University, SeoulRussia Institute of High Energy Physics, Protovino Joint Institute for Nuclear Research, Dubna Kurchatov Institute, Moscow PNPI, St. Petersburg Nuclear Physics Institute, St. Petersburg St. Petersburg State Technical University, St. PetersburgSweden Lund University, Lund

12 Countries; 57 Institutions; 460 Participants


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The Relativistic Heavy Ion Collider• Primarily designed to collide heavy ions• Main design purpose: search and discovery mission for

quark-gluon plasma, state of matter believed to have existed 10 millionths of a second after the Big Bang.

• Most versatile collider in the world! Au-Au, p-Au, polarized(!) p-p, other combinations . . .– asymmetric species possible due to independent rings with

separate steering magnets

• First polarized proton collider in world! Special magnets and other equipment installed to measure and maintain polarization.


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The Relativistic Heavy Ion Collider

located at Brookhaven National Laboratory

Long Island,

New York

RHIC as Seen from Space


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Getting a Bit Closer


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The PHENIX Detector at the Collision Point2 central spectrometers- Track charged particles and detect electromagnetic processes

2 forward spectrometers- Identify and track muons

3 global detectors- Determine when there’s a collision


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The PHENIX Detector


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How Can We Investigate the Proton’s Spin at PHENIX?

• Collide polarized protons in different configurations and see what we observe in our detector

• Most often examining asymmetries– e.g. difference in the number of a certain particle produced when the

beams have the same vs. opposite polarization– Same number produced gives asymmetry = 0.– All from one configuration and none from the other gives +1 or -1.

• Knowing what partonic processes (involving quarks and gluons) led to production of the observed particle gives us a handle on the quarks’ and gluons’ contribution to the spin.

CB

CBAsymmetry


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• Looking at asymmetry in production of a meson (a quark-antiquark pair) called the 0, which decays quickly ( ~ 10-16 s!) to two photons.

• Find 0’s by looking for photon pairs that combine to the right mass.

• Single-spin asymmetry: only look at difference in production when one beam is polarized up vs. down and average over the polarization states of the other beam.

Invariant mass of photon pair

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What I’m Doing: Transverse Single-Spin Asymmetry in Neutral Pion Production

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Part III: Being a Graduate Student


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Applying and Getting In• Letters of recommendation• Personal statement

– good to identify an area of interest (e.g. high-energy experimental physics for me) but not be too specific unless you’re going expressly to work with a particular professor (and that professor has agreed!)

• Research and other experience • Grades• General and Physics GRE

• Diverse research, strength or expansion in the areas you think you might be interested in• Comfortable size of the department and grad program• Friendly, cooperative atmosphere (difficult to gauge beforehand)• How quickly they get students into research• High percentage of entering students who finish • Reasonable average time to graduation

What they want from you

What you should look for from them


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Experiences I had as an undergrad• Research every summer, senior project

– Locally in a lab at my university

– Summer student at Brookhaven National Lab

– Summer student at CERN in Geneva, Switzerland

– Senior project

– Also did research with a group from my (first) graduate institution the summer before starting there

• Conferences

• Organizing Society of Physics Students events

• Visiting grad schools spring break junior year

REU

CEU


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The first couple years of grad school• Classes

• Teaching assistant or perhaps research assistant

• Research over the summer--important!

• Financial support– everyone fully supported in Ph.D. programs,

including international students!• Tuition covered and get a stipend as well (~$20,000)

– TA, RA, fellowship (e.g. NSF)– Master’s programs often have no financial support


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Qualifying Exams• Nearly every Ph.D. program requires you to pass some kind of

“qualifying” or “candidacy” exam before you’re “promoted to candidacy” for the doctorate

• Timing, format, and scope of the exam depends on the program, but generally speaking, you have to pass by the beginning of the third year, and the exam is supposed to cover more or less everything you’ve ever learned in physics(!)

• Can be intimidating (I certainly thought so), but I also have to admit that the comprehensive review also did me a lot of good

• Find out ahead of time what percentage of students typically pass--you probably don’t want a school that “weeds out” students via their qualifying exam


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Choosing a research group/advisor• Theory vs. experiment

• What area of physics

• Large vs. small local group, large vs. small collaboration

• Travel or relocation involved?

• How independent do you want to be?– i.e. is a super-busy advisor

right for you?

• You’re going to be working with these people for the next few years--you’d better like them! And be comfortable working with them.– Talk to older students in the

group!!

• Even if the group expects you to be independent, push to get a strong introduction/orientation in the first couple months– e.g. suggest a journal club,

schedule regular discussions with advanced students, . . .


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A few years of full-time research• Often start spring of second year or summer after

• First year of research mostly non-thesis work– Experimentalists: hardware or software

– Theorists: lots of reading!

• Then want to identify a specific thesis topic to spend another two or three years on– Not as intimidating as I originally imagined! There’s

usually a set of physics topics that the group is interested in, and you’ll choose and develop one of these, rather than having to come up with a completely new, brilliant physics question that’s never been addressed before.


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• Academic research at university or national lab

• Industrial research

• Medical physics--quickly expanding field!

• Teach– quite respectable salaries for Master’s or Ph.D. teaching high school (need

education qualifications, though)

• Scientific policy – program for grad students to spend time in Washington exists

• Forensic physics--law enforcement and investigation

• Scientific journalism

• Scientific outreach and education for the public

• Software and programming

• Finance, statistics

What can you do with a graduate degree in physics, anyway?

Not by any means a complete list!


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Do I have a personal life?

• Go out to dinner in NYC once a week with students/ postdocs in my group after our weekly journal club

• Play ultimate at BNL twice a week May-October• Take Japanese lessons for the fun of it--every Friday at BNL• Have a wonderfully patient husband (met at CERN!) who

graciously puts up with my busy lifestyle• Together we have friends and colleagues over for dinner

relatively often or invite them out for other activities• We also find time (and money!) for occasional three-day

weekend trips and at least one long “vacation” a year to see his family in Italy.

Well, that’s a matter of opinion of course, but . . .

All in all, I’m certainly not complaining . . .


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The path I took to end up here

• Yale ‘95-‘99, Bachelor’s in physics, music

• U. of Chicago ‘99-‘00 (grad school)

• Milan, Italy ‘00-‘01 (teaching English and music)

• BNL ‘01-‘02 (research job)

• Columbia ‘02-present (grad school once again)

Probably not something you’d want to emulate, but it might be good to know you can stray from the straight and narrow.


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+ Physics = ?• Personally, never any problems as a woman in physics• Bothered me a bit that half of my funding at BNL for

“minorities” in science• Much more conscious instead of my age (at BNL) and

having gone through the less math- and physics-focused American education system (in classes)

• Tend to look at advantages of being one of few women– People remember you better

– Can play a different social role

• Number of women in physics increasing slowly but surely


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Final words• Being a physicist involves more than physics

– People skills, presentation skills, computing skills, writing skills, organization and leadership skills, . . .

• A degree in physics isn’t just for physicists

Graduating from college and finding yourself a “freshman” in life again can be daunting. Take advantage

of the resources around you, and assume people are interested in you until you find out otherwise!

Feel free to contact me in the [email protected]


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Extra Slides


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• Hadrons are made of confined quarks and gluons with net zero color

• Hadrons interact by exchanging other hadrons

proton

proton

pionThe Strong Force

• Quarks are held together by exchanging “colored” gluons– V~1/r at short distance– V~kr at long distances

• We say that quarks and gluons are confined in hadrons – mesons and baryons Confinement!


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Spin of the proton: Current state of affairs

• S = 1/2 = (1/2) q + G + Lq + LG

• q = 0.2 +- 0.1

• G = 1.8 +- 1.0

• Experiments hunting for G include– PHENIX and STAR at RHIC: p-p– COMPASS at CERN: -N– HERMES at DESY: e-N


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The RHIC Layout

Run-2 configuration

installed for Run-3

“Blue” and “yellow” rings

Siberian Snakes

BRAHMS & PP2PP

STARPHENIX

AGS

LINACBOOSTER

Pol. Proton Source500 A, 300 s

Spin Rotators

Partial Siberian Snake

200 MeV Polarimeter AGS Internal PolarimeterRf Dipoles

RHIC pC Polarimeters

PHOBOS


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Dealing with busy people• Schedule regular, fixed meetings, ideally around

something that can’t be moved (e.g. a professor’s lecture)

• Ask explicitly what the best way to contact them is

• If it’s someone who has specific responsibilities with respect to you, do your best to be honest if you’re dissatisfied and feel they’re not meeting (your expectation of) those responsibilities

• Give positive feedback as well--sometimes we students need to help in “training” our professors!


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Other difficult-to-deal-with advisor traits to watch out for

• Unrealistic expectations about how long it’ll take you to do something

• Too many branching suggestions of diminishing importance

• Not paying attention to details of what you’re doing

Documents

Columbia University Christine Aidala December 2003 Solving the Proton Spin Crisis My Work (and Life!) as a Graduate Student on the Experiment