1. From a CEU ’98er: 9 Years and 5 Research Projects Later University of Massachusetts Amherst Christine Aidala October 11, 2007 DNP WNSL BNL CERN DESY You are (back) here

2. C. Aidala, DNP, October 11, 2007 2 Life beyond problem sets Despite the fact that becoming a physicist typically means spending six years or more sitting through lectures and doing zillions of problem sets, this isn’t representative at all of what it’s like to be a physicist! Opportunities to perform research and attend conferences give you much more of a feel of what it’d be like beyond those initial years of coursework...

3. C. Aidala, DNP, October 11, 2007 3 Undergraduate research: Opportunities for exploration During your undergraduate career a great and flexible time to explore different fields of research! Through a few summer internships and/or 1- or 2- semester projects, you can see firsthand much more than it’ll be easy to see once in grad school, where changing research group after the end of your second year often means adding extra time onto your degree

4. C. Aidala, DNP, October 11, 2007 4 My own experiences Low-energy nuclear structure at Wright Nuclear Structure Lab, Yale University (nuclear fusion- evaporation cross section studies, 100 MeV beam on fixed target) Relativistic heavy ion physics at Brookhaven National Lab (detector simulation, 200 GeV per nucleon center- of-mass) Proton-proton particle physics at CERN (detector hardware and data acquisition, 14 TeV c.m.) Summer, through my university, shown at ‘98 CEU Summer REU Since the summer after my freshman year, have woven my way through various energies and collision systems in nuclear and particle physics

5. C. Aidala, DNP, October 11, 2007 5 My own experiences Nucleon spin structure at DESY (simulations for proposed polarized proton-electron collider, 300 GeV c.m.) e+e- particle physics at CERN (exotic physics searches, 200 GeV c.m.) More relativistic heavy ion physics and more nucleon spin structure at Brookhaven National Lab (a whole bunch of stuff in the past six years..., 200 GeV c.m.) Senior project, two semesters Summer before grad school Temporary employment, grad school, and postdoc... Teaching English and music in Italy for 1 ½ years...

6. C. Aidala, DNP, October 11, 2007 6 My career in pictures... WNSL BNL CERN DESY You are (back) here Energy (eV) Experiment # Energies I’ve Worked At

7. C. Aidala, DNP, October 11, 2007 7 Finding a passion... Maybe I actually missed my “true” calling as a condensed matter theorist (you can never try everything!), or even as a park ranger (got a summer job offer from the National Park Service a couple weeks after I’d agreed to take my first research job!) But among the areas I have explored, I’ve found a passion in one of them...

8. C. Aidala, DNP, October 11, 2007 8 And finding a niche I’ve also found a community of people that I respect and enjoy –With comfortable room for me to make meaningful scientific contributions Nucleon structure, in particular its spin structure, is a community in which I’ve come to feel at home

9. C. Aidala, DNP, October 11, 2007 9 Studying Proton Structure If can’t see individual quarks and gluons (“partons”), how to determine the proton’s structure? Inelastic scattering—shoot a high-energy beam (e.g. of electrons) at the proton to break it up, and try to understand what happens –Electron exchanges a photon with quarks, because quarks carry electromagnetic charge as well as color Describe proton structure in terms of parton distribution functions (pdf’s) - Probability of scattering off of a parton carrying a particular fraction of the proton’s momentum (“Bjorken-x” variable) (Recall that even if protons are in a stationary target, have non-zero momentum in center-of-mass frame)

10. C. Aidala, DNP, October 11, 2007 10 Proton Structure and Momentum Fraction Halzen and Martin, “Quarks and Leptons”, p. 201 x Bjorken 1 1 1 1/3 x Bjorken 1/3 1 Valence Sea A point particle 3 valence quarks 3 bound valence quarks and some slow sea quarks Small x What momentum fraction would the scattering particle carry if the proton were made of …

11. C. Aidala, DNP, October 11, 2007 11 What Have We Learned? Conclusions from decades of inelastic scattering data investigating proton momentum structure: –3 “valence” quarks carry (on average) the largest single momentum fractions of the proton –But lots of gluons and “sea” quark-antiquark pairs in the proton as well! Gluons carry ~50% of total momentum of proton. What about the spin structure of the proton? - Do inelastic scattering with polarized protons! (spin directions all aligned) ~~ ?

12. C. Aidala, DNP, October 11, 2007 12 Proton Surprising data from late 1980s! 1987: Only 12% +- 16% of proton’s spin carried by quarks’ spins! The Proton Spin Crisis begins!! Spin Quark 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 naively 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 spin and orbital angular momentum of quarks and gluons, but this hasn’t been easy to measure! gluon

13. C. Aidala, DNP, October 11, 2007 13 Quark and Gluon Helicity Distributions up quarks down quarks sea quarks gluon EMC, SMC at CERN E142 to E155 at SLAC HERMES at DESY In valence region (x Bj >~0.1), note up quarks have large spin contribution in same direction as proton spin and down quarks have (smaller) contribution opposite to proton - Reminiscent of ½ + ½ - ½ = ½, but numbers don’t add up! Sea quarks just add to our difficulties!! Can gluon spin account for what’s missing?? x Bj We’re trying to find out at RHIC!

14. C. Aidala, DNP, October 11, 2007 14 The Relativistic Heavy Ion Collider

15. C. Aidala, DNP, October 11, 2007 15 The whole story? Six years after the first polarized proton run at RHIC, have we measured the gluon’s spin? Present RHIC data suggest gluon spin contribution to proton spin can’t make up what’s missing! –Proton Spin Crisis continues!!! Orbital angular momentum of quarks and gluons the only other possibility, but nobody has been able to measure it yet! Data from several facilities over a number of years will be necessary to put together a more complete picture of nucleon spin structure Spin Quark Spin Gluon Spin Orbital Angular Momentum

16. C. Aidala, DNP, October 11, 2007 16 My whole story? Far from it! After initially getting involved in nucleon structure research as an undergraduate, I’m looking forward to continuing upon a long, exciting, and rewarding future in the field Best wishes for finding your own “home” within the wide and inspiring world of physics