Stefano Di Vita Summer Students Sessions Talk About

Stefano Di Vita Summer Students Sessions Talk About m. SUGO with Extra Vogon Dimensions in a Cubic Hyperspace in d=42 spontaneously broken by Boredons 16/08/06 CERN Students Sessions Stefano Di Vita 1

Slide number Zero ¡ ¡ ¡ Hello! And I’m Stèfano (not Stefàno, the accent goes on I’m the having ‘e’!!) a great time! I’m a wanna-be theorist, I’m a Summer student, I’m studying SUper. SYmmetry here @ CERN DO YOU EXPECT ME TO TALK ABOUT THAT? 16/08/06 CERN Students Sessions Stefano Di Vita NO! 2

Between the static quark model and QCD: basic facts about THE PARTON MODEL (A theorist hanging out @ CERN) STEFANO DI VITA (Universita’ degli Studi Roma Tre) 16/08/06 CERN Students Sessions Stefano Di Vita 3

Schedule “Drive out” the quarks from their hadronic “nest” ¡ Scare you all with some formulae ¡ Spot some of the properties of partons ¡ Prove that theoretical physics can be enormously boring… especially at 9. 15 in That’s why I the morning! always wake up at 11!! ¡ 16/08/06 CERN Students Sessions Stefano Di Vita 4

DEEP INELASTIC SCATTERING (1) Kinematics 1960 s SLAC-MIT experiments Q , v are INDEPENDENT!! Note the elastic limit Define the useful quantity 16/08/06 CERN Students Sessions Stefano Di Vita 5

DEEP INELASTIC SCATTERING (2) e-He analogy: spotting the CONSTITUENTS 0, 2 After Hofstadter ( 1956) If inelastic scattering is due to INCOHERENT ELASTIC SCATTERING from the N=4 constituents (nucleons) Elastic e-p X=0. 25 Elastic e-He 1 0, 4 X=1 x INELASTIC e-He Around x=0. 25 Then the inelastic peak should be at 16/08/06 CERN Students Sessions Stefano Di Vita 6

DEEP INELASTIC SCATTERING (2) e-He analogy: POINTLIKE constituents UNAFFECTED INELASTIC e. After Hofstadter (He 1956) Around x=0. 25 REDUCED 0, 1 Elastic e-p X=0. 25 0, 2 REDUCED Elastic e-He 0, 4 1 X=1 x Suppressed by a factor 67 This behaviour is called SCALING and reveals the existence of POINTLIKE CONSTITUENTS of the target 16/08/06 CERN Students Sessions Stefano Di Vita 7

DEEP INELASTIC SCATTERING (4) electrons scattering on a proton 0. 145 0. 293 0. 484 1 Resonances AT HIGHER Q 2 the cross section SCALES, indicating scattering from Elastic peak POINTLIKE CONSTITUENTS! Broad continuum Are(quasithey Gell-Mann’s quarks? elastic constituent scattering) After Bartel et al. ( 1968) 16/08/06 CERN Students Sessions Stefano Di Vita 8

Some UNAVOIDABLE Formulae: Structure Functions If the inelastic scattering is due to ELASTIC scattering from the constituents (mass m) 16/08/06 CERN Students Sessions Stefano Di Vita 9

Bjorken Scaling Hypothesis Summarizing, we can formulate the scaling hypothesis: In the DIS regime fixed It MEANS that the photon scatters against something POINTLIKE: It’s GOOD because you can EXPERIMENTALLY TEST it!!! After Miller et al. ( 1972) After Friedman and Kendall ( 1972) IT WORKS!! 16/08/06 CERN Students Sessions Bjorken Stefano Di Vita 10

The Parton Model (1) LET PARTONS BE!! • Pointlike particles R. P. Feynman • Different kinds (different quarks? ) • Carry a fraction x of the proton momentum P • Have a mass roughly a fraction x of the proton mass M The scaling variable 16/08/06 CERN Students Sessions Stefano Di Vita 11

The Parton Model (2): DIS at the parton level Hypotheses: ¡ The proton is made up of POINTLIKE PARTONS ¡ Inelastic scattering is a SUPERPOSITION of ELASTIC scattering e-parton Redefine the GLOBAL Integral Sumstructure over functions proton over momentum parton types fractions + “bonus” Callan-Gross relation 16/08/06 CERN Students Sessions Parton Density Function (Prob. of having a fraction x) Stefano Di Vita Cross section “structure” for parton i Parton charge 12

The Parton Model (3) implications: e. g. SEA QUARKS ØPARTONS HAVE SPIN ½ (related to the Callan-Gross relation) THE QUARKS!! Ø pairs have OPPOSITE quantum numbers A proton (uud) remains a proton even if it contains an ARBITRARY NUMBER OF Only the NET BALANCE matters!! A PROTON 16/08/06 CERN Students Sessions SEA QUARKS Stefano Di Vita 13

What did I tell you? ¡ ¡ ¡ I’m having FUN @ CERN DIS (ep>e. X) evidences SCALING behaviour Scaling is due to the existence of POINTLIKE CONSTITUENTS of p (partons) Inelastic scattering is due to the INCOHERENT SUPERPOSITION of elastic scattering on partons Parton model doesn’t forbid the presence of SEA QUARKS 16/08/06 CERN Students Sessions Stefano Di Vita 14

The end… Thanks to ¡ You all! I can’t believe you’ve been listening (? ) to my delirium ¡ The Summer Student Staff! You have arranged everything for us in such a brilliant way ¡ My supervisors G. Altarelli and M. Seymour! I swear I’ll go back to my SUSY book after this talk ¡ All my friends here! Thanx for the great time I’m having this summer… I owe you all another party : ) ¡ Myself! Thanx for reminding me I want to be a physicst 16/08/06 CERN Students Sessions Stefano Di Vita 15

What is missing? This is just the beginning. In fact: ¡ ¡ I didn’t explain why quarks have SPIN ½ I didn’t mention neither neutrino-nucleon nor electron neutron DIS, so I couldn’t tell you that experiments support the hypotheses that Ø Quarks have FRACTIONARY charge Ø the existence of GLUONS ¡ ¡ I didn’t tell you about the valence/sea quarks ratio I didn’t tell you that there are VIOLATIONS to Bjorken scaling (see QCD!) 16/08/06 CERN Students Sessions Stefano Di Vita 16