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Standard Model of Particle Physics

The Structure of the Nucleon 3.5 decades of investigation Arie Bodek - U. of Rochester Miami March 30, 2007. Standard Model of Particle Physics. Marriage of Particle Physics and Cosmology/ Astrophysics. The Structure of the Nucleon. =1 Fermi. 10 -15 m =1 fm = 1 Fermi. Standard Model.

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Standard Model of Particle Physics

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  1. The Structure of the Nucleon 3.5 decades of investigation Arie Bodek - U. of RochesterMiami March 30, 2007 Standard Model of Particle Physics Marriage of Particle Physics and Cosmology/ Astrophysics

  2. The Structure of the Nucleon =1 Fermi 10-15 m =1 fm = 1 Fermi

  3. Standard Model proton mass = 0.938 GeV/c2

  4. Particle Collisions of Fast moving High Energy Protons - Quantum Chromodynbamics low momentum transfer Q2 - slow moving large momentum transfer Q2 - fast moving - evolution in Q2

  5. 1960-1968 • ELASTIC Electron Scattering - Hofstadter Nobel Prize • Proton and neutron have a • finite size (about 1 Fermi). Q2=-q2=square of the four momentum transfer Q2=-q2=square of the four momentum transfer pf, E’ Electron or muon out (lower energy E’)  = E - E’ = energy transfer pi,E Electron or muon Energy E ELASTIC- final state is one Proton with mass W=M Proton Target mass M P INELASTIC- final state is Proton plus pions (Mass W>>M) Feynman diagram

  6. 1960-1968 ELASTIC Electron Scattering Proton and neutron have a finite size (about 1 Fermi)- Form Factors(like optical scattering from a cloudy sphere -inteference) F (q) =Form Factor = Fourier transform of charge distribution Form factor=1 -->point like particle

  7. Interpretation of Form Factors In non-relativistic limit, form factors are Fourier transforms of distributions: Spin 1/2 particles have two elastic electromagnetic form factors: GE: electric form factor GM: magnetic form factor

  8. Calcium Nucleus Form Factor Lead Nucleus Form Factor Lead 208 Falls more steeply 502 MeV Calcium 40 497 MeV

  9. Calcium Nucleus 4 Fermi Lead Nucleus 6 Fermi

  10. Scattering from Protons and Neutrons - Experiment snows a Dipole Form Factor GEp, GMp and GMn roughly follow the Dipole Form Factor. The 0.71 GeV is determined from a fit to the world’s data. An Exponential distribution has dipole form factor: We find

  11. Proton form factors Ratio to Dipole Current status 2007 exponential charge and magnetic distributions Gep Gmp Proton form factors ratio to dipole

  12. Neutron form factors ratio to dipole - current status -2007 Electric - Total charge =0 :Positive on inside, negative on outside Magnetic distribution- exponential. Neutron charge densities Gen Gmn Neutron form factors ratio to dipole

  13. Why do theorists like this experiment so much? - Victor Weisskopf Electron scattering SLAC MIT 1968-1974 - my PhD thesis experiment

  14. Inelastic scattering: Resonance region pf, E’ pi,E P W=1.238 GeV Electron out(lower energy E’)  = E - E’ = energy transfer x =Q2 / (2M) Q2=-q2=square of the four momentum transfer in GeV2 INELASTIC- final state is Proton plus pions (Mass W >>M = 0.938 GeV

  15. ‘The electron scattering data in the Resonance Region is the “Frank Hertz Experiment” of the Proton. V. Weisskopf * (former faculty member at Rochester and MIT) when he showed these data at an MIT Colloquium in 1971 (* died April 2002 at age 93) e-P scattering A. Bodek PhD thesis 1972 [ PRD 20, 1471(1979) ] Proton Data Electron Energy = 4.5, 6.5 GeV Data W=1.238 GeV

  16. Particle Physics pre -1968 simplistic view • Many different models for Hadron Structure- proton had a finite size, and there were hadron resonances - easily described mathmatically by the quark model. • Quarks was considered more of a convenient way to model a symmetry rather than real particles (since none were ever observed and they had strange properties like 1/3 charge. • “Real Particle Physics” were done at hardon machine where “Resonances” and new particles were being studied and discovered (spectroscopy, group theory, partial wave analysis, resonances, Regge poles etc.)

  17. Deep Inelastic Scattering (DIS): Large Q2 large (using proton mass = 0.938 GeV as a scale) low Q2 Q2=0.07 Q2=0.22 pf, E’ pi,E P Q2=0.85 Q2=1.4 Electron out(lower energy E’)  = E - E’ = energy transfer Q2=3 Q2=9 Q2=-q2=square of the four momentum transfer in GeV2 Q2=15 Q2=25 x =Q2 / (2M) High Q2

  18. Q2 1968: Surprise at W>2 GeV

  19. Bjorken SCALING First pointed out by Feynman) mf=mf =0 light pointlike partons Proton is composed of point-like partons with very small mass P. q in the laboratory = M --> x =Q2 / (2M) (Feynman)

  20. ‘The electron scattering data in the Deep Inelastic Region is the “Rutherford Experiment” of the proton’ Deep Inelastic Scattering Proton is composed of point like particles with very small mass Carrying a fraction x =Q2 / (2M) of the proton momentum when the proton is viewed in a fast moving frame. The proton structure function is only be a function of x (scaling) But what are those partons? Are they quarks? What do the Frank Hertz” and“Rutherford Experiment” of the proton’ have in common? A: Quarks! And QCD

  21. (1) What are the Parton Charges? (2) What are the Parton Spin • 1968 - SLAC e-p scaling ==> Point like Partons in the nucleon (Bjorken/Feyman) MIT-SLAC group:Led by Friedman, Kendall, Taylor. (1) Neutron/Proton ratio - Partons are fractionally charged like quarks (Bodek PhD. MIT 1972) • A. Bodek et al., COMPARISONS OF DEEP INELASTIC ep AND en CROSS-SECTIONS.Phys.Rev.Lett.30:1087,1973. (SLAC Exp. E49) N =d d u + sea 1/3 1/3 2/3 P = u u d + sea 2/3 2/3 1/3 Large x N/P -> 0.25 Explained by valence d/u [ (1/3) / (2/3)]2 =1/4 Small x : N/P=1 explained by sea quarks

  22. What is the spin of the Partons? Riordan PhD Thesis MIT 1973 Electrons scatter by interacting with electric charge of the partons. It the partons have spin, then there is also a much larger magnetic scattering. Compare Ratio of electric scattering / magnetic scattering R=L/ T (small) Partons are spin 1/2 E.M. Riordan, A. Bodek et al., EXTRACTION OF R = L/T FROM DEEP INELASTIC eP AND eD CROSS-SECTIONS. Phys.Rev.Lett.33:561,1974. A. Bodek et al.,EXPERIMENTAL STUDIES OF THE NEUTRON AND PROTON ELECTROMAGNETIC STRUCTURE FUNCTIONS. Phys.Rev.D20:1471-1552,1979.

  23. A: Nobel Prize 1990 - Friedman, Kendall, Taylorfor their pioneering investigations concerning deep inelastic scattering of electrons on protons and bound neutrons, which have been of essential importance for the development of the quark model in particle physics." Front row: Richard Taylor, Jerome Friedman, Henry Kendall. Second row:Arie Bodek, David Coward, Michael Riordan, Elliott Bloom, James Bjorken, Roger (Les) Cottrell, Martin Breidenbach, Gutherie Miller, Jurgen Drees, W.K.H. (Pief) Panofsky, Luke Mo, William Atwood. Not pictured: Herbert (Hobey) DeStaebler Graduate students in italics

  24. The Quest for higher Precision (for me) for the next 3.5 decades starts here 1972 Integral of F2(x) did not add up to 1.0. Missing momentum attributed to “gluons”. Like Pauli’s missing energy in beta decay attributed to neutrinos*Gluons were “Discovered” in 1970, way before gluon jets were observed in PETRA.Scatter shows F2(x, Q2) as expected from bremstrahlung of gluons by struck quarks in initial of final states.Scaling violations from “gluon” emission seen in 1973 as predicted Quantum Chromodynamics (QCD) but not believed yet. QCD was not an accepted theory. q - q pair gluon quark proton

  25. If scaling violations are from QCD at high Q2 are Logarithmic --> it is interesting, scaling is only approximate, but is this new theory right? Harvard, Politzer and deRujua - log Q2 If scaling violations are from binding effects at low Q2 (called higher twist) --> not interesting -----> scaling will become exact at high Q2 - 1/Q2 proton quark

  26. quark-antiquark pair created from vacuum Quantum Chromodynamics QCD relative strength Similar to QED … except the gauge field carries the charge asymptotic freedom distance energy density, temperature quark Strong color field Energy grows with separation !!! “white” 0 (confined quarks) E=mc2 ! “white” proton (confined quarks) “white” proton Thanks to Mike Lisa (OSU) for parts of this animation

  27. and A. Bodek et al.,. Phys.Rev.D20:1471-1552,1979& **Note: years later we show Higher Twist come from both binding and NNLO QCD – see U. K. Yang, A. Bodek,STUDIES OF HIGHER TWIST AND HIGHER ORDER EFFECTS IN NLO AND NNLO QCD ANALYSIS OF LEPTON NUCLEON SCATTERING DATA ON F2 AND R L/T . Eur. Phys. J. C13 (2000) 241 245. • First observation of Scaling Violations SLAC -Higher Twist or QCD ? ** E. M. Riordan, A. Bodek et al., TESTS OF SCALING OF THE PROTON ELECTROMAGNETIC STRUCTURE FUNCTIONSPhys.Lett.B52:249,1974.&

  28. QCD and quark-parton model Proton uud (Valence) bound with colored gluons and a sea of quark-antiquark pairs which increase with Q2. All ar bound together by the color force. Neutron ddu (Valence) bound with colored gluons and a sea of quark-antiquark pairs which increase with Q2. Charge Symmetry Neutron is the same as a Proton, with each u quark replaced with a d quarkand each d quark replace with a u quark.

  29. "Physics is generally paced by technology and not by the physical laws. We always seem to ask more questions than we have tools to answer.” Wolfgang K. H. Panofsky • Questions in 1980-2004 LO QCD, anti-quarks, strange and charm quarks (hadronic charm production), individual PDFs , longitudinal structure function, quarks in nuclei , high statistics electron, muon and neutrino scattering experiments, NLO and NNLO QCD, origin of higher twist corrections, proton-antiproton collisions, W Asymmetry and d/u, Drell-Yan and Z rapidity distributions, application to neutrino oscillations, - • A Detailed understanding of Nucleon Structure Required 35 additional years of Experiments at Different Laboratories, New Detectors, Analysis Techniques and Theoretical Tools - AND also sorting out which experiments are right and which experiments are wrong • A. BodekPanofsky Prize 2004 • "For broad, sustained, and insightful contributions to elucidating the structure of the nucleon, using a wide variety of probes, tools and methods at many laboratories."

  30. 1974: Fermilab and CERN, muon and neutrino beams up to 250 GeV Because of parity violation, comparisons of neutrino and antineutrino scattering are different for scattering from quarks versus scattering from antiquarks - use it to measure the antiquark distributions in the nucleon

  31. NEUTRINOS only scatter from (-1/3) charge quarks (e.g. d, s quarks) And -2/3 charge anti-quarks (e.g. u, c) m-   m- W+ W+ u +2/3 d +1/3 d -1/3 u -2/3 m-  m-  W+ W+ +4/3 Not possible d +1/3 Not possible +5/3 u +2/3

  32. Anti-NEUTRINOS only scatter from (+2/3) charge quarks (e.g. u,c quarks) And +1/3 charge anti-quarks (e.g. d, s)  m+ m+  W- W- d -1/3 u +2/3 d +1/3 u -2/3  m+ m+  W- W- Not possible -5/3 u -2/3 -4/3 not possible d -1/3

  33. Neutrinos on quarks Neutrinos on antiquarks weak

  34. Low Q2 What is the composition at High Q2 By taking sum and difference F2 (x, Q2) = x [ q (x, Q2) + q (x, Q2) ] (all quarks) xF3 (x, Q2) = x [ q (x, Q2) - q (x, Q2) ] (Valence quarks only)

  35. Neutral current charged current Scattering from strange quarks CCFR - Chicago-Columbia-Fermilab-Rochester

  36. neutrino muon

  37. C: Strange Quarks in the Nucleon - Caltech-Fermilab -Later- CCFR (Columbia -Chicago-Fermilab-Rochester) and -Later- NuTeV Neutrino Collaborations at Fermilab LAB E. Dimuon event The Strange Sea Anti-quarks are about 1/2 of the average of u and d sea - Sea is not SU3 Symmetric.

  38. Strange Quarks in the Nucleon - (Caltech-Fermilab, later CCFR Columbia -Chicago-Fermilab-Rochester) and NuTeV Neutrino Collaborations at Fermilab Karol Lang, AN EXPERIMENTAL STUDY OF DIMUONS PRODUCED IN HIGH-ENERGY NEUTRINO INTERACTIONS. UR-908 (1985) Ph.D. Thesis (Rochester) Now Professor at UT Austin K. Lang et al.(CCFR-Rochester PhD), NEUTRINO PRODUCTION OF DIMUONS. Z.Phys.C33:483,1987 (leading order analysis) The Strange Sea Anti-quarks are about 1/2 of the average of u and d sea - not SU3 Symmetric. A.O. Bazarko et al., (CCFR-Columbia PhD) DETERMINATION OF THE STRANGE QUARK CONTENT OF THE NUCLEON FROM A NEXT-TO-LEADING ORDER QCD ANALYSIS OF NEUTRINO CHARM PRODUCTION. Z.Phys.C65:189-198,1995 M. Goncharovet al. (NuTeV K.State PhD). PRECISE MEASUREMENT OF DIMUON PRODUCTION CROSS-SECTIONS IN MUON NEUTRINO FE AND MUON ANTI-NEUTRINO FE DEEP INELASTIC SCATTERING AT THE TEVATRON.Phys.Rev.D64:112006,2001

  39. Precision Neutrino Experiments REQUIRE good Hadron Calorimetry and Muon Energy calibration (~0.3%) 10 cm Fe Sampling, simultaneous neutrino running and hadron and muon test beams D.A. Harris, J. Yu et al( NuTeV-Rochester-FNAL) PRECISION CALIBRATION OF THE NUTEV CALORIMETER. UR-1561 Nucl. Inst. Meth. A447 (2000) W.K. Sakumoto et al. (CCFR-Rochester), CALIBRATION OF THE CCFR TARGET CALORIMETER. Nucl.Instrum.Meth.A294:179-192,1990. Developed Fe-scintillator compensating calorimeter. 3mx3m large counters with wavelength shifting readout

  40. W.G. Seligman et al. (CCFR Columbia PhD),IMPROVED DETERMINATION OF S FROM NEUTRINO NUCLEON SCATTERING. Phys. Rev. Lett. 79 (1997) 1213-1216.

  41. Valence quarks H. Kim (Columbia PhD) et al. D.Harris et. al., (CCFR) MEASUREMENT OFS (Q2) FROM THE GROSS- LLEWELLYN SMITH SUM RULE. Phys. Rev. Lett. 81 (1998) 3595-3598

  42. Why go for more precision ? To within 15%, the theory of Quantum Chromodynamics was confirmed ---> Nobel Prize 2004 (Gross- Politzer -Wilczek) The various quark, anti-quark and gluon distributions were measured to 10%-15% precision (not in all regions) ---> Why do better? It turns out, we really needed to do better at high energies We also needed to do better at low energies.

  43. Proton-Antiproton Collisions at very high energies Beamline High Energy- Proton-Antiproton (CDF/Dzero) collisions are actually parton-parton collisions (free nucleons). All searches for new physics require a detailed understanding of the parton structure of the proton.

  44. High Energy- Proton-Antiproton (CDF/Dzero) collisions are actually parton-parton collisions (free nucleons) All experiment in hadron colliders are limited by the knowledge of parton distribution functions (PDF’s)

  45. Precision Neutrino Experiments CCFR/NuTeV Un Ki Yang UR-1583,2000 Ph.D. Thesis, (Rochester) Lobkowicz Prize, U of R; URA Best Thesis Award Fermilab 2001 (now at Univ. of Chicago) Un-Ki Yang et al..MEASUREMENTS OF F2 AND XF3 FROM CCFR MUON NEUTRINO-FE AND MUON ANTI-NEUTRINO-FE DATA IN A PHYSICS MODEL INDEPENDENT WAY. By CCFR/NuTeV Phys.Rev.Lett.86:2742-2745,2001 Comparing muon and neutrinos

  46. Quark Distributions in Nuclei A. Bodek et al Phys.Rev.Lett.51:534, 1983 (SLAC Expt. E49, E87 empty tgt data 1970,1972)

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