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Proton Structure Functions and at HERA

Proton Structure Functions and at HERA. Max Klein (H1, DESY Zeuthen). -Introduction -F2 and FL - and xg -High Q2 -Parton Distributions -Outlook. QCD Montpellier 2003. klein@ifh.de. HERA. circumference: 6.3 km. protons: 920 GeV positrons: 27.6 GeV. HERA -tunnel. H1.

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Proton Structure Functions and at HERA

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  1. Proton Structure Functions and at HERA Max Klein (H1, DESY Zeuthen) -Introduction -F2 and FL - and xg -High Q2 -Parton Distributions -Outlook QCD Montpellier 2003 2.7.2003 MK @Montpellier klein@ifh.de

  2. HERA • circumference: 6.3 km • protons: 920 GeV • positrons: 27.6 GeV • HERA -tunnel • H1 • protons • positrons • ZEUS quarks are pointlike down to • positrons the world‘s best microscope • protons 2.7.2003 MK @Montpellier

  3. Deep Inelastic Scattering at low x and Q2 /ZEUS DIS npert. regime low x 2.7.2003 MK @Montpellier

  4. Low x Physics – the ‚rise‘ of F2(x) Strong interaction dynamics at high parton densities and small coupling constant 1992 data 1997 data luminosity 0.2  20 pb-1 detector upgrades uncertainty 20%  2-3% 2.7.2003 MK @Montpellier

  5. Low x important for QCD and LHC parton Luminosity at Super high energy neutrino physics • Most accurate data on F2(x,Q2) from HERA published so far in DIS region (2-3%) 2.7.2003 MK @Montpellier

  6. Low Q2 data from near beam detector (ZEUS) and shifted vertex (H1) How does F2 behave in transition region to soft physics? 2.7.2003 MK @Montpellier

  7. rise towards x0 Derivative: independent of x for x<0.01 to within exp uncertainty H1 preliminary, DIS02, svx data 2000 PhysLett B520(01)183 2.7.2003 MK @Montpellier

  8. Independence of ln F2 derivative of x justifies simple ansatz for x dependence at given Q2 change of behaviour at Q2 near 1 GeV2 rich phenomenology and search for new theoretical concept higher precision to observe ln 1/x terms! 2.7.2003 MK @Montpellier low x

  9. interaction dynamics changes at low x for Q2 ~ 1 GeV2 at larger Q2 (in DIS region) xg determines the rise of F2(x) below the gluon distribution vanishes and becomes valence like distribution conventional pQCD analyses become unstable  needs further constraint, from FL at low x conventional QCD is bound to fail. new hadronic state „Colour Glass Condensate“ LMcL et al 2.7.2003 MK @Montpellier

  10. exploring perturbative QCD H1 EPJ C21(01)33 2.7.2003 MK @Montpellier

  11. H1-DIS measurement of alphas with H1 and BCDMS data joint determination of alphas, xg, V,A no interest in quarks  two pdfs only 9 F2 = 3 xV +11xA = 4xU+xD • chi2+1 well defined two consistent exp data sets x space: C.Pascaud, F.Zomer, DESY 96-266 2.7.2003 MK @Montpellier

  12. HERA results on the strong coupling constant from F2 H1 0.1150 +- 0.0017(exp) + 0.0009 - 0.0007(model) proton data and only H1+BCDMS Q2(H1)>3, Q2(BCDMS)>7GeV2,W2>10GeV2 if: systematíc errors are not fitted: +0.0005 NMC replaces BCDMS 0.116+-0.003 (exp) 4 light flavours: +0.0003 BCDMS deuteron data added: 0.1158 +- 0.0016 (exp) EPJ C21(01)33 R.Wallny Thesis 01-058 ZEUS 0.1166 +- 0.0008(unc) +- 0.0032(corr) +- 0.0036(norm) +- 0.0018(model) p:BCDMS,NMC,E665 d:NMC,E665 d/p: NMC xF3: CCFR systematíc errors are not allowed to vary in chi2 minimisation Q2>2.5 GeV2, W2>20GeV2, RT-VFNS fit alphas, xg, uv, dv, sea, dbar-ubar (MRST) if fixed flavour scheme is used: +0.0010 M.Botje programme hep-ex/0208023 PR D67(03)012007 2.7.2003 MK @Montpellier

  13. NNLO corrections to pQCD NLO folklore: vary renorm. scale (¼ .. 4) Q2  determines thy error observation: H1/ZEUS: too large chi2 variations H1: quote uncertainty of +-0.005 ZEUS: use (1/2.. 2) : mention uncertainty of +- 0.004 moment analyses: compare NLO with NNLO: -0.001 (Santiago & Yndurain) NP, hep-ph/0102247 full calculations to 3 loop anomalous dimension progressing NNLO has to include charm treatment in NNLO (mc +-100MeV is +-.0005) higher experimental precision of HERA F2: challenge is less than 1 per cent with efficient tracking + high resolution calorimetry + accurate/lots of lumi MK DESY Forum , 25. 03. 2003

  14. the problem of the BCDMS data systematic errors of BCDMS data alphas (BCDMS) very low and strongly y dependent („electron method“) low y – large x region in conflict with SLAC F2 shifts imposed by QCD fit to BCDMS data MK DESY Forum , 25. 03. 2003

  15. the problems of the NMC data • NMC drives fit to high alphas • unbound fit requires 1/Q2 terms W cut not enough • for Q2>5GeV2: small impact left but then smaller alphas preferred • remeasure at HERA with Ep/2 the medium Q2 - larger x region with large luminosity. Systematics superior over fixed target exps. cf also A.Vogt DIS96 Roma MK DESY Forum , 25. 03. 2003

  16. gluon momentum density xg depends on c treatment! xg is not an observable MK DESY Forum , 25. 03. 2003

  17. determination of the gluon momentum density to NLO fixed flavour nr scheme Laenen, Riemersma, Smith, vanNeerven need precision data at low Q2, all x! H1 EPJ C21(01)33 2.7.2003 MK @Montpellier

  18. Correlation of alphas and xg is resolvable in DIS fits  determination of alphas and of the gluon distribution inclusive DIS fits yield very small gluon density at large x – jets? MK DESY Forum , 25. 03. 2003

  19. reduced cross section y=1-E‘/Ee E‘ > 3 GeV e ID with Si 2.7.2003 MK @Montpellier

  20. longitudinal structure function at low Q2 2.7.2003 MK @Montpellier

  21. the longitudinal structure function provides a further constraint to the gluon density  testing QCD to h.o. H1 EPJ C21(01)33 2.7.2003 MK @Montpellier FL

  22. determination of the longitudinal structure function y<0.9 (this is E‘~2..3 GeV!) assumption on F2 more accurate data at large Q2 to come consistent with NLO QCD i.e. scaling violations of F2 limited to smallest x H1: EPJ C21(01)33, hep-ex/0304003 EPJ 2.7.2003 MK @Montpellier

  23. FL known to 20% in analyses with F2 calculated as x-l or in pQCD • need to vary Ep to measure FL(x,Q2) more accurately and direct 2.7.2003 MK @Montpellier

  24. access to FL using radiative events ~36pb-1 ISR reduces Ee  variation of y=Q2/sx ZEUS preliminary 2.7.2003 MK @Montpellier

  25. electroweak unification in DIS full data 1994-2000 H1 94-00, hep-ex/0304003 EPJ 2.7.2003 MK @Montpellier

  26. Lumi upgrade ZEUS 96-97, DESY 02-105, Phys.Rev. D67(2003)012007 H1 94-00, DESY 03-038, hep-ex/0304003 EPJ 2.7.2003 MK @Montpellier

  27. neutral currents at high x,Q2: effects of Z exchange HERA 2 high Q2 simulation NC uncertainty ~2% CC uncertainty ~3% HERA2: 10 times the luminosity of HERA1 A.Mehta DIS01 2.7.2003 MK @Montpellier

  28. exploratory measurements of xF3 e+ 100 pb-1 e- 15 pb-1 requires maximum possible luminosity direct access to valence quarks parity conserving H1: EPJ C19(2001)269 and hep-ex/0304003; ZEUS: hep-ex/0208040, EPJ 2.7.2003 MK @Montpellier

  29. Sensitive to different Parton flavours • e+ to down quarks • e- to up quarks • still statistics limited • x maximum 0.4 • best u/d separation • with ep/en at HERA • important for pdf‘s hep-ex/0304003 2.7.2003 MK @Montpellier

  30. CC data not fitted hep-ex/0208023. 2.7.2003 MK @Montpellier

  31. parton distribution functions from NLO QCD fits (H1) CC and NC cross sections are sensitive only to U, antiU, D,antiD • new H1 NLO QCD fit in which uv,dv,sea are replaced by these observables No ad hoc pdf parameter Parameterisations from Chi2 saturation light flavours (xg consistent) First pdf determination with H1 data alone, requires assumption on sea symmetry until eD data at low x exist 2.7.2003 MK @Montpellier

  32. F2 charm beauty to follow Silicon detectors vital ICHEP02 2.7.2003 MK @Montpellier

  33. ZEUS upgrades STT MVD new beam pipe 2.7.2003 MK @Montpellier

  34. H1 upgrades 2.7.2003 MK @Montpellier

  35. parity violation in F2 (gamma-Z) singlet MK DIS01 Bologna 2.7.2003 MK @Montpellier

  36. helicity dependence of charged current cross section search for r.h. currents classic measurement, possible with modest luminosity but maximum polarisation A.Mehta DIS01. 2.7.2003 MK @Montpellier

  37. summary +Low x discovered the rise of F2 and thus a field of rich theoretical developments, including the final state +pQCD for structure function data tested over 4 orders of magnitude in momentum transfer squared, yet + the ultimate precision of data and thy (N3LO) is still to be / is being approached (F2 1%, FL 5%, hiQ2 2% NC, 3% CC, about!) + F2c and F2D evolve towards precision testing grounds HERA I HERA II + high luminosity, Silicon detectors, improved calibrations  large x, high Q2 (competetive searches) + NC,CC unfold pdf‘s, employ polarisation and charge dependence of cross sections, xg at high x??, F2b + high accuracy, low Ep runs to determine strong coupling constant with 1% accuracy and to measure FL(x) Currently HERA‘s lifetime is limited to 2006/07. Many more years are necessary to employ its scientific potential. There wasn‘t a DIS programme limited to protons at fixed energy, and HERA is a much richer laboratory than any fixed target experiment before. 2.7.2003 MK @Montpellier

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