Proton Structure Functions and at HERA Max Klein

Proton Structure Functions and at HERA Max Klein (H 1, DESY Zeuthen) -Introduction -F 2 and FL - and xg -High Q 2 -Parton Distributions -Outlook 2. 7. 2003 MK @Montpellier QCD Montpellier 2003 klein@ifh. de

HERA circumference: 6. 3 km protons: 920 Ge. V positrons: 27. 6 Ge. V HERA -tunnel H 1 the world‘s best microscope 2. 7. 2003 MK @Montpellier s proton pos it rons positrons ZEUS pr s oton quarks are pointlike down to

Deep Inelastic Scattering at low x and Q 2 /ZEUS DIS npert. regime low x 2. 7. 2003 MK @Montpellier

Low x Physics – the ‚rise‘ of F 2(x) Strong interaction dynamics at high parton densities and small coupling constant 1997 data 1992 data luminosity 0. 2 20 pb-1 detector upgrades uncertainty 20% 2 -3% 2. 7. 2003 MK @Montpellier

Low x important for QCD and LHC parton Luminosity at Super high energy neutrino physics • Most accurate data on F 2(x, Q 2) from HERA published so far in DIS region (2 -3%) 2. 7. 2003 MK @Montpellier

Low Q 2 data from near beam detector (ZEUS) and shifted vertex (H 1) How does F 2 behave in transition region to soft physics? 2. 7. 2003 MK @Montpellier

rise towards x 0 Derivative: independent of x for x<0. 01 to within exp uncertainty H 1 preliminary, DIS 02, svx data 2000 Phys. Lett B 520(01)183 2. 7. 2003 MK @Montpellier

Independence of ln F 2 derivative of x justifies simple ansatz for x dependence at given Q 2 change of behaviour at Q 2 near 1 Ge. V 2 rich phenomenology and search for new theoretical concept higher precision to observe ln 1/x terms! 2. 7. 2003 MK @Montpellier low x

• interaction dynamics changes at low x for Q 2 ~ 1 Ge. V 2 at larger Q 2 (in DIS region) xg determines the rise of F 2(x) below the gluon distribution vanishes and becomes valence like distribution conventional p. QCD analyses become unstable needs further constraint, from FL at low x conventional QCD is bound to fail. new hadronic state „Colour Glass Condensate“ LMc. L et al 2. 7. 2003 MK @Montpellier

exploring perturbative QCD H 1 EPJ C 21(01)33 2. 7. 2003 MK @Montpellier

H 1 -DIS measurement of alphas with H 1 and BCDMS data joint determination of alphas, xg, V, A no interest in quarks two pdfs only 9 F 2 = 3 x. V +11 x. A = 4 x. U+x. D chi 2+1 well defined two consistent exp data sets x space: C. Pascaud, F. Zomer, DESY 96 -266 2. 7. 2003 MK @Montpellier

HERA results on the strong coupling constant from F 2 • H 1 0. 1150 +- 0. 0017(exp) + 0. 0009 - 0. 0007(model) proton data and only H 1+BCDMS Q 2(H 1)>3, Q 2(BCDMS)>7 Ge. V 2, W 2>10 Ge. V 2 • ZEUS EPJ C 21(01)33 R. Wallny Thesis 01 -058 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) 0. 1166 +- 0. 0008(unc) +- 0. 0032(corr) +- 0. 0036(norm) +- 0. 0018(model) p: BCDMS, NMC, E 665 d: NMC, E 665 d/p: NMC x. F 3: CCFR systematíc errors are not allowed to vary in chi 2 minimisation Q 2>2. 5 Ge. V 2, W 2>20 Ge. V 2, RT-VFNS hep-ex/0208023 fit alphas, xg, uv, dv, sea, dbar-ubar (MRST) PR D 67(03)012007 if fixed flavour scheme is used: +0. 0010 M. Botje programme 2. 7. 2003 MK @Montpellier

NNLO corrections to p. QCD NLO folklore: vary renorm. scale (¼. . 4) Q 2 determines thy error observation: H 1/ZEUS: too large chi 2 variations H 1: 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 +-100 Me. V is +-. 0005) higher experimental precision of HERA F 2: challenge is less than 1 per cent with efficient tracking + high resolution calorimetry + accurate/lots of lumi MK DESY Forum , 25. 03. 2003

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 F 2 MK DESY Forum , 25. 03. 2003 shifts imposed by QCD fit to BCDMS data

the problems of the NMC data • NMC drives fit to high alphas • unbound fit requires 1/Q 2 terms W cut not enough • for Q 2>5 Ge. V 2: small impact left but then smaller alphas preferred remeasure at HERA with Ep/2 the medium Q 2 - larger x region with large luminosity. Systematics superior over fixed target exps. MK DESY Forum , 25. 03. 2003 cf also A. Vogt DIS 96 Roma

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

determination of the gluon momentum density to NLO fixed flavour nr scheme Laenen, Riemersma, Smith, van. Neerven need precision data at low Q 2, all x! H 1 EPJ C 21(01)33 2. 7. 2003 MK @Montpellier

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

reduced cross section y=1 -E‘/Ee E‘ > 3 Ge. V e ID with Si 2. 7. 2003 MK @Montpellier

longitudinal structure function at low Q 2 2. 7. 2003 MK @Montpellier

the longitudinal structure function provides a further constraint to the gluon density testing QCD to h. o. H 1 EPJ C 21(01)33 2. 7. 2003 MK @Montpellier FL

determination of the longitudinal structure function y<0. 9 (this is E‘~2. . 3 Ge. V!) assumption on F 2 more accurate data at large Q 2 to come consistent with NLO QCD i. e. scaling violations of F 2 limited to smallest x H 1: EPJ C 21(01)33, hep-ex/0304003 EPJ 2. 7. 2003 MK @Montpellier

FL known to 20% in analyses with F 2 calculated as x-l or in p. QCD need to vary Ep to measure FL(x, Q 2) more accurately and direct 2. 7. 2003 MK @Montpellier

access to FL using radiative events ~36 pb-1 ISR reduces Ee variation of y=Q 2/sx ZEUS preliminary 2. 7. 2003 MK @Montpellier

electroweak unification in DIS full data 1994 -2000 H 1 94 -00, hep-ex/0304003 EPJ 2. 7. 2003 MK @Montpellier

Lumi upgrade ZEUS 96 -97, DESY 02 -105, Phys. Rev. D 67(2003)012007 2. 7. 2003 MK @Montpellier H 1 94 -00, DESY 03 -038, hep-ex/0304003 EPJ

neutral currents at high x, Q 2: effects of Z exchange HERA 2 high Q 2 simulation NC uncertainty ~2% CC uncertainty ~3% HERA 2: 10 times the luminosity of HERA 1 A. Mehta DIS 01 2. 7. 2003 MK @Montpellier

exploratory measurements of x. F 3 e+ 100 pb-1 e- 15 pb-1 requires maximum possible luminosity direct access to valence quarks parity conserving H 1: EPJ C 19(2001)269 and hep-ex/0304003; ZEUS: hep-ex/0208040, EPJ 2. 7. 2003 MK @Montpellier

• 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

CC data not fitted hep-ex/0208023. 2. 7. 2003 MK @Montpellier

parton distribution functions from NLO QCD fits (H 1) CC and NC cross sections are sensitive only to U, anti. U, D, anti. D new H 1 NLO QCD fit in which uv, dv, sea are replaced by these observables No ad hoc pdf parameter Parameterisations from Chi 2 saturation light flavours (xg consistent) First pdf determination with H 1 data alone, requires assumption on sea symmetry until e. D data at low x exist 2. 7. 2003 MK @Montpellier

F 2 charm beauty to follow Silicon detectors vital ICHEP 02 2. 7. 2003 MK @Montpellier

STT 2. 7. 2003 MK @Montpellier MVD new beam pipe ZEUS upgrades

2. 7. 2003 MK @Montpellier H 1 upgrades

parity violation in F 2 (gamma-Z) singlet 2. 7. 2003 MK @Montpellier MK DIS 01 Bologna

helicity dependence of charged current cross section search for r. h. currents classic measurement, possible with modest luminosity but maximum polarisation A. Mehta DIS 01. 2. 7. 2003 MK @Montpellier

summary HERA II +Low x discovered the rise of F 2 and thus a field of rich theoretical developments, including the final state +p. QCD for structure function data tested over 4 orders of magnitude in momentum transfer squared, yet + the ultimate precision of data and thy (N 3 LO) is still to be / is being approached (F 2 1%, FL 5%, hi. Q 2 2% NC, 3% CC, about!) + F 2 c and F 2 D evolve towards precision testing grounds + high luminosity, Silicon detectors, improved calibrations large x, high Q 2 (competetive searches) + NC, CC unfold pdf‘s, employ polarisation and charge dependence of cross sections, xg at high x? ? , F 2 b + 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