Proton Structure Functions and at HERA Max Klein (H1, DESY Zeuthen) QCD Montpellier Introduction -F2 and FL - and xg -High Q2 -Parton Distributions -Outlook

ZEUS H1 positrons protons HERA -tunnel protons: 920 GeV positrons: 27.6 GeV circumference: 6.3 km HERA the world‘s best microscope quarks are pointlike down to

Deep Inelastic Scattering at low x and Q2 /ZEUS DIS npert. regime low x

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

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

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

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

low x 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!

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

exploring perturbative QCD H1 EPJ C21(01)33

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

HERA results on the strong coupling constant from F2 hep-ex/ PR D67(03) EPJ C21(01)33 R.Wallny Thesis H (exp) (model) proton data and only H1+BCDMS Q2(H1)>3, Q2(BCDMS)>7GeV2,W2>10GeV2 if: systematíc errors are not fitted: NMC replaces BCDMS (exp) 4 light flavours: BCDMS deuteron data added: (exp) ZEUS (unc) (corr) (norm) (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: M.Botje programme

MK DESY Forum, 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 ZEUS: use (1/2.. 2) : mention uncertainty of moment analyses: compare NLO with NNLO: (Santiago & Yndurain) NP, hep-ph/ full calculations to 3 loop anomalous dimension progressing NNLO has to include charm treatment in NNLO (mc +-100MeV is ) 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, 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 systematic errors of BCDMS data the problem of the BCDMS data

MK DESY Forum, cf also A.Vogt DIS96 Roma  remeasure at HERA with Ep/2 the medium Q2 - larger x region with large luminosity. Systematics superior over fixed target exps. 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 the problems of the NMC data

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

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

MK DESY Forum, 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?

reduced cross section y=1-E‘/Ee E‘ > 3 GeV e ID with Si

longitudinal structure function at low Q2

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

determination of the longitudinal structure function H1: EPJ C21(01)33, hep-ex/ EPJ 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

 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

access to FL using radiative events ~36pb -1 ISR reduces E e  variation of y=Q2/sx ZEUS preliminary

electroweak unification in DIS full data H , hep-ex/ EPJ

ZEUS 96-97, DESY , Phys.Rev. D67(2003)012007H , DESY , hep-ex/ EPJ  Lumi upgrade

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

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

hep-ex/ 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/ CC data not fitted

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

F2 charm ICHEP02 beauty to follow Silicon detectors vital

ZEUS upgrades STTMVD new beam pipe

H1 upgrades

parity violation in F2 (gamma-Z) MK DIS01 Bologna singlet

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

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 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. + 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)