Structure Functions at HERA Max Klein (H1, DESY Zeuthen) Status and Future RADCOR 02 Kloster Banz Introduction -F2 at Low x -Measurement of alphas and xg -High Q2 -Quark Distributions -FL now and then -Summary no jets, spin

HERA ZEUS H1 positrons protons HERA -tunnel protons: 920 GeV positrons: 27.5 GeV circumference: 6.3 km

introduction 1997 luminosity 0.2  20 pb-1 detector upgrades uncertainty 20%  2-3%

deep inelastic scattering at low x and Q2 most recent, 0.6pb-1 H1 DIS 02 Cracow low x

kinematic reconstruction BST SPACAL low x preliminary (H1) small photoproduction bgd: E-pz, BST track

low x

reduced cross section y<0.8 low x

Fractal Proton Structure – Self Similarity log dependence of (unintegrated parton) density fit to H197 low Q2 data and to ZEUS 97 BPT T.Lastovicka hep-ph/ EPJ in print for 172 points, D2=1 low x

low x

QCD below its applicability low x ZEUS hep-ex/

rise towards x  0 should have lowered Ee low x derivative independent of x for x<0.01 to within exp uncertainty PhysLett B520(01)183 H1 preliminary, DIS02, svx data 2000

PhysLett B520(01)183 derivative ~ lnQ2 still higher accuracy desirable low x

low x

exploring perturbative QCD alphas H1 EPJ C21(01)33

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! alphas

DIS measurement of alphas with H1 and BCDMS data alphas y(BCDMS) > 0.3 Q2(BCDMS) >7 GeV2  no NMC, E665  chi2+1 well defined is BCDMS correct?  low Ep run H1 EPJ C21(01)33 joint determination of alphas, xg, V,A F2 =xV/3 +11xA/9 = 4xU/9+xD/9 xg ~x bg

Results on the strong coupling constant hep-ex/ alphas EPJ C21(01)33 H (exp) (model) if: systematíc errors are not fitted: NMC replaces BCDMS (exp) 4 light flavours: BCDMS deuteron data added: (exp) large chi2 variations if Q2  (¼.. 4) Q2 renormalisation scale: (H1)  (1/2.. 2) : (ZEUS) not included in error 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, RTvfns, b(uv)=1/2, b(dv)=1/2 fit alphas, xg, uv, dv, sea, dbar-ubar (MRST) if fixed flavour scheme is used:

electroweak unification in DIS K.Long ICHEP02 high Q2 full data

ICHEP02 H1 preliminaryhigh Q2

ICHEP02 H1 preliminaryhigh Q2

neutral currents at high x,Q2 high Q2 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; ZEUS: hep-ex/ high Q2 direct access to valence quarks parity conserving e+ 100 pb-1 e- 15 pb-1 requires maximum possible luminosity

hep-ex/ high Q2 CC data (ZEUS) high Q2 CC data not fitted

ICHEP02 prel. high Q2 CC data (H1) high Q2

MK high x Philadelphia 00 pdf e+, 250pb-1 e-, 250pb-1 simulation HERA2

A.Mehta DIS01. CC polarisation dependence high Q2 search for r.h. currents classic measurement, possible with modest luminosity but maximum polarisation

parity violation in F2 (gamma-Z) MK DIS01 Bologna high Q2

parton distribution functions from NLO QCD fits ZEUS hep-ex/ ; H1 ICHEP02 pdf

parton distribution functions from NLO QCD fits (H1) H1 ICHEP02 pdf CC and NC cross sections are sensitive only to U, antiU, D,antiD (F2N has c-s admixture)  new H1 NLO QCD fit in which uv,dv,sea are replaced by the observables light flavours (xg consistent) possible with H1 data alone with assumption on sea symmetry

sea symmetry (simulation of ed) MK, DIS 02 pdf 40pb-1 ep 20pb-1 ed note (s-c)/3 =5/18 W2(cc)-F2N

up and down quarks at high Q2 ZEUS hep-ex/ ; H1 ICHEP02 pdf

access to the longitudinal structure function FL H1 EPJ C21(01)33

determination of the longitudinal structure function FL H1: EPJ C21(01)33, DIS01 and ICHEP02 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 simulation with lowered Ep FL MK Ringberg H1 internal 02: bins and Ep choices may be optimised 3..4 beam energies L ~ Ep systematics challenge smallest E‘ (BST: E/p) ultimate accuracy of ~5% Q2~1 GeV2: redo i.a.region

F2 charm FL ICHEP02 beauty to follow Silicon detectors vital

diffractive partons FL H1, DIS02

summary +Low x physics discovered as a new field of theoretical development and experimental fun + so far pQCD is consistent with structure function data but 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 HERA1 HERA2 HERA3 + 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?? + high accuracy, low Ep runs determine strong coupling constant with 1% accuracy and measure FL(x) + explore flavour decomposition at low x (eD) + discover saturation (eA) + understand confinement (better) + spin structure of the proton at low x and high Q2

ZEUS upgrades ZEUS expected to be operational in 2006 (U.Schneekloth at Durham) STTMVD new beam pipe

H1 upgrades major upgrades. H1 expected to be operational for years to come and follow – design 1986!

Workshops its time to conclude DESY directorate asks for proposals by end of 2003 Physics Ressources TESLA synch.radiation