2.7.2003 MK @Montpellier

Proton Structure Functions and at HERA

s

s

Max Klein (H1, DESY Zeuthen)

QCD Montpellier 2003

-Introduction-F2 and FL - and xg-High Q2 -Parton Distributions-Outlook

klein@ifh.de

s

2.7.2003 MK @Montpellier

ZEUS H1 positrons

positrons

protons

protons

HERA -tunnel

protons: 920 GeV positrons: 27.6 GeV

circumference: 6.3 km

m1810

HERA

the world‘s best microscope

quarks are pointlike down to

2.7.2003 MK @Montpellier

Deep Inelastic Scattering at low x and Q2

/ZEUS

25

2

10

4

GeVs

sxyxyEEQ pe

DIS

npert. regime

low x

2.7.2003 MK @Montpellier

1992 data

1997 data

luminosity 0.2 20 pb-1detector upgradesuncertainty 20% 2-3%

Low x Physics – the ‚rise‘ of F2(x)

Strong interaction dynamics at high partondensities and small coupling constant

2.7.2003 MK @Montpellier

•Most accurate data on F2(x,Q2) from HERA published so far in DIS region (2-3%)

Low x important forQCD and

LHC parton Luminosity at

Super high energyneutrino physics

52 103/ sMxx Wdu

2.7.2003 MK @Montpellier

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

rise towards x0

Derivative: independent of xfor x<0.01 to within exp uncertainty

PhysLett B520(01)183

H1 preliminary, DIS02, svx data 2000

2.7.2003 MK @Montpellier 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!

xcxF )(2

2.7.2003 MK @Montpellier

• 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

exploring perturbative QCD

xgQ

Fs

22

lnH1 EPJ C21(01)33

2.7.2003 MK @Montpellier

H1-DIS measurement of alphas with H1 and BCDMS data

chi2+1 well definedtwo consistent exp data sets

x space: C.Pascaud, F.Zomer, DESY 96-266

joint determination of alphas, xg, V,Ano interest in quarks two pdfs only

9 F2 = 3 xV +11xA = 4xU+xD

)2(4

1

)23(4

3

vv

du

vv

du

duuA

duV

2.7.2003 MK @Montpellier

HERA results on the strong coupling constant from F2

hep-ex/0208023PR D67(03)012007

EPJ C21(01)33R.Wallny Thesis 01-

058

•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)

•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 minimisationQ2>2.5 GeV2, W2>20GeV2, RT-VFNSfit alphas, xg, uv, dv, sea, dbar-ubar (MRST)if fixed flavour scheme is used: +0.0010M.Botje programme

MK DESY Forum , 25. 03. 2003

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

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 , 25. 03. 2003

cf also A.Vogt DIS96 Roma

remeasure at HERA with Ep/2the medium Q2 - larger x region with large luminosity. Systematicssuperior 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 , 25. 03. 2003

xgQ

Fs

22

ln

gluon momentum density

xg depends on c treatment!xg is not an observable

2.7.2003 MK @Montpellier

determination of the gluon momentum density to NLO

H1 EPJ C21(01)33

fixed flavour nr schemeLaenen, Riemersma, Smith, vanNeerven

need precision data at low Q2, all x!

MK DESY Forum , 25. 03. 2003

Correlation of alphas and xg is resolvable in DIS fits

determination of alphasand of the gluon distribution

inclusive DIS fits yield very smallgluon density at large x – jets?

2.7.2003 MK @Montpellier

reduced cross section Lr FyyF ])1(1/[ 222

y=1-E‘/EeE‘ > 3 GeVe ID with Si

2.7.2003 MK @Montpellier

longitudinal structure function at low Q2

2.7.2003 MK @Montpellier

the longitudinal structure function provides a further constraint to the gluon density testing QCD to h.o.

FL

H1 EPJ C21(01)33

2.7.2003 MK @Montpellier

determination of the longitudinal structure function

H1: EPJ C21(01)33, hep-ex/0304003 EPJ

y<0.9(this is E‘~2..3 GeV!)

assumption on F2

more accurate dataat large Q2 to come

consistent with NLO QCDi.e. scaling violations of F2

limited to smallest x

2.7.2003 MK @Montpellier

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

access to FL using radiative events ~36pb-1

ISR reduces Ee variation of y=Q2/sx

ZEUS preliminary

2.7.2003 MK @Montpellier

electroweak unification in DIS

full data 1994-2000

H1 94-00, hep-ex/0304003 EPJ

2.7.2003 MK @Montpellier

ZEUS 96-97, DESY 02-105, Phys.Rev. D67(2003)012007 H1 94-00, DESY 03-038, hep-ex/0304003 EPJ

Lumi upgrade

2.7.2003 MK @Montpellier

neutral currents at high x,Q2: effects of Z exchange

HERA 2

high Q2 simulationNC uncertainty ~2%CC uncertainty ~3%

A.Mehta DIS01

HERA2: 10 times the luminosity of HERA1

2.7.2003 MK @Montpellier

exploratory measurements of xF3

32

33 2 xHavxGaxF ZeeZe

H1: EPJ C19(2001)269 and hep-ex/0304003; ZEUS: hep-ex/0208040, EPJ

3/]2[)]()([23 vvdduu duxddaeuuaexxG

direct access to valence quarksparity conserving

e+ 100 pb-1 e- 15 pb-1

requires maximum possible luminosity

2.7.2003 MK @Montpellier

hep-ex/0304003

•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

2.7.2003 MK @Montpellier

hep-ex/0208023.

CC data not fitted

2.7.2003 MK @Montpellier

parton distribution functions from NLO QCD fits (H1)

CC and NC cross sectionsare sensitive only to U, antiU, D,antiD

new H1 NLO QCD fitin which uv,dv,sea arereplaced by these observablesNo ad hoc pdf parameter

Parameterisations from Chi2saturation

light flavours (xg consistent)

First pdf determination withH1 data alone, requiresassumption on sea symmetryuntil eD data at low x exist

2.7.2003 MK @Montpellier

F2 charm

ICHEP02

beauty to follow

Silicon detectors vital

2.7.2003 MK @Montpellier

ZEUS upgrades

STT MVD new beam pipe

2.7.2003 MK @Montpellier

H1 upgrades

2.7.2003 MK @Montpellier

parity violation in F2 (gamma-Z)

MK DIS01 Bologna

)(9/2)(2

)4/()(/

2

122

qqxqqvexG

ududFGaA

qq

vvvvZx

eZ singlet

2.7.2003 MK @Montpellier

A.Mehta DIS01.

helicity dependence of charged current cross section

search for r.h. currents

classic measurement, possiblewith modest luminosity but maximum polarisation

2.7.2003 MK @Montpellier

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 yearsare necessary to employ its scientific potential. There wasn‘ta DIS programme limited to protons at fixed energy, and HERAis 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)