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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
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
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)