Recent results from HERA and their impact for LHC

0.8 MB·English

by  K. Lipka for the H1

Recent results from HERA and their impact for LHC
K.Lipka1,afortheH1andZEUSCollaborations
DeutschesElectronenSynchrotronDESYHamburg
Abstract. Recent measurements of inclusive and semi-inclusive deep inelastic scattering in electron-proton
collisionsatHERAarereviewed.Thesemeasurementsareusedtodeterminethepartondistributionfunctions
(PDFs)oftheproton,anecessaryinputtotheorypredictionsforhadroncolliders.AnintroductiontothePDF
determinationwithanemphasisonHERAPDFsispresented.TheorypredictionsbasedonHERAPDFarecom-
2
1 paredtoaselectionofrecentLHCandTevatronmeasurements.Theimpactofjetandcharmproductionmea-
0 surementsonthePDFsisdiscussed.
2

n
1 Introduction The NC (and similarly CC) cross section can be ex-
a
J pressedintermsofthegeneralizedstructurefunctions:

1
2 Adeepunderstandingoftheprotonstructureisoneofthe d2σe±p 2πα2(cid:104) (cid:105)
mcisoestknimowpolerdtagnetotofpthicesPianrtomnoDdeisrntripbaurttiiocnleFpuhnyctsiiocns.sA(PDprFes-) dxdQNC2 = xQ4 Y+F˜2±∓Y−xF˜3±−y2F˜L± ,
]
x of the proton is essential in order to make predictions for
e the Standard Model and beyond the Standard Model pro- whereY± =1±(1−y)2withybeingthetransferredfraction
- of the lepton energy. The (generalized) structure function
p cessesathadroncolliders. F (F˜ ) is the dominant contribution to the cross section,
e The cross sections of processes in proton-(anti)proton xF2˜ is2importantathighQ2andF˜ issizableonlyathighy.
h collisionsarefactorizedbyaconvolutionofthematrixele- 3 L
[ IntheframeworkofperturbativeQCDthestructurefunc-
mentofparton-partoninteractionandtheprotonstructure. tions are directly related to the parton distribution func-

1 Thelatterisdescribedbypartondensityfunctions(PDFs).
tions,i.e.inleadingorder(LO) F isthemomentumsum
v A PDF, fi(x,Q2), represents the probability of finding in ofquarkandanti-quarkdistributio2ns, F ≈ x(cid:80)e2(q+q),
6 the proton a parton i (quark or gluon) carrying a fraction andxF isrelatedtotheirdifference,xF2 ≈ x(cid:80)2qe a (q−
8 xoftheprotonmomentumwith Qbeingtheenergyscale 3 3 q q
q).Athigherorders,termsrelatedtothegluondensitydis-
4 of the hard interaction. In case of proton-(anti)proton in-
4 teractionsPDFsofbothprotonsentermultiplicativelyinto tribution (αsg) appear. In analogy to neutral currents, the
.
1 thecalculationoftheprocesscrosssection.Thereforethe
20 prarteecicsrioosns-osfecthtieonPDprFesdiisctoiofnpsa.rItnictuhlearlaimstpdoerctaadnecse,ftohreamcceua-- e +_ e +_ , (cid:105)e
1
surements of lepton-nucleon and proton-antiproton scat-
:
v tering have been used to determine the proton PDFs. At +_
(cid:97)/Z, W
i lowtomediumxthePDFsareconstrainedbyHERAdata.
X
The measurements at fixed target experiments and Teva-
r tron contribute mainly at high x. The recent precise data p X
a
fromTevatronandtheLHCexperimentshavethepotential PDF
toimprovetheprecisiononthePDFsfurther.
Fig. 1. Diagrams of neutral NC and charged CC current deep
inelasticscatteringprocesses.Thesymbolsdenotetheparticles,
thelabel”X”denotesthehadronicfinalstate.
2 Proton Structure and DIS at HERA
inclusiveCCepcrosssectioncanbeexpressedintermsof
structure functions and in LO the e+p and e−p cross sec-
The knowledge of the proton PDFs is obtained to a large
tionsaresensitivetodifferentquarkdensities:
extent from the measurements of the structure functions
in deep inelastic scattering (DIS) experiments. In Fig. 1. e+ : σ˜e+p = x[u+c]+(1−y)2x[d+s]
thediagramofDISisrepresented.Theleptonisscattered CC
offthenucleonviatheexchangeofaγorZ0-boson(neu- e− : σ˜e−p = x[u+c]+(1−y)2x[d+s].
CC
tral current, NC, process) or via the exchange of a W±-
boson(chargedcurrent,CC).Herethescatteringofanelec-
AtHERAatDESYinHamburg,electrons(orpositrons)
tron(orpositron)offtheprotonisdiscussed. werecollidedwithprotonsatcentre-of-massenergies √s=
225−318GeV.ThemeasurementsoftheNCandCCcross
a e-mail:[email protected] sections from HERA extend the kinematic regime in Q2
EPJWebofConferences
bymorethantwoordersofmagnitudewithrespecttothe beusedintheHERAPDFapproach.Thereforedirecttests
fixed target experiments and cover the wide x range from ofthemodelsarepossible.ThefullstatisticsoftheHERA
10−7 to 0.7. At the HERA collider experiments, H1 and inclusive CC and NC data are used for NLO and NNLO
ZEUS,thecrosssectionsofNCandCCDISaremeasured QCD fits resulting in HERAPDF1.5 [3]. As an example,
withhighprecision.Themeasurementsofthetwoexperi- the combined NC cross sections are shown in Fig. 2 to-
mentsarecombinedandarefurtherusedtodeterminepar- getherwithQCDpredictionbasedonHERAPDF1.5NLO.
tondistributionfunctionsHERAPDF[2]. The QCD analysis HERAPDF1.5 follows the formal-
ism, model and paramatrisation assumptions as reported
in [2]. The QCD predictions for the structure functions
are obtained by solving the DGLAP evolution equations
3 HERAPDF
atNLO(orNNLO)inthe MS schemewiththerenormal-
isationandfactorisationscaleschosentobeQ2.TheQCD
ThePDFsaredeterminedfromthestructurefunctionmea-
predictionsforthestructurefunctionsareobtainedbythe
surementsusingthecorrespondingcoefficientfunctionscal-
convolution of the PDFs with the NLO coefficient func-
culated to a certain order in perturbative QCD (pQCD).
tions calculated using the general mass variable flavour
Thestructurefunctions,andinturnthePDFs,dependonx
numberRTscheme[4].FortheparametrisationofPDFsat
andQ.Thex-dependenceofthepartondistributionsisnot
theinputscalethegenericform xf(x) = AxB(1−x)C(1+
yetcalculableinpQCDandhastobeparametrizedatacer-
Ex2)isused.TheparametrisedPDFsarethegluondistri-
tain starting scale Q . The dependence on Q is described
0 bution,thevalencequarkdistributionsandtheu-typeand
by the DGLAP evolution equations [1]. Starting from a
d-typeanti-quarkdistributions.Thenormalisationparame-
parameterisationofthePDFsatastartingscale,eitherby
tersAareconstrainedbythequarknumberandmomentum
makingad-hocassumptionsontheiranalyticalformorby
sum-rules.
using the neural-net technology, fits to various sets of ex-
perimentaldata,withHERADISdatabeingthebackbone,
are performed within the DGLAP evolution scheme. The
H1 and ZEUS HERA I+II PDF Fit
rttihevseeuPlQtDiCnFgDPpcaDarlFacmsuldeaettrpiiozenantdiisoonpn,etrthfhoeeromtrreedadet,rmtihneenwtahsoisfcuhmhetphatevioypneqsrutauabrrobkuas-t, xf 000...888111 xg (× 0.05) HexEpR. uAnQPcDe2rF t=.1. 51 N00N0L0O G(preeVl.)2March 2011
tucuhonnenccesecirrhsttoaateiiicnnnettciyyefosoo.rffTttthhhheeeevsPdeaDaldtuFaaests.aoeHfts1s eαantissnd( cZMdlEeuUZtdeS)eramdniidnntethsheethtPreeDaetFxmpfieetrniatmnodefnttthhaeel 000000000.........464646222 xS (× 0.05) mpaordaeml eutnrcizearttxi.odnv uncxeurtv. APDF Structure Function Working Group
2±(x,Q)(cid:109)r,NC103 HHEERRAA II++IIII NNCC ee+-pp ((pprxr ee=l l.0.).)02 (x300.0)HHEERRAAPPDDFF11..55 ee+-pp August 2010 00010-4 10-3 10-2 10-1 x 1HER
102 x = 0.032 (x170.0) Fig. 3. The parton distribution functions from HERAPDF1.5
x = 0.05 (x90.0)
x = 0.08 (x50.0) NNLO. The gluon and sea distributions are scaled down by a
10 x = 0.13 (x20.0) factor of 20. The experimental, model and parametrisation un-
x = 0.18 (x8.0) certaintiesareshown.
1
x = 0.25 (x2.4)
1100--21 xx == 00..4605 (x0.7) HERA Inclusive Working Group ppatearrQiaImmn2eeF=ntirtgia1s.la0u3t0ino0tchn0eeriGntpaateihrnVtetoi2densead,treiteshrtmersihibvnouaawrttiiinaoot.ninosIonnHfoEaHfdREmdARiotPiAdoDePnlFDit1noF.p5atuNhrteesNpaLeenxOrd--
102 103 104 Q2/ 1G05eV2 formedandprovidedasadditionaleigenvectors.Themodel
uncertainties are evaluated by varying the input assump-
Fig. 2. Inclusive DIS cross sections for NC in e± collisions at tionsonminimumQ2 ofthedatausedinthefit,thestran-
HERA.ThemeasurementsoftheH1andZEUSexperimentsare
genessfractionandthemassesofheavyquarks.Thepara-
combined.Open(closed)symbolsrepresente−p(e+p)scattering.
metrisation uncertainty is formed by an envelope of the
The shaded curves represent QCD prediction based on HERA-
maximaldeviationsfromthecentralfitvaryingparametri-
PDF1.5NLO.
sation assumptions. HERAPDF1.5NLO and NNLO sets
aretherecommendedHERAPDFstobeusedforthepre-
ThepartondistributionsHERAPDF [2]aredetermined dictionsofprocessesattheLHC.Thecorrespondingeigen-
using only combined HERA DIS data, where the corre- vectorsareavailable[5].
lations of the systematic uncertainties are properly taken
intoaccount.Thisallowstheusageoftheconventionalχ2
tolerance of ∆χ2 = 1. Since this QCD analysis is solely 4 Benchmarking HERAPDF
basedonepdata,thePDFsdonotdependontheapproach
fornuclearcorrectionsneededforfixedtargetdata.Several The PDFs are intrinsic properties of the proton and are
phenomenological schemes of heavy quark treatment can therefore process-independent. Cross section predictions
Presentedatthe2011HadronColliderPhysicssymposium(HCP-2011),Paris,France,November14-182011
for processes in proton-(anti)proton collisions can be ob- TheW-bosonmuonasymmetryasmeasuredbytheCMS
tainedusingHERAPDF,evolvedinQ2usingDGLAPequa- experiment [10] is shown in Fig. 6. The measurement is
tions. comparedtoNLOpredictions[12]obtainedusingHERA-
The measurements of jet production at hadron collid- PDF1.5NLO, MSTW08 [13] and CT10W[14] PDFs. The
ersisanimportantinstrumenttoprobePDFsathighxand predictionbasedonHERAPDF1.5NLOdescribesthedata
also provide additional constraints on the value α (M ). well.
S Z
InFig.4thejetproductioncrosssectionsasmeasuredby
D0experiment[6]ispresented.Themeasurementiscon-
fronted with the QCD prediction at NLO [7,8] based on CMS preliminary 234 pb-1 at s = 7 TeV
HprEedRiActPioDnF.I1n.5FNigL.O5.tThheejedtamtaeiassvuerreymweenltlfdreosmcrAibTeLdAbyStehxis- etry 0.3 p µ > 25 GeV
m T
m
y
s
A W(cid:65) µ(cid:105)
Tevatron inclusive jet cross sections e 0.2
GeV]1100191 D0 RunII harg MCFM:
jetjet2 [pb/dp/dyd(cid:109)T11111010000-0-35731 N+L nOoj0en.tp4+e +<r t (u|H|yryEbjejeRtat|t |Ai< v<P e0 D0 .c8F.4o 1( r.(xr5x. )1 10036)) Muon C 0.1 HMCETS1RT0AWWP2D0F081N.5L (Oprel.)
10-5 0.8 < |yjet| < 1.2 0 1 2
1100--97 1.6 < |yj1et.|2 < < 2 |.y0j e(tx| <1 01-.66) (x 10-3) Muon Pseudorapidity |(cid:100)|
10-11
10-13 2.0 < |yjet| < 2.4 (x 10-9) Fig. 6. The W muon charge asymmetry as measured by the
10-15 100 200 300 400 500 600 700
pjet [GeV] CMSexperiment.Themeasurement(closedsymbols)iscompared
T
Fig.4.Jetproductioncrosssectionasafunctionofthejettrans- to the NLO prediction [12] using HERAPDF1.5NLO (shaded
versemomentumfordifferentrangesofpseudorapidity,asmea- band),MSTW08NLO(dottedline)andCT10W(dashedline).
suredbytheD0collaboration.Thedataarerepresentedbyclosed
symbols. The measurement is compared to the QCD calcula-
tionatNLObasedonHERAPDF1.5NLO.ThetotalPDFuncer- TopquarkpairproductionattheLHCprobesthegluon
taintyandhadronisationcorrectionsonthepredictionisshown densityathigh x.InFig.7thecross-sectionmeasurement
asshadedbands. of top pair production is shown as a function of the top-
quarkpolemassincomparisontoapproximateNNLOcal-
culations[16,17]basedonHERAPDF1.5NNLO.Thethe-
periment[9]inacentralrapiditybinisshownincompar-
oryuncertaintyaccountsforthevariationoftheQCDscales,
ison with NLO predictions using HERAPDF1.5NLO to-
PDFserrorandthevariationofα (M )inthePDF.Forthe
S Z
getherwithseveralotherPDFs.TheQCDpredictionusing
PDF uncertainty of HERAPDF1.5NNLO, only the eigen-
HERAPDF1.5NLOdescribesthedataverywell.
vectors for experimental errors are used. The predictions
describethedataverywell.
/d|y|Q 6.6)/dpT 111...4682 anti-ktCHD TEa jetERatQAs.P 6RD. 6F=0 1.4.0 (0.0<|y|<0HG.3EJ)RR (cid:54) A2PPD0F0D(8CFL 19.05) __ss (pb) (pb) t t t t600 CMS Praeplipmroixn.a NrNyL, O√s ×= H7E TReAVP,D FL1=51N.N1L4O fb-1
E
CT 1.2 errors: scale variations × 68% CL PDFexp × aS(MZ)
2(d|y|/d(cid:109)0 0.81 400 LAahnregnesn feetl da le.t al.
/dpT 0.6
/(cid:109)
2d 0.4 ATLAS Preliminary
102 103 200
p[GeV]
T
Measured cross section
Fig.5.Inclusivejetproductioncrosssectionasafunctionofthe Cross section corrected for mpole (Langenfeld et al.)
t
jettransversemomentum,asmeasuredbytheATLAScollabora- Measured cross section dependence on mMC
tionintherapidityrange0<y<0.3Thejetsareidentifiedusing 0140 150 160 170 180t 190
theanti-k algorithmwithR=0.4.Thedataarerepresentedina mmppoollee ((GGeeVV))
t tt
ratio(stars)totheQCDprediction,usingCTEQ6.6[11]asaref-
Fig. 7. The top-pair production cross section measured by the
erencePDFs.ThecentralvaluefortheQCDcalculationatNLO
CMS experiment (closed square) shown at the assumption on
basedonHERAPDF1.5NLOisrepresentedbyclosedcirclessur-
thetopmass,usedintheanalysis.Themassdependenceofthe
roundedbytheerrorbandshownasthehashedarea.
tt¯cross section according to approximate NNLO QCD predic-
tions[16]and [17]arerepresentedbytheshadedandhashed
band,respectively.Thedependenceoftheexperimentalmeasure-
Production of electroweak bosons provides important
mentontheassumptiononthem inthesimulationusedforeffi-
constraints on the light quark distributions. For example, t
ciencyanddetectorcorrectionsisshowninbylightshadedband.
the W lepton charge asymmetry A(W) = (σW+−σW−) ≈
l (σW++σW−) Theclosedcirclerepresentsthecrosssectionmeasurement,cor-
(uv−dv) is sensitive to the valence u and d quark ratio. rectedforthetoppolemass,extractedusingthecalculation[16].
uv+dv+2usea
EPJWebofConferences
5 Global benchmarking excercise 6.1 IncludingjetdatainthePDFfit:HERAPDF1.6
Presently,thedeterminationofPDFsiscarriedoutbysev- In addition to the combined HERA inclusive DIS data as
eralgroups,namelyMSTW[18],CTEQ[19],NNPDF[20], used in the QCD analysis HERAPDF1.5, H1 and ZEUS
HERAPDF [2], AB(K)M [21] and GJR [22]. The large measurementsofjetproductioncrosssections[24]arein-
number of PDF parameters and their treatment in the fit- cluded in the PDF fit. The resulting parton distributions
tingprocedurewithinthedifferentgroupsresultsindiffer- HERAPDF1.6 [25] are determined using a fixed value of
ences of the PDFs provided. In order to study these dif- α (M )andalsousingα (M )asafreeparameterinthe
S Z S Z
ferences,abenchmarkingexerciseisbeingcarriedoutby fit. The impact of the inclusion of jet data in the PDF fit
the PDF4LHC working group [23] formed by the mem- on the gluon distribution and the value of α is demon-
S
bers of the PDF fitting groups mentioned above. As an strated in Fig. 9. Here, the PDFs obtained using the in-
example, the NLO prediction for the Higgs cross section clusive data only (HERAPDF1.5) and the PDFs resulting
(M =120GeV)attheLHCisshowninFig.8fordiffer- fromincludingthejetdata(HERAPDF1.6)aredetermined
H
ent PDF sets as a function of α (M ). For different PDF using α (M ) as a free parameter in the QCD analysis.
S Z S Z
groups not only the value of α (M ), but also the run- IncaseofthesimultaneousfitofPDFsandα inHERA-
S Z s
ning of the strong coupling is different, resulting in dif- PDF1.5,theuncertaintiesonthegluonPDFbecomeslarge
ferent cross section predictions. The HERAPDF is an ac- atlow xbutassoonasthejetdataareincluded,thecorre-
lation between the gluon PDF and α (M ) is reduced, re-
s Z
sultinginsignificantlyreduceduncertaintiesonthegluon
NLO gg(cid:65)H at the LHC (s = 7 TeV) for M = 120 GeV PDF. In Fig. 10 the quality of the PDF fit in terms of χ2
H
pb)pb) 1133
( ((cid:109)(cid:109)HH1122..55
H1 and ZEUS HERA I+II PDF Fit H1 and ZEUS HERA I+II PDF Fit with Jets
Fusigin.g8d.iNffeLrOen11110011Ht111111....5502025511Pi00g..D11g11OIV44nFesunrteteircsr::c a PPl DeDraFrF00ro o+ot..r(cid:95)11n sbSl11ytas66hrseseLc00H..t11i11Co88nwpitr00h..e1122d√icst68i%00o=.. C11MCCNHAGn.22TTNEBJLSE1RR22.PK7Ts 0PQ0WDAM8D6FP00.F2DT986((cid:95)(cid:95).F1Me1SS.0((00VMM..H11.222Z2Z44))= 1G. Watt (April 2011)20 GeV) xf 000000000000............46846846800022211110-4xxgS ((×× 00..0055))10-3 H empfxarEoperdRe.a e um(cid:95)Aln seuP(ctMnDercriFZzet1)a.1r0tt.-5i.2ofn ( purnecQl.e)r 2t .= 101 0G-xx1udevvV2 x1HERAPDF Structure Function Working GroupMarch 2011 xf 000000000000............00046846846822211110-4xxxxSgSg ((((×××× 0000....00005555))))10-3 empHfxarEoperdRe.a e um(cid:95)Aln seuP(ctMnDercriFZzet1)a.1r0tt.-6i.2o (np urenlQc.)e r2t .= 101 0G-xxxx1ududevvvvV2 x1HERAPDF Structure Function Working GroupMarch 2011
Fig.9.Leftpanel:ThepartondistributionfunctionsfromHER-
APDF1.5. Right panel: the parton distribution functions from
tiveparticipantinthebenchmarkingexercise.Incontrastto HERAPDF1.6 (with HERAjet data included in thefit). In both
otherPDFgroups,HERAPDFisnotrestrictedtoonepar- cases,theQCDanalysisisperformettreatingαs(MZ)asafree
ticular heavy flavour treatment scheme, several schemes parameterinthefit.ThePDFsarepresentedforQ2=10GeV2.
areimplementedandcanbetested.Also,byprovidingthe
PDF eigenvectors for model parameter and parametriza-
tionvariations,HERAPDFallowsfortestsofspecificpa- isrepresentedasafunctionoftheassumptiononthevalue
rameterisationandmodelassumptionsduringtheQCDana- ofαS(MZ).IncaseofHERAPDF1.5,whereonlyinclusive
lysisofdifferentdatasets.Inthefollowing,theinclusionof data are used, a very shallow minimum in the χ2 distri-
semi-inclusive DIS data in the QCD analysis HERAPDF butionisobserved.Theinclusionofthejetmeasurements
and the impact of these data on assumptions on α (M ) in the fit results in the clear minimum, which allows the
S Z
andthecharmquarkmassvalueinthePDFfitisdiscussed. simultaneousdeterminationofthePDFsandαS(MZ).
H1 and ZEUS (prel.)
6SflPitcnooeaDcuSvmblFpouoeislus-tihmiirnwvngetcphihlr-eαDueoinSnsdIgi.SiuvclnTuceldcotuhlaimnuoetsardnedei.e,avifTdssopetuhrrriernoiedbe,vtmjuoiaientdteittceohnaplneutrasodidQindniidnCnuigtHtchDiDtoteiEhonIapeSRnanrlajoiAellsctiytokoPdsdneniiaDsrsaetjtaetnFcrotadtisglinaynetnhtttsshhdeeeenosrhsntQerwiotaCtiivnhvtDyhgee 22 - (cid:114)(cid:114)min11205050 HHEERRAAPPDDFF11..56f HERAPDF Structure Function Working Group March 2011
analysiscanhelpdisentanglingtheeffectsfromthegluon 0.114 0.116 0.118 0.12 0.122 0.124 0.126
(cid:95)(M)
and α in the PDF fit. Similarly, charm and beauty pro- S Z
S
ductioninepcollisionsprovidedirectaccesstothegluon Fig. 10. Distribution of χ2 for PDF fit as a function of the as-
distribution in the proton, which also depends on the as- sumptionontheα (M )value.Thedashedlinecorrespondsto
S Z
sumptionofthecharmandbeautymassvaluesusedinthe HERAPDF1.5,whereonlyinclusiveDISdataareused.Thesolid
PDFfit. linerepresentsHERAPDF1.6,wherethejetdataareincluded.
Presentedatthe2011HadronColliderPhysicssymposium(HCP-2011),Paris,France,November14-182011
Avalueofα (M ) = 0.1202 ± 0.0013(exp)±0.0007 values of the PDF fit including the charm data are deter-
s Z
(mod/param)±0.0012(hadronisation)+0.0045(scale)isdeter- mined as a function of the input values of charm quark
−0.0036
mined [25]. This result is in very good agreement with mass,mmod,usingdifferentheavyquarkschemes,asshown
c
different results of α determination at HERA and with inFig.12.
S
the world average as shown in Fig. 11. It is important to DifferentassumptionsonmmodinVFNschemesimpact
c
note, that the dominant uncertainty arises from the varia- the charm contribution to the sea quark distribution and
tion of the renormalization and factorisation scales in the thusaffectthecompositionofxU(x)fromthexu(x)andthe
NLOcalculationforthejetcrosssections.Thisvariationis
xc(x)contributions.Theseinturninfluencethevalueofthe
used to mimic the effect of the missing contribution from W± andZ crosssectionpredictionsatLHC.InFig.13the
higherorders. NLO prediction [12] for the W+ production cross section
isshown,usingpartondistributionsevaluatedwithdiffer-
entassumptionsonmmod invariousheavyquarkschemes.
H1 and ZEUS (prel.) c
WSZPZPHEHEHP.hhuurEE 11EeByyrrol..UU ssie RmrlhPP..to lSShhhLLAiidnkwgyyee a Pessttiihattrnn ,.... yDQ EJJv BBccQ..uFe 2llCC65r ..2r.144k 66 aPkk9775.nT6h,,g,,TT o11y13m e26jjs 6r(ee 4.32m( u J2 tt0((ss.02l12 .tC0000 ik7099)16j)2e04T86)),t --ms6098079u (l2t0ij0e9)ts 00..1111 00..1122 et00hx...p 11u.33 n(cid:95)(cid:95)ucnssec((rMMet.rtZZ.)) HERAPDF Structure Function Working Group March 2011 2(cid:114)11026800000000 HHE1R aAnPdDSRRAZ FM-TTCZA1 OVsoCE.Ft0pTOaNUt- nifT+mSud- Sl(cid:114)aFilsr c2ed(cd(pprreell..)) ERA Inclusive Working Group August 2010
H
Fig.11.ThesummaryofαS(MZ)determinationresultsusingthe 1.2 1.4 1.6 1.8
jetproductionatHERAascomparedtotheworldaverage.The
mmodel / GeV
c
upper point corresponds to the simultaneous determination of
αS(MZ)andthePDF,asdescribedinthetext.Theexperimental Fig.12.Comparisonoftheχ2distributionsoffitstotheinclusive
uncertaintiesarerepresentedbysolidlines,thetheoryuncertain- HERAI+Fc¯c datausingdifferentheavyflavourschemesrepre-
tiesareshownbydashedlines. sentedasline2sofdifferentstyles.
6.2 CharmquarkmeasurementsinthePDFfit. b 64
Thefactorizationscheme,usedforthePDFdetermination / n(cid:109)+W 62 WHE+R (APs D= F71 T.0e V+) Fc2c(prel.) ugust 2010
A
dtheepepnrdostoonn, wthheicahssuvamripetsiodneopnentdhiengnuomnbtehreovfaflluaevooufrsthine 60 p
u
o
scale,whichhastobecomparedtothethreshold,atwhich 58 Gr
g
ctqhhuraaerrsmkhso.aldTndhisebrdeeefaotuertreym,qtihnueeadrtkrbesyactmtahneenbmteaotsfrsehaoetfeadvcyhaasqrmupaararktnosdnasbn.edTauthhtiyes 56 RRTT sotpatnimdaisredd usive Workin
ainsstuhmepQtiCoDnsaonnalythseisirofmtahsesepsrohtaovnestpraurcttiucruel.arDiimffeproernttanacpe- 54 SAZM-CAOVCFTON-fTSu-l (cid:114)l ERA Incl
52 H
proaches to treat heavy quark (heavy quark schemes) are 1.2 1.4 1.6 1.8
usedbydifferentPDFfittinggroups,correspondingtodif- mmcodel / GeV
√
fbeurtenaltstoreiamtmpleynitnogfdmiffaessretnecrmessiinntpheertiunrtbearptirveetactaiolcnulaantdioanss-, aFifgu.n1c3ti.oNnLoOfmpmreoddiicntitohneoinfpσuWt+PDatFt.hTehLeHliCnefsorshows =pre7dTicetVioanss
c
sumptionsonthevaluesoftheheavyquarkmasses.Mea- for different VFN schemes. The stars show the predictions ob-
surements of charm and beauty production can help con- tainedwiththeoptimalvalueofmmodusedinagivenscheme.The
c
strainingsomeoftheseassumptions.Thecharmcontribu- dashedhorizontallinesindicatetherangeofσW+,determinedfor
tion, Fc, to the proton structure function F is measured mmod=mmod(opt).
2 2 c c
atH1andZEUSusingdifferentcharmtaggingtechniques.
Thesemeasurementsarecombined[27]takingintoaccount
the correlations of the systematic uncertainties. The com- Takingintoaccountthewholespreadofcrosssectionpre-
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2
clusiveDIScrosssections,andtheeffectonthePDFsus- ontheW+ productioncrosssectionarisesduetoassump-
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2
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