proton structure from hera and the impact for the lhcnuclphys.sinp.msu.ru/conf/epp10/lipka.pdf ·...
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Proton Structure from HERA
and the impact for the LHC
Katerina Lipka, DESY
for the H1 and ZEUS Collaborations
Lomonosov Conference on High Energy Physics 2013
partons (quarks & qluons)
u
u
d
valence quarks (u, d)
→ most quantum propertiesBUT:Mu~0.003 MN , Md~0.006 MN
Origin of the proton mass: QCD energy
parton composition, coupling, masses and
momentum distributions
nucleons (protons, neutrons)mass MN ~ 1 GeV
Proton structure: fundamental subject in matter studies
baryonic matter
1
Electron scatters off a charged constituent (parton) of the proton
Identify the charged partons with quarks
γ, Z0 exchange: Neutral Current (NC)
W± exchange: Charged Current (CC)
Learn about the nucleon structure via lepton-nucleon scattering
• Point-like constituents (partons) behave incoherently
• Probability f(x) for a parton f to carry the fraction x of the nucleon momentum is an
intrinsic property of the nucleon, i.e. process independent
Electron-proton scattering in parton picture
Proton structure in quark-parton model
2
Learn about the nucleon structure via lepton-nucleon scattering
Electron-proton scattering in parton picture Kinematics
~1.6 fm
Proton
rQ2
4-momentum transfer Q2 defines distance scale r at which proton is probed
Q2 =-q2 photon virtuality r ≈ hc/Q = 0.2[fm]/Q[GeV]
Proton structure in quark-parton model
• Point-like constituents (partons) behave incoherently
• Probability f(x) for a parton f to carry the fraction x of the nucleon momentum is an
intrinsic property of the nucleon, i.e. process independent
3
Learn about the nucleon structure via lepton-nucleon scattering
Proton structure in quark-parton model
Q2 =-q2 photon virtualityx=-q2/2p·q Bjorken scaling
Infinite proton momentum frame:
partons do not interact, move parallel to the proton,massless, no transverse momentum
parton i carries fraction xi of Pp
0<xi<1, ∑xi =1
• Point-like constituents (partons) behave incoherently
• Probability f(x) for a parton f to carry the fraction x of the nucleon momentum is an
intrinsic property of the nucleon, i.e. process independent
Electron-proton scattering in parton picture Kinematics
4
Lepton-proton scattering cross section and proton structure functions
Proton structure in quark-parton model
γ*, Z
Q2 =-q2 photon virtualityx=-q2/2p·q Bjorken scalingy inelasticity
d2σe±p
dxdQ2∝ 2πα2
xQ4
�(1 + (1− y)2)F2 − y2FL ∓ xF3
�
F2 ∝ x�
f
qf + qf
Neutral Current
Bjorken scaling: if partons do not interact, q=q(x); F2=F2(x)
parton distributions
measured cross-section
structure functions
• Point-like constituents (partons) behave incoherently
• Probability f(x) for a parton f to carry the fraction x of the nucleon momentum is an
intrinsic property of the nucleon, i.e. process independent
5
Parton Distribution Functions: number of partons in the proton, carrying momentum between xP and (x+dx)P, as resolved at Q2.
Scaling violation: F2(x)→F2(x,Q2), q(x)→q(x,Q2)
Quarks do interact via gluon exchange. Probability via splitting functions:
PqqPgqPqg Pgg
q(z)
q(x)
g(z-x)q(z)
g(x)
q(z-x) g(z) q(z-x)
q(x)
g(z)
g(x)
g(z-x)
Proton structure in Quantum ChromoDynamics
6
Parton Distribution Functions: number of partons in the proton, carrying momentum between xP and (x+dx)P, as resolved at Q2.
Scaling violation: F2(x)→F2(x,Q2), q(x)→q(x,Q2)
Quarks do interact via gluon exchange. Probability via splitting functions:
PqqPgqPqg Pgg
q(z)
q(x)
g(z-x)q(z)
g(x)
q(z-x) g(z) q(z-x)
q(x)
g(z)
g(x)
g(z-x)
Proton structure in Quantum ChromoDynamics
∂q(x,Q2)∂lnQ2
∝� 1
x
dz
z
�q(z, Q2)Pqq
�x
z
�+ g(z, Q2)Pqg
�x
z
��
∂g(x,Q2)∂lnQ2
∝� 1
x
dz
z
�q(z, Q2)Pgq
�x
z
�+ g(z, Q2)Pgg
�x
z
�� Quark and gluon PDFcoupled in DGLAP
Additional dependence on Q2 quantitatively described in perturbative QCD via Dokshitzer-Gribov-Lipatov-Altarelli-Parisi (DGLAP) Evolution Equations
PDFs determined experimentally, mostly using data on Deep Inelastic Scattering6
World-only ep collider
DIS at Hadron-Electron-Ring-Accelerator at DESY
HERA measurements
protons
electrons
Ep=460-920 GeV Ee=27.6 GeV
E2 d
N/d
E (G
eV c
m-2
sr-1
s-1
)
Energies and rates of cosmic ray particles
compatible with
50 TeV γ beam on a fixed p target
e p
Unique machine to study the proton structure
7
World-only ep collider
protons
electrons
Central Tracker
• HERA I : 1992-2000
• HERA II: 2003-2007
• collider experiments
H1 & ZEUS,√smax= 318 GeV
• integrated Luminosity
~0.5 fb-1/ experiment
Ep=460-920 GeV
HERA switched off June 2007, analyses ongoing on the way to final precisionH1 and ZEUS combine experimental data accounting for systematic correlations HERA performs the QCD analysis of (semi) inclusive DIS data (HERAPDF)H1 and ZEUS collaborations provide/support the PDF Fitting Tool (HERAFitter)
DIS at Hadron-Electron-Ring-Accelerator at DESY
Ee=27.6 GeV
7
E1
E2
s = τs = x1x2s
x1,2 =M√
s× exp(±y)
Q = M
Kinematics reconstructed from the scattered lepton (or hadronic final state)
Reconstruction of x1 and x2 not straightforward
fi(x)
DIS at HERA: clean lepton probe
Proton-proton collision at LHC
Kinematics at HERA as compared to the LHC
8
fi(x)
DIS at HERA: clean lepton probe HERA covers low, medium x range of the LHCQ2 evolution via QCD
12
HERA
TEVATRON
LHC
DGLAP
HERA data: backbone for PDF determination
E1
E2
s = τs = x1x2s
x1,2 =M√
s× exp(±y)
Q = M
Proton-proton collision at LHC
Kinematics at HERA as compared to the LHC
9
DIS cross sections provide an access to parton distribution functions in proton
LO : F2 ∝�
i
(qi(x) + qi(x))
LO : F3 ∝�
i
(qi(x)− qi(x))
NLO : FL ∝ x · αS · g(x,Q2)
d2σe±P
dxdQ2=
2πα2
xQ4[Y+F2 ∓ Y−xF3 − y2FL]
dominant contribution
γ/Z interference
contribution from gluon
γ, Z Exchange: Neutral Current ep → e X
σe+pCC ∝ x{(u + c) + (1− y)2(d + s)}
σe−pCC ∝ x{(u + c) + (1− y)2(d + s)}
W± Exchange: Charged Current ep → ν X
sensitive to individual quark flavours
Structure functions in DIS and proton PDFs
10
precision 1.5% for Q2 < 500 GeV2
arXiv:1208:6138
JHEP 1209:061 (2012)
sensitivity to valence compositiongluon distribution via scaling violations
xF γZ3 ∝ x · qval
F γZ2 ∝ q · q
JHEP 1209:061 (2012)
Q2=1500 GeV2
Recent results on Neutral Current Cross Sections
11
JHEP 1209:061 (2012)
HERA II: improvement in precision: e+ (e-) p by a factor of 3 (10) luminosity wrt. HERA I
improved sensitivity to quark flavour composition
Recent results on Charged Current Cross Sections
12
H1 and ZEUS
HER
A In
clus
ive
Wor
king
Gro
upA
ugus
t 201
0
x = 0.02 (x300.0)
x = 0.032 (x170.0)
x = 0.05 (x90.0)
x = 0.08 (x50.0)
x = 0.13 (x20.0)
x = 0.18 (x8.0)
x = 0.25 (x2.4)
x = 0.40 (x0.7)
x = 0.65
Q2/ GeV2
r,N
C(x
,Q2 )
HERA I+II NC e+p (prel.)HERA I+II NC e-p (prel.)
HERAPDF1.5 e+pHERAPDF1.5 e-p
±
10-2
10-1
1
10
10 2
10 3
10 2 10 3 10 4 10 5
0
0.5
1
1.5
2
0
0.5
1
0
0.2
0.4
0.6
0.8
H1 and ZEUS
r,C
C(x
,Q2 )
Q2 = 300 GeV2
-
Q2 = 500 GeV2 Q2 = 1000 GeV2 Q2 = 1500 GeV2
Q2 = 2000 GeV2 Q2 = 3000 GeV2
10-2 10-1
Q2 = 5000 GeV2
10-2 10-1
Q2 = 8000 GeV2
x
HER
A In
clus
ive
Wor
king
Gro
upA
ugus
t 201
0
10-2 10-1
Q2 = 15000 GeV2
10-2 10-1
Q2 = 30000 GeV2
x
HERA I+II CC e-p (prel.)HERAPDF1.5
Neutral Current Charged Current
Preliminary H1 and ZEUS measurements are combined accounting for correlationsImpressive precision up to high Q2 and high xQCD analysis of combined HERA NC and CC data: HERAPDF
Combined HERA DIS Cross Sections
13
0.2
0.4
0.6
0.8
1
-410 -310 -210 -110 1
0.2
0.4
0.6
0.8
1
HERAPDF1.5 (prel.)
exp. uncert.
model uncert. parametrization uncert.
x
xf 2 = 10 GeV2Q
vxu
vxd
0.05)×xS (
0.05)×xg (
HER
A S
truc
ture
Fun
ctio
ns W
orki
ng G
roup
July
201
0
H1 and ZEUS HERA I+II Combined PDF Fit
0.2
0.4
0.6
0.8
1
Model assumptions:
Qmin2=3.5 GeV2 , αs(MZ)=0.1176
mc=1.4 GeV; mb=4.75 GeV; fs(Q02)=0.31
DGLAP evolution (QCDNUM, arXiv:1005.1481)
Heavy quarks: massive
Variable Flavour Number Scheme
Scales: µr = µf = Q2 , starting scale 1.9 GeV2
Experimentally uncertainty (Δχ2 =1)
Parameterization at starting scale:
HERAI +HERAII (prel.)
HERAPDF1.5: most precise DIS data, recommended HERA PDF set
HERA parton density functions
14
HERAPDF1.5 NLO and NNLO most precise DIS data, proper treatment of correlation of errors, allows for model studies
0
0.2
0.4
0.6
0.8
1
-410 -310 -210 -110 10
0.2
0.4
0.6
0.8
1
HERAPDF1.5 NNLO (prel.)
exp. uncert.
model uncert. parametrization uncert.
x
xf 2 = 10000 GeV2Q
vxu
vxd
0.05)×xS (
0.05)×xg (
HER
APD
F St
ruct
ure
Func
tion
Wor
king
Gro
upM
arch
201
1
H1 and ZEUS HERA I+II PDF Fit
0
0.2
0.4
0.6
0.8
1
NNLO
Describes LHC data very well, used in ATLAS, CMS and LHCb analyses
Available in LHAPDF with eigenvectors for uncertainties and αs variation
Final combination of HERA inclusive data and QCD analysis on the way (HERAPDF2.0)
HERA parton density functions
15
i 1
0×
NC
/Je
t -210
1
210
410
610
810
1010
T,JetP710 20 50
DijetTP710 20 50
[GeV]TrijetTP 710 20 50
2 < 200 GeV2 150 < Q (i = 10)
2 < 270 GeV2 200 < Q (i = 8)
2 < 400 GeV2 270 < Q (i = 6)
2 < 700 GeV2 400 < Q (i = 4)
2 < 5000 GeV2 700 < Q (i = 2)
2 < 15000 GeV2 5000 < Q (i = 0)
had cNLO
= 0.118sCT10, QCDNUMNLOJet++ and fastNLO
Inclusive Jet Normalised
DijetNormalised
TrijetNormalised H1
Preliminary
(Multi)-jet production directly sensitive to the strong coupling constant
< 1% experimental error
Nuclear Physics B 864 (2012) 1
αS(MZ)=0.1206 (exp) (theory)+ 0.0023- 0.0022
+ 0.0042- 0.0035 αS(MZ)=0.1163 (exp) (theory)+ 0.0011
- 0.0011+ 0.0042- 0.0042
Measure αs running in a single experimentdifferent measurement methods agree
PhotoproductionQ2~0
DIS, 150 GeV2 < Q2 < 15000 GeV2
Precision QCD: jet production at HERA
16
c, b
g(x)
γe
p
c, b
stringent test of QCD, direct probe of the gluon
use different tagging methods:- meson reconstruction,- large mass and long lifetime
combination: - orthogonal uncertainties- take into account correlations
0
0.2
0
0.5
0
0.5
0
0.5
red
cc_
H1 VTX
H1 D* HERA-II
H1 D* HERA-I
ZEUS c µ X
ZEUS D* 98-00
ZEUS D* 96-97
ZEUS D0
ZEUS D+ H1 and ZEUSQ2=2.5 GeV2 Q2=5 GeV2 Q2=7 GeV2
Q2=12 GeV2 Q2=18 GeV2 Q2=32 GeV2
Q2=60 GeV2 Q2=120 GeV2 Q2=200 GeV2
Q2=350 GeV2
10-4 10-3 10-2
Q2=650 GeV2
10-4 10-3 10-2
Q2=2000 GeV2
HERA
10-4 10-3 10-2
x
Eur. Phys. J. C 73:2311 (2013), [arXiv:1211.1182]
Additional Constraints on PDFs: Charm at HERA
17
c, b
g(x)
γe
p
c, b
stringent test of QCD, direct probe of the gluon
use different tagging methods:- meson reconstruction,- large mass and long lifetime
combination: - orthogonal uncertainties- take into account correlations
0
0.2
0
0.5
0
0.5
0
0.5
red
cc_
H1 VTX
H1 D* HERA-II
H1 D* HERA-I
ZEUS c µ X
ZEUS D* 98-00
ZEUS D* 96-97
ZEUS D0
ZEUS D+ H1 and ZEUSQ2=2.5 GeV2 Q2=5 GeV2 Q2=7 GeV2
Q2=12 GeV2 Q2=18 GeV2 Q2=32 GeV2
Q2=60 GeV2 Q2=120 GeV2 Q2=200 GeV2
Q2=350 GeV2
10-4 10-3 10-2
Q2=650 GeV2
10-4 10-3 10-2
Q2=2000 GeV2
HERA
10-4 10-3 10-2
x
Eur. Phys. J. C 73:2311 (2013), [arXiv:1211.1182]
Q2=18 GeV2
HERA
H1 and ZEUS
H1 VTX
H1 D* HERA-II
H1 D* HERA-I
ZEUS c µ X
ZEUS D* 98-00
ZEUS D* 96-97
ZEUS D0
ZEUS D+
x
red
cc_
10-3 10-20
0.2
0.4
0.6
Precision ~ 5% at medium Q2 reached
Additional Constraints on PDFs: Charm at HERA
17
Inclusion of charm: reduced uncertainty on gluon, charm and light sea...mostly due to better constrained charm-quark mass
Eur
. Phy
s. J
. C 7
3:23
11 (2
013)
, [ar
Xiv
:121
1.11
82]
Additional Constraints on PDFs: Charm at HERA
18
Consistent with the world averagemc(mc)wa = 1.275 ±0.025 GeV
perform PDF fit varying mc in
FFNS coefficients
Determination of mc(mc) MS at NLO Study mc -choice in variable flavor number schemes
Different schemes prefer different Mc
Eur
. Phy
s. J
. C 7
3:23
11 (2
013)
, [ar
Xiv
:121
1.11
82]
Additional Constraints on PDFs: Charm at HERA
mc(mc) = 1.26 ± 0.05exp
±0.03mod±0.02par±0.02αs GeV
19
Study mc -choice in variable flavor number schemes
Different schemes prefer different Mc
Prediction for W+ (W-, Z ) production at the LHC
Uncertainty due to differences in charm treatmentin PDFs significantly reduced by using optimal Mc
Eur
. Phy
s. J
. C 7
3:23
11 (2
013)
, [ar
Xiv
:121
1.11
82]
Additional Constraints on PDFs: Charm at HERA
20
HERAFitter: Open-Source Modular Tool for QCD AnalysisDeveloped at HERA, extended to LHC and theory groups, https://www.herafitter.org/HERAFitterStudy the impact of different data on PDFs and test different theory approaches
experimental input
processes: NC, CC DIS, jets, diffraction, heavy quarks (c,b,t)Drell-Yan, W production
theoretical calculations/toolsHeavy quark schemes: MSTW, CTEQ, ABMJets, W, Z production: fastNLO, ApplgridTop production NNLO (Hathor)QCD Evolution DGLAP (QCDNUM) kT factorisationAlternative tools NNPDF reweightingOther models Dipole model + Different error treatment models + Tools for data combination (HERAaverager)
H1 and ZEUS
Q2 / GeV2
r,N
C(x
,Q2 )
x=0.0002x=0.002
x=0.008
x=0.032
x=0.08
x=0.25
HERA I NC e+pZEUSH1
+
0
0.2
0.4
0.6
0.8
1
1.2
1.4
1.6
1 10 10 2 10 3 10 4
[GeV]T
p210 310
/d|y
|T
(CTE
Q 6
.6)/d
p0
2/d
|y|/d
T/d
p2 d 0.4
0.6
0.8
1
1.2
1.4
1.6
1.8
2(CL90)PDF jets. R =0.4 (0.0<|y|<0.3) tanti-k
DataCTEQ 6.6HERAPDF 1.0
HERAPDF 1.5
GJR 2008
ATLAS Preliminary
[GeV]jetT
p100 200 300 400 500 600 700
[pb/
GeV
]je
tT
dpje
t/d
y2 d
-1510
-1310
-1110
-910
-710
-510
-310
-11010
310
510
710
910
1110D0 RunII
NLOjet++ (HERAPDF1.5)
)6| < 0.4 (x 10jet|y
)3| < 0.8 (x 10jet0.4 < |y
| < 1.2 jet0.8 < |y
)-3| < 1.6 (x 10jet1.2 < |y
)-6| < 2.0 (x 10jet1.6 < |y
)-9| < 2.4 (x 10jet2.0 < |y
+ nonperturbative corr.
Tevatron inclusive jet cross sections
experiments: HERA, Tevatron, LHC, fixed target
0
0.2
0.4
0.6
0.8
1
-410 -310 -210 -110 10
0.2
0.4
0.6
0.8
1
HERAPDF1.5 NNLO (prel.)
exp. uncert.
model uncert. parametrization uncert.
x
xf 2 = 10 GeV2Q
vxu
vxd
0.05)×xS (
0.05)×xg (
HER
APD
F St
ruct
ure
Func
tion
Wor
king
Gro
upM
arch
201
1
H1 and ZEUS HERA I+II PDF Fit
0
0.2
0.4
0.6
0.8
1
PDF or DPDF,...
αS (MZ),mc,mb,mt, fs,..
Theory predictions
Benchmarking
Comparison of schemes
HER
AFi
tter
21
Summary
HERA data are unique and of particular importance for PDF determination
• HERA II inclusive DIS cross section measurements are published
• H1+ZEUS combination and analysis towards HERAPDF2.0 ongoing
• HERA jet and charm data provide additional constrains on αS and charm-quark mass
HERA Expertise in QCD analysis preserved in HERAFitter development
• developed and supported by several experiments and theory groups
• allows experimentalists to perform QCD analysis and test theory approaches
• open source program, successfully used by the LHC experiments
22
Determination of parton density functions
x-dependence of PDFs is not calculable in perturbative QCD:
parameterize at a starting scale Q20 : f(x)=AxB(1-x)C(1+Dx+Ex2)
evolve these PDFs using DGLAP equations to Q2>Q20
construct structure functions from PDFs and coefficient functions:
predictions for every data point in (x, Q2) – plane
χ2- fit to the experimental data
Structure function factorization: for the exchange of Boson V (γ, Z, W±)
calculable in pQCDfrom measured cross sections
FV2 (x,Q2) =
�
i=q,q,g
� 1
xdz × CV,i
2 (x
z, Q2, µF , µR, αS)× fi(z, µF , µR)
HERA Inclusive DIS Measurements at highest Q2]2
[pb/
GeV
2/d
Qd
-710
-510
-310
-110
10
]2 [GeV2Q310 410
p CCH1 ep CC+H1 e
p CC HERA IIZEUS ep CC HERA II+ZEUS e
p CC (HERAPDF 1.5)SM ep CC (HERAPDF 1.5)+SM e
p NCH1 ep NC+H1 e
p NC HERA IIZEUS ep NC HERA II+ZEUS e
p NC (HERAPDF 1.5)SM ep NC (HERAPDF 1.5)+SM e
y < 0.9 = 0eP
HERA
[%] eP-100 -50 0 50 100
[pb]
CC
0
20
40
60
80
100
120p Scattering±HERA Charged Current e
2 > 400 GeV2Q y < 0.9
X p +e
X p e
HERAPDF 1.5
HERAPDF 1.5
H1 ZEUS
H1 ZEUS
NC and CC cross sections at large scales:SM: zero cross section for a RH e- or LH e+
HERA textbook measurements in electroweak physics
Electroweak unification Good agreement with the SM
Inclusive HERA I and II dataprecision NC: ~1.5%, CC: ~4%
Charged Current
Neutral Current
arXiv:1208.6138JHEP 1209:061 (2012)EPJC 62 (2009) 625EPJC 70 (2010) 945EPJC 61 (2009) 223
6
µi measured value at point i
δi statistical, uncorrelated systematic error
γjj – correlated systematic error
bj – shift of correlated systematic error sources
mi _ true value (corresponds to min χ2)
Measurements performed sometimes in slightly different range of (x,Q2)
swimming to the common (x,Q2) grid via NLO QCD in massive scheme
Combination ProcedureMinimized value:
HERAPDF1.7: DIS+ low energy+jets+charm
0.2
0.4
0.6
0.8
1
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0.2
0.4
0.6
0.8
1
HERAPDF1.7 (prel.) exp. uncert. model uncert. parametrization uncert.
HERAPDF1.6 (prel.)
x
xf 2 = 10 GeV2Q
vxu
vxd
0.05)×xS (
0.05)×xg (
HER
APD
F St
ruct
ure
Func
tion
Wor
king
Gro
upJu
ne 2
011
HERA I+II inclusive, jets, charm PDF Fit
0.2
0.4
0.6
0.8
1Flexible parametrization
heavy flavours:
mc=1.5±0.15 GeV
αS (MZ)=0.119
steeper gluon as HERAPDF1.6
Including the jet and the charm data: decouple the gluon from αS and mc
FV2 (x,Q2) =
�
i=q,q,g
� 1
xdz × CV,i
2 (x
z, Q2, µF , µR, αS)× fi(z, µF , µR)
Heavy Quarks and PDF Fits
Factorization:
i - number of active flavours in the proton: defines the factorization (HQ) scheme
• i fixed : Fixed Flavour Number Scheme (FFNS)
only light flavours in the proton: i = 3 (4)
c- (b-) quarks massive, produced in boson-gluon fusion
Q2 » mHQ2 : can be less precise, NLO coefficients contain terms ~
• i variable: Variable Flavour Number Scheme (VFNS)
- Zero Mass VFNS: all flavours massless. Breaks down at Q2 ~mHQ2
- Generalized Mass VFNS: different implementations provided by PDF groups smooth matching with FFNS for Q2 →mHQ
2 must be assured
ln� Q
mHQ
�
QCD analysis of the proton structure: treatment of heavy quarks essential
HQ contributions to the proton structure function F2 : (e.g. charm)
Direct test of HQ schemes in PDF fits
Heavy Quark Production at HERAHeavy quarks in ep scattering produced in boson-gluon fusion
Contribution to total DIS cross section:
charm: ~ 30% at large Q2
beauty: at most few %
Gluon directly involved: cross-check of g(x) from NC and CC DIS cross sections
c (b)
c (b)
g(x)
γe
p
[GeV]cM1.2 1.4 1.6 1.8
) c (M2
550
600
650
700
750
800HERA-I inclusiveCharm + HERA-I inclusive
H1 and ZEUS
RT standard
0.06 GeV±=1.50 optcM
HERA Charm Data test PDFs obtained with inclusive DIS
2=2.5 GeV2Q 2= 5 GeV2Q 2= 7 GeV2Q
2=12 GeV2Q 2=18 GeV2Q 2=32 GeV2Q
2=60 GeV2Q 2=120 GeV2Q 2=200 GeV2Q
2=350 GeV2Q 2=650 GeV2Q 2=2000 GeV2Q
redc
c
0
0.2
0
0.5
0
0.5
0
0.5
-410 -310 -210 -410 -310 -210x
-410 -310 -210
HERA HERAPDF1.5
H1 and ZEUS
HERAPDF is obtained using only inclusive HERA DIS NC and CC data, use VFNSDescribes charm cross-sections very goodUncertainty band mostly due to variation of charm quark mass in PDF: 1.35<mc<1.65 GeV
Sensitivity to charm mass in PDF fit increased once HERA charm data used
together with inclusive DIS data
inclusive DIS only
inclusive+ charm DIS
Consistent with the world averagemc(mc)wa = 1.275 ±0.025 GeV
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H1 and ZEUS
Charm + HERA-I inclusive
0.05 GeV±)=1.26 c(mcm
QCD Predictions at NLO (~αs2) and NNLO (~αs3) describe data very wellRunning mass of charm quark is used in coefficient functions in QCD analysis
HERA Charm Data vs QCD Analysis in FFNS
perform PDF fit varying mc in
FFNS coefficients
Determine mc(mc) in MS at NLO
mc(mc) = 1.26 ± 0.05exp
±0.03mod±0.02par±0.02αs GeV
HERA Charm Data vs QCD Analysis in VFNS
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HERA
MSTW08NNLO
MSWT08NNLO (opt.)
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HERA
CT10NLO
CT10NNLO (prel.)
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Data are confronted to predictions using Variable-Flavour Number Scheme at NLO (αs) and NNLO (αs2)
Predictions using heavy quark coefficients at higher order describe data better at lower Q2
[GeV] cM1.2 1.4 1.6 1.8
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H1 and ZEUS
Charm + HERA-I inclusive
Charm mass in Variable Flavor Number Scheme
Study charm mass choice in PDF using different VFNS implementations using HERAFitter
Different schemes prefer different Mc
different implementation of VFNSuse mcpole in the HQ coefficients
matching between Nflavor to Nflavor+1,(choosing an interpolation approach and different methods for truncation of the perturbative series)→ definition of mc(pole) gets as uncertain as matching conditions: mcpole → Mc
parameter Mc is implicitly used in predictions for the LHC processes using VFNS PDFs (CTEQ, MSTW, NNPDF, HERAPDF)
Effect of charm mass in VFNS PDF on σ(W, Z) at NLO
Larger Mc → more gluons, less charm → more light quarks → larger σW
NLO prediction for W+ (W-, Z ) production at the LHC: dependence on charm mass in PDF
Effect of charm mass in VFNS PDF on σ(W, Z) at NLO
Larger Mc → more gluons, less charm → more light quarks → larger σW
Only one HQ schemeMc variation in PDF
1.3 < Mc < 1.5 GeV
3% uncertainty on W prediction
NLO prediction for W+ (W-, Z ) production at the LHC: dependence on charm mass in PDF
Effect of charm mass in VFNS PDF on σ(W, Z) at NLO
Larger Mc → more gluons, less charm → more light quarks → larger σW
Only one HQ schemeMc variation in PDF
1.3 < Mc < 1.5 GeV
3% uncertainty on W prediction
Using different HQ schemes:
+ 7% uncertainty
Several HQ schemes
NLO prediction for W+ (W-, Z ) production at the LHC: dependence on charm mass in PDF
Data sensitivity to different heavy quark treatments in PDFs
[GeV]cM1.2 1.4 1.6 1.8
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-W
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= 7 TeVs
Charm + HERA-I inclusive
H1 and ZEUS
NLO prediction for W+ (W-, Z ) production at the LHC: dependence on charm mass in PDF
Uncertainty due to differences in charm treatment in PDFs significantly reduced by using optimal Mc in each HQ scheme in PDF
< 2%
[GeV] cM1.2 1.4 1.6 1.8
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H1 and ZEUS
Charm + HERA-I inclusive
Use optimal Mc in each scheme
Prediction using mc=1.4 GeV
Error band: PDF uncertainty
Experimental error
Parametrization variation
Model assumptions
including mc variation
Heavy Quarks in PDFs and W/Z at LHC
√s=14 TeV
rapidity
NLO ⊗ HERAPDF1.0
Prediction of W± cross section @ LHC: dominant uncertainty due to PDF
mc variation in PDF: significant uncertainty on W@LHC in central region
(HERA)PDF and top quark at the LHC Top quark at CMS: cross section @ approx. NNLO
mtpole (GeV)
t t_
(pb)
approx. NNLO (Langenfeld et al.) × HERAPDF15NNLO
only PDF uncertainties (68% CL):experimentalparametrizationmodel variations: Q2 > 5 GeV2
CMS (Prel.) CMS-PAS-TOP-11-005 (2011)
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Dominant uncertainty: variation of Q2min imposed on data used in the fit
top quark production at the LHC has potential to constrain the high-x gluon
Q2=4mt2
thanks A. Cooper-Sarkar
HERAPDF1.5NNLO
PDF fits using HERA jet data: fixed αS
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H1 and ZEUS HERA I+II PDF Fit with Jets
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APD
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Inclusion of jet data into the PDF fit using fixed αS does not have large impact
Inclusive DIS data: combined HERAI+HERAII
Jet data:H1 high Q2 , EPJ C65 (2010) low Q2, EPJ C67 (2010)
ZEUS incl. jets PLB547 (2002) incl.+2jets NP B765 (2007)
PDF Fit: - flexible parametrisation- αs(MZ) fixed
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PDF fits with free αS (MZ)
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HERAPDF1.5f (prel.) )
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APD
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H1 and ZEUS HERA I+II PDF Fit
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APD
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HERAPDF1.6 (prel.) )
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H1 and ZEUS HERA I+II PDF Fit with Jets
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PDF fits with free αS (MZ)
Inclusion of jet data into the PDF fit decouples the gluon and αS (MZ)
αS (MZ) from PDF fits including HERA jet data
)Z
(MS
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in2
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HERAPDF1.5fHERAPDF1.6
HER
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)Z
(Ms
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Z(Ms
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exp. uncert.th. uncert.
World averageS. Bethke, Eur. Phys. J. C64, 689 (2009)
jets 98-00TZEUS incl. kPhys. Lett. B 649, 12 (2007)
jets 96-97TZEUS incl. kPhys. Lett. B 547, 164 (2002)
multijetsT k2H1 low QEur. Phys. J. C67, 1 (2010)
multijetsT norm. k2H1 high QEur. Phys. J. C65, 363 (2010)
HERAPDF1.6Preliminary
H
ERA
Stru
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Mar
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H1 and ZEUS (prel.)Scan of the αS (MZ) in the PDF fit
+ jet data
no jet data
PDF and αS (MZ) determined in the common fit:αS (MZ)= 0.1202 ± 0.0013exp ± 0.0007model/param ± 0.0012had+0.0045scale
From including the Jet data in the PDF fit: determine gluon and αS (MZ)