w+charm poster
TRANSCRIPT
Measurement of the produc1on ofa W boson in associa1on with a charm quark in pp collisions at √s = 7 TeV with the ATLAS detector
Giacomo Snidero (Queen Mary University of London)
Giacomo Snidero for W+charm analysis team (G. Aad, H. Arnold, L. Caminada, L. Cerrito, K. Lohwasser, M. Shapiro, G. Snidero, M. Vanadia, C. Weiser)
• Select events sample with a charm-‐jet, idenFfied by a semileptonic decay into a muon within the jet(soJ muon tagging, c-‐jet: pT >25 GeV, |η| <2.5).
• Cut-‐and-‐count events to obtain signal yield.
• Major backgrounds(data-‐driven esFmated):W+light-‐jets, mulF-‐jets,Z+jets (muon chan. only). Other backgrounds (Monte Carlo esFmated): t-‐quark, di-‐bosons.
• Leading systemaFc uncertainFes:c-‐quark decay modelling, jet energy scale.
W+c-‐jet analysis• Select events sample with D(*) meson hadronic decays, reconstructed from tracks with the correct charge combinaFon. 4 decay channels: D→ Kππ , D* → D0π with D0 → Kπ/Kππ0/Kπππ (D(*): pT >8 GeV, |η| <2.2).
• Signal yield measured from fits to the mass distribuFons in the different decay channels.
• Major backgrounds (data-‐driven esFmated): W+light-‐jets, mulF-‐jets.Other backgrounds: t-‐quark.
• Leading systemaFc uncertainFes:tracking efficiency, signal modelling.
W+D(*) analysis
The producFon of a W boson in associaFon with a single charm quark (W+charm) is studied using 4.6 pb−1 of pp collision data at √s = 7 TeV collected with the ATLAS detector at the Large Hadron Collider (LHC) [1]. In events in which a W boson decays to an electron or muon, the charm quark is tagged either by its semileptonic decay to muons (W+c-‐jet) or by the presence of a charmed meson (W+D(*)). Cross secFons integrated over a fiducial kinemaFc range and differenFal as a funcFon of the pseudorapidity of the lepton from the W boson decay are reported. Results are compared to the predicFons of next-‐to-‐leading order QCD calculaFons obtained from different parton distribuFon funcFon (PDF) sets. The measured cross secFons support the hypothesis of an SU(3) symmetric composiFon of the light quark sea in the proton.
Abstract
• W+charm cross secFon measured with a total uncertainty of ~ 5-‐7%.
• W+charm favours PDF sets with enhanced s-‐quark contribuFon (ATLAS-‐epWZ12, NNPDF2.3coll), supporFng symmetric light quark sea. PDF sets with suppressed s-‐quark sea (NNPDF2.3, MSTW2008) are disfavoured.
• Consistent picture from the W+c-‐jet and the W+D(*) analyses.
• Measured strange-‐to-‐down PDF raFo:
• W++c/W-‐+c cross secFon raFos, which provide sensiFvity to strange/anF-‐strange PDF difference, indicate a symmetry to within ~ 3%.
Results
• W+charm is produced at LO by the scauering of a gluon with a down-‐type quark (d, s, b). The contribuFon of each quark flavour is determined by CKM matrix. At LHC energy, the strange-‐quarks iniFated processes account for about 90% of the total.
• W+charm is thus sensiFve to the strange PDF, which is loosely constrained by neutrino-‐nucleon deep inelasFc scauering data [2]. Some PDF analyses suggest s-‐quark sea is suppressed with respect to the d-‐quark sea; others, like an ATLAS analysis using W/Z cross secFons data [3], support a SU(3) flavour symmetric sea.
• The W boson is selected via its leptonic decay into muon or electron (pTl >20 GeV, pTν >25 GeV, mTW >40 GeV).• Two independent analyses, differing in the the c-‐quark tagging method, are performed: W+c-‐jet and W+D(*).• The W boson and c-‐quark charges have a full correlaFon → signal has "opposite sign" events. Backgrounds are (moistly) charge symmetric and thus reduced by evaluaFng the signal yields as the difference between opposite and same charge (OS-‐SS) events. (W+cc/bb backgrounds cancel out).
Measurement moFvaFon & strategy
m(D) [GeV]1.75 1.8 1.85 1.9 1.95 2 2.05 2.1 2.15 2.2
OS-
SS E
vent
s/12
MeV
0
500
1000
1500
2000 ATLAS Internal-1 Ldt = 4.6 fb∫
= 7 TeVs
WD±π±π
±
K→±D
DataFitSignalBackground
) [MeV]0 m = m(D*)-m(DΔ135 140 145 150 155 160 165 170 175 180 185
OS-
SS E
vent
s/M
eV
0200400600800
1000120014001600 ATLAS Internal
-1 Ldt = 4.6 fb∫ = 7 TeVs
WD*±π)±π
±
(K→±π0D →±D*
DataFitSignalBackground
) [MeV]0 m = m(D*)-m(DΔ135 140 145 150 155 160 165 170 175 180 185
OS-
SS E
vent
s/M
eV
0100200300400500600700800900 ATLAS Internal
-1 Ldt = 4.6 fb∫ = 7 TeVs
WD*±π)0π±π
±
(K→±π0D →±D*
DataFitSignalBackground
) [MeV]0 m = m(D*)-m(DΔ135 140 145 150 155 160 165 170 175 180 185
OS-
SS E
vent
s/M
eV
0200400600800
1000120014001600 ATLAS Internal
-1 Ldt = 4.6 fb∫ = 7 TeVs
WD*
±
π)±π
±
π±π
±
(K→±π0D →±D*
DataFitSignalBackground
Figure 17. Results of the fits to the distributions of m(D) and �m = m(D
⇤) � m(D
0) in
OS-SS WD
(⇤) events. The fit results are shown in the inclusive sample defined by p
DT > 8GeV
and |⌘D| < 2.2: D
± ! K
⌥⇡
±⇡
± (top left), D
⇤± ! D
0⇡
± ! (K
⌥⇡
±)⇡
± (top right),D
⇤± ! D
0⇡
± ! (K
⌥⇡
±⇡
0)⇡
± (bottom left) and D
⇤± ! D
0⇡
± ! (K
⌥⇡
±⇡
⌥⇡
±)⇡
± (bottomright). The data distributions are shown by the filled markers, where the error bars show the sta-tistical uncertainty. The fit result is shown by the solid line. The filled histogram represents thesignal template normalised according to the fit result, while the contribution of the combinatorialbackground is shown by the dotted line.
– 51 –
m(D)
ATLAS UK 2014
25
where
�ki = µ
ikm
i
1�
X
j
�
ij,kbj �
X
j
(�theo)ij,kbtheoj
!. (12)
The notation follows that introduced in Equation 9.1624
The matrix (�theo)ij,k represents the relative correlated1625
systematic uncertainties on the theory predictions and1626
quantifies the influence of the uncertainty source j on the1627
prediction in bin i and data set k. The parameters btheoj1628
are defined analogously to the parameters bj and rep-1629
resent the shifts introduced by a correlated uncertainty1630
source j of the predictions. The �2-function is minimized1631
with respect to bj and b
theoj with the cross-section mea-1632
surements, µ, fixed to the values determined in Section1633
IXA.1634
Equation 11 is further extended to account for asym-1635
metric uncertainties on the predictions. The asymmetric1636
uncertainties are described by parabolic functions1637
fi(btheoj ) = !i,j(b
theoj )2 + �i,jb
theoj , (13)
which replace the terms (�theo)ij,kbtheoj of Equation 11.1638
The coe�cients of fi(btheoj ) are determined from the val-1639
ues of the cross sections calculated when the parameter1640
corresponding to source j is set to its nominal value +S
+i,j1641
and �S
�i,j where the S±
i,j are the up and down uncertain-1642
ties of the respective PDF sets [75]. The coe�cients are1643
given by1644
�i,j =1
2
�S
+i,j � S
�i,j
�(14)
!i,j =1
2
�S
+i,j + S
�i,j
�. (15)
The �
2-minimization procedure implemented in the1645
HERAFitter framework [72, 76–78] is used. The cross-1646
section measurements di↵erential in |⌘`| are used to as-1647
sess the quantitative agreement between the data and the1648
PDF predictions.1649
The results of the �
2-minimization procedure are1650
shown in Table IX. The measured cross sections are1651
in agreement with all PDF predictions but disfavor1652
NNPDF2.3. In addition to the total �2, Table IX also1653
shows the individual contributions to the �
2 from the1654
experimental uncertainties, the uncertainties on the pre-1655
dictions and the scale uncertainty. For the predictions1656
obtained with MSTW2008 and NNPDF2.3 the scale1657
uncertainty is the dominant uncertainty. An improved1658
accuracy in the theory calculation could enhance the sen-1659
sitivity of the presented measurements to the PDF sig-1660
nificantly.1661
For values x 0.1, the HERAPDF1.5 PDF is mainly1662
constrained by the precise measurement of the proton1663
structure function F2(x,Q2) at HERA [72] which fixes1664
the quark-charge-squared weighted sum of quark and1665
anti-quark contributions but has no sensitivity to the fla-1666
vor composition of the total light sea. In the HERA-1667
PDF1.5 PDF, the strange quark distribution is ex-1668
pressed as an x-independent fraction, fs = s/(d + s).1669
The central value fs = 0.31 at Q
2 = 1.9 GeV2 is cho-1670
sen to be consistent with determinations of this fraction1671
using the neutrino-nucleon scattering data with an un-1672
certainty spanning the range from 0.23 to 0.38. This1673
model uncertainty is parameterized as an eigenvector in1674
the �
2-minimization.1675
The �
2-minimization procedure not only gives infor-1676
mation about the overall compatibility of the predictions1677
with the data, but also allows constraints on the PDF1678
eigenvectors to be obtained. HERAPDF1.5 is the only1679
publicly available PDF set where the e↵ect of varying the1680
strange density is parameterized by one eigenvector (fs).1681
The �
2-minimization procedure discussed above can be1682
used as follows to calculate a value for fs based solely1683
on the measurements discussed here while ignoring all1684
previous measured or assumed values of fs. The �
2-1685
minimization is repeated for theHERAPDF1.5 PDF set1686
after artificially increasing the uncertainty of the strange1687
fraction fs. This procedure corresponds to a free fit of the1688
eigenvector representing fs while all other eigenvectors1689
are constrained to the values determined for the HERA-1690
PDF1.5 PDF. A value of1691
rs ⌘ 0.5(s+ s)/d = fs/(1� fs) = 0.96+0.16�0.18
+0.21�0.24
is determined at Q
2 = 1.9 GeV2 and is independent of1692
x as implemented in the HERAPDF1.5 PDF. The first1693
uncertainty represents the experimental and theoretical1694
uncertainties and the second uncertainty corresponds to1695
the scale uncertainty of the W + c calculation. Since the1696
scale uncertainty is the dominant uncertainty, its e↵ect1697
is assessed separately by repeating the fit under the as-1698
sumption of perfect knowledge of the scale. The resulting1699
strange fraction is shown in Figure 14 as a function of x1700
at Q2 = m
2W . For the HERAPDF1.5 PDF the s-quark1701
sea density is similar to that of the d-quark sea at low1702
values of x, while it is suppressed at higher values of x.1703
The ATLAS Wc/WD
(⇤) data on the other hand favor a1704
symmetric light quark sea over the whole x range relevant1705
for the presented measurement (10�3 to 10�1).1706
The value of rs determined in this study is in ex-1707
cellent agreement with the value of rs = 1.00+0.25�0.28 ob-1708
tained in the combined analysis of W and Z production1709
at Q2 = 1.9 GeV2 and x = 0.023 by ATLAS [9] and sup-1710
ports the hypothesis of an SU(3) symmetric light quark1711
sea. Figure 14 also shows that the x-dependence of rs ob-1712
tained from the ATLAS-epWZ12 PDF is in good agree-1713
ment with this study.1714
X. ADDITIONAL RESULTS1715
A. WD(⇤)1716
In this section, the measurements of the cross-section1717
ratio �
OS�SSfid (WD
(⇤))/�fid(W ) di↵erential in p
D(⇤)
T are1718
presented. The measurements are compared to theo-1719
retical predictions obtained from aMC@NLO using the1720
0.96 +0.16 +0.21�0.18 �0.24
[GeV]T
SMT jet p30 40 50 60 70 80 90 100 110 120
OS-
SS E
vent
s / 5
GeV
00.20.40.60.8
11.21.41.61.8
22.2
310×
DataW+c W+lightZ+jetsMultijetTop+Diboson
InternalATLAS-1Ldt = 4.6 fb∫ = 7 TeV, s
1,2 jetsνµ→W
[GeV]T
Soft muon p5 10 15 20 25 30
OS-
SS E
vent
s / 2
GeV
0
0.5
1
1.5
2
2.5
310×
DataW+c W+lightZ+jetsMultijetTop+Diboson
InternalATLAS-1Ldt = 4.6 fb∫ = 7 TeV, s
1,2 jetsνµ→W
Figure 9. Distribution of the SMT jet pT (left) and soft muon pT (right) in OS-SS events ofthe W+1,2 jets sample for the muon channel. The normalisations of the W+light and Z/�
⇤+jetsbackgrounds and the shape and normalisation of the multijet background are obtained with data-driven methods. All other backgrounds are estimated with MC simulations and normalised to theirtheoretical cross sections. The signal contribution is normalised to the measured yields.
7 Cross-section determination697
7.1 Definition of the fiducial phase space698
The cross sections �
OS�SSfid (WD
(⇤)) and �
OS�SSfid (Wc) are measured in a common fiducial699
region defined in terms of the W -boson kinematics as follows:700
• p
`T > 20GeV and |⌘`| < 2.5701
• p
⌫T > 25GeV702
• m
WT > 40GeV703
where `, ⌫ are the lepton and the neutrino from the decay W ! `⌫. The leptons are704
defined at the Born level, i.e. before QED FSR radiation. As discussed in the following,705
the measured raw yields are corrected for detector effects to obtain the cross sections in the706
fiducial region of the measurement. The charm quark is identified either by a D
(⇤) meson,707
and the corresponding cross section measures the production of events with p
D(⇤)T > 8GeV708
and |⌘D| < 2.2, or through a muon from the semileptonic decay of a charmed hadron709
embedded in a jet of particles with p
jetT > 25GeV and |⌘jet| < 2.5. In the latter case, the710
cross section measures the production of events with exactly one c-jet and any additional711
jet, or with a total of 1 or 2 jets exclusively of which only one is a c-jet (the 1-jet and 2-jet712
exclusive cross sections are discussed in Section 10.2). Truth jets are constructed from stable713
truth particles, including muons and neutrinos, using the anti-kT algorithm with a distance714
parameter of 0.4. The lepton, all photons within �R < 0.1 from it, and the neutrino715
originating from the W decay are not used to construct the jets. The c-jet is defined as716
– 23 –
[1] ATLAS CollaboraFon, ATL-‐COM-‐PHYS-‐2013-‐1354; [2] NuTeV CollaboraFon, Phys.Rev. D64 (2001) 112006; [3] ATLAS CollaboraFon, Phys.Rev.Leu. 109 (2012) 012001.
References
26
CT10 MSTW2008 HERAPDF1.5 ATLAS-epWZ12 NNPDF2.3 NNPDF2.3coll
W
+c (partial �2
/ndof) 3.8/11 6.1/11 3.5/11 3.1/11 8.5/11 2.9/11
W
�c (partial �2
/ndof) 9.0/11 10.3/11 8.3/11 6.3/11 10.5/11 6.1/11
W
+D
� (partial �2/ndof) 3.6/4 3.7/4 3.7/4 3.4/4 3.8/4 3.4/4
W
�D
+ (partial �2/ndof) 3.7/4 4.6/4 3.3/4 2.0/4 4.7/4 1.6/4
W
+D
⇤� (partial �2/ndof) 2.9/4 6.0/4 2.2/4 1.7/4 8.1/4 1.6/4
W
�D
⇤+ (partial �2/ndof) 3.0/4 4.4/4 2.4/4 1.6/4 4.2/4 1.4/4
Nexp 114 114 114 114 114 114
Ntheo 28 22 16 20 40 40
Correlated �
2 (exp) 0.8 1.8 0.9 1.1 2.2 1.0
Correlated �
2 (theo) 6.8 4.4 3.7 0.1 10.1 0.2
Correlated �
2 (scale) 0.6 2.5 1.1 0.0 2.7 0.0
Total �2/ndof 33.6/38 41.3/38 28.0/38 19.2/38 52.1/38 18.2/38
Probability 67.4% 32.9% 88.4% 99.5% 6.4% 99.7%
TABLE IX. Quantitative comparison of fiducial cross sections to di↵erent PDF predictions. The table shows the partial �2/ndof
for the di↵erent cross-section measurements, the number of nuisance parameters for the experimental sources of systematicuncertainties (Nexp), the number of nuisance parameters for the uncertainties on the predictions (Ntheo) as well as the correlated�
2 corresponding to the experimental uncertainties, the uncertainties on the predictions and the scale uncertainty. Furthermore,the total �2
/ndof and corresponding probability are given.
x
-310 -210 -110
d)/s =
0.5
(s+
sr
0.50.60.70.80.9
11.11.21.31.41.5
data)*(HERAPDF1.5 + ATLAS Wc/WDATLAS-epWZ12HERAPDF1.5
ATLAS internal W2 = m2Q
FIG. 14. Ratio of strange-to-down sea quark distributionsrs = 0.5(s + s)/d as a function of x as assumed in HERA-PDF1.5 PDF compared to the ratio obtained from the fitincluding the ATLAS Wc/WD
(⇤) data and the ratio obtainedfrom ATLAS-epWZ12. The ratio rs is shown at Q2 = m
2W .
CT10 NLO PDF in Figure 15. The ratio is on average1721
8% higher in data than in simulation. The shape of the1722
p
D(⇤)
T spectrum is reasonably well described by the MC,1723
although a slight excess in data compared to MC simula-1724
tion is observed in the highest pD(⇤)
T bin, suggesting that1725
the pD(⇤)
T spectrum in data might be slightly harder than1726
the aMC@NLO prediction.1727
The measured integrated cross-section ratios in the1728
fiducial region are shown in Table X.1729
�
OS�SSfid (WD
(⇤))/�fid(W ) [%]
W
+D
� 0.55± 0.06 (stat)± 0.02 (syst)
W
+D
⇤� 0.66± 0.03 (stat)± 0.03 (syst)
W
�D
+ 1.06± 0.08 (stat)± 0.04 (syst)
W
�D
⇤+ 1.05± 0.04 (stat)± 0.05 (syst)
TABLE X. Measured fiducial cross-section ratios�
OS�SSfid (WD
(⇤))/�fid(W ) together with the statisticaland systematical uncertainty.
B. Wc1730
In addition to the Wc fiducial cross section for a W bo-1731
son with exactly one jet containing a c-hadron and any1732
number of additional jets, the cross section is measured1733
with the requirements defined in Section VIIA, except1734
for requiring either exactly 1 or 2 jets of which only one1735
contains a c-hadron. The results, including the ratio R
±c ,1736
averaged between the electron and muon channels, are1737
shown in Table XI. Figure 16 shows the measured Wc1738
fiducial cross sections with exactly one or two jets com-1739
pared to aMC@NLO predictions with the CT10 NLO1740
PDF set. The aMC@NLO central values do not describe1741
the one-to-two-jets ratio well. The Alpgen predictions1742
normalized to the W -inclusive NNLO cross section are1743
also shown for reference. The Alpgen central values1744
underestimate the data measurements for both samples1745
with one and two jets however the one-to-two-jets ratio1746
is well described.1747
Finally, in order to minimize the systematic uncertain-1748
ties due to the extrapolation to the fiducial phase space,1749
the cross sections are determined in a phase space as spec-1750
23
(aMC@NLO,CT10)fidOS-SSσ(Data)/fid
OS-SSσ
0.6 0.8 1 1.2 1.4 1.6 1.8 2 2.2 2.4
(aM
C@NL
O,C
T10)
fidOS-
SSσ
(Dat
a)/
fidOS-
SSσ 0.6
0.81
1.21.41.61.8
22.22.4
-D+ vs W-D*+W
c+ vs W-D+W
c+ vs W-D*+W
ATLAS Internal-1 Ldt = 4.6 fb∫
= 7 TeV (2011)s68% CL ellipse area
Hashed: meas. uncert.Open: tot. uncert.
y=x
(aMC@NLO,CT10)fidOS-SSσ(Data)/fid
OS-SSσ
0.8 1 1.2 1.4 1.6 1.8 2 2.2 2.4 2.6
(aM
C@NL
O,C
T10)
fidOS-
SSσ
(Dat
a)/
fidOS-
SSσ
0.81
1.21.41.61.8
22.22.42.6
+D- vs W+D*-W
c- vs W+D-W
c- vs W+D*-W
ATLAS Internal-1 Ldt = 4.6 fb∫
= 7 TeV (2011)s68% CL ellipse area
Hashed: meas. uncert.Open: tot. uncert.
y=x
FIG. 11. 68% C.L. contours of the measured cross sections normalized to the theoretical prediction obtained from theaMC@NLO simulation using the CT10 PDF. The filled ellipses show the experimental uncertainties, while the open ellipsesshow the total uncertainties, including the uncertainties of the prediction. The left figure shows the correlations among theW
+D
⇤�, W+D
� and W
+c cross sections, while the right figure is for W�
D
⇤+, W�D
+ and W
�c.
c)-(WfidOS-SSσ)/c+(Wfid
OS-SSσ0.4 0.6 0.8 1 1.2 1.4
CT10MSTW2008NNPDF2.3HERAPDF1.5ATLAS-epWZ12NNPDF2.3collWc
aMC@NLO
ATLAS Internal-1 Ldt = 4.6 fb∫
= 7 TeV (2011)s
Data 0.02 ± 0.03 ±0.90
StatStat+syst
)+)*(D-(WOS-SSfidσ)/-)*(D+(WOS-SS
fidσ0.4 0.6 0.8 1 1.2 1.4
Data 0.01± 0.05 ±0.92
StatStat+syst
)*(WD
ATLAS Internal-1 Ldt = 4.6 fb∫
= 7 TeV (2011)s
FIG. 12. Measured ratios �
OS�SSfid (W+
c)/�OS�SSfid (W�
c) (left) and �
OS�SSfid (W+
D
(⇤)�)/�OS�SSfid (W�
D
(⇤)+) (right) resultingfrom the averaging procedure compared to di↵erent PDF predictions based on aMC@NLO. The blue vertical lines show thecentral values of the measurements, the inner error bands show the statistical uncertainties and the outer error bands the totalexperimental uncertainties. The PDF predictions are shown by the black markers. The error bars on the predictions correspondto the 68% C.L. PDF uncertainties.
in Figure 13. Similar predictions of the shapes of the1619
|⌘`| distributions are obtained by the di↵erent PDF sets.1620
The predictions mainly di↵er in their normalization. The1621
predicted shapes are in reasonable agreement with the1622
measured distributions.1623
In order to perform a quantitative comparison of themeasurement and the di↵erent PDF predictions, the �
2-function introduced in Equation 9 is extended to include
the uncertainties on the theoretical predictions:
�
2 =
X
k,i
w
ik
hµ
ik �m
i⇣1 +
Pj �
ij,kbj +
Pj(�
theo)ij,kbtheoj
⌘i2
(�ista,k)2�k
i + (�iunc,kmi)2
+X
j
b
2j +
X
j
(btheoj )2, (11)
22
[pb]fidOS-SSσ
10 20 30 40 50 60 70
CT10MSTW2008NNPDF2.3HERAPDF1.5ATLAS-epWZ12NNPDF2.3collc+W
aMC@NLO
ATLAS Internal-1 Ldt = 4.6 fb∫
= 7 TeV (2011)s
Data 1.8 [pb]± 0.9 ±33.6
StatStat+syst
[pb]fidOS-SSσ
10 20 30 40 50 60 70
CT10MSTW2008NNPDF2.3HERAPDF1.5ATLAS-epWZ12NNPDF2.3collc-W
aMC@NLO
ATLAS Internal-1 Ldt = 4.6 fb∫
= 7 TeV (2011)s
Data 1.9 [pb]± 0.8 ±37.3
StatStat+syst
[pb]OS-SSfidσ
5 10 15 20 25 30 35
Data 0.8 [pb]± 1.9 ±17.8
StatStat+syst
-D+W
ATLAS Internal-1 Ldt = 4.6 fb∫
= 7 TeV (2011)s
[pb]OS-SSfidσ
5 10 15 20 25 30 35
Data 1.0 [pb]± 1.8 ±22.4
StatStat+syst
+D-W
ATLAS Internal-1 Ldt = 4.6 fb∫
= 7 TeV (2011)s
[pb]OS-SSfidσ
5 10 15 20 25 30 35
Data 1.0 [pb]± 0.9 ±21.2
StatStat+syst
-D*+W
ATLAS Internal-1 Ldt = 4.6 fb∫
= 7 TeV (2011)s
[pb]OS-SSfidσ
5 10 15 20 25 30 35
Data 1.0 [pb]± 0.8 ±22.1
StatStat+syst
+D*-W
ATLAS Internal-1 Ldt = 4.6 fb∫
= 7 TeV (2011)s
FIG. 10. Measured fiducial cross sections compared to di↵erent PDF predictions based on aMC@NLO. The solid vertical lineshows the central value of the measurement, the inner error band corresponds to the statistical uncertainty and the outer errorband to the quadratic sum of the statistical and systematic uncertainties. The PDF predictions are shown by markers. Theinner error bars on the theoretical predictions show the 68% confidence level uncertainties obtained from the error sets providedwith each PDF set, while the outer error bar represents the total theoretical uncertainty (quadratic sum of PDF, parton shower,fragmentation and scale uncertainties).
can be written as1611
Ass =< s(x,Q2) > � < s̄(x,Q2) >
< s(x,Q2) >⇡ R
±c (CT10)�R
±c (Data),
(10)
where the s and s distributions are averaged over the1612
W + c phase space. A value of Ass = (2 ± 3)% is ob-1613
tained for the combination of the Wc and WD
(⇤) analy-1614
ses. The quoted uncertainty is dominated by statistical1615
uncertainties.1616
The dependence of the cross section on |⌘`|, along with1617
predictions of aMC@NLO with various PDFs, is shown1618
22
[pb]fidOS-SSσ
10 20 30 40 50 60 70
CT10MSTW2008NNPDF2.3HERAPDF1.5ATLAS-epWZ12NNPDF2.3collc+W
aMC@NLO
ATLAS Internal-1 Ldt = 4.6 fb∫
= 7 TeV (2011)s
Data 1.8 [pb]± 0.9 ±33.6
StatStat+syst
[pb]fidOS-SSσ
10 20 30 40 50 60 70
CT10MSTW2008NNPDF2.3HERAPDF1.5ATLAS-epWZ12NNPDF2.3collc-W
aMC@NLO
ATLAS Internal-1 Ldt = 4.6 fb∫
= 7 TeV (2011)s
Data 1.9 [pb]± 0.8 ±37.3
StatStat+syst
[pb]OS-SSfidσ
5 10 15 20 25 30 35
Data 0.8 [pb]± 1.9 ±17.8
StatStat+syst
-D+W
ATLAS Internal-1 Ldt = 4.6 fb∫
= 7 TeV (2011)s
[pb]OS-SSfidσ
5 10 15 20 25 30 35
Data 1.0 [pb]± 1.8 ±22.4
StatStat+syst
+D-W
ATLAS Internal-1 Ldt = 4.6 fb∫
= 7 TeV (2011)s
[pb]OS-SSfidσ
5 10 15 20 25 30 35
Data 1.0 [pb]± 0.9 ±21.2
StatStat+syst
-D*+W
ATLAS Internal-1 Ldt = 4.6 fb∫
= 7 TeV (2011)s
[pb]OS-SSfidσ
5 10 15 20 25 30 35
Data 1.0 [pb]± 0.8 ±22.1
StatStat+syst
+D*-W
ATLAS Internal-1 Ldt = 4.6 fb∫
= 7 TeV (2011)s
FIG. 10. Measured fiducial cross sections compared to di↵erent PDF predictions based on aMC@NLO. The solid vertical lineshows the central value of the measurement, the inner error band corresponds to the statistical uncertainty and the outer errorband to the quadratic sum of the statistical and systematic uncertainties. The PDF predictions are shown by markers. Theinner error bars on the theoretical predictions show the 68% confidence level uncertainties obtained from the error sets providedwith each PDF set, while the outer error bar represents the total theoretical uncertainty (quadratic sum of PDF, parton shower,fragmentation and scale uncertainties).
can be written as1611
Ass =< s(x,Q2) > � < s̄(x,Q2) >
< s(x,Q2) >⇡ R
±c (CT10)�R
±c (Data),
(10)
where the s and s distributions are averaged over the1612
W + c phase space. A value of Ass = (2 ± 3)% is ob-1613
tained for the combination of the Wc and WD
(⇤) analy-1614
ses. The quoted uncertainty is dominated by statistical1615
uncertainties.1616
The dependence of the cross section on |⌘`|, along with1617
predictions of aMC@NLO with various PDFs, is shown1618
σ(W-‐+c-‐jet) σ(W++D*-‐)
σ(W+)/σ(W-‐)W+c-‐jet rs
No
trev
iew
ed
,fo
rin
tern
al
circu
la
tio
no
nly
November 15, 2013 – 11 : 44 DRAFT 13
parton momentum fraction x-510 -410 -310 -210 -110
)d/s fr
actio
n of
ant
i-stra
nge
to a
nti-d
own
quar
ks (
0
0.5
1
1.5
2
2.5NNPDF2.3 collider onlyCT10NNPDF2.3epWZMSTW2008HERA1.5
Figure 2: Depicted is the ratio of the anti-strange to the anti-down quark PDF distribution for di↵erentPDFs evaluated at the scale Q2 = M2
W = (80.385GeV)2. This is a measure of di↵erences in the partondistributions for strange and down sea quarks. The range in x relevant for the measurement presentedin here is from 10�1 to 10�3. If no error bands are present, the PDF set in question fixes this fractionwithout assigning an uncertainty.
PDF raFos/d
c-‐jet pT
(meas.+theo.) (scale)