Phenomenology of top-quark pair
production at the LHC: studies with DiffTop
Marco Guzzi, Katerina Lipka and Sven-Olaf Moch
DESY Hamburg
arXiv:1406.0386
“ICHEP 2014” Valencia, Spain, 2 - 9 July 2014
Outline and motivations
◮
Top-quark pair production at the LHC is crucial for many
phenomenological applications/investigations:
-Physics beyond the SM (⇒ distortions/bumps in
distributions like Mt t̄ ),
-extent of QCD factorization,
-PDFs determination in QCD analyses,
-Correlation between αs , top-quark mass mt , and the gluon.
◮
New data available: the CMS and ATLAS collaborations
published measurements of differential cross sections for t t̄
pair production as a function of different observables of
interest, with unprecedented accuracy:
9
8
T
-1
1 dσ
σ dpt GeV
e/µ + Jets Combined
7
Data
MadGraph
MC@NLO
POWHEG
Approx. NNLO
CMS, 5.0 fb-1 at s = 7 TeV
1 dσ
σ dyt
CMS, 5.0 fb-1 at s = 7 TeV
×10
-3
10
0.7
e/µ + Jets Combined
Data
MadGraph
MC@NLO
POWHEG
Approx. NNLO
0.6
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(arXiv:1009.4935)
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(arXiv:1105.5167)
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Data
MadGraph
MC@NLO
POWHEG
15
10-4
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CMS, 5.0 fb-1 at s = 7 TeV
×10
-3
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1 dσ
σ tt GeV
dp
1 dσ GeV-1
σ
dmtt
CMS, 5.0 fb-1 at s = 7 TeV
e/µ + Jets Combined
2.5
yt
T
5
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mtt GeV
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ptt GeV
T
√
R
The CMS Collaboration EPJC 2013, Ldt = 5.0[fb]−1 , S = 7 TeV,
√
R
TOP-12-028 → Ldt ≈ 12[fb]−1 , S = 8 TeV (more in Ivan Asin’s talk)
-1
1 dσ
σ dm GeV
Data
ALPGEN+HERWIG
10-3
tt
ALPGEN+HERWIG
T
-1
1 dσ
σ dpt GeV
Data
MC@NLO+HERWIG
10-3
MC@NLO+HERWIG
POWHEG+HERWIG
POWHEG+HERWIG
ATLAS Preliminary
∫ L dt = 4.6 fb
∫ L dt = 4.6 fb
10
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-4
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s = 7 TeV
s = 7 TeV
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Data
ATLAS Preliminary
Data
∫ L dt = 4.6 fb
ALPGEN+HERWIG
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ALPGEN+HERWIG
T
-1
1 dσ
σ tt GeV
dp
T
MC@NLO+HERWIG
s = 7 TeV
1
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MC@NLO+HERWIG
POWHEG+HERWIG
POWHEG+HERWIG
ATLAS Preliminary
∫ L dt = 4.6 fb
-1
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s = 7 TeV
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-5
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Data
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tt
The ATLAS Collaboration ATLAS-CONF-2013-099, lepton+jets,
√
R
Ldt = 4.6[fb]−1 , S = 7 TeV
We want to exploit the full potential of these new (and
forthcoming) data
◮
We need tools incorporating the current state-of-the-art of
QCD calculations.
◮
Some of them are already on the market, for some others work
is still in progress (these calculations are very challenging)
In the meanwhile...
◮
Here we present a tool DiffTop for calculating t t̄ differential
cross sections in 1PI kinematic at approximate NNLO O(αs4 ).
Recent progress
NLO exact computations available since many years:
◮ Nason, Dawson, Ellis (1988); Beenakker, Kuijif, Van Neerven, Smith
(1989); Meng, Schuler, Smith, Van Neerven (1990); Beenakker, Van
Neerven, Schuler, Smith (1991); Mangano, Nason, Rodolfi (1992).
The NNLO O(αs4 ) full QCD calculation for the t t̄ total cross
section has been accomplished recently
◮
Czakon, Fiedler, Mitov (2013); Czakon, Mitov (2012), (2013);
Baernreuther, Czakon, Mitov (2012)
◮
Top++ Czakon, Mitov (2011); Hathor Aliev, Lacker,
Langenfeld, Moch, Uwer, Wiedermann (2011)
Exact NLO tools available
◮
MCFM Campbell, Ellis, Williams; MadGraph5 Alwall, Maltoni,
et al.; MC@NLO Frixione, Stoeckli, Torrielli, Webber, White;
POWHEG Alioli, Hamilton, Nason, Oleari, Re.
While exact NLO calculations for t t̄ total and differential cross
sections have been implemented into publicly available Monte
Carlo numerical codes,
full NNLO calculations for the t t̄ production cross section at
differential level are not yet available.
NLO predictions are not accurate enough to describe the data:
◮
◮
perturbative corrections are large,
systematic uncertainties associated to various scales
entering the calculation are important.
LHC 7 TeV, mt= 173 GeV, MSTW08 PDFs
MCFM NLO
MCFM mt/2 < Q < 2 mt
DiffTop approx nnlo
mt/2 < Q < 2 mt
1.4
dσ/dPT[pb/GeV]
1.2
1
0.8
0.6
0.4
0.2
0
50
100
150
200
250
300
350
400
PtT [GeV]
–
1.3
–
dσ/dpT/σ (pp→tt+X) , mt=173 GeV
1.3
Uncertainty due to scale variation, µr=µf
approx. NNLO × MSTW08NNLO
MCFM × MSTW08NLO
1.2
theory/data, dσ/dpT/σ
theory/data, dσ/dpT/σ
1.2
dσ/dpT/σ (pp→tt+X) , mt=173 GeV
Uncertainty due to scale variation, µr=µf
approx. NNLO × MSTW08NNLO
1.1
1
0.9
MCFM × MSTW08NLO
1.1
1
0.9
data CMS, √s=7 TeV
0.8
50
100
150
200
data ATLAS, √s=7 TeV
250
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t
400
p (GeV)
T
0.8
50
100
150
200
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300
t
350
p (GeV)
T
QCD threshold resummation: instruments to re-factorize the cross section in
certain kinematic limits ⇒ approx. predictions
Sterman (1986)
Approx. NNLO including threshold resummation
◮
Kidonakis, Sterman (1997); Laenen, Oderda, Sterman (1998)
◮
Kidonakis (2001); Kidonakis, Laenen, Moch, Vogt (2001)
◮
Czakon, Mitov, Sterman, (2009); Kidonakis (2010); Moch, Uwer,
Vogt (2012); Cacciari, Czakon, Mangano, Mitov, Nason (2012)
◮
Beneke, Falgari, Klein, Piclum, Schwinn, Ubiali, Yan, (2012)
(TOPIXS total inclusive Xsec.)
Progress in Soft Collinear Effective Theory (SCET)
◮
Ahrens, Ferroglia, Neubert, Pecjak, Yang (2010), (2011), (2012)
Development of tools for phenomenology: DiffTop
Public NLO/NNLO codes (in particular for differential cross
section computations) are important for the experimental groups
and for QCD analyses to determine PDFs
PROSA: Proton Structure Analyses in Hadronic Collisions
https://prosa.desy.de
activity 2013 - 2014 on DESY side
DiffTop: a Mellin-space resummation computer code for
computing total and differential cross section for heavy-flavor
production at hadron colliders at approx. NNLO within threshold
resummation
Implementation based on the calculation by Kidonakis, Moch,
Laenen, Vogt (2001).
Resummation in single-particle inclusive (1PI) and
pair-invariant mass kinematics (PIM)
Near the threshold heavy-quark hadroproduction in 1PI kinematics
is dominated by the partonic subprocesses
i(k1 ) + j(k2 ) → Q(p1 ) + X [Q̄](p2′ )
p2′ = p̄2 + k
(1)
where is k any additional radiation, and s4 = p2′ − m2 → 0
momentum at the threshold.
In the pair-invariant mass kinematics (PIM)
i(k1 ) + j(k2 ) → Q Q̄(p ′ ) + X ′ (k)
X ′ (k) = 0 the reaction is at the threshold p ′2 = M 2 .
(2)
What’s in the box ?
The factorized differential cross section is written as
S2
d 2 σ(S, T1 , U1 )
dT1 dU1
=
X Z
i,j=q,q̄,g
1
x1−
dx1
x1
Z
1
x2−
dx2
fi/H1 (x1 , µ2F )fj/H2 (x2 , µ2F )
x2
×ωij (s, t1 , u1 , mt2 , µ2F , αs (µ2R )) + O(Λ2 /mt2 ) ,
(0)
ωij (s4 , s, t1 , u1 ) = ωij +
(2)
αs (1)
π ωij
+
αs 2
π
(2)
ωij + · · ·
where ωij at parton level in 1PI is
3
(2)
2
2
2
σ̂ij (3) ln (s4 /mt )
Born αs (µR )
Dij
= s
= Fij
du1 dt1 π2
s4
+
1PI
2
2
2
ln
(s
/m
)
ln(s
/m
)
1
4
4
(2)
(1)
(0)
(2)
t
t
+Dij
+ Dij
+ Dij
+ Rij δ(s4 ) .
s4
s4
s4 +
+
+
(2)
ωij
2
The contribution of the 2-loop soft-anomalous dimension (Kidonakis
(2010)) is also included which formally is beyond the NNLL accuracy.
What is it good for?
Top-quark pair production at LHC probes high-x gluon and the
differential cross section is strongly correlated at x ≈ 0.1:
7 TeV LHC parton kinematics
9
10
WJS2010
8
10
x1,2 = (M/7 TeV) exp(±y)
Q=M
M = 7 TeV
7
10
6
❍
5
10
4
M = 1 TeV
❍❍
❍
❥
❍
M = 100 GeV
10
Q
2
2
(GeV )
10
3
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y= 6
2
4
0
2
4
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2
10
M = 10 GeV
1
fixed
target
HERA
10
0
Figure by J. Stirling
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-2
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approx. NNLO × CT10NNLO, mt=173 GeV
approx. NNLO × MST08NNLO, mt=173 GeV
LHC 7 TeV
1
LHC 7 TeV
1
1 GeV < p < 100 GeV
t
1 GeV < p < 100 GeV
t
T
T
100 GeV < p < 200 GeV
100 GeV < p < 200 GeV
t
200 GeV < p < 300 GeV
0.5
T
t
300 GeV < p < 400 GeV
T
0
-0.5
-1 -6
10
T
t
200 GeV < p < 300 GeV
0.5
cos(φ)
cos(φ)
t
T
t
T
t
300 GeV < p < 400 GeV
T
0
-0.5
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xgluon
-1 -6
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-1
1
xgluon
Here we choose MSTW08 and CT10 as representative. ABM11,
HERA1.5 and NNPDF2.3 show a similar behavior.
What is it good for?
Top-quark pair production at LHC probes high-x gluon (x ≈ 0.1): but
there is a strong correlation between g (x), αs and the top-quark mass mt
that we want to pin down
◮
Precise measurements of the total and differential cross section of t t̄
pair production provide us with a double handle on these quantities
◮
Precise measurements of the absolute differential cross section
constrain the gluon PDF
◮
The shape of the differential cross section is modified by mt and αs
(very sensitive)
◮
extraction of mt will benefit from the interplay between these two
measurements. (recent CMS paper PLB (2014))
Interface to fastNLO(In collaboration with D. Britzger)
DiffTop has been succesfully interfaced to fastNLO.
This is important for applications in PDF fits, because NNLO
computations are generally CPU time consuming.
0
R
F
ci,n (µR , µF ) = ci,n
+ log(µR )ci,n
+ log(µF )ci,n
+ ...
beyond the NLO one has double log contributions
(2,F )
.. + log2 (µF )ci,n
(2,R)
+ log2 (µR )ci,n
(2,R F )
+ log(µF ) log(µR )ci,n
♠DiffTop is now included into HERAFitter for PDF analyses
Work is in progress on numerics and fastNLO grids generation to make
all publicly available soon.
DiffTop Results
In what follows:
◮
PDF unc. are computed by following the prescription given by
each PDF group at 68% CL ;
◮
The uncertainty associated to αs (MZ ) is given by the central
value as given by each PDF group ±∆αs (MZ ) = 0.001;
◮
◮
Scale unc. is obtained by variations mt /2 ≤ µR = µF ≤ 2mt ;
Uncertanty associated to the top-quark mass is estimated by
using mt = 173 GeV (Pole mass) ±∆mt = 1 GeV.
–
–
dσ/dpT/σ (pp→tt+X) , mt=173 GeV
theory/data, dσ/dpT/σ
theory/data, dσ/dpT/σ
δmt= 1 GeV
PDF 68%CL
µr=µf var.
αS
50
100
150
200
data CMS, √s=7 TeV
250
1.1
1
δmt= 1 GeV
0.9
1.1
1
δmt= 1 GeV
PDF 68%CL
µr=µf var.
αS
0.9
PDF 68%CL
µr=µf var.
αS
300
350
400
0.8
50
100
150
200
250
300
t
0.8
-2.5
350
-2
-1.5
-1
-0.5
t
p (GeV)
T
dσ/dy (pp→tt+X) (1/GeV)
approx. NNLO × MST08NNLO, mt=173 GeV
1.5
total uncertainty
δmt= 1 GeV
1
0.5
–
–
further uncertainty
contributions:
PDF 68%CL
µr=µf var.
αS
0
0.5
1
1.5
2
2.5
y
p (GeV)
T
dσ/dpT (pp→tt+X) (pb/GeV)
approx. NNLO × MSTW08, total unc.
1.2
data ATLAS, √s=7 TeV
1
0.8
dσ/dy/σ (pp→tt+X) , mt=173 GeV
approx. NNLO × MSTW08, total unc.
data CMS, √s=7 TeV
1.1
0.9
–
dσ/dpT/σ (pp→tt+X) , mt=173 GeV
1.2
approx. NNLO × MSTW08, total unc.
theory/data, dσ/dy/σ
1.2
t
approx. NNLO × MST08NNLO, mt=173 GeV
100
80
total uncertainty
µr=µf var.
PDF 68%CL
αS
δmt= 1 GeV
60
40
20
relative error
relative error
1.2
1.1
1
0.9
0
50
100
150
200
250
300
350
t
400
p (GeV)
T
1.1
1
0.9
0.8
-3
-2
-1
0
1
2
3
y
t
t
Uncertainties for the top pT
and y t distribution obtained by using DiffTop with MSTW08NNLO PDFs. PDF and
αs (MZ ) errors are evaluated at the 68% CL.
–
–
dσ/dpT/σ (pp→tt+X) , mt=173 GeV
theory/data, dσ/dpT/σ
theory/data, dσ/dpT/σ
δmt= 1 GeV
PDF 68%CL
µr=µf var.
αS
50
100
150
200
data CMS, √s=7 TeV
250
1.1
1
δmt= 1 GeV
0.9
1.1
1
δmt= 1 GeV
PDF 68%CL
µr=µf var.
αS
0.9
PDF 68%CL
µr=µf var.
αS
300
350
400
0.8
50
100
150
200
250
300
t
0.8
-2.5
350
-2
-1.5
-1
-0.5
0
0.5
1
1.5
2
t
p (GeV)
p (GeV)
T
dσ/dy (pp→tt+X) (1/GeV)
approx. NNLO × CT10NNLO, mt=173 GeV
1.5
total uncertainty
δmt= 1 GeV
1
0.5
–
further uncertainty
contributions:
PDF 68%CL
µr=µf var.
αS
approx. NNLO × CT10NNLO, mt=173 GeV
100
80
total uncertainty
µr=µf var.
PDF 68%CL
αS
δmt= 1 GeV
60
40
20
relative error
relative error
1.2
1.1
1
0.9
0
50
100
150
200
250
300
350
t
400
p (GeV)
T
1.1
1
0.9
0.8
-3
-2
-1
2.5
y
T
–
dσ/dpT (pp→tt+X) (pb/GeV)
approx. NNLO × CT10, total unc.
1.2
data ATLAS, √s=7 TeV
1
0.8
dσ/dy/σ (pp→tt+X) , mt=173 GeV
approx. NNLO × CT10, total unc.
data CMS, √s=7 TeV
1.1
0.9
–
dσ/dpT/σ (pp→tt+X) , mt=173 GeV
1.2
approx. NNLO × CT10, total unc.
theory/data, dσ/dy/σ
1.2
0
1
2
3
y
t
As in the previous slide but with CT10 NNLO PDFs. PDF and αs (MZ ) errors are evaluated at the 68% CL.
t
–
–
dσ/dpT/σ (pp→tt+X) , mt=173 GeV
theory/data, dσ/dpT/σ
theory/data, dσ/dpT/σ
δmt= 1 GeV
50
1
PDF × αS 68%CL
0.9
δmt= 1 GeV
µr=µf var.
µr=µf var.
150
data CMS, √s=7 TeV
1.1
PDF × αS 68%CL
100
200
250
300
350
400
0.8
50
100
1.1
1
δmt= 1 GeV
0.9
PDF × αS 68%CL
µr=µf var.
150
200
250
300
t
0.8
-2.5
350
-2
-1.5
-1
-0.5
0
0.5
1
1.5
2
t
p (GeV)
p (GeV)
T
dσ/dy (pp→tt+X) (1/GeV)
approx. NNLO × ABM11NNLO, mt=173 GeV
1.5
total uncertainty
δmt= 1 GeV
1
–
further uncertainty
contributions:
PDF × αS 68%CL
µr=µf var.
0.5
approx. NNLO × ABM11NNLO, mt=173 GeV
100
µr=µf var.
total uncertainty
PDF × αS 68%CL
80
δmt= 1 GeV
60
40
20
relative error
relative error
1.2
1.1
1
0.9
0
50
100
150
200
250
300
350
t
400
p (GeV)
T
1.1
1
0.9
0.8
-3
-2
-1
0
1
2
3
y
t
As in the previous slide but with ABM11 NNLO PDFs. Here the uncertainty on αs (MZ ) is already part of the
total PDF uncertainty.
2.5
y
T
–
dσ/dpT (pp→tt+X) (pb/GeV)
approx. NNLO × ABM11, total unc.
1.2
data ATLAS, √s=7 TeV
1
0.8
dσ/dy/σ (pp→tt+X) , mt=173 GeV
approx. NNLO × ABM11, total unc.
data CMS, √s=7 TeV
1.1
0.9
–
dσ/dpT/σ (pp→tt+X) , mt=173 GeV
1.2
approx. NNLO × ABM11, total unc.
theory/data, dσ/dy/σ
1.2
t
–
–
dσ/dpT/σ (pp→tt+X) , mt=173 GeV
theory/data, dσ/dpT/σ
theory/data, dσ/dpT/σ
δmt= 1 GeV
PDF 68%CL + var.
µr=µf var.
αS
50
100
150
200
data CMS, √s=7 TeV
250
300
1.1
1
δmt= 1 GeV
0.9
δmt= 1 GeV
PDF 68%CL + var.
µr=µf var.
αS
αS
350
400
0.8
50
100
150
200
250
300
0.8
-2.5
350
-2
-1.5
-1
-0.5
t
T
1
–
further uncertainty
contributions:
PDF 68%CL + var.
µr=µf var.
αS
0.5
–
total uncertainty
δmt= 1 GeV
dσ/dy (pp→tt+X) (1/GeV)
approx. NNLO × HERAPDF1.5NNLO, mt=173 GeV
1.5
approx. NNLO × HERAPDF1.5NNLO, mt=173 GeV
80
total uncertainty
µr=µf var.
PDF 68%CL+var.
αS
δmt= 1 GeV
60
40
20
1.6
relative error
1.4
100
1.2
1
0
50
100
150
200
250
300
350
400
t
p (GeV)
T
As in the previous slide but with HERA1.5 NNLO PDFs.
1.4
1.2
1
0.8
-3
-2
-1
0
0.5
1
1.5
2
2.5
y
p (GeV)
T
dσ/dpT (pp→tt+X) (pb/GeV)
1
µr=µf var.
t
0.8
1.1
0.9
PDF 68%CL + var.
p (GeV)
relative error
approx. NNLO × HERAPDF1.5, total unc.
1.2
data ATLAS, √s=7 TeV
1
0.8
dσ/dy/σ (pp→tt+X) , mt=173 GeV
approx. NNLO × HERAPDF1.5, total unc.
data CMS, √s=7 TeV
1.1
0.9
–
dσ/dpT/σ (pp→tt+X) , mt=173 GeV
1.2
approx. NNLO × HERAPDF1.5, total unc.
theory/data, dσ/dy/σ
1.2
0
1
2
3
y
t
t
–
–
dσ/dpT/σ (pp→tt+X) , mt=173 GeV
theory/data, dσ/dpT/σ
theory/data, dσ/dpT/σ
δmt= 1 GeV
PDF 68%CL
µr=µf var.
αS
50
100
150
200
data CMS, √s=7 TeV
250
1.1
1
δmt= 1 GeV
0.9
1.1
1
δmt= 1 GeV
PDF 68%CL
µr=µf var.
αS
0.9
PDF 68%CL
µr=µf var.
αS
300
350
400
0.8
50
100
150
200
250
300
t
0.8
-2.5
350
-2
-1.5
-1
-0.5
t
p (GeV)
T
dσ/dy (pp→tt+X) (1/GeV)
approx. NNLO × NNPDF2.3 NNLO, mt=173 GeV
1.5
total uncertainty
δmt= 1 GeV
1
–
–
further uncertainty
contributions:
µr=µf var.
αS
0.5
100
approx. NNLO × NNPDF2.3 NNLO, mt=173 GeV
80
total uncertainty
µr=µf var.
PDF 68%CL
αS
δmt= 1 GeV
60
40
20
relative error
relative error
1.2
1.1
1
0.9
0
50
100
150
200
250
300
350
400
t
p (GeV)
T
As in the previous slide but with NNPDF2.3 NNLO PDFs.
1.1
1
0.9
0.8
-3
-2
-1
0
0.5
1
1.5
2
2.5
y
p (GeV)
T
dσ/dpT (pp→tt+X) (pb/GeV)
approx. NNLO × NNPDF2.3, total unc.
1.2
data ATLAS, √s=7 TeV
1
0.8
dσ/dy/σ (pp→tt+X) , mt=173 GeV
approx. NNLO × NNPDF2.3, total unc.
data CMS, √s=7 TeV
1.1
0.9
–
dσ/dpT/σ (pp→tt+X) , mt=173 GeV
1.2
approx. NNLO × NNPDF2.3, total unc.
theory/data, dσ/dy/σ
1.2
0
1
2
3
y
t
t
–
dσ/dy (pp→tt+X) (pb)
1
HERAPDF1.5NNLO
NNPDF2.3NNLO
0.5
80
1.2
0.6
NNPDF2.3NNLO
ABM11NNLO
20
1.4
0.8
HERAPDF1.5NNLO
MSTW08NNLO
40
1.2
1
CT10NNLO
60
1.4
σ/σCT10
σ/σCT10
approx. NNLO, mt=173 ±1 GeV (total uncertainty)
100
total uncertainty
CT10NNLO
MSTW08NNLO
ABM11NNLO
–
dσ/dpT (pp→tt+X) (pb/GeV)
approx. NNLO, mt=173 ±1 GeV
1.5
1
0.8
0.6
0
50
100
150
200
250
300
350
t
400
p (GeV)
T
-3
-2
-1
0
1
2
3
y
√
PDF uncertainties S = 7 TeV pTt and y t distributions: comparison
between all PDF sets (bands are total unc.).
t
–
dσ/dy/σ (pp→tt+X) , mt=173±1 GeV
1.3
approx. NNLO, total unc.
CT10NNLO
MSTW08NNLO
ABM11NNLO
HERAPDF1.5NNLO
NNPDF2.3NNLO
1.2
theory/data, dσ/dpT/σ
–
dσ/dpT/σ (pp→tt+X) , mt=173±1 GeV
approx. NNLO, total unc.
CT10NNLO
HERAPDF1.5NNLO
MSTW08NNLO
NNPDF2.3NNLO
ABM11NNLO
1.2
theory/data, dσ/dy/σ
1.3
1.1
1
0.9
1.1
1
0.9
data CMS, √s=7 TeV
0.8
50
100
150
data CMS, √s=7 TeV
200
250
300
350
400
0.8
-2.5
-2
-1.5
-1
-0.5
t
0
0.5
1
1.5
2
2.5
y
p (GeV)
T
t
–
1.3
dσ/dpT/σ (pp→tt+X) , mt=173±1 GeV
approx. NNLO, total unc.
CT10NNLO
MSTW08NNLO
ABM11NNLO
HERAPDF1.5NNLO
NNPDF2.3NNLO
theory/data, dσ/dpT/σ
1.2
1.1
1
0.9
data ATLAS, √s=7 TeV
0.8
50
100
150
200
250
300
350
t
p (GeV)
T
PDF uncertainties
√
t
S = 7 TeV pT
and y t distributions: ratio to the LHC measurements (bands are total unc.).
Conclusions
◮
We have shown phenomenological results relevant for hadron
colliders obtained by using DiffTop.
◮
DiffTop code and relative FastNLO tables will be released
for a public use.
◮
Precise data for the diff. Xsec. will constrain the gluon at
large-x once included in PDF fits.
◮
More data is needed: absolute differential cross section data
will bring more information.
◮
DiffTop will be continuosly updated on the theory side: a
new branch for the PIM kinematic is currently under
development.
◮
Looking forward to see all this machinery at work in fits of
PDFs.
BACKUP
Quality check:
NLO Exact Calculation vs approx NLO
mt = 173 GeV; Q=mt; CT10 NLO
1.1
MCFM NLO
approx NLO, Q=mt
1
0.9
dσ/dPT[pb/GeV]
0.8
0.7
0.6
0.5
0.4
0.3
0.2
0.1
0
0
50
100
150
t
PT [GeV]
Beenakker, Kujif, Smith, Van Neerven, 1989, Dawson, Ellis, Nason, 1988-89
200
250