nnpdf3.0: parton distributions for the lhc run...

NNPDF3.0: PARTON DISTRIBUTIONS FOR

THE LHC RUN IIChristopher S. Deans (University of Edinburgh)

On behalf of the NNPDF collaboration:R. D. Ball, V. Bertone, S. Carrazza, CSD, L. Del Debbio, S. Forte, P. Groth-Merrild, A. Guffanti, N. P. Hartland, Z. Kassabov, J. I. Lattore, J. Rojo, L. Rottoli, Maria Ubiali

28th April 2015

DIS2015 Dallas, Texas

Christopher S. Deans DIS2015, 28/04/15

OUTLINE

• NNPDF3.0: - Methodology- Data- Closure testing- Results

• Recent work: - PDFs with threshold resummation- Towards NNPDF3.1

• Summary

2


• New PDF set released last November

• arXiv:1410.8849, JHEP 04(2015)040

• LO, NLO and NNLO sets with different values of and different datasets are available from LHAPDF (lhapdf.hepforge.org)

NNPDF3.0ar

Xiv

:141

0.88

49v3

[he

p-ph

] 4

Mar

201

5

NNPDF Edinburgh 2014/15IFUM-1034-FTCERN-PH-TH/2013-253

OUTP-14-11pCAVENDISH-HEP-14-11

Parton distributions for the LHC Run II

The NNPDF Collaboration:Richard D. Ball1,2, Valerio Bertone2, Stefano Carrazza4,2,

Christopher S. Deans1, Luigi Del Debbio1, Stefano Forte4, Alberto Guffanti5,Nathan P. Hartland1, José I. Latorre3, Juan Rojo6 and Maria Ubiali7

1 The Higgs Centre for Theoretical Physics, University of Edinburgh,JCMB, KB, Mayfield Rd, Edinburgh EH9 3JZ, Scotland

2 PH Department, TH Unit, CERN,CH-1211 Geneva 23, Switzerland

3 Departament d’Estructura i Constituents de la Matèria, Universitat de Barcelona,Diagonal 647, E-08028 Barcelona, Spain

4 Dipartimento di Fisica, Università di Milano and INFN, Sezione di Milano,Via Celoria 16, I-20133 Milano, Italy

5 Niels Bohr International Academy and Discovery Center,Niels Bohr Institute, University of Copenhagen,Blegdamsvej 17, DK-2100 Copenhagen, Denmark

6 Rudolf Peierls Centre for Theoretical Physics, 1 Keble Road,University of Oxford, OX1 3NP Oxford, UK

7 The Cavendish Laboratory, University of Cambridge,J.J. Thomson Avenue, CB3 0HE, UK

Abstract

We present NNPDF3.0, the first set of parton distribution functions (PDFs) determined witha methodology validated by a closure test. NNPDF3.0 uses a global dataset including HERA-IIdeep-inelastic inclusive cross-sections, the combined HERA charm data, jet production fromATLAS and CMS, vector boson rapidity and transverse momentum distributions from ATLAS,CMS and LHCb, W+c data from CMS and top quark pair production total cross sections fromATLAS and CMS. Results are based on LO, NLO and NNLO QCD theory and also includeelectroweak corrections. To validate our methodology, we show that PDFs determined frompseudo-data generated from a known underlying law correctly reproduce the statistical distribu-tions expected on the basis of the assumed experimental uncertainties. This closure test ensuresthat our methodological uncertainties are negligible in comparison to the generic theoretical andexperimental uncertainties of PDF determination. This enables us to determine with confidencePDFs at different perturbative orders and using a variety of experimental datasets ranging fromHERA-only up to a global set including the latest LHC results, all using precisely the samevalidated methodology. We explore some of the phenomenological implications of our results forthe upcoming 13 TeV Run of the LHC, in particular for Higgs production cross-sections.

1

3

http://lhapdf.hepforge.org


NNPDF APPROACH

• Parameterise parton distributions using neural networks

• Perform a genetic algorithm minimisation to find best-fit PDFs

• Cross-validation to prevent neural networks from over-learning

• Capture PDF uncertainties by generating set of Monte Carlo replica PDFs

• Fit using large, global dataset, including data from fixed target DIS and DY, HERA, Tevatron and LHC

4

• New code completely rewritten in C++, with new structure to improve efficiency and promote modularity between theory and fitting.

• New mutation strategy exploiting the structure of the neural networks to obtain a better fit results in a shorted amount of time.

• Improved cross-validation which prevents the fit from stopping too early while still protecting against over-learning.

• New positivity constraints covering a wider range of observables over a larger kinematic range.

3.0 IMPROVEMENTS


x-6

10-5

10 -410-3

10 -210 -110 1

]2

[ G

eV

2 T /

p2

/ M

2Q

1

10

210

310

410

510

610

710FT DIS

HERA1

FT DY

TEV EW

TEV JET

ATLAS EW

LHCB EW

LHC JETS

HERA2

ATLAS JETS 2.76TEV

ATLAS HIGH MASS

ATLAS WpT

CMS W ASY

CMS JETS

CMS WC TOT

CMS WC RAT

LHCB Z

TTBAR

NNPDF3.0 NLO dataset

NNPDF3.0: DATASET

• HERA: HERA-II structure function data from H1 & Zeus, combined charm production data

• ATLAS: 2.76 TeV inclusive jet data, high-mass Drell-Yan and W pT distributions, top quark pair production total cross-section

• CMS: 7 TeV inclusive jet data, muon asymmetry, W+c production, double differential Drell-Yan distributions, top quark pair production cross-section

• LHCb: Z rapidity distribution

Large amount of new data included in the fit:

5

… plus data from NNPDF2.3


-410

-310

-210

-110

1

10

210

(GeV)T

p200 400 600 800 1000 1200 1400 1600 1800 2000

|y|

0

0.5

1

1.5

2

2.5

| for gg-channelδCMS 2011 - | | for gg-channelδCMS 2011 - |

NNPDF3.0: THEORY

• Use fast interfaces at NLO (APPLgrid, FastNLO, aMCfast) to generate FKtables

• For NNLO fits, supplement NLO theory for hadron data with k-factors

• Jet data included at NNLO using threshold calculation in regions where the gg channel agrees with exact calculation (Pires et al.)

• Electroweak corrections from FEWZ3.1 for neutral current datasets included as additional factor

6

Percentage difference between approximate and exact calculation for gg channel


NNPDF3.0: CLOSURE TESTINGValidate methodology by fitting to pseudo-data generated using known PDFs

Generate pseudo-data using underlying law and experimental covariance matrix

Fit pseudo-data using standard fitting methodology

Compare results obtained from fit to underlying law

Define underlying law based on chosen PDF set (MSTW, NNPDF, CT etc.)


NNPDF3.0: CLOSURE TEST RESULTS• Reproduce central of input set to within 1% (Fit

=1.00, input =1.01)

• Additionally reproduce of individual datasets (see right)

• PDF central values reproduced (with expected fluctuations)

• Theory within one sigma of fit central value in ~70% of fits.

8

Experiments

NMC SLACBCDMS

CHORUSNTVDMN

HERA1AV

ZEUSHERA2

H1HERA2

HERAF2CHARM

DYE886DYE605

CDF D0 ATLASCMS LHCB

TOP

2χ

0

0.2

0.4

0.6

0.8

1

1.2

1.4

1.6

1.8

2

for experiments2χDistribution of

2χClosure test 2χMSTW2008nlo

2χClosure test central 2χMSTW2008nlo central

for experiments2χDistribution of

)σDifference to theory (-5 -4 -3 -2 -1 0 1 2 3 4 5

Entri

es

020406080

100120140160180200 Replica distribution

Gaussian distribution

Distribution of single replica fits in level 2 uncertainties

x5−10 4−10 3−10 2−10 1−10 1

)2xg

(x,Q

2−1−

01

2

34

5

67

Closure test fit to MSTW2008 pseudo-data

Closure test fit

MSTW2008



x5−10 4−10 3−10 2−10 1−10 1

)2xg

(x,Q

2−1−

01

2

34

5

67

Closure test fit to NNPDF2.3 pseudo-data

Closure test fit

NNPDF2.3


CLOSURE TEST PDFS

x5−10 4−10 3−10 2−10 1−10 1

)2xg

(x,Q

2−1−

01

2

34

5

67


Closure test fit

NNPDF3.0


x5−10 4−10 3−10 2−10 1−10 1

)2xg

(x,Q

2−1−

01

2

34

5

67

Closure test fit to CT10 pseudo-data

Closure test fit

CT10

Closure test fit to CT10 pseudo-data

x5−10 4−10 3−10 2−10 1−10 1

)2xg

(x,Q

2−1−

01

2

34

5

67


Closure test fit

MSTW2008



Number of Generations310 410 510

2χ

-410

-310

-210

-110Old (2.3) genetic algorithm

New genetic algorithm

Effectiveness of Genetic Algorithm in Level 0 Closure Tests

NNPDF3.0: NOISELESS CLOSURE TEST• When generating closure test

pseudo-data, it’s possible to control level of noise

• Closure test with no noise provides test of basic fitting ability

• Ideal of zero (expect slightly above for fixed length fit)

10

x-510 -410 -310 -210 -110 1

)2

xg(x

,Q

-2

-1

0

1

2

3

4

5

6

7

Level 0 closure test vs. MSTW

Level 0 Closure Test Fit

MSTW2008nlo68cl


x-510 -410 -310 -210 -110 1

)2

(x,Q

ux

0

0.2

0.4

0.6

0.8

1

1.2


Level 0 Closure Test Fit

MSTW2008nlo68cl



NNPDF3.0: RESULTS

11


x -510 -410 -310 -210 -110

)2 (

x, Q

+x

s

-0.1

0

0.1

0.2

0.3

0.4

0.5

0.6

0.72 = 2 GeV2 = 0.118, QSαNNPDF3.0 NLO,

NNPDF3.0

NNPDF2.3

2 = 2 GeV2 = 0.118, QSαNNPDF3.0 NLO,

NNPDF3.0 RESULTS: PDFS

x -510 -410 -310 -210 -110

)2x

g ( x

, Q

-1

0

1

2

3

4

52 = 2 GeV2 = 0.118, QSαNNLO,

NNPDF3.0

NNPDF2.3

2 = 2 GeV2 = 0.118, QSαNNLO,

x -510 -410 -310 -210 -110

)2 (

x, Q

Σx

00.5

11.5

22.5

33.5

44.5

52 = 2 GeV2 = 0.118, QSαNNLO,

NNPDF3.0

NNPDF2.3

2 = 2 GeV2 = 0.118, QSαNNLO,

• General agreement with 2.3; differences of ~1σ due to new data/improved methodology

• Reduction of uncertainties in many PDFs

• Impact of extended positivity in s+


( GeV )XM10210 310

Qua

rk -

Qua

rk L

umin

osity

0.85

0.9

0.95

1

1.05

1.1

1.15

1.2

)=0.118 - Ratio to NNPDF3.0Z

(MSαLHC 13 TeV, NNLO,

NNPDF3.0CT10MMHT14



PDF LUMINOSITIES

( GeV )XM10210 310

Qua

rk -

Antiq

uark

Lum

inos

ity

0.85

0.9

0.95

1

1.05

1.1

1.15

1.2



NNPDF3.0CT10MMHT14



( GeV )XM10210 310

Qua

rk -

Glu

on L

umin

osity

0.85

0.9

0.95

1

1.05

1.1

1.15

1.2



NNPDF3.0CT10MMHT14



( GeV )XM10210 310

Glu

on -

Glu

on L

umin

osity

0.85

0.9

0.95

1

1.05

1.1

1.15

1.2



NNPDF3.0CT10MMHT14




x -410 -310 -210 -110

) [re

f] 2

) [ne

w] /

V (

x, Q

2V

( x, Q

0.85

0.9

0.951

1.05

1.1

1.151.2

1.25

1.32 GeV4 = 102 = 0.118, QSαNNLO,

Global Fit

No LHC data

2 GeV4 = 102 = 0.118, QSαNNLO,

IMPACT OF LHC DATA

x -410 -310 -210 -110

) [re

f] 2

( x,

Q+

) [ne

w] /

s2

( x,

Q+ s 0.8

0.9

1

1.1

1.2

1.3

2 GeV4 = 102 = 0.118, QSαNNLO,

Global Fit

No LHC data

2 GeV4 = 102 = 0.118, QSαNNLO,

x -410 -310 -210 -110

) [re

f] 2

) [ne

w] /

g (

x, Q

2g

( x, Q

0.85

0.9

0.95

1

1.05

1.1

1.15

1.2

1.252 GeV4 = 102 = 0.118, QSαNNLO,

Global Fit

No LHC data

2 GeV4 = 102 = 0.118, QSαNNLO, • Compare NNPDF3.0 fits with and without LHC data

• Reduction of uncertainties in large-x gluon, light-quarks

• Also available on LHAPDF: HERA-only, HERA+ATLAS, HERA+CMS, NoJet PDFs


x -510 -410 -310 -210 -110

)2x

g ( x

, Q

-1

0

1

2

3

4

52 = 2 GeV2 = 0.118, QSαNNLO,

Global

=1.1maxαConservative,

=1.2maxαConservative,

2 = 2 GeV2 = 0.118, QSαNNLO,

CONSERVATIVE DATASET PDFS• PDFs generated by fitting reduced fully

consistent dataset

• Consistency determined by calculating P( ) for each dataset, (see arXiv:1012:0836)

• Results compatible with global fit, with larger uncertainties

αmax = 1.1 αmax = 1.2 αmax = 1.3 Global fitχ2nlo χ

2nnlo χ

2nlo χ

2nnlo χ

2nlo χ

2nnlo χ

2nlo χ

2nnlo

Total 0.96 1.01 1.06 1.10 1.12 1.16 1.23 1.29NMC d/p 0.91 0.91 0.89 0.89 0.88 0.89 0.92 0.93

NMC σNC,p - - - - - - 1.63 1.52SLAC - - - - 1.77 1.19 1.59 1.13

BCDMS - - 1.11 1.15 1.12 1.16 1.22 1.29CHORUS - - 1.06 1.02 1.09 1.07 1.11 1.09NuTeV 0.35 0.34 0.62 0.64 0.70 0.70 0.70 0.86HERA-I 0.97 0.98 1.02 1.00 1.02 0.99 1.05 1.04

ZEUS HERA-II - - - - 1.41 1.48 1.40 1.48H1 HERA-II - - - - - - 1.65 1.79HERA σcNC - - 1.21 1.32 1.20 1.31 1.27 1.28E886 d/p 0.30 0.30 0.43 0.40 0.44 0.46 0.53 0.48E886 p - - 1.18 1.40 1.27 1.53 1.19 1.55E605 1.04 1.10 0.74 0.83 0.75 0.88 0.78 0.90

CDF Z rapidity - - - - - - 1.33 1.53CDF Run-II kt jets - - 1.01 2.01 1.04 1.84 0.96 1.80

D0 Z rapidity 0.56 0.61 0.62 0.71 0.60 0.69 0.57 0.61ATLAS W,Z 2010 - - 1.19 1.13 1.19 1.17 1.19 1.23

ATLAS 7 TeV jets 2010 0.96 1.65 1.08 1.58 1.10 1.54 1.07 1.36ATLAS 2.76 TeV jets 1.03 0.38 1.38 0.36 1.35 0.35 1.29 0.33ATLAS high-mass DY - - - - - - 2.06 1.45

ATLAS W pT - - - - - - 1.13 -CMS W electron asy 0.98 0.84 0.82 0.72 0.85 0.73 0.87 0.73CMS W muon asy - - - - - - 1.81 1.72CMS jets 2011 0.90 2.09 0.96 2.09 0.99 2.10 0.96 1.90

CMS W + c total - - - - - - 0.96 0.84CMS W + c ratio - - - - - - 2.02 1.77CMS 2D DY 2011 - - - - 1.20 1.30 1.23 1.36LHCb W rapidity - - 0.69 0.65 0.74 0.69 0.71 0.72LHCb Z rapidity - - 1.23 1.78 1.11 1.58 1.10 1.59

σ(tt̄) - - - - - - 1.43 0.66

Table 11: The experimental χ2 values at NLO and NNLO for NNPDF3.0 fits to conservative datasetscorresponding to three different values of the threshold αmax (see text). In each case, the χ2 is shown forthe datasets which pass the conservative cut. The values for the global fit (same as in Tab. 9) are alsoshown for ease of comparison.

datasets such as the H1 HERA-II data, the ATLAS high-mass Drell-Yan data, and the CMSW+c data are excluded even from the least conservative set, the one with αmax = 1.3. On theother hand, the CMS inclusive jet data is included for all values of αmax; note that for thisdataset the experimental χ2 shown in Tab. 11 is significantly worse than the t0 value used forminimization and the determination of P (α).

The maximally consistent dataset, found with αmax = 1.1, includes the NMC d/p data, theNuTeV and HERA-I DIS data, the Drell-Yan data from E866 and E605, the D0 Z rapidity, theATLAS and CMS inclusive jets and the CMS W electron asymmetry.

In Tab. 12, we furthermore compare the mean, mode and median of the P (α) distributionsfor the experiments excluded from the NNLO conservative fit with αmax = 1.1 when the globalfit is used as prior (i.e. the same numbers for the corresponding entries in Tab. 10), to thesame quantities computed using as a prior the conservative fit itself. All the peak values ofP (α) deteriorate when using the conservative set as a prior, as they ought to. Clearly, thisdeterioration will be maximal for datasets which are internally consistent, but inconsistent with

91


• NNPDF3.0 fit including deuteron corrections to fixed-target DIS and DY data (Thorne et al., arXiv:1412.3989)

• Non-negligible difference only for down PDF

• CMS W+c and ATLAS WZ data provide information on strangeness content

• Fits with excluding different sets of relevant data find general agreement

• Shown:

x 2−10 1−10

) [re

f] 2

) [ne

w] /

d (

x, Q

2d

( x, Q

0.9

0.95

1

1.05

1.1

1.15

1.2

2 GeV4 = 102 = 0.118, QSαNNPDF3.0 NLO,

No deuteron corrections

MMHT14 deuteron corrections

2 GeV4 = 102 = 0.118, QSαNNPDF3.0 NLO,

x -310 -210 -110

00.20.40.60.8

11.21.41.61.8

22 = 2 GeV2 = 0.118, QSαNNLO,

Global Fit

no Neutrino Data

no W+c Data

no Neutrino, W+c Data

2 = 2 GeV2 = 0.118, QSαNNLO,

rs =s+ s̄

ū+ d̄

rs =s+ s̄

ū+ d̄(1)

1

DEUTERON CORRECTIONS

PROTON STRANGENESS


LHC CROSS-SECTIONS

• Consistent results between 2.3 and 3.0 across many LHC observables

• Slightly larger uncertainties in general: due to improvements in methodology, better exploration of parameter space

• Decrease in ggH cross-section due to softer gg luminosity

• Again change is due to improved methodology, similar results for 3.0 global and 2.3data fits

17

( gg

> H

) [p

b]σ

43

44

45

46

47

=0.118SαNNPDF3.0 NNLO, LHC 13 TeV, iHixs1.3.3,

NNPDF2.32.3data

GlobalConservative

noJetsnoLHC

HERAonly

=0.118SαNNPDF3.0 NNLO, LHC 13 TeV, iHixs1.3.3,

Ratio to NNPDF2.30.92 0.94 0.96 0.98 1 1.02 1.04 1.06 1.08 1.1 1.12 1.14

=0.118, MadGraph5_aMC@NLO fNLOSαLHC 13 TeV,

- e+ -> e0p + p -> Zeν + -> e

+p + p -> W

eν - -> e-p + p -> W

tp + p -> t

tp + p -> H t

c -p + p -> W

+ jetγp + p ->

eν +p + p -> H e

- e+p + p -> H e

+ jeteν +p + p -> e

NNPDF3.0NNPDF2.3

NNPDF3.0 cons

=0.118, MadGraph5_aMC@NLO fNLOSαLHC 13 TeV,


RECENT WORK

18

Christopher S. Deans DIS2015, 28/04/1519 In the NLO+NLL fit, effects of resummation can be large, up to -10% (for quarks) and +30% (for gluons) at high-x, relevant for the production of new BSM particles!!

5

PDFs with threshold resummation Effects of threshold resummation most relevant for large-x DIS structure functions and for Drell-Yan

forward rapidity distributions! Threshold resummation not available for inclusive jets, so compare with DIS+DY+top NNPDF3.0 baseline!

!

Juan Rojo PDF4LHC, CERN, 13/04/2015

THRESHOLD RESUMMATION• First PDF sets at NLO+NLL and NNLO+NNLL

• Soft-gluon resummation most relevant for DIS at large-x and Drell-Yan at forward rapidities

• Perform fit (plus baseline) with DIS, DY and top data — code not yet available for inclusive jet processes

• Preliminary results for NLO+NLL: shifts in quark and gluon at large-x, relevant for production of BSM particles

PRELI

MINAR

Y

PRELI

MINAR

Y


x-510 -410 -310 -210 -110 1

Rat

io

0.6

0.8

1

1.2

1.4

1.6xu(x,Q), comparison plot

NNPDF30 NLO

NNPDF30 NLO + RW(LHCb W)

Q = 1.41 GeV

Gen

erat

ed b

y A

PFEL

2.0.

1: V

.Ber

tone

, S.C

arra

zza,

J.R

ojo

(arX

iv:1

310.

1394

)

TOWARDS NNPDF3.1

• New Data: Final combined HERA results, Tevatron WZ, many new LHC processes incl. ATLAS 1,2,3-jet cross-sections, ATLAS top differential distribution, LHCb W, Z rapidity, CMS 8TeV Drell-Yan, ATLAS prompt photon

• Running quark mass effects

• Fitted charm PDF: parameterisation with 9 independent flavors

• PDF evolution and DIS cross-sections calculated in APFEL; optimised theory calculation in fit

20

NNPDF3.0 reweighted with LHCb W data


SUMMARY

• NNPDF3.0: - Next generation PDF set, available now on LHAPDF- Large amount of new data from HERA, ATLAS, CMS and LHCb- New theory: Electroweak corrections, top cross-sections, jet data at NNLO- Improved fitting methodology fully validated using closure tests

• Looking ahead: - First PDF set including NLL and NNLL soft-gluon resummation effects- NNPDF3.1: More LHC data, HERA combined dataset, running quark masses, Fitted charm PDF

• Also available: - NNPDF2.3QED: PDFs with QED evolution + photon, arXiv:1308.0598- NNPDFpol1.1: Polarised neural network PDFs, arXiv:1406.5539

21

nnpdf3.0: parton distributions for the lhc run...

Documents