SLIDE 1 nCTEQ15 nuclear parton distributions with uncertainties
Tomáš Ježo Università di Milano-Bicocca INFN, Sezione di Milano-Bicocca
In collaboration with:
- A. Kusina, K. Kovařík, D. B. Clark, C. Keppel,
- F. Lyonnet, J. Morfín, F. I. Olness, J. Owens,
- I. Schienbein, J. Y. Yu
[DOI: 10.1103/PhysRevD.93.085037] 14 June 2016
SLIDE 2 Introduction
structure of nuclei
[DOI: 10.1103/PhysRevD.93.085037] ▸ Parton Density Functions (PDFs) ▹ Describe the structure of nucleons ▹ f(x,Q); x momentum fraction, Q scale ▹ Q dependence calculable ▹ x dependence obtained from a fit to data ▸ Nuclear Parton Density Functions (nPDFs) ▹ Describe the structure of nuclei ▹ Nucleus not just and ensamble
⬥ weighted average over protons and neutrons ⬥ nuclear correction
=
D 2 2 Fe
BCDMS(85)
SLAC/NMC param.
BCDMS(87) SLAC-E049(83) SLAC-E139(94) SLAC-E140(94)
EMC dip
SLIDE 3
Introduction
structure of nuclei
[DOI: 10.1103/PhysRevD.93.085037] ▸ Nuclear Parton Density Functions (nPDFs) ▹ Describe the structure of nuclei ▹ Nucleus not just and ensamble of free nucleons ⬥ weighted average over protons and neutrons ⬥ nuclear correction ▸ We fit data from collisions of nuclei to obtain nPDFs ▹ Factorization & DGLAP evolution ⬥ Allows for a definition of universal (n)PDF ▹ Isospin symmetry ▹ Bound proton PDFs: same evolution and sum rules as free proton PDFs (neglecting contributions from x > 1 region) ▹ Observables calculated as
SLIDE 4
Introduction
available nPDFs
[DOI: 10.1103/PhysRevD.93.085037] ▸ Multiplicative nuclear correction factors ▹ HKN: Hirai, Kumano, Nagai [PRC 76, 065207 (2007), arXiv:0709.3038] ▹ EPS: Eskola, Paukkunen, Salgado [JHEP 04 (2009) 065, arXiv:0902.4154] ▹ DSSZ: de Florian, Sassot, Stratmann, Zurita [PRD 85, 074028 (2012), arXiv:1112.6324] ▸ Native nuclear PDFs ▹ nCTEQ [PRD 80, 094004 (2009), arXiv:0907.2357, arXiv:1509.00792]
SLIDE 5
nCTEQ framework
[DOI: 10.1103/PhysRevD.93.085037] ▸ Functional form of the bound proton PDF same as for the free proton (CTEQ6M, x restricted to 0 < x < 1) ▸ A-dependent fit parameters (reduces to free proton for A = 1) ▸ PDFs for nucleus (A, Z) (bound neutron PDF by isospin symmetry)
Introduction
SLIDE 6
Fit
data sets
[DOI: 10.1103/PhysRevD.93.085037]
▸ NC DIS & DY ▸ Single pion production (new) ▸ Neutrino (to be included later)
SLIDE 7
methods and parameters
[DOI: 10.1103/PhysRevD.93.085037] ▸ 16+2 free parameters ▹ 7 gluon ▹ 7 valence ▹ 2 sea ▹ 2 pion data normalizations ▸ Fit properties: ▹ fit @NLO ▹ ▹ ACOT heavy quark scheme ▸ Error analysis: ▹ use Hessian method ▹ tolerance (every nuclear target within 90% C.L.) ▸ Kinematic cuts: ▹ ▹ 708 (DIS & DY) + 32 ( ) = 740 data points after cuts
Fit
SLIDE 8
quality of the fit
[DOI: 10.1103/PhysRevD.93.085037]
Fit
SLIDE 9
Results
▸ Bound proton PDFs ▸ Compare nCTEQ fits: ▹ nCTEQ with data ▹ nCTEQnp without data
impact of data
[DOI: 10.1103/PhysRevD.93.085037]
SLIDE 10
▸ Bound proton PDFs ▸ Compare nCTEQ fits: ▹ nCTEQ with data ▹ nCTEQnp without data [DOI: 10.1103/PhysRevD.93.085037]
Results
impact of data
SLIDE 11
▸ Nuclear correction factor ▸ Compare nCTEQ fits: ▹ nCTEQ with data ▹ nCTEQnp without data [DOI: 10.1103/PhysRevD.93.085037]
Results
impact of data
SLIDE 12
▸ Compare with other fits: ▹ nCTEQ15 ▹ EPS09 ▹ DSSZ ▹ HKN07 [DOI: 10.1103/PhysRevD.93.085037] ▸ Nuclear correction factor
Results
comparison with other fits
SLIDE 13
▸ Bound proton PDFs ▸ Compare with other fits: ▹ nCTEQ15 ▹ EPS09 ▹ DSSZ ▹ HKN07
comparison with other fits
[DOI: 10.1103/PhysRevD.93.085037]
Results
SLIDE 14
Results
[DOI: 10.1103/PhysRevD.93.085037]
valence distributions
SLIDE 15 ▸ for and fits is very similar (~590) ⇒ no preference for either of the solutons in the data ▸ Differences between u and d valence distributions washed
▸ Hessian error analysis does not account for this ⇒ one solution not in the error band of the other solution [DOI: 10.1103/PhysRevD.93.085037]
Results
valence distributions
SLIDE 16
▸ Full lead nucleus distribution [DOI: 10.1103/PhysRevD.93.085037]
Results
valence distributions
SLIDE 17
Results
[DOI: 10.1103/PhysRevD.93.085037]
description of fitted data
SLIDE 18
[DOI: 10.1103/PhysRevD.93.085037]
Results
description of fitted data
SLIDE 19
[DOI: 10.1103/PhysRevD.93.085037]
Results
description of fitted data
SLIDE 20
[DOI: 10.1103/PhysRevD.93.085037]
Results
description of fitted data
SLIDE 21
[DOI: 10.1103/PhysRevD.93.085037]
Results
description of fitted data
SLIDE 22
[DOI: 10.1103/PhysRevD.93.085037]
Summary
▸ error PDFs released: ▹ Available on the nCTEQ website: http://ncteq.hepforge.org (and LHAPDF) ▹ T wo fits provided: with and without pion production data ▸ Differences in valence distributions observed ▹ Impact of different assumptions entering nPDF analyses ▹ Uncertainties are strongly underestimated (assumptions replace uncertainties) ▸ Regardless of big differences in valence distributions the fitted data described very well
SLIDE 23
[DOI: 10.1103/PhysRevD.93.085037]
Summary
▸ error PDFs released: ▹ Available on the nCTEQ website: http://ncteq.hepforge.org (and LHAPDF) ▹ T wo fits provided: with and without pion production data ▸ Differences in valence distributions observed ▹ Impact of different assumptions entering nPDF analyses ▹ Uncertainties are strongly underestimated (assumptions replace uncertainties) ▸ Regardless of big differences in valence distributions the fitted data described very well
SLIDE 24 [DOI: 10.1103/PhysRevD.93.085037]
Outlook
recent developments
▸ Study the impact of LHC data employing reweighting ▹ rapidity distribution of charged leptons in W
+/-
