Observation of nuclear modifications in W± boson production in pPb collisions at <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" altimg="si1.svg"><mml:msqrt><mml:mrow><mml:msub><mml:mrow><mml:mi>s</mml:mi></mml:mrow><mml:mrow><mml:mi mathvariant="normal">NN</mml:mi></mml:mrow></mml:msub></mml:mrow></mml:msqrt><mml:mo linebreak="goodbreak" linebreakstyle="after">=</mml:mo><mml:mn>8.16</mml:mn><mml:mspace width="0.25em"/><mml:mtext>TeV</mml:mtext></mml:math>

We present a model-independent determination of the nuclear parton distribution functions (nPDFs) using machine learning methods and Monte Carlo techniques based on the NNPDF framework. The neutral-current deep-inelastic nuclear structure functions used in our previous analysis, nNNPDF1.0, are complemented by inclusive and charm-tagged cross-sections from charged-current scattering. Furthermore, we include all available measurements of W and Z leptonic rapidity distributions in proton-lead collisions from ATLAS and CMS at $$ \sqrt{s} $$ s = 5.02 TeV and 8.16 TeV. The resulting nPDF determination, nNNPDF2.0, achieves a good description of all datasets. In addition to quantifying the nuclear modifications affecting individual quarks and antiquarks, we examine the implications for strangeness, assess the role that the momentum and valence sum rules play in nPDF extractions, and present predictions for representative phenomenological applications. Our results, made available via the LHAPDF library, highlight the potential of high-energy collider measurements to probe nuclear dynamics in a robust manner.

Section: Jhep09(2020)183mentioning

confidence: 99%

Section: Jhep09(2020)183mentioning

confidence: 99%

Section: Notation and Conventionsmentioning

confidence: 99%

See 1 more Smart Citation

nNNPDF2.0: quark flavor separation in nuclei from LHC data

Khalek

Ethier

Rojo

et al. 2020

“…The production of electroweak bosons at the LHC has already been studied in several collision systems, at various energies and rapidities [19][20][21][22][23][24][25][26][27][28][29][30][31][32]. At midrapidity, the data in different collision systems are generally well described by theoretical calculations both with and without nuclear modification of the PDFs [21][22][23][24][25][26][27][28][29][30][31]. In fact, the covered Bjorken-x range at midrapidity extends over the antishadowing and shadowing region (depending on the transition value, even into the EMC region).…”

Section: Introductionmentioning

confidence: 99%

“…As a result, their competing effects reduce the final effect of nuclear modifications. However, at larger rapidities and therefore lower x, there are increasingly stronger deviations between calculations with models that either do or do not include nuclear modification of the PDFs [20,31]. The data taken at the LHC are in a kinematic regime in (x, Q 2 ) which is also sensitive to contributions coming from quark flavors such as charm and strange, present as sea quarks in the nucleons [33].…”

Section: Introductionmentioning

confidence: 99%

Z-boson production in p-Pb collisions at $$ \sqrt{s_{\mathrm{NN}}} $$ = 8.16 TeV and Pb-Pb collisions at $$ \sqrt{s_{\mathrm{NN}}} $$ = 5.02 TeV

Acharya

Adamová

Adler

et al. 2020

Self Cite

Measurement of Z-boson production in p-Pb collisions at $$ \sqrt{s_{\mathrm{NN}}} $$ s NN = 8.16 TeV and Pb-Pb collisions at $$ \sqrt{s_{\mathrm{NN}}} $$ s NN = 5.02 TeV is reported. It is performed in the dimuon decay channel, through the detection of muons with pseudorapidity −4 < ημ< −2.5 and transverse momentum $$ {p}_{\mathrm{T}}^{\mu } $$ p T μ > 20 GeV/c in the laboratory frame. The invariant yield and nuclear modification factor are measured for opposite-sign dimuons with invariant mass 60 < mμμ< 120 GeV/c2 and rapidity 2.5 <$$ {y}_{\mathrm{cms}}^{\mu \mu} $$ y cms μμ < 4. They are presented as a function of rapidity and, for the Pb-Pb collisions, of centrality as well. The results are compared with theoretical calculations, both with and without nuclear modifications to the Parton Distribution Functions (PDFs). In p-Pb collisions the center-of-mass frame is boosted with respect to the laboratory frame, and the measurements cover the backward (−4.46 <$$ {y}_{\mathrm{cms}}^{\mu \mu} $$ y cms μμ < −2.96) and forward (2.03 <$$ {y}_{\mathrm{cms}}^{\mu \mu} $$ y cms μμ < 3.53) rapidity regions. For the p-Pb collisions, the results are consistent within experimental and theoretical uncertainties with calculations that include both free-nucleon and nuclear-modified PDFs. For the Pb-Pb collisions, a 3.4σ deviation is seen in the integrated yield between the data and calculations based on the free-nucleon PDFs, while good agreement is found once nuclear modifications are considered.

A QCD analysis of LHCb D-meson data in p+Pb collisions

Eskola

Helenius

Paakkinen

et al. 2020

We scrutinize the recent LHCb data for D 0-meson production in p+Pb collisions within a next-to-leading order QCD framework. Our calculations are performed in the SACOT-m T variant of the general-mass variable-flavour-number scheme (GM-VFNS), which has previously been shown to provide a realistic description of the LHC p+p data. Using the EPPS16 and nCTEQ15 nuclear parton distribution functions (PDFs) we show that a very good agreement is obtained also in the p+Pb case both for cross sections and nuclear modification ratios in the wide rapidity range covered by the LHCb data. Encouraged by the good correspondence, we quantify the impact of these data on the nuclear PDFs by the Hessian reweighting technique. We find compelling direct evidence of gluon shadowing at small momentum fractions x, with no signs of parton dynamics beyond the collinear factorization. We also compare our theoretical framework to a fixed-order calculation supplemented with a parton shower. While the two frameworks differ in the absolute cross sections, these differences largely cancel in the nuclear modification ratios. Thus, the constraints for nuclear PDFs appear solid.