- Open Access
- Access by Xinjiang University
Determination of nuclear PDFs using Markov chain Monte Carlo methods
Phys. Rev. D 114, 034037 – Published 18 August, 2026
DOI: https://doi.org/10.1103/6bpd-yrm4
Abstract
Global QCD analyses of nuclear parton distribution functions (nPDFs) have traditionally relied on the Hessian method for uncertainty estimation. However, the inherent Gaussian approximation and reliance on local curvature often prove insufficient for nPDF fits, which are frequently characterized by limited data constraints and non-Gaussian likelihoods. In this paper, we present the first nPDF determination based on Markov Chain Monte Carlo (MCMC) techniques, implemented within the nCTEQ framework using an adaptive Metropolis-Hastings algorithm. The MCMC approach enables a direct mapping of the posterior distribution and reveals a highly nontrivial parameter-space structure, including multiple modes and pronounced non-Gaussian behavior, particularly for the valence PDFs. We perform the first single-nucleus global analysis of lead PDFs using exclusively lead data and compare it to a multi-nuclei fit employing a standard analytic dependence. The inclusion of lighter nuclei reduces quark uncertainties and modifies the shape of the lead PDFs, while leaving the gluon distribution largely unaffected. A complementary Hessian analysis exposes systematic limitations of the Gaussian approximation. Our results demonstrate that MCMC methods provide a more reliable framework for uncertainty quantification in nPDF determinations.
Physics Subject Headings (PhySH)
Article Text
References (111)
- M. Klasen and H. Paukkunen, Nuclear parton distribution functions after the first decade of LHC data, Annu. Rev. Nucl. Part. Sci. 74, 49 (2024).
- J. J. Ethier and E. R. Nocera, Parton distributions in nucleons and nuclei, Annu. Rev. Nucl. Part. Sci. 70, 43 (2020).
- F. Arleo et al., Nuclear cold QCD: Review and future strategy, Phys. Rev. C 113, 040501 (2026).
- K. Kovarik et al., nCTEQ15—Global analysis of nuclear parton distributions with uncertainties in the CTEQ framework, Phys. Rev. D 93, 085037 (2016).
- P. Duwentäster, T. Ježo, M. Klasen, K. Kovařík, A. Kusina, K. F. Muzakka, F. I. Olness, R. Ruiz, I. Schienbein, and J. Y. Yu, Impact of heavy quark and quarkonium data on nuclear gluon PDFs, Phys. Rev. D 105, 114043 (2022).
- K. J. Eskola, P. Paakkinen, H. Paukkunen, and C. A. Salgado, EPPS21: A global QCD analysis of nuclear PDFs, Eur. Phys. J. C 82, 413 (2022).
- R. Abdul Khalek, R. Gauld, T. Giani, E. R. Nocera, T. R. Rabemananjara, and J. Rojo, nNNPDF3.0: Evidence for a modified partonic structure in heavy nuclei, Eur. Phys. J. C 82, 507 (2022).
- I. Helenius, M. Walt, and W. Vogelsang, NNLO nuclear parton distribution functions with electroweak-boson production data from the LHC, Phys. Rev. D 105, 094031 (2022).
- H. Khanpour, M. Soleymaninia, S. A. Tehrani, H. Spiesberger, and V. Guzey, Nuclear parton distribution functions with uncertainties in a general mass variable flavor number scheme, Phys. Rev. D 104, 034010 (2021).
- D. de Florian, R. Sassot, P. Zurita, and M. Stratmann, Global analysis of nuclear parton distributions, Phys. Rev. D 85, 074028 (2012).
- M. Hirai, S. Kumano, and T. H. Nagai, Determination of nuclear parton distribution functions and their uncertainties in next-to-leading order, Phys. Rev. C 76, 065207 (2007).
- D. Stump, J. Pumplin, R. Brock, D. Casey, J. Huston, J. Kalk, H. L. Lai, and W. K. Tung, Uncertainties of predictions from parton distribution functions. 1. The Lagrange multiplier method, Phys. Rev. D 65, 014012 (2001).
- J. Pumplin, D. R. Stump, and W. K. Tung, Multivariate fitting and the error matrix in global analysis of data, Phys. Rev. D 65, 014011 (2001).
- K. J. Eskola, P. Paakkinen, and H. Paukkunen, Non-quadratic improved Hessian PDF reweighting and application to CMS dijet measurements at 5.02 TeV, Eur. Phys. J. C 79, 511 (2019).
- W. T. Giele and S. Keller, Implications of hadron collider observables on parton distribution function uncertainties, Phys. Rev. D 58, 094023 (1998).
- R. Abdul Khalek, J. J. Ethier, and J. Rojo (NNPDF Collaboration), Nuclear parton distributions from lepton-nucleus scattering and the impact of an electron-ion collider, Eur. Phys. J. C 79, 471 (2019).
- M. N. Costantini, M. Madigan, L. Mantani, and J. M. Moore, A critical study of the Monte Carlo replica method, J. High Energy Phys. 12 (2024) 064.
- D. W. Hogg and D. Foreman-Mackey, Data analysis recipes: Using Markov chain Monte Carlo, Astrophys. J. Suppl. Ser. 236, 11 (2018).
- S. Brooks, A. Gelman, G. Jones, and X. Meng, Handbook of Markov chain Monte Carlo (CRC Press, Boca Raton, 2011).
- W. T. Giele, S. A. Keller, and D. A. Kosower, Parton distribution function uncertainties, arXiv:hep-ph/0104052.
- Y. G. Gbedo and M. Mangin-Brinet, Markov chain Monte Carlo techniques applied to parton distribution functions determination: Proof of concept, Phys. Rev. D 96, 014015 (2017).
- N. T. Hunt-Smith, A. Accardi, W. Melnitchouk, N. Sato, A. W. Thomas, and M. J. White, Determination of uncertainties in parton densities, Phys. Rev. D 106, 036003 (2022).
- N. T. Hunt-Smith, W. Melnitchouk, F. Ringer, N. Sato, A. W. Thomas, and M. J. White, Accelerating markov chain Monte Carlo sampling with diffusion models, Comput. Phys. Commun. 296, 109059 (2024).
- F. Capel, R. Aggarwal, M. Botje, A. Caldwell, O. Schulz, and A. Verbytskyi, Novel parton density determination code, Phys. Rev. D 110, 014024 (2024).
- M. N. Costantini, L. Mantani, J. M. Moore, V. S. Sánchez, and M. Ubiali, Colibri: A new tool for fast-flying PDF fits, Eur. Phys. J. C 86, 22 (2026).
- M. N. Costantini, L. Mantani, J. M. Moore, and M. Ubiali, A linear PDF model for Bayesian inference, J. High Energy Phys. 04 (2026) 068.
- P. Risse, N. Derakhshanian, T. Jezo, K. Kovarik, and A. Kusina, Determination of proton PDF uncertainties with Markov chain Monte Carlo, Phys. Rev. D 113, 054049 (2026).
- T. Jezo et al., nCTEQ26 nuclear parton distribution functions (MS-TP-26-23).
- A. Accardi, L. T. Brady, W. Melnitchouk, J. F. Owens, and N. Sato, Constraints on large- parton distributions from new weak boson production and deep-inelastic scattering data, Phys. Rev. D 93, 114017 (2016).
- J. Pumplin, D. Stump, R. Brock, D. Casey, J. Huston, J. Kalk, H. L. Lai, and W. K. Tung, Uncertainties of predictions from parton distribution functions. 2. The Hessian method, Phys. Rev. D 65, 014013 (2001).
- S. S. Wilks, The large-sample distribution of the likelihood ratio for testing composite hypotheses, Ann. Math. Stat. 9, 60 (1938).
- K. F. Muzakka et al., Compatibility of neutrino DIS data and its impact on nuclear parton distribution functions, Phys. Rev. D 106, 074004 (2022).
- R. D. Ball, L. Del Debbio, S. Forte, A. Guffanti, J. I. Latorre, J. Rojo, and M. Ubiali (NNPDF Collaboration), Fitting parton distribution data with multiplicative normalization uncertainties, J. High Energy Phys. 05 (2010) 075.
- N. Metropolis, A. W. Rosenbluth, M. N. Rosenbluth, A. H. Teller, and E. Teller, Equation of state calculations by fast computing machines, J. Chem. Phys. 21, 1087 (1953).
- W. K. Hastings, Monte Carlo sampling methods using Markov chains and their applications, Biometrika 57, 97 (1970).
- C. Robert and G. Casella, Monte Carlo Statistical Methods. Springer Texts in Statistics (Springer, New York, 2005).
- H. Haario, E. Saksman, and J. Tamminen, An adaptive Metropolis algorithm, Bernoulli 7, 223 (2001).
- A. Gelman, G. Roberts, and W. Gilks, Efficient Metropolis jumping rules, in Bayesian Statistics V (Oxford University Press, New York, 1996), pp. 599–608.
- A. Gelman, W. R. Gilks, and G. O. Roberts, Weak convergence and optimal scaling of random walk Metropolis algorithms, Ann. Appl. Probab. 7, 110 (1997).
- S. Duane, A. D. Kennedy, B. J. Pendleton, and D. Roweth, Hybrid Monte Carlo, Phys. Lett. B 195, 216 (1987).
- J. Albert, C. Balazs, A. Fowlie, W. Handley, N. Hunt-Smith, R. R. de Austri, and M. White (DarkMachines High Dimensional Sampling Group), A comparison of Bayesian sampling algorithms for high-dimensional particle physics and cosmology applications, Comput. Phys. Commun. 315, 109756 (2025).
- A. Kusina et al., Impact of LHC vector boson production in heavy ion collisions on strange PDFs, Eur. Phys. J. C 80, 968 (2020).
- A. Kusina, F. Lyonnet, D. B. Clark, E. Godat, T. Jezo, K. Kovarik, F. I. Olness, I. Schienbein, and J. Y. Yu, Vector boson production in pPb and PbPb collisions at the LHC and its impact on nCTEQ15 PDFs, Eur. Phys. J. C 77, 488 (2017).
- A. Kusina, T. Stavreva, S. Berge, F. I. Olness, I. Schienbein, K. Kovarik, T. Jezo, J. Y. Yu, and K. Park, Strange quark PDFs and implications for Drell-Yan boson production at the LHC, Phys. Rev. D 85, 094028 (2012).
- G. Aad et al. (ATLAS Collaboration), boson production in collisions at measured with the ATLAS detector, Phys. Rev. C 92, 044915 (2015).
- ATLAS Collaboration, Measurement of production in collision at with ATLAS detector at the LHC.
- V. Khachatryan et al. (CMS Collaboration), Study of Z boson production in pPb collisions at , Phys. Lett. B 759, 36 (2016).
- V. Khachatryan et al. (CMS Collaboration), Study of W boson production in pPb collisions at , Phys. Lett. B 750, 565 (2015).
- A. M. Sirunyan et al. (CMS Collaboration), Observation of nuclear modifications in boson production in pPb collisions at , Phys. Lett. B 800, 135048 (2020).
- R. Aaij et al. (LHCb Collaboration), Observation of production in proton-lead collisions at LHCb, J. High Energy Phys. 09 (2014) 030.
- J. Adam et al. (ALICE Collaboration), W and Z boson production in p-Pb collisions at , J. High Energy Phys. 02 (2017) 077.
- J. M. Campbell, R. K. Ellis, and W. T. Giele, A multi-threaded version of mcfm, Eur. Phys. J. C 75, 246 (2015).
- T. Carli, D. Clements, A. Cooper-Sarkar, C. Gwenlan, G. P. Salam, F. Siegert, P. Starovoitov, and M. Sutton, A posteriori inclusion of parton density functions in NLO QCD final-state calculations at hadron colliders: The applgrid project, Eur. Phys. J. C 66, 503 (2010).
- B. B. Abelev et al. (ALICE Collaboration), production and nuclear effects in pPb collisions at , J. High Energy Phys. 02 (2014) 073.
- R. Aaij et al. (LHCb Collaboration), Study of production and cold nuclear matter effects in collisions at , J. High Energy Phys. 02 (2014) 072.
- B. B. Abelev et al. (ALICE Collaboration), Measurement of prompt -meson production in collisions at , Phys. Rev. Lett. 113, 232301 (2014).
- B. B. Abelev et al. (ALICE Collaboration), Suppression of production in p-Pb collisions at , J. High Energy Phys. 12 (2014) 073.
- B. B. Abelev et al. (ALICE Collaboration), Production of inclusive and in p-Pb collisions at , Phys. Lett. B 740, 105 (2015).
- J. Adam et al. (ALICE Collaboration), Rapidity and transverse-momentum dependence of the inclusive nuclear modification factor in p-Pb collisions at , J. High Energy Phys. 06 (2015) 055.
- G. Aad et al. (ATLAS Collaboration), Measurement of differential production cross sections and forward-backward ratios in collisions with the ATLAS detector, Phys. Rev. C 92, 034904 (2015).
- J. Adam et al. (ALICE Collaboration), -meson production in -Pb collisions at and in pp collisions at , Phys. Rev. C 94, 054908 (2016).
- M. Aaboud et al. (ATLAS Collaboration), Measurement of quarkonium production in proton–lead and proton–proton collisions at 5.02 TeV with the ATLAS detector, Eur. Phys. J. C 78, 171 (2018).
- A. M. Sirunyan et al. (CMS Collaboration), Measurement of prompt and nonprompt production in and collisions at , Eur. Phys. J. C 77, 269 (2017).
- R. Aaij et al. (LHCb Collaboration), Study of prompt meson production in collisions at , J. High Energy Phys. 10 (2017) 090.
- R. Aaij et al. (LHCb Collaboration), Prompt and nonprompt production and nuclear modification in collisions at , Phys. Lett. B 774, 159 (2017).
- A. M. Sirunyan et al. (CMS Collaboration), Measurement of prompt production cross sections in proton-lead and proton-proton collisions at , Phys. Lett. B 790, 509 (2019).
- S. Acharya et al. (ALICE Collaboration), Measurement of prompt , , , and production in p–Pb collisions at , J. High Energy Phys. 12 (2019) 092.
- S. Acharya et al. (ALICE Collaboration), Measurement of nuclear effects on production in p-Pb collisions at , J. High Energy Phys. 07 (2020) 237.
- A. Kusina, J.-P. Lansberg, I. Schienbein, and H.-S. Shao, Gluon shadowing in heavy-flavor production at the LHC, Phys. Rev. Lett. 121, 052004 (2018).
- A. Kusina, J.-P. Lansberg, I. Schienbein, and H.-S. Shao, Reweighted nuclear PDFs using heavy-flavor production data at the LHC, Phys. Rev. D 104, 014010 (2021).
- P. Duwentäster, L. A. Husová, T. Ježo, M. Klasen, K. Kovařík, A. Kusina, K. F. Muzakka, F. I. Olness, I. Schienbein, and J. Y. Yu, Impact of inclusive hadron production data on nuclear gluon PDFs, Phys. Rev. D 104, 094005 (2021).
- B. A. Kniehl, G. Kramer, I. Schienbein, and H. Spiesberger, Inclusive - production in collisions with massive charm quarks, Phys. Rev. D 71, 014018 (2005).
- B. A. Kniehl, G. Kramer, I. Schienbein, and H. Spiesberger, Collinear subtractions in hadroproduction of heavy quarks, Eur. Phys. J. C 41, 199 (2005).
- M. Butenschon and B. A. Kniehl, Reconciling production at HERA, RHIC, Tevatron, and LHC with NRQCD factorization at next-to-leading order, Phys. Rev. Lett. 106, 022003 (2011).
- G. T. Bodwin, E. Braaten, and G. P. Lepage, Rigorous QCD analysis of inclusive annihilation and production of heavy quarkonium, Phys. Rev. D 51, 1125 (1995); 55, 5853(E) (1997).
- G. Onengut et al. (CHORUS Collaboration), Measurement of nucleon structure functions in neutrino scattering, Phys. Lett. B 632, 65 (2006).
- M. A. G. Aivazis, F. I. Olness, and W.-K. Tung, Leptoproduction of heavy quarks. 1. General formalism and kinematics of charged current and neutral current production processes, Phys. Rev. D 50, 3085 (1994).
- M. A. G. Aivazis, J. C. Collins, F. I. Olness, and W.-K. Tung, Leptoproduction of heavy quarks. 2. A unified QCD formulation of charged and neutral current processes from fixed target to collider energies, Phys. Rev. D 50, 3102 (1994).
- V. Bertone, apfel++: A new PDF evolution library in c++, Proc. Sci. DIS2017 (2018) 201 [arXiv:1708.00911].
- P. Risse, V. Bertone, T. Ježo, K. Kovařík, A. Kusina, F. I. Olness, and I. Schienbein, Heavy quark mass effects in charged-current deep-inelastic scattering at approximate NNLO in the Aivazis-Collins-Olness-Tung scheme, Phys. Rev. D 112, 114004 (2025).
- U. Wolff (ALPHA Collaboration), Monte Carlo errors with less errors, Comput. Phys. Commun. 156, 143 (2004); 176, 383(E) (2007).
- W. A. Link and M. J. Eaton, On thinning of chains in MCMC, Methods Ecol. Evol. 3, 112 (2012).
- M. Riabiz, W. Y. Chen, J. Cockayne, P. Swietach, S. A. Niederer, L. Mackey, and C. J. Oates, Optimal thinning of MCMC output, J. R. Stat. Soc. Ser. B Stat. Methodol. 84, 1059 (2022).
- A. Buckley, J. Ferrando, S. Lloyd, K. Nordström, B. Page, M. Rüfenacht, M. Schönherr, and G. Watt, lhapdf6: Parton density access in the LHC precision era, Eur. Phys. J. C 75, 132 (2015).
- A. Putze, L. Derome, D. Maurin, L. Perotto, and R. Taillet, A Markov chain Monte Carlo for galactic cosmic ray physics: I. Method and results for the leaky box model, Astron. Astrophys. 497, 991 (2009).
- R. V. Craiu and J. S. Rosenthal, Bayesian computation via Markov chain Monte Carlo, Annu. Rev. Stat. Appl. 1, 179 (2014).
- R. Ruiz et al., Target mass corrections in lepton–nucleus DIS: Theory and applications to nuclear PDFs, Prog. Part. Nucl. Phys. 136, 104096 (2024).
- J.-w. Qiu, QCD factorization and rescattering in proton nucleus collisions, arXiv:hep-ph/0305161.
- N. Derakhshanian, P. Risse, T. Jezo, M. Klasen, K. Kovarik, and A. Kusina, MCMC-based nuclear PDFs for lead (pb)—Posterior samples and lhapdf grids, 10.5281/zenodo.19204901 (2026).
- S. Acharya et al. (ALICE Collaboration), Inclusive production at forward and backward rapidity in p-Pb collisions at , J. High Energy Phys. 07 (2018) 160.
- S. Acharya et al. (ALICE Collaboration), production in p–Pb collisions at , Phys. Lett. B 806, 135486 (2020).
- R. Aaij et al. (LHCb Collaboration), Study of production and cold nuclear matter effects in collisions at , J. High Energy Phys. 07 (2014) 094.
- R. Aaij et al. (LHCb Collaboration), Study of production in collisions at , J. High Energy Phys. 11 (2018) 194; 02 (2020) 093(E).
- D. M. Alde et al., Nuclear dependence of dimuon production at 800 GeV. FNAL-772 experiment, Phys. Rev. Lett. 64, 2479 (1990).
- M. A. Vasiliev et al. (FNAL E866 Collaboration), Parton energy loss limits and shadowing in Drell-Yan dimuon production, Phys. Rev. Lett. 83, 2304 (1999).
- P. Amaudruz et al. (New Muon Collaboration), A reevaluation of the nuclear structure function ratios for D, He, , C and Ca, Nucl. Phys. B441, 3 (1995).
- M. Arneodo et al. (New Muon Collaboration), The dependence of the nuclear structure function ratios, Nucl. Phys. B481, 3 (1996).
- M. Arneodo et al. (New Muon Collaboration), The dependence of the structure function ratio and the difference in deep inelastic muon scattering, Nucl. Phys. B481, 23 (1996).
- A. Airapetian et al. (HERMES Collaboration), Measurement of in deep-inelastic scattering on nuclei, arXiv:hep-ex/0210068.
- J. Gomez et al., Measurement of the -dependence of deep inelastic electron scattering, Phys. Rev. D 49, 4348 (1994).
- M. Arneodo et al. (New Muon Collaboration), The structure function ratios and at small , Nucl. Phys. B441, 12 (1995),
- M. R. Adams et al. (E665 Collaboration), Shadowing in inelastic scattering of muons on carbon, calcium and lead at low , Z. Phys. C 67, 403 (1995),
- J. Ashman et al. (European Muon Collaboration), Measurement of the ratios of deep inelastic muon—nucleus cross-sections on various nuclei compared to deuterium, Phys. Lett. B 202, 603 (1988).
- M. Arneodo et al. (European Muon Collaboration), Measurements of the nucleon structure function in the range and in deuterium, carbon and calcium, Nucl. Phys. B333, 1 (1990).
- G. Bari et al. (BCDMS Collaboration), A measurement of nuclear effects in deep inelastic muon scattering on deuterium, nitrogen and iron targets, Phys. Lett. B 163, 282 (1985).
- A. Bodek et al., A comparison of the deep inelastic structure functions of deuterium and aluminum nuclei, Phys. Rev. Lett. 51, 534 (1983).
- A. Bodek et al., Electron scattering from nuclear targets and quark distributions in nuclei, Phys. Rev. Lett. 50, 1431 (1983).
- S. Dasu et al., Measurement of kinematic and nuclear dependence of in deep inelastic electron scattering, Phys. Rev. D 49, 5641 (1994).
- A. C. Benvenuti et al. (BCDMS Collaboration), Nuclear effects in deep inelastic muon scattering on deuterium and iron targets, Phys. Lett. B 189, 483 (1987).
- J. Ashman et al. (European Muon Collaboration), A measurement of the ratio of the nucleon structure function in copper and deuterium, Z. Phys. C 57, 211 (1993).
- M. R. Adams et al. (E665 Collaboration), Saturation of shadowing at very low , Phys. Rev. Lett. 68, 3266 (1992).