A Determination of the Charm Content of the Proton

Richard D. Ball, Valerio Bertone, Marco Bonvini, Stefano Carrazza, Stefano Forte, Alberto Guffanti, Nathan P. Hartland, Juan Rojo, Luca Rottoli

Research output: Contribution to JournalArticleAcademicpeer-review

Abstract

We present an unbiased determination of the charm content of the proton, in which the charm parton distribution function (PDF) is parametrized on the same footing as the light quarks and the gluon in a global PDF analysis. This determination relies on the calculation of deep-inelastic structure functions in the FONLL scheme, generalized to account for massive charm-initiated contributions. In contrast to the usual situation in which the charm PDF is assumed to be generated perturbatively by pair radiation off gluons and light quarks, vanishing at a scale set by the value of the charm mass m_c, we find that the fitted charm PDF vanishes within uncertainties at a scale Q~1.5 GeV for all x<~0.1, independent of the value of m_c used in the coefficient functions. We also find some evidence that the charm PDF at large x>~0.1 and low scales does not vanish, but rather has an "intrinsic" component, very weakly scale dependent and almost independent of the value of m_c, carrying about 1% of the total momentum of the proton. The uncertainties in all other PDFs are only slightly increased by the inclusion of fitted charm, while the dependence of these PDFs on m_c is significantly reduced. When the EMC charm structure function dataset is included, it is well described by the fit, and PDF uncertainties in the fitted charm PDF are significantly reduced, though we verify that excluding the EMC data does not qualitatively modify any of our findings. The increased stability with respect to m_c persists at high scales and is the main implication of our results for LHC phenomenology. Fitting the charm PDF modifies the predictions for processes such as high p_T and large rapidity charm pair production and Z+c production, and thus we expect that future LHC data will further constrain the charm content of the proton.
Original languageEnglish
Pages (from-to)647
Number of pages46
JournalEuropean Physical Journal C. Particles and Fields
VolumeC76
Issue number11
DOIs
Publication statusPublished - 2016

Fingerprint

Distribution functions
Protons
protons
partons
distribution functions
Electromagnetic compatibility
Momentum
quarks
Radiation
gluons
pair production
phenomenology
Uncertainty
inclusions
momentum

Cite this

Ball, R. D., Bertone, V., Bonvini, M., Carrazza, S., Forte, S., Guffanti, A., ... Rottoli, L. (2016). A Determination of the Charm Content of the Proton. European Physical Journal C. Particles and Fields, C76(11), 647. https://doi.org/10.1140/epjc/s10052-016-4469-y
Ball, Richard D. ; Bertone, Valerio ; Bonvini, Marco ; Carrazza, Stefano ; Forte, Stefano ; Guffanti, Alberto ; Hartland, Nathan P. ; Rojo, Juan ; Rottoli, Luca. / A Determination of the Charm Content of the Proton. In: European Physical Journal C. Particles and Fields. 2016 ; Vol. C76, No. 11. pp. 647.
@article{26b6ab0e1f99401d9972e2b258e57eb6,
title = "A Determination of the Charm Content of the Proton",
abstract = "We present an unbiased determination of the charm content of the proton, in which the charm parton distribution function (PDF) is parametrized on the same footing as the light quarks and the gluon in a global PDF analysis. This determination relies on the calculation of deep-inelastic structure functions in the FONLL scheme, generalized to account for massive charm-initiated contributions. In contrast to the usual situation in which the charm PDF is assumed to be generated perturbatively by pair radiation off gluons and light quarks, vanishing at a scale set by the value of the charm mass m_c, we find that the fitted charm PDF vanishes within uncertainties at a scale Q~1.5 GeV for all x<~0.1, independent of the value of m_c used in the coefficient functions. We also find some evidence that the charm PDF at large x>~0.1 and low scales does not vanish, but rather has an {"}intrinsic{"} component, very weakly scale dependent and almost independent of the value of m_c, carrying about 1{\%} of the total momentum of the proton. The uncertainties in all other PDFs are only slightly increased by the inclusion of fitted charm, while the dependence of these PDFs on m_c is significantly reduced. When the EMC charm structure function dataset is included, it is well described by the fit, and PDF uncertainties in the fitted charm PDF are significantly reduced, though we verify that excluding the EMC data does not qualitatively modify any of our findings. The increased stability with respect to m_c persists at high scales and is the main implication of our results for LHC phenomenology. Fitting the charm PDF modifies the predictions for processes such as high p_T and large rapidity charm pair production and Z+c production, and thus we expect that future LHC data will further constrain the charm content of the proton.",
author = "Ball, {Richard D.} and Valerio Bertone and Marco Bonvini and Stefano Carrazza and Stefano Forte and Alberto Guffanti and Hartland, {Nathan P.} and Juan Rojo and Luca Rottoli",
year = "2016",
doi = "10.1140/epjc/s10052-016-4469-y",
language = "English",
volume = "C76",
pages = "647",
journal = "European Physical Journal C. Particles and Fields",
issn = "1434-6044",
publisher = "Springer New York",
number = "11",

}

Ball, RD, Bertone, V, Bonvini, M, Carrazza, S, Forte, S, Guffanti, A, Hartland, NP, Rojo, J & Rottoli, L 2016, 'A Determination of the Charm Content of the Proton' European Physical Journal C. Particles and Fields, vol. C76, no. 11, pp. 647. https://doi.org/10.1140/epjc/s10052-016-4469-y

A Determination of the Charm Content of the Proton. / Ball, Richard D.; Bertone, Valerio; Bonvini, Marco; Carrazza, Stefano; Forte, Stefano; Guffanti, Alberto; Hartland, Nathan P.; Rojo, Juan; Rottoli, Luca.

In: European Physical Journal C. Particles and Fields, Vol. C76, No. 11, 2016, p. 647.

Research output: Contribution to JournalArticleAcademicpeer-review

TY - JOUR

T1 - A Determination of the Charm Content of the Proton

AU - Ball, Richard D.

AU - Bertone, Valerio

AU - Bonvini, Marco

AU - Carrazza, Stefano

AU - Forte, Stefano

AU - Guffanti, Alberto

AU - Hartland, Nathan P.

AU - Rojo, Juan

AU - Rottoli, Luca

PY - 2016

Y1 - 2016

N2 - We present an unbiased determination of the charm content of the proton, in which the charm parton distribution function (PDF) is parametrized on the same footing as the light quarks and the gluon in a global PDF analysis. This determination relies on the calculation of deep-inelastic structure functions in the FONLL scheme, generalized to account for massive charm-initiated contributions. In contrast to the usual situation in which the charm PDF is assumed to be generated perturbatively by pair radiation off gluons and light quarks, vanishing at a scale set by the value of the charm mass m_c, we find that the fitted charm PDF vanishes within uncertainties at a scale Q~1.5 GeV for all x<~0.1, independent of the value of m_c used in the coefficient functions. We also find some evidence that the charm PDF at large x>~0.1 and low scales does not vanish, but rather has an "intrinsic" component, very weakly scale dependent and almost independent of the value of m_c, carrying about 1% of the total momentum of the proton. The uncertainties in all other PDFs are only slightly increased by the inclusion of fitted charm, while the dependence of these PDFs on m_c is significantly reduced. When the EMC charm structure function dataset is included, it is well described by the fit, and PDF uncertainties in the fitted charm PDF are significantly reduced, though we verify that excluding the EMC data does not qualitatively modify any of our findings. The increased stability with respect to m_c persists at high scales and is the main implication of our results for LHC phenomenology. Fitting the charm PDF modifies the predictions for processes such as high p_T and large rapidity charm pair production and Z+c production, and thus we expect that future LHC data will further constrain the charm content of the proton.

AB - We present an unbiased determination of the charm content of the proton, in which the charm parton distribution function (PDF) is parametrized on the same footing as the light quarks and the gluon in a global PDF analysis. This determination relies on the calculation of deep-inelastic structure functions in the FONLL scheme, generalized to account for massive charm-initiated contributions. In contrast to the usual situation in which the charm PDF is assumed to be generated perturbatively by pair radiation off gluons and light quarks, vanishing at a scale set by the value of the charm mass m_c, we find that the fitted charm PDF vanishes within uncertainties at a scale Q~1.5 GeV for all x<~0.1, independent of the value of m_c used in the coefficient functions. We also find some evidence that the charm PDF at large x>~0.1 and low scales does not vanish, but rather has an "intrinsic" component, very weakly scale dependent and almost independent of the value of m_c, carrying about 1% of the total momentum of the proton. The uncertainties in all other PDFs are only slightly increased by the inclusion of fitted charm, while the dependence of these PDFs on m_c is significantly reduced. When the EMC charm structure function dataset is included, it is well described by the fit, and PDF uncertainties in the fitted charm PDF are significantly reduced, though we verify that excluding the EMC data does not qualitatively modify any of our findings. The increased stability with respect to m_c persists at high scales and is the main implication of our results for LHC phenomenology. Fitting the charm PDF modifies the predictions for processes such as high p_T and large rapidity charm pair production and Z+c production, and thus we expect that future LHC data will further constrain the charm content of the proton.

U2 - 10.1140/epjc/s10052-016-4469-y

DO - 10.1140/epjc/s10052-016-4469-y

M3 - Article

VL - C76

SP - 647

JO - European Physical Journal C. Particles and Fields

JF - European Physical Journal C. Particles and Fields

SN - 1434-6044

IS - 11

ER -