Impact of LHC vector boson production in heavy ion collisions on strange PDFs
A. Kusina, T. Ježo, D. B. Clark, P. Duwentäster, E. Godat, T. J. Hobbs, J. Kent, M. Klasen, K. Kovařík, F. Lyonnet, K. F. Muzakka, F. I. Olness, I. Schienbein, J. Y. Yu
Abstract
Abstract The extraction of the strange quark parton distribution function (PDF) poses a long-standing puzzle. Measurements from neutrino-nucleus deep inelastic scattering (DIS) experiments suggest the strange quark is suppressed compared to the light sea quarks, while recent studies of $$W^\pm /Z$$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:mrow> <mml:msup> <mml:mi>W</mml:mi> <mml:mo>±</mml:mo> </mml:msup> <mml:mo>/</mml:mo> <mml:mi>Z</mml:mi> </mml:mrow> </mml:math> boson production at the LHC imply a larger strange component at small x values. As the parton flavor determination in the proton depends on nuclear corrections, e.g. from heavy-target DIS, LHC heavy ion measurements can provide a distinct perspective to help clarify this situation. In this investigation we extend the nCTEQ15 nPDFs to study the impact of the LHC proton-lead $$W^\pm /Z$$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:mrow> <mml:msup> <mml:mi>W</mml:mi> <mml:mo>±</mml:mo> </mml:msup> <mml:mo>/</mml:mo> <mml:mi>Z</mml:mi> </mml:mrow> </mml:math> production data on both the flavor differentiation and nuclear corrections. This complementary data set provides new insights on both the LHC $$W^\pm /Z$$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:mrow> <mml:msup> <mml:mi>W</mml:mi> <mml:mo>±</mml:mo> </mml:msup> <mml:mo>/</mml:mo> <mml:mi>Z</mml:mi> </mml:mrow> </mml:math> proton analyses and the neutrino-nucleus DIS data. We identify these new nPDFs as nCTEQ15WZ . Our calculations are performed using a new implementation of the nCTEQ code ( nCTEQ++ ) based on C++ which enables us to easily interface to external programs such as HOPPET, APPLgrid and MCFM. Our results indicate that, as suggested by the proton data, the small x nuclear strange sea appears larger than previously expected, even when the normalization of the $$W^{\pm }/Z$$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:mrow> <mml:msup> <mml:mi>W</mml:mi> <mml:mo>±</mml:mo> </mml:msup> <mml:mo>/</mml:mo> <mml:mi>Z</mml:mi> </mml:mrow> </mml:math> data is accommodated in the fit. Extending the nCTEQ15 analysis to include LHC $$W^\pm /Z$$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:mrow> <mml:msup> <mml:mi>W</mml:mi> <mml:mo>±</mml:mo> </mml:msup> <mml:mo>/</mml:mo> <mml:mi>Z</mml:mi> </mml:mrow> </mml:math> data represents an important step as we advance toward the next generation of nPDFs.