Abstract
We studied the impact of future electron ion collider inclusive and semi-inclusive polarized deep inelastic scattering data will have on the determination of the helicity parton distributions. Supplementing the Monte Carlo sampling variant of the DSSV14 analysis with pseudodata on polarized inclusive and semi-inclusive electron-proton deep inelastic scattering with updated uncertainty estimates and for two different center-of-mass-system energies, $\sqrt{s}=44.7\text{ }\text{ }\mathrm{GeV}$ and $\sqrt{s}=141.4\text{ }\text{ }\mathrm{GeV}$, respectively, and on inclusive electron-helium collisions at $\sqrt{s}=115.2\text{ }\text{ }\mathrm{GeV}$, we find a remarkable improvement in the determination of the helicity distributions, especially at low parton momentum fraction $x$. While inclusive electron-proton data at the lowest energy configuration constrain significantly the gluon polarization down to $x\ensuremath{\sim}{10}^{\ensuremath{-}4}$, the higher energy configuration strengthens the constraint and extends it one decade further. On the other hand, semi-inclusive data achieves the hitherto elusive flavor separation for sea quarks that cannot be obtained from any other inclusive electromagnetic measurement. Collisions with helium complement inclusive proton measurements, pushing the constraints on the combined quark plus antiquark $u$, $d$ and $s$ polarizations to an unprecedented level.
Highlights
We studied the impact of future electron ion collider inclusive and semi-inclusive polarized deep inelastic scattering data will have on the determination of the helicity parton distributions
Supplementing the Monte Carlo sampling variant of the DSSV14 analysis with pseudodata on polarized inclusive and semi-inclusive electron-proton deep inelastpicffiffiscattering with updpatffieffi d uncertainty estimates and for two different center-of-mass-system energiesp, ffiffi inclusive electron-helium collisions at s s 1⁄4 44.7 GeV 1⁄4 115.2 GeV, and s 1⁄4 we find a
Unclear how much of the missing spin is carried by the gluons and how much should be associated to the orbital angular momentum of partons. In this quest for the origin of the proton spin, the measurement of hadrons and jets produced at high transverse momentum in polarized proton-proton collisions at the Brookhaven National Laboratory-Relativistic Heavy Ion Collider (BNL-RHIC) has set a crucial milestone [3]
Summary
Ever since the pioneering measurements of the EMC experiment at CERN suggested that quarks and antiquarks are only responsible for a small fraction of the proton spin [1], challenging the naive quark-parton model picture, the way in which the proton spin builds up from its fundamental constituents, quarks and gluons, has remained an open question [2]. In spite of the very successful RHIC spin program, the gluon helicity distribution can be at best conjectured for values of the momentum fraction below x ∼ 10−2 Besides these fundamental questions on the role of the gluon polarization, and that of the orbital angular momentum, the way in which each particular quark flavor contributes to the proton spin is work in progress. Adding the inclusive e(plecffisffitr1⁄4on1-4p1roGtoenV)DIrSougdhaltya at the higher duplicates the c.m.s. impact energy on the gluon polarization uncertainty and extends the constraints one decade further in the parton momentum fraction In this way the EIC would probe partons carrying down to a hundred thousandth of the proton momentum.
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