Spin-dependent Gluon Research Articles

Single-spin asymmetry ofJ/ψproduction inp+p,p+Al, andp+Aucollisions with transversely polarized proton beams atsNN=200 GeV

We report the transverse single-spin asymmetries of $J/\psi$ production at forward and backward rapidity, $1.2<|y|<2.2$, as a function of $J/\psi$ transverse momentum ($p_T$) and Feynman-$x$ ($x_F$). The data analyzed were recorded by the PHENIX experiment at the Relativistic Heavy Ion Collider in 2015 from $p$$+$$p$, $p$$+$Al, and $p$$+$Au collisions with transversely polarized proton beams at $\sqrt{s_{_{NN}}}=200$ GeV. At this collision energy, single-spin asymmetries for heavy-flavor particle production of $p$$+$$p$ collisions provide access to the spin-dependent gluon distribution and higher-twist correlation functions inside the nucleon, such as the gluon Qiu-Sterman and trigluon correlation functions. Proton+nucleus collisions offer an excellent opportunity to study nuclear effects on the correlation functions. The data indicate negative asymmetries at the two-standard-deviation level in the $p$$+$Au data for $p_T<2$ GeV/$c$ at both forward and backward rapidity, while in $p$$+$$p$ and $p$$+$Al collisions the asymmetries are consistent with zero within the range of experimental uncertainties.

Testing the parity of the Higgs boson through linearly polarized gluons

The role of transverse momentum dependent (TMD) gluonic parton distributions is discussed for proton collisions at high energies. In particular the production of two real photons in proton collisions in the kinematical regime of small transverse pair momenta may be used to obtain information on gluon TMDs. While spin-dependent gluon TMDs can be studied in polarized proton collisions at RHIC the effect of linearly polarized gluons on unpolarized proton collisions at the LHC may be utilized to determine the parity of the Higgs boson.

Hadron plus photon production in polarized hadronic collisions at next-to-leading order accuracy

We compute the next-to-leading order QCD corrections to the polarized (and unpolarized) cross sections for the production of a hadron accompanied by an opposite-side prompt photon. This process, being studied at RHIC, permits us to reconstruct partonic kinematics using experimentally measurable variables. We study the correlation between the reconstructed momentum fractions and the true partonic ones, which in the polarized case might allow us to reveal the spin-dependent gluon distribution with a higher precision.

Longitudinal spin physics with the PHENIX detector at RHIC

The Relativistic Heavy Ion Collider (RHIC) at Brookhaven National Laboratory has demonstrated the unique ability to collide beams of polarized protons at center of mass energies from GeV to 500 GeV. The spin-dependent gluon distribution function of the proton, Δg(x), can be determined from such collisions, through processes such as p + p → π + X, p + p → γ + X, p + p → η + X, and others. The results of analyses for these kinds of processes in PHENIX will be presented, some of which provide strong constraints on the contribution of gluon spin to the spin of the proton.Flavor-separated spin-dependent quark and antiquark distribution functions can also be extracted in polarized p+p collisions, from parity-violation in the production of W bosons, which we observe indirectly from their decay into leptons. Our progress in determining the W-production yield from our selection of p + p → e + X events will be presented.

Extraction of g1p, g1d and δg/g from HERMES data

HERMES collected deep-inelastic scattering (DIS) events of 27.6 GeV longitudinally polarised positrons off longitudinally polarised hydrogen and deuterium gas targets internal the HERA storage ring. Double-spin asymmetries A∥p,d of cross sections in inclusive DIS allow the precise extraction of spin structure functions of the proton g1p(x,Q2) and the deuteron g1d(x,Q2) in the kinematic range 0.0041 ≤ x ≤ 0.9 and 0.18 GeV ≤ Q2 ≤ 20GeV2. Furthermore, double-spin asymmetries of inclusive production of charged hadrons as a function of transverse momentum pt have been measured. For pt > 1 GeV the asymmetries are sensitive to the spin dependent gluon distribution function δg. Using a Leading Order Monte Carlo model to obtain information on the background asymmetry and background process kinematics, δg/g has been extracted.

Spin-dependent DGLAP evolution equations andtdistribution of longitudinally polarized structure functions in leading order and next-to-leading order at lowx

We obtain spin-dependent singlet, nonsinglet, and gluon structure functions by solving Dokshitzer-Gribov-Lipatov-Altarelli-Parisi evolution equations in leading order and next-to-leading order at low $x$. The Taylor series expansion method is used to solve the evolution equations. We also calculated $t$ evolution of longitudinally polarized proton and neutron structure functions ${g}_{1}^{p}$ and ${g}_{1}^{n}$, respectively, and the results are compared with SLAC E143 data.

Exploring the polarization of gluons in the nucleon

We give an overview of the current status of investigations of the polarization of gluons in the nucleon. We describe some of the physics of the spin-dependent gluon parton distribution and its phenomenology in high-energy polarized hadronic scattering. We also review the recent experimental results.

QCD predictions for the spin dependent photonic structure functiong1γ(x,Q2)in the lowxregion of future linear colliders

The spin dependent structure function ${g}_{1}^{\ensuremath{\gamma}}{(x,Q}^{2})$ of the polarized photon is analyzed within the formalism based upon the unintegrated spin dependent parton distributions incorporating the LO Altarelli-Parisi evolution and the double ${\mathrm{ln}}^{2}(1/x)$ resummation at low values of Bjorken parameter x. We analyze the effects of the double ${\mathrm{ln}}^{2}(1/x)$ resummation on the behavior of ${g}_{1}^{\ensuremath{\gamma}}{(x,Q}^{2})$ in the low x region which may be accessible in future linear ${e}^{+}{e}^{\ensuremath{-}}$ and $e\ensuremath{\gamma}$ colliders. The sensitivity of the predictions on the possible nonperturbative gluon content of the polarized photons is analyzed. Predictions for spin dependent gluon distribution $\ensuremath{\Delta}{g}^{\ensuremath{\gamma}}{(x,Q}^{2})$ are also given.

Spin effects in diffractive reactions

Double spin asymmetries in the diffractive $Q \bar Q$ and $J/\Psi$ leptoproduction are discussed. It is shown that the asymmetries for longitudinally polarized lepton and longitudinally or transversely polarized proton can be used to study spin dependent gluon distribution of the proton at small $x$.

Polarized parton distribution in the relativistic quark exchange framework

The Spin dependent gluon and sea quark distributions of the proton and the neutron are extracted in the leading order (LO) and the next-to-leading order (NLO) QCD. The relativistic quark exchange model is used to calculate the related valence quark spin dependent structure function. The inverse Mellin transform technique is performed to evaluate the polarized x-dependent distributions of the gluon and the sea quark from the various moments of the valence quarks. It is shown that the calculated spin structure functions (SSF) of the proton and the neutron are in good agreement with the available data, such as E143, SMC, E142, E154 and Hermes experiments. A comparison is also made with the other theoretical models. Finally it is shown that the above calculated parton distributions improve the SSF of the proton and the neutron.

Hard processes with spin-dependent parton distributions

To test a possible color-octet contribution of heavy quarkonium productions, we propose ψ′-productions for small- p T regions, where the color-singlet ψ′ state cannot be produced by the gluon-gluon fusion owing to charge conjugation. We also point out that these processes are very useful to deduce informations of spin-dependent gluon distributions Δg.

Semi-inclusive Λc+ leptoproductions and polarized gluon distributions

In order to extract the behavior and magnitude of the spin-dependent gluon distribution, we propose a semi-inclusive $\Lambda_c^+$ production using unpolarized lepton beams and polarized proton targets. The correlation between the target proton spin and the spin of $\Lambda_c^+$ produced in the target fragmentation region might be very effective for testing various models of polarized gluons.

Diffractive [formula omitted] leptoproduction as a way to measure the polarized gluon distribution

The cross section of diffractive J Ψ lepto- (and photo-) production on a polarized target is calculated in the leading log approximation of pQCD assuming a nonrelativistic J Ψ wave function. In this approximation the spin-spin asymmetry in the small x region is close to 2ΔG G for the γ ∗ + p → J Ψ + p reaction, providing a promising tool to study the spin dependent gluon distribution ΔG( x, q 2).

The Spin-Dependent Gluon Distribution in a Proton

By using the positivity condition of distribution functions together with the unpolarized and polarized experimental data, we restrict the x dependence of the polarized gluon distribution. If we take the form of the spin-dependent gluon distribution as δG(x)=Bxγ(1−x)p as a typical form, the γ and p are restricted as γ≲ −0.3 and p≳10.

How to probe the spin-dependent gluon distributions

How to probe the spin-dependent gluon distributions

Gluon asymmetries in the leptoproduction of J/ψ

We study J/ψ production, in deep inelastic scattering experiments with polarised beams and polarised targets. The spin asymmetries are seen to depend strongly on the particular form of the spin dependent gluon distributions used. Therefore, it should be possible in these experiments, to discriminate between different parametrizations of polarised gluon distributions, and hence between the distinctly different physical pictures of the proton spin underlying these parametrizations.

Spin dependent gluon densities from largeP T photon and dimuon production

We investigate spin asymmetries in highpT photon and dimuon production and show that the spin dependent gluon density can be extracted reliably frompp collisions with these final states. The statement remains true even when the balancing jet is not observed. Hence fixed target experiments can be used to measure the spin dependent gluon density. We also compute the asymmetries in\(p\bar p\) collisions, and show that the EMC measurement of the spin structure function can be verified and the spin dependent gluon density can be extracted from these experiments.

Spin dependent gluon densities from largeP T photon and dimuon production

Spin dependent gluon densities from largeP T photon and dimuon production

Measurable effects of the spin dependent gluon distribution

The QCD interpretation of the recent EMC data on polarized muon scattering off polarized proton target indicates that the first moment of the polarized gluon distribution is large. Assuming a simple parametrization of the polarized gluon distribution satisfying this constraint, I show that a surprisingly large spin asymmetry is present in hadroproduction and photoproduction of two jets.