arXiv subjects

Jacques Soffer

Publications and source records attributed to Jacques Soffer.

At least 73 records · Page 4Linked to original sources

arXiv2003

Transverse single-spin asymmetries in gauge boson production

Transverse single-spin asymmetries (SSA) in inclusive reactions are now considered to be directly related to the transverse momentum $k_{T}$ of the fundamental partons involved in the process. Several possible leading-twist QCD mechanisms have been proposed to explain the available data, in particular the Sivers effect which was resurrected recently. We show that from the measurement of transverse SSA in inclusive production of gauge bosons, one can learn more about the Sivers functions and possibly to achieve a reliable flavor separation.

hep-ph↗

arXiv2002

Looking into the Future of Spin and QCD

Several stimulating open questions in high energy spin physics will be described together with the striking progress recently achieved in this field. In view of the new experimental facilities and the new tools, soon available, I will try to anticipate what we will learn next. The prospects for the future are excellent and clearly, some exciting times are ahead of us.

hep-ph↗

arXiv2002

Impact-Picture Phenomenology for $π^{\pm}p, K^{\pm}p$ and $pp, \bar p p$

We present an extension to $π^{\pm} p$ and $K^{\pm} p$ elastic scattering at high energies of the impact-picture phenomenology we first proposed more than twenty years ago, for $p p$ and $\bar p p$ elastic scattering. We show, in particular, that the analytic form of the opacity function for the proton obtained previously is compatible with the experimental results on $πp$ and $K p$ elastic scattering at high energies. It is proposed that $π^{\pm}$ and $K^{\pm}$ external beams be provided from CERN-LHC, so that their elastic scattering from protons can be studied at higher energies. Our phenomenology for $p p$ and $\bar p p$ elastic scattering is updated by including new data and we give predictions for future experiments at BNL-RHIC and CERN-LHC.

hep-ph↗

arXiv2002

Phenomenological Relation between Distribution and Fragmentation Functions

We study the relation between the quark distribution function q(x) and the fragmentation function D_q(z) based on a general form D_q(x) = C(z)z^{alpha}q(z) for valence and sea quarks. By adopting two known parametrizations of quark distributions for the proton, we find three simple options for the fragmentation functions that can provide a good description of the available experimental data on proton production in e^+ e^- inelastic annihilation. These three options support the revised Gribov-Lipatov relation D_q(z) = z q(z) at z --> 1, as an approximate relation for the connection between distribution and fragmentation functions. The three options differ in the sea contributions and lead to distinct predictions for antiproton production in the reaction p+p --> p-bar+X, thus they are distinguishable in future experiments at RHIC-BNL.

hep-ph↗

arXiv2002

Bjorken sum rule at low Q^2

A description of the generalized Gerasimov-Drell-Hearn sum rules for proton and neutron is suggested, using their relation to the Bjorken sum rule. The results support an earlier conjecture, that the structure function g_T features a smooth Q^2-dependence, while the structure function g_2 is changing rapidly, due to the elastic contribution to the Burkhardt-Cottingham sum rule. A possible violation of this later sum rule is briefly discussed.

hep-ph↗

arXiv2002

Virtual photon structure functions and positivity constraints

We study the three positivity constraints among the eight virtual photon structure functions, derived from the Cauchy-Schwarz inequality and which are hence model-independent. The photon structure functions obtained from the simple parton model show quite different behaviors in a massive quark or a massless quark case, but they satisfy, in both cases, the three positivity constraints. We then discuss an inequality which holds among the unpolarized and polarized photon structure functions $F_1^γ$, $g_1^γ$ and $W_{TT}^τ$, in the kinematic region $Λ^2\ll P^2 \ll Q^2$, where $-Q^2 (-P^2)$ is the mass squared of the probe (target) photon, and we examine whether this inequality is satisfied by the perturbative QCD results.

hep-ph↗

arXiv2002

Accessing Transversity in Double-Spin Asymmetries at the BNL-RHIC

We give upper bounds for transverse double-spin asymmetries in polarized proton-proton collisions by saturating the positivity constraint for the transversity densities at a low hadronic resolution scale. We consider prompt photon, jet, pion, and heavy flavor production at the BNL Relativistic Heavy Ion Collider (RHIC). Estimates of the expected statistical accuracy for such measurements are presented, taking into account the acceptance of the RHIC detectors.

hep-ph↗

arXiv2001

New prospects for polarized hyperon fragmentation functions

We study the inclusive production of $Λ$ ($\bar Λ$) in several high energy collision processes ($e^+e^-, e^{\pm}p, ν(\bar ν)p, pp$), in view of an accurate determination of the unpolarized and polarized fragmentation functions of a quark into a $Λ$ ($\bar Λ$). For polarized fragmentation functions the inaccuracy and the scarcity of present data do not allow to distinguish between various theoretical models. We will indicate how future measurements will provide ways to discriminate between them and also how to achieve a necessary quark flavor separation. A possible extension to the production of the other hyperons ($Σ^{\pm,0}, Ξ^{-,0}$), will be also briefly discussed.

hep-ph↗

arXiv2001

Helicity and Transversity Distribution of Nucleon and $Λ$-Hyperon from $Λ$ Fragmentation

It is shown that $Λ$-hyperon fragmentation in charged lepton deep inelastic scattering (DIS) on a polarized nucleon target can provide sensitive information concerning the quark helicity and transversity distributions for both nucleon and $Λ$-hyperon at large $x$. Numerical predictions are given for the spin transfers of the produced $Λ$, when the target nucleon is polarized either longitudinally or transversely, and with the nucleon and $Λ$ quark distributions evaluated both in an SU(6) quark-spectator-diquark model and in a perturbative QCD (pQCD) based model. It is also shown that the predicted spin transfers have different behaviors for proton and neutron targets, and this can provide sensitive tests of different predictions for the quark helicity and transversity distributions of the $d$ valence quark of the proton at large $x$.

hep-ph↗

arXiv2001

Quark Distributions of Octet Baryons from SU(3) Symmetry

SU(3) symmetry relations between the octet baryons are introduced in order to connect both the unpolarized and polarized quark distributions of the octet baryons with those of the nucleon. Two different parametrizations of the nucleon quark distributions are used. A new scenario of quark flavor and spin structure of the $Λ$ is found and compared with two other models: a perturbative QCD based analysis and a quark diquark model. The $u$ and $d$ quarks inside the $Λ$ are predicted to be positively polarized at large Bjorken variable $x$ in the new scenario. By using an approximate relation connecting the quark fragmentation functions with the quark distributions, the hadron polarizations of the octet baryons in $e^+e^-$-annihilation, polarized charged lepton deep inelastic scattering (DIS) processes, and neutrino (antineutrino) DIS processes are predicted. The predictions for $Λ$ polarizations in several processes are compatible with the available data at large fragmentation momentum fraction $z$, and support the prediction of positively polarized $u$ and $d$ quarks inside the $Λ$ at large $x$. Predictions for Drell-Yan processes from $Σ^{\pm}$ and $Ξ^-$ beams on an isoscalar target are also given and discussed.

hep-ph↗

arXiv2001

Spin Transfers for Baryon Production in Polarized pp Collisions at RHIC-BNL

We consider the inclusive production of longitudinally polarized baryons in ${\vec p}p$ collisions at RHIC-BNL, with one longitudinally polarized proton. We study the spin transfer between the initial proton and the produced baryon as a function of its rapidity and we elucidate its sensitivity to the quark helicity distributions of the proton and to the polarized fragmentation functions of the quark into the baryon. We make predictions using an SU(6) quark spectator model and a perturbative QCD (pQCD) based model. We discuss these different predictions, and what can be learned from them, in view of the forthcoming experiments at RHIC-BNL.

hep-ph↗

arXiv2000

CP-violation in high-energy collisions of polarized protons

We study the possibility of a large CP/T-violation in lepton pair production in the collisions of polarized protons at RHIC-BNL. We propose the single transverse spin asymmetry which quantifies the possible CP/T-violating effect in this reaction as a sensitive indicator of physics beyond the standard model(SM). We consider two examples of mechanisms beyond the SM which can generate a non-zero asymmetry of this type. They rely on the R-parity violating interactions of supersymmetric models and on phenomenological tensor interactions. We estimate the prospects for observing this effect in future experiments.

hep-ph↗

arXiv2000

The Flavor and Spin Structure of Hyperons from Quark Fragmentation

We systematically study the hadron longitudinal polarizations of the octet baryons at large $z$ from quark fragmentations in $e^+e^-$-annihilation, polarized charged lepton deep inelastic scattering (DIS) process, and neutrino (antineutrino) DIS process, based on predictions of quark distributions for the octet baryons in the SU(6) quark-spectator-diquark model and a perturbative QCD based counting rule analysis. We show that the $e^+e^-$-annihilation and polarized charged lepton DIS process are able to distinguish between the two different predictions of the hyperon polarizations. We also find that the neutrino/antineutrino DIS process is ideal in order to study both the valence content of the hyperons and the antiquark to hyperon (quark to anti-hyperon) fragmentations, which might be related to the sea content of hyperons.

hep-ph↗

arXiv2000

Prospects for Spin Physics at RHIC

Colliding beams of 70% polarized protons at up to $\sqrt{s}$=500 GeV, with high luminosity, L=2$\times10^{\rm 32}$ cm$^{-2}$sec$^{-1}$, will represent a new and unique laboratory for studying the proton. RHIC-Spin will be the first polarized-proton collider and will be capable of copious production of jets, directly produced photons, and $W$ and $Z$ bosons. Features will include direct and precise measurements of the polarization of the gluons and of $\bar{u}$, $\bar{d}$, $u$, and $d$ quarks in a polarized proton. Parity violation searches for physics beyond the standard model will be competitive with unpolarized searches at the Fermilab Tevatron. Transverse spin will explore transversity for the first time, as well as quark-gluon correlations in the proton. Spin dependence of the total cross section and in the Coulomb nuclear interference region will be measured at collider energies for the first time. These qualitatively new measurements can be expected to deepen our understanding of the structure of matter and of the strong interaction.

hep-ph↗

arXiv2000

The Quark-Antiquark Asymmetry of the Nucleon Sea from $Λ$ and $\barΛ$ Fragmentation

We present a general analysis of the spin transfer for $Λ$ and $\barΛ$ production in deep-inelastic scattering of polarized charged leptons on the nucleon, and find that the pattern of different behaviors of $Λ$ and $\barΛ$ production observed by the E665 Collaboration suggests the possibility of quark-antiquark asymmetries either in the quark to $Λ$ fragmentation functions and/or in the quark and antiquark distributions of the target proton. We also point out that the strange-antistrange asymmetry of the nucleon sea may produce an observable contribution to the different behaviors of $Λ$ and $\barΛ$ production. We find that a softer $\bar{s}(x)$ than $s(x)$ as predicted by the light-cone baryon-meson fluctuation model of intrinsic quark-antiquark pairs of the nucleon sea might lead to a reasonable picture. However, the magnitude is still too small to explain the E665 data and the conclusion has also strong model-dependence. This may suggest the importance of quark-antiquark asymmetry in the quark to $Λ$ fragmentation functions, provided that the E665 data are confirmed.

hep-ph↗

arXiv2000

$Λ$, $\barΛ$ Polarization and Spin Transfer in Lepton Deep-Inelastic Scattering

The flavor and helicity distributions of the $Λ$ and $\barΛ$ hyperons for both valence and sea quarks are calculated in a perturbative QCD (pQCD) based model. We relate these quark distributions to the fragmentation functions of the $Λ$ and $\barΛ$, and calculate the $z$-dependence of the longitudinal spin transfer to the $Λ$ and $\barΛ$ in lepton deep-inelastic scattering (DIS). It is shown that the spin transfer to the $Λ$ is compatible with the first HERMES results at DESY and further tests are suggested. We also make predictions for the $z$-dependence of the $Λ$ and $\barΛ$ longitudinal polarizations in neutrino (antineutrino) DIS processes. We investigate the sea contribution to the fragmentation functions, and we test a possible scenario where sea quarks in $Λ$ (or sea antiquarks in $\barΛ$) are negatively polarized, whereas sea antiquarks in the $Λ$ (or sea quarks in $\barΛ$) are positively polarized. The asymmetry of the polarized fragmentation functions of sea quarks and antiquarks to $Λ$ and $\barΛ$ provides a way to understand the different behaviour between the $Λ$ and $\barΛ$ spin transfers observed in the recent E665 experiment at FNAL.

hep-ph↗

arXiv1999

Quark Flavor Separation in $Λ$-Baryon Fragmentation

It is shown that neutrino and antineutrino deep inelastic scattering of unpolarized and polarized $Λ$ and $\barΛ$ productions, can provide a clean separation of unpolarized and polarized fragmentation functions of a quark into a $Λ$, for both light-flavor quarks and antiquarks and also for strange quarks. Combining with $Λ$ and $\barΛ$ productions in polarized electron deep inelastic scattering, one can systematically measure or check the various flavor and spin dependent fragmentation functions. Such measurements can provide crucial tests of different predictions concerning the spin structure of hadrons and the quark-antiquark asymmetry of the nucleon sea.

hep-ph↗

arXiv1998

The Quark Spin Distributions of the Nucleon

The quark helicity measured in polarized deep inelastic scattering is different from the quark spin in the rest frame of the nucleon. We point out that the quark spin distributions $Δq_{RF}(x)$ are connected with the quark helicity distributions $Δq(x)$ and the quark transversity distributions $δq(x)$ by an approximate relation: $Δq_{RF}(x) + Δq(x)=2 δq(x)$. This relation will be useful in order to measure the rest frame (or quark model) spin distributions of the nucleon once the quark helicity distributions and quark transversity distributions are themselves measured. We also calculate the $x$-dependent quark transversity distributions $δq(x)$ and quark spin distributions $Δq_{RF}(x)$ in a light-cone SU(6) quark-spectator model, and present discussions on possible effect from the sea quark-antiquark pairs.

hep-ph↗