Jet Handedness Research Articles

Handedness correlation from quark polarization

Jet handedness as a measure of quark and/or gluon polarizations has been proposed for nearly 30 years. It was demonstrated by measuring the correlation of jet handedness in the electron positron annihilation process. Once parameters are determined, the method could be used to measure quark and/or gluon polarizations in other experiments. The reported data provided evidence for the jet handedness and handedness correlation. However, the jet handedness correlation measured in the electron positron annihilation process from the opposite jets contradicts theoretical prediction by a sign. In order to explain this, we present a chromo-hydrogen-like model in this paper. According to calculations, both jet handedness and handedness correlation depend on not only the polarization of the fragmenting valence quark but also the polarization of the sea quark. It is the appearance of the sea quark polarization that can solve the contradiction. In other words, measurements of jet handedness and handedness correlation can be used to determine the sea quark polarization.

Dihadron fragmentation functions in the quark-jet model: Longitudinally polarized quarks

We study the dihadron fragmentation functions (DiFF) of longitudinally polarized quarks into pion pairs. The quark-jet framework is used to model the sequential hadronization of a polarized quark into hadrons, where the polarization transfer to the remnant quark in each hadron emission step is calculated using the spin density matrix formalism. Using Monte Carlo (MC) simulations of the hadronization process, we find a nonvanishing helicity dependent DiFF, $G_1^\perp$ , which is also related to the longitudinal jet handedness. A method is developed for extracting the angular moments of this DiFF, which enter the expressions for the azimuthal asymmetries for an electron-positron annihilation process into two pairs of hadrons from back-to-back jets and the dihadron production in semi-inclusive deep inelastic scattering. Finally, we derive explicit integral expressions for DiFFs where only two hadrons are emitted by a quark and use them to validate our MC results for both unpolarized and helicity dependent DiFFs.

Di-hadron fragmentation and mapping of the nucleon structure

The fragmentation of a colored parton directly into a pair of colorless hadrons is a non-perturbative mechanism that offers important insights into the nucleon structure. Di-hadron fragmentation functions can be extracted from semi-inclusive electron-positron annihilation data. They also appear in observables describing the semi-inclusive production of two hadrons in deep-inelastic scattering of leptons off nucleons or in hadron-hadron collisions. When a target nucleon is transversely polarized, a specific chiral-odd di-hadron fragmentation function can be used as the analyzer of the net density of transversely polarized quarks in a transversely polarized nucleon, the so-called transversity distribution. The latter can be extracted through suitable single-spin asymmetries in the framework of collinear factorization, thus in a much simpler framework with respect to the traditional one in single-hadron fragmentation. At subleading twist, the same chiral-odd di-hadron fragmentation function provides the cleanest access to the poorly known twist-3 parton distribution $e(x)$, which is intimately related to the mechanism of dynamical chiral symmetry breaking in QCD. When sensitive to details of transverse momentum dynamics of partons, the di-hadron fragmentation functions for a longitudinally polarized quark can be connected to the longitudinal jet handedness to explore possible effects due to $CP-$violation of the QCD vacuum. In this review, we outline the formalism of di-hadron fragmentation functions, we discuss different observables where they appear and we present measurements and future worldwide plans.

Vorticity and hydrodynamic helicity in heavy-ion collisions in the hadron-string dynamics model

The hydrodynamic helicity separation effect in noncentral heavy-ion collisions is investigated using the hadron-string dynamics (HSD) model. Computer simulations are done to calculate velocity and hydrodynamic helicity on a mesh in a small volume around the center of the reaction. The time dependence of hydrodynamic helicity is observed for various impact parameters and different calculation methods. Comparison with a similar earlier work is carried out. A new quantity related to jet handedness is used to probe for $p$-odd effects in the final state.

Interference fragmentation functions in electron-positron annihilation

We study the process of electron-positron annihilation into back-to-back jets, where in each jet a pair of hadrons is detected. The orientation of these two pairs with respect to each other can be used to extract the interference fragmentation functions in a clean way, for instance from BELLE or BABAR experiment data. This is of relevance for studies of the transversity distribution function. In particular, we focus on two azimuthal asymmetries. The first one has already been studied by Artru and Collins, but is now expressed in terms of interference fragmentation functions. The second asymmetry is new and involves a function that is related to longitudinal jet handedness. This asymmetry offers a different way of studying handedness correlations.

How could the proton transversity be measured

The perspectives of two new nonstandard methods of transversal quark polarization measurement are considered: the jet handedness and the so-called "Collins effect" due to spin dependent T-odd fragmentation function responsible for the left-right asymmetry in fragmenting of transversally polarized quarks. Recent experimental indications in favor of these effects are observed: 1.The correlation of the T-odd one-particle fragmentation functions found by DELPHI in $Z\to 2$-jet decay. Integrated over the fraction of longitudinal and transversal momenta, this correlation is of 1.6% order, which means order of 13% for the analyzing power. 2.A rather large ($\approx10%$) handedness transversal to the production plane observed in the diffractive production of ($\pi^-\pi^+\pi^-$) triples from nuclei by the $40 {\rm GeV/c}$ $\pi^-$--beam. It shows a clear dynamic origin and resembles the single spin asymmetry behavior. All this makes us hope to use these effects in polarized DIS experiments for transversity measurement. The first estimation of transversity was done by using the azimuthal asymmetry in semi-inclusive DIS recently measured by HERMES and SMC.

QCD tests with polarized beams

We present three QCD studies performed by the SLD experiment at SLAC, utilizing the highly polarized SLC electron beam. We examined particle production differences in light quark and antiquark hemispheres, and observed more high momentum baryons and K−'s than antibaryons and K+'s in quark hemispheres, consistent with the “leading particle” hypothesis. We performed a search for jet handedness in light q- and q¯-jets. Assuming Standard Model values of quark polarization in Z0 decays, we have set an improved upper limit on the analysing power of the handedness method. We studied the correlation between the Z0 spin and the event-plane orientation in polarized Z0 decays into three jets. The CP-even and T-odd triple product S → Z ⋅ ( k → 1 × k → 2 ) formed from the two fastest jet momenta, k → 1 and k → 2 , and the Z0 polarization vector S → Z , is sensitive to physics beyond the Standard Model.

CP-violating effect of QCD vacuum in quark fragmentation

We demonstrate that the non-trivial CP-violating structure of QCD vacuum can lead to an observable effect in e +e − → q q → 2- jet annihilation. We find that the sign of the jet handedness correlation can be opposite to that predicted by factorization of q q fragmentation and CP-conjugation of the two jets. A simple model estimation of the handedness correlation magnitude is given.

A search for jet handedness in hadronic Z0 decays

We have searched for signatures of polarization of partons in hadronic jets from Z 0 → qq¯ decays using the ‘jet handedness’ method. We find no evidence for jet handedness in a sample of light quark jets. We set an upper limit of 9.1% on magnitude of the analyzing power of this technique at the 95% C.L. We have studied an alternative definition of jet handedness and found no signal.

Search for jet handedness in hadronic Z0 decays.

We have searched for signatures of polarization in hadronic jets from $Z^0 \to q \bar{q}$ decays using the ``jet handedness'' method. The polar angle asymmetry induced by the high SLC electron-beam polarization was used to separate quark jets from antiquark jets, expected to be left- and right-polarized, respectively. We find no evidence for jet handedness in our global sample or in a sample of light quark jets and we set upper limits at the 95% C.L. of 0.063 and 0.099 respectively on the magnitude of the analyzing power of the method proposed by Efremov {\it et al.}

Study of parton spin-dependent distributions in hard proton-proton collisions through measurement of handedness

Polarization of partons emitted in hard scattering of an unpolarized proton beam from a polarized hydrogen target can be found through a measurement of jet handedness. Two definitions of handedness are suggested with zero and essentially nonzero contributions of gluon jets. A sensitivity of the handedness to the valence, sea quark and gluon distributions is considered. Handedness properties under the charge conjugation and flavorSU (2) transformations are investigated. An option to study the spin-dependent parton distributions in hard scattering of the unpolarized HERA proton beam from the polarized internal hydrogen target is discussed.

Determining the polarized parton distributions of the proton via jet handedness

We study some phenomenological aspects of the recently suggested concept of jet handedness. It is shown that it offers a promising possibility to uncover the parton distributions of transversely or longitudinal polarized protons.

Jet handedness as a measure of quark and gluon polarization

We introduce a new concept, the handedness of a jet, which can be used to determine the polarization of a high-energy quark or gluon produced in a hard collision. The method can be tested in e +e - → 2 jets at the Z 0 peak where the polarization of the emerging quarks is known and correlation between jet handedness and parton polarization could be determined. Subsequently, this correlation could be used in other contexts to determine the parton polarization from a measurement of jet handedness. In particular, the method could be very useful for measuring quark and gluon polarization and the quark “transversity” distribution in the proton.