Subscribe to the gold package and get unlimited access to Shamra Academy
Register a new userRevisiting spin alignment of heavy mesons in its inclusive production
136
0
0.0
(
0
)
Authors
J.P.Ma
Ask ChatGPT about the research
No Arabic abstract
In the heavy quark limit inclusive production rate of a heavy meson can be factorized, in which the nonperturbative effect related to the heavy meson can be characterized by matrix elements defined in the heavy quark effective theory. Using this factorization, predictions for the full spin density matrix of a spin-1 and spin-2 meson can be obtained and they are characterized only by one coefficient representing the nonperturbative effect. Predictions for spin-1 heavy meson are compared with experiment performed at $e^+e^-$ colliders in the energy range from $sqrt{s}=10.5$GeV to $sqrt{s}=91$GeV, a complete agreement is found for $D^*$- and $B^*$-meson. For $D^{**}$ meson, our prediction suffers a large correction, as indicated by experimental data. There exists another approach by taking heavy mesons as bound systems, in which the total angular momentum of the light degrees of freedom is 1/2 and 3/2 for spin-1 and spin-2 meson respectively, then the diagonal parts of spin density matrices can be obtained. However, there are distinct differences in the predictions from the two approaches and they are discussed in detail.
rate research
Read More
We develop a formalism for computing inclusive production cross sections of heavy quarkonia based on the nonrelativistic QCD and the potential nonrelativistic QCD effective field theories. Our formalism applies to strongly coupled quarkonia, which include excited charmonium and bottomonium states. Analogously to heavy quarkonium decay processes, we express nonrelativistic QCD long-distance matrix elements in terms of quarkonium wavefunctions at the origin and universal gluonic correlators. Our expressions for the long-distance matrix elements are valid up to corrections of order $1/N_c^2$. These expressions enhance the predictive power of the nonrelativistic effective field theory approach to inclusive production processes by reducing the number of nonperturbative unknowns, and make possible first-principle determinations of long-distance matrix elements once the gluonic correlators are known. Based on this formalism, we compute the production cross sections of $P$-wave charmonia and bottomonia at the LHC, and find good agreement with measurements.
We study inclusive production of doubly heavy baryon at a $e^+e^-$ collider and at hadron colliders through fragmentation. We study the production by factorizing nonpertubative- and perturbative effects. In our approach the production can be thought as a two-step process: A pair of heavy quarks can be produced perturbatively and then the pair is transformed into the baryon. The transformation is nonperturbative. Since a heavy quark moves with a small velocity in the baryon in its rest frame, we can use NRQCD to describe the transformation and perform a systematic expansion in the small velocity. At the leading order we find that the baryon can be formed from two states of the heavy-quark pair, one state is with the pair in $^3S_1$ state and in color ${bf bar 3}$, another is with the pair in $^1S_0$ state and in color ${bf 6}$. Two matrix elements are defined for the transformation from the two states, their perturbative coefficients in the contribution to the cross-section at a $e^+e^-$ collider and to the function of heavy quark fragmentation are calculated. Our approach is different than previous approaches where only the pair in $^3S_1$ state and in color ${bf bar 3}$ is taken into account. Numerical results for $e^+e^-$ colliders at the two $B$-factories and for hadronic colliders LHC and Tevatron are given.
The spin alignment matrix element rho_{00} for the vector mesons K^{*0} and phi(1020) has been measured in RHIC at central rapidities. These measurements are consistent with the absence of polarization with respect to the reaction plane in mid-central Au + Au collisions whereas, when measured with respect to the production plane in the same reactions and in p + p collisions, a non-vanishing and p_perp-dependent rho_{00} is found. We show that this behavior can be understood in a simple model of vector meson production where the spin of their constituent quarks is oriented during hadronization as the result of Thomas precession.
After an introduction motivating the study of quarkonium production, we review the recent developments in the phenomenology of quarkonium production in inclusive scatterings of hadrons and leptons. We naturally address data and predictions relevant for the LHC, the Tevatron, RHIC, HERA, LEP, B factories and EIC. An up-to-date discussion of the contributions from feed downs within the charmonium and bottomonium families as well as from b hadrons to charmonia is also provided. This contextualises an exhaustive overview of new observables such as the associated production along with a Standard Model boson (photon, W and Z), with another quarkonium, with another heavy quark as well as with light hadrons or jets. We address the relevance of these reactions in order to improve our understanding of the mechanisms underlying quarkonium production as well as the physics of multi-parton interactions, in particular the double parton scatterings. An outlook towards future studies and facilities concludes this review.
We show that the cross section for inclusive charm production exhibits geometric scaling in a large range of photon virtualities. In the HERA kinematic domain the saturation momentum $Q_{sat}^2(x)$ stays below the hard scale $mu_c^2=4m_c^2$, implying charm production probing mostly the color transparency regime and unitarization effects being almost negligible. We derive our results considering two saturation models which are able to describe the DESY ep collider HERA data for the proton structure function at small values of the Bjorken variable $x$. A striking feature is the scaling on $tau=Q_2^2/Q_{sat}^2(x)$ above saturation limit, corroborating recent theoretical studies.
Log in to be able to interact and post comments
comments
Fetching comments
Sign in to be able to follow your search criteria
