Measurements of lifetimes can be done in two ways. For very short lived particles, the width can be measured. For long lived ones, the lifetime can be directly measured, for example, using a displaced vertex. Practically, the lifetime cannot be extracted for particles with intermediate lifetimes. We show that for such cases information about the lifetime can be extracted for heavy colored particles that can be produced with known polarization. For example, a $t$-like particle with intermediate lifetime hadronizes into a superposition of the lowest two hadronic states, $T^*$ and $T$ (the equivalent of $B^*$ and $B$). Depolarization effects are governed by time scales that are much longer than the hadronization time scale, $\lqcd^{-1}$. After a time of order $1/Δm$, with $Δm \equiv m(T^*)-m(T)$, half of the initial polarization is lost. The polarization is totally lost after a time of order $1/Γ_γ$, with $Γ_γ= Γ(T^*\to Tγ)$. Thus, by comparing the initial and final polarization, we get information on the particle's lifetime.
Spin effects in high energy fragmentation processes can provide us with important information on hadronization mechanisms and spin structure of hadrons. It can in particular give new tests to the hadronization models. In this talk, we make a brief introduction to the different topics studied in this connection and a short summary of the available data. After that, we present a short summary of the main theoretical results we obtained in studying these different topics. The talk was mainly based on the publications [4-8] which have been finished in collaboration with C.Boros, Liu Chun-xiu and X…
We present the main theoretical aspects of the quantum mechanical string+${}^3P_0$ model of polarized quark fragmentation for pseudoscalar and vector meson production. The model is an extension of the Lund string fragmentation model that systematically includes the quark spin degree of freedom assuming the ${}^3P_0$ mechanism of quark pair production at string breaking. The recently achieved introduction of vector mesons accounts for the spin correlations between the latter and the quark of the fragmentation chain. The string+${}^3P_0$ model reproduces transverse spin effects such as the Colli…
If new TeV scale particles are discovered, it will be important to determine their width. There is, however, a problematic region, where the width is too small to be determined directly, and too large to generate a secondary vertex. For a collection of colored, spin polarized particles, hadronization depolarizes the particles prior to their decay. The amount of depolarization can be used to probe the lifetime in the problematic region. In this paper we apply this method to a realistic scenario of a top-like particle that can be produced at the LHC. We study how depolarization affects the angul…
We suggested that longitudinal polarization of Lambda produced in e+e- annihilation at LEP energies can provide useful information on hadronization mechanism in general and on testing the validity of different pictures for the spin content of baryon in describing the fragmentation process in particular. We present the results obtained from the calculations based on two very much different pictures.We compare the results with the recent ALEPH data and make suggestions for future measurements.
In this work we study the possibility that the gamma ray excess (GRE) at the Milky Way galactic center come from the annihilation of dark matter with a $(1,0)\oplus(0,1)$ space-time structure (spin-one dark matter, SODM). We calculate the production of prompt photons from initial state radiation, internal bremsstrahlung, final state radiation including the emission from the decay products of the $μ, τ$ or hadronization of quarks. Next we study the delayed photon emission from the inverse Compton scattering (ICS) of electrons (produced directly or in the prompt decay of $μ, τ$ leptons or in the…
We analyze the hadronic freeze-out in ultra-relativistic heavy ion collisions at RHIC in a transport approach which combines hydrodynamics for the early, dense, deconfined stage of the reaction with a microscopic non-equilibrium model for the later hadronic stage at which the hydrodynamic equilibrium assumptions are not valid. With this ansatz we are able to self-consistently calculate the freeze-out of the system and determine space-time hypersurfaces for individual hadron species. The space-time domains of the freeze-out for several hadron species are found to be actually four-dimensional, a…
$Λ\bar Λ$ spin correlations in high-energy collisions from quantum channels: an open quantum system view of hadronization
CERN（欧洲核子研究中心）；Instituto Galego de Física de Altas Enerxías, Universidade de Santiago de Compostela（加利西亚高能物理研究所，圣地亚哥-德孔波斯特拉大学）；EHU Quantum Center and Department of Physical Chemistry, University of the Basque Country UPV/EHU（巴斯克地区大学量子中心与物理化学系）；DIPC - Donostia International Physics Center（多诺斯蒂亚国际物理中心）；IKERBASQUE, Basque Foundation for Science（伊克尔巴斯基奎，巴斯克科学基金会）
$SU(N_c)$ colour-singlet restriction, along with flavour and spin symmetry, on thermal partonic ensemble is shown to recombine the partons with internal colour structure into colour-singlet multi-quark clusters which can be identified with various hadronic modes at a given temperature. This provides a possible basis for recombination model for hadronization of quark-gluon plasma. This also leads to a natural explanation for the ratio of (anti)protons to pions and the quark number scaling of the elliptic flow coefficient in relativistic heavy-ion collisions.
We discuss the consequence of global polarization of the produced quarks in non-central heavy-ion collisions on the spin alignment of vector mesons. We show that the alignment is quite different for different hadronization scenarios. These results can be tested directly by measuring the vector mesons' alignment through angular distributions of the decay products with respect to the reaction plane. Such angular distributions will give rise to azimuthal anisotropy $v_2$ of the decay products in the collision frame. Constraints provided by the data on the azimuthal anisotropy of hadron spectra at…
Based on the parity violation in Standard Model, we study the dependence of the lifetime on the polarization of an initial-state fermion in weak interactions. The fermion lifetime was usually calculated in terms of spin states. However, after comparing spin states with helicity states and chirality states, it is pointed out that a spin state is helicity degenerate, and the spin state and the helicity state are entirely different. Using helicity states, we calculate the lifetime of polarized muons. The result shows that the lifetime of right-handed polarized muons is always greater than that of…
The fermion lifetime was usually calculated in terms of spin states. However, after comparing spin states with helicity states and chirality states, it is pointed out that a spin state is helicity degenerate, and so it can not be used for discussion of the dependence of lifetime on the polarization of an initial-state fermion. Using helicity states, we calculate the lifetime of polarized muons. The result shows that the lifetime of right-handed polarized muons is always greater than that of left-handed polarized muons with the same speed in flight.
Heavy-quark spin precession as a magnetic field chronometer
Instituto de Ciencias Nucleares, UNAM（墨西哥国立自治大学核科学研究所）；School of Physical Sciences, National Institute of Science Education and Research（印度国家科学教育与研究学院物理科学学院）
The time evolution of Mach-like structure (the splitting of the away side peak in di-hadron $Δϕ$ correlation) is presented in the framework of a dynamical partonic transport model. With the increasing of the lifetime of partonic matter, Mach-like structure can be produced and developed by strong parton cascade process. Not only the splitting parameter but also the number of associated hadrons ($N_{h}^{assoc}$) increases with the lifetime of partonic matter and partonic interaction cross section. Both the explosion of $N_{h}^{assoc}$ following the formation of Mach-like structure and the corres…
