ترغب بنشر مسار تعليمي؟ اضغط هنا

Calculating the initial energy density in heavy ion collisions by including the finite nuclear thickness

100   0   0.0 ( 0 )
 نشر من قبل Zi-Wei Lin
 تاريخ النشر 2020
  مجال البحث
والبحث باللغة English




اسأل ChatGPT حول البحث

The initial energy density produced in heavy ion collisions can be estimated with the Bjorken energy density formula after choosing a proper formation time $tau{_{rm F}}$. However, the Bjorken formula breaks down at low energies because it neglects the finite nuclear thickness. Here we include both the finite time duration and finite longitudinal extension of the initial energy production. When $tau{_{rm F}}$ is not too much smaller than the crossing time of the two nuclei, our results are similar to those from a previous study that only considers the finite time duration. In particular, we find that at low energies the initial energy density has a much lower maximum value but evolves much longer than the Bjorken formula, while at large-enough $tau{_{rm F}}$ and/or high-enough energies our result approaches the Bjorken formula. We also find a qualitative difference in that our maximum energy density $epsilon^{rm max}$ at $tau{_{rm F}}=0$ is finite, while the Bjorken formula diverges as $1/tau{_{rm F}}$ and the previous result diverges as $ln (1/tau{_{rm F}})$ at low energies but as $1/tau{_{rm F}}$ at high energies. Furthermore, our solution of the energy density approximately satisfies a scaling relation. As a result, the $tau{_{rm F}}$-dependence of $epsilon^{rm max}$ determines the $A$-dependence, and the weaker $tau{_{rm F}}$-dependence of $epsilon^{rm max}$ in our results at low energies means a slower increase of $epsilon^{rm max}$ with $A$.



قيم البحث

اقرأ أيضاً

We calculate the cross section and transverse-momentum ($P_{bot}$) distribution of the Breit-Wheeler process in relativistic heavy-ion collisions and their dependence on collision impact parameter ($b$). To accomplish this, the Equivalent Photon Appr oximation (EPA) was generalized in a more differential way compared to the approach traditionally used for inclusive collisions. In addition, a lowest-order QED calculation with straightline assumption was performed as a standard baseline for comparison. The cross section as a function of $b$ is consistent with previous calculations using the equivalent one-photon distribution function. Most importantly, the $P_{bot}$ shape from this model is strongly dependent on impact parameter and can quantitatively explain the $P_{bot}$ broadening observed recently by RHIC and LHC experiments. This broadening effect from the initial QED field strength should be considered in studying possible trapped magnetic field and multiple scattering in a Quark-Gluon Plasma (QGP). The impact-parameter sensitive observable also provides a controllable tool for studying extreme electromagnetic fields.
In non-central relativistic heavy ion collisions, the created matter possesses a large initial orbital angular momentum. Particles produced in the collisions could be polarized globally in the direction of the orbital angular momentum due to spin-orb it coupling. Recently, the STAR experiment has presented polarization signals for $Lambda$ hyperons and possible spin alignment signals for $phi$ mesons. Here we discuss the effects of finite coverage on these observables. The results from a multi-phase transport and a toy model both indicate that a pseudorapidity coverage narrower than $|eta|< sim 1$ will generate a larger value for the extracted $phi$-meson $rho_{00}$ parameter; thus a finite coverage can lead to an artificial deviation of $rho_{00}$ from 1/3. We also show that a finite $eta$ and $p_T$ coverage affect the extracted $p_H$ parameter for $Lambda$ hyperons when the real $p_H$ value is non-zero. Therefore proper corrections are necessary to reliably quantify the global polarization with experimental observables.
Four models for the initial conditions of a fluid dynamic description of high energy heavy ion collisions are analysed and compared. We study expectation values and event-by-event fluctuations in the initial transverse energy density profiles from Pb -Pb collisions. Specifically, introducing a Fourier-Bessel mode expansion for fluctuations, we determine expectation values and two-mode correlation functions of the expansion coefficients. The analytically solveable independent point-sources model is compared to an initial state model based on Glauber theory and two models based on the Color Glass Condensate framework. We find that the large wavelength modes of all investigated models show universal properties for central collisions and also discuss to which extent general properties of initial conditions can be understood analytically.
A recently proposed method, based on quadrupole and multiplicity fluctuations in heavy ion collisions, is modified in order to take into account distortions due to the Coulomb field. This is particularly interesting for bosons produced in heavy ion c ollisions, such as $d$ and $alpha$ particles. We derive temperatures and densities seen by the bosons and compare to similar calculations for fermions. The resulting energy densities agree rather well with each other and with the one derived from neutrons. This suggests that a common phenomenon, such as the sudden opening of many reaction channels and/or a liquid gas phase transition, is responsible for the agreement.
We show that the transverse-mass and rapidity spectra of protons and pions produced in Au-Au collisions at sqrt(sNN) = 2.4 GeV can be well reproduced in a thermodynamic model assuming single freeze-out of particles from a spherically symmetric hypers urface. This scenario corresponds to a physical picture used by Siemens and Rasmussen in the original formulation of the blast-wave model. Our framework modifies and extends this approach by incorporation of a Hubble-like expansion of QCD matter and inclusion of resonance decays. In particular, the Delta(1232) resonance is taken into account, with a width obtained from the virial expansion. Altogether, our results bring evidence for substantial thermalization of the matter produced in heavy-ion collisions in a few GeV energy regime and its nearly spherical expansion.
التعليقات
جاري جلب التعليقات جاري جلب التعليقات
سجل دخول لتتمكن من متابعة معايير البحث التي قمت باختيارها
mircosoft-partner

هل ترغب بارسال اشعارات عن اخر التحديثات في شمرا-اكاديميا