The ratio of (pseudo)rapidity density of transverse energy and the (pseudo)rapidity density of charged particles, which is a measure of the mean transverse energy per particle, is an important observable in high energy heavy-ion collisions, which reveals about the mechanism of particle production and the freeze-out criteria. Its collision energy and centrality dependence is exactly like the chemical freeze-out temperature till top RHIC energy. The LHC measurement at $\sqrt{s_{NN}}$ = 2.76 TeV brings up new challenges to rule out the mechanisms of gluon saturation or non-equilibrium phenomena being prevalent at high energies, which could contribute to the above observable. The Statistical Hadron Gas Model (SHGM) with a static fireball approximation has been successful in describing both the centrality and energy dependence till top RHIC energies. However, the SHGM predictions for higher energies are highly underestimated by the LHC data. In order to understand this, we have incorporated radial flow effect in an excluded volume SHGM. The hard-core radius of baryons at lower collision energies plays an important role in the description of a hadronic system. In view of this, in order to make a complete energy dependence study from FAIR to LHC energies, we have considered an excluded volume SHGM. Our studies suggest that the collective flow plays an important role in describing $E_{T}/N_{ch}$ and it could be one of the possible parameters to explain the jump observed in $E_{T}/N_{ch}$ from RHIC to LHC energies. Predictions for the LHC measurements at $\sqrt{s_{NN}}$ = 5.02 TeV are given.
Motivated by the first measurements of the experiment CMS at the LHC at $\sqrt{s}=0.9$ and 2.36 TeV, we discuss energy dependence of average transverse momentum of the secondary particles in hadron production in pp collisions. We suggest a possible explanation of this dependence as a result of collective rotation of the transient state and associate its further possible decrease with flattening off at higher energies with transition to the genuine QGP state of matter.
The charged-particle multiplicity distribution and the transverse-energy distribution measured in heavy-ion collisions at top RHIC and LHC energies are described using the two-component model approach based on a convolution of the Monte Carlo Glauber model with the Weibull model for particle production. The model successfully describes the multiplicity and transverse-energy distribution of minimum-bias collision data for a wide range of energies. The Weibull-Glauber model can be used to determine the centrality classes in heavy-ion collisions as an alternative to the conventional negative bino…
We calculate the $n$th order of $2k$-particle azimuthal cumulants $c_n\{2k\}$ based on transverse momentum conservation (TMC) and collective flow $v_n$(n=2,3). We demonstrate that the TMC effect only leads to a nonzero $c_n\{2k\}$ with the sign of $(-1)^{nk}$ and the magnitude inversely proportional to $(N-2k)^{nk}$. The interplay between TMC and collective flow can change the signs of $c_2\{4\}$, $c_3\{2\}$ and $c_3\{4\}$ at some values of multiplicity $N$, which could provide a good probe to study the onset of collectivity and search for the substructure of proton in small colliding systems.
In the present work, we study the recent collision energy and multiplicity dependence of the charged particle transverse momentum spectra as measured by the ALICE collaboration in $pp$ collisions at $\sqrt{s}$ = 5.02 and 13 TeV using the non-extensive Tsallis distribution and the Boltzmann-Gibbs Blast Wave (BGBW) model. A thermodynamically consistent form of the Tsallis distribution is used to extract the kinetic freeze-out parameters from the transverse momentum spectra of charged particles at mid-rapidity. In addition, a comprehensive study of fitting range dependence of transverse momentum …
We study the charged particle and transverse energy production mechanism from AGS, SPS, RHIC to LHC energies in the framework of nucleon and quark participants. At RHIC and LHC energies, the number of nucleons-normalized charged particle and transverse energy density in pseudorapidity, which shows a monotonic rise with centrality, turns out to be an almost centrality independent scaling behaviour when normalized to the number of participant quarks. A universal function which is a combination of logarithmic and power-law, describes well the charged particle and transverse energy production both…
We review the charged particle and photon multiplicity, and transverse energy production in heavy-ion collisions starting from few GeV to TeV energies. The experimental results of pseudorapidity distribution of charged particles and photons at different collision energies and centralities are discussed. We also discuss the hypothesis of limiting fragmentation and expansion dynamics using the Landau hydrodynamics and the underlying physics. Meanwhile, we present the estimation of initial energy density multiplied with formation time as a function of different collision energies and centralities…
Transverse momentum spectra of the reaction products from proton-proton and nucleus-nucleus collisions are discussed within the phenomenological frameworks of statistical phase-space and string fragmentation models. It will be shown that a string fragmentation model can accommodate all of the observations discussed here and consequently it is claimed that no conclusion about the thermal nature or collective expansion of the created system may be derived from observed transverse momentum spectra.
In the framework of a multisource thermal model, we describe experimental results of the transverse momentum spectra of final-state light flavour particles produced in gold-gold (Au-Au), copper-copper (Cu-Cu), lead-lead (Pb-Pb), proton-lead ($p$-Pb), and proton-proton ($p$-$p$) collisions at various energies, measured by the PHENIX, STAR, ALICE, and CMS Collaborations, by using the Tsallis-standard (Tsallis form of Fermi-Dirac or Bose-Einstein), Tsallis, and two- or three-component standard distributions which can be in fact regarded as different types of "thermometers" or "thermometric scales…
Charged Higgs boson may be produced at hadron colliders via the decay of top quarks. At the LHC, The large production cross section of top quarks pairs will make it one of the earliest channels allowing to search for physics beyond the standard model. Assuming the decay $H^+ \to τ^+ν$, previous searches have so far considered only hadronic tau decays. Here we show that by using appropriate kinematical variables (transverse mass observables), leptonic tau decays can be used as well, for both observing and possibly measuring the mass of the charged Higgs boson. This can increase the overall expe…
The preliminary NA49 results on the energy dependence of transverse momentum fluctuations over the whole SPS energy range exhibit an unexpected effect. The $Φ_{p_{T}}$ fluctuation measure - used by the NA49 experiment - manifests a different behavior for different charge combinations. Whereas the $Φ_{p_{T}}$ is consistent with zero and independent of energy for negatively charged particles, it significantly increases for both all charged and positively charged particles at lower SPS energies. The string-hadronic model UrQMD is applied here to explain this effect. The UrQMD simulations show tha…
We find that collective flow model which can successfully analyze charged particle distributions at AGS and lower SPS (less than 20Gev/n). but fails to analyze that of at RHIC. The tails of distribution of charged particle at RHIC has a jump from the collective flow model calculation as the energy increases. Thermalization Component Model is presented based on collective flow to study the multiplicity distributions at RHIC in this paper. It is realized that the region of phase space of collective flow can reflect that of thermalization region. By comparing the contributions of particle product…
Transverse Momentum, $p_T$, spectra is of prime importance in order to extract crucial information about the evolution dynamics of the system of particles produced in the collider experiments. In this work, the transverse momentum spectra of charged hadrons produced in $PbPb$ collision at $5.02$ TeV has been analyzed using different distribution functions in order to gain strong insight into the information that can be extracted from the spectra. We have also discussed the applicability of Pearson distribution on the spectra of charged hadron at $5.02$ TeV.
For beam energies from SPS to RHIC, the transverse energy per charged particle, $E_T/N_{\textrm{ch}}$, saturates at a value of approximately 0.8 GeV. A direct connection between this value and the freeze-out criterium $E/N \approx 1$ GeV for the primordial energy and particle number in the hadronic resonance gas model is established.
We present our analysis of the available experimental data on correlation between mean transverse momentum and charged particles multiplicity ($\langle p_T \rangle$-$N_{ch}$) at central rapidity in $pp$ and $p\bar{p}$ collisions at $\sqrt{s}$ from 17 GeV to 7 TeV. A multi-pomeron exchange model based on Regge-Gribov approach provides quantitative description of $\langle p_T \rangle$-$N_{ch}$ correlation data and their energy dependence. Results are found to be in agreement with string fusion model hypothesis.
The spin of the $τ$ lepton in the semiletonic process ${\bar{B}}^0\rightarrow D^{+} τ^- {\barν}$ can be polarized in the direction which is normal to the reaction plane, if the charged Higgs boson exists and its coupling to quarks has a complex phase. We calculate this transverse polarization of the $τ$ lepton by using the experimentally measured $B$ to $D$ transition form factors.
The centrality dependence of the charged multiplicity, transverse energy, and elliptic flow coefficient is studied in a hydrodynamic model, using a variety of different initializations which model the initial energy or entropy production process as a hard or soft process, respectively. While the charged multiplicity depends strongly on the chosen initialization, the p_t-integrated elliptic flow for charged particles as a function of charged particle multiplicity and the p_t-differential elliptic flow for charged particles in minimum bias events turn out to be almost independent of the initial …
The transverse energy and the charged particle multiplicity at midrapidity are evaluated in a single-freeze-out model for different centrality bins at RHIC at $\sqrt{s_{NN}}=130$ and 200 GeV. The predictions of the model are done at the freeze-out parameters determined earlier from measured particle yields and $p_{T}$ spectra. The results agree qualitatively well with the experimental data.
Transverse momentum spectra, $d^2σ/(dηdp_T^2)$, of charged hadron production in $pp$-collisions are considered in terms of a recently introduced two component model. The shapes of the particle distributions vary as a function of c.m.s. energy in the collision and the measured pseudorapidity interval. In order to extract predictions on the double-differential cross-sections $d^2σ/(dηdp_T^2)$ of hadron production for future LHC-measurements the different sets of available experimental data have been used in this study.
In this study, we systematically investigate deformed Xe-Xe collisions at 5.44 TeV center of mass energy. We exploit the Monte Carlo HYDJET++ model to compute transverse momentum ($p_{T}$) distribution, nuclear modification factor $R_{AA}$ and relative suppression in terms of $R_{CP}$ as a function of transverse momentum and centrality of collision of charged hadrons in body-body and tip-tip geometrical configurations, respectively. We have compared HYDJET++ model results to those from ALICE experimental data and AMPT model (String-Melting version) results. Minimum bias Xe-Xe collisions show a…
In relativistic nucleus-nucleus collisions the transverse energy per charged particle, E_T/N_ch, increases rapidly with beam energy and remains approximately constant at about 800 MeV for beam energies from SPS to RHIC. It is shown that the hadron resonance gas model describes the energy dependence, as well as the lack of centrality dependence, qualitatively. The values of E_T/N_ch are related to the chemical freeze-out criterium E/N about 1 GeV valid for primordial hadrons.
Transverse Spherocity is an event structure variable which provide an effective way to disentangle the data into hard and soft components of the processes corresponding to events with small and large numbers of multi-parton interactions (MPI), respectively. Recent experimental results in small systems from the LHC suggest the importacnce of transverse spherocity variable in the classification of the events. In this contribution, we have studied the dynamics of identified particle production in Xe-Xe collisions at $\sqrt{s_{NN}}$ = 5.44 TeV using A Multi-Phase Transport Model (AMPT) and the rec…
The transverse energy and charged particle multiplicity at midrapidity and their ratio are evaluated in a statistical model with the longitudinal and transverse flows for different centrality bins at RHIC at $\sqrt{s_{NN}}=130$ and 200 GeV. Full description of decays of hadron resonances is applied in these estimations. The predictions of the model at the freeze-out parameters, which were determined independently from measured particle yields and $p_{T}$ spectra, agree qualitatively well with the experimental data. The observed overestimation of the ratio can be explained for more central coll…
Recent experimental observations of the charged hadron properties in $U+U$ collisions at $193$ GeV contradict many of the theoretical models of particle production including two-component Monte Carlo Glauber model. The experimental results show a small correlation between the charged hadron properties and the initial geometrical configurations (e.g. body-body, tip-tip etc.) of $U+U$ collisions. In this article, we have modified the Monte Carlo HYDJET++ model to study the charged hadron production in $U+U$ collisions at $193$ GeV center-of-mass energy in tip-tip and body-body initial configurat…
The main aim of this paper is a new determination of transverse momentum dependence of unpolarized fragmentation function (TMD FFs) in single inclusive hadron production in electron-positron annihilation (SIA) process. Motivated by the need for a reliable and consistent determination of TMD FFs, we use the most recent TMD production cross sections of charged pions ($π^\pm$), kaons ($K^\pm$) and protons/antiprotons ($p/\bar{p}$) measured in inclusive $e^+e^-$ collisions by Belle Collaboration. These datasets are the first transverse momentum dependence of identified light charged hadron measure…
An accelerated particle sees the Minkowski vacuum as thermally excited, and the particle moves stochastically due to an interaction with the thermal bath. This interaction fluctuates the particle's transverse momenta like the Brownian motion in a heat bath. Because of this fluctuating motion, it has been discussed that the accelerated charged particle emits extra radiation (the Unruh radiation) in addition to the classical Larmor radiation, and experiments are under planning to detect such radiation by using ultrahigh intensity lasers constructed in near future. There are, however, counterargu…
We present a Monte Carlo truth study examining nuclear effects in charged-current neutrino interactions using observables constructed in the transverse plane. Three distributions are introduced that show very weak dependence on neutrino flux and its associated uncertainty. Measurements comparing these distributions between quasi-elastic-like and single charged pion final states will provide new constraints of nuclear effects. It is suggested that the on-axis position in the NuMI beam provides the correct flux to take advantage of this reduced energy dependence in measuring nuclear effect-gener…
The pp collisions have been studied for a long time, however, there are still some effects which are not completely understood, such as the long range angular correlations and the flow patterns in high multiplicity events, which were recently discovered at the LHC. In a recent work it was demonstrated that in Pythia 8, multi-parton interactions and color reconnection can give some of the observed effects similar to the collective flow well known from heavy-ion collisions. Now using the same model, a study based on mid-rapidity charged hadron transverse spherocity is presented. The main purpose…
Transverse energy and charged particle pseudorapidity densities at midrapidity and their ratio, $dE_{T}/dη\mid_{mid} / dN_{ch}/dη|_{mid}$, are evaluated in a statistical model with longitudinal and transverse flows for the wide range of colliders, from AGS to RHIC at $\sqrt{s_{NN}}=200$ GeV. Evaluations are done at freeze-out parameters established independently from fits to observed particle yields and $p_{T}$ spectra. Decays of hadron resonances are treated thoroughly and are included in derivations of $dE_{T}/dη|_{mid}$ and $dN_{ch}/dη|_{mid}$. The predictions of the model agree well with t…
Global variables such as the transverse energy and the charged particle multiplicity and their ratio are evaluated, in a statistical model with expansion, for heavy-ion collisions from AGS to RHIC at $\sqrt{s_{NN}}=200$ GeV. Full description of decays of hadron resonances is applied. The predictions of the model done at the freeze-out parameters established independently from observed particle yields and $p_{T}$ spectra agree well with the experimental data. However, some (explicable) overestimation of the ratio has been found.
Striking events with isolated charged leptons, large missing transverse momentum and large transverse momentum of the hadronic final state were observed at the electron proton collider HERA in a data sample corresponding to a luminosity of about 130 pb-1. The H1 collaboration observed 11 events with isolated electrons or muons and with transverse momentum above 25 GeV. Only 3.4+-0.6 events were expected from Standard Model (SM) processes. Six of these events have a transverse momentum of greater than 40 GeV, while 1.3+-0.3 events were expected. The ZEUS collaboration observed good agreement wi…
We study the collective excitations in a dissipative charged fluid at zero chemical potential when an external magnetic field is present. While in the absence of magnetic field, four collective excitations appear in the fluid, we find five hydrodynamic modes in presence of magnetic field. This implies that the magnetic field splits the degeneracy between the transverse shear modes. Using linear response theory, we then compute the retarded response functions. In particular, it turns out that the correlation between charge and the energy fluctuations will no longer vanish, even at zero chemical…
Multiplicity and Transverse Spherocity dependence of $\langle p_{\rm T} \rangle$ fluctuations of charged particles in p$-$p collisions at $\sqrt{s}$ = 7 and 13 TeV
We compare the transverse momentum (p_T) distribution of inclusive light-charged-particle production measured by the CDF Collaboration at the Fermilab Tevatron with the theoretical prediction evaluated at next-to-leading order in quantum chromodynamics (QCD) using fragmentation functions recently determined through a global data fit. While, in the lower p_T range, the data agree with the prediction within the theoretical error or slightly undershoot it, they significantly exceed it in the upper p_T range, by several orders of magnitude at the largest values of p_T, where perturbation theory sh…
The transverse energies and the charged particle multiplicities at midrapidity as well as their ratio, $dE_{T}/dη\mid_{mid} / dN_{ch}/dη|_{mid}$, are evaluated in a statistical model with expansion for the wide range of heavy-ion collisions, from AGS to RHIC at $\sqrt{s_{NN}}=200$ GeV. Full description of decays of hadron resonances is applied in calculations of both $dE_{T}/dη|_{mid}$ and $dN_{ch}/dη|_{mid}$. The predictions of the model at the freeze-out parameters, established independently from observed particle yields and $p_{T}$ spectra, agree well with the experimental data.
The hadronic $\kt$-spectrum inside a high energy jet is determined including corrections of relative magnitude $\cO{\sqrt{α_s}}$ with respect to the Modified Leading Logarithmic Approximation (MLLA), in the limiting spectrum approximation (assuming an infrared cut-off $Q_0 =\lqcd$) and beyond ($Q_0\ne\lqcd$). The results in the limiting spectrum approximation are found to be, after normalization, in impressive agreement with measurements by the CDF collaboration. A new integral representation for the "hump-backed" plateau is also reported.
The transverse momentum distributions of hadrons produced in p-p collisions at LHC energies of Root(sNN) = 0.9 TeV, 2.76 TeV and Root(sNN) = 7.0 TeV have been studied using a unified statistical thermal freeze-out model. A good agreement is seen between the theoretical calculations and experimental data. The extracted thermal freeze-out parameters reveal the presence of significant collective flow and a well defined temperature in the system thus indicating the formation of a thermally equilibrated hydrodynamic system in p-p collisions at LHC. The transverse momentum distributions of protons a…
The transverse momentum $(p_T)$ spectra of charged particles measured in Au + Au collisions from the beam energy scan (BES) program, Cu + Cu collisions at $\sqrt{s_{NN}}=62.4$, 200 GeV at the RHIC and Pb + Pb, Xe + Xe collisions at the LHC are investigated in the framework of Tsallis thermodynamics. The theory can describe the experimental data well for all the collision systems, energies and centralities investigated. The collision energy and centrality dependence of the Tsallis distribution parameters, i.e., the temperature $T$ and the nonextensive parameter $q$, for the \mbox{A + A} collisi…
The scenario of a collective expansion of matter created in proton-proton (p-p) collisions at the CERN Large Hadron Collider (LHC) is discussed. Assuming a small transverse size and a formation time of 0.1fm/c of the source we observe the build up of a substantial transverse flow in relativistic hydrodynamic simulations. In order to demonstrate the collectivity in p-p collisions we propose to look at the multiplicity dependence of the elliptic flow coefficient. If high multiplicity events originate from azimuthally asymmetric events containing two flux tubes, an observable signal above the sta…
The mid-rapidity transverse momentum spectra of hadrons and the available rapidity distributions of the strange hadrons produced in p-p collisions at LHC energy root(snn) = 0.9 TeV and root(snn)= 7.0 TeV have been studied using a unified statistical thermal freeze-out model. The calculated results are found to be in good agreement with the experimental data. The theoretical fits of the transverse momentum spectra using the model calculations provide the thermal freeze-out conditions in terms of the temperature and collective flow parameters for different hadronic species. The study reveal the …
Rapid 3+1D transverse plus Bjorken collective expansion in $A+A$ collisions at ultra-relativistic energies is shown to reduce substantially the azimuthal asymmetry resulting from jet quenching. While the azimuthal asymmetry in non-central collisions, $v_2(p_T>2 \rm{GeV/c})\sim 0.15$ reported by STAR at RHIC, can be accounted for by spatially anisotropic jet energy loss through a 1+1D expanding gluon plasma with $dN^g/dy\sim 1000$, we show that if rapid transverse collective expansion of the plasma is assumed, then the asymmetry due to jet quenching may be reduced below the observed level. Poss…
The hadronic tau decay channel offers by far the best signature for heavy charged Higgs boson search at the LHC in the large $\tanβ$ region. By exploiting the distinct polarization of the tau and its large transverse mass, along with the accompanying missing--$p_T$, one can probe for a charged Higgs boson up to a mass of about 600 GeV in an essentially background-free environment. The transverse mass distribution of the tau jet also provides a fairly unambiguous estimate of the charged Higgs boson mass.
Hadronic freezeout during the evolution of the medium created in heavy-ion collisions is an important phenomena. It is quite useful to find a universal freezeout condition for each and every nuclear collisions. In this article, we have constructed a hybrid model to calculate the ratio of transverse energy to total mean multiplicity $E_{T} /N_{ch}$, since this ratio can possibly act as a freezeout condition in heavy-ion collision experiments. Present hybrid model blends two approaches : Tsallis statistics and wounded quark approach. Recently, Tsallis statistics has been reliably used to obtain …
We consider two possible sources of the $T$-violating muon transverse polarization in the process $K^+ \to μ^+ νγ$: electromagnetic final state interaction in the SM and contribution due to charged-Higgs exchange diagrams in the framework of the Weinberg three doublets model. It is shown that at the one-loop level of the SM the muon transverse polarization, $P_T^{SM}$, varies within $(0.0 ÷1.1 \cdot 10^{-3})$ in the Dalitz plot region. Averaged value of the muon polarization, $<P^{SM}_T>$, in the kinematic region of $E_γ\geq 20$ MeV is equal to $4.76\cdot 10^{-4}$. In the case of the model wit…
