arXiv subjects

Firooz Arash

Publications and source records attributed to Firooz Arash.

15 recordsLinked to original sources

arXiv2017

Contribution of Orbital Angular Momentum to the Nucleon Spin

We have calculated the Orbital Angular Momentum of quarks and gluons in the nucleon. The calculations are carried out in the next to leading order utilizing the so-called valon model. It is found that the average quark orbital angular momentum is positive, but small, and the average gluon orbital angular momentum is negative and large. We also report on some regularities about the total angular momentum of the quarks and the gluon, as well as on the orbital angular momentum of the separate partons. We have also provided partonic angular momentum, $L^{q,g}$ as a function of $Q^2$.

hep-ph↗

arXiv2014

Polarization Test of Higgs Spin and Parity

A polarization test is applied to determine the spin and the parity of the observed resonance at LHC, which is believed to be the expected "Higgs" particle. The test is based on very general principles and is completely independent of dynamical assumptions. We have also identified a set of observables that discriminate resonances with $J^P=0^+,0^-, 2^-$ and $2^+$. Furthermore, the same set can be used to gain useful and important information on the magnitude of each helicity amplitude contributing to the $gg\rightarrow γγ$ process .

hep-ph↗

arXiv2010

Non-Singlet spin structure function in the valon model and low x scaling behavior of $g_{1}^{NS}$ and $g_1^p$

A next-to-leading order QCD calculation of non-singlet spin structure function, $g_{1}^{NS} $ is presented within the valon representation of Hadrons. In the valon model, it is assumed that a nucleon is composed of three dressed valence quarks: the valons which have their own internal structure, the valence quark with its associated sea quarks and gluons. The results are in good agreement with all available data from SMC, E143, HERMES and with the newly released data from COMPASS experiments. It appears that the small x tail of $g_{1}^{NS}$ can be described by a single Regge-type exchange. The relevant parameter of this exchange is given. Finally we show that the polarized proton structure function has a scaling behavior at small x. The relevant parameters of this behavior are given too.

hep-ph↗

arXiv2010

Gluon Polarization In Nucleon

In the context of the so-called valon model, we calculate $\frac{δg}{g}$ and show that although it is small and compatible with the measured values, the gluon contribution to the spin of nucleon can be sizable. The smallness of $\frac{δg}{g}$ in the measured kinematical region should not be interpreted as $δg$ being small. In fact, $δg$ itself at small x, and the first moment of the polarized gluon distribution in the nucleon, $Δg(Q^2)$, are large

hep-ph↗

arXiv2008

Valence Quark Polarization In the Nucleon And the Deuteron Data

Within the framework of the so-called "valon" model, we argue that a substantial part of the nucleon spin, about 40%, is carried by the polarized valence quarks. The remaining is the result of cancellations between gluon polarization and the orbital angular momentum, where the gluon polarization is the dominant one. It is shown that the sea quark contribution to the spin of any hadron is simply marginal and consistent with zero. Our findings point to a substantially smaller value for a_8 thaninferred from hyperon- $β$ decay, suggesting that fullSU(3) symmetric assumption needs to be reconsidered. New and emerging experimental data tend to support this finding. Finally, we show that within the model described here the experimental data on the polarized structure functions $g_{1}^{p,n,d}$ are reproduced.

hep-ph↗

arXiv2007

Polarized Structure of Nucleon in the Valon Representation

We have utilized the concept of valon model to calculate the spin structure functions of proton, neutron and deuteron. The valon structure itself is universal and arises from the perturbative dressing of the valence quark in QCD. Our results agree rather well with all the relevant experimental data on $g_{1}^{p, n, d}$ and $g_{A}/g_{v}$, and suggests that the sea quark contribution to the spin of proton is consistent with zero. It also reveals that while the total quark contribution to the spin of valon is almost constant at $Q^{2}>=1$ the gluon contribution grows with the increase of $Q^2$ and hence requiring a sizable negative orbital angular momentum component $L_z$. This component along with the singlet and non-singlet parts are calculated in the Next-to-Leading order in QCD. We speculate that gluon contribution to the spin content of the proton is about 60% for all $Q^2$ values. Finally, we show that the size of gluon polarization and hence, $L_{z}$, is sensitive to the initial scale$Q_{0}^{2}$.

hep-ph↗

arXiv2005

Hadronic Structure from Perturbative dressing in QCD - The Valon Model

In the Framework of {\it{valon model}} we have calculated the parton distribution in a valon for both the polarized and unpolarized cases. These distributions are originated purely from the dressing of a valence quark in QCD and are common to all hadrons. Structure functions, $F_{2}^{p,π}$, are obtained, which agree rather well with the experimental results. A simple relation between $F_{2}^{p}$ and $F_{2}^π$ is inferred. For the polarized structure function, $g_{1}$ while the model gives good agreement with data, it requires a sizable angular momentum contribution to the spin of the valon, and hence to that of proton. This contribution is calculated.

hep-ph↗

arXiv2004

Meson Structure Functions in Valon Model

Parton distributions in a {\it{valon}} in the next-to-leading order is used to determine the patron distributions in pion and kaon. The validity of the valon model is tested and shown that the partonic content of the valon is universal and independent of the valon type. We have evaluated the valon distribution in pion and kaon, and in particular it is shown that the results are in good agreement with the experimental data on pion structure in a wide range of $x=[10^{-4},1]$

hep-ph↗

arXiv2003

Constituent Quark and Hadronic Structure in the Next-to-Leading Order

The structure of a dressed quark is utilized to evaluate the structure function of proton and pion. It is found that there is a simple relationship between $F_{2}^{p}$ and $F_{2}^π$. The ambiguity in the normalization of $F_{2}^π$ is discussed. Furthermore, the polarization structure function of the constituent (dressed) quark is calculated in the leading order. While, it does produce all the available data on polarized hadronic structure, it requires a significant contribution to the proton spin from the orbital angular momentum.

hep-ph↗

arXiv2003

Pion Structure Function $F_{2}^π$ in the Valon Model

Partonic structure of constituent quark (or{\it{valon}}) in the Next-to-Leading Order is used to calculate pion structure function. This is a further demonstration of the finding that the constituent quark structure is universal, and once it is calculated, the Structure of any hadron can be predicted thereafter, using a convolution method, without introducing any new free parameter. The results are compared with the pion structure function from ZEUS Coll. Leading Neutron Production in $e^{+}p$ collisions at HERA. We found good agreement with the experiment. A resolution for the issue of normalization of the experimental data is suggested. In addition, the proportionality of $F_{2}^π$ and $F_{2}^{p}$, which have caused confusion in the normalization of ZEUS data is discussed and resolved.

hep-ph↗

arXiv2001

Basic Structure in Hadrons

We have calculated the Structure function a constituent quark in the NLO and from it we have derived the structure functions of hadrons. We found that perturbative generation of hadron structure falls short of conforming with data by a few percent. This is due to the presence of soft gluon and its radiation in the hadron. This contribution is modeled into our calculations. It is also responsible for the breaking of flavor symmetry in the nucleon sea.

hep-ph↗

arXiv2000

From Constituent Quark to Hadron Structure in the Next-to-Leading Order: Nucleon and Pion

We calculate the partonic structure of constituent quark in the Next-to-Leading Order for the first time. The structure of any hadron can be obtained thereafter using a convolution method. Such a procedure is used to generate the structure function of proton and pion in NLO. It is shown that while the constituent quark structure is generated purely perturbatively and accounts to most part of the hadronic structure, there is a few percent contributions coming from the nonperturbative sector in the hadronic structure. This contribution plays the key role in explaining the SU(2) symmetry breaking of the nucleon sea and the observed violation of Gottfried sum rule. These effects are calculated. Excellent agreement with data in a wide range of $x=[10^{-6}, 1]$ and $Q^{2}=[0.5, 5000]$ $GeV^{2}$ is reached for proton structure function. We have also calculated Pion structure and compared it with the existing data. Again nice agreement is achieved.

hep-ph↗

arXiv1999

Constituent Quarkstructur and $F^{p}_{2}$ Data

We have calculated the partonic structure of a constituent quark in the leading order in QCD for the first time and examined its ipmlications on the proton structure function, $F^{p}_{2}, data from HERA. It turned out that although qualitatively it agrees with the data but for a finer refinement we need to consider an {\it{inherent}} component due to gluons which act as the binding agent between constituents quarks in the proton. Good agreement with nucleon structure function, $F_{2}(x,Q^{2})$, for a wide range of $x=[10^{-6} ,1]$ and $Q^{2}=[0.5, 5000]$ $GeV^{2}$ is reached. {\bf{PACS Numbers 13.60 Hb, 12.39.-x, 13.88 +e, 12.20.Fv}}

hep-ph↗

arXiv1999

Next-to-Leading Order Description of Nucleon Structure Function In Valon Model

We have improved and examined the applicability of the valon model where the structure of any hadron is determined by the structure of its constituent quarks. Nucleon structure functions are calculated within this model in the Next-to-Leading order. The results compare well with the experimental data. The model handles the bound state problem and the calculations show a flat or almost flat behavior for $F_{2}$ which sets in at some region of $x\leq 10^{-5}$at fixed $Q^{2}$. The emergence of this behavior is a consequence of the model and was not put in a priori as a theoretical guess. It seems that such a flatness can be inferred from HERA data, although, not completely confirmed yet. A set of parton distributions are given and their evolutions are tested. Some qualitative implications of the model for the spin structure of the proton is discussed.

hep-ph↗

arXiv1999

Nuclear Structure Functions from Constituent Quark Model

We have used the notion of the constituent quark model of nucleon, where a constituent quark carries its own internal structure, and applied it to determine nuclear structure functions ratios. It is found that the description of experimental data require the inclusion of strong shadowing effect for $x<0.01$. Using the idea of vector meson dominance model and other ingredients this effect is calculated in the context of the constituent quark model. It is rather striking that the constituent quark model, used here, gives a good account of the data for a wide range of atomic mass number from A=4 to A=204.

nucl-th↗