arXiv subjects

S. Kumano

Publications and source records attributed to S. Kumano.

At least 91 records · Page 5Linked to original sources

arXiv2010

Radiative decay of Lambdac(2940)+ in a hadronic molecule picture

The Lambdac(2940)+ baryon with quantum numbers J(P) = 1/2(+) is considered as a molecular state composed of a nucleon and D* meson. We give predictions for the width of the radiative decay process Lambdac(2940)+ to Lambdac(2286)+ gamma in this interpretation. Based on our results we argue that an experimental determination of the radiative decay width of Lambdac(2940)+ is important for the understanding of its intrinsic properties.

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arXiv2010

Determination of fragmentation functions and their application to exotic-hadron search

We discuss studies on determination of fragmentation functions and an application to exotic-hadron search by using characteristic differences between favored and disfavored functions. The optimum fragmentation functions are determined for pion, kaon, and proton in the leading order (LO) and next-to-leading order (NLO) of the running coupling constant alpha_s by global analyses of hadron-production data in electron-positron annihilation. Various parametrization results are much different in disfavored-quark and gluon fragmentation functions; however, we show that they are within uncertainties of the determined functions by using the Hessian method for uncertainty estimation. We find that the uncertainties are especially large in the disfavored-quark and gluon fragmentation functions. NLO improvements are explicitly shown in the determination by comparing uncertainties of the LO and NLO functions. Next, we propose to use differences between favored and disfavored fragmentation functions for determining internal quark configurations of exotic hadrons. We make a global analysis for f_0 (980) for finding its internal configuration; however, uncertainties are too large to specify the structure at this stage.

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arXiv2010

Tensor-polarized quark and antiquark distribution functions in a spin-one hadron

To understand orbital-angular-momentum contributions is becoming crucial for clarifying nucleon-spin issue in the parton level. Twist-two structure functions b_1 and b_2 for spin-one hadrons could probe orbital-angular-momentum effects, which reflect a different aspect from current studies for the spin-1/2 nucleon, since they should vanish if internal constituents are in the S state. These structure functions are related to tensor structure in spin-one hadrons. Studies of such tensor structure will open a new field of high-energy spin physics. The structure functions b_1 and b_2 are described by tensor-polarized quark and antiquark distributions delta_T-q and delta_T-qbar. Using HERMES data on the b_1 structure function for the deuteron, we made an analysis of extracting the distributions delta_T-q and delta_T-qbar in a simple x-dependent functional form. Optimum distributions are proposed for the tensor-polarized valence and antiquark distribution functions from the analysis. A finite tensor polarization is obtained for antiquarks if we impose a constraint that the first moments of tensor-polarized valence-quark distributions vanish. It is interesting to investigate a physics mechanism to create a finite tensor-polarized antiquark distribution.

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arXiv2009

Using branching processes in nuclei to reveal dynamics of large-angle, two-body scattering

We demonstrate that hard branching 2\to 3 particle processes with nuclei provide an effective way to determine the momentum transfers needed for effects of point-like configurations to dominate large angle 2\to 2 processes. In contrast with previously proposed approaches, the discussed reaction allows the effects of the transverse size of configurations to be decoupled from effects of the space-time evolution of these configurations.

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arXiv2009

Nuclear effects in neutrino-nucleus DIS

We explain the current status of nuclear parton distribution functions in connection with neutrino-nucleus interactions. Neutrino deep inelastic scattering (DIS) measurements have been done for heavy nuclear targets such as iron and lead. In order to extract structure functions of the nucleon, one needs to remove nuclear effects from the data. However, recent studies indicate that there are inconsistencies in nuclear modifications between charged-lepton and neutrino scattering measurements. Nuclear medium effects could be also an origin for the NuTeV anomaly in the weak-mixing angle. In addition, the modifications could affect neutrino-oscillation experiments because some DIS events of neutrino-oxygen nucleus interactions are contained. On the other hand, the nuclear medium effects themselves are interesting and important for describing nuclei in terms of quark and gluon degrees of freedom.

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arXiv2009

Novel two-to-three hard hadronic processes and possible studies of generalized parton distributions at hadron facilities

We consider a novel class of hard branching hadronic processes a+b->c+d+e, where hadrons c and d have large and nearly opposite transverse momenta and large invariant energy which is a finite fraction of the total invariant energy. We use color transparency logic to argue that these processes can be used to study quark generalized parton distributions (GPDs) for baryons and mesons in hadron collisions hence complementing and adding to the studies of GPDs in the exclusive DIS (deep inelastic scattering) processes. We propose that a number of GPDs can be investigated in hadron facilities such as J-PARC (Japan Proton Accelerator Research Complex) facility and GSI-FAIR (Gesellschaft fur Schwerionenforschung -Facility for Antiproton and Ion Research) project. In this work, the GPDs for the nucleon and for the N->Delta transition are studied in the reaction N+N->N+pi+B, where N, pi, and B are a nucleon, a pion, and a baryon (nucleon or Delta), respectively, with a large momentum transfer between B (or pi) and the incident nucleon. In particular, the Efremov-Radyushkin-Brodsky-Lepage (ERBL) region of the GPDs can be measured in such exclusive reactions. We estimate the cross section of the processes N+N->N+pi+B by using current models for relevant GPDs and information about large angle pi N reactions. We find that it will be feasible to measure these cross sections at the high-energy hadron facilities, and get novel information about the nucleon structure, for example, contributions of quark orbital angular momenta to the nucleon spin. The studies of N->Delta transition GPDs could be valuable also for investigating electromagnetic properties of the transition.

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arXiv2009

Determination of gluon polarization from deep inelastic scattering and collider data

We investigate impact of $π^0$-production data at Relativistic Heavy Ion Collider (RHIC) and future E07-011 experiment for the structure function $g_1$ of the deuteron at the Thomas Jefferson National Accelerator Facility (JLab) on studies of nucleonic spin structure, especially on the polarized gluon distribution function. By global analyses of polarized lepton-nucleon scattering and the $π^0$-production data, polarized parton distribution functions are determined and their uncertainties are estimated by the Hessian method. Two types of the gluon distribution function are investigated. One is a positive distribution and the other is a node-type distribution which changes sign at $x \sim 0.1$. Although the RHIC $π^0$ data seem to favor the node type for $Δg(x)$, it is difficult to determine a precise functional form from the current data. However, it is interesting to find that the gluon distribution $Δg(x)$ is positive at large $x$ ($>0.2$) due to constraints from the scaling violation in $g_1$ and RHIC $π^0$ data. The JLab-E07-011 measurements for $g_1^d$ should be also able to reduce the gluon uncertainty, and the reduction is comparable to the one by RUN-5 $π^0$-production data at RHIC. The reduction is caused by the error correlation between polarized antiquark and gluon distributions and by a next-to-leading-order (NLO) gluonic effect in the structure function $g_1^d$. We find that the JLab-E07-011 data are accurate enough to probe the NLO gluonic term in $g_1$. Both RHIC and JLab data contribute to better determination of the polarized gluon distribution in addition to improvement on polarized quark and antiquark distributions.

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arXiv2008

Projections of structure functions in a spin-one hadrons

There exist new polarized structure functions in a spin-one hadron. In deep inelastic electron scattering from a spin-one hadron, there are eight structure functions F_1, F_2, g_1, g_2, b_1, b_2, b_3, and b_4. We derive projections to these eight functions from the hadron tensor W^{mu nu} by combinations of the hadron momentum and its polarization vectors.

hep-ph↗

arXiv2008

High-energy hadron physics at J-PARC

The J-PARC facility is near completion and experiments will start in 2009 on nuclear and particle physics projects. In this article, the J-PARC facility is introduced, and possible projects are discussed in high-energy hadron physics by using the primary proton beam of 30-50 GeV. There are proposed experiments on charm-production and Drell-Yan processes as well as single spin asymmetries for investigating quark and gluon structure of the nucleon and nuclei. Parton-energy loss could be studied in the Drell-Yan processes. There is also a proposal on hadron-mass modifications in a nuclear medium by using the proton beam. In addition, possible topics include transition from hadron to quark degrees of freedom by elastic pp scattering, color transparency by (p,2p), short-range correlation in nuclear force by (p,2pN), tensor structure functions for spin-one hadrons, fragmentation functions, and generalized parton distributions in the ERBL region although proposals are not written on these projects. If proton-beam polarization is attained, it is possible to investigate details of nucleon spin structure. In the last part of this article, our own studies are explained on parton distribution functions in connection with the J-PARC projects.

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arXiv2008

Parton fragmentation in the vacuum and in the medium

We present the mini-proceedings of the workshop on ``Parton fragmentation in the vacuum and in the medium'' held at the European Centre for Theoretical Studies in Nuclear Physics and Related Areas (ECT*, Trento) in February 2008. The workshop gathered both theorists and experimentalists to discuss the current status of investigations of quark and gluon fragmentation into hadrons at different accelerator facilities (LEP, B-factories, JLab, HERA, RHIC, and Tevatron) as well as preparations for extension of these studies at the LHC. The main physics topics covered were: (i) light-quark and gluon fragmentation in the vacuum including theoretical (global fits analyses and MLLA) and experimental (data from e+e-, p-p, e-p collisions) aspects, (ii) strange and heavy-quark fragmentation, (iii) parton fragmentation in cold QCD matter (nuclear DIS), and (iv) medium-modified fragmentation in hot and dense QCD matter (high-energy nucleus-nucleus collisions). These mini-proceedings consist of an introduction and short summaries of the talks presented at the meeting.

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arXiv2008

Determination of f_0(980) Structure by Fragmentation Functions

We discuss internal structure of an exotic hadron by using fragmentation functions. The fragmentation functions for the f_0(980) meson are obtained by a global analysis of e^++e^- \to f_0+X data. Quark configuration of the f_0(980) could be determined by peak positions and second moments of the obtained fragmentation functions.

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arXiv2008

Proposal for exotic-hadron search by fragmentation functions

It is proposed that fragmentation functions should be used to identify exotic hadrons. As an example, fragmentation functions of the scalar meson f_0(980) are investigated. It is pointed out that the second moments and functional forms of the u- and s-quark fragmentation functions can distinguish the tetraquark structure from $q\bar q$. By the global analysis of f_0 (980) production data in electron-positron annihilation, its fragmentation functions and their uncertainties are determined. It is found that the current available data are not sufficient to determine its internal structure, while precise data in future should be able to identify exotic quark configurations.

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arXiv2007

Determination of nuclear parton distribution functions and their uncertainties at next-to-leading order

Nuclear parton distribution functions (NPDFs) are determined by global analyses of experimental data on structure-function ratios F_2^A/F_2^{A'} and Drell-Yan cross-section ratios σ_{DY}^A/σ_{DY}^{A'}. The analyses are done in the leading order (LO) and next-to-leading order (NLO) of running coupling constant α_s. Uncertainties of the NPDFs are estimated in both LO and NLO for finding possible NLO improvement. Valence-quark distributions are well determined, and antiquark distributions are also determined at x<0.1. However, the antiquark distributions have large uncertainties at x>0.2. Gluon modifications cannot be fixed at this stage. Although the advantage of the NLO analysis, in comparison with the LO one, is generally the sensitivity to the gluon distributions, gluon uncertainties are almost the same in the LO and NLO. It is because current scaling-violation data are not accurate enough to determine precise nuclear gluon distributions. Modifications of the PDFs in the deuteron are also discussed by including data on the proton-deuteron ratio F_2^D/F_2^p in the analysis. A code is provided for calculating the NPDFs and their uncertainties at given x and Q^2 in the LO and NLO.

hep-ph↗

arXiv2007

Global NLO Analysis of Nuclear Parton Distribution Functions

Nuclear parton distribution functions (NPDFs) are determined by a global analysis of experimental measurements on structure-function ratios F_2^A/F_2^{A'} and Drell-Yan cross section ratios σ_{DY}^A/σ_{DY}^{A'}, and their uncertainties are estimated by the Hessian method. The NPDFs are obtained in both leading order (LO) and next-to-leading order (NLO) of α_s. As a result, valence-quark distributions are relatively well determined, whereas antiquark distributions at x>0.2 and gluon distributions in the whole x region have large uncertainties. The NLO uncertainties are slightly smaller than the LO ones; however, such a NLO improvement is not as significant as the nucleonic case.

hep-ph↗

arXiv2007

Global analysis of hadron-production data in e^+ e^- annihilation for determining fragmentation functions

Fragmentation functions of pion, kaon, and nucleon are determined by global analyses of hadron-production data in $e^+e^-$ annihilation. It is particularly important that uncertainties of the fragmentation functions are estimated for the first time. We found that light-quark and gluon fragmentation functions have large uncertainties, so that one should be careful in using these functions for hadron-production processes in heavy-ion collisions and lepton scattering. The analysis is extended to possible exotic hadron search by fragmentation functions. We found that internal structure of $f_0 (980)$, such as $s\bar s$ or tetraquark configuration, can be determined by noting differences between favored and disfavored fragmentation functions.

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arXiv2007

Global analysis for determining fragmentation functions and their uncertainties in light hadrons

Fragmentation functions are determined for the pion, kaon, and proton by analyzing charged-hadron production data in electron-positron annihilation. It is important that uncertainties of the determined fragmentation functions are estimated in this analysis. Analysis results indicate that gluon and light-quark functions have large uncertainties especially at small Q^2. We find that next-to-leading-order (NLO) uncertainties are significantly reduced in comparison with leading-order (LO) ones in the pion and kaon. The fragmentation functions are very different in various analysis groups. However, all the recent functions are roughly within the estimated uncertainties, which indicates that they are consistent with each other. We provide a code for calculating the fragmentation functions and their uncertainties at a given kinematical point of z and Q^2 by a user.

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arXiv2007

Determination of fragmentation functions and their uncertainties

Fragmentation functions and their uncertainties are determined for pion, kaon, and proton by a global $χ^2$ analysis of charged-hadron production data in electron-positron annihilation and by the Hessian method for error estimation. It is especially important that the uncertainties of the fragmentation functions are estimated in this analysis. The results indicate that the fragmentation functions, especially gluon and light-quark fragmentation functions, have large uncertainties at small $Q^2$. There are large differences between widely-used functions by KKP (Kniehl, Kramer, and Pötter) and Kretzer; however, they are compatible with each other and also with our functions if the uncertainties are taken into account. We find that determination of the fragmentation functions is improved in next-to-leading-order (NLO) analyses for the pion and kaon in comparison with leading-order ones. Such a NLO improvement is not obvious in the proton. Since the uncertainties are large at small $Q^2$, the uncertainty estimation is very important for analyzing hadron-production data at small $Q^2$ or $p_T$ ($Q^2, p_T^2 << M_Z^2$) in lepton scattering and hadron-hadron collisions. A code is available for general users for calculating obtained fragmentation functions.

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arXiv2006

Constraint on Δg(x) from π^0 production at RHIC

We determine the polarized gluon distribution Δg(x) by a global analysis using current DIS and π^0 asymmetry data. The π^0 data from RHIC-Spin experiments provide a strong constraint on Δg(x), so that its uncertainty is reduced. However, a sign problem appears in the analysis using π^0 data, which means that positive and negative distributions are allowed for Δg(x). These two types of solutions are discussed.

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