Study of bulk matter properties through strange quark hadrons with the STAR experiment

Relativistic heavy ion collisions are the ideal experimental tool to explore the QCD phase diagram. Several results show that a very hot medium with a high energy density and partonic degrees of freedom is formed in these collisions, creating a new state of matter. Measurements of strange hadrons can bring important information about the bulk properties of such matter. The elliptic flow of strange hadrons such as phi, K(S)(0), Lambda, Xi and Omega shows that collectivity is developed at partonic level and at intermediate p(T) the quark coalescence is the dominant mechanism of hadronization. The nuclear modification factor is an another indicator of the presence of a very dense medium. The comparison between measurements of Au+Au and d+Au collisions, where only cold nuclear matter effects are expected, can shed more light on the bulk properties. In these proceedings, recent results from the STAR experiment on bulk matter properties are presented.

NLL QCD contribution of the electromagnetic dipole operator to B -> Xs gamma gamma with a massive strange quark

We calculate the O(αs) corrections to the double differential decay width dΓ77/(ds1ds2) for the process B¯→Xsγγ, originating from diagrams involving the electromagnetic dipole operator O7. The kinematical variables s1 and s2 are defined as si=(pb−qi)2/m2b, where pb, q1, q2 are the momenta of the b quark and two photons. We introduce a nonzero mass ms for the strange quark to regulate configurations where the gluon or one of the photons become collinear with the strange quark and retain terms which are logarithmic in ms, while discarding terms which go to zero in the limit ms→0. When combining virtual and bremsstrahlung corrections, the infrared and collinear singularities induced by soft and/or collinear gluons drop out. By our cuts the photons do not become soft, but one of them can become collinear with the strange quark. This implies that in the final result a single logarithm of ms survives. In principle, the configurations with collinear photon emission could be treated using fragmentation functions. In a related work we find that similar results can be obtained when simply interpreting ms appearing in the final result as a constituent mass. We do so in the present paper and vary ms between 400 and 600 MeV in the numerics. This work extends a previous paper by us, where only the leading power terms with respect to the (normalized) hadronic mass s3=(pb−q1−q2)2/m2b were taken into account in the underlying triple differential decay width dΓ77/(ds1ds2ds3).

Production of K*(892)(0) and phi(1020) in pp collisions at root s=7 TeV

The production of K*(892)(0) and phi(1020) in pp collisions at root s = 7 TeV was measured by the ALICE experiment at the LHC. The yields and the transverse momentum spectra d(2)N/dydp(T) at midrapidity vertical bar y vertical bar < 0.5 in the range 0 < p(T) < 6 GeV/c for K*(892)(0) and 0.4 < p(T) < 6 GeV/c for phi(1020) are reported and compared to model predictions. Using the yield of pions, kaons, and Omega baryons measured previously by ALICE at root s = 7 TeV, the ratios K*/K-, phi/K*, phi/ K-, phi/pi(-), and (Omega + <(Omega)over bar>)/phi are presented. The values of the K*/K-, phi/K* and phi/K- ratios are similar to those found at lower centre-of-mass energies. In contrast, the phi/pi(-) ratio, which has been observed to increase with energy, seems to saturate above 200 GeV. The (Omega + (Omega) over bar)/phi ratio in the p(T) range 1-5 GeV/ c is found to be in good agreement with the prediction of the HIJING/B (B) over bar v2.0model with a strong colour field.

Search for charged Higgs bosons in top quark decays

Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)

(O8, O8) contribution to B¯ → Xsγγ at O(αs)

In this analysis, we present the contribution associated with the chromomagnetic dipole operator O8 to the double differential decay width dΓ/(ds1ds2) for the inclusive process B¯→Xsγγ. The kinematical variables s1 and s2 are defined as si=(pb−qi)2/m2b, where pb, q1, q2 are the momenta of b quark and two photons. This contribution (taken at tree level) is of order αs, like the recently calculated QCD corrections to the contribution of the operator O7. In order to regulate possible collinear singularities of one of the photons with the strange quark, we introduce a nonzero mass ms for the strange quark. Our results are obtained for exact ms, which we interpret as a constituent mass being varied between 400 and 600 MeV. Numerically it turns out that the effect of the (O8, O8) contribution to the branching ratio of B¯→Xsγγ does not exceed +0.1% for any kinematically allowed value of our physical cutoff parameter c, confirming the expected suppression of this contribution relative to the QCD corrections to dΓ77/(ds1ds2).

Determination of the magnetic moment by QCD sum rules

The magnetic moment of the Λ hyperon is calculated using the QCD sum-rule approach of Ioffe and Smilga. It is shown that μΛ has the structure μΛ=(2/3(eu+ed+4es)(eħ/2MΛc)(1+δΛ), where δΛ is small. In deriving the sum rules special attention is paid to the strange-quark mass-dependent terms and to several additional terms not considered in earlier works. These terms are now appropriately incorporated. The sum rule is analyzed using the ratio method. Using the external-field-induced susceptibilities determined earlier, we find that the calculated value of μΛ is in agreement with experiment.

Deconfinement phase Transition including perturbative QCD corrections in (proto)neutron star matter

Deconfinement phase transition and neutrino trapping in (proto)neutron star matter are investigated in a chiral hadronic model (also referred to as the FST model) for the hadronic phase (HP) and in the color-flavor-locked (CFL) quark model for the deconfined quark phase. We include a perturbative QCD correction parameter alpha(s) in the CFL quark matter equation of states. It is shown that the CFL quark core with K-0 condensation forms in neutron star matter with the large value of alpha(s). If the small value of alpha(s) is taken, hyperons suppress the CFL quark phase and the HP is dominant in the high-density region of (proto)neutron star matter. Neutrino trapping makes the fraction of the CFL quark matter decrease compared with those without neutrino trapping. Moreover, increasing the QCD correction parameter alpha(s) or decreasing the bag constant B and the strange quark mass m(s) can make the fraction of the CFL quark matter increase, simultaneously, the fraction of neutrino in protoneutron star matter increases, too. The maximum masses and the corresponding radii of (proto)neutron stars are not sensitive to the QCD correction parameter alpha(s).

Phase transition to color-flavor-locked matter and condensation of Goldstone bosons in neutron star matter

Deconfinement phase transition and condensation of Goldstone bosons in neutron star matter are investigated in a chiral hadronic model (also referred as to the FST model) for the hadronic phase (HP) and in the color-flavor-locked (CFL) quark model for the deconfined quark phase. It is shown that the hadronic-CFL mixed phase (MP) exists in the center of neutron stars with a small bag constant, while the CFL quark matter cannot appear in neutron stars when a large bag constant is taken. Color superconductivity softens the equation of state (EOS) and decreases the maximum mass of neutron stars compared with the unpaired quark matter. The K-0 condensation in the CFL phase has no remarkable contribution to the EOS and properties of neutron star matter. The EOS and the properties of neutron star matter are sensitive to the bag constant B, the strange quark mass m(s) and the color superconducting gap Delta. Increasing B and m(s) or decreasing Delta can stiffen the EOS which results in the larger maximum masses of neutron stars.

QCD求和规则对S夸克质量的研究

QCD求和规则是强子物理中的一种非常有效的非微扰方法，它从流的算符乘积展开开始，引入算符乘积展开式的真空期望值，把微扰和非微扰效应分开处理：微扰效应包含在展开系数中，非微扰效应则由算符的真空凝聚值表示。然后利用色散关系，把算符乘积展开式的真空期望值与一个含有强子物理参数的色散积分联系起来，这样就能够计算有关强子的物理量。 本文首先系统介绍了QCD求和规则的基本原理、基本方法，然后结合Dominguez，Gend和Paver的工作[14]，展开式保留了的算符d=4凝聚值，采用新的参数化渐近自由阈以下谱函数的方法：即根据文献[25]，用实验上了解得比较清楚的两个共振态的贡献来参数化谱函数，计算了s夸克的质量，得到了在动量标度为1Gev时，s夸克的跑动质量为219MeV。在误差范围内，这是一个理论上可以接受的结果，本文计算得到的跑动质量的值能为考察动量转移为1GeV时的质量效应提供参考。 关键词：QCD求和规则 算符乘积展开 色散关系 Borel变换 夸克质

NU-PROCESS IN EXOTIC MODELS

The exact physical conditions generating the abundances of r-elements in environments such as supernovae explosions are still under debate. We evaluated the characteristics expected for the neutrino wind in the proposed model of type-II supernova driven by conversion of nuclear matter to strange matter. Neutrinos will change the final abundance of elements after freeze out of r-process nucleosynthesis, specially those close to mass peaks.

Can the X(4350) narrow structure be a 1(-+) exotic state?

Using the QCD sum rules we test if the new narrow structure, the X(4350) recently observed by the Belle Collaboration, can be described as a J(PC) = 1(-+) exotic D(s)(*)D(s0)(*) molecular state. We consider the contributions of condensates up to dimension eight, we work at leading order in alpha(s) and we keep terms which are linear in the strange quark mass Ins. The mass obtained for such state is m(Ds*Ds0*) = (5.05 +/- 0.19) GeV. We also consider a molecular 1(-+), D(s)(*)D(s0)(*); current and we obtain m(D*D0*) = (4.92 +/- 0.08) GeV. We conclude that it is not possible to describe the X(4350) structure as a 1(-+) D(s)(*)D(s0)(*) molecular state. (C) 2010 Elsevier B.V. All rights reserved.

SU(3) mass-splittings of heavy-baryons in QCD

We extract directly (for the first time) the charmed (C = 1) and bottom (B = -1) heavy-baryons (spin 1/2 and 3/2) mass-splittings due to SU(3) breaking using double ratios of QCD spectral sum rules (QSSR) in full QCD, which are less sensitive to the exact value and definition of the heavy quark mass, to the perturbative radiative corrections and to the QCD continuum contributions than the simple ratios commonly used for determining the heavy baryon masses. Noticing that most of the mass-splittings are mainly controlled by the ratio kappa <(S) over bars >/<(d) over bard > of the condensate, we extract this ratio, by allowing 1 sigma deviation from the observed masses of the Xi(c.b) and of the Omega(c). We obtain: kappa = 0.74(3), which improves the existing estimates: kappa = 0.70(10) from light hadrons. Using this value, we deduce M(Omega b) = 6078.5(27.4) MeV which agrees with the recent CDF data but disagrees by 2.4 sigma with the one from D0. Predictions of the Xi(Q)` and of the spectra of spin 3/2 baryons containing one or two strange quark are given in Table 2. Predictions of the hyperfine splittings Omega(Q)* - Omega(Q) and Xi(Q)* - Xi(Q) are also given in Table 3. Starting for a general choice of the interpolating currents for the spin 1/2 baryons, our analysis favours the optimal value of the mixing angle b similar or equal to (-1/5-0) found from light and non-strange heavy baryons. (C) 2010 Elsevier B.V. All rights reserved.

A QCD sum rule calculation for the Y(4140) narrow structure

We use the QCD sum rules to evaluate the mass of a possible scalar mesonic state that couples to a molecular D(s)*(D) over bar (s)* current. We find a mass m(Ds)*(Ds)* = (4.14 +/- 0.09) GeV, which is in an excellent agreement with the recently observed Y(4140) charmonium state. We consider the contributions of condensates up to dimension-eight, we work at leading order in alpha(s) and we keep terms which are linear in the strange quark mass m(s). We also consider a molecular D*(D) over bar* current and we obtain m m(D)*(D)* = (4.13 +/- 0.10), around 200 MeV above the mass of the Y(3930) charmonium state. We conclude that it is possible to describe the Y(4140) structure as a D(s)*(D) over bar (s)* molecular state or even as a mixture of D(s)*(D) over bar (s)* and D*(D) over bar* molecular states. (C) 2009 Elsevier B.V. All rights reserved.

QCD sum rule calculation for the charmonium-like structures in the J/psi phi and J/psi omega invariant mass spectra

Using the QCD sum rules we test if the charmonium-like structure Y(4274), observed in the J/psi phi invariant mass spectrum, can be described with a D(s)(D) over bar (s0)(2317)+ h.c. molecular current with J(PC) = 0(-+). We consider the contributions of condensates up to dimension ten and we work at leading order in alpha(s). We keep terms which are linear in the strange quark mass m(s). The mass obtained for such state is mD(s)D(s0) = (4.78 +/- 0.54) GeV. We also consider a molecular 0(-+) D (D) over bar (0)(2400)+ h.c. current and we obtain m(DD0) = (4.55 +/- 0.49) GeV. Our study shows that the newly observed Y(4274) in the J/psi phi invariant mass spectrum can be, considering the uncertainties, described using a molecular charmonium current. (C) 2011 Elsevier B.V. All rights reserved.