Showing papers on "Charm quark published in 2010"

The QCD equation of state with dynamical quarks

Abstract: The present paper concludes our investigation on the QCD equation of state with 2+1 staggered flavors and one-link stout improvement. We extend our previous study [JHEP 0601:089 (2006)] by choosing even finer lattices. Lattices with $N_t=6,8$ and 10 are used, and the continuum limit is approached by checking the results at $N_t=12$. A Symanzik improved gauge and a stout-link improved staggered fermion action is utilized. We use physical quark masses, that is, for the lightest staggered pions and kaons we fix the $m_\pi/f_K$ and $m_K/f_K$ ratios to their experimental values. The pressure, the interaction measure, the energy and entropy density and the speed of sound are presented as functions of the temperature in the range $100 ...1000 \textmd{MeV}$. We give estimates for the pion mass dependence and for the contribution of the charm quark. We compare our data to the equation of state obtained by the "hotQCD" collaboration.

The QCD equation of state with dynamical quarks

Abstract: The present paper concludes our investigation on the QCD equation of state with 2+1 staggered flavors and one-link stout improvement. We extend our previous study (JHEP 0601:089 (2006)) by choosing even finer lattices. Lattices with Nt = 6,8 and 10 are used, and the continuum limit is approached by checking the results at Nt = 12. A Symanzik improved gauge and a stout-link improved staggered fermion action is utilized. We use physical quark masses, that is, for the lightest staggered pions and kaons we fix the m�/fK and mK/fK ratios to their experimental values. The pressure, the interaction measure, the energy and entropy density and the speed of sound are presented as functions of the temperature in the range 100...1000MeV. We give estimates for the pion mass dependence and for the contribution of the charm quark. We compare our data to the equation of state obtained by the "hotQCD" collaboration.

Light hadrons from lattice QCD with light (u, d), strange and charm dynamical quarks

Abstract: We present results of lattice QCD simulations with mass-degenerate up and down and mass-split strange and charm (N f = 2 + 1 + 1) dynamical quarks using Wilson twisted mass fermions at maximal twist. The tuning of the strange and charm quark masses is performed at two values of the lattice spacing a ≈ 0:078 fm and a ≈ 0:086 fm with lattice sizes ranging from L ≈ 1:9 fm to L ≈ 2:8 fm. We measure with high statistical precision the light pseudoscalar mass m PS and decay constant f PS in a range 270 ≲ m PS ≲ 510 MeV and determine the low energy parameters f 0 and $ {\bar{l}_{3,4}} $ of SU(2) chiral perturbation theory. We use the two values of the lattice spacing, several lattice sizes as well as different values of the light, strange and charm quark masses to explore the systematic effects. A first study of discretisation effects in light-quark observables and a comparison to N f = 2 results are performed.

Light hadrons from lattice QCD with light (u,d), strange and charm dynamical quarks

Abstract: We present results of lattice QCD simulations with mass-degenerate up and down and mass-split strange and charm (N_f = 2+1+1) dynamical quarks using Wilson twisted mass fermions at maximal twist. The tuning of the strange and charm quark masses is performed at two values of the lattice spacing a~0.078 fm and a~0.086 fm with lattice sizes ranging from L~1.9 fm to L~2.8 fm. We measure with high statistical precision the light pseudoscalar mass m_PS and decay constant f_PS in a range 270 < m_PS < 510 MeV and determine the low energy parameters f_0, l_3 and l_4 of SU(2) chiral perturbation theory. We use the two values of the lattice spacing, several lattice sizes as well as different values of the light, strange and charm quark masses to explore the systematic effects. A first study of discretisation effects in light-quark observables and a comparison to N_f=2 results are performed.

The Benefits of B ---> K* l+ l- Decays at Low Recoil

Abstract: Using the heavy quark effective theory framework put forward by Grinstein and Pirjol we work out predictions for B -> K* l+ l-, l = (e, mu), decays for a softly recoiling K*, i.e., for large dilepton masses sqrt{q^2} of the order of the b-quark mass m_b. We work to lowest order in Lambda/Q, where Q = (m_b, sqrt{q^2}) and include the next-to-leading order corrections from the charm quark mass m_c and the strong coupling at O(m_c^2/Q^2, alpha_s). The leading Lambda/m_b corrections are parametrically suppressed. The improved Isgur-Wise form factor relations correlate the B -> K* l+ l- transversity amplitudes, which simplifies the description of the various decay observables and provides opportunities for the extraction of the electroweak short distance couplings. We propose new angular observables which have very small hadronic uncertainties. We exploit existing data on B -> K* l+ l- distributions and show that the low recoil region provides powerful additional information to the large recoil one. We find disjoint best-fit solutions, which include the Standard Model, but also beyond-the-Standard Model ones. This ambiguity can be accessed with future precision measurements.

Scaling studies of QCD with the dynamical highly improved staggered quark action

Abstract: We study the lattice spacing dependence, or scaling, of physical quantities using the highly improved staggered quark (HISQ) action introduced by the HPQCD/UKQCD Collaboration, comparing our results to similar simulations with the asqtad fermion action. Results are based on calculations with lattice spacings approximately 0.15, 0.12, and 0.09 fm, using four flavors of dynamical HISQ quarks. The strange and charm quark masses are near their physical values, and the light-quark mass is set to 0.2 times the strange-quark mass. We look at the lattice spacing dependence of hadron masses, pseudoscalar meson decay constants, and the topological susceptibility. In addition to the commonly used determination of the lattice spacing through the static quark potential, we examine a determination proposed by the HPQCD Collaboration that uses the decay constant of a fictitious ''unmixed ss'' pseudoscalar meson. We find that the lattice artifacts in the HISQ simulations are much smaller than those in the asqtad simulations at the same lattice spacings and quark masses.

Average up/down, strange and charm quark masses with Nf=2 twisted mass lattice QCD

Abstract: We present a high precision lattice calculation of the average up/down, strange and charm quark masses performed with Nf=2 twisted mass Wilson fermions. The analysis includes data at four values of the lattice spacing and pion masses as low as ~270 MeV, allowing for accurate continuum limit and chiral extrapolation. The strange and charm masses are extracted by using several methods, based on different observables: the kaon and the eta_s meson for the strange quark and the D, D_s and eta_c mesons for the charm. The quark mass renormalization is carried out non-perturbatively using the RI-MOM method. The results for the quark masses in the MSbar scheme read: m_ud(2 GeV)= 3.6(2) MeV, m_s(2 GeV)=95(6) MeV and m_c(m_c)=1.28(4) GeV. We also obtain the ratios m_s/m_ud=27.3(9) and m_c/m_s=12.0(3).

Precise Charm to Strange Mass Ratio and Light Quark Masses from Full Lattice QCD

Abstract: By using a single formalism to handle charm, strange, and light valence quarks in full lattice QCD for the first time, we are able to determine ratios of quark masses to 1%. For m(c)/m(s) we obtain 11.85(16), an order of magnitude more precise than the current PDG average. Combined with 1% determinations of the charm quark mass now possible this gives m(s)(2 GeV)=92.4(1.5) MeV. The MILC result for m(s)/m(l)=27.2(3) yields m(l)(2 GeV)=3.40(7) MeV for the average of u and d quark masses.

Langevin diffusion of heavy quarks in non-conformal holographic backgrounds

Abstract: The Langevin diffusion process of a relativistic heavy quark in a non-conformal holographic setup is analyzed. The bulk geometry is a general, five-dimensional asymptotically AdS black hole. The heavy quark is described by a trailing string attached to a flavor brane, moving at constant velocity. From the equations describing linearized fluctuations of the string world-sheet, the correlation functions defining a generalized Langevin process are constructed via the AdS/CFT prescription. In the local limit, analytic expressions for the Langevin diffusion and friction coefficients are obtained in terms of the bulk string metric. Modified Einstein relations between these quantities are also derived. The spectral densities associated to the Langevin correlators are analyzed, and simple analytic expressions are obtained in the small and large frequency limits. Finally, a numerical analysis of the jet-quenching parameter, and a comparison to RHIC phenomenology are performed in the case of Improved Holographic QCD. It is shown that the jet-quenching parameter is not enough to describe energy loss of very energetic charm quarks and the full Langevin correlators are needed.

B! K l + l decays at low recoil

Abstract: Using the heavy quark eective theory framework put forward by Grinstein and Pirjol we work out predictions for B! K l + l , l = e; , decays for a softly recoiling K , i.e., for large dilepton masses p q 2 of the order of the b-quark mass mb. We work to lowest order in =Q, where Q = (mb; p q 2 ) and include the next-to-leading order corrections from the charm quark mass mc and the strong coupling atO(m 2 =Q 2 ; s). The leading =mb corrections are parametrically suppressed. The improved Isgur-Wise form factor relations correlate the B! K l + l transversity amplitudes, which simplies the description of the various decay observables and provides opportunities for the extraction of the electroweak short distance couplings. We propose new angular observables which have very small hadronic uncertainties. We exploit existing data on B! K l + l distributions and show that the low recoil region provides powerful additional information to the large recoil one. We nd disjoint best-t solutions, which include the Standard Model, but also beyond-the-

Small shear viscosity in the semiquark gluon plasma

Abstract: At nonzero temperature in QCD, about the deconfining phase transition there is a semiquark gluon plasma (semi-QGP), where the expectation value of the (renormalized) Polyakov loop is less than one. This can be modeled by a semiclassical expansion about a constant field for the vector potential, ${A}_{0}$, which is diagonal in color. We compute the shear viscosity in the semi-QGP by using the Boltzmann equation in the presence of this background field. To leading, logarithmic order in weak coupling, the dominant diagrams are given by the usual scattering processes of $2\ensuremath{\rightarrow}2$ particles. For simplicity we also assume that both the number of colors and flavors are large. Near the critical temperature ${T}_{c}$, where the expectation value of the Polyakov loop is small, the overall density of colored fields decreases according to their color representation, with the density of quarks vanishes linearly with the loop, and that of gluons, quadratically. This decrease in the overall density dominates changes in the transport cross section. As a result, relative to that in the perturbative QGP, near ${T}_{c}$ the shear viscosity in the semi-QGP is suppressed by two powers of the Polyakov loop. In a semiclassical expansion, the suppression of colored fields depends only upon which color representation they lie in, and not upon their mass. That light and heavy quarks are suppressed in a common manner may help to explain the behavior of charm quarks at RHIC.

Dissociation of a heavy meson in the quark medium

Abstract: We investigate the dissociation of a heavy meson in the medium composed of light quarks and gluons. In the quark-gluon plasma, the dissociation length of the heavy meson becomes short as the temperature or quark chemical potential increases. On the contrary, in the hadronic phase the dissociation length becomes large as the chemical potential increases, due to the different dissociation mechanism with one used in the quark-gluon plasma.

Charmonium from Statistical Hadronization of Heavy Quarks: A Probe for Deconfinement in the Quark-Gluon Plasma

Abstract: We review the statistical hadronization picture for charmonium production in ultra-relativistic nuclear collisions. Our starting point is a brief reminder of the status of the thermal model description of hadron production at high energy. Within this framework an excellent account is achieved of all data for hadrons built of (u,d,s) valence quarks using temperature, baryo-chemical potential and volume as thermal parameters. The large charm quark mass brings in a new (non-thermal) scale which is explicitely taken into account by fixing the total number of charm quarks produced in the collision. Emphasis is placed on the description of the physical basis for the resulting statistical hadronization model. We discuss the evidence for statistical hadronization of charmonia by analysis of recent data from the SPS and RHIC accelerators. Furthermore we discuss an extension of this model towards lower beam energies and develop arguments about the prospects to observe medium modifications of open and hidden charm hadrons. With the imminent start of the LHC accelerator at CERN, exciting prospects for charmonium production studies at the very high energy frontier come into reach. We present arguments that, at such energies, charmonium production becomes a fingerprint of deconfinement: even if no charmonia survive in the quark-gluon plasma, statistical hadronization at the QCD phase boundary of the many tens of charm quarks expected in a single central Pb-Pb collision could lead to an enhanced, rather than suppressed production probability when compared to results for nucleon-nucleon reactions scaled by the number of hard collisions in the Pb-Pb system.

Why heavy and light quarks radiate energy with similar rates

Abstract: The dead-cone effect has been predicted to reduce the magnitude of energy loss and jet quenching for heavy flavors produced with large p{sub T} in heavy-ion collisions. On the contrary, data from the Relativistic Heavy Ion Collider demonstrate a strong suppression of high-p{sub T} electrons from charm and bottom decays. We show that vacuum radiation of a highly virtual quark produced at high p{sub T} with a stripped-off color field develops a much wider dead cone, which screens the one related to the quark mass. Lacking the field, gluons cannot be radiated within this cone until the color field is regenerated and the quark virtuality cools down to the scale of the order of the quark mass. However, this takes longer than is essential for the observed jet quenching, leading to similar nuclear effects for the light and charm quark jets. Open beauty is expected to radiate much less within the p{sub T} range studied so far in heavy-ion collisions.

Pseudoscalar decay constants from N_f=2+1+1 twisted mass lattice QCD

Abstract: We present first results for the pseudoscalar decay constants $f_K$, $f_D$ and $f_{D_s}$ from lattice QCD with N_f=2+1+1 flavours of dynamical quarks. The lattice simulations have been performed by the European Twisted Mass collaboration (ETMC) using maximally twisted mass quarks. For the pseudoscalar decay constants we follow a mixed action approach by using so called Osterwalder-Seiler fermions in the valence sector for strange and charm quarks. The data for two values of the lattice spacing and several values of the up/down quark mass is analysed using chiral perturbation theory.

Condensate Enhancement and D-Meson Mixing in Technicolor Theories

Abstract: Since the pioneering work of Eichten and Lane it has been known that the scale of the interactions responsible for the generation of the strange-quark mass in extended technicolor theories must, absent any Glashow-Iliopoulos-Maiani mechanism for suppressing flavor-changing neutral currents, be greater than of order 1000 TeV. In this paper we point out that the constraint from the neutral D-meson system is now equally strong, implying that the charm quark mass must also arise from flavor dynamics at a scale this high. We then quantify the degree to which the technicolor condensate must be enhanced in order to yield the observed quark masses, if the extended technicolor scale is of order 1000 TeV. Our results are intended to provide a framework in which to interpret and apply the results of lattice studies of conformal strongly interacting gauge theories, and the corresponding numerical measurements of the anomalous dimension of the mass operator in candidate theories of walking technicolor.

D and D_s in mass loaded flux tube

Abstract: Heavy-light hadrons are studied in a mass loaded flux tube model. The study indicates that the dynamics of mesons and baryons containing a c quark is described well by the mass loaded flux tube. The hypothesis of good diquark-antiquark degeneracy is found reasonable in heavy-light quark systems. The spectrum of charmed (D) and charmed strange (Ds) mesons is systematically computed. D and Ds in 1D multiplets are predicted to have lower masses in comparison with other theoretical predictions. The predicted masses of the 1−(13D1) and the 3−(13D3) Ds agree well with those of recently observed Ds1(2700)± and DsJ(2860), respectively.

Light Higgs boson decaying to four charm quarks

Abstract: We present a simple supersymmetric model where the dominant decay mode of the lightest Higgs boson is h{yields}2{eta}{yields}4c, where {eta} is a light pseudoscalar and c is the charm quark. For such decays the Higgs mass can be smaller than 100 GeV without conflict with experiment. Together with the fact that both the Higgs and the pseudoscalar {eta} are pseudo-Goldstone bosons, this resolves the little hierarchy problem.

Constraining weak annihilation using semileptonic D decays

Abstract: The recently measured semileptonic D{sub s} decay rate can be used to constrain weak annihilation (WA) effects in semileptonic D and B decays. We revisit the theoretical predictions for inclusive semileptonic D{sub (s)} decays using a variety of quark mass schemes. The most reliable results are obtained if the fits to B decay distributions are used to eliminate the charm quark mass dependence, without using any specific charm mass scheme. Our fit to the available data shows that WA is smaller than commonly assumed. There is no indication that the WA octet contribution (which is better constrained than the singlet contribution) dominates. The results constrain an important source of uncertainty in the extraction of |V{sub ub}| from inclusive semileptonic B decays.

Extracting CP violation and strong phase in D decays by using quantum correlations in psi(3770)-> D0\bar{D}0 -> (V_1V_2)(V_3V_4) and psi(3770)->D0\bar{D}0 -> (V_1V_2)(K pi)

Abstract: The charm quark offers interesting opportunities to cross-check the mechanism of CP violation precisely tested in the strange and beauty sectors. In this paper, we exploit the angular and quantum correlations in the D\bar{D} pairs produced through the decay of the psi(3770) resonance in a charm factory to investigate CP-violation in two different ways. We build CP-violating observables in psi(3770) -> D\bar{D} -> (V_1V_2)(V_3 V_4) to isolate specific New Physics effects in the charm sector. We also consider the case of psi(3770) -> D\bar{D} -> (V_1V_2)(K\pi) decays, which provide a new way to measure the strong phase difference delta between Cabibbo-favored and doubly-Cabibbo suppressed D decays required in the determination of the CKM angle gamma. Neglecting the systematics, we give a first rough estimate of the sensitivities of these measurements at BES-III with an integrated luminosity of 20 fb^-1 at psi(3770) peak and at a future Super tau-charm factory with a luminosity of 10^35 cm^-2.s^-1.

Effects of the charm quark on the QCD equation of state

Abstract: We study the effects of the addition of the charm quark on the QCD equation of state at zero and nonzero chemical potential on lattices with $N_t=6$. Our ensembles are quenched with respect to charm and the charm quark is a valence staggered quark. Along the trajectory of constant physics the ratio $m_s/m_c$ is kept constant after tuning the charm quark mass at a lattice spacing of about 0.09 fm. We find that the charm quark has a significant contribution to the equation of state at zero chemical potential already at temperatures between about $1.2T_c$ and $2T_c$. The additional contribution at nonzero chemical potential vanishes within the current statistical uncertainty.

Production and elliptic flow of heavy quarks at RHIC and LHC within a partonic transport model

Abstract: Production and elliptic flow of heavy quarks are investigated in nucleus-nucleus collisions at RHIC and LHC within the Boltzmann Approach of MultiParton Scatterings (BAMPS). The initial heavy quark yield is estimated with the leading order mini-jet model and compared to PYTHIA for several parton distribution functions. Secondary production of heavy quarks in the quark-gluon plasma is examined within the full 3+1 dimensional BAMPS simulation of heavy ion collisions. At RHIC this yield is negligible, but for LHC charm production in the QGP plays a significant role. In addition, we study the elliptic flow of charm quarks at RHIC with the result that leading order processes are not sufficient to describe the experimental data.

Quark-diquark model description for double charm baryons

Abstract: We report here the mass spectrum and magnetic moments of ccq(q u,d,s) systems in the potential model framework by assuming the inter-quark potential as the colour coulomb plus power form with power index ν varying between 0.1 to 2.0. Here the two charm quarks are considered for the diquark states. The conventional one gluon exchange interaction has been employed to get the hyperfine and the fine structure between different states. We have predicted many low-lying states whose experimental verification can exclusively support the quark-diquark structure of the baryons.

A Lattice QCD Calculation of the Charmonium Spectrum

Abstract: On November 11, 1974 the $J/\Psi$ charmonium particle was discovered simultaneously on both coasts of the United States. This state is mainly built up from a charm quark and an anti-charm quark. Until then only three so-called flavors of quarks were known experimentally: up, down and strange. Since then several new charmonium resonances have been discovered whose properties could mostly be accounted for by nonrelativistic potential models with a confining force. However, many of the very recent discoveries are at variance with this simplistic picture. One such example is the so-called $X(3872)$ particle. Future dedicated experiments like {\it PANDA} at {\it FAIR} in Darmstadt are expected to produce large charmonium data samples that will help to further explore the properties of old and new such states. Quarks are an elementary building block of visible matter. They interact via the strong interaction, which is described by the theory of {\it Quantum Chromo Dynamics (QCD)}. With the help of numerical simulations in the framework of {\it Lattice QCD}, i.e. QCD on a discretized spacetime, this work tries to shed light on the masses and structure of charmonium states, including the more exotic ones.

Infrared and Ultraviolet QCD dynamics with quark mass for J=0,1 mesons

Abstract: By using a previously developed phenomenological kernel for the study of the light quark QCD sector and dynamical chiral symmetry breaking effects we will examine the relative infrared and ultraviolet QCD dynamics for J=0,1 meson properties. For the same reasons we extend and explore a quark mass depended generalization of the kernel in the heavy quark region and we also compare with the original model. The relation between the dynamics of the quark propagator and the effective kernel with the J=0,1 QQ and qQ mesons and quarks Compton size is also discussed.