Variation Of Quark Masses Research Articles

Bb¯ kinematic correlations in cold nuclear matter

Background: The LHCb Collaboration has studied a number of kinematic correlations between $B$-hadron pairs through their subsequent decays to $J/\psi$ pairs at 7 and 8 TeV for four minimum values of the $J/\psi$ $p_T$. Purpose: In this work, these measurements are compared to calculations of $b \bar b$ pairs and their hadronization and inclusive decays to $J/\psi J/\psi$ are compared to the same observables. Potential cold matter effects on the $b \bar b$ pair observables are discussed to determine which are most likely to provide insights about the system and why. Methods: The calculations, employing the exclusive HVQMNR code, assume the same intrinsic $k_T$-broadening and fragmentation as in [R. Vogt, Phys. Rev. C {\bf 98} (2018) 034907]. The pair distributions presented by LHCb are calculated in this approach, both for the parent $b \bar b$ and the $J/\psi J/\psi$ pairs produced in their decay. The sensitivity of the results to the intrinsic $k_T$ broadening is shown. The theoretical uncertainties due to the $b$ quark mass and scale variations on both the initial $b \bar b$ pairs and the resulting $J/\psi$ pairs are also shown. Possible effects due to the presence of the nucleus are studied by increasing the size of the $k_T$ broadening and modification of the fragmentation parameter. Results: Good agreement with the LHCb data is found for all observables. The parent $b \bar b$ distributions are more sensitive to the $k_T$ broadening than are the final-state $J/\psi$ pairs. Conclusions: Next-to-leading order calculations with $k_T$ broadening, as in [R. Vogt, Phys. Rev. C {\bf 98} (2018) 034907], can describe all correlated observables. Multiple measurements of correlated observables are sensitive to different nuclear effects which can help distinguish between them.

Theoretical uncertainties in exclusive electroproduction of S-wave heavy quarkonia

In this work, we revise the conventional description of J/psi (1S), Upsilon (1S), psi '(2S) and Upsilon '(2S) elastic photo- and electroproduction off a nucleon target within the color dipole picture and carefully study various sources of theoretical uncertainties in calculations of the corresponding electroproduction cross sections. For this purpose, we test the corresponding predictions using a bulk of available dipole cross section parametrisations obtained from deep inelastic scattering data at HERA. Specifically, we provide the detailed analysis of the energy and hard-scale dependencies of quarkonia yields employing the comprehensive treatment of the quarkonia wave functions in the Schrödinger equation based approach for a set of available c-bar{c} and b-bar{b} interquark interaction potentials. Besides, we quantify the effect of Melosh spin rotation, the Q^2-dependence of the diffractive slope and an uncertainty due to charm and bottom quark mass variations.

Roles of Be7(n,p)Li7 resonances in big bang nucleosynthesis with time-dependent quark mass and a possible Li reduction

Big bang nucleosynthesis (BBN) has been used as a probe of beyond-standard physics in the early Universe, which includes a time-dependent quark mass m_q. We investigate effects of a quark mass variation delta m_q on the cross sections of the 7Be(n, p)7Li reaction and primordial light element abundances taking into account roles of 8Be resonances in the reaction during BBN. This resonant reaction has not been investigated although behaviors of low-lying resonances are not trivial. It is found that a resonance at the resonance energy E_r=0.33 MeV enhances the reaction rate and lowers the 7Li abundance significantly when the quark mass variation is negative. Based upon up-to-date observational limits on primordial abundances of D, 4He and Li, the quark mass variation in the BBN epoch are derived. In a model in which the resonance energies of the reactions 3He(d, p)4He and 3H(d, n)4He are insensitive to the quark mass, we find that the Li abundance can be consistent with observations for delta m_q/m_q = (4--8) times 10^{-3}.

Heavy quarkonium production through the top quark rare decays via the channels involving flavor changing neutral currents

In the paper, we discuss the possibility of observation of heavy quarkoniums via the processes involving flavor changing neutral currents (FCNC). More explicitly, we systematically calculate the production of heavy charmonium and (c{bar{b}})-quarkonium through the top quark semi-exclusive rare FCNC decays in the framework of the non-relativistic QCD (NRQCD) factorization theory. Our results show that the total decay widths Gamma _{trightarrow eta _c} =1.20^{+1.04+1.14}_{-0.51-0.45}times 10^{-16} GeV, Gamma _{trightarrow J/psi } =1.37^{+1.03+1.30}_{-0.51-0.51}times 10^{-16} GeV, Gamma _{trightarrow B_c}=2.06^{+0.17+0.91}_{-0.17-0.54}times 10^{-18} GeV, and Gamma _{trightarrow B^*_c}=6.27^{+0.63+2.78}_{-0.62-1.64}times 10^{-18} GeV, where the uncertainties are from variation of quark masses and renormalization scales. Even though the decay widths are small, it is important to make a systematic study on the production of charmonium and (c{bar{b}})-quarkonium through the top-quark decays via FCNC in the Standard Model, which will provide useful guidance for future new physics research from the heavy quarkonium involved processes.

Hyperfine splitting in simple ions for the search of the variation of fundamental constants

Numerous few-electron atomic systems are considered which can be used effectively for observing a potential variation of the fine-structure constant $\alpha$ and the electron-proton mass ratio $m_e/m_p$. We examine optical magnetic dipole transitions between hyperfine-structure components in heavy highly charged H-like and Li-like ions with observably high sensitivity to a variation of $\alpha$ and $m_e/m_p$. The experimental spectra of the proposed systems consist of a strong single line, which simplifies significantly the data analysis and shortens the necessary measurement time. Furthermore, we propose systems for an experimental test of the variation of quark masses and discuss the expected level of accuracy in assessing its limitations. Finally, we establish which constraints on the variation of these fundamental constants could be provided by measurements with a hyperfine-structure highly-charged-ion clock and some reference clock, showing that a significant improvement of the current limitations can be reached.

NLO Monte Carlo predictions for heavy-quark production at the LHC: pp collisions in ALICE

Next-to-leading order (NLO) QCD predictions for the production of heavy quarks in proton-proton collisions are presented within three different approaches to quark mass, resummation and fragmentation effects. In particular, new NLO and parton shower simulations with POWHEG are performed in the ALICE kinematic regime at three different centre-of-mass energies, including scale and parton density variations, in order to establish a reliable baseline for future detailed studies of heavy-quark suppression in heavy-ion collisions. Very good agreement of POWHEG is found with FONLL, in particular for centrally produced D^0, D^+ and D^*+ mesons and electrons from charm and bottom quark decays, but also with the generally somewhat higher GM-VFNS predictions within the theoretical uncertainties. The latter are dominated by scale rather than quark mass variations. Parton density uncertainties for charm and bottom quark production are computed here with POWHEG for the first time and shown to be dominant in the forward regime, e.g. for muons coming from heavy-flavour decays. The fragmentation into D_s^+ mesons seems to require further tuning within the NLO Monte Carlo approach.

Quark mass variations of nuclear forces, BBN, and all that

Quark mass variations of nuclear forces, BBN, and all that

Reinvestigation of Quark Masses Variations on Big Bang Nucleosynthesis

We report the constraints from primordial nucleosynthesis on a possible time-dependent quark mass. The variation may affect binding energies and Q values as well as resonance properties of light elements through the hadron mass variation in the nucleon–nucleon interaction. Updated light-element abundances and uncertainties along with a new detailed analysis of the resonance properties on the crucial 3He(d, p)4He reaction imply a narrower range on the possible quark-mass variations in the early universe. The optimum concordance region reduces to a value consistent with no variation.

Quark-mass variation effect on big bang nucleosynthesis

We calculate the effect of variation in the light-current quark mass, mq, on standard big bang nucleosynthesis. A change in mq at during the era of nucleosynthesis affects nuclear reaction rates, and hence primordial abundances, via changes the binding energies of light nuclei. It is found that a relative variation of δmq/mq = 0.016 ± 0.005 provides better agreement between observed primordial abundances and those predicted by theory. This is largely due to resolution of the existing discrepancies for 7Li. However this method ignores possible changes in the position of resonances in nuclear reactions. The predicted 7Li abundance has a strong dependence on the cross-section of the resonant reactions 3He (d, p) 4He and t (d, n) 4He. We show that changes in mq at the time of BBN could shift the position of these resonances away from the Gamow window and lead to an increased production of 7Li, exacerbating the lithium problem.

Search for variation of fundamental constants and violations of fundamental symmetries using isotope comparisons

Atomic microwave clocks based on hyperfine transitions, such as the caesium standard, tick with a frequency that is proportional to the magnetic moment of the nucleus. This magnetic moment varies strongly between isotopes of the same atom, while all atomic electron parameters remain the same. Therefore the comparison of two microwave clocks based on different isotopes of the same atom can be used to constrain variation of fundamental constants. In this paper we calculate the neutron and proton contributions to the nuclear magnetic moments, as well as their sensitivity to any potential quark mass variation, in a number of isotopes of experimental interest including 201,199Hg and 87,85Rb, where experiments are underway. We also include a brief treatment of the dependence of the hyperfine transitions to variation in nuclear radius, which in turn is proportional to any change in quark mass. Our calculations of expectation-values of proton and neutron spin in nuclei are also needed to interpret measurements of violations of fundamental symmetries.

Time-dependent quark masses and big bang nucleosynthesis revisited

We reinvestigate the constraints from primordial nucleosynthesis on a possible time-dependent quark mass. The limits on such quark-mass variations are particularly sensitive to the adopted observational abundance constraints. Hence, in the present study we have considered updated light-element abundances and uncertainties deduced from observations. We also consider new nuclear reaction rates and an independent analysis of the influence of such quark-mass variations on the resonance properties of the important 3He(d,p)4He reaction. We find that the updated abundance and resonance constraints imply a narrower range on the possible quark-mass variations in the early universe. We also find that, contrary to previous investigations, the optimum concordance region reduces to a (95% C.L.) value of -0.005 < delta m_q/m_q < 0.007 consistent with no variation in the averaged quark mass.

Quark mass variation constraints from Big Bang nucleosynthesis

We study the impact on the primordial abundances of light elements created by a variation of the quark masses at the time of Big Bang nucleosynthesis (BBN). In order to navigate through the particle and nuclear physics required to connect quark masses to binding energies and reaction rates in a model-independent way, we use lattice QCD data and a hierarchy of effective field theories. We find that the measured $^{4}\mathrm{He}$ abundances put a bound of $\ensuremath{-}1%\ensuremath{\lesssim}\ensuremath{\delta}{m}_{q}/{m}_{q}\ensuremath{\lesssim}0.7%$ on a possible variation of quark masses. The effect of quark mass variations on the deuterium abundances can be largely compensated by changes of the baryon-to-photon ratio $\ensuremath{\eta}$. Including bounds on the variation of $\ensuremath{\eta}$ coming from WMAP results and adding some additional assumptions further narrows the range of allowed values of $\ensuremath{\delta}{m}_{q}/{m}_{q}$.

Effect of quark mass variation on big bang nucleosynthesis

We calculate the effect of variation in the light-current quark mass, mq, on standard big bang nucleosynthesis. A change in mq during the era of nucleosynthesis affects nuclear reaction rates, and hence primordial abundances, via changes in the binding energies of light nuclei. It is found that a relative variation of δmq/mq=0.016±0.005 provides better agreement between observed primordial abundances and those predicted by theory. This is largely due to resolution of the existing discrepancies for 7Li. However this method ignores possible changes in the position of resonances in nuclear reactions. The predicted 7Li abundance has a strong dependence on the cross-section of the resonant reactions He3(d,p)He4 and t(d,n)He4. We show that changes in mq at the time of BBN could shift the position of these resonances away from the Gamow window and lead to an increased production of 7Li, exacerbating the lithium problem.

Sensitivity of hyperfine structure to nuclear radius and quark mass variation

To search for the temporal variation of the fundamental constants one needs to know dependence of atomic transition frequencies on these constants. We study the dependence of the hyperfine structure of atomic $s$-levels on nuclear radius and, via radius, on quark masses. An analytical formula has been derived and tested by the numerical relativistic Hartree-Fock calculations for Rb, Cd$^+$, Cs, Yb$^+$ and Hg$^+$. The results of this work allow the use of the results of past and future atomic clock experiments and quasar spectra measurements to put constrains on time variation of the quark masses.

Limits on cosmological variation of quark masses and strong interaction

We discuss limits on the variation of ${(m}_{q}/{\ensuremath{\Lambda}}_{\mathrm{QCD}}).$ The results are obtained by studying the $n\ensuremath{-}\ensuremath{\alpha}$ interaction during the big bang, Oklo natural nuclear reactor data, and limits on the variation of the proton g factor from quasar absorption spectra.

Limits on cosmological variation of strong interaction and quark masses from big bang nucleosynthesis, cosmic, laboratory and Oklo data

Recent data on cosmological variation of the electromagnetic fine structure constant from distant quasar (QSO) absorption spectra have inspired a more general discussion of possible variation of other constants. We discuss variation of strong scale and quark masses. We derive the limits on their relative change from (i) primordial Big-Bang Nucleosynthesis (BBN); (ii) Oklo natural nuclear reactor, (iii) quasar absorption spectra, and (iv) laboratory measurements of hyperfine intervals.

String potential model: Spinless quarks.

We propose a generalization of the usual potential model of quark bound states in which the confining flux tube is a dynamical object carrying both angular momentum and energy. The QQ\ifmmode\bar\else\textasciimacron\fi{}-string system with spinless quarks is quantized using an implicit operator technique and the resulting relativistic wave equation is solved. For heavy quarks the usual Schr\"odinger valence-quark model is recovered. The Regge slope with light quarks agrees with the classical rotating-string result and is significantly larger than that given by the normal potential model. Quark mass variation and the effects of short-range forces are also considered.

Photoproduction of charmonium

Photoproduction of ortho and para charm-anticharm bound states is considered in the framework of the Cheng-Wu picture. Non-Abelian gauge gluons mediate the interaction between the c c -pair and the nucleon. The angular distributions of ψ c and η c are determined. The influence of multigluon exchanges and quark mass variation is studied.