Thu·Aug 10, 2017Thursday·August 10, 2017

1. 01*

   Strong and radiative decays of excited vector mesons and predictions for a new $\varphi (1930)$ resonance

   Milena Piotrowska🇵🇱 · Christian Reisinger🇩🇪 · Francesco Giacosa🇩🇪

   We study the phenomenology of two nonets of excited vector mesons, $\{\rho (1450)$, $K^{\ast }(1410)$, $\omega (1420)$, $\varphi (1680)\}$ and $\{\rho (1700),$ $K^{\ast }(1680),\omega (1650),$ $\varphi (???)\},$ which (roughly) correspond to radially excited $2^3{S}_1$ and to orbitally excited $1^3{D}_1$ vector mesons. We evaluate the strong and radiative decays of these mesons into pseudoscalar and ground-state vector mesons by using an effective relativistic QFT model based on flavour symmetry. We compare decay widths and branching ratios with various experimental results listed in the PDG. An overall agreement of theory with experiment reinforces the standard quark-antiquark assignment of the resonances mentioned above. Predictions for not yet measured quantities are also made. In particular, we shall also make predictions for the not-yet discovered $s\bar{s}$ state of the $1^3{D}_1$ nonet, denoted as $\varphi (???)$. Its mass can be estimated to be about $1930$ MeV, hence we shall call this putative state $\varphi (1930).$ Its main decays are into $K{K}^{\ast }(892)$ (about $200$ MeV) and $KK$ (about $100$ MeV). Since this state couples also to $\gamma \eta ,$ it can be searched in the near future in the photoproduction-based experiments GlueX and CLAS12 at Jefferson Lab.

   hep-phPRD(2017)·40 citations
2. 02*

   $B_s^0\to {\ell }^{+}{\ell }^{-}\gamma$ as a Test of Lepton Flavor Universality

   Diego Guadagnoli🇫🇷 · Meril Reboud🇫🇷 · Roman Zwicky🇬🇧

   We discuss a number of strategies to reduce the $\mathcal{B}(B_s^0\to {\ell }^{+}{\ell }^{-}\gamma )$ theoretical error, and make such a measurement a new probe of the interactions that are interesting in the light of present-day flavor discrepancies. In particular, for low di-lepton invariant mass we propose to exploit the close parenthood between $\mathcal{B}(B_s^0\to {\ell }^{+}{\ell }^{-}\gamma )$ and the measured $\mathcal{B}(B_s^0\to \varphi (\to K^{+}{K}^{-})\gamma )$. For high $q^2$, conversely, we exploit the fact that the decay is dominated by two form-factor combinations, plus contributions from broad charmonium that we model accordingly. We construct the ratio $R_{\gamma }$, akin to $R_K$ and likewise sensitive to lepton-universality violation. Provided the two rates in this ratio are integrated in a suitable region that minimises bremsstrahlung contributions while maximising statistics, the ratio is very close to unity and the form-factor dependence cancels to an extent that makes it a new valuable probe of lepton-universality violating contributions in the effective Hamiltonian. We finally speculate on additional ideas to extract short-distance information from resonance regions, which are theoretically interesting but statistically limited at present.

   hep-phJHEP(2017)·41 citations
3. 03*

   DirectDM: a tool for dark matter direct detection

   Fady Bishara🇬🇧 · Joachim Brod🇩🇪 · Benjamin Grinstein🇺🇸 · Jure Zupan🇺🇸

   We provide a Mathematica package, DirectDM, that takes as input the Wilson coefficients of the relativistic effective theory describing the interactions of dark matter with quarks, gluons and photons, and matches it onto an effective theory describing the interactions of dark matter with neutrons and protons. The nonperturbative matching is performed at leading order in a chiral expansion. The one-loop QCD and QED renormalization-group evolution from the electroweak scale down to the hadronic scale, as well as finite corrections at the heavy quark thresholds are taken into account. We also provide an interface with the package DMFormFactor so that, starting from the relativistic effective theory, one can directly obtain the event rates for direct detection experiments.

   hep-phastro-ph.CO89 citations
4. 04*

   Heavy-Quark Hybrid Mass Splittings: Hyperfine and "Ultrafine"

   Richard F. Lebed🇺🇸 · Eric S. Swanson🇺🇸

   It is argued that the heavy-quark limit of QCD requires a certain combination of hyperfine mass splittings in heavy-quark hybrid-meson multiplets to be unusually small. This observation will assist in the exploration of the heavy-quark hybrid spectrum at facilities such as PANDA. Alternatively, a large measured value for this mass splitting indicates that at least one member of the multiplet must contain significant light-quark degrees of freedom.

   hep-phhep-exFew Body Syst.(2018)·10 citations
5. 05*

   $a_0(980)-f_0(980)$ mixing in ${\chi }_{c1}\to {\pi }^0{f}_0(980)\to {\pi }^0{\pi }^{+}{\pi }^{-}$ and ${\chi }_{c1}\to {\pi }^0{a}_0(980)\to {\pi }^0{\pi }^0\eta$

   M. Bayar🇹🇷 · V. R. Debastiani🇪🇸

   We study the isospin breaking in the reactions ${\chi }_{c1}\to {\pi }^0{\pi }^{+}{\pi }^{-}$ and ${\chi }_{c1}\to {\pi }^0{\pi }^0\eta$ and its relation to the $a_0(980)-f_0(980)$ mixing, which was measured by the BESIII Collaboration. We show that the same theoretical model previously developed to study the ${\chi }_{c1}\to \eta {\pi }^{+}{\pi }^{-}$ reaction (also measured by BESIII), and further explored in the predictions to the ${\eta }_c\to \eta {\pi }^{+}{\pi }^{-}$, can be successfully employed in the present study. We assume that the ${\chi }_{c1}$ behaves as an $SU(3)$ singlet to find the weight in which trios of pseudoscalars are created, followed by the final state interaction of pairs of mesons to describe how the $a_0(980)$ and $f_0(980)$ are dynamically generated, using the chiral unitary approach in coupled channels. The isospin violation is introduced through the use of different masses for the charged and neutral kaons, either in the propagators of the pairs of mesons created in the ${\chi }_{c1}$ decay, or in the propagators inside the $T$ matrix, constructed through the unitarization of the scattering and transition amplitudes of pairs of pseudoscalar mesons. We find that violating isospin inside the $T$ matrix makes the ${\pi }^0\eta \to {\pi }^{+}{\pi }^{-}$ amplitude nonzero, which gives an important contribution and also enhances the effect of the $K\bar{K}$ term. Also, we find that in the total amplitude the most important effect is the isospin breaking inside the $T$ matrix, due to the constructive sum of ${\pi }^0\eta \to {\pi }^{+}{\pi }^{-}$ and $K\bar{K}\to {\pi }^{+}{\pi }^{-}$, which is essential to get a good agreement with the experimental measurement of the mixing.

   hep-phPLB(2017)·14 citations
6. 06*

   Magnetized quark-gluon plasma at the LHC

   V. Skalozub🇺🇦 · P. Minaev🇺🇦

   In QCD, the strengths of the large scale temperature dependent chromomagnetic, $B_3,B_8$, and usual magnetic, $H$, fields spontaneously generated in quark-gluon plasma after the deconfinement phase transition (DPT), are estimated. The consistent at high temperature effective potential accounting for the one-loop plus daisy diagrams is used. The heavy ion collisions at the LHC and temperatures T not much higher than the phase transition temperature $T_d$ are considered. The critical temperature for the magnetized plasma is found to be $T_d(H)$ ~ $110-120$ MeV. This is essentially lower compared to the zero field value $T_d(H=0)$~ $160-180$ MeV usually discussed in the literature. Due to contribution of quarks, the color magnetic fields act as the sources generating H. The strengths of the fields are $B_3(T),B_8(T)\sim 10^{18}-10^{19}G,H(T)\sim 10^{16}-10^{17}G$ for temperatures T ~ 160 - 220 MeV. At temperatures $T<110-120$ MeV the effective potential minimum value being negative approaches to zero. This is signaling the absence of the background fields and color confinement.

   hep-phPhys.Part.Nucl.Lett.(2018)·3 citations
7. 07*

   Repulsive baryonic interactions and lattice QCD observables at imaginary chemical potential

   Volodymyr Vovchenko🇩🇪 · Attila Pasztor🇩🇪 · Zoltan Fodor🇩🇪 · Sandor D. Katz🇭🇺 · Horst Stoecker🇩🇪

   The first principle lattice QCD methods allow to calculate the thermodynamic observables at finite temperature and imaginary chemical potential. These can be compared to the predictions of various phenomenological models. We argue that Fourier coefficients with respect to imaginary baryochemical potential are sensitive to modeling of baryonic interactions. As a first application of this sensitivity, we consider the hadron resonance gas (HRG) model with repulsive baryonic interactions, which are modeled by means of the excluded volume correction. The Fourier coefficients of the imaginary part of the net-baryon density at imaginary baryochemical potential -- corresponding to the fugacity or virial expansion at real chemical potential -- are calculated within this model, and compared with the $N_t=12$ lattice data. The lattice QCD behavior of the first four Fourier coefficients up to $T\simeq 185$ MeV is described fairly well by an interacting HRG with a single baryon-baryon eigenvolume interaction parameter $b\simeq 1$ fm${}^3$, while the available lattice data on the difference ${\chi }_2^B-{\chi }_4^B$ of baryon number susceptibilities is reproduced up to $T\simeq 175$ MeV.

   hep-phhep-latnucl-thPLB(2017)·116 citations
8. 08*

   Quasi-two-body decays $B\to {\eta }_c(1S,2S)[\rho (770),\rho (1450),\rho (1700)\to ]\pi \pi$ in the perturbative QCD approach

   Ya Li🇨🇳 · Ai-Jun Ma🇨🇳 · Zhou Rui🇨🇳 · Zhen-Jun Xiao🇨🇳

   In this paper, we calculated the branching ratios of the quasi-two-body decays $B\to {\eta }_c(1S,2S)$ $[\rho (770),\rho (1450),\rho (1700)\to ]\pi \pi$ by employing the perturbative QCD (PQCD) approach. The contributions from the $P$-wave resonances $\rho (770)$, $\rho (1450)$ and $\rho (1700)$ were taken into account. The two-pion distribution amplitude ${\Phi }_{\pi \pi }^{\mathrm{P}}$ is parameterized by the vector current time-like form factor $F_{\pi }$ to study the considered decay modes. We found that (a) the PQCD predictions for the branching ratios of the considered quasi-two-body decays are in the order of $10^{-7}\sim 10^{-6}$, while the two-body decay rates $\mathcal{B}(B\to {\eta }_c(1S,2S)(\rho (1450),\rho (1700)))$ are extracted from those for the corresponding quasi-two-body decays; (b) the whole pattern of the pion form factor-squared $|F_{\pi }{|}^2$ measured by the BABAR Collaboration could be understood based on our theoretical results; (c) the general expectation based on the similarity between $B\to {\eta }_c\pi \pi$ and $B\to J/\psi \pi \pi$ decays are confirmed: $R_2({\eta }_c)\approx 0.45$ is consistent with the measured $R_2(J/\psi )\approx 0.56\pm 0.09$ within errors; and (d) new ratios $R_3({\eta }_c(1S))$ and $R_4({\eta }_c(2S))$ among the branching ratios of the considered decay modes are defined and could be tested by future experiments.

   hep-phNPB(2017)·17 citations
9. 09*

   The Stationary Points and Structure of High-Energy Scattering Amplitude

   A.P. Samokhin🇷🇺 · V.A. Petrov🇷🇺

   The ISR and the 7 TeV LHC data indicate that the differential cross-section of elastic proton-proton scattering remains almost energy-independent at the transferred momentum $t\approx -0.21{\mathrm{GeV}}^2$ at the level of $\approx 7.5\mathrm{mb}/{\mathrm{GeV}}^2$. This property of $d\sigma /dt$ (the "first" stationary point) appears due to the correlated growth of the total cross-section and the local slope parameter and can be expressed as a relation between the latter quantities. We anticipate that this property will be true up to 13 TeV. This enables us to normalize the preliminary TOTEM data for $d\sigma /dt$ at 13 TeV and $0.05<|t|<3.4{\mathrm{GeV}}^2$ and predict the values of $d\sigma /dt$ at this energy. These data give an evidence of the second stationary point at $t\approx -2.3{\mathrm{GeV}}^2$ at the level of $\approx 33\mathrm{nb}/{\mathrm{GeV}}^2$. The energy evolution of $d\sigma /dt$ looks as if the high energy elastic scattering amplitude is a sum of two similar terms. We argue that the existence of the two stationary points and the two-component structure of the high energy elastic scattering amplitude are general properties for all elastic processes.

   hep-phhep-exNPA(2018)·13 citations
10. 10*

    Probing the CP-Violation effects in the $h\tau \tau$ coupling at the LHC

    Xin Chen🇨🇳 · Yongcheng Wu🇨🇳

    A new method used to calculate the neutrino for all major tau hadronic decay event by event at the LHC is presented. It is possible because nowadays better detector description is available. With the neutrino fully reconstructed, matrix element for each event can be calculated, the mass of the Higgs particle can also be calculated event by event with high precision. Based on these, the prospect of measuring the Higgs CP mixing angle with $h\to \tau \tau$ decays at the LHC is analyzed. It is predicted that, with a detailed detector simulation, with 3 ab${}^{-1}$ of data at $\sqrt{s}=13$ TeV, a significant improvement of the measurement of the CP mixing angle to a precision of $5.2^{\circ }$ can be achieved at the LHC, which outperforms the sensitivity from lepton EDM searches up to date in the $h\tau \tau$ coupling.

    hep-phPLB(2019)·15 citations
11. 11*

    A COHERENT enlightenment of the neutrino Dark Side

    Pilar Coloma🇺🇸 · M. C. Gonzalez-Garcia🇪🇸 · Michele Maltoni🇪🇸 · Thomas Schwetz🇩🇪

    In the presence of non-standard neutrino interactions (NSI), oscillation data are affected by a degeneracy which allows the solar mixing angle to be in the second octant (aka the dark side) and implies a sign flip of the atmospheric mass-squared difference. This leads to an ambiguity in the determination of the ordering of neutrino masses, one of the main goals of the current and future experimental neutrino program. We show that the recent observation of coherent neutrino--nucleus scattering by the COHERENT experiment, in combination with global oscillation data, excludes the NSI degeneracy at the $3.1\sigma$ ($3.6\sigma$) CL for NSI with up (down) quarks.

    hep-phhep-exPRD(2017)·173 citations
12. 12*

    $Z\gamma$ production at NNLO including anomalous couplings

    John M. Campbell🇺🇸 · Tobias Neumann🇺🇸 · Ciaran Williams🇺🇸

    In this paper we present a next-to-next-to-leading order (NNLO) QCD calculation of the processes $pp\to l^{+}{l}^{-}\gamma$ and $pp\to \nu \bar{\nu }\gamma$ that we have implemented in MCFM. Our calculation includes QCD corrections at NNLO both for the Standard Model (SM) and additionally in the presence of $Z\gamma \gamma$ and $ZZ\gamma$ anomalous couplings. We compare our implementation, obtained using the jettiness slicing approach, with a previous SM calculation and find broad agreement. Focusing on the sensitivity of our results to the slicing parameter, we show that using our setup we are able to compute NNLO cross sections with numerical uncertainties of about $0.1\%$, which is small compared to residual scale uncertainties of a few percent. We study potential improvements using two different jettiness definitions and the inclusion of power corrections. At $\sqrt{s}=13$ TeV we present phenomenological results and consider $Z\gamma$ as a background to $H\to Z\gamma$ production. We find that, with typical cuts, the inclusion of NNLO corrections represents a small effect and loosens the extraction of limits on anomalous couplings by about $10\%$.

    hep-phhep-exJHEP(2017)·52 citations
13. 13*

    Quarks in a polar model

    V. N. Salomatov🇷🇺

    Current-quark masses are compared to the rest masses allowed by the Helmholtz equation in a polar model. Within the uncertainty of the current u quark mass determination, the current quark mass coincides with the rest mass allowed by the Helmholtz equation in the polar model in accordance with the second root of the zero Neumann function. Current d quark mass coincides with the rest mass calculated in accordance with the third root of the Bessel zero function. On the basis of a comparison of these results with the results obtained earlier for ordinary real particles u and d quarks stability is discussed.

    hep-phPhys.Essays(2018)·0 citations
14. 14*

    Non-Abelian gauge preheating

    Peter Adshead🇺🇸 · John T. Giblin Jr🇺🇸 · Zachary J. Weiner🇺🇸

    We study preheating in models where a scalar inflaton is directly coupled to a non-Abelian $SU(2)$ gauge field. In particular, we examine $m^2{\varphi }^2$ inflation with a conformal, dilaton-like coupling to the non-Abelian sector. We describe a numerical scheme that combines lattice gauge theory with standard finite difference methods applied to the scalar field. We show that a significant tachyonic instability allows for efficient preheating, which is parametrically suppressed by increasing the non-Abelian self-coupling. Additionally, we comment on the technical implementation of the evolution scheme and setting initial conditions.

    hep-phastro-ph.COhep-thPRD(2017)·45 citations
15. 15*

    Classification without labels: Learning from mixed samples in high energy physics

    Eric M. Metodiev🇺🇸 · Benjamin Nachman🇺🇸 · Jesse Thaler🇺🇸

    Modern machine learning techniques can be used to construct powerful models for difficult collider physics problems. In many applications, however, these models are trained on imperfect simulations due to a lack of truth-level information in the data, which risks the model learning artifacts of the simulation. In this paper, we introduce the paradigm of classification without labels (CWoLa) in which a classifier is trained to distinguish statistical mixtures of classes, which are common in collider physics. Crucially, neither individual labels nor class proportions are required, yet we prove that the optimal classifier in the CWoLa paradigm is also the optimal classifier in the traditional fully-supervised case where all label information is available. After demonstrating the power of this method in an analytical toy example, we consider a realistic benchmark for collider physics: distinguishing quark- versus gluon-initiated jets using mixed quark/gluon training samples. More generally, CWoLa can be applied to any classification problem where labels or class proportions are unknown or simulations are unreliable, but statistical mixtures of the classes are available.

    hep-phhep-exstat.MLJHEP(2017)·283 citations

* Reconstructed cohort: no mailing for this day survives in the archive. Papers are grouped by their submission times and arXiv's announcement cut-off, assuming announcement without delay; positions follow identifier order. Validated at ~91% exact-day agreement against the archived era.