hep-ex

The $S$ -wave resonance contributions to the three-body decays $B^0_{(s)}\to η_c f_0(X)\to η_cπ^+π^-$ in perturbative QCD approach

In this paper, we study the three-body decays $B^0/B^0_s \to η_c f_0(X)\to η_c π^+π^-$ by employing the perturbative QCD (PQCD) factorization approach. We evaluate the $S$ -wave resonance contributions by using the two-pion distribution amplitude $Φ_{ππ}^{\rm S}$ . The Breit-Wigner formula for the $f_0(500)$ , $f_0(1500)$ , and $f_0(1790)$ resonances and the Flatté model for the $f_0(980)$ resonance are adopted to parameterize the time-like scalar form factors $F_{s}(ω^2)$ . We also use the D.~V.~Bugg model to parameterize the $f_0(500)$ and compare the relevant theoretical predictions from different models. We found the following results: (a) the PQCD predictions for the branching ratios are ${\cal B}(B^0\to η_c f_0(500)[π^+π^-])= \left ( 1.53 ^{+0.76}_{-0.35} \right ) \times 10^{-6}$ for Breit-Wigner model and ${\cal B}(B^0\to η_c f_0(500)[π^+π^-])= \left ( 2.31 ^{+0.96}_{-0.48} \right ) \times 10^{-6}$ for D.~V.~Bugg model; (b) ${\cal B}(B_s\to η_c f_0(X)[π^+π^-] ) =\left ( 5.02^{+1.49}_{-1.08} \right )\times 10^{-5}$ when the contributions from $f_0(X)=(f_0(980),f_0(1500),f_0(1790))$ are all taken into account; and (c) The considered decays could be measured at the ongoing LHCb exp

Hadron Spectroscopy, exotics and $B_c^+$ physics at LHCb

The LHCb experiment is designed to study properties and decays of heavy flavored hadrons produced from $pp$ collisions at the LHC. During Run~1, it has recorded the world's largest data sample of beauty and charm hadrons, enabling precision spectroscopy studies of such particles. Several important results obtained by LHCb, such as the discovery of the first pentaquark states and the first unambiguous determination of the $Z_c(4430)^-$ as an exotic state, have dramatically increased the interest on spectroscopy of heavy hadrons. An overview of the latest LHCb results on the subject, including the discovery of four strange exotic states decaying as $X \to J/ψϕ$ , is presented. LHCb has also made significant contributions to the field of $B_c^+$ physics, the lowest bound state of the heavy flavor $\bar{b}$ and $c$ quarks. A synopsis of the the latest results is given.

Quarkonium Production in an Improved Color Evaporation Model

We propose an improved version of the color evaporation model to describe heavy quarkonium production. In contrast to the traditional color evaporation model, we impose the constraint that the invariant mass of the intermediate heavy quark-antiquark pair to be larger than the mass of produced quarkonium. We also introduce a momentum shift between heavy quark-antiquark pair and the quarkonium. Numerical calculations show that our model can describe the charmonium yields as well as ratio of $ψ^\prime$ over $J/ψ$ better than the traditional color evaporation model.

Hadronic production of $D(2550)$ , $D^(2600)$ , $D(2750)$ , $D^_1(2760)$ and $D^*_3(2760)$

Hadronic decays of radially excited $2D$ $D(2^3D_1)$ , $D(2^3D_3)$ , $D(2D_2)$ and $D(2D^\prime_2)$ have been studied in a $^3P_0$ model. All OZI-allowed decay channels of these $2D$ $D$ resonances have been given, and relevant decay widths have been calculated. $D(2550)$ , $D^*(2600)$ , $D(2750)$ , $D^*_1(2760)$ and $D^*_3(2760)$ can be produced in hadronic decays of $D(2^3D_1)$ , $D(2^3D_3)$ , $D(2D_2)$ and $D(2D^\prime_2)$ . In different assignments, hadronic decay widths and some relevant ratios from the $2D$ $D$ resonances to $D(2550)$ , $D^*(2600)$ , $D(2750)$ , $D^*_1(2760)$ or $D^*_3(2760)$ final states have been predicted, which may provide some more information to identify these resonances in forthcoming experiments.

Flavor violating leptonic decays of the Higgs boson

Recent data from the ATLAS and CMS detectors at the Large Hadron Collider at CERN give a hint of possible violation of flavor in the leptonic decays of the Higgs boson. In this work we analyze the flavor violating leptonic decays $H^0_1\to l_i \bar l_j$ ( $i\neq j$ ) within the framework of an MSSM extension with a vectorlike leptonic generation. Specifically we focus on the decay mode $H^0_1\to μτ$ . The analysis is done including tree and loop contributions involving exchange of $W, Z$ , charge and neutral higgs and leptons and mirror leptons, charginos and neutralinos and sleptons and mirror sleptons. It is found that a substantial branching ratio of $H^0_1\to μτ$ , i.e., of as much a ${\cal{O}}(1)\%$ , can be achieved in this model, the size hinted by the ATLAS and CMS data. The flavor violating decays $H^0_1\to eμ, eτ$ are also analyzed and found to be consistent with the current experimental limits. An analysis of the dependence of flavor violating decays on CP phases is given. The analysis is extended to include flavor decays of the heavier Higgs bosons. A confirmation of the flavor violation in Higgs boson decays with more data that is expected from LHC at $\sqrt s=13$ TeV will b

preprint2015arXiv

Next-to-next-to-leading-order QCD corrections to $χ_{c0,2}\rightarrow γγ$

We calculate the next-to-next-to-leading-order (NNLO) perturbative corrections to $P$ -wave quarkonia annihilation decay to two photons, in the framework of nonrelativistic QCD (NRQCD) factorization. The order- $α_s^2$ short-distance coefficients associated with each helicity amplitude are presented in a semi-analytic form, including the "light-by-light" contributions. With substantial NNLO corrections, we find disquieting discrepancy when confronting our state-of-the-art predictions with the latest \textsf{BESIII} measurements, especially fail to account for the measured $χ_{c2}\toγγ$ width. Incorporating the effects of spin-dependent forces would even exacerbate the situation, since it lifts the degeneracy between the nonperturbative NRQCD matrix elements of $χ_{c0}$ and $χ_{c2}$ toward the wrong direction. We also present the order- $α_s^2$ predictions to $χ_{b0,2}\toγγ$ , which await the future experimental test.

Contributions of axion-like particles to lepton dipole moments

Contributions of a spin 0 axion-like particle (ALP) to lepton dipole moments, g-2 and EDMs, are examined. Barr-Zee and light-by-light loop effects from a light pseudoscalar ALP are found to be capable of resolving the long-standing muon g-2 discrepancy at the expense of relatively large ALP-gammagamma couplings. The compatibility of such large couplings with direct experimental constraints and perturbative unitarity bounds is discussed. Future tests of such a scenario are described. For CP violating ALP couplings, the electron EDM is found to probe much smaller, theoretically more easily accommodated ALP interactions. Future planned improvement in electron EDM searches is advocated as a way to not only significantly constrain ALP parameters but also, to potentially unveil a new source of CP violation which could have far reaching ramifications.

Chiral heavy fermions in a two Higgs doublet model: 750 GeV resonance or not

We revisit models where a heavy chiral 4th generation doublet of fermions is embedded in a class of two Higgs doublets models (2HDM) with a discrete $Z_2$ symmetry, which couples the "heavy" scalar doublet only to the 4th generation fermions and the "light" one to the Standard Model (SM) fermions - the so-called 4G2HDM introduced by us several years ago. We study the constraints imposed on the 4G2HDM from direct searches of heavy fermions, from precision electroweak data (PEWD) and from the measured production and decay signals of the 125 GeV scalar, which in the 4G2HDM corresponds to the lightest CP-even scalar h. We then show that the recently reported excess in the $γγ$ spectrum around 750 GeV can be accommodated by the heavy CP-even scalar of the 4G2HDM, H, resulting in a unique choice of parameter space: negligible mixing (sinα~ O(0.001)) between the two CP-even scalars h,H and heavy 4th generation quark and lepton masses m_t',m_b' < 400 GeV and $m_{ν'},m_{τ'}$ > 900 GeV, respectively. Whether or not the 750 GeV γγresonance is confirmed, interesting phenomenology emerges in q' - Higgs systems (q'=t',b'), that can be searched for

Search for the effect of massive bodies on atomic spectra and constraints on Yukawa-type interactions of scalar particles

We propose a new method to search for hypothetical scalar particles that have feeble interactions with Standard-Model particles. In the presence of massive bodies, these interactions produce a non-zero Yukawa-type scalar-field magnitude. Using radio-frequency spectroscopy data of atomic dysprosium, as well as atomic clock spectroscopy data, we constrain the Yukawa-type interactions of a scalar field with the photon, electron, and nucleons for a range of scalar-particle masses corresponding to length scales $> 10$ cm. In the limit as the scalar-particle mass $m_ϕ\to 0$ , our derived limits on the Yukawa-type interaction parameters are: $Λ_γ\gtrsim 8 \times 10^{19}$ GeV, $Λ_e \gtrsim 1.3 \times 10^{19}$ GeV, and $Λ_N \gtrsim 6 \times 10^{20}$ GeV. Our measurements also constrain combinations of interaction parameters, which cannot otherwise be probed with traditional anomalous-force measurements. We suggest further measurements to improve on the current level of sensitivity.

Searches for R-parity-violating supersymmetry in pp collisions at sqrt(s) = 8 TeV in final states with 0-4 leptons

Results are presented from searches for R-parity-violating supersymmetry in events produced in pp collisions at sqrt(s) = 8 TeV at the LHC. Final states with 0, 1, 2, or multiple leptons are considered independently. The analysis is performed on data collected by the CMS experiment corresponding to an integrated luminosity of 19.5 inverse femtobarns. No excesses of events above the standard model expectations are observed, and 95% confidence level limits are set on supersymmetric particle masses and production cross sections. The results are interpreted in models featuring R-parity-violating decays of the lightest supersymmetric particle, which in the studied scenarios can be either the gluino, a bottom squark, or a neutralino. In a gluino pair production model with baryon number violation, gluinos with a mass less than 0.98 and 1.03 TeV are excluded, by analyses in a fully hadronic and one-lepton final state, respectively. An analysis in a dilepton final state is used to exclude bottom squarks with masses less than 307 GeV in a model considering bottom squark pair production. Multilepton final states are considered in the context of either strong or electroweak production of super

Particle Identification at Belle II

We report on the charged particle identification (PID) systems for the upcoming Belle II experiment. The time of propagation counter in the central region and the proximity focusing ring imaging Cherenkov counters with aerogel radiator in the forward region will be used as the PID devices. They are expected to provide a kaon identification efficiency of more than 94% at a low pion misidentification probability of 4%. The motivation for the upgrade, method, and status of both systems are discussed.

Measurement of the mass of the top quark in decays with a J/psi meson in pp collisions at 8 TeV

A first measurement of the top quark mass using the decay channel t to (W to l nu) (b to J/psi + X to mu+ mu- + X) is presented. The analysis uses events selected from the proton-proton collisions recorded with the CMS detector at the LHC at a center-of-mass energy of 8 TeV. The data correspond to an integrated luminosity of 19.7 inverse femtobarns, with 666 t t-bar and single top quark candidate events containing a reconstructed J/psi candidate decaying into an oppositely-charged muon pair. The mass of the (J/psi + l) system, where l is an electron or a muon from W boson decay, is used to extract a top quark mass of 173.5 +/- 3.0 (stat) +/- 0.9 (syst) GeV.

Test of scintillating bars coupled to Silicon Photomultipliers for a charged particle tracking device

The results obtained in laboratory tests, using scintillator bars read by silicon photomultipliers are reported. The present approach is the first step for designing a precision tracking system to be placed inside a free magnetized volume for the charge identification of low energy crossing particles. The devised system is demonstrated able to provide a spatial resolution better than 2 mm.

Nonperturbative Transverse Momentum Effects in Dihadron and Direct Photon-Hadron Angular Correlations

Two-particle angular correlations have long been used as an observable for measuring the initial-state partonic transverse momentum $k_T$ . Sensitivity to this small transverse momentum scale allows nonperturbative transverse momentum dependent effects to be probed in high $p_T$ dihadron and direct photon-hadron correlations. The observable $p_{out}$ , the out-of-plane transverse momentum component from a near-side $π^0$ or direct photon, is sensitive to initial-state $k_T$ and final-state fragmentation transverse momentum $j_T$ and thus can probe nonperturbative transverse-momentum-dependent effects. In the transverse-momentum-dependent framework, nearly back-to-back particle production in $p$ + $p$ collisions with a measured final-state hadron has been predicted to break factorization due to the possibility of gluon exchanges with colored remnants in the initial and final states. For this reason, the interacting partons are predicted to be correlated; however, there is so far no quantitative prediction for the magnitude of such effects. In this talk, recent measurements of dihadron and direct-photon hadron correlations in $p$ + $p$ collisions at $\sqrt{s}$ =510 GeV at the PHENIX experim

NLO QCD Predictions for off-shell $t \bar t$ and $t \bar t H$ Production and Decay at a Linear Collider

We present predictions for $t \bar t$ and $t \bar t H$ production and decay at future lepton colliders including non-resonant and interference contributions up to next-to-leading order (NLO) in perturbative QCD. The obtained precision predictions are necessary for a future precise determination of the top-quark Yukawa coupling, and allow for top-quark phenomenology in the continuum at an unprecedented level of accuracy. Simulations are performed with the automated NLO Monte-Carlo framework WHIZARD interfaced to the OpenLoops matrix element generator.

Large-area silica aerogel for use as Cherenkov radiators with high refractive index, developed by supercritical carbon dioxide drying

This study presents the development of large-area (18 $\times$ 18 $\times$ 2 cm $^3$ ), high refractive index ( $n \sim$ 1.05) hydrophobic silica aerogel tiles for use as Cherenkov radiators. These transparent aerogel tiles will be installed in a Cherenkov detector for the next-generation accelerator-based particle physics experiment Belle II, to be performed at the High Energy Accelerator Research Organization (KEK) in Japan. Cracking has been eliminated from the prototype aerogel tiles by improving the supercritical carbon dioxide (scCO $_2$ ) extraction procedure when drying the wet gel tiles. Finally, a method of mass-producing aerogel tiles for the actual detector was established. It was confirmed that the experimentally manufactured aerogel tiles meet the required optical and hydrophobic characteristics and have a uniform tile density.

A new MC-based method to evaluate the fission fraction uncertainty at reactor neutrino experiment

Uncertainties of fission fraction is an important uncertainty source for the antineutrino flux prediction in a reactor antineutrino experiment. A new MC-based method of evaluating the covariance coefficients between isotopes was proposed. It was found that the covariance coefficients will varying with reactor burnup and which may change from positive to negative because of fissioning balance effect, for example, the covariance coefficient between $^{235}$ U and $^{239}$ Pu changes from 0.15 to -0.13. Using the equation between fission fraction and atomic density, the consistent of uncertainty of fission fraction and the covariance matrix were obtained. The antineutrino flux uncertainty is 0.55\% which does not vary with reactor burnup, and the new value is about 8.3\% smaller.

Rare $B$ Decays as Tests of the Standard Model

One of the most interesting puzzles in particle physics today is that new physics is expected at the TeV energy scale to solve the hierarchy problem, and stabilise the Higgs mass, but so far no unambiguous signal of new physics has been found. Strong constraints on the energy scale of new physics can be derived from precision tests of the electroweak theory and from flavour-changing or CP-violating processes in strange, charm and beauty hadron decays. Decays that proceed via flavour-changing-neutral-current processes are forbidden at the lowest perturbative order in the Standard Model and are, therefore, rare. Rare $b$ hadron decays are playing a central role in the understanding of the underlying patterns of Standard Model physics and in setting up new directions in model building for new physics contributions. In this article the status and prospects of this field are reviewed.

The Muon g-2 Experiment Overview and Status as of June 2016

The Muon g-2 Experiment at Fermilab will measure the anomalous magnetic moment of the muon to a precision of 140 parts per billion, which is a factor of four improvement over the previous E821 measurement at Brookhaven. The experiment will also extend the search for the electric dipole moment (EDM) of the muon by approximately two orders of magnitude, with a sensitivity down to $10^{-21}$ e.cm. Both of these measurements are made by combining a precise measurement of the 1.45T storage ring magnetic field with an analysis of the modulation of the decay rate of higher-energy positrons (from anti-muons), recorded by 24 calorimeters and 3 straw tracking detectors. The recent progress in the alignment of the electrostatic quadrapole plates and the trolley rails inside the vacuum chambers, and in establishing the uniform storage ring magnetic field will be described.

Precise Determination of the U-235 Reactor Antineutrino Cross Section per Fission

We investigate which among the reactor antineutrino fluxes from the decays of the fission products of $^{235}\text{U}$ , $^{238}\text{U}$ , $^{239}\text{Pu}$ , and $^{241}\text{Pu}$ may be responsible for the reactor antineutrino anomaly if the anomaly is due to a miscalculation of the antineutrino fluxes. We find that it is very likely that at least the calculation of the $^{235}\text{U}$ flux must be revised. From the fit of the data we obtain the precise determination $σ_{f,235} = ( 6.33 \pm 0.08 ) \times 10^{-43} \, \text{cm}^2 / \text{fission}$ of the $^{235}\text{U}$ cross section per fission, which is more precise than the calculated value and differs from it by $2.2σ$ . The cross sections per fission of the other fluxes have large uncertainties and in practice their values are undetermined by the fit.

Search for rare B meson decays at the BaBar experiment

b to s transitions are flavour-changing neutral current (FCNC) processes that play an important role in the search for physics beyond the Standard Model (SM). Contributions from virtual particles in the loop are predicted to deviate observables, such as the branching fraction, from their SM expectations. Using data from the BaBar experiment, we present the first search for the rare decay B to K tau tau. The BABAR results on the measurement of the angular asymmetries of B to Kstar l l, where l is an electron or muon, are also reported. In addition, using a time-dependent analysis of B to KS0 pi pi gamma, the mixing induced CP-asymmetry for the radiative FCNC decay, B to KS0 rho gamma, is measured, along with an amplitude analysis of the m (K pi) and m (K pi pi) spectrum.

CHANTI: a Fast and Efficient Charged Particle Veto Detector for the NA62 Experiment at CERN

The design, construction and test of a charged particle detector made of scintillation counters read by Silicon Photomultipliers (SiPM) is described. The detector, which operates in vacuum and is used as a veto counter in the NA62 experiment at CERN, has a single channel time resolution of 1.14 ns, a spatial resolution of ~2.5 mm and an efficiency very close to 1 for penetrating charged particles.

APFELgrid: a high performance tool for parton density determinations

We present a new software package designed to reduce the computational burden of hadron collider measurements in Parton Distribution Function (PDF) fits. The APFELgrid package converts interpolated weight tables provided by APPLgrid files into a more efficient format for PDF fitting by the combination with PDF and $α_s$ evolution factors provided by APFEL. This combination significantly reduces the number of operations required to perform the calculation of hadronic observables in PDF fits and simplifies the structure of the calculation into a readily optimised scalar product. We demonstrate that our technique can lead to a substantial speed improvement when compared to existing methods without any reduction in numerical accuracy.

Implications of $δ_{CP}=-90^\circ$ towards determining hierarchy and octant at T2K and T2K-II

The T2K experiment has provided the first hint for the best-fit value for the leptonic CP phase $δ_{CP} \sim -90^\circ$ from neutrino data. This is now corroborated by the NO $ν$ A neutrino runs. We study the implications for neutrino mass hierarchy and octant of $θ_{23}$ in the context of this data assuming that the true value of $δ_{CP}$ in nature is $-90^\circ$ . Based on simple arguments on degeneracies in the probabilities we show that a clear signal of $δ_{CP}=-90^\circ$ coming from T2K neutrino (antineutrino) data is only possible if the true hierarchy is normal and the true octant is higher (lower). Thus if the T2K neutrino and antineutrino data are fitted separately and both give the true value of $δ_{CP}=-90^\circ$ , this will imply that nature has chosen the true hierarchy to be normal and $θ_{23} \approx 45^\circ$ . However we find that the combined fit of neutrino and antineutrino data will still point to true hierarchy as normal but the octant of $θ_{23}$ will remain undetermined. We do our analysis for both, the current projected exposure ( $7.8 \times 10^{21}$ pot) and planned extended exposure ( $20 \times 10^{21}$ pot). We also present the CP discovery potential of T2K e

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Y. Zhang

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Y. Zhang contributes to research discovery and scholarly infrastructure.

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Y. Li

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L. Zhang

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CMS Collaboration

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