Neutral Hadrons Research Articles

Interaction and Identification of the Di-Hadronic Molecules

In this article, we study the interesting problem of identification and interaction of the hadronic molecules. The One Boson Exchange potential along with Yukawa screen like potential in their relative s-wave state is used for the calculation of the mass spectra. Along with interaction potential, we propose the two color neutral hadrons pursue the dipole-like interaction for formation of the hadronic molecule. For the identification, we use the Weinberg’s compositeness theorem to distinguish hadronic molecules from other hadronic states. With the present interaction potential, we have calculated the mass spectra of di-mesonic states, namely, $$K\overline{K}$$ , $$\rho \overline{\rho }$$ , $$K^{*}\overline{K^{*}}$$ , $$D\overline{D^{*}}$$ ( $$\overline{D}D^{*}$$ ), $$D^{*}\overline{D^{*}}$$ , $$B\overline{B^{*}}$$ , $$B^{*}\overline{B^{*}}$$ , $$D^{*\pm }\overline{D_{1}^{0}}$$ , $$ D^{0}\overline{K^{\pm }}$$ , $$D^{*0}\overline{K^{\pm }}$$ , with their possible quantum number.

Large-Scale Distributed Training Applied to Generative Adversarial Networks for Calorimeter Simulation

In recent years, several studies have demonstrated the benefit of using deep learning to solve typical tasks related to high energy physics data taking and analysis. In particular, generative adversarial networks are a good candidate to supplement the simulation of the detector response in a collider environment. Training of neural network models has been made tractable with the improvement of optimization methods and the advent of GP-GPU well adapted to tackle the highly-parallelizable task of training neural nets. Despite these advancements, training of large models over large data sets can take days to weeks. Even more so, finding the best model architecture and settings can take many expensive trials. To get the best out of this new technology, it is important to scale up the available network-training resources and, consequently, to provide tools for optimal large-scale distributed training. In this context, our development of a new training workflow, which scales on multi-node/multi-GPU architectures with an eye to deployment on high performance computing machines is described. We describe the integration of hyper parameter optimization with a distributed training framework using Message Passing Interface, for models defined in keras [12] or pytorch [13]. We present results on the speedup of training generative adversarial networks trained on a data set composed of the energy deposition from electron, photons, charged and neutral hadrons in a fine grained digital calorimeter.

Measurement of cos2β in B0→D(*)h0 with D→KS0π+π− decays by a combined time-dependent Dalitz plot analysis of BaBar and Belle data

We report measurements of $\sin{2\beta}$ and $\cos{2\beta}$ from a time-dependent Dalitz plot analysis of $B^{0} \to D^{(*)} h^{0}$ with $D \to K_{S}^{0} \pi^{+} \pi^{-}$ decays, where the light unflavored and neutral hadron $h^{0}$ is a $\pi^{0}$, $\eta$, or $\omega$ meson. The analysis is performed with a combination of the final data sets of the \babar\ and Belle experiments containing $471 \times 10^{6}$ and $772 \times 10^{6}$ $B\bar{B}$ pairs collected at the $\Upsilon\left(4S\right)$ resonance at the asymmetric-energy B factories PEP-II at SLAC and KEKB at KEK, respectively. We measure $\sin{2\beta} = 0.80 \pm 0.14 \,(\rm{stat.}) \pm 0.06 \,(\rm{syst.}) \pm 0.03 \,(\rm{model})$ and $\cos{2\beta} = 0.91 \pm 0.22 \,(\rm{stat.}) \pm 0.09 \,(\rm{syst.}) \pm 0.07 \,(\rm{model})$. The result for the direct measurement of the angle is $\beta = \left( 22.5 \pm 4.4 \,(\rm{stat.}) \pm 1.2 \,(\rm{syst.}) \pm 0.6 \,(\rm{model}) \right)^{\circ}$. The last quoted uncertainties are due to the composition of the $D^{0} \to K_{S}^{0} \pi^{+} \pi^{-}$ decay amplitude model, which is newly established by a Dalitz plot amplitude analysis of a high-statistics $e^{+}e^{-} \to c\bar{c}$ data sample as part of this analysis. We find the first evidence for $\cos2\beta>0$ at the level of $3.7$ standard deviations. The measurement excludes the trigonometric multifold solution $\pi/2 - \beta = (68.1 \pm 0.7)^{\circ}$ at the level of $7.3$ standard deviations and therefore resolves an ambiguity in the determination of the apex of the CKM Unitarity Triangle. The hypothesis of $\beta = 0^{\circ}$ is ruled out at the level of $5.1$ standard deviations, and thus CP violation is observed in $B^{0} \to D^{(*)} h^{0}$ decays.

First Evidence for cos2β>0 and Resolution of the Cabibbo-Kobayashi-Maskawa Quark-Mixing Unitarity Triangle Ambiguity.

We present first evidence that the cosine of the CP-violating weak phase 2β is positive, and hence exclude trigonometric multifold solutions of the Cabibbo-Kobayashi-Maskawa (CKM) Unitarity Triangle using a time-dependent Dalitz plot analysis of B^{0}→D^{(*)}h^{0} with D→K_{S}^{0}π^{+}π^{-} decays, where h^{0}∈{π^{0},η,ω} denotes a light unflavored and neutral hadron. The measurement is performed combining the final data sets of the BABAR and Belle experiments collected at the ϒ(4S) resonance at the asymmetric-energy B factories PEP-II at SLAC and KEKB at KEK, respectively. The data samples contain (471±3)×10^{6}BB[over ¯] pairs recorded by the BABAR detector and (772±11)×10^{6}BB[over ¯] pairs recorded by the Belle detector. The results of the measurement are sin2β=0.80±0.14(stat)±0.06(syst)±0.03(model) and cos2β=0.91±0.22(stat)±0.09(syst)±0.07(model). The result for the direct measurement of the angle β of the CKM Unitarity Triangle is β=[22.5±4.4(stat)±1.2(syst)±0.6(model)]°. The measurement assumes no direct CP violation in B^{0}→D^{(*)}h^{0} decays. The quoted model uncertainties are due to the composition of the D^{0}→K_{S}^{0}π^{+}π^{-} decay amplitude model, which is newly established by performing a Dalitz plot amplitude analysis using a high-statistics e^{+}e^{-}→cc[over ¯] data sample. CP violation is observed in B^{0}→D^{(*)}h^{0} decays at the level of 5.1 standard deviations. The significance for cos2β>0 is 3.7 standard deviations. The trigonometric multifold solution π/2-β=(68.1±0.7)° is excluded at the level of 7.3 standard deviations. The measurement resolves an ambiguity in the determination of the apex of the CKM Unitarity Triangle.

Neutral hadrons disappearing into the darkness

We study the invisible decay of neutral hadrons in a representative model of the dark sector. The mesons ${K}_{L}$ and ${B}^{0}$ decay into the dark sector with branching rates that can be at the current experimental limits. The neutron decays with a rate that could either explain the neutron lifetime puzzle (although only for an extreme choice of the parameters and a fine-tuned value of the masses) or be just above the current limit of its invisible decay (${\ensuremath{\tau}}_{N}^{\mathrm{inv}}\ensuremath{\gtrsim}{10}^{29}\text{ }\text{ }\mathrm{years}$) if kinematically allowed. These invisible decays of ordinary matter provide a novel and promising window into new physics that should be vigorously pursued.

Proton-Induced Radiation Damage in BaF2, LYSO, and PWO Crystal Scintillators

Future high-energy physics experiments at the energy and intensity frontiers will face a challenge of severe radiation environment from both ionization dose and charged and neutral hadrons. The high-luminosity large hadron collider, for example, will present an environment, where up to 130 Mrad ionization dose, $3 \times 10^{14}$ charged hadrons/cm2 and $5 \times 10^{15}$ neutrons/cm2 are expected. In this paper, we report our investigation on charged hadron-induced radiation damage in BaF2, LYSO/LFS, and PWO crystals up to $3 \times 10^{15}$ protons/cm2 by using 800-MeV protons at the Los Alamos Neutron Science Center. Comparison is made between radiation damages induced by protons and ionization dose alone.

Hadronic vs. electromagnetic pulse shape discrimination in CsI(Tl) for high energy physics experiments

Pulse shape discrimination using CsI(Tl) scintillators to perform neutral hadron particle identification is explored with emphasis towards application at high energy electron-positron collider experiments. Through the analysis of the pulse shape differences between scintillation pulses from photon and hadronic energy deposits using neutron and proton data collected at TRIUMF, it is shown that the pulse shape variations observed for hadrons can be modelled using a third scintillation component for CsI(Tl), in addition to the standard fast and slow components. Techniques for computing the hadronic pulse amplitudes and shape variations are developed and it is shown that the intensity of the additional scintillation component can be computed from the ionization energy loss of the interacting particles. These pulse modelling and simulation methods are integrated with GEANT4 simulation libraries and the predicted pulse shape for CsI(Tl) crystals in a 5 × 5 array of 5 × 5 × 30 cm3 crystals is studied for hadronic showers from 0.5 and 1 GeV/c KL0 and neutron particles. Using a crystal level and cluster level approach for photon vs. hadron cluster separation we demonstrate proof-of-concept for neutral hadron detection using CsI(Tl) pulse shape discrimination in high energy electron-positron collider experiments.

Measurement of tau polarisation in Z/gamma ^{*}rightarrow tau tau decays in proton\u2013proton collisions at sqrt{s}=8 TeV with the ATLAS detector

This paper presents a measurement of the polarisation of tau leptons produced in Z/gamma ^{*}rightarrow tau tau decays which is performed with a dataset of proton—proton collisions at sqrt{s}=8 TeV, corresponding to an integrated luminosity of 20.2 fb^{-1} recorded with the ATLAS detector at the LHC in 2012. The Z/gamma ^{*}rightarrow tau tau decays are reconstructed from a hadronically decaying tau lepton with a single charged particle in the final state, accompanied by a tau lepton that decays leptonically. The tau polarisation is inferred from the relative fraction of energy carried by charged and neutral hadrons in the hadronic tau decays. The polarisation is measured in a fiducial region that corresponds to the kinematic region accessible to this analysis. The tau polarisation extracted over the full phase space within the Z/gamma ^{*} mass range of 66 < m_{Z/gamma ^{*}} < 116 GeV is found to be P_{tau } =-0.14 pm 0.02 (text {stat}) pm 0.04 (text {syst}). It is in agreement with the Standard Model prediction of P_{tau } =-0.1517 pm 0.0019, which is obtained from the ALPGEN event generator interfaced with the PYTHIA 6 parton shower modelling and the TAUOLA tau decay library.

The CMS Particle Flow Algorithm

The event reconstruction at the Compact Muon Solenoid (CMS) experiment at the CERN Large Hadron Collider (LHC) is predominantly based on the Particle Flow algorithm. This algorithm for a global event description uses the information from all subdetector systems, unlike the previous, traditional approaches that were focused on the localized information in each subdetector. These traditional methods use the raw information (tracks, hits), while the Particle Flow algorithm completely reconstructs the event by identifying and reconstructing the comprehensive list of final-state particles (photons, electrons, muons, charged and neutral hadrons), resulting in superior reconstruction of jets, missing transverse energy, tau leptons, electrons and muons. This approach also allows for efficient identification and mitigation of the pileup effect. The concept and performance of the Particle Flow algorithm, together with the prospects for its development in the context of the upgraded CMS detector, are presented in this overview.

Performance of Crystal Scintillators in a Severe Radiation Environment Caused by Protons

Future high energy physics experiments at the energy and intensity frontiers will face challenges from a severe radiation environment caused by both ionization dose and charged and neutral hadrons. This paper reports an investigation on proton induced radiation damage in various crystal scintillators. Large size BGO, LFS and PWO crystals of 18 to 22 cm long were irradiated by 800 MeV protons up to 3 × 1015 p/cm2 at the WNR facility of LANSCE with longitudinal transmittance measured in situ. LYSO plates of 14 × 4 × 1.5 mm3 were irradiated by 24 GeV protons up to 8.2 × 1015 p/cm2 at the IRRAD facility of CERN. Degradations in both transmittance and light output are reported. The results show an excellent radiation hardness of LYSO/LFS crystals against charged hadrons.

Software compensation in particle flow reconstruction

The particle flow approach to calorimetry benefits from highly granular calorimeters and sophisticated software algorithms in order to reconstruct and identify individual particles in complex event topologies. The high spatial granularity, together with analogue energy information, can be further exploited in software compensation. In this approach, the local energy density is used to discriminate electromagnetic and purely hadronic sub-showers within hadron showers in the detector to improve the energy resolution for single particles by correcting for the intrinsic non-compensation of the calorimeter system. This improvement in the single particle energy resolution also results in a better overall jet energy resolution by improving the energy measurement of identified neutral hadrons and improvements in the pattern recognition stage by a more accurate matching of calorimeter energies to tracker measurements. This paper describes the software compensation technique and its implementation in particle flow reconstruction with the Pandora Particle Flow Algorithm (PandoraPFA). The impact of software compensation on the choice of optimal transverse granularity for the analogue hadronic calorimeter option of the International Large Detector (ILD) concept is also discussed.

Tau Lepton Reconstruction in ATLAS

Tau leptons play a key role in many measurements and searches within and beyond the Standard Model of particle physics performed at the LHC. We present here the performance of the reconstruction, identification and energy measurement algorithms for hadronic tau lepton decays currently used by the ATLAS collaboration. We also introduce a new reconstruction method which uses the individual charged and neutral hadrons in tau decays to improve the 4-momentum resolution, while also providing increased sensitivity to tau polarization and Higgs CP state measurements.

Single event effects in high-energy accelerators

The radiation environment encountered at high-energy hadron accelerators strongly differs from the environment relevant for space applications. The mixed-field expected at modern accelerators is composed of charged and neutral hadrons (protons, pions, kaons and neutrons), photons, electrons, positrons and muons, ranging from very low (thermal) energies up to the TeV range. This complex field, which is extensively simulated by Monte Carlo codes (e.g. FLUKA) is due to beam losses in the experimental areas, distributed along the machine (e.g. collimation points) and deriving from the interaction with the residual gas inside the beam pipe. The resulting intensity, energy distribution and proportion of the different particles largely depends on the distance and angle with respect to the interaction point as well as the amount of installed shielding material. Electronics operating in the vicinity of the accelerator will therefore be subject to both cumulative damage from radiation (total ionizing dose, displacement damage) as well as single event effects which can seriously compromise the operation of the machine. This, combined with the extensive use of commercial-off-the-shelf components due to budget, performance and availability reasons, results in the need to carefully characterize the response of the devices and systems to representative radiation conditions.

Finite volume effects on the electric polarizability of neutral hadrons in lattice QCD

We study the finite volume effects on the electric polarizability for the neutron, neutral pion, and neutral kaon using eight dynamically generated two-flavor nHYP-clover ensembles at two different pion masses: 306(1) and 227(2) MeV. An infinite volume extrapolation is performed for each hadron at both pion masses. For the neutral kaon, finite volume effects are relatively mild. The dependence on the quark mass is also mild and a reliable chiral extrapolation can be performed along with the infinite volume extrapolation. Our result is $\alpha_{K^0}^\mbox{phys}=0.356(74) \times 10^{-4} \mbox{fm}^3$. In contrast, for neutron the electric polarizability depends strongly on the volume. After removing the finite volume corrections, our neutron polarizability results are in good agreement with $\chi$PT. For the connected part of the neutral pion polarizability, the negative trend persists, and it is not due to finite volume effects, but likely sea quark charging effects.

Reconstruction of hadronic decay products of tau leptons with the ATLAS experiment.

This paper presents a new method of reconstructing the individual charged and neutral hadrons in tau decays with the ATLAS detector. The reconstructed hadrons are used to classify the decay mode and to calculate the visible four-momentum of reconstructed tau candidates, significantly improving the resolution with respect to the calibration in the existing tau reconstruction. The performance of the reconstruction algorithm is optimised and evaluated using simulation and validated using samples of Zrightarrow tau tau and Z(rightarrow mu mu )+jets events selected from proton–proton collisions at a centre-of-mass energy sqrt{s}=8,text {TeV}, corresponding to an integrated luminosity of 5 mathrm{fb}^{-1}.

Hadronic calorimeter shower size: Challenges and opportunities for jet substructure in the superboosted regime

Hadrons have finite interaction size with dense material, a basic feature common to known forms of hadronic calorimeters (HCAL). We argue that substructure variables cannot use HCAL information to access the microscopic nature of jets much narrower than the hadronic shower size, which we call superboosted massive jets. It implies that roughly 15% of their transverse energy profile remains inaccessible due to the presence of long-lived neutral hadrons. This part of the jet substructure is also subject to order-one fluctuations. We demonstrate that the effects of the fluctuations are not reduced when a global correction to jet variables is applied. The above leads to fundamental limitations in the ability to extract intrinsic information from jets in the superboosted regime. The neutral fraction of a jet is correlated with its flavor. This leads to an interesting and possibly useful difference between superboosted W/Z/h/t jets and their corresponding backgrounds. The QCD jets that form the background to the signal superboosted jets might also be qualitatively different in their substructure as their mass might lie at or below the Sudakov mass peak. Finally, we introduce a set of zero-cone longitudinal jet substructure variables and show that while they carry information that might be useful in certain situations, they are not in general sensitive to the jet substructure.

Parton-medium cross-section and average QGP viscosity in lead–lead collisions at the LHC

The recent experimental CMS and E-by-E ATLAS data on the elliptic anisotropy of particles in Pb–Pb collisions are used to extract parton medium cross-section and the quark–gluon plasma (QGP) viscosity-to-entropy ratio within the incomplete equilibration medium model. Our method assumes extrapolation of the measured pseudorapidity spectrum of charged particles to low-pT range. Then the rapidity distribution of both charged and neutral hadrons is restored. The extracted value of the parton-medium cross section is found to be It yields for the ratio of shear viscosity to entropy density in QGP phase. The last result is in a good agreement with the estimates obtained by calculations within the viscous hydrodynamics.

First Observation of CP Violation in B[over ¯]^{0}→D_{CP}^{(*)}h^{0} Decays by a Combined Time-Dependent Analysis of BABAR and Belle Data.

We report a measurement of the time-dependent CP asymmetry of B[over ¯]^{0}→D_{CP}^{(*)}h^{0} decays, where the light neutral hadron h^{0} is a π^{0}, η, or ω meson, and the neutral D meson is reconstructed in the CP eigenstates K^{+}K^{-}, K_{S}^{0}π^{0}, or K_{S}^{0}ω. The measurement is performed combining the final data samples collected at the ϒ(4S) resonance by the BABAR and Belle experiments at the asymmetric-energy B factories PEP-II at SLAC and KEKB at KEK, respectively. The data samples contain (471±3)×10^{6} BB[over ¯] pairs recorded by the BABAR detector and (772±11)×10^{6} BB[over ¯] pairs recorded by the Belle detector. We measure the CP asymmetry parameters -η_{f}S=+0.66±0.10(stat)±0.06(syst) and C=-0.02±0.07(stat)±0.03(syst). These results correspond to the first observation of CP violation in B[over ¯]^{0}→D_{CP}^{(*)}h^{0} decays. The hypothesis of no mixing-induced CP violation is excluded in these decays at the level of 5.4 standard deviations.

Strangeness Production in Deep-Inelastic ep Scattering at HERA

The production of neutral strange hadrons is studied using deep-inelastic events measured with the H1 detector at HERA. The measurements of K s 0 and Λ(Λ) productions are made in two regions of phase space defined by the negative

Measurements of direct CP-violating asymmetries in charmless decays of bottom baryons.

We report final measurements of direct CP-violating asymmetries in charmless decays of neutral bottom hadrons to pairs of charged hadrons with the upgraded Collider Detector at the Fermilab Tevatron. Using the complete √s=1.96 TeV proton-antiproton collisions data set, corresponding to 9.3 fb⁻¹ of integrated luminosity, we measure A(Λ(b)⁰→pπ⁻)=+0.06±0.07(stat)±0.03(syst) and A(Λ(b)⁰→pK⁻)=-0.10±0.08(stat)±0.04(syst), compatible with no asymmetry. In addition we measure the CP-violating asymmetries in B(s)⁰→K⁻π⁺ and B⁰→K⁺π⁻ decays to be A(B(s)⁰→K⁻π⁺)=+0.22±0.07(stat)±0.02(syst) and A(B⁰→K⁺π⁻)=-0.083±0.013(stat)±0.004(syst), respectively, which are significantly different from zero and consistent with current world averages.