A. Lath

In this paper, we review recent theoretical progress and the latest experimental results in jet substructure from the Tevatron and the LHC. We review the status of and outlook for calculation and simulation tools for studying jet substructure. Following up on the report of the Boost 2010 workshop, we present a new set of benchmark comparisons of substructure techniques, focusing on the set of variables and grooming methods that are collectively known as 'top taggers'. To facilitate further exploration, we have attempted to collect, harmonize and publish software implementations of these techniques.

We have compared the decay rates of KL and KS to π+π− and π0π0 final states using a subset of the data from the KTeV experiment (E832) at Fermilab. We find that the direct-CP-violation parameter Re(ε′/ε) is equal to [28.0±3.0(stat)±2.8(syst)]×10−4. This result definitively establishes the existence of CP violation in a decay process.Received 27 May 1999DOI:https://doi.org/10.1103/PhysRevLett.83.22©1999 American Physical Society

We present a series of measurements based on ${K}_{L,S}\ensuremath{\rightarrow}{\ensuremath{\pi}}^{+}{\ensuremath{\pi}}^{\ensuremath{-}}$ and ${K}_{L,S}\ensuremath{\rightarrow}{\ensuremath{\pi}}^{0}{\ensuremath{\pi}}^{0}$ decays collected in 1996--1997 by the $\mathrm{KTeV}$ experiment (E832) at Fermilab. We compare these four $\stackrel{\ensuremath{\rightarrow}}{K}\ensuremath{\pi}\ensuremath{\pi}$ decay rates to measure the direct $\mathrm{CP}$ violation parameter $\mathrm{Re}({\ensuremath{\epsilon}}^{\ensuremath{'}}/\ensuremath{\epsilon})=(20.7\ifmmode\pm\else\textpm\fi{}2.8)\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}4}.$ We also test $\mathrm{CPT}$ symmetry by measuring the relative phase between the $\mathrm{CP}$ violating and $\mathrm{CP}$ conserving decay amplitudes for $\stackrel{\ensuremath{\rightarrow}}{K}{\ensuremath{\pi}}^{+}{\ensuremath{\pi}}^{\ensuremath{-}}$ $({\ensuremath{\varphi}}_{+\ensuremath{-}})$ and for $\stackrel{\ensuremath{\rightarrow}}{K}{\ensuremath{\pi}}^{0}{\ensuremath{\pi}}^{0}$ $({\ensuremath{\varphi}}_{00}).$ We find the difference between the relative phases to be $\ensuremath{\Delta}\ensuremath{\varphi}\ensuremath{\equiv}{\ensuremath{\varphi}}_{00}\ensuremath{-}{\ensuremath{\varphi}}_{+\ensuremath{-}}=(+0.39\ifmmode\pm\else\textpm\fi{}0.50)\ifmmode^\circ\else\textdegree\fi{},$ and the deviation of ${\ensuremath{\varphi}}_{+\ensuremath{-}}$ from the superweak phase to be ${\ensuremath{\varphi}}_{+\ensuremath{-}}\ensuremath{-}{\ensuremath{\varphi}}_{\mathrm{SW}}=(+0.61\ifmmode\pm\else\textpm\fi{}1.19)\ifmmode^\circ\else\textdegree\fi{};$ both results are consistent with $\mathrm{CPT}$ symmetry. In addition, we present new measurements of the ${K}_{L}$-${K}_{S}$ mass difference and ${K}_{S}$ lifetime: $\ensuremath{\Delta}m=(5261\ifmmode\pm\else\textpm\fi{}15)\ifmmode\times\else\texttimes\fi{}{10}^{6}\ensuremath{\Elzxh}{\mathrm{s}}^{\ensuremath{-}1}$ and ${\ensuremath{\tau}}_{S}=(89.65\ifmmode\pm\else\textpm\fi{}0.07)\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}12}\mathrm{s}.$

We report on a search for the decay K(L)-->pi(0)&mgr;(+)&mgr;(-) carried out as a part of the KTeV experiment at Fermilab. This decay is expected to have a significant CP violating contribution and a direct measurement will either support the Cabibbo-Kobayashi-Maskawa mechanism for CP violation or point to new physics. Two events were observed in the 1997 data with an expected background of 0.87+/-0.15 events, and we set an upper limit B(K(L)-->pi(0)&mgr;(+)&mgr;(-))<3. 8x10(-10) at the 90% confidence level.

The strong coupling αs(M2Z) has been measured using hadronic decays of Z0 bosons collected by the SLD experiment at SLAC. The data were compared with QCD predictions both at fixed order O(α2s) and including resummed analytic formulas based on the next-to-leading logarithm approximation. In this comprehensive analysis we studied event shapes, jet rates, particle correlations, and angular energy flow, and checked the consistency between αs(M2Z) values extracted from these different measures. Combining all results we obtain αs(M2Z)= 0.1200±0.0025 (expt) ±0.0078 (theor), where the dominant uncertainty is from uncalculated higher order contributions.Received 19 September 1994DOI:https://doi.org/10.1103/PhysRevD.51.962©1995 American Physical Society

We present measurements of ${\mathit{R}}_{\mathit{b}}$ using the SLD at the SLC. The analyses use 2D and 3D impact parameter tags and a displaced 3D vertex tag which all exploit the small size and stability of the ${\mathit{e}}^{+}$${\mathit{e}}^{\mathrm{\ensuremath{-}}}$ interaction point and the precision 3D CCD pixel vertex detector to achieve high bb\ifmmode\bar\else\textasciimacron\fi{}-tagging efficiencies and purities. The combined measurement yields ${\mathit{R}}_{\mathit{b}}$=0.229\ifmmode\pm\else\textpm\fi{}0.011 and is consistent with standard model predictions. \textcopyright{} 1996 The American Physical Society.

We report the first observation of a manifestly CP violating effect in the K(L)-->pi(+)pi(-)e(+)e(-) decay mode. A large asymmetry was observed in the distribution of these decays in the CP-odd and T-odd angle straight phi between the decay planes of the e(+)e(-) and pi(+)pi(-) pairs in the K(L) center of mass system. After acceptance corrections, the overall asymmetry is found to be [13.6+/-2. 5(stat)+/-1.2(syst)]%. This is the largest CP-violating effect yet observed when integrating over the entire phase space of a mode and the first such effect observed in an angular variable.

We present a measurement of the charge asymmetry delta(L) in the mode K(L)-->pi(+/-)e(-/+)nu based on 298 x 10(6) analyzed decays. We measure a value of delta(L) = [3322+/-58(stat)+/-47(syst)]x10(-6), in good agreement with previous measurements and 2.4 times more precise than the current best published result. The result is used to place more stringent limits on CPT and DeltaS = DeltaQ violation in the neutral kaon system.

We report on a search for the decay KL→π0ν¯ν, carried out as a part of E799-II, a rare KL decay experiment at Fermilab. Within the standard model, the KL→π0ν¯ν decay is dominated by direct CP violating processes, and thus an observation of the decay implies confirmation of direct CP violation. No events were observed, and we set an upper limit for the branching ratio of KL→π0ν¯ν to be <5.9×10−7 at the 90% confidence level.Received 8 July 1999DOI:https://doi.org/10.1103/PhysRevD.61.072006©2000 American Physical Society

Abstract Aluminum (Al) has gained popularity for surface plasmon resonance-based applications due to its affordability and compatibility with CMOS technology at the nanoscale. Over angle-interrogation mode, plasmonic interactions occurring at the metal-dielectric junction, are the outcomes of the attenuated total internal reflection phenomenon. Modified Al-based Kretschmann configuration results in phase-matching conditions that are seen as resonant points in the reflection characteristics. In our work, we have engineered an Al-based plasmonic device utilizing Antimonene as a 2D nanomaterial for bio-sensing purposes in the Near-Infrared (NIR) spectral domain. The study investigates the performance of Surface Plasmon Resonance (SPR) based refractive index sensor using different 2D nanomaterials with an optimized Al thickness of 30 nm. A comparative analysis of Al-based Kretschmann configurations in the presence of Graphene, Black Phosphorus, MXene, and Antimonene is presented using engineered intermediate layers. It is observed that the Al-antimonene-based plasmonic device exhibits improved sensing parameters in the NIR optical window.

We report on a new measurement of the decay ${K}_{L}\ensuremath{\rightarrow}{\ensuremath{\pi}}^{0}\ensuremath{\gamma}\ensuremath{\gamma}$ by the KTeV experiment at Fermilab. We determine the ${K}_{L}\ensuremath{\rightarrow}{\ensuremath{\pi}}^{0}\ensuremath{\gamma}\ensuremath{\gamma}$ branching ratio to be $(1.68\ifmmode\pm\else\textpm\fi{}0.07\ifmmode\pm\else\textpm\fi{}0.08)\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}6}$. Our data show the first evidence for a low-mass $\ensuremath{\gamma}\ensuremath{\gamma}$ signal as predicted by recent $O({p}^{6})$ chiral perturbation calculations which include vector meson exchange contributions. From our data, we extract a value for the effective vector coupling ${a}_{V}\phantom{\rule{0ex}{0ex}}=\phantom{\rule{0ex}{0ex}}\ensuremath{-}0.72\ifmmode\pm\else\textpm\fi{}0.05\ifmmode\pm\else\textpm\fi{}0.06$.

We present the first measurement of the form factor ratios g(1)/f(1) (direct axial vector to vector), g(2)/f(1) (second class current), and f(2)/f(1) (weak magnetism) for the decay Xi(0)-->Sigma(+)e(-)nu macro(e) using the KTeV (E799) beam line and detector at Fermilab. From the Sigma(+) polarization measured with the decay Sigma(+)-->p pi(0) and the e(-)-nu; correlation, we measure g(1)/f(1) to be 1.32+/-(0.21)(0.17)(stat)+/-0.05(syst), assuming the SU(3)(f) (flavor) values for g(2)/f(1) and f(2)/f(1). Our results are all consistent with exact SU(3)(f) symmetry.

We present results of a search for a new form of hadronic matter, a six-quark, dibaryon state called the H0, a state predicted to exist in several theoretical models. Analyzing data collected by experiment E799-II at Fermilab, we searched for the decay H0-->Lambdappi(-) and found no candidate events. We place an upper limit on [B(H0-->Lambdappi(-))dsigma(H)/dOmega]/(dsigma(Xi)/dOmega) and, in the context of published models, exclude the region of lightly bound mass states just below the LambdaLambda mass threshold, 2.194<M(H)<2.231 GeV/c(2), with lifetimes from approximately 5x10(-10) sec to approximately 1x10(-3) sec.

We searched for the appearance of π+π− pairs with invariant mass ≥648MeV/c2 in a neutral beam. Such an observation could signify the decay of a long-lived light neutral particle. We find no evidence for this decay. Our null result severely constrains the existence of an R0 hadron, which is the lightest bound state of a gluon and a light gluino (g˜g), and thereby also the existence of a light gluino. Depending on the photino mass, we exclude the R0 in the mass and lifetime ranges of 1.2–4.6GeV/c2 and 2×10−10–7×10−4s, respectively.Received 18 July 1997DOI:https://doi.org/10.1103/PhysRevLett.79.4083©1997 American Physical Society

We report on a search for the decay KL-->pi(0)e+e- carried out by the KTeV/E799 experiment at Fermilab. This decay is expected to have a significant CP violating contribution and the measurement of its branching ratio could support the Cabibbo-Kobayashi-Maskawa mechanism for CP violation or could point to new physics. Two events were observed in the 1997 data with an expected background of 1.06+/-0.41 events, and we set an upper limit B(KL-->pi(0)e+e-)<5.1 x 10(-10) at the 90% confidence level.

Using an impact parameter tag to select an enriched sample of Z0→bb¯ events, and the net momentum-weighted track charge to identify the sign of the charge of the underlying b quark, we have measured the left-right forward-backward asymmetry for b quark production as a function of polar angle. Based on 1.8pb−1 of Z0 decay data produced with a mean electron beam polarization of Pe=63%, this yields a direct measurement of the extent of parity violation in the Zbb coupling of Ab=0.87±0.11(stat)±0.09(syst).Received 3 October 1994DOI:https://doi.org/10.1103/PhysRevLett.74.2890©1995 American Physical Society

In 1992, L.G. Levchuk noted that the asymmetries measured in M\o ller scattering polarimeters could be significantly affected by the intrinsic momenta of the target electrons. This effect is largest in devices with very small acceptance or very high resolution in laboratory scattering angle. We use a high resolution polarimeter in the linac of the polarized SLAC Linear Collider to study this effect. We observe that the inclusion of the effect alters the measured beam polarization by -14% of itself and produces a result that is consistent with measurements from a Compton polarimeter. Additionally, the inclusion of the effect is necessary to correctly simulate the observed shape of the two-body elastic scattering peak.

The parity-violating parameters Ab and Ac are directly measured by the SLD experiment at the SLAC Linear Collider in e+e− collisions with polarized electrons at the Z0 resonance. Leptons with distinctive total and transverse momenta are used to select and analyze Z0→bb¯ and Z0→cc¯ events. Ab and Ac are extracted by forming the left-right forward-backward asymmetry in electron beam polarization and quark polar angle. From our 1993 sample of 1.8 pb–1 of Z0 decay data with an average electron beam polarization of 63% we find Ab=0.91±0.14 (stat) ±0.07 (syst) and Ac=0.37±0.23 (stat) ±0.21 (syst).Received 4 October 1994DOI:https://doi.org/10.1103/PhysRevLett.74.2895©1995 American Physical Society

We report on two null searches, one for the spontaneous appearance of ${\ensuremath{\pi}}^{+}{\ensuremath{\pi}}^{\ensuremath{-}}$ pairs, another for a single ${\ensuremath{\pi}}^{0}$, consistent with the decay of a long-lived neutral particle into hadrons and an unseen neutral particle. For the lowest level gluon-gluino bound state, known as the ${R}^{0}$, we exclude the decays ${R}^{0}\ensuremath{\rightarrow}{\ensuremath{\pi}}^{+}{\ensuremath{\pi}}^{\ensuremath{-}}\stackrel{\ifmmode \tilde{}\else \~{}\fi{}}{\ensuremath{\gamma}}$ and ${R}^{0}\ensuremath{\rightarrow}{\ensuremath{\pi}}^{0}\stackrel{\ifmmode \tilde{}\else \~{}\fi{}}{\ensuremath{\gamma}}$ for the masses of ${R}^{0}$ and $\stackrel{\ifmmode \tilde{}\else \~{}\fi{}}{\ensuremath{\gamma}}$ in the theoretically allowed range. In the most interesting ${R}^{0}$ mass range, $\ensuremath{\le}3\mathrm{GeV}/{c}^{2}$, we exclude ${R}^{0}$ lifetimes from $3\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}10}\mathrm{sec}$ to as high as ${10}^{\ensuremath{-}3}\mathrm{sec}$, assuming perturbative QCD production for the ${R}^{0}$.

We report the first branching fraction measurement of the decay ${K}_{L}\ensuremath{\rightarrow}{\ensuremath{\pi}}^{+}{\ensuremath{\pi}}^{\ensuremath{-}}{e}^{+}{e}^{\ensuremath{-}}$. With a sample of 46 candidates, and an expected background level of 9.4 events, the branching fraction is determined to be $B({K}_{L}\ensuremath{\rightarrow}{\ensuremath{\pi}}^{+}{\ensuremath{\pi}}^{\ensuremath{-}}{e}^{+}{e}^{\ensuremath{-}})\phantom{\rule{0ex}{0ex}}=\phantom{\rule{0ex}{0ex}}[3.2\ifmmode\pm\else\textpm\fi{}0.6(\mathrm{stat})\ifmmode\pm\else\textpm\fi{}0.4(\mathrm{syst})]\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}7}$. This measurement was carried out as part of the Fermilab KTeV (E799-II) experiment and is in good agreement with the expectations from the mechanisms of direct emission and inner bremsstrahlung.

Bhabha scattering with polarized electrons at the ${Z}^{0}$ resonance has been measured with the SLD experiment at the SLAC Linear Collider. The first measurement of the left-right asymmetry in Bhabha scattering is presented, yielding the effective weak mixing angle of ${sin}^{2}{\ensuremath{\theta}}_{W}^{\mathrm{eff}}\phantom{\rule{0ex}{0ex}}=\phantom{\rule{0ex}{0ex}}0.2245\ifmmode\pm\else\textpm\fi{}0.0049\ifmmode\pm\else\textpm\fi{}0.0010$. The effective electron couplings to the ${Z}^{0}$ are extracted from a combined analysis of polarized Bhabha scattering and the left-right asymmetry previously published: ${\ensuremath{\upsilon}}_{e}\phantom{\rule{0ex}{0ex}}=\phantom{\rule{0ex}{0ex}}\ensuremath{-}0.0414\ifmmode\pm\else\textpm\fi{}0.0020$ and ${a}_{e}\phantom{\rule{0ex}{0ex}}=\phantom{\rule{0ex}{0ex}}\ensuremath{-}0.4977\ifmmode\pm\else\textpm\fi{}0.0045$.

We report on the analysis of the rare decay K(L)-->mu(+)mu(-)gamma the 1997 data from the KTeV experiment at Fermilab. A total of 9327 candidate events are observed with 2.4% background, representing a factor of 40 increase in statistics over the current world sample. We find that B(K(L)-->mu(+)mu(-)gamma) = (3.62 +/- 0.04(stat) +/- 0.08(syst)) x 10(-7). The form factor parameter alpha(K*) is measured to be alpha(K*) = -0.160(+0.026)(-0.028). In addition, we make the first measurement of the parameter alpha from the D'Ambrosio-Isidori-Portolés form factor, finding alpha = -1.54 +/- 0.10. In that model, this alpha measurement limits the Cabibbo-Kobayashi-Maskawa parameter rho>-0.2.

Abstract A large hadron calorimeter and muon tracking device using plastic streamer tubes has been constructed in the iron flux-return structure for the SLD detector at SLAC. Various studies of the operating characteristics of the streamer tubes of this system are presented. Emphasis is placed on the tracking capabilities of the device and on the optimization of the high voltage and readout electronics.

We observe 441 K(L)-->e(+)e(-)e(+)e(-) candidate events with a background of 4.2 events and measure B(K(L)-->e(+)e(-)e(+)e(-)) = [3.72+/-0.18(stat)+/-0.23(syst)]x10(-8) in the KTeV/E799II experiment at Fermilab. Using the distribution of the angle between the planes of the e(+)e(-) pairs, we measure the CP parameters beta(CP) = -0.23+/-0.09(stat)+/-0.02(syst) and gamma(CP) = -0.09+/-0.09(stat)+/-0.02(syst). We also present the first detailed study of the e(+)e(-) invariant mass spectrum in this decay mode.

We have performed studies of the K(0)(L)-->pi(+)pi(-)gamma direct emission ( DE) and inner Bremsstrahlung ( IB) vertices, based on data collected by KTeV during the 1996 Fermilab fixed target run. We find a(1)/a(2) = -0.737+/-0.034 GeV2 for the DE form-factor parameter in the rho-propagator parametrization, and report on fits of the form factor to linear and quadratic functions as well. We concurrently measure gamma(K(0)(L)-->pi(+)pi(-)gamma,E(*)(gamma)>20 MeV)/gamma(K(0)(L)-->pi(+)pi(-)) = (20.8+/-0.3)x10(-3), and a K(0)(L)-->pi(+)pi(-)gamma DE/(DE+IB) branching ratio of 0.683+/-0.011.

The recent discovery of a large CP violating asymmetry in KL-->pi+pi-e+e- mode has prompted us to seach for the associated KL-->pi 0 pi 0 e+e- decay mode in the KTeV-E799 experiment at Fermilab. In 2.7 x 10(11) K(L) decays, one candidate event has been observed with an expected background of 0.3 event, resulting in an upper limit for the KL-->pi 0 pi 0 e+e- branching ratio of 6.6 x 10(-9) at the 90% C.L.

We have implemented triggers for hadronically decaying tau leptons within a framework of the CDF Run 2 trigger system. We describe the triggers, along with their physics motivations, and report on their initial performance.

The branching ratio of the rare decay ${\ensuremath{\pi}}^{0}\ensuremath{\rightarrow}{e}^{+}{e}^{\ensuremath{-}}$ has been measured in E799-II, a rare kaon decay experiment using the KTeV detector at Fermilab. We observed 275 candidate ${\ensuremath{\pi}}^{0}\ensuremath{\rightarrow}{e}^{+}{e}^{\ensuremath{-}}$ events, with an expected background of $21.4\ifmmode\pm\else\textpm\fi{}6.2$ events which includes the contribution from Dalitz decays. We measured $B[{\ensuremath{\pi}}^{0}\ensuremath{\rightarrow}{e}^{+}{e}^{\ensuremath{-}},({m}_{{e}^{+}{e}^{\ensuremath{-}}}{/m}_{{\ensuremath{\pi}}^{0}}{)}^{2}&gt;0.95]\phantom{\rule{0ex}{0ex}}=\phantom{\rule{0ex}{0ex}}(6.09\ifmmode\pm\else\textpm\fi{}0.40\ifmmode\pm\else\textpm\fi{}0.24)\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}8}$, where the first error is statistical and the second systematic. This result is the first significant observation of the excess rate for this decay above the unitarity lower bound.

The infrared-ultraviolet properties of quantum gravity suggest on very general grounds that hard short distance scattering processes are highly suppressed for center of mass scattering energies beyond the fundamental Planck scale. If this scale is not too far above the electroweak scale, these nonperturbative quantum gravity effects could be manifest as an extinction of high transverse momentum jets at the LHC. To model these effects, we implement an extinction Monte Carlo modification of the PYTHIA event generator based on a Veneziano form factor with a large absorptive branch cut modification of hard QCD scattering processes. Using this we illustrate the leading effects of extinction on the inclusive jet transverse momentum spectrum at the LHC. We estimate that an extinction mass scale of up to roughly half the center of mass beam collision energy could be probed with high statistics data. Experimental searches at the LHC for jet extinction would be complementary to ongoing searches for the related phenomenon of excess production of high multiplicity final states.

We present a direct measurement of Ac=2vcac(vc2+ac2) from the left-right forward-backward asymmetry of D*+ and D+ mesons in Z0 events produced with the longitudinally polarized SLAC Linear Collider beam. These Z0→cc¯ events are tagged on the basis of event kinematics and decay topology from a sample of hadronic Z0 decays recorded by the SLAC Large Detector. We measure Ac0=0.73±0.22(stat)±0.10(syst).Received 10 April 1995DOI:https://doi.org/10.1103/PhysRevLett.75.3609©1995 American Physical Society

We have studied the rare weak radiative hyperon decay Xi degrees -->Sigma degrees gamma in the KTeV experiment at Fermilab. We have identified 4045 signal events over a background of 804 events. The dominant Xi degrees -->Lambdapi degrees decay, which was used for normalization, is the only important background source. An analysis of the acceptance of both modes yields a branching ratio of B(Xi degrees -->Sigma degrees gamma)/B(Xi degrees -->Lambdapi degrees ) = (3.34+/-0.05+/-0.09)x10(-3). By analyzing the final state decay distributions, we have also determined that the Sigma degrees emission asymmetry parameter for this decay is alpha(XiSigma) = -0.63+/-0.09.

We have searched for signatures of polarization in hadronic jets from $Z^0 \to q \bar{q}$ decays using the ``jet handedness'' method. The polar angle asymmetry induced by the high SLC electron-beam polarization was used to separate quark jets from antiquark jets, expected to be left- and right-polarized, respectively. We find no evidence for jet handedness in our global sample or in a sample of light quark jets and we set upper limits at the 95% C.L. of 0.063 and 0.099 respectively on the magnitude of the analyzing power of the method proposed by Efremov {\it et al.}

We report a measurement of the average $B$-hadron lifetime using data collected with the SLD detector at the SLC in 1993. An inclusive analysis selected three-dimensional vertices with $B$-hadron lifetime information in a sample of 50k $Z^{0}$ decays. A lifetime of $1.564\pm0.030\,(\rm stat)\pm 0.037\,(\rm syst)$~ps was extracted from the decay length distribution of these vertices using a binned maximum-likelihood method.

We present a new measurement of the branching ratio of the decay K_L -> pi e nu gamma (Ke3g) with respect to K_L -> pi e nu (Ke3), and the first study of the photon energy spectrum in this decay. We find BR(Ke3g, E*g>30 MeV, theta*_eg>20 deg)/BR(Ke3) = 0.908 +- 0.008 (stat.) +0.013-0.012 (syst.). Our measurement of the spectrum is consistent with inner bremsstrahlung as the only source of photons in Ke3g.

We have determined the strong coupling alpha-s from a comprehensive study of energy-energy correlations (EEC) and their asymmetry (AEEC) in hadronic decays of Z0 bosons collected by the SLD experiment at SLAC. The data were compared with all four available predictions of QCD calculated up to O(alpha-s**2) in perturbation theory, and also with a resummed calculation matched to all four of these calculations. We find large discrepancies between alpha-s values extracted from the different O(alpha-s**2) calculations. We also find a large renormalization scale ambiguity in alpha-s determined from the EEC using the O(alpha-s**2) calculations; this ambiguity is reduced in the case of the AEEC, and is very small when the matched calculations are used. Averaging over all calculations, and over the EEC and AEEC results, we obtain alpha-s(MZ)=0.124+0.003-0.004(exp.) +-0.009(theory).

We report on a study of the decay KL→e+e−γγ carried out as a part of the KTeV/E799 experiment at Fermilab. The 1997 data yielded a sample of 1543 events, including an expected background of 56±8 events. An effective form factor was determined from the observed distribution of the e+e− invariant mass. Using this form factor in the calculation of the detector acceptance, the branching ratio was measured to be B(KL→e+e−γγ,Eγ*>5MeV)=(5.84±0.15(stat)±0.32(syst))×10−7. Received 23 October 2000DOI:https://doi.org/10.1103/PhysRevD.64.012003©2001 American Physical Society

A measurement of the lifetime of the τ lepton has been made using a sample of 1671 Z0→τ+τ− decays collected by the SLD detector at the SLC. The measurement benefits from the small and stable collision region at the SLC and the precision pixel vertex detector of the SLD. Three analysis techniques have been used: decay length, impact parameter, and impact parameter difference methods. The combined result is ττ=297±9 (stat)±5(syst) fs.Received 7 June 1995DOI:https://doi.org/10.1103/PhysRevD.52.4828©1995 American Physical Society

We use K(L)'s in the 100-200 GeV energy range to produce 147 candidate events of the axial vector pair K1(1270)-K1(1400) in the nuclear Coulomb field of a Pb target and determine the radiative widths Gamma(K1(1400)-->K0+gamma)=280.8+/-23.2(stat)+/-40.4(syst) keV and Gamma(K1(1270)-->K0+gamma)=73.2+/-6.1(stat)+/-28.3(syst) keV. These first measurements appear to be lower than the quark-model predictions. We also place upper limits on the radiative widths for K(*)(1410) and K(*)(2)(1430) and find that the latter is vanishingly small in accord with SU(3) invariance in the naive quark model.

We have observed the decay ${K}_{L}\ensuremath{\rightarrow}{\ensuremath{\mu}}^{+}{\ensuremath{\mu}}^{\ensuremath{-}}\ensuremath{\gamma}\ensuremath{\gamma}$ at the KTeV experiment at Fermilab. This decay presents a formidable background to the search for new physics in ${K}_{L}\ensuremath{\rightarrow}{\ensuremath{\pi}}^{0}{\ensuremath{\mu}}^{+}{\ensuremath{\mu}}^{\ensuremath{-}}.$ The 1997 data yielded a sample of 4 signal events, with an expected background of $0.155\ifmmode\pm\else\textpm\fi{}0.081$ events. The branching ratio is $\mathcal{B} {(K}_{L}\ensuremath{\rightarrow}{\ensuremath{\mu}}^{+}{\ensuremath{\mu}}^{\ensuremath{-}}\ensuremath{\gamma}\ensuremath{\gamma})=[{10.4}_{\ensuremath{-}5.9}^{+7.5}\mathrm{}(\mathrm{stat})\ifmmode\pm\else\textpm\fi{}0.7\mathrm{}(\mathrm{syst})]\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}9}$ with ${m}_{\ensuremath{\gamma}\ensuremath{\gamma}}&gt;~1 \mathrm{MeV}{/c}^{2},$ consistent with a QED calculation which predicts $(9.1\ifmmode\pm\else\textpm\fi{}0.8)\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}9}.$

We have collected a 43 event sample of the decay K(L)-->e(+)e(-)mu(+)mu(-) with negligible backgrounds and measured its branching ratio to be (2.62+/-0.40+/-0.17)x10(-9). We see no evidence for CP violation in this decay. In addition, we set the 90% confidence upper limit on the combined branching ratios for the lepton flavor violating decays K(L)-->e(+/-)e(+/-)mu(-/+)mu(-/+) at B(K(L)-->e(+/-)e(+/-)mu(-/+)mu(-/+))< or =1.23x10(-10), assuming a uniform phase space distribution.

We report on the first observation of the decay KL -> pi0 ee gamma by the KTeV E799 experiment at Fermilab. Based upon a sample of 48 events with an estimated background of 3.6 +/- 1.1 events, we measure the KL -> pi0 ee gamma branching ratio to be (2.34 +/- 0.35 +/- 0.13)x10^{-8}. Our data agree with recent O(p^6) calculations in chiral perturbation theory that include contributions from vector meson exchange through the parameter a_V. A fit was made to the KL -> pi0 ee gamma data for a_V with the result -0.67 +/- 0.21 +/- 0.12, which is consistent with previous results from KTeV.

The SLD detector at the Stanford Linear Accelerator Center is a general purpose device for studying e{sup +}{epsilon}{sup {minus}} interaction at the Z{sup 0}. The SLD calorimeter system consists of two parts: a lead Liquid Argon Calorimeter (LAC) with both electromagnetic (22 radiation lengths) and hadronic sections (2.8 absorption lengths) housed inside the coil, and the Warm Ion limited streamer tubes Calorimeter (WIC) outside the coil which uses as radiator the iron of the flux return for the magnetic field. The WIC completes the measurement of the hadronic shower energy ({approximately}85% on average is contained in the LAC) and it provides identification and tracking for muons over 99% of the solid angle. In this note we report on the construction, test and commissioning of such a large system.

A search for long-lived particles (LLPs) produced in association with a Z boson is presented. The study is performed using data from proton-proton collisions with a center-of-mass energy of 13 TeV recorded by the CMS experiment during 2016-2018, corresponding to an integrated luminosity of 117 fb$^{-1}$. The LLPs are assumed to decay to a pair of standard model quarks that are identified as displaced jets within the CMS tracker system. Triggers and selections based on Z boson decays to electron or muon pairs improve the sensitivity to light LLPs (down to 15 GeV). This search provides sensitivity to beyond the standard model scenarios which predict LLPs produced in association with a Z boson. In particular, the results are interpreted in the context of exotic decays of the Higgs boson to a pair of scalar LLPs (H $\to$ SS). The Higgs boson decay branching fraction is constrained to values less than 6% for proper decay lengths of 10-100 mm and for LLP masses between 40 and 55 GeV. In the case of low-mass ($\approx$15 GeV) scalar particles that subsequently decay to a pair of b quarks, the search is sensitive to branching fractions $\mathcal{B}$(H $\to$ SS) $\lt$ 20% for proper decay lengths of 10-50 mm. The use of associated production with a Z boson increases the sensitivity to low-mass LLPs of this analysis with respect to gluon fusion searches. In the case of 15 GeV scalar LLPs, the improvement corresponds to a factor of 2 at a proper decay length of 30 mm.

A measurement of inclusive four-jet production in proton-proton collisions at a center-of-mass energy of 13\TeV is presented. The transverse momenta of jets within $\lvert\eta\rvert \lt$ 4.7 reach down to 35, 30, 25, and 20 GeV for the first-, second-, third-, and fourth-leading jet, respectively. Differential cross sections are measured as functions of the jet transverse momentum, jet pseudorapidity, and several other observables that describe the angular correlations between the jets. The measured distributions show sensitivity to different aspects of the underlying event, parton shower, and matrix element calculations. In particular, the interplay between angular correlations caused by parton shower and double-parton scattering contributions is shown to be important. The double-parton scattering contribution is extracted by means of a template fit to the data, using distributions for single-parton scattering obtained from Monte Carlo event generators and a double-parton scattering distribution constructed from inclusive single-jet events in data. The effective double-parton scattering cross section is calculated and discussed in view of previous measurements and of its dependence on the models used to describe the single-parton scattering background.

A brief description is given of the SLD calorimeter system, with emphasis on the iron calorimeter/muon identifier. Design choices and expected performance are summarized.

We present a comparison of the strong couplings of light (u, d, and s), c, and b quarks determined from multijet rates in flavor-tagged samples of hadronic Z0 decays recorded with the SLC Large Detector at the SLAC Linear Collider. Flavor separation on the basis of lifetime and decay multiplicity differences among hadrons containing light, c, and b quarks was made using the SLD precision tracking system. We find αudssαalls=0.987±0.027(stat)±0.022(syst)±0.022(theory), αcsαalls=1.012±0.104±0.102±0.096, and αbsαalls=1.026±0.041±0.041±0.030.Received 16 December 1994DOI:https://doi.org/10.1103/PhysRevD.53.R2271©1996 American Physical Society

Compton scattering provides a fast and accurate measurement of the longitudinal polarization of electron beams available at linear colliders. At the SLC, green (532 nm) circularly polarized light from an Nd:YAG laser, frequency doubled, collides nearly head-on with electrons after they have passed the e/sup +/e/sup -/ interaction point but before they have encountered any dipole bending magnets. Unique to this application, the recoil electrons, rather than scattered photons, are detected, after being momentum analyzed by the bending magnets nearest to the interaction point. Thus we achieve spatial separation of several centimeters between electrons from scattering at different Compton angles.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

The entire data acquisition chain, from the custom made front-end electronics to the Fastbus readout and data reduction module, for the digital readout of the SLD (see ref. [1]: SLD design report, SLAC-Report 73 (1984)) limited streamer tube Warm Iron Calorimeter and Muon Identifier is described. Also described is a Fastbus cosmic logic unit being developed to achieve the capability of reading cosmic ray events, also during the intercrossing time, for apparatus monitoring and calibration purposes.

There is a long history of searches for new physics using resonances or leptons in the final state. We present searches for new physics that may have neither leptons or resonances in the final state. In these cases, the searches must be model driven. Examples include models of Dark Matter, Large Extra Dimensions, long lived particle, Magnetic Monopoles or Microscopic Black Holes. The analyses presented were performed at the ATLAS and CMS experiments at the Large Hadron Collider.

Charge-dependent anisotropy Fourier coefficients ($v_n$) of particle azimuthal distributions are measured in pPb and PbPb collisions at $ \sqrt{\smash[b]{s_{_{\mathrm{NN}}}}} = $ 5.02 TeV with the CMS detector at the LHC. The normalized difference in the second-order anisotropy coefficients ($v_2$) between positively and negatively charged particles is found to depend linearly on the observed event charge asymmetry with comparable slopes for both pPb and PbPb collisions over a wide range of charged particle multiplicity. In PbPb, the third-order anisotropy coefficient, $v_3$, shows a similar linear dependence with the same slope as seen for $v_2$. The observed similarities between the $v_2$ slopes for pPb and PbPb, as well as the similar slopes for $v_2$ and $v_3$ in PbPb, are compatible with expectations based on local charge conservation in the decay of clusters or resonances, and constitute a challenge to the hypothesis that the observed charge asymmetry dependence of $v_2$ in heavy ion collisions arises from a chiral magnetic wave.

We present a novel computational approach for extracting weak signals, whose exact location and width may be unknown, from complex background distributions with an arbitrary functional form. We focus on datasets that can be naturally presented as binned integer counts, demonstrating our approach on the CERN open dataset from the ATLAS collaboration at the Large Hadron Collider, which contains the Higgs boson signature. Our approach is based on Gaussian Process (GP) regression - a powerful and flexible machine learning technique that allowed us to model the background without specifying its functional form explicitly, and to separate the background and signal contributions in a robust and reproducible manner. Unlike functional fits, our GP-regression-based approach does not need to be constantly updated as more data becomes available. We discuss how to select the GP kernel type, considering trade-offs between kernel complexity and its ability to capture the features of the background distribution. We show that our GP framework can be used to detect the Higgs boson resonance in the data with more statistical significance than a polynomial fit specifically tailored to the dataset. Finally, we use Markov Chain Monte Carlo (MCMC) sampling to confirm the statistical significance of the extracted Higgs signature.

We present a novel computational approach for extracting weak signals, whose exact location and width may be unknown, from complex background distributions with an arbitrary functional form. We focus on datasets that can be naturally presented as binned integer counts, demonstrating our approach on the CERN open dataset from the ATLAS collaboration at the Large Hadron Collider, which contains the Higgs boson signature. Our approach is based on Gaussian Process (GP) regression - a powerful and flexible machine learning technique that allowed us to model the background without specifying its functional form explicitly, and to separate the background and signal contributions in a robust and reproducible manner. Unlike functional fits, our GP-regression-based approach does not need to be constantly updated as more data becomes available. We discuss how to select the GP kernel type, considering trade-offs between kernel complexity and its ability to capture the features of the background distribution. We show that our GP framework can be used to detect the Higgs boson resonance in the data with more statistical significance than a polynomial fit specifically tailored to the dataset. Finally, we use Markov Chain Monte Carlo (MCMC) sampling to confirm the statistical significance of the extracted Higgs signature.

We present a preliminary measurement of the rate of gluon splitting into bottom quarks, g -> b bbar, in hadronic Z0 decays collected by SLD between 1996 and 1998. The analysis was performed by looking for secondary bottom production in 4-jet events of any primary flavour. 4-jet events were identified, and a topological vertex-mass technique was applied to each jet in order to identify b or bbar jets. The upgraded CCD based vertex detector gives very high B-tagging efficiency, especially for B hadrons of the low energies typical of this process. The two most nearly collinear b/bbar jets were tagged as originating from g -> b bbar. We measured the rate of secondary b/bbar production per hadronic event, g_bb, to be (3.07+-0.71(stat.)+-0.66(syst.)) * 10**-3.