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arXiv2012

Direct Measurement of Backgrounds using Reactor-Off Data in Double Chooz

Double Chooz is unique among modern reactor-based neutrino experiments studying $\bar ν_e$ disappearance in that data can be collected with all reactors off. In this paper, we present data from 7.53 days of reactor-off running. Applying the same selection criteria as used in the Double Chooz reactor-on oscillation analysis, a measured background rate of 1.0$\pm$0.4 events/day is obtained. The background model for accidentals, cosmogenic $β$-$n$-emitting isotopes, fast neutrons from cosmic muons, and stopped-$μ$ decays used in the oscillation analysis is demonstrated to be correct within the uncertainties. Kinematic distributions of the events, which are dominantly cosmic-ray-produced correlated-background events, are provided. The background rates are scaled to the shielding depths of two other reactor-based oscillation experiments, Daya Bay and RENO.

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arXiv2012

Study of the Hadronic Transitions $Υ$(2S)$\rightarrow (η,π^0)Υ$(1S) at Belle

We study the rare hadronic transitions $Υ(2S)\rightarrow Υ(1S)η$ and $Υ(2S)\rightarrow Υ(1S)π^0$ using a sample of 158 $\times 10^6$ $Υ(2S)$ decays collected with the Belle detector at the KEKB asymmetric-energy $e^+ e^-$ collider. We observe the $η$ meson decay to $γγ$ and $π^+π^-π^0$ final states; the $Υ(1S)$ is reconstructed in the $μ^+μ^-$ and $e^+e^-$ decay modes. We measure the ratios of branching fractions (${\mathcal B}$) $\frac{{\mathcal B}(Υ(2S)\rightarrowΥ(1S)η)}{{\mathcal B}(Υ(2S)\rightarrowΥ(1S)π^+π^-)}$ = (1.99$\pm$0.14 (stat) $\pm$0.11 (syst)) $\times 10^{-3}$ and $\frac{{\mathcal B}(Υ(2S)\rightarrowΥ(1S)π^0)}{{\mathcal B}(Υ(2S)\rightarrowΥ(1S)π^+π^-)} < 2.3 \times 10^{-4}$ at the 90% confidence level (CL). Assuming the value ${\mathcal B}(Υ(2S) \rightarrow Υ(1S)π^-π^+)$ = (17.92$\pm$0.26)%, we obtain $ {\mathcal B}(Υ(2S)\rightarrowΥ(1S)η) = (3.57 \pm 0.25 ({\rm stat})\ \pm 0.21 ({\rm syst}))\times 10^{-4} $ and $ {\mathcal B}(Υ(2S)\rightarrowΥ(1S)π^0) < 4.1\times 10^{-5}\ ({\rm 90%\ CL}). $

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arXiv2012

Observation of $η_{c}$ decay into $Σ^{+}\barΣ^{-}$ and $Ξ^{-}\barΞ^{+}$ final states

Using a data sample of $2.25\times10^{8}$ $J/ψ$ events collected with the BESIII detector, we present the first observation of the decays of $η_{c}$ mesons to $Σ^{+}\barΣ^{-}$ and $Ξ^{-}\barΞ^{+}$. The branching fractions are measured to be $(2.11\pm0.28_{\rm stat.}\pm0.18_{\rm syst.}\pm0.50_{\rm PDG})\times10^{-3}$ and $(0.89\pm0.16_{\rm stat.}\pm0.08_{\rm syst.}\pm0.21_{\rm PDG})\times10^{-3}$ for $η_{c} \to Σ^{+}\barΣ^{-}$ and $Ξ^{-}\barΞ^{+}$, respectively. These branching fractions provide important information on the helicity selection rule in charmonium-decay processes.

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arXiv2012

Measurement of D0-D0bar Mixing and CP Violation in Two-Body D0 Decays

We present a measurement of D0-D0bar mixing and CP violation using the ratio of lifetimes simultaneously extracted from a sample of D0 mesons produced through the flavor-tagged process D*+ -> D0 pi+, where D0 decays to K-+pi+-, K-K+, or pi-pi+, along with the untagged decays D0 -> K-+pi+- and D0 -> K-K+. The lifetimes of the CP-even, Cabibbo-suppressed modes K-K+ and pi-pi+ are compared to that of the CP-mixed mode K-+pi+- in order to measure yCP and DeltaY. We obtain yCP = [0.72 +- 0.18 (stat) +- 0.12 (syst)]% and DeltaY = [0.09 +- 0.26 (stat) +- 0.06 (syst)]%, where DeltaY constrains possible CP violation. The yCP result excludes the null mixing hypothesis at 3.3 sigma significance. This analysis is based on an integrated luminosity of 468 fb-1 collected with the BaBar detector at the PEP-II asymmetric-energy e+e- collider.

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arXiv2013

Search for $η$ and $η'$ Invisible Decays in $J/ψ\toϕη$ and $ϕη'$

Using a sample of $(225.3\pm 2.8)\times 10^{6}$ $J/ψ$ decays collected with the BESIII detector at BEPCII, searches for invisible decays of $η$ and $η^\prime$ in $J/ψ\toϕη$ and $ϕη^\prime$ are performed. Decays of $ϕ\to K^{+}K^{-}$ are used to tag the $η$ and $η^\prime$ decays. No signals above background are found for the invisible decays, and upper limits at the 90% confidence level are determined to be $2.58\times10^{-4}$ for the ratio $\frac{\mathcal{B}(η\to\rm{invisible})}{\mathcal{B}(η\toγγ)}$ and $2.39\times10^{-2}$ for $\frac{\mathcal{B}(η^\prime\to\rm{invisible})}{\mathcal{B}(η^\prime \toγγ)}$.

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arXiv2012

Phenomenology of Photon-Jets

One of the challenges of collider physics is to unambiguously associate detector based objects with the corresponding elementary physics objects. A particular example is the association of calorimeter-based objects such as "jets", identified with a standard (IR-safe) jet algorithm, with the underlying physics objects, which may be QCD-jets (arising from a scattered parton), electrons, photons and, as discussed here, photon-jets (a group of collinear photons). This separation is especially interesting in the context of Higgs searches, where the signal includes both di-photon (in the Standard Model) and di-photon-jet decays (in a variety of Beyond the Standard Model scenarios), while QCD provides an ever-present background. Here we describe the implementation of techniques from the rapidly evolving area of jet-substructure studies to not only enhance the more familiar photon-QCD separation, but also separately distinguish photon-jets, i.e., separate usual jets into three categories: single photons, photon-jets and QCD. The efficacy of these techniques for separation is illustrated through studies of simulated data.

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arXiv2013

Pushing the SUSY Higgs mass towards 125 GeV with a color adjoint

We show that inclusion of a TeV scale chiral superfield transforming in the adjoint representation of the color SU(3) to the MSSM particle content modifies the renormalization group running of some parameters in such a way that a 125 GeV mass of the light Higgs boson is accommodated more comfortably than in cMSSM / mSUGRA. Put differently, the introduction of a color adjoint TeV scale superfield helps resurrecting lighter choices for the stop and gluino which are otherwise disfavored in cMSSM / mSUGRA.

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arXiv2013

Indirect Probes of Supersymmetry Breaking in the JEM-EUSO Observatory

In this paper we propose indirect probes of the scale of supersymmetry breaking, through observations in the Extreme Universe Space Observatory onboard Japanese Experiment Module (JEM-EUSO). We consider scenarios where the lightest supersymmetric particle is the gravitino, and the next to lightest (NLSP) is a long lived slepton. We demonstrate that JEM-EUSO will be able to probe models where the NLSP decays, therefore probing supersymmetric breaking scales below $5 \times 10^6$ GeV. The observatory field of view will be large enough to detect a few tens of events per year, depending on its energy threshold. This is complementary to a previous proposal (Albuquerque et al., 2004) where it was shown that 1 Km$^3$ neutrino telescopes can directly probe this scale. NLSPs will be produced by the interaction of high energy neutrinos in the Earth. Here we investigate scenarios where they subsequently decay, either in the atmosphere after escaping the Earth or right before leaving the Earth, producing taus. These can be detected by JEM-EUSO and have two distinctive signatures: one, they are produced in the Earth and go upwards in the atmosphere, which allows discrimination from atmospheric taus and, second, as NLSPs are always produced in pairs, coincident taus will be a strong signature for these events. Assuming that the neutrino flux is equivalent to the Waxman-Bahcall limit, we determine the rate of taus from NLSP decays reaching JEM-EUSO's field of view.

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arXiv2012

Polishing a shiny Higgs with matrix elements

After the recent discovery of a Standard Model Higgs boson-like particle at the LHC, the question of its couplings to known and unknown matter is eminent. In this letter, we present a method that allows for an enhancement in S/B(irreducible) of the order of 100% in $pp\to (h\to γγ) jj$ for a center of mass energy of 8 and 14 TeV. This is achieved by applying the matrix element method. We discuss the implications of detector resolution effects and various approximations of the involved event simulation and reconstruction. The matrix element method provides a reliable, stable, and efficient handle to separate signal from background, and the gluon and weak boson fusion components involved in this process. Employing this method, a more precise Higgs boson coupling extraction can be obtained, and our results are of immediate relevance for current searches.

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arXiv2013

Discovery and Mass Spectroscopy via Mixed Di-Boson Production at the LHC in a 4-Site Model with a Composite Higgs Boson

We investigate the scope of the Large Hadron Collider (LHC) in probing the parameter space of a 4-Site (4S) model supplemented by one composite Higgs state. We concentrate on the yield of `mixed' di-boson production giving three leptons and missing (transverse) energy in the final state, i.e., events induced via the sub-process $q\bar q' -> l^+ν_l l^{'+}l^{'-}$ + ${\rm{c.c.}}$, where $q,q'$ are quarks and $l,l'=e,μ$ in all possible combinations, signature which enables the production in the intermediate steps of all additional -- with respect to the Standard Model (SM) -- neutral and charged gauge bosons belonging to the spectrum of this scenario, all of which in resonant topologies. We not only find this channel to be accessible over the background but also show that, after a dedicated cut-based analysis, kinematical reconstruction of all such resonances is always possible. We finally compare the yield of the mixed di-boson mode to that of the `charged' di-boson one and find that the former is of lesser scope than the latter at smaller gauge boson masses but it overcomes it at higher values, thereby revealing itself a viable search mode covering new regions of parameter space.

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arXiv2013

Hyperfine splitting and the experimental candidates for η_b(2S)

Predictions for the hyperfine splitting of 2S bottomonia are compared with the two recent experimental candidates for the η_b(2S). The smaller splitting of the Belle state is consistent with unquenched lattice QCD computations, many potential models, and a model-independent relation which works well for charmonia. The larger splitting for the state extracted from CLEO data is inconsistent with most predictions.

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arXiv2012

Observation of ψ(4040) and ψ(4160) decay into ηJ/ψ

The cross section for e^+e^- \to ηJ/ψbetween \sqrt{s}=3.8 GeV/c^2 and 5.3 GeV/c^2 is measured via initial state radiation using 980 fb^{-1} of data on and around the Υ(nS)(n=1,2,3,4,5) resonances collected with the Belle detector at KEKB. Two resonant structures at the ψ(4040) and ψ(4160) are observed in the ηJ/ψinvariant mass distribution. Fitting the mass spectrum with the coherent sum of two Breit-Wigner functions, one obtains BR(ψ(4040)\toηJ/ψ)\cdotΓ_{ee}^{ψ(4040)} = (4.8\pm0.9\pm1.4) eV and BR(ψ(4160)\toηJ/ψ)\cdotΓ_{ee}^{ψ(4160)} = (4.0\pm0.8\pm1.4) eV for one solution and BR(ψ(4040)\toηJ/ψ)\cdotΓ_{ee}^{ψ(4040)} = (11.2\pm1.3\pm1.9) eV and BR(ψ(4160)\toηJ/ψ)\cdotΓ_{ee}^{ψ(4160)} = (13.8\pm1.3\pm2.0) eV for the other solution, where the first errors are statistical and the second are systematic. This is the first measurement of this hadronic transition mode of these two states, and the partial widths to ηJ/ψare found to be about 1 MeV. There is no evidence for the Y(4260), Y(4360), ψ(4415), or Y(4660) in the ηJ/ψfinal state, and upper limits of their production rates in e^+e^- annihilation are determined.

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arXiv2012

Leading and Next-to-Leading Order Gluon Polarisation in the Nucleon and Longitudinal Double Spin Asymmetries from Open Charm Muoproduction

The gluon polarisation in the nucleon was measured using open charm production by scattering 160 GeV/c polarised muons off longitudinally polarised protons or deuterons. The data were taken by the COMPASS collaboration between 2002 and 2007. A detailed account is given of the analysis method that includes the application of neural networks. Several decay channels of D^0 mesons are investigated. Longitudinal spin asymmetries of the D meson production cross-sections are extracted in bins of D^0 transverse momentum and energy. At leading order QCD accuracy the average gluon polarisation is determined as (Delta g/G)^LO=-0.06 +/- 0.21 (stat.) +/- 0.08 (syst.) at the scale ~13 (GeV/c)^2 and an average gluon momentum fraction ~ 0.11. For the first time, the average gluon polarisation is also obtained at next-to-leading order QCD accuracy as (Delta g/G)^NLO = -0.13 +/- 0.15 (stat.) +/- 0.15 (syst.) at the scale ~ 13 (\GeV/c)^2 and ~ 0.20.

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arXiv2013

Diffractive photon production at high momentum transfer in $ep$ collisions

The diffractive photon production at large momentum transfer and large energies is a probe of the parton dynamics of the diffractive exchange. In this paper we revisit the leading order (LO) BFKL equation approach for this process and estimate, for the first time, the differential and total cross sections considering the next-to-leading order (NLO) corrections for the BFKL characteristic function. We obtain a reasonable agreement with the DESY HERA data.

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arXiv2013

Fragmentation with a Cut on Thrust: Predictions for B-factories

When high-energy single-hadron production takes place inside an identified jet, there are important correlations between the fragmentation and phase-space cuts. For example, when one-hadron yields are measured in on-resonance B-factory data, a cut on the thrust event shape T is required to remove the large b-quark contribution. This leads to a dijet final state restriction for the light-quark fragmentation process. Here we complete our analysis of unpolarized fragmentation of (light) quarks and gluons to a light hadron h with energy fraction z in e+ e- -> dijet + h at the center-of-mass energy Q=10.58 GeV. In addition to the next-to-next-to-leading order resummation of logarithms of 1-T, we include the next-to-leading order (NLO) nonsingular O(1-T) contribution to the cross section, the resummation of threshold logarithms of 1-z, and the leading nonperturbative contribution to the soft function. Our results for the correlations between fragmentation and the thrust cut are presented in a way that can be directly tested against B-factory data. These correlations are also observed in Pythia, but are surprisingly smaller at NLO.

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arXiv2013

New Scalar Contributions to $h\to Zγ$

We calculate the Higgs decay rate of $h\to Zγ$ by including the contributions from new scalars with arbitrary quantum numbers of the weak isospin ($T$) and hypercharge ($Y$) in the standard model. We find that our general formula for the decay rate of $h\to Zγ$ matches with that for $h\to γγ$ in the limit of $m_Z=0$, but it is different from those in the literature. To illustrate our result, by taking the current $2σ$ excess of the $h\to γγ$ rate measured by the LHC, we examine the corresponding shift for the $Zγ$ decay channel due to the new scalar. We show that the enhancement or reduction of the $h\to Zγ$ rate only depends on the relative size of $T$ and the absolute value of $Y$. Explicitly, we predict $0.76<R_{Zγ}\equiv Γ(h\to Zγ)/Γ_{SM}(h\to Zγ)<2.05$ by imposing the observed range of $1.5<R_{γγ}\equiv Γ(h\to Zγγ)/Γ_{SM}(h\toγγ)<2$, which is independent of the number of multiplets and the couplings to the Higgs particle as long as the scalars are heavier than 200 GeV. This result provides a clear signature for the future LHC measurements to test physics beyond the standard model.

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arXiv2013

Evidence for the decay B0 --> K+K-pi0

We report a search for charmless hadronic decays of neutral B mesons to the final state K+K-pi0. The results are based on a 711 fb^-1 data sample that contains 772x10^6 BB-bar pairs, and was collected at the Y(4S) resonance with the Belle detector at the KEKB asymmetric-energy e+e- collider. We find the first evidence for this decay with a significance of 3.5 standard deviations and measure its branching fraction as BF(B0 --> K+K-pi0) = [2.17 +/- 0.60(stat) +/- 0.24 (syst)]x10^-6.

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arXiv2013

Search for fractionally charged particles in pp collisions at sqrt(s) = 7 TeV

A search is presented for free heavy long-lived fractionally charged particles produced in pp collisions at sqrt(s) = 7 TeV. The data sample was recorded by the CMS detector at the LHC and corresponds to an integrated luminosity of 5.0 inverse femtobarns. Candidate fractionally charged particles are identified by selecting tracks with associated low charge measurements in the silicon tracking detector. Observations are found to be consistent with expectations for background processes. The results of the search are used to set upper limits on the cross section for pair production of fractionally charged, massive spin-1/2 particles that are neutral under SU(3)[C] and SU(2)[L]. We exclude at 95% confidence level such particles with electric charge +/-2e/3 with masses below 310 GeV, and those with charge +/-e/3 with masses below 140 GeV.

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