Using pp collision data corresponding to an integrated luminosity of 8.5 fb−1 recorded by the LHCb experiment at center-of-mass energies of s=7, 8, and 13 TeV, the observation of an excited Bc+ ...state in the Bc+π+π− invariant-mass spectrum is reported. The observed peak has a mass of 6841.2±0.6(stat)±0.1(syst)±0.8(Bc+) MeV/c2, where the last uncertainty is due to the limited knowledge of the Bc+ mass. It is consistent with expectations of the Bc*(2S31)+ state reconstructed without the low-energy photon from the Bc*(1S31)+→Bc+γ decay following Bc*(2S31)+→Bc*(1S31)+π+π−. A second state is seen with a global (local) statistical significance of 2.2σ (3.2σ) and a mass of 6872.1±1.3(stat)±0.1(syst)±0.8(Bc+) MeV/c2, and is consistent with the Bc(2S10)+ state. These mass measurements are the most precise to date.
We reexamine the discovery potential at hadron colliders of high-mass right-handed (RH) gauge bosons WR-an inherent ingredient of left-right symmetric models (LRSM). We focus on the regime where the ...WR is very heavy compared to the heavy Majorana neutrino N, and we investigate an alternative signature for WR→N decays. The produced neutrinos are highly boosted in this mass regime. Subsequently, their decays via off-shell WR bosons to jets, i.e., N→ℓ±jj, are highly collimated, forming a single neutrino jet (jN). The final-state collider signature is then ℓ±jN, instead of the widely studied ℓ±ℓ±jj. Present search strategies are not sensitive to this hierarchical mass regime due to the breakdown of the collider signature definition. We take into account QCD corrections beyond next-to-leading order (NLO) that are important for high-mass Drell-Yan processes at the 13 TeV Large Hadron Collider (LHC). For the first time, we evaluate WR production at NLO with threshold resummation at next-to-next-to-leading logarithm (NNLL) matched to the threshold-improved parton distributions. With these improvements, we find that a WR of mass MWR=3(4)5 TeV and mass ratio of (mN/MWR)<0.1 can be discovered with a 5–6σ statistical significance at 13 TeV after 10(100)2000 fb−1 of data. Extending the analysis to the hypothetical 100 TeV Very Large Hadron Collider (VLHC), 5σ can be obtained for WR masses up to MWR=15(30) with approximately 100 fb−1 (10 ab−1). Conversely, with 0.9(10)150 fb−1 of 13 TeV data, MWR<3(4)5 TeV and (mN/MWR)<0.1 can be excluded at 95% C.L.; with 100 fb−1 (2.5 ab−1) of 100 TeV data, MWR<22(33) TeV can be excluded.
In LHC searches for new and rare phenomena the top-associated channel pp→tt‾W±+X is a challenging background that multilepton analyses must overcome. Motivated by sustained measurements of enhanced ...rates of same-sign and multi-lepton final states, we reexamine the importance of higher jet multiplicities in pp→tt‾W±+X that enter at O(αs3α) and O(αs4α), i.e., that contribute at NLO and NNLO in QCD in inclusive tt‾W± production. Using fixed-order computations, we estimate that a mixture of real and virtual corrections at O(αs4α) in well-defined regions of phase space can arguably increase the total tt‾W± rate at NLO by at least 10%−14%. However, by using non-unitary NLO multi-jet matching, we estimate that these same corrections are at most 10%−12%, and at the same time exhibit the enhanced jet multiplicities that are slightly favored by data. This seeming incongruity suggests a need for the full NNLO result. We comment on implications for the tt‾Z process.
The Pc(4380) and Pc(4450) states observed recently by the LHCb experiment were proposed to be either D¯Σc* or D¯*Σc bound states. We analyze the decay behaviors of two such types of hadronic ...molecules within the effective Lagrangian framework. With branching ratios of ten possible decay channels calculated, it is found that the two types of hadronic molecules have distinguishable decay patterns. While the D¯Σc* molecule decays dominantly to the D¯*Λc channel with a branching ratio by 2 orders of magnitude larger than to D¯Λc, the D¯*Σc molecule decays to these two channels with a difference of less than a factor of 2. Our results show that the total decay width of Pc(4380) as the spin-parity-32− D¯Σc* molecule is about a factor of 2 larger than the corresponding value for the D¯*Σc molecule. It suggests that the assignment of the D¯Σc* molecule for Pc(4380) is more favorable than the D¯*Σc molecule. In addition, Pc(4450) seems to be a D¯*Σc molecule with JP=52+ in our scheme. Based on these partial decay widths of the Pc states, we estimate the cross sections for the reactions γp→J/ψp and πp→J/ψp through the s-channel Pc states. The forthcoming γp experiment at JLAB and the πp experiment at JPARC should be able to pin down the nature of these Pc states.
The radiative decay Λb0→Λγ is observed for the first time using a data sample of proton-proton collisions corresponding to an integrated luminosity of 1.7 fb−1 collected by the LHCb experiment at a ...center-of-mass energy of 13 TeV. Its branching fraction is measured exploiting the B0→K*0γ decay as a normalization mode and is found to be B(Λb0→Λγ)=(7.1±1.5±0.6±0.7)×10−6, where the quoted uncertainties are statistical, systematic, and systematic from external inputs, respectively. This is the first observation of a radiative decay of a beauty baryon.
Motivated by TeV-scale neutrino mass models, we propose a systematic treatment of heavy neutrino (N) production at hadron colliders. Our simple and efficient modeling of the vector boson fusion (VBF) ...W±γ→Nℓ± and Nℓ±+nj signal definitions resolve collinear and soft divergences that have plagued past studies, and is applicable to other color-singlet processes, e.g., associated Higgs (W±h), sparticle (ℓ˜±νℓ˜), and charged Higgs (h±±h∓) production. We present, for the first time, a comparison of all leading N production modes, including both gluon fusion (GF) gg→Z*/h*→Nνℓ(−) and VBF. We obtain fully differential results up to next-to-leading order (NLO) in QCD accuracy using a Monte Carlo tool chain linking feynrules, nloct, and madgraph5_amc@nlo. Associated model files are publicly available. At the 14 TeV LHC, the leading order GF rate is small and comparable to the NLO Nℓ±+1j rate; at a future 100 TeV Very Large Hadron Collider, GF dominates for mN=300–1500 GeV, beyond which VBF takes the lead.
We perform an analysis within the Standard Model of B0,+→K*0,+μ+μ− decays in light of the recent measurements from the LHCb experiment, showing that new data strengthen the need for sizable hadronic ...contributions and correlations among them. We then extend our analysis to new physics via the Standard Model effective theory, and carry out a state-of-the-art fit of available b → sℓ+ℓ− data, including possible hadronic contributions. We find the case of a fully left-handed operator standing out as the simplest scenario with a significance of almost 6σ.
We present predictions for the gluon-fusion Higgs pT spectrum at third resummed and fixed order ( N3 LL′ + N3 LO ) including fiducial cuts as required by experimental measurements at the Large Hadron ...Collider. Integrating the spectrum, we predict for the first time the total fiducial cross section to third order ( N3 LO ) and improved by resummation. The N3 LO correction is enhanced by cut-induced logarithmic effects and is not reproduced by the inclusive N3 LO correction times a lower-order acceptance. These are the highest-order predictions of their kind achieved so far at a hadron collider.
A search for the decays Bc+→J/ψD(*)0K+ and Bc+→J/ψD(*)+K*0 is performed with data collected at the LHCb experiment corresponding to an integrated luminosity of 3 fb−1. The decays Bc+→J/ψD0K+ and ...Bc+→J/ψD*0K+ are observed for the first time, while first evidence is reported for the Bc+→J/ψD*+K*0 and Bc+→J/ψD+K*0 decays. The branching fractions of these decays are determined relative to the Bc+→J/ψπ+ decay. The Bc+ mass is measured, using the J/ψD0K+ final state, to be 6274.28±1.40(stat)±0.32(syst) MeV/c2. This is the most precise single measurement of the Bc+ mass to date.
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