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Register a new userPursuing interpretations of the HERA large-Q2 data
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We explore interpretations of the anomaly observed by H1 and ZEUS at HERA in deep-inelastic e^+ p scattering at very large Q^2. We discuss the possibilities of new effective interactions and the production of a narrow state of mass 200 GeV with leptoquark couplings. We compare these models with the measured Q^2 distributions: for the contact terms, constraints from LEP2 and the Tevatron allow only a few choices of helicity and flavour structure that could roughly fit the HERA data. The data are instead quite consistent with the Q^2 distribution expected from a leptoquark state. We study the production cross sections of such a particle at the Tevatron and at HERA. The absence of a signal at the Tevatron disfavours the likelihood that any such leptoquark decays only into e^+ q. We then focus on the possibility that the leptoquark is a squark with R-violating couplings. In view of the present experimental limits on such couplings, the most likely production channels are e^+d -> scharm_L or perhaps e^+d->stop, with e^+s->stop a more marginal possibility. Possible tests of our preferred model include the absence both of analogous events in e^- p collisions and of charged current events, and the presence of detectable cascade decays whose kinematical signatures we discuss. We also discuss the possible implications for K->pi nu nubar, neutrinoless double-beta decay, the Tevatron and for e^+ e^- ->q qbar and neutralinos at LEP2.
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An excess of events at large Q2 with a positron in the final state has been observed at HERA which, if confirmed, would be a signal of new physics. It is not clear at present if a signal of comparable rate is also seen in the charged current channel (with an antineutrino in the final state). In this note we analyse the implications of the presence of such a signal in models of new physics based on contact terms, leptoquarks and squarks with R-violating decays. We find that in all cases the most likely possibility is that the charged current signal is absent. As a consequence if this signal is present the resulting indications are very selective. In particular for squarks only charged current events with multi-quark final states are possible with quite definite predictions on the spectrum of supersymmetric particles.
A number of methods have been proposed recently which exploit multiple highly-correlated interpretations of events, or of jets within an event. For example, Qjets reclusters a jet multiple times and telescoping jets uses multiple cone sizes. Previous work has employed these methods in pseudo-experimental analyses and found that, with a simplified statistical treatment, they give sizable improvements over traditional methods. In this paper, the improvement gain from multiple event interpretations is explored with methods much closer to those used in real experiments. To this end, we derive a generalized extended maximum likelihood procedure. We study the significance improvement in Higgs to bb with both this method and the simplified method from previous analysis. With either method, we find that using multiple jet radii can provide substantial benefit over a single radius. Another concern we address is that multiple event interpretations might be exploiting similar information to that already present in the standard kinematic variables. By examining correlations between kinematic variables commonly used in LHC analyses and invariant masses obtained with multiple jet reconstructions, we find that using multiple radii is still helpful even on top of standard kinematic variables when combined with boosted decision trees. These results suggest that including multiple event interpretations in a realistic search for Higgs to bb would give additional sensitivity over traditional approaches.
We study inclusive $J/psi$ photoproduction at NLO at large $P_T$ at HERA and the EIC. Our computation includes NLO QCD leading-$P_T$ corrections, QED contributions via an off-shell photon as well as those from $J/psi$+charm channels. For the latter, we employ the variable-flavour-number scheme. Our results are found to agree with the latest HERA data by H1 and provide, for the first time, a reliable estimate of the EIC reach for such a measurement. Finally, we demonstrate the observability of $J/psi$+charm production and the sensitivy to probe the non-perturbative charm content of the proton at high $x$, also known as intrinsic charm, at the EIC.
We sketch a novel method to search for light di-leptonic resonances by exploiting precision measurements of Drell-Yan production. Motivated by the recent hints of lepton flavour universality violation in $B to K^{ast} ell^+ ell^-$, we illustrate our proposal by studying the case of spin-1 resonances that couple to muons and have masses in the range of a few GeV. We show that the existing LHC data on $pp to Z/gamma^ast to mu^+ mu^-$ put non-trivial constraints on light di-muon resonance interpretations of $B$ decay anomalies in a model-independent fashion. The impact of our proposal on the long-standing discrepancy in the anomalous magnetic moment of the muon is also briefly discussed.
We study the inclusive J/psi production at large transverse momenta at lepton-hadron colliders in the limit when the exchange photon is quasi real, also referred to as photoproduction. Our computation includes the leading-P_T leading-v next-to-leading alpha_s corrections. In particular, we consider the contribution from J/psi plus another charm quark, by employing for the first time in quarkonium photoproduction the variable-flavour-number scheme. We also include a QED-induced contribution via an off-shell photon which remained ignored in the literature and which we show to be the leading contribution at high P_T within the reach of the EIC. In turn, we use our computation of J/psi+charm to demonstrate its observability at the future EIC and the EIC sensitivity to probe the non-perturbative charm content of the proton at high x.
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