<Emphasis Type="Italic">Z</Emphasis>′ discovery potential at the LHC in the minimal <Emphasis Type="Italic">B</Emphasis>–<Emphasis Type="Italic">L</Emphasis> extension of the standard model

We present the Large Hadron Collider (LHC) discovery potential in the Z′ sector of a \(U(1)_{B\mbox{--}L}\) enlarged Standard Model (that also includes three heavy Majorana neutrinos and an additional Higgs boson) for \(\sqrt{s}=7\), 10 and 14 TeV centre-of-mass (CM) energies, considering both the \(Z'_{B\mbox{--}L}\rightarrow e^{+}e^{-}\) and \(Z'_{B\mbox{--}L}\rightarrow\mu^{+}\mu^{-}\) decay channels. The comparison of the (irreducible) backgrounds with the expected backgrounds for the DØ experiment at the Tevatron validates our simulation. We propose an alternative analysis that has the potential to improve the DØ sensitivity. Electrons provide a higher sensitivity to smaller couplings at small \(Z'_{B\mbox{--}L}\) boson masses than do muons. The resolutions achievable may allow the \(Z'_{B\mbox{--}L}\) boson width to be measured at smaller masses in the case of electrons in the final state. The run of the LHC at \(\sqrt{s}=7\) TeV, assuming at most \(\int\mathcal{L} \sim1\) fb^?1, will be able to give similar results to those that will be available soon at the Tevatron in the lower mass region, and to extend them for a heavier M _Z′.     

Process <Emphasis Type="Italic">γ</Emphasis>*<Emphasis Type="Italic">γ</Emphasis> → <Emphasis Type="Italic">σ</Emphasis> at large virtuality of <Emphasis Type="Italic">γ</Emphasis>*

The process γ*γ → σ is investigated in the framework of the SU(2)×SU(2) chiral NJL model. The form factor of the process is derived for arbitrary virtuality of γ* in the Euclidean kinematic domain. The asymptotic behavior of this form factor resembles the asymptotic behavior of the γ*γ → π form factor.     

The quest for <Emphasis Type="Italic">μ</Emphasis> → <Emphasis Type="Italic">e</Emphasis><Emphasis Type="Italic">γ</Emphasis>: present and future

The quest for μ → eγ is one of the most important endeavors to search for New Physics beyond the Standard Model. In this talk I will review the current status of the experimental searches by the MEG Collaboration at PSI. I will also present a study of the experimental limiting factors that will define the ultimate performances, and hence the sensitivity, in the search for μ → eγ with continuous muon beams of extremely high rate (one or even two orders of magnitude larger than the present beams), whose construction is under consideration for the next decade.     

Ortho-para conversion in the muonic molecule <Emphasis Type="Italic">pp</Emphasis><Emphasis Type="Italic">μ</Emphasis>

The ortho-para conversion due to the interaction between the nuclear magnetic moments and the atomic electron is considered in the muonic molecule (ppμ)e produced in the ortho state. It is shown that the rate of this transition is w≈0.466 s^?1, which is much less than the rate of the transition induced by the mixing of states having opposite parities with respect to the inversion of the muon coordinates.     

Inclusive <Emphasis Type="Italic">J</Emphasis>/<Emphasis Type="Italic">ψ</Emphasis> photoproduction and polarization at HERA in the <Emphasis Type="Italic">k</Emphasis><Subscript><Emphasis Type="Italic">T</Emphasis></Subscript>-factorization approach

We investigate the inclusive photoproduction of J/ψ mesons at HERA within the framework of the k _T -factorization QCD approach. Our study is based on the color singlet model supplemented with the relevant off-shell matrix elements and the CCFM and KMR unintegrated gluon densities in a proton and in a photon. Both the direct and resolved photon contributions are taken into account. Our predictions are compared with the recent experimental data taken by the H1 and ZEUS collaborations. Special attention is put on the J/ψ polarization parameters λ and ν, which are sensitive to the production dynamics.     

Measurement of <Emphasis Type="Italic">Z</Emphasis> → <Emphasis Type="Italic">ττ</Emphasis> → <Emphasis Type="Italic">e</Emphasis>µ inclusive process at Large Hadron Collider

In several scenarios of beyond Standard Model physics a new heavy resonance is invoked which may decay preferentially, to a pair of taus. Identification of the decay of Standard Model Z resonance to tau pairs at LHC via subsequent decays of the taus to leptons as well as hadrons is the first step towards the discovery. A method has been suggested to discriminate Z to tau pair to electron+muon final state against various backgrounds, for early phase of 14 TeV LHC.     

The cusp effect in <Emphasis Type="Italic">η</Emphasis>′→<Emphasis Type="Italic">η</Emphasis><Emphasis Type="Italic">π</Emphasis><Emphasis Type="Italic">π</Emphasis> decays

Strong final-state interactions create a pronounced cusp in η′→η π ⁰ π ⁰ decays. We adapt and generalize the non-relativistic effective field theory framework developed for the extraction of π π scattering lengths from K→3π decays to this case. The cusp effect is predicted to have an effect of more than 8% on the decay spectrum below the π ⁺ π ⁻ threshold.     

Hadroproduction of direct <Emphasis Type="Italic">J/ψ</Emphasis> and <Emphasis Type="Italic">ψ</Emphasis>′ mesons in the fragmentation of gluons and <Emphasis Type="Italic">c</Emphasis> quarks at high energies

The transverse-momentum spectra of direct J/ψ and ψ′ mesons in pp interactions at the Tevatron collider energy of \(\sqrt s = 1.8\) TeV are calculated on the basis of nonrelativistic QCD, the fragmentation model, the k_T-factorization approach, and the standard parton model. The contribution of gluon fragmentation is shown to exceed the contribution of c-quark fragmentation both within the parton model and within the k_T-factorization approach. Experimental data of the CDF Collaboration agree with the assumption that gluon fragmentation plays a dominant role in the \(Q\bar Q[^3 S_1 ,8]\) octet state, with the nonperturbative matrix element taking approximately equal values in the parton model and in the k_T-factorization approach.     

<Emphasis Type="Italic">J</Emphasis>/<Emphasis Type="Italic">ψ</Emphasis> suppression and <Emphasis Type="Italic">p</Emphasis><Subscript><Emphasis Type="Italic">T</Emphasis></Subscript> spectra in RHIC and LHC energy collisions

In a hydrodynamic model, we have studied J/ψ production in Au+Au/Cu+Cu collisions at RHIC energy, GeV. At the initial time, J/ψ’s are randomly distributed in the fluid. As the fluid evolves in time, the free streaming J/ψ’s are dissolved if the local fluid temperature exceeds a threshold temperature T _J/ψ . Sequential melting of charmonium states (χ _c , ψ ^′ and J/ψ), with melting temperatures , T _J/ψ ≈2T _c and feed-down fraction F≈0.3, explains the PHENIX data on the centrality dependence of J/ψ suppression in Au+Au collisions. J/ψ p _T spectra and the nuclear modification factor in Au+Au collisions are also well explained in the model. The model however overpredicts the centrality dependence of J/ψ suppression in Cu+Cu collisions by 20–30%. The J/ψ p _T spectra are underpredicted by 20–30%. The model predicts that in central Pb+Pb collisions at LHC energy,  GeV, J/ψ’s are suppressed by a factor of ∼10. The model predicted a J/ψ p _T distribution in Pb+Pb collisions at LHC is similar to that in Au+Au collisions at RHIC.     

Hunting for the alpha: <Emphasis Type="Italic">B</Emphasis> → ρρ, <Emphasis Type="Italic">B</Emphasis> → ππ, <Emphasis Type="Italic">B</Emphasis> → πρ

The hypothesis of the smallness of penguin contributions to charmless strangeless \(B_d (\bar B_d )\) decays allows one to determine with high accuracy the value of the angle α from the currently available B → ρρ, B → ππ, and B → πρ decay data.     

Semileptonic (lepton,neutrino and jets) <Emphasis Type="Italic">WW</Emphasis>/<Emphasis Type="Italic">WZ</Emphasis> resonances searches at √<Emphasis Type="Italic">s</Emphasis> = 8 and 13 TeV with the ATLAS detector at the LHC

This talk presents the analyses results of the diboson (WW or WZ) resonances production search in pp collisions at √s = 8 and 13 TeV with the ATLAS detector at the LHC with the semileptonic final state. As benchmark signal models Randall-Sundrum bulk model for KK G* → WW and Heavy Vector Triplet model for W′ → WZ and Z′ → WW are used. No significant excess for diboson resonances production is observed and upper limits on the production cross section times branching fraction of G*, W′ and Z′ are determined at 95% CL.     

Search for <Emphasis Type="Italic">B</Emphasis><Subscript><Emphasis Type="Italic">s</Emphasis></Subscript> → <Emphasis Type="Italic">ϕ</Emphasis>µµ decay at the Large Hadron Collider

As B _s -mesons will be produced abundantly at the LHC, the observability of the flavour-changing-neutral-current decay mode B _s → ϕμ⁺μ⁻ has been studied in CMS at the LHC centre-of-mass energy of 10 TeV. With an integrated luminosity of 100 pb⁻¹, an upper limit of 6.7 × 10⁻⁶ on the branching ratio is expected to be obtained. The potential at 7 TeV with a luminosity of 1 fb⁻¹ is expected to be better.     

Transversity and T-odd PDFs from Drell–Yan processes with <Emphasis Type="Italic">pp</Emphasis>, <Emphasis Type="Italic">pD</Emphasis> and <Emphasis Type="Italic">DD</Emphasis> collisions

We estimate the single-spin asymmetries (SSA) which provide the access to transversity as well as to Boer–Mulders and Sivers PDFs via investigation of the single-polarized Drell–Yan (DY) processes with pp, pD and DD collisions available to RHIC, NICA, COMPASS, and J-PARC. The feasibility of these SSA is studied with the new generator of polarized DY events. The estimations performed demonstrate that there exist kinematical regions where SSA are presumably measurable. Most useful for PDFs extraction are the limiting kinematical ranges, where one can neglect the sea PDFs contributions which occur at large values of the Bjorken variable x. It is of interest that, contrary to the Sivers PDF, the transversity PDF is presumably accessible only in a particular kinematical region. Contrary to the option with the symmetric collider mode (RHIC, NICA), this is of importance for the COMPASS experiment and the future J-PARC facility, where the fixed-target mode is available.     

Contribution of final-state interaction to the branching ratio of <Emphasis Type="Italic">B</Emphasis>→<Emphasis Type="Italic">J</Emphasis>/<Emphasis Type="Italic">ψ</Emphasis><Emphasis Type="Italic">D</Emphasis>

To test the validity of perturbative QCD (pQCD) and investigate its range of application, one should look for a suitable process. B→J/ψ D is a promising candidate. The linear momentum of the products is relatively small, so that there may exist a region where exchanged gluons are soft and the perturbative treatment may fail, so that the non-perturbative effect would be significant. We attribute such non-perturbative QCD effects to the long-distance final-state interaction (FSI) which is estimated in this work. We find that the contribution from the FSI to the branching ratio is indeed sizable and may span the rather wide range of 10⁻⁶∼10⁻⁵ and cover a region where the pQCD prediction is of the same order. A more accurate measurement of its branching ratio may provide important information about the application region of pQCD and help to clarify the picture of inelastic rescattering (i.e. FSI), which is generally believed to play an important role in B decays.     

Can the RHIC <Emphasis Type="Italic">J</Emphasis>/<Emphasis Type="Italic">ψ</Emphasis> puzzle(s) be settled at LHC?

One observes strong suppression effects for hard probes, e.g. the production of J/ψ or high-p _T particles, in nucleus–nucleus (AA) collisions at RHIC. Surprisingly, the magnitude of the suppression is quite similar to that at SPS. In order to establish whether these features arise due to the presence of a thermalized system of quarks and gluons formed in the course of the collision, one should investigate the impact of suppression mechanisms which do not explicitly involve such a state. We calculate shadowing for gluons in the Glauber–Gribov theory and propose a model invoking a rapidity-dependent absorptive mechanism motivated by energy-momentum conservation effects. Furthermore, final-state suppression due to interaction with comoving matter (hadronic or pre-hadronic) has been shown to describe the data at SPS. We extend this model by including the backward reaction channel, i.e. recombination of open charm, which is estimated directly from pp data at RHIC. Strong suppression of charmonium both in pA and AA collisions at LHC is predicted. This is in stark contrast with the predictions of models assuming QGP formation and thermalization of heavy quarks.