Production of the charged top-pions from TC2 model at the TeV energy e<Superscript>-</Superscript>γ colliders

The top-pions (Π_t ^0,±) and the top-Higgs (h_t ⁰) are the typical particles predicted by the topcolor-assisted technicolor (TC2) model and the observation of these particles can be regarded as direct evidence of the TC2 model. In this paper, we study three pair production processes of these new particles at the next generation eγ colliders, i.e., e^-γ→e^-Π_t ⁺Π_t ^-, e^-γ→ν_eΠ_t ^-Π_t ⁰ and e^-γ→ν_eΠ_t ^-h_t ⁰. The results show that the production rates can reach the level 10⁰–10¹ fb with reasonable parameter values. So one can expect that enough signals could be produced in future high- energy linear collider experiments. Furthermore, the flavor-changing (FC) decay modes Π_t ^-→bc̄, Π_t ⁰(h_t ⁰)→tc̄ can provide us with the typical signal to detect these new particles. PACS 12.60Nz; 14.80.Mz; 12.15.LK; 14.65.Ha     

Detecting an invisible Higgs boson at Fermilab Tevatron and CERN LHC

In this paper, we study the observability of an invisible Higgs boson at Fermilab Tevatron and CERN LHC through the production channel qq̄→ZH→ℓ⁺ℓ^-+P/_T, where/P_T is reconstructed from the ℓ⁺ℓ^- with ℓ=e or μ. A new strategy is proposed to eliminate the largest irreducible background, namely qq̄→Z(→ℓ⁺ℓ^-)Z(→νν̄). This strategy utilizes the precise measurements of qq̄→Z(→ℓ⁺ℓ^-)Z(→ℓ⁺ℓ^-). For m_H=120 GeV and with luminosity 30 fb^-1 at Tevatron, a 5σ observation of the invisible Higgs boson is possible. For m_H=114∼140 GeV with only 10 fb^-1 luminosity at LHC, a discovery signal over 5σ can be achieved. PACS 14.80.Cp     

Probing R-parity violating interactions from top-quark polarization at LHC

In the minimal supersymmetric standard model the R-parity violating interactions can induce anomalous top pair productions at the LHC through the t-channel process d_Rd̄_R→t_Lt̄_L by exchanging a slepton or by the u-channel process d_Rd̄_R→t_Rt̄_R exchanging a squark. Such top pair productions with a certain chirality cause top-quark polarization in the top pair events. We found that at the LHC, due to the large statistics, the statistical significance of the polarization observable, and thus the probing ability for the corresponding R-parity violating couplings, is much higher than at the Tevatron upgrade. PACS 14.65.Ha; 14.80.Ly     

Probing new physics through B mixing: Status, benchmarks and prospects

As is well known, B⁰ _d,s–B̄⁰ _d,s mixing offers a profound probe into the effects of physics beyond the standard model. The data obtained at the e⁺e^- B factories have already provided valuable insights into the B_d-meson system, and very recently also the B⁰ _s–B̄⁰ _s oscillation frequency ΔM_s has been measured at the Tevatron. We give a critical discussion of the interpretation of these data in terms of model-independent new-physics parameters. We address in particular the impact of the uncertainties of the relevant input parameters, set benchmarks for their accuracies as required by future precision measurements at the LHC, and explore the prospects for new CP-violating effects in the B_s system. To complement our model-independent analysis, we also discuss the constraints imposed by the CDF measurement of ΔM_s on popular models of new physics, namely scenarios with an extra Z’ boson and supersymmetry. We find that the new data still leave sizeable room for new-physics contributions to B⁰ _s–B̄⁰ _s mixing, which could be detected at the LHC.     

Supersymmetric contributions to B→DK and the determination of angle γ

We analyze supersymmetric contributions to the branching ratios and CP asymmetries of B^-→D⁰K^- and B^-→D̄⁰K^- processes. We investigate the possibility that supersymmetric CP violating phases can affect our determination for the angle γ in the unitary triangle of Cabibbo–Kobayashi–Maskawa mixing matrix. We calculate the gluino and chargino contributions to b→u(c̄s) and b→c(ūs) transitions in a model independent way by using the mass insertion approximation method. We also revise the D⁰–D̄⁰ mixing constraints on the mass insertions between the first and second generations of the up sector. We emphasize that in case of negligible D⁰–D̄⁰ mixing, one should consider simultaneous contributions from more than one mass insertion in order to be able to obtain the CP asymmetries of these processes within their 1σ experimental range. However, with a large D⁰–D̄⁰ mixing, one finds a significant deviation between the two asymmetries and it becomes natural to have them of the order of the central values of their experimental measurements.     

What can we learn from the decay of NX(1625) in the molecule picture?

Considering two assumptions on the molecular state, i.e. the S-wave Λ̄–K^- and S-wave Σ̄⁰–K^- molecular states, we study the possible decays of N̄_X(1625) that include N̄_X(1625)→K^-Λ̄,π⁰p̄,ηp̄,π^-n̄. Our results indicate that (1) if N̄_X(1625) is the Λ̄–K^- molecular state, K^-Λ̄ is the main decay mode of N̄_X(1625), and the branching ratios of the rest decay modes are tiny; (2) if N̄_X(1625) is the Σ̄⁰–K^- molecular state, the branching ratio of N̄_X(1625)→K^-Λ̄ is one or two orders smaller than that of N̄_X(1625)→π⁰p̄,ηp̄,π^-n̄. Thus the search for N̄_X(1625)→π⁰p̄,ηp̄,π^-n̄ will be helpful to shed light on the nature of N̄_X(1625). PACS 13.30.Eg, 13.75.Jz     

Model-independent determination of the top Yukawa coupling from LHC and ILC

We show how a measurement of the process pp→tt̄H⁰+X at the Large Hadron Collider (LHC) and a measurement of the Higgs boson branching ratios BR(H⁰→bb̄) and BR(H⁰→W⁺W^-) at a future linear electron positron collider (ILC) can be combined to extract a value of the top quark Yukawa coupling in a model-independent way. We find that for masses with 120 GeV/c²<m_H<200 GeV/c² a measurement precision of 15% including systematic uncertainties can be achieved for integrated luminosities of 300 fb^-1 at the LHC and 500 fb^-1 at the ILC at a centre-of-mass energy of 350 GeV.     

MSSM Higgs boson searches at the Tevatron and the LHC: Impact of different benchmark scenarios

The Higgs boson search has shifted from LEP2 to the Tevatron and will subsequently move to the LHC. The current limits from the Tevatron and the prospective sensitivities at the LHC are often interpreted in specific MSSM scenarios. For heavy Higgs boson production and subsequent decay into or τ⁺τ^–, the present Tevatron data allow one to set limits in the M_A–tan β plane for small M_A and large tan β values. Similar channels have been explored for the LHC, where the discovery reach extends to higher values of M_A and smaller tan β. Searches for MSSM charged Higgs bosons, produced in top decays or in association with top quarks, have also been investigated at the Tevatron and the LHC. We analyze the current Tevatron limits and prospective LHC sensitivities. We discuss how robust they are with respect to variations of the other MSSM parameters and possible improvements of the theoretical predictions for Higgs boson production and decay. It is shown that the inclusion of supersymmetric radiative corrections to the production cross sections and decay widths leads to important modifications of the present limits on the MSSM parameter space. The impact on the region where only the lightest MSSM Higgs boson can be detected at the LHC is also analyzed. We propose to extend the existing benchmark scenarios by including additional values of the higgsino mass parameter μ. This affects only slightly the search channels for a SM-like Higgs boson, while having a major impact on the searches for non-standard MSSM Higgs bosons.     

Virtual effects of split-SUSY in Higgs productions at linear colliders

In split supersymmetry, gauginos and higgsinos are the only supersymmetric particles possibly accessible at foreseeable colliders like the CERN Large Hadron Collider (LHC) and the International Linear Collider (ILC). In order to account for the cosmic dark matter measured by WMAP, these gauginos and higgsinos are stringently constrained and could be explored at the colliders through their direct productions and/or virtual effects in some processes. The clean environment and high luminosity of the ILC render the virtual effects at percent level meaningful in unraveling the new physics effects. In this work we assume split supersymmetry and calculate the virtual effects of the WMAP-allowed gauginos and higgsinos in the Higgs productions e⁺e^-→Zh and e⁺e^-→ν_eν̄_eh through WW fusion at the ILC. We find that the production cross section of e⁺e^-→Zh can be altered by a few percent in some part of the WMAP-allowed parameter space, while the correction to the WW fusion process e⁺e^-→ν_eν̄_eh is below 1%. Such virtual effects are correlated with the cross sections of chargino pair productions and can offer complementary information in probing split supersymmetry at the colliders. PACS 14.80.Ly; 95.35.+d     

Flavour-changing effects on e+e-→Hbs̄,Hb̄s in the MSSM

Flavour-changing effects originating from the exchange of scalar particles in the processes e⁺e^-→H^xbs̄,H^xb̄s, with H^x≡h⁰,H⁰,A⁰, are investigated in the minimal supersymmetric standard model with non-minimal flavour violation at the one-loop level. The dominating SUSY-QCD contributions with squark–gluino loops are calculated and discussed. We consider the SUSY scenario with non-minimal flavour mixing in the down-type squark-mass matrix. The flavour-changing cross sections are derived, and we discuss the dependence on the MSSM parameters and the strength of flavour mixing. The values for the cross section can reach 10^-4 pb for the production of the heavy Higgs boson H⁰ or A⁰, and only 10^-7 pb for the light Higgs boson h⁰. Non-decoupling behaviour occurs for both h⁰,H⁰ production in the case of a common heavy SUSY mass scale.     

The ATLAS discovery potential for MSSM neutral Higgs bosons decaying to a μ<Superscript>+</Superscript>μ<Superscript>-</Superscript> pair in the mass range up to 130 GeV

Results are presented on the discovery potential for MSSM neutral Higgs bosons in the m_h-max scenario. The region of large cosβ, between 15 and 50, and mass between ≈95 and 130 GeV is considered in the framework of the ATLAS experiment at the large hadron collider (LHC), for a centre-of-mass energy = 14 TeV. This parameter region is not fully covered by the present data either from LEP or from Tevatron. The h/A bosons, supposed to be very close in mass in that region, are studied in the channel h/A→μ⁺μ^- accompanied by two b-jets. The study includes a method to control the most copious background, Z→μ⁺μ^- accompanied by two b-jets. A possible contribution of the H boson to the signal is also considered.     

Pair production of charged Higgs bosons in the left–right twin Higgs model at the ILC and LHC

The left–right twin Higgs (LRTH) model predicts the existence of a pair of charged Higgs bosons φ^±. In this paper, we study the production of the charged Higgs boson pair φ^± at the international linear collider (ILC) and the CERN large hadron collider (LHC). The numerical results show that the production rates are at the level of several tens fb at the ILC, and the process e⁺e^-→φ⁺φ^- can produce adequately distinct multi-jet final states. We also discuss the charged Higgs boson pair production via the process qq̄→φ⁺φ^- at the LHC and estimate in this case the production rates. We find that, as long as the charged Higgs bosons are not too heavy, they can be abundantly produced at the LHC. The possible signatures of these new particles might be detected at the ILC and LHC experiments. PACS 12.60.Fr; 14.80.Mz; 14.65.Ha; 12.15.Lk     

Exploring CP violation and penguin effects through B0d→D+D- and B0s→D+sD-s

The decay B⁰ _d→D⁺D^- offers an interesting probe of CP violation, but it requires control of penguin effects, which can be done through B⁰ _s→D⁺ _sD^- _s by means of the U-spin flavour symmetry of strong interactions. Recently, the Belle collaboration reported indications of large CP violation in the B⁰ _d decay, which were, however, not confirmed by BaBar, and first signals of the B⁰ _s channel were observed at the Tevatron. In view of these developments and the quickly approaching start of the LHC, we explore the allowed region in observable space for CP violation in B⁰ _d→D⁺D^-, perform theoretical estimates of the relevant hadronic penguin parameters and observables, and we address questions both about the most promising strategies for the extraction of CP-violating phases and about the interplay with other measurements of CP violation and the search for new physics. As far as the latter aspect is concerned, we point out that the B⁰ _q→D_q ⁺D^- _q system provides a setting for the determination of the B⁰ _q–B̄⁰ _q mixing phases (q∈{d,s}) that is complementary to the conventional B⁰ _d→J/ψK_S and B⁰ _s→J/ψφ modes with respect to possible new-physics effects in the electroweak penguin sector.     

On radiative QCD backgrounds to exclusive H→bb̄ production at the LHC and a photon collider

Central exclusive Higgs boson production, pp→p⊕H⊕p, at the LHC and s-channel resonant Higgs production in the photon-collider option of the ILC can provide a very important contribution to the comprehensive study of the Higgs sector. Especially attractive is the bb̄ Higgs decay mode, which for certain MSSM scenarios may become the discovery channel in exclusive Higgs production at the LHC and the photon collider (PC). Strongly suppressed and controllable backgrounds is an obvious requirement for the success of these exclusive measurements. One of the main sources of background comes from additional gluon radiation which leads to a three-jet bb̄g final state. We perform an explicit calculation of the subprocesses gg→qq̄g and γγ→qq̄g, where the incoming particles are required to be in a J_z=0 state and the two gluons form a colour singlet, and investigate the salient properties of these potentially important background processes.     

Chiral color quark symmetry and possible constraints on the <Emphasis Type="Italic">G</Emphasis>′-boson mass from tevatron and LHC data

A gauge model featuring a chiral color symmetry of quarks was considered, and possible manifestations of this symmetry in proton-antiproton and proton-proton collisions at the Tevatron and LHC energies were studied. The cross section s_{t[`(t)]</sub>\sigma _{t\bar t} for the production of t[`(t)]t\bar t quark pairs at the Tevatron and the forward-backward asymmetry A_FB<sup>p[`(p)]</sup>A_{FB}^{p\bar p} in this process were calculated and analyzed with allowance for the contributions of the G′-boson predicted by the chiral color symmetry of quarks, the G′-boson massm <sub>G′</sub> and the mixing angle θ <sub>G</sub> being treated as free parameters of the model. Limits on m <sub>G′</sub> versus θ <sub>G</sub> were studied on the basis of data from the Tevatron on s<sub>t[`(t)]}\sigma _{t\bar t} and A_FB^p[`(p)]A_{FB}^{p\bar p}, and the region compatible with these data within one standard deviation was found in the m _G′-θ _G plane. The region ofm _G′-mass values that is appropriate for observing the G′-boson at LHC is discussed.     

Measurements of the absolute branching fractions for D→K̄πe+νe, D→K̄*e+νe and determination of Γ(D+→K̄*0e+νe)/Γ(D+→K̄0e+νe)

Using the data of about 33 pb^-1 collected at and around 3.773 GeV with the BES-II detector at the BEPC collider, we have studied the exclusive semileptonic decays D⁺→K^-π⁺e⁺ν_e, D⁰→K̄⁰π^-e⁺ν_e, D⁺→K̄^*0e⁺ν_e and D⁰→K^*-e⁺ν_e. The absolute branching fractions for the decays are measured to be BF(D⁺→K^-π⁺e⁺ν_e)=(3.50±0.75±0.27)%, BF(D⁰→K̄⁰π^-e⁺ν_e)=(2.61±1.04±0.28)%, BF(D⁺→K̄^*0e⁺ν_e)=(5.06±1.21±0.40)% and BF(D⁰→K^*-e⁺ν_e)=(2.87±1.48±0.39)%. The ratio of the vector to pseudoscalar semileptonic decay rates Γ(D⁺→K̄^*0e⁺ν_e)/Γ(D⁺→K̄⁰e⁺ν_e) is determined to be 0.57±0.17±0.02.     

B- c→η’ℓ-ν̄ decay and lepton polarization asymmetry

In this paper we study the lepton polarization asymmetry for the semileptonic OZI-forbidden annihilation decay B^- _c→η’ℓ^-ν̄, where ℓ=μ,τ. Our results show that the branching ratios turn out to be of order 10^-4. Besides, we find that longitudinal, transversal and normal components of lepton polarizations can be measured for both μ and τ decay modes in the future experiments at the LHC. PACS 14.40.Nd; 13.20.He; 13.60.-r; 11.30.Er     

Bs,d→ππ,πK,KK: status and prospects

Several years ago, it was pointed out that the U-spin-related decays B_d→π⁺π^-, B_s→K⁺K^- and B_d→π^∓K^±, B_s→π^±K^∓ offer interesting strategies for the extraction of the angle γ of the unitarity triangle. Using the first results from the Tevatron on the B_s decays and the B-factory data on B_u,d modes, we compare the determinations of γ from both strategies, study the sensitivity on U-spin-breaking effects, discuss the resolution of discrete ambiguities, predict observables that were not yet measured but will be accessible at LHCb, explore the extraction of the width difference ΔΓ_s from untagged B_s→K⁺K^- rates, and address the impact of new physics. The data for the B_d→π⁺π^-, B_s→K⁺K^- system favour the BaBar measurement of direct CP violation in B_d→π⁺π^-, which will be used in the numerical analysis and result in a fortunate situation, yielding γ=(66.6^+4.3+4.0 _-5.0-3.0)^°, where the latter errors correspond to a generous estimate of U-spin-breaking effects. On the other hand, the B_d→π^∓K^±, B_s→π^±K^∓ analysis leaves us with 26°≤γ≤70°, and points to a value of the B_s→π^±K^∓ branching ratio that is larger than the current Tevatron result. An important further step will be the measurement of mixing-induced CP violation in B_s→K⁺K^-, which will also allow us to extract the B⁰ _s–B̄⁰ _s mixing phase unambiguously with the help of B_s→J/ψφ at the LHC. Finally, the measurement of direct CP violation in B_s→K⁺K^- will make the full exploitation of the physics potential of the B_s,d→ππ,πK,KK modes possible.     

Understanding the newly observed Y(4008) by Belle

Very recently a new enhancement around 4.05 GeV was observed by the Belle experiment. We discuss some possible assignments for this enhancement, i.e. the ψ(3S) and D^*D̄^* molecular states. In these two assignments, Y(4008) can decay into J/ψπ⁰π⁰ with a branching ratio comparable with that of Y(4008)→J/ψπ⁺π^-. Thus, one suggests high energy experimentalists to look for Y(4008) in J/ψπ⁰π⁰ channel. Furthermore one proposes further experiments to search for the missing channels DD̄, DD̄^*+h.c. and especially χ_cJπ⁺π^-π⁰ and η_cπ⁺π^-π⁰, which will be helpful to distinguish the ψ(3S) and D^*D̄^* molecular state assignments for this new enhancement. PACS 13.30.Eg 13.75.Lb