arXiv subjects

S. Prelovsek

Publications and source records attributed to S. Prelovsek.

50 records · Page 3Linked to original sources

arXiv2002

The rare decays of D mesons

The flavor changing transitions in the c->u gamma, c->u gamma gamma and c->u l+ l- offer the possibility to search for new physics in the charm sector. We investigate dominant decay mechanisms in the radiative decays D->V gamma, D->P(V) l+ l-, D->gamma gamma and we discuss chances to see physics beyond the standard model in these decays. In addition, we analyze Cabibbo allowed D->K pi gamma decays with nonresonant K pi, and we probe the role of light vector mesons in these decays.

hep-ph↗

arXiv2001

Rare charm meson decays D->Pl^+l^- and c->ul^+l^- in SM and MSSM

We study the nine possible rare charm meson decays D->Pl^+l^- (P=pi,K,eta,eta') using the Heavy Meson Chiral Lagrangians and find them to be dominated by the long distance contributions. The decay D^+ -> pi^+l^+l^- with the branching ratio 1*10^(-6) is expected to have the best chances for an early experimental discovery. The short distance contribution in the five Cabibbo suppressed channels arises via the c->ul^+l^- transition; we find that this contribution is detectable only in the D->pi l^+l^- decay, where it dominates the differential spectrum at high-q^2. The general Minimal Supersymmetric Standard Model can enhance the c->ul^+l^- rate by up to an order of magnitude; its effect on the D->Pl^+l^- rates is small since the c->ul^+l^- enhancement is sizable in low-q^2 region, which is inhibited in the hadronic decay.

hep-ph↗

arXiv2001

Top Quark Production at TeV Energies as a Potential SUSY Detector

We consider the process of top-antitop production from electron-positron annihilation, for c. m. energies in the few TeV regime, in the MSSM theoretical framework. We show that, at the one loop level, the \underline{slopes} of a number of observable quantities in an energy region around 3 TeV are only dependent on $\tanβ$. Under optimal experimental conditions, a combined measurement of slopes might identify $\tanβ$ values in a range $\tanβ< 2$, $\tanβ>20$ with acceptable precision.

hep-ph↗

arXiv2000

$c\to uγ$ in the minimal supersymmetric standard model

The minimal supersymmetric standard model (MSSM) with universal soft breaking terms has a negligible effect on the rare $c\to uγ$ decay rate. We therefore study a general model with non-universal soft breaking terms constrained by vacuum stability and the experimental upper bound on the mass difference of the neutral charm mesons. It turns out that gluino exchange can enhance the standard model rate by up to two orders of magnitudes; in contrast, the contributions from charginos and neutralinos remain at least an order of magnitude below the QCD corrected standard model rate.

hep-ph↗

arXiv2000

A Possible Arena for Searching New Physics - the $Γ(D^0 \to ρ^0 γ)/Γ(D^0 \to ωγ)$ Ratio

We propose to investigate flavour changing neutral currents in the $c \to u γ$ transition through the measurement of the difference between $Γ(D^0 \to ρ^0 γ)$ and $Γ(D^0 \to ωγ)$. This is based on the observation that $D^0 \to (d \bar d) γ$ is due to long distance physics while $D^0 \to (u \bar u) γ$ arises from the $c \to u γ$ transition. The effect of $ρ- ω$ mixing is included. A difference in the decay widths of more than about 30% would be indicative of new physics.

hep-ph↗

arXiv1999

FCNC transition $c\to uγ$ in $B_c\to B_u^*γ$ decay

We propose the $B_c\to B_u^*γ$ decay as the most suitable probe for the flavour changing neutral transition $c\to uγ$. We estimate the short and long distance contributions to this decay within the standard model and we find them to be comparable; this is in contrast to radiative decays of $D$ mesons, that are completely dominated by the long distance contributions. Since the $c\to uγ$ transition is very sensitive to the physics beyond the standard model, the standard model prediction $Br(B_c\to B_u^*γ)\sim 10^{-8}$ obtained here opens a new window for future experiments. The detection of $B_c\to B_u^*γ$ decay at branching ratio well above $10^{-8}$ would signal new physics.

hep-ph↗

arXiv1999

Probing $c\to uγ$ in $B_c\to B_u^*γ$ decay

Flavour changing neutral current (FCNC) transitions $c\to uγ$ and $c\to ul^+l^-$ are very rare in the standard model and present an interesting probe for the physics beyond it. We study long distance contamination to these short distance processes in different hadron decays. As the most suitable probe for $c\to uγ$ transition we propose $B_c\to B_u^*γ$ decay. Its detection at the branching ratio well above $10^{-8}$ would signal new physics. The $c\to ul^+l^-$ transition may be probed at high $m_{ll}$ in $D\to πl^+l^-$. The decays $D\to Vγ$ and $D\to Vl^+l^-$ ($V$ is a light vector meson) are less suitable, since they are dominated by the long distance effects.

hep-ph↗

arXiv1999

FCNC transitions $c\to uγ$ and $s\to dγ$ in $B_c\to B_u^γ$ and $B_s\to B_d^γ$ decays

hep-ph↗

arXiv1998

Resonant and nonresonant contributions to the weak $D\to Vl^+l^-$ decays

The Cabibbo suppressed decays $D\to Vl^+l^-$ (V is light vector meson) present in principle the opportunity to observe the short distance FCNC transition $c\to ul^+l^-$, which is sensitive to physics beyond the Standard Model. We analyze these as well as the Cabibbo allowed $D \to V l^+ l^-$ decays within the Standard Model, where in addition to the short distance dynamics also the long distance dynamics is present. The long distance contribution is induced by the effective nonleptonic weak Lagrangian accompanied by the emission of a virtual photon, which occurs resonantly via conversion from a vector meson $ρ^0, ω$ or $ϕ$ or nonresonantly as direct emission from a $D$ meson. We calculate the branching ratios for all $D\to Vl^+l^-$ decays using the model, which combines heavy quark symmetry and chiral perturbation theory. The short distance contribution due to $c\to ul^+l^-$ transition, which is present only in the Cabibbo suppressed decays, is found to be three orders of magnitude smaller than the long distance contribution. The branching ratios well above $10^{-7}$ for Cabibbo suppressed decays could signal new physics. The most frequent decays are the Cabibbo allowed decays, which are expected at the rates, that are not much lower than the present experimental upper limit: $D_s^+\to ρ^+μ^+μ^-$ is expected at the branching ratio of approximately $3\cdot 10^{-5}$, while $D^0\to\bar K^{*0}μ^+μ^-$ is expected at $1.7\cdot 10^{-6}$.

hep-ph↗

arXiv1998

Long distance contributions in $D \to V γ$ decays

Using the factorization scheme for the nonleptonic $D \to V V_0$ weak amplitudes, we classify all diagrams which arise in $D \to V γ$ decays and calculate them with the help of the hybrid model which combines the heavy quark effective theory and the chiral Lagrangian approach. Thus we determine the long distance contribution to the amplitudes of Cabibbo allowed and Cabibbo suppressed $D \to Vγ$ decays. The calculation of the expected range of the branching ratios of nine different $D \to V γ$ channels is compared with results of other approaches. The present work establishes an increase of the parity violating contribution in these decays in comparison with previous analyses.

hep-ph↗

arXiv1998

Radiative decays of D mesons

The short-distance contribution due to the $c\to uγ$ penguin as well as long-distance contributions are considered in an analysis of $D\to Vγ$ decays, the latter being dominant. The matrix elements for nine $D\to Vγ$ transitions are calculated using a hybrid model which combines heavy quark effective theory and the chiral Lagrangian. We present the expected range of the branching ratios for these decays, the most frequent ones $D^0\to \bar{K}^{*0}γ$ and $D^+_s \to ρ^+γ$, being a few times $10^{-4}$.

hep-ph↗

arXiv1998

The CP violating asymmetry in $B^{\pm} \to M {\bar M} π^{\pm}$ decays

We analyze the asymmetry in the partial widths for the decays $B^{\pm} \to M {\bar M} π^{\pm}$ ($ M = π^+, K ^+, π^0, η$), which results from the interference of the nonresonant decay amplitude with the resonant amplitude for $B^{\pm} \to χ_{c0} π^{\pm} $ followed by the decay $χ_{c0} \to M {\bar M} $. The CP violating phase $γ$ can be extracted from the measured asymmetry. We find that the partial width asymmetry for $B^\pm \to π^+ π^- π^\pm$ is about $0.33~sin γ$, and about $0.45~ sin γ$ for $B^\pm \to K^+ K^-π^\pm$, while it is somewhat smaller for $B^\pm \to π^0 π^0 π^\pm$ and $B^\pm \to ηηπ^\pm$. Potential sources of uncertainties in these results, primarily coming from poorly known input parameters, are discussed.

hep-ph↗

arXiv1998

Can FCNC transition $c\to ul^+l^-$ be seen in $D\to Vl^+l^-$ decays?

The decays $D\to Vl^+l^-$ present in principle the opportunity to observe the short distance FCNC transition $c\to ul^+l^-$, which is sensitive to the physics beyond the Standard Model. We analyze the $D \to V l^+ l^- $ decays within the Standard Model, where in addition to the short distance dynamics also the long distance dynamics is present. The short distance contribution due to $c\to ul^+l^-$ transition, which is present only in the Cabibbo suppressed decays, is found to be three orders of magnitude smaller than the long distance contribution. The branching ratios well above $10^{-7}$ for Cabibbo suppressed decays could signal new physics. The most frequent decays are the Cabibbo allowed decays $D_s^+\toρ^+μ^+μ^-$ and $D^0\to\bar K^{*0}μ^+μ^-$, which are expected at the branching ratios of $3\cdot 10^{-5}$ and $1.7\cdot 10^{-6}$, respectively. These rates are not much lower than the present experimental upper limit.

hep-ph↗

arXiv1998

Signal for CP violation in $B^{\pm} \to P {\bar P} π^{\pm}$ decays

We analyze the partial rate asymmetry in $B^{\pm} \to P {\bar P} π^{\pm}$ decays ($ P = π^+, K ^+, π^0, η$) which results from the interference of the nonresonant decay amplitude and the resonant amplitude for $B^{\pm} \to χ_{c0} π^{\pm} $ followed by the decay $χ_{c0} \to P {\bar P} $. The CP violating phase $γ$ can be extracted from the measured asymmetry. We find that the partial rate asymmetry for $B^\pm \to π^+ π^- π^\pm$ is $0.33~sin γ$, while for $B^\pm \to K^+ K^-π^\pm$ it amounts $0.45~ sin γ$.

hep-ph↗