The effect of new physics on

Liu, James T.; Ng, Daniel

doi:10.1016/0370-2693(94)01364-i

Cited by 8 publications

(1 citation statement)

References 35 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…Furthermore, proposed extensions of the standard model would imply additional potentially measurable deviations in Rb from the minimal standard model value [3]. Currently, the average Ra measurement at the CERN e+ecollider LEP is N 20 high [4] compared to the standard model value. The Rs measurements are performed by applying cuts to event or hemisphere characteristics which distinguish the decay of a B hadron from others.…”

Section: Introductionmentioning

confidence: 99%

Measurements ofRbwith impact parameters and displaced vertices

Abe¹,

Abt²,

Ahn³

et al. 1996

Phys. Rev. D

View full text Add to dashboard Cite

We present measurements of Rs using the SLD at the SLC. The analyses use 2D and 3D impact parameter tags and a displaced 3D vertex tag which all exploit the small size and stability of the e+e-interaction point and the precision 3D CCD pixel vertex detector to achieve high b&tagging efficiencies and purities. The combined measurement yields Rb = 0.229 f 0.011 and is consistent with standard model predictions.PACS number(s): 13.38.Dg, 13.65.+i

show abstract

Section: Introductionmentioning

confidence: 99%

Measurements ofRbwith impact parameters and displaced vertices

Abe¹,

Abt²,

Ahn³

et al. 1996

Phys. Rev. D

View full text Add to dashboard Cite

show abstract

Chargino mass and Rb anomaly

Chankowski

Pokorski

1996

Nuclear Physics B

View full text Add to dashboard Cite

We re-egzamine the possible magnitude of the supersymmetric contribution to R b with imposed all available phenomenological constraints and demanding good quality of the global fit to the precision electroweak data. For low tan β we find a new region of the parameter space, with M 2 ≈ |µ| and µ < 0 where R b remains large, ∼ 0.2180 even for the lighter chargino as heavy as 90 − 100 GeV. It is an interesting mixture of the up-higgsino and gaugino. The rôle of various phenomenological constraints is discussed in analitic form and importance of small but non-negligible left-right mixing in the stop sector is emphasized in this context. The large tan β option for enhancement of R b is also reviewed. The available data do not rule out this scenario. A considerable excitement has recently been inspired by the R b and R c anomaly [1,2,3,4,5,6,7,8,9]. The succesful tests of the Standard Model (SM), to a per mille level [10], are challenged by the measurements of the partial widths of the Z 0 decays into bb and cc quarks which disagree with the SM predictions for m t = 180(170) GeV at the level of 3.7(3.5) and 2.5(2.5) standard deviations, respectively [11]. If both results are confirmed, the SM and its simplest supersymmetric extension, the Minimal Supersymmetric Standard Model (MSSM), are ruled out. However, since the R b anomaly is statistically more significant, it is also of interest to discuss the possibility of explaining only the larger than in the SM value of R b . Even if R c is fixed to its SM prediction, R c = 0.172 the then measured value of R b = 0.2206 ± 0.0016 is still 3 standard deviations away from its SM value. The issue has been addressed in particular in the framework of the MSSM [2,3,4,5,6,7,8,9]. It is well known already for some time that in the MSSM there are new contributions to the Z 0 bb vertex which can significantly enhance the value of R b (but not R c ) if some superpartners are sufficiently light [12,2,4,5,6,8,9]. More specifically, for low (large) tan β the dominant contributions are chargino-stop (CP −odd Higgs boson and chargino-stop) loops.Any improvement in R b must not destroy the perfect agreement of the SM with the other precision LEP measurements and must be consistent with several other experimental constraints (which will be listed later on). It is, therefore, important to discuss the changes in R b in the context of global fits to the electroweak data (and with all additional constraints included). Such fits in the effective low energy MSSM (unconstrained by any GUT assumptions about the pattern of soft supersymmetry breaking scalar masses) have shown that it is realistic to obtain the values of R b up to R b = 0.2180(0.2190) for small (large) tan β values [5]. Although still away by 1.5σ (1.0σ) even from the central experimental value obtained with R c fixed to its SM value, those results provide an interesting improvement over the SM prediction R b = 0.2158 (0.2160) for m t = 180 (170) GeV. At the same time the overall best χ 2 is smaller than in the SM fits by ∆χ 2 ...

show abstract

αs(MZ2
Kim¹,
Kim²,
Lee³
et al. 1996
Phys. Rev. D
4
0
3
0
View full text Add to dashboard Cite

We implement global fits to CERN LEP data with nonuniversal interactions. Values of Rb consistent with experiment and aa consistent with low energy experiments are obtained. We also find that the x2 is better than the standard model. We argue that other kinds of new physics are needed to explain the difference between the values of cr,(Mi) from low energy experiments and from the three-jet ratio.PACS number(s): 12.38.Qk, 13.87.0sRecently the Collider Detector of Fermilab (CDF) Collaboration l&sated evidence for a top quark with a mass rn* -175 GeV [l]. Such a heavy top quark affects the partial width of 2 --t b6, and recent analysis indicates that the experimentally measured value for the ratio Rb = r(Z + b$)/r(Z + hadron) is higher than the standard model (SM) prediction at a 2.5~ level [2,3]. This discrepancy may be the first signal for new physics beyond the SM if it is confirmed by future experiments. A number of possible scenarios of new physics are being suggested to explain this Rb discrepancy [4-61.A nonuniversal interaction acting on only the third generation is an attractive candidate for new physics which can explain the Rg discrepancy since the SM predictions for other flavors should not be disrupted by the new physics. Models of this type are motivated by the idea that the top quark has a mass of the order of the weak scale and would play a key role in electroweak symmetry breaking via top quark condensation [7]. Considering the general approach, the anomalous nonuniversal interaction terms are SU(2)r. x U(l)y invariant and the b quark will take part in top quark interactions when the left-handed doublet is involved. This can result in a modification of the 2 + b6 vertex. We parametrize the nonuniversal interaction effects in the 2 --t b6 vertex by introducing the parameters n=,~. These parameters shift the SM tree level couplings of the neutral currents ~L,R to the effective couplings gETR:

show abstract

The effect of new physics on

Cited by 8 publications

References 35 publications

Measurements ofRbwith impact parameters and displaced vertices

Measurements ofRbwith impact parameters and displaced vertices

Chargino mass and Rb anomaly

αs(MZ2
Kim¹,
Kim²,
Lee³
et al. 1996
Phys. Rev. D
4
0
3
0
View full text Add to dashboard Cite

Contact Info

Product

Resources

About

The effect of new physics on

Cited by 8 publications

References 35 publications

Measurements ofRbwith impact parameters and displaced vertices

Measurements ofRbwith impact parameters and displaced vertices

Chargino mass and Rb anomaly

αs(MZ2Kim1, Kim2, Lee3 et al. 1996Phys. Rev. D4030View full textAdd to dashboardCite

Contact Info

Product

Resources

About

αs(MZ2
Kim¹,
Kim²,
Lee³
et al. 1996
Phys. Rev. D
4
0
3
0
View full text Add to dashboard Cite