6,127 research outputs found
CP-violation in cascade decays at the LHC
No full textWe study the potential to observe CP-violating effects in various supersymmetric cascade
decay chains at the LHC. Asymmetries composed by triple products of
momenta of the final state particles are sensitive to CP-violating
effects. We analytically calculate the cascade decays including the relevant spin correlations to compute the parton level asymmetry. In addition, we use Monte Carlo simulations to estimate the sensitivity of the LHC to the CP-violating observables.
Due to large boosts that dilute the asymmetries, these can be
difficult to observe at the LHC. However, if all particle masses in a cascade decay are
known, it may be possible to reconstruct all momenta in the decay chains. We can then recover the full asymmetry on an
event-by-event basis even when we have missing momentum due to a stable
lightest supersymmetric particle. After the reconstruction, the non-diluted CP-violating signal gets
significantly enhanced so that an observation may become feasible.
A fully hadronic study has also been completed to produce the best estimate of the viability of these obseravbles at the LHC. We include both standard model and SUSY backgrounds in the study. Our conclusions state that given a favourable scenario, CP-violation may be observed in SUSY at the 3-sigma level over a wide range of CP-phases with 500 1/fb of data
Branching fraction and CP asymmetry of the decays B+→K0Sπ+ and B+→K0SK+
No full textAn analysis of B+ → K0
Sπ+ and B+ → K0
S K+ decays is performed with the LHCb experiment. The pp
collision data used correspond to integrated luminosities of 1 fb−1 and 2 fb−1 collected at centre-ofmass
energies of
√
s = 7 TeV and
√
s = 8 TeV, respectively. The ratio of branching fractions and the
direct CP asymmetries are measured to be B(B+ → K0
S K+
)/B(B+ → K0
Sπ+
) = 0.064 ± 0.009 (stat.) ±
0.004 (syst.), ACP(B+ → K0
Sπ+
) = −0.022 ± 0.025 (stat.) ± 0.010 (syst.) and ACP(B+ → K0
S K+
) =
−0.21 ± 0.14 (stat.) ± 0.01 (syst.). The data sample taken at
√
s = 7 TeV is used to search for
B+
c
→ K0
S K+ decays and results in the upper limit ( fc · B(B+
c
→ K0
S K+
))/( fu · B(B+ → K0
Sπ+
)) <
5.8 × 10−2 at 90% confidence level, where fc and fu denote the hadronisation fractions of a ¯b
quark
into a B+
c or a B+ meson, respectively
IS CP A GAUGE-SYMMETRY
No full textConventional solutions to the strong CP problem all require the existence of global symmetries. However, quantum gravity may destroy global symmetries, making it hard to understand why the electric dipole moment of the neutron (EDMN) is so small. We suggest here that CP is actually a discrete gauge symmetry, and is therefore not violated by quantum gravity. We show that four-dimensional CP can arise as a discrete gauge symmetry in theories with dimensional compactification, if the original number of Minkowski dimensions equals 8k + 1, 8k + 2 or 8k + 3, and if there are certain restrictions on the gauge group; these conditions are met by superstrings. CP may then be broken spontaneously below 10(9) GeV, explaining the observed CP violation in the kaon system without inducing a large EDMN. We discuss the phenomenology of such models, as well as the peculiar properties of cosmic ''CP strings'' which could be produced at the compactification scale. Such strings have the curious property that a particle carried around the string is turned into its CP conjugate. A single CP string renders four-dimensional space-time nonorientable
Measurement of the time-dependent CP asymmetry in B0 -> J/ψ KS0 decays
No full textThis Letter reports a measurement of the CP violation observables SJ/ψK0S and CJ/ψK0S in the decay channel B0→J/ψK0S performed with 1.0 fb−1 of pp collisions at s√=7 TeV collected by the LHCb experiment. The fit to the data yields SJ/ψK0S=0.73±0.07(stat)±0.04(syst) and CJ/ψK0S=0.03±0.09(stat)±0.01(syst). Both values are consistent with the current world averages and within
expectations from the Standard Model
Measurement of the CP-violating phase \phi s in Bs->J/\psi\pi+\pi- decays
No full textMeasurement of the mixing-induced CP-violating phase phi_s in Bs decays is of prime importance in probing new physics. Here 7421 +/- 105 signal events from the dominantly CP-odd final state J/\psi pi+ pi- are selected in 1/fb of pp collision data collected at sqrt{s} = 7 TeV with the LHCb detector. A time-dependent fit to the data yields a value of phi_s=-0.019^{+0.173+0.004}_{-0.174-0.003} rad, consistent with the Standard Model expectation. No evidence of direct CP violation is found
Automatic Nelson-Barr solutions to the strong CP puzzle
No full textWe discuss a simple model, based on the gauge group , where the
Nelson-Barr solution to the strong CP problem is implemented. This model
automatically provides a high quality solution to the strong CP puzzle. Weak CP
violation in the lepton sector arises in the same fashion as in the quark
sector. We derive explicit expressions for the flavor changing couplings of the
electroweak and Higgs bosons. These expressions are more general than the
particular model considered. Constraints from finite naturalness are briefly
discussed. We briefly also discuss related models based on the gauge group B-L.Comment: 9 pages and 2 figures. v3: discussion mu-e conversion added, matches
published version in PR
A study of CP violation in B±→DK±B±→DK± and B±→Dπ±B±→Dπ± decays with D→KS0K±π∓ final states
No full textA first study of CP violation in the decay modes B± → [K0S K ±π∓]Dh± and B± → [K0S K ∓π±]Dh±, where h labels a K or π meson and D labels a D0 or D0 meson, is performed. The analysis uses the LHCb data set collected in pp collisions, corresponding to an integrated luminosity of 3 fb−1. The analysis is sensitive to the CP-violating CKM phase γ through seven observables: one charge asymmetry in each of the four modes and three ratios of the charge-integrated yields. The results are consistent with measurements of γ using other decay modes
Constraining Nelson-Barr Models with Generalized CP Transformations through Decoupling Analysis
No full textThis thesis aims to study a novel solution to the Strong CP Problem. As no experimental signals of an axion have been found yet, the Nelson-Barr mechanism is gaining more and more popularity. After a review of the Standard Model and the Strong CP Problem, a model is introduced which combines the Nelson-Barr mechanism with a non-conventional CP transformation of order 4. A slightly improved calculation of the 2-loop contribution to θ is presented and the decoupling limits of the model are discussed. While the abso- lute scales of the model evade prediction, a combination of the energy scales and Yukawa couplings is found that can be constrained. Fitting the model via Markov Chain Monte Carlo algorithm to experimental results supports these findings. For the fit, a focus on CP violating observables in the quark and meson sector is chosen. While the solution to the Strong CP problem might lie at energies far above the experimentally accessible scales, our results show a novel way to still constrain at least specific combinations of these high- energy scales. In the future, these results can work as a starting point to help constrain new creative model building ideas
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