Measurement Of CP Violation Research Articles

Hybrid photon detectors for the LHCb RICH system

The LHCb experiment, currently being commissioned at CERN, uses two Ring Imaging Cherenkov (RICH) detectors as its principal particle identification system. These detectors are essential in allowing LHCb to perform the precision measurements of CP-violation in B-meson mixing and decays for which the experiment was designed. The photodetectors used in the LHCb RICH system are Hybrid Photon Detectors (HPDs), which employ a vacuum photocathode and a solid-state pixel sensor. The operating principle and production process of the HPDs are described. The performance criteria for the HPDs is outlined, along with the qualification procedures carried out at dedicated test facilities. The compiled results of tests performed on more than 500 HPDs are presented. The performance of the HPDs in a 25 ns structured test-beam and during the RICH commissioning process with the HPDs installed is discussed. Finally, the time alignment of the HPDs via a pulsed laser system is described.

S-waves and the measurement ofCPviolating phases inBsdecays

Heavy, as yet undiscovered particles, can affect measurements of CP violation in the B system. Measuring CP violation in the Bs system provides an excellent place to observe such effects since Standard Model sources are predicted to produce very small effects. The angle -2beta_s, the "phase of Bs-\bar{B}s mixing," thought to be best measured in Bs -> J/psi\phi decays is of order -0.04, while the CP violating asymmetry in Bs -> \phi\phi is predicted to be zero, due to the cancellation of the mixing phase with the decay phase. Recent measurements of \beta_s in J/psi\phi, while not definitive, are much larger than the Standard Model predictions. Measurements in the B^o and Ds+ systems of analogous modes point toward a 5-10% contamination of S-wave K+K- under the \phi peak. This S-wave was not taken into account in these recent analyses. Furthermore this S-wave can also materialize as a f0(980) meson that decays to \pi+\pi-, making the final state J/psi f0 useful for measuring \beta_s with the added advantage of not requiring an angular analysis. Rate estimates, while not precise, predict four to five times fewer such events than those in the J/psi\phi mode. The error on \beta_s, however, may be similar. We also remark on S-wave problems with the Bs -> \phi\phi mode, and possible systematic checks using Bs -> \phi f0.

Time-dependent Dalitz plot measurement ofCPparameters inB0→KS0π+π−decays

We present a time-dependent Dalitz plot measurement of CP violation parameters in B0 --> Ks Pi+ Pi- decays. These results are obtained from a large data sample that contains 657 million BBbar pairs collected at the Y(4S) resonance with the Belle detector at the KEKB asymmetric-energy e+e- collider. For the CP violation parameters, we obtain two consistent solutions that describe the data well. The first of these solutions may be preferred by external information from other measurements. There is no evidence for direct CP violation in B0 --> rho0(770) Ks, B0 --> f0(980) Ks and B0 --> K*+(892) Pi-, while measurements of mixing-induced CP violation in B0 --> rho0(770) Ks, B0 --> f0(980) Ks decays are consistent with that of b --> c cbar s decays. We also measured the phase difference between B0 --> K*+(892) Pi- and B0B --> K*-(892) Pi+ which may be used to extract phi3.

Measurement of CP violation in stop cascade decays at the LHC

We study the potential observation at the LHC of CP-violating effects in stop production and subsequent cascade decays, $gg\to \tilde{t}_{i}\tilde{t}_{i}$ , $\tilde{t}_{i}\to t\tilde{\chi}^{0}_{j}$ , $\tilde{\chi}^{0}_{j}\to \tilde{\chi}^{0}_{1}\ell^{+}\ell^{-}$ , within the Minimal Supersymmetric Standard Model. We study T-odd asymmetries based on triple products between the different decay products. There may be a large CP asymmetry at the parton level, but there is a significant dilution at the hadronic level after integrating over the parton distribution functions. Consequently, even for scenarios where large CP intrinsic asymmetries are expected, the measurable asymmetry is rather small. High luminosity and precise measurements of masses, branching ratios and CP asymmetries may enable measurements of the CP-violating parameters in cascade decays at the LHC.

Mixing and CP Violation at D0

We present several mixing and CP violation measurements utilizing up to 2.8 fb − 1 of proton-antiproton collisions collected by the D0 experiment at the Fermilab Tevatron. The achieved precision of some of these measurements is of the same level as the expected deviation predicted by some extensions of the Standard Model. One result suggests a tantalizing hint of new physics.

Chiral Perturbation Theory from Charged Kaon Decays at NA48/2

Chiral Perturbation Theory, as a low-energy effective field theory of strong interactions, is a very useful tool to study the interactions of kaons. The NA48/2 experiment, whose primary goal was the measurement of direct CP violation in the decays of charged kaons, has however collected enough statistics to check the ChPT predictions for several decay modes of charged kaons.

LONG BASELINE NEUTRINO EXPERIMENTS WITH TWO-DETECTOR SETUP

I discuss why and how powerful is the two-detector setting in neutrino oscillation experiments. I cover three concrete examples: (1) reactor θ13 experiments, (2) T2KK, Tokai-to-Kamioka-Korea two-detector complex for measuring CP violation, determining the neutrino mass hierarchy, and resolving the eight-fold parameter degeneracy, (3) two-detector setting in a neutrino factory at baselines 3000 km and 7000 km for detecting effects of non-standard interactions (NSI) of neutrinos.

The LHCb Detector at the LHC

The LHCb experiment is dedicated to precision measurements of CP violation and rare decays of B hadrons at the Large Hadron Collider (LHC) at CERN (Geneva). The initial configuration and expected performance of the detector and associated systems, as established by test beam measurements and simulation studies, is described.

An overview of the status of the LHCb RICH detectors

The LHCb experiment will make precision measurements of CP violation and rare b-hadron decays. Efficient particle identification with high purity over a wide momentum range is vital to these aims. The experiment employs two ring-imaging Cherenkov (RICH) detectors with three radiators, silica aerogel, C 4F 10 and CF 4, to cover the momentum range from around 1–100 GeV/ c. The RICH system employs a number of innovative techniques, both in hardware and software. A total of 484 custom-built pixel Hybrid Photon Detectors (HPDs) will be used to measure the spatial positions of Cherenkov photons with wavelengths in the range 200–600 nm, covering an active area of around 3.3 m 2. The production of the HPDs has now been completed and the tube quality, including the photo-cathode quantum efficiency, far exceeds expectations. The installation of RICH 1 is almost complete; RICH 2 has been installed and aligned, and commissioning is almost complete. Reconstruction studies incorporating realistic backgrounds indicate excellent kaon efficiencies of around 97% and pion misidentification probabilities of around 6%, averaged over the full momentum range. This paper provides a general overview of the status of the LHCb RICH project, with emphasis on the readiness for LHC start-up and for physics.

D0-D̄0 mixing and CP violation at BES-III**Supported by Knowledge Innovation Project of CAS (U-612, U-530 (IHEP)) and 100 Talents Program of CAS

Recently, both BaBar and Belle experiments found evidences of neutral D mixing. In this paper, we discuss the sensitivities of the measurements of D mixing parameters at BES-III. With CP tag technique at ψ(3770) peak, the extraction of the strong phase difference in D0 → Kπ decay at BES-III are discussed. We also make an estimate on the measurements of the mixing rate RM by using the coherent data at ψ(3770) peak. The CP violation in D system is predicted with an unobserved level in the Standard Model. Any significant CP violation in the D system indicates the existence of new physics. The sensitivity of the measurements of CP violation in the D system is estimated in the coherent D decays. Finally, the search for the rare D decays are discussed, in which some of the forbidden decays are smoking gun of new physics.

On the impact of systematical uncertainties for the CP violation measurement in superbeam experiments

Superbeam experiments can, in principle, achieve impressive sensitivities for CP violation in neutrino oscillations for large �13. We study how those sensitivities depend on assumptions about systematical uncertainties. We focus on the second phase of T2K, the so-called T2HK experiment, and we explicitly include a near detector in the analysis. Our main result is that even an idealised near detector cannot remove the dependence on systematical uncertainties completely. Thus additional information is required. We identify certain combinations of uncertainties, which are the key to improve the sensitivity to CP violation, for example the ratio of electron to muon neutrino cross sections and efficiencies. For uncertainties on this ratio larger than 2%, T2HK is systematics dominated. We briefly discuss how our results apply to a possible two far detector configuration, called T2KK. We do not find a significant advantage with respect to the reduction of systematical errors for the measurement of CP violation for this setup.

Improved Measurement ofCPViolation in NeutralBDecays tocc¯s

We present updated measurements of time-dependent CP asymmetries in fully-reconstructed neutral B decays to several CP eigenstates containing a charmonium meson. The measurements use a data sample of (383+/-4)x10(6) Upsilon(4S)-->BB[over] decays collected with the BABAR detector at the PEP-II B factory. We determine sin2beta = 0.714+/-0.032(stat)+/-0.018(syst) and |lambda|=0.952+/-0.022(stat)+/-0.017(syst).

Bs,d→ππ,πK,KK: status and prospects

Several years ago, it was pointed out that the U-spin-related decays Bd→π+π-, Bs→K+K- and Bd→π∓K±, Bs→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 Bs decays and the B-factory data on Bu,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 ΔΓs from untagged Bs→K+K- rates, and address the impact of new physics. The data for the Bd→π+π-, Bs→K+K- system favour the BaBar measurement of direct CP violation in Bd→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 Bd→π∓K±, Bs→π±K∓ analysis leaves us with 26°≤γ≤70°, and points to a value of the Bs→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 Bs→K+K-, which will also allow us to extract the B0 s–B0 s mixing phase unambiguously with the help of Bs→J/ψφ at the LHC. Finally, the measurement of direct CP violation in Bs→K+K- will make the full exploitation of the physics potential of the Bs,d→ππ,πK,KK modes possible.

Exploring CP violation and penguin effects through B0 d→D+D- and B0 s→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→Dq +D- q system provides a setting for the determination of the B0 q–B0 q mixing phases (q∈{d,s}) that is complementary to the conventional B0 d→J/ψKS and B0 s→J/ψφ modes with respect to possible new-physics effects in the electroweak penguin sector.

Beauty 2006 – Conference Summary and Future Prospects

The status of B physics, CP violation and related measurements at the time of the Beauty 2006 conference are summarized. Particular attention is given to the exciting prospects that lie ahead, at the commencement of the LHC era, and beyond.

Tracking with the LHCb spectrometer: Detector performance and track reconstruction

The LHCb experiment aims to measure CP violation and rare B-decays. For this, a tracking system is constructed consisting of a silicon micro-strip vertex locator close to the interaction point, and tracking detectors around a dipole magnet. The resulting tracking performance is estimated from simulation to yield 95% efficiency. The momentum and impact parameter resolutions vary between 0.35% and 0.5%, and 20 and 160 μ m , respectively.

On puzzles and non-puzzles in B→ππ,πK decays

Recently, we have seen interesting progress in the exploration of CP violation in B0 d→π+π-: the measurements of mixing-induced CP violation by the BaBar and Belle collaborations are now in good agreement with each other, whereas the picture of direct CP violation is still unclear. Using the branching ratio and direct CP asymmetry of B0 d→π-K+, this situation can be clarified. We predict $\mathcal{A}_{CP}^{\text{dir}}(B_d\to\pi^+\pi^-)=-0.24\pm0.04$ , which favours the BaBar result, and we extract γ=(70.0+3.8 -4.3)°, which agrees with the unitarity triangle fits. Extending our analysis to other B→πK modes and B0 s→K+K- with the help of the SU(3) flavour symmetry and plausible dynamical assumptions, we find that all observables with colour-suppressed electroweak penguin contributions are measured to be in excellent agreement with the standard model. As far as the ratios Rc,n of the charged and neutral B→πK branching ratios are concerned, which are sizeably affected by electroweak penguin contributions, our standard-model predictions have almost unchanged central values but significantly reduced errors. Since the new data have moved quite a bit towards these results, the “B→πK puzzle” for the CP conserving quantities has been significantly reduced. However, the mixing-induced CP violation of B0 d→π0KS does look puzzling; if confirmed by future measurements, this effect could be accommodated through a modified electroweak penguin sector with a large CP violating new-physics phase. Finally, we point out that the established difference between the direct CP asymmetries of B±→π0K± and Bd→π∓K± appears to be generated by hadronic and not by new physics.

The importance of the silicon tracker to the BaBar physics program

The silicon tracker, SVT, built for the BaBar detector has been essential to the execution of the experiment's primary goal: the measurement of time-dependent CP violation in B meson decays. Not only has it performed nearly perfectly, it has not even needed any parts replaced for radiation damage, and it has enabled the experiment to carry out a broader physics program than originally envisioned. We review briefly the SVT, its performance, and its key role in three measurements at BaBar: sin 2 β in B → J ψ K S , time-dependent CP violation in B → K S π 0 , and D 0 – D ¯ 0 mixing.

CP violation in neutrino mass matrix

We constructed rephasing invariant measures of CP violation with elements of the neutrino mass matrix, in the basis in which the charged lepton mass matrix is diagonal. We discuss some examples of neutrino mass matrices with texture zeroes, where the present approach is applicable and demonstrate how it simplifies an analysis of CP violation. We applied our approach to study CP violation in all the phenomenologically acceptable 3-generation two-zero texture neutrino mass matrices and shown that in any of these cases there is only one CP phase which contributes to the neutrino oscillation experiment and there are no Majorana phases.

NEW RESULTS ON CP VIOLATION IN B MESON DECAY

The Belle experiment has started in 1999 and has collected more than 600 fb-1 data at the ϒ(4S) resonance with the KEK-B asymmetric energy e+e- collider. In this contribution, the results of CP-violation measurement in B meson decays are presented. The large CP asymmetry arises thorough the interference between [Formula: see text] mixing and decay. The results yield constraints on the angles of the unitarity triangle, which is related to the Kobayashi-Maskawa quark mixing matrix. We discuss the status of the measurements on ϕ1, ϕ2 and ϕ3 with various methods.