Measurement Of CP Violation Research Articles

Recent results on CP violation B0s meson decays

Measurements of CP violation in B0s mesons decays provide an excellent method to test the prediction of the Standard Model and search for effect of new physics beyond it. With the first 1 fb−1 √ of data collected in pp collisions at √s = 7TeV the LHCb experiment performed the world best precision measurements of the CP-violating phase φs and on the decay width difference ΔΓs. The analysis of the B0s → φφ decay and the measurement of the B0s lifetime in decays to CP eigenstates are also presented.

RareBdecays andCP-Violation in theBsystem with the ATLAS Detector

A search for the rare decay Bs0 → µ+µ− has been performed with the ATLAS detector at the Large Hadron Collider LHC in proton-proton collisions at a centre of mass energy of √s = 7 TeV using 2.4 fb−1 of integrated luminosity. The observed number of signal events is consistent with the background expectations and the resulting upper limit on the branching fraction is set to ℬ(Bs0 → µ+µ−) < 2.2(1.9) × 10−8 at 95% (90%) confidence level. A time dependent measurement of CP-violation in the exclusive decay channel Bs0 → J/ψ(µ+µ−)ϕ(K+K−) has been performed with an integrated luminosity of 4.9 fb−1 at an energy of √s = 7 TeV. The resulting measurements of the CP-violation weak mixing phase ϕs = 0.22 ± 0.41 (stat.) ± 0.10 (syst.) rad and the decay width difference ΔΓs = 0.053 ± 0.021 (stat.) ± 0.008 (syst.) ps−1 are consistent with the theoretical predictions of the Standard Model and the world average values.

Search for new physics in heavy quark decays at LHCb

Heavy quark decays are an excellent laboratory to search for physics beyond the Standard Model. The LHCb detector is specially design to measure CP violation parameters and rare decays processes involving decays containing b– or c– quarks. In this paper, recent LHCb measurements concerning CP violation parameters in the BS0 and charm sector, as well as measurements of rare b→sl+l− transitions, are presented.

Calibration and Performance Monitoring of the LHCb Vertex Locator

The LHCb experiment is dedicated to searching for New Physics effects in the heavy flavour sector, precise measurements of CP violation and rare heavy meson decays. Precise tracking and vertexing around the interaction point is crucial in achieving these physics goals. The LHCb VELO (VErtex LOcator) silicon micro-strip detector is the highest precision vertex detector at the LHC and is located at only 8.2 mm from the proton beams. The high spatial resolution (down to 4 microns single hit precision) is obtained by a complex chain of processing algorithms to suppress noise and reconstruct clusters. These are implemented in large FPGAs, with over one million parameters that need to be individually optimised. Previously [1], we presented a novel approach that has been developed to optimise the parameters and integrating their determination into the full software framework of the LHCb experiment. Presently we report on the experience gained from regular operation of the calibration and monitoring software with the collision data taken in 2011 by the LHCb experiment. Both the VELO performance and its impact on the physics results will be detailed.

CP violation measurements with the ATLAS detector

The ATLAS experiment at the Large Hadron Collider measures CP violation in the neutral Bs0 meson system through the exclusive decay Bs0→J/ψ(μ+μ−)ϕ(K+K−) by analysing time dependent angular correlations of the final state. With 4.9fb−1 of integrated luminosity recorded in 2011 in pp collisions at the LHC at a centre of mass energy of s=7 TeV, first ATLAS results on the values of the CP-violating phase ϕs, the decay width difference ΔΓs as well as other physics parameters of the Bs0 meson decay have been obtained and will be presented here.

Searches for New Sources of CP and T Violation at BaBar

We present recent results from searches for new sources of CP and T violation from the B, charm, and τ sectors from BaBar. From the B sector, we search for CP violation in B decays to three kaons, and to Kℓ+ℓ−, and present the first direct observation of T violation using B0→J/ψK0. In the charm sector, we search for a T-odd correlation in D+ decays to K+K0π+π−. And in the τ sector, we measure CP violation in τ− decays to K0π−ντ. Highlights of these new results include the worldʼs first observation of T violation that is fully experimentally independent of CP violation, and a 3.1σ deviation from the Standard Model predictions for CP violation in τ−→K0π−ντ.

Direct CP violation at LHCb

During 2011, LHCb has collected an integrated luminosity of 1.0fb−1 giving rise to a large variety of measurements. Among these, measurements of direct CP violation in B decays play a central role. Three different analyses are presented: the first evidence of CP violation in the Bs0 system and the observation of CP violation in the B0 system, using B0→Kπ and Bs0→πK decay channels; the evidence of CP violation in B±→DK± decays with the first observation of the suppressed ADS mode; and a preliminary result showing the evidence of CP asymmetry in charmless three-body charged B decays.

MEASUREMENT OF CP-VIOLATION IN $D^0/\bar{D}^0$

Charm physics has played all along a central role in particle physics, however, the level of attention on it has tremendously increased in the last years because of the observation of "fast" [Formula: see text] flavor oscillations and because of very recent observed hints of CP-violation. While in the past these would have been unambiguously interpreted as signs of New Physics (NP), the revisitation of theoretical expectations, prompted by the latest experimental measurements, makes the picture not clear. This brief review covers the current status of CP-violating measurements in the [Formula: see text] system, both on the experimental and theoretical sides.

BRIEF REVIEW OF CHARM PHYSICS

Charm physics has attracted increased attention after the first evidence for charm mixing was observed in 2007. The level of attention has risen sharply after LHCb reported first evidence for CP violation in the charm sector. Neither mixing nor CP violation have been established by a single unambiguous measurement to date. This review covers the status of mixing and CP violation measurements and comments on the challenges on the road ahead, both on the experimental and theoretical side, and on ways to tackle them.

Experimental constraints from flavour changing processes and physics beyond the Standard Model.

Flavour physics has a long tradition of paving the way for direct discoveries of new particles and interactions. Results over the last decade have placed stringent bounds on the parameter space of physics beyond the Standard Model. Early results from the LHC, and its dedicated flavour factory LHCb, have further tightened these constraints and reiterate the ongoing relevance of flavour studies. The experimental status of flavour observables in the charm and beauty sectors is reviewed in measurements of CP violation, neutral meson mixing, and measurements of rare decays.

ESTIMATE OF CP VIOLATION FOR THE LBNE PROJECT AND δCP

Measurements of CP violation (CPV) and the basic δ CP parameter are the goals of the LBNE Project, which is being planned. Using the expected energy and baseline parameters for the LBNE Project, CPV and the dependence of CPV on δ CP are estimated, to help in the planning of this project.

Using Large Area Microchannel Plate Photodetectors in the Next Generation Water Cherenkov Neutrino Detectors

The next generation of neutrino experiments will require massive water Cherenkov detectors to reach the sensitivity needed to measure CP violation in the lepton sector and the neutrino mass hierarchy. The Large Area Picosecond Photodetector Development (LAPPD) Collaboration is developing new methods to fabricate a 20 cm2 thin planar microchannel plate photo-multiplier tube (MCP) at a cost comparable to those of traditional photomultiplier tubes (PMT). The application of these novel devices to large water Cherenkov detectors could significantly enhance background rejection and vertex resolution in these detectors by improving spatial and timing information. We present details of the MCP fabrication method, and preliminary results from testing and characterization facilities at Argonne National Laboratory. The application of these devices to neutrino detectors is also discussed.

On the universality of CP violation in [formula omitted] processes

We show that new physics which breaks the left-handed SU(3)Q quark flavor symmetry induces contributions to CP violation in ΔF=1 couplings which are approximately universal, in that they are not affected by flavor rotations between the up and the down mass bases. (Only the short distance contributions are universal, while observables are also affected by hadronic matrix elements.) Therefore, such flavor violation cannot be aligned, and is constrained by the strongest bound from either the up or the down sectors. We use this result to show that the bound from ϵ′/ϵ prohibits an SU(3)Q breaking explanation of the recent LHCb evidence for CP violation in D meson decays. Another consequence of this universality is that supersymmetric alignment models with a moderate mediation scale are consistent with the data, and are harder to probe via CP violating observables. With current constraints, therefore, squarks need not be degenerate. However, future improvements in the measurement of CP violation in D–D¯ mixing will start to probe alignment models.

First Evidence of DirectCPViolation in Charmless Two-Body Decays ofBs0Mesons

Using a data sample corresponding to an integrated luminosity of 0.35 fb-1 collected by LHCb in 2011, we report the first evidence of CP violation in the decays of Bs0} mesons to K±π∓ pairs, ACP(Bs0→Kπ)=0.27±0.08(stat)±0.02(syst), with a significance of 3.3σ. Furthermore, we report the most precise measurement of CP violation in the decays of B0 mesons to K±π∓ pairs, ACP(B0→Kπ)=-0.088±0.011(stat)±0.008(syst), with a significance exceeding 6σ.

Measurement of the CP violating phase [formula omitted] in [formula omitted

Measurement of mixing-induced CP violation in B¯s0 decays is of prime importance in probing new physics. So far only the channel B¯s0→J/ψϕ has been used. Here we report on a measurement using an LHCb data sample of 0.41 fb−1, in the CP odd eigenstate J/ψf0(980), where f0(980)→π+π−. A time-dependent fit of the data with the B¯s0 lifetime and the difference in widths of the heavy and light eigenstates constrained to the values obtained from B¯s0→J/ψϕ yields a value of the CP violating phase of −0.44±0.44±0.02 rad, consistent with the Standard Model expectation.

Measurement of the γ angle from tree decays at the LHCb experiment

An overview of plans for the measurement of gamma at the LHCb experiment will be shown. The gamma angle is the least accurately known parameter of the CKM unitary triangle. The LHCb experiment at the CERN LHC aims to perform precision heavy flavour and CP violation measurements, including improving the knowledge of gamma. Focus will be put on methods using B meson decays at the tree level, within the Standard Model framework. The early data recorded by the experiment, from pp collisions at sqrt{s} = 7 TeV, allowed observations of the first signals of the B decay modes that will be used to perform this measurement.

Initial Performance from the NOνA Surface Prototype Detector

Abstract NOνA, the NuMI Off-Axis νe Appearance experiment, will study νμ → νe oscillations characterized by the mixing angle θ13. Provided θ13 is large enough, NOνA may ultimately determine the ordering of the neutrino masses and measure CP violation in neutrino oscillations. A complementary pair of detectors will be constructed ∼14 mrad off beam axis to optimize the energy profile of the neutrinos. This system consists of a surface based 14 kTon liquid scintillatior tracking volume located 810 km from the main injector source (NuMI) in Ash River, Minnesota and a smaller underground 222 Ton near detector at the Fermilab. The first neutrino signals at the Ash River Site are expected prior to the 2012 accelerator shutdown. In the meantime, a near detector surface prototype has been completed and neutrinos from two Fermilab sources have been observed using the same highly segmented PVC and liquid scintillator detector system that will be deployed in the full scale experiment. Design and initial performance characteristics of this prototype system are being fed back into the design for the full NOνA program.

Performance of LHCb Silicon Tracker Detector in the LHC

The LHCb experiment is designed to perform high-precision measurements of CP violation and search for New Physics using the enormous flux of beauty and charmed hadrons produced at the LHC. The LHCb detector is a single-arm spectrometer with excellent tracking and particle identification capabilities. The Silicon Tracker is part of the tracking system and measures very precisely the particle trajectories coming from the interaction point in the region of high occupancies around the beam axis. The LHCb Silicon Tracker covers a total sensitive area of about 12 m(2) using silicon micro-strip technology. This paper reports on the operation and performance of the Silicon Tracker during the Physics data taking at the LHC. (C) 2012 Published by Elsevier B.V. Selection and/or peer review under responsibility of the organizing committee for TIPP 11.

The LHCb Upgrade

Abstract The LHCb experiment is designed to perform high-precision measurements of CP violation and search for New Physics using the enormous flux of beauty and charmed hadrons produced at the LHC. The LHCb detector is a single-arm spectrometer with excellent tracking and particle identification capabilities. The operation and the results obtained from the data collected in 2010 and 2011 demonstrate that the detector is robust and functioning very well. In the next years, LHCb will measure a large number of interesting channels in heavy flavor decays. However, the limit of 1 fb−1 of data per year cannot be overcome without improving the detector. An upgraded spectrometer with a 40MHz readout and a much more flexible software-based triggering system will increase the data rate as well as the efficiency specially in the hadronic channels, widening our physics scope beyond that of heavy flavor. Here, the different possibilities under study for the different detectors are reviewed as well as the ongoing R&D activities.

Precision measurement of CP Violation in D0 → π+π−

We report a measurement of the CP violating asymmetry in D0 → π+π− decays using approximately 215,000 decays reconstructed in about 5.94 fb−1 of CDF data. We use the strong D*+ → D0π+ decay ("D* tag") to identify the flavor of the charmed meson at production time and exploit CP-conserving strong cc̄ pair-production in pp̄ collisions. Higher statistic samples of Cabibbo-favored D0 → K−π+ decays with and without D* tag are used to highly suppress systematic uncertainties due to detector effects. The result is the world's most precise measurement to date and it is fully consistent with no CP violation.