Heavy Flavor Sector Research Articles

New Physics searches in heavy flavours in ATLAS

Precision determinations of the flavour sector allow the search for indirect new physics signatures. At the forefront of these studies are the determinations of interference of new physics with known $\upDelta F=1$ and $\upDelta F=2$ processes. The ATLAS collaboration explores this area with competitive results measuring the CP violating phase $\phi_s$ from $B^0_s\to J/\psi \phi$ decays and investigating rare $B$ decays with dileptons in the final state with data collected at the Large Hadron Collider. In this paper, the latest ATLAS results relevant for new physics searches in the heavy flavour sector will be discussed.

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.

Open heavy flavor in Pb + Pb collisions at [formula omitted] within a transport model

The space–time evolution of open heavy flavor is studied in Pb + Pb collisions at s=2.76TeV using the partonic transport model Boltzmann Approach to MultiParton Scatterings (BAMPS). An updated version of BAMPS is presented which allows interactions among all partons: gluons, light quarks and heavy quarks. Heavy quarks, in particular, interact with the rest of the medium via binary scatterings with a running coupling and a Debye screening which is matched by comparing to hard thermal loop calculations. The lack of radiative processes in the heavy flavor sector is accounted for by scaling the binary cross section with a phenomenological factor K=3.5, which describes well the elliptic flow v2 and nuclear modification factor RAA at RHIC. Within this framework we calculate in a comprehensive study the v2 and RAA of all interesting open heavy flavor particles at the LHC: electrons, muons, D mesons, and non-prompt J/ψ from B mesons. We compare to experimental data, where it is already available, or make predictions. To do this accurately next-to-leading order initial heavy quark distributions are employed which agree well with proton–proton data of heavy flavor at s=7TeV.

Heavy Flavour Hadron Spectroscopy: Challenges and Future Prospects

During the last few years, wealth of new experimental results in the heavy flavor hadron sector has become available. The diversity, quantity and accuracy of the data are impressive and include many surprising spectroscopic results. Following the discovery of ηb states and the excited ηc(2S) states many excited states of open charm and beauty mesons and plethora of exotic states are reported. Discoveries of many new hadrons at B-factories have shed light on a new class of hadrons beyond the ordinary mesons. Many of these states awaits for its right identification. Though we have the theory (QCD) for the strong interaction, we are still far from extracting the major part of the hadron properties from it. These properties at the hadronic scale obviously play relevant role in many searches for new physics and new phenomenon. For obvious reasons, heavy flavour sector offers unique opportunities in this case. For example, the quarkonium systems are crucially important to improve our understanding of QCD as it falls in the low energy region where the non-perturbative effects dominate. Thus the heavy quarks / quark-antiquark bound states are ideal laboratory where our understanding of non-perturbative QCD and its interplay with perturbative QCD may be tested. A comparative review of different model predictions for example in the case of heavy flavor hadronic systems will be highlighted. The quarkonium studies may be used as a benchmark for our understanding of QCD and for the precise determination of standard model strong interaction parameters such as the constituent quark masses, αs, the confinement strength (string tension) etc.

Heavy flavour production and spectroscopy at LHCb

We summarize the main measurements performed with the LHCb detector on production and spectroscopy in the heavy flavour sector, using data samples recorded during 2010 and 2011 data taking in proton-proton collisions at $\sqrt s=7$\,TeV .

A Novel Approach to Detector Calibration Parameter Determination and Detector Monitoring

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 detector is the highest precision vertex detector at the LHC and is located at only 8 mm from the proton beams. The high spatial point precision (up to 4 μm single hit precision) is facilitated by a complex chain of processing algorithms to suppress noise and reconstruct clusters. These are implemented in FPGAs, with over one million individually optimised parameters. A novel approach has been developed to optimise the parameters, integrating their determination into the full software framework of the LHCb experiment. While FPGAs are commonly used in HEP, their parameters are typically set by standalone software. However, the VELO complex processing chain would only achieve optimal performance and full sensitivity monitoring through optimisation integrated with the full reconstruction framework of the experiment. This off-line software framework performs a bit perfect emulation of the FPGAs hardware processing, and is fully integrated into the LHCb software, rather than standalone. The software platform facilitates: developing and understanding the behaviour of the processing algorithms; optimizing the parameters of the algorithms that will be loaded into the FPGAs; and monitoring the performance of the detector. This framework has also been adopted by the Silicon Tracker detector of LHCb. This novel approach has been successfully applied to the collision data taken in 2010 by the LHCb experiment. The initial calibration of the VELO detector has been performed using the emulation suite. The software is used to monitor the noise of the detector, pedestals stability, hit reconstruction performance and other detector parameters.

A barrel TOF for STAR at RHIC

With the successful runs of the multi-gap resistive plate chamber (MRPC)-based time-of-flight (TOF) prototypes in the solenoid tracker at RHIC (relativistic heavy ion collider) (STAR) for the past several years, a full barrel TOF is being built to take part in data taking in late 2008. Together with other sub-detectors in STAR this TOF will greatly enhance the reach of the STAR scientific programme significantly by extending the particle identification (PID) capability. It will allow STAR to extract the maximum amount of information available from soft physics measures on an event-by-event basis. It will also extend its power to the heavy flavour sector by increasing the signal-to-noise ratios for charm hadron reconstructions for D0, D+, D+s, J/ψ, enabling STAR to make systematic studies of charm thermalization and charm meson flow. The physics results achieved by the TOF prototypes as well as the goal of the full TOF expectable are presented.

Radiative meson transitions in the quark model

Radiative meson transitions in the light and heavy flavor sector are investigated in a potential quark model. Relativistic corrections and higher order diagrams are analyzed. The decay rates calculated with the relativistic corrections taken into account are in most of the cases in better agreement with the experimental values. Higher order diagrams seem to have larger a effect for the light quark decays.

Precision measurements of electroweak gauge boson parameters at LEP

Over ten years after the start-up of LEP and four years after the completion of the energy scans around the Z resonance the analyses of the Z parameters by the four experiments Aleph, Delphi and L3 are final and the Opal results are very close to final. The analyses of the polarisation of τ leptons and measurements of the production rates and forward-backward asymmetries in the heavy flavour sector are approaching their finalisation. Recent data taking nearly doubled the statistics of W ± pair events available at Lep and lead to significantly improved preliminary measurements of the W ± pair production cross section, the W mass and branching fractions as well as improved limits on non-standard couplings at the triple gauge boson vertices. Altogether, in combination with measurements of the weak mixing angle at the SLC and the top quark mass at the Tevatron, these results provide stringent test of the Standard Model of the electroweak interaction and constrain its last missing parameter, the mass of the Higgs boson.

Mesonic M1 transitions in a relativistic potential model of independent quarks

The radiative transitions among the low-lying vector and pseudoscalar mesons in the light and heavy flavour sector are investigated in a relativistic potential model of independent quarks. The partial decay widths of several possible mesonic M1 transitions are calculated in a static approximation within the conventional picture of photon emission by a confined quark and/or antiquark. The results obtained in most of the cases are in an overall agreement with the experimental values. The predictions in heavy meson decays are comparable to those of other model calculations.

Weak decay constants of light and heavy pseudoscalar mesons

We investigate the weak leptonic decays of light and heavy pseudoscalar mesons in a relativistic quark model of independent quarks. We perform a static calculation of the decay constantfM purely on grounds of simplicity. In order to minimize the possible uncertainty in the static calculation, we estimate the ratios of the decay constants which are found to be in good agreement, in the heavy flavor sector, with the predictions of other models available in the literature and existing experimental data. However, there is a noticeable discrepancy in the current prediction for pion decay constant which demonstrates the inherent limitations of the static approximation in the study of non-strange light mesons.

Radiative decay of light and heavy mesons.

The [ital M]1 transition among the vector ([ital V]) and pseudoscalar ([ital P]) mesons in the light and heavy flavor sectors has been investigated in a potential model of independent quarks. Going beyond the static approximation, to add some momentum dependence due to the recoil effect in a more realistic calculation, we find an improvement in the results for the radiative decay of light flavored mesons. However, our prediction on the decay rates for the mesons ([ital D][sup *] and [ital B][sup *]) in the heavy flavor sector remains unaffected and compares well with those of other model calculations.

Quarkonium baryons in the topological soliton model

We show that the bound state version of the topological soliton model for the baryons, which is consistent with both chiral symmetry in the light quark sector and heavy quark spin symmetry in the heavy flavour sector, implies that the c c and b b pseudoscalar mesons form bound states with nucleons, the binding energy increasing with the heavy meson (quark) mass. The result qualitatively agrees with the earlier QCD-based results that heavy quarkonia should bind to nuclei, although the prediction that the binding energy grows with the heavy quark mass disagrees with the (approximate) QCD-based results.