Search for FCNC in top-quark events in ATLAS

Searches for flavor changing neutral current (FCNC) processes in top-quark production and decays by the ATLAS Collaboration are presented. Data collected from $pp$ collisions at the LHC at a centre-of-mass energy of 7 TeV during 2011, corresponding to an integrated luminosity of 2.05/fb, are used. In a first analysis single top-quarks produced via FCNC are searched for. Candidate events with a semileptonic top-quark decay signature are classified as signal or background-like events by using several kinematic variables as input to a neural network. No signal is observed in the neural network output distribution and a Bayesian upper limit is placed on the production cross-section. The observed upper limit is converted using a model-independent approach into upper limits on the coupling strengths k_{ugt}/Lambda < 6.9x10^{-3}/TeV and k_{cgt}/Lambda < 1.6x10^{-2}/TeV, where Lambda is the new physics scale, and on the branching fractions BF(t-->ug) cg) < 2.7x10^{-4}. A second search is performed for top-quark pair-production events, with one top quark decaying through the t-->Zq FCNC (q=u,c) channel, and the other through the Standard Model dominant mode t-->Wb. Only the decays of the Z boson to charged leptons and leptonic W-boson decays are considered as signal. No evidence for an FCNC signal is found and thus an upper limit on the t-->Zq branching ratio of BF(t-->Zq)<0.73% is set at the 95% confidence level.Comment: Conference proceedings, ICHEP 2012, Melbourn

Top physics with 0.70-1.08/fb of pp collisions with the ATLAS detector at the LHC

With data collected during the first half of 2011 pp run of the Large Hadron Collider at \surds = 7 TeV, a substantial data sample of high p_T triggers, 1.08/fb, has been collected by the ATLAS detector. Measurements of the production of top-quark pairs and single top-quarks in different channels, the top-quark mass, the top-quark pair charge asymmetry and spin correlations, and the W helicity fractions in top-quark decays are presented, as well as two searches for new physics effects involving top-quark pairs.Comment: Proceedings of the Lepton Photon 2011 Conference, to appear in "Pramana - journal of physics". 4 pages, 12 figure

Single top: prospects at LHC

Single top quark processes are interesting as direct probes of the $Wtb$ vertex, and are also an important background in searches of the Higgs boson and beyond the standard model physics. Both ATLAS and CMS have performed studies with simulated data to estimate the expected uncertainty on the production cross section measurements of the three single top processes ($t$-channel, s-channel, $tW$ production) in the first years of LHC operations. Results in the different channels and for the two experiments are reported.Comment: 8 pages, 4 figures, presented at TOP2008: International Workshop on Top-Quark Physics, La Biodola, Isola d'Elba, Italy, 18-24 May 200

Top-quark physics at the Large Hadron Collider

This experimental review gives an overview of top-quark measurements performed by the two general purpose-detectors ATLAS and CMS during the first few years of running of the Large Hadron Collider. In the years 2010 - 2012 each experiment collected 5 fb$^{-1}$ of pp collision data at $\sqrt{s} = 7$ TeV and 20 fb$^{-1}$ at $\sqrt{s} = 8$ TeV, allowing detailed studies of top-quark production and decays, and measurements of the properties of the top quark with unprecedented precision.Comment: 54 pages, 42 figures, 2 tables. Accepted for publication in J. Phys.

Top-quark production measurements

Recent measurements of top-quark production at hadron colliders are reviewed. The inclusive top-quark pair production is determined at four centre-of-mass energies at Tevatron and LHC with experimental uncertainties that are close to the uncertainties in theoretical calculations at next-to-next-to-leading order in QCD. Several differential measurements are performed and compared to simulation. Production of single top quarks is studied in the three different production channels. Top-quark pair production with neutral and charged vector bosons has been observed by the LHC experiments. Finally, production of additional heavy flavour quark pairs ($b\bar{b}$, $t\bar{t}$) is studied or searched for.Comment: on behalf of the ATLAS, CDF, CMS, D0 and LHCb Collaborations. Conference proceedings for Lepton Photon, Ljubljana, 17-22 August 2015, 21 pages, 18 figure

Diamond Prototypes for the ATLAS SLHC Pixel Detector

Vertex detectors at future hadron colliders will need to cope with large particle fluences. Diamond is a particularly radiation hard material and exhibits further properties that makes it an attractive material for such detectors. Within the RD42 collaboration several chemical vapor deposition diamond samples are being studied in the form of strip and pixel detectors. While the quality of the poly-crystalline diamond samples is constantly increasing and the feasibility of producing wafers has been demonstrated, recently a single-crystal diamond pixel detector has been assembled and characterized in a 100 GeV particle beam at CERN. Results on performance, detection efficiency, spatial resolution and charge collection are reported here together with the latest radiation damage studies.Comment: 3 pages, 8 figures, 1st International conference on Technology and Instrumentation in Particle Physics (TIPP09

Charmless 2- and 3-body B decays and the angle alpha (phi2)

We present preliminary measurements of branching fractions and CP-asymmetry parameters in two- and three-body charmless hadronic B decays. The available data sample consists of 227 million Upsilon(4S) B decays collected with the BABAR detector at the PEP-II asymmetric-energy e+e- collider at SLAC. We establish the observation of the decays B --> pi0 pi0 and B0 --> K0K0bar and constrain the CKM angle alpha with a full SU(2) isospin analysis in the B --> pi pi system and with a B0 --> pi+ pi- pi0 time-dependent Dalitz plot analysis.Comment: 8 pages, 4 figures, contributed to the Proceedings of ICHEP'0

The SHiP experiment at CERN

The current status of the proposed SHiP experiment at the CERN Beam Dump Facility is presented. SHiP is a general-purpose fixed-target experiment. The 400 GeV/$c$ proton beam extracted from the SPS will be dumped on a heavy target to integrate $2 \times 10^{20}$ protons on target in five years. The detector, based on a long vacuum tank followed by a spectrometer and particle identification detectors, will allow to probe a variety of models with light long-lived exotic particles and masses below ${\cal O}(10)$ GeV/$c^2$. The main focus will be the physics of the so-called hidden portals, i.e. the search for dark photons, light scalars and pseudo-scalars, and heavy neutrinos. The sensitivity to heavy neutrinos will allow to probe, in the mass range between the kaon and the charm meson mass, a coupling range for which baryogenesis and active neutrino masses could also be explained. A second dedicated detector will study neutrinos and explore light dark matter.Comment: 8 pages, 4 figures, presented at the 3rd World Summit on Exploring the Dark Side of the Universe, Guadeloupe Islands, March 9-13 202

Search for Antimatter with the AMS Cosmic Ray Detector

Antimatter search results of the Alpha Magnetic Spectrometer (AMS) detector are presented. About 100 million triggers were collected in the 1998 precursor flight onboard space shuttle Discovery. This ten day mission exposed the detector on a 51.7 degrees orbit at an altitude around 350 km. Identification of charged cosmic rays is achieved by multiple energy loss and time-of-flight measurements. Bending inside the 0.15 T magnetic volume yields a measurement of the absolute value of the particle's rigidity. The supplemental knowledge of the sense of traversal identifies the sign of the charge. In the rigidity range 1 < R < 140 GV no antinucleus at any rigidity was detected, while 2.86 million helium and 165 thousand heavy nuclei were precisely measured. Hence, upper limits on the flux ratio antinuclei-to-nuclei are given. Different prior assumptions on the antimatter spectrum are considered and corresponding limits are given.Comment: 5 pages, 6 figures, presented at the XXXth International Meeting on Fundamental Physics, Jaca, Spain, January 200