119805142
Recent FOCUS results on charm mixing and CP violation
We summarize recent results on CP violation and mixing based on a high statistics photo-produced charm sample collected by the FOCUS experiment. We compare the lifetimes of two neutral D meson decays: D0 → K−π+ and D0 → K−K+. A mixing parameter for the neutral D system (yCP) is obtained under the assumption that K−π+ is an equal mixture of CP odd and even eigenstates. In addition, we searched for a CP width asymmetry in D+ → K−K+π+, D0 → K−K+ and D0 → π−π+. We found no evidence for CP violation by comparing the decay rates for the particle and antiparticle.
118099621
A measurement of the polarization asymmetry of the tau lepton using the L3 detector at LEP
With a data sample of e e events collected in the L detector at LEP during we did a measurement of the polarization of leptons as a function of the production polar angle with respect to the incident e beam direction We used the following prong decay channels e e and a As the result we obtained the asymmetries A and Ae Combining this with the previous data measurement by L we ob tained A and Ae These asymmetries gave the ratio of vector to axial vector weak neutral coupling con stants for electrons as g V g e A and for taus as g V g A The numbers are consistent with the hypothesis of e lepton universality Assuming the e neutral current universality the e ective electroweak mixing angle is calculated as sin e w Advisor Professor Aihud Pevsner
5633838
Recent Results on CP Lifetime Differences of Neutral D Mesons
The mixing parameter y_cp for the neutral D system can be obtained by comparing the lifetimes of CP eigenstate decays of the D mesons. Recent results on the lifetime differences from the Belle, CLEO, FOCUS(E831) experiments are summarized in this article. The neutral D decay modes analyzed by the experiments are: The D0->Kpi mode with the assumption that it is an equal mixture of CP even and odd eigenstates, and the CP even modes D0->KK and D0->pipi.
119679827
RECENT FOCUS RESULTS ON CHARM MIXING
We present the recent result on CP mixing based on a high statistics photoproduced charm sample collected by the FOCUS experiment. We compare the lifetimes of two neutral D meson decays: D0→K- π+ and D0→K-K+. A mixing parameter for the neutral D system (yCP) is obtained under the assumption that K-π+ is an equal mixture of CP odd and even eigenstates.
118421849
Tau physics from LEP
We briefly review recent analysis on the tau lepton by four LEP experiments, ALEPH, DELPHI, L3 and OPAL, based on data samples generated at the Z peak. Intrinsic properties of the tau lepton as well as applications to various physics topics are treated from an experimental point of view. The summarized analysis subjects include lifetime, leptonic branching ratios, hadronic decay structures, dipole moments, related electroweak and QCD properties, and the mass of the tau neutrino.
117044003
Parity violation in electron scattering from carbon: A progress report
An experiment is being performed at the MIT Bates Linear Accelerator Center to measure the parity-violating asymmetry in the elastic scattering of longitudinally polarized electrons from Carbon. The asymmetry, which is due to the isoscalar component of the neutral weak current, is predicted to be about 0.6{times}10{sup {minus}6}. We have recently obtained preliminary data with polarized electrons. The status of the experiment is discussed.
59435944
UsingMT2to distinguish dark matter stabilization symmetries
We examine the potential of using colliders to distinguish models with parity (Z_2) stabilized dark matter (DM) from models in which the DM is stabilized by other symmetries, taking the latter to be a Z_3 symmetry for illustration. The key observation is that a heavier mother particle charged under a Z_3 stabilization symmetry can decay into one or two DM particles along with Standard Model (SM) particles. This can be contrasted with the decay of a mother particle charged under a parity symmetry; typically, only one DM particle appears in the decay chain. In arXiv:1003.0899, some of us studied the distributions of visible invariant mass from the decay of a single such mother particle in order to highlight the resulting distinctive signatures of Z_3 symmetry versus parity symmetry stabilized dark matter candidates. We now describe a complementary study which focuses on decay chains of the two mother particles which are necessarily present in these events. We also include in our analyss the missing energy/momentum in the event. For the Z_3 symmetry stabilized mothers, the resulting inclusive final state can have two, three or four DM particles. In contrast, models with Z_2 symmetry can have only two. We show that the shapes and edges of the distribution of M_T2-type variables, along with ratio of the visible momentum/energy on the two sides of the event, are powerful in distinguishing these different scenarios.
118786272
Non SUSY Searches at Tevatron
We present results on physics beyond Standard Model except SUSY with data mostly corresponding to an integrated luminosity of 200 ∼ 300 pb−1 in pp collisions at s = 1.96 TeV at the CDF and D0, Fermilab Tevatron collider experiments. New results on the searches for new phenomena include extra Z′ and W′ bosons, extra dimensions, leptoquarks, excited electrons as well as monopoles. We found no evidence and set the stringent limits on the signature and models.
116401557
Test beam results from prototype scintillating tile calorimeters with fiber readout
85450376
Simple “invariance” of two-body decay kinematics
We study the two-body decay of a mother particle into a massless daughter. We further assume that the mother particle is unpolarized and has a generic boost distribution in the laboratory frame. In this case, we show analytically that the laboratory frame energy distribution of the massless decay product has a peak, whose location is identical to the (xed) energy of that particle in the rest frame of the corresponding mother particle. Given its simplicity and \invariance" under changes in the boost distribution of the mother particle, our nding should be useful for the determination of masses of mother particles. In particular, we anticipate that such a procedure will then not require a full reconstruction of this two-body decay chain (or for that matter, information about the rest of the event). With this eventual goal in mind, we make a proposal for extracting the peak position by tting the data to a well-motivated analytic function describing the shape of such an energy distribution. This tting function is then tested on the theoretical prediction for top quark pair production and its decay, and it is found to be quite successful in this regard. As a proof of principle of the usefulness of our observation, we apply it for measuring the mass of the top quark at the LHC, using simulated data and including experimental eects. PACS numbers: 11.80.Cr It is very well-known that in the rest frame of a mother particle undergoing a two-body decay, the energy of each of the daughter particles is xed in terms of mother and the daughter particle masses. Turning this fact around, we can determine the mass of the mother particle if we can measure these rest-frame energies of the daughter particles. However, often the mother particle is produced in the laboratory with a boost, that too with a magnitude and direction which is (a priori) not known. Moreover, the boost of mother particles produced at hadron colliders is dierent in each event. Such a boost distribution depends on the production mechanism of the particle and on the structure functions of the hadrons in the initial state of the collision, and is thus a complicated function. In turn, the fact that the mother has a dierent boost in each event implies that when we consider the observed energy of the two-body decay product in the laboratory frame, we get a distribution in it. Thus it seems like the information that was encoded in the rest frame energy is lost, and we are prevented from extracting (at least at an easily tractable level) the mass of the mother particle along the lines described above. We show that, remarkably, if one of the daughter particles from the two-body decay is massless and the mother is unpolarized, then such is not the case. Specically, in this case, we demonstrate that the distribution of the daughter particle’s energy in the laboratory frame has a peak precisely at its corresponding rest-frame energy. This result is interesting per se. Furthermore, we expect that it will lead to formulation of new methods for mass measurements. Obviously, for this purpose, we need to be able to determine the location of this peak accurately from the observed energy distribution of the massless daughter. To this end, we propose and motivate an analytic function that can be used to t the data on the energy distribution and thus extract the peak position. We show that this function is a suitable one using the top quark decay, t! W b, as a test case, namely, it ts very well the theory prediction for energy spectrum of the resulting b-jets. Simulating a realistic experimental situation, we then show that we can extract the value of the top mass from the position of the peak in the b-jet energy distribution along with the well-measured mass of the W boson. Let us consider the decay of a heavy particle B of mass mB, i.e., B! Aa where a is a massless visible particle. For the subsequent arguments, the properties of the particle A (other than its mass denoted by mA) are irrelevant. In the rest frame of particle B, the energy of the particle a is simply given by E = m 2 m 2 2mB :