122200845
Search for same-sign top-quark pair production at $ \sqrt {s} = 7 $ TeV and limits on flavour changing neutral currents in the top sector
An inclusive search for same-sign top-quark pair production in pp collisions at $ \sqrt {s} = 7 $ TeV is performed using a data sample recorded with the CMS detector in 2010, corresponding to an integrated luminosity of 35 pb−1. This analysis is motivated by recent studies of $ \text{p}\bar{\text{p}} \to \text{t}\bar{\text{t}} $ reporting mass-dependent forward-backward asymmetries larger than expected from the standard model. These asymmetries could be due to Flavor Changing Neutral Currents (FCNC) in the top sector induced by t-channel exchange of a massive neutral vector boson (Z′). Models with such a Z′ also predict enhancement of same-sign top-pair production in pp or $ \text{p}\bar{\text{p}} $ collisions. Limits are set as a function of the Z′ mass and its couplings to u and t quarks. These limits disfavour the FCNC interpretation of the Tevatron results.
10401636
Search for di-muon decays of a low-mass Higgs boson in radiative decays of the Υ(1S)
We search for di-muon decays of a low-mass Higgs boson (A^0) produced in radiative Υ(1S) decays. The Υ(1S) sample is selected by tagging the pion pair in the Υ(2S,3S) → π^+ π^-Υ(1S) transitions, using a data sample of 92.8 × 10^6 Υ(2S) and 116.8 × 10^6 Υ(3S) events collected by the BABAR detector. We find no evidence for A^0 production and set 90% confidence level upper limits on the product branching fraction B(Υ(1S) → γA^0) × B(A^0 → μ^ +μ^-) in the range of (0.28-9.7) × 10^(-6) for 0.212 ≤ m_A^0 ≤ 9.20  GeV/c^2. The results are combined with our previous measurements of Υ(2S,3S) → γA^0, A^0 → μ^+μ^- to set limits on the effective coupling of the b quark to the A^0.
2621524
Study of the mass and spin-parity of the Higgs boson candidate via its decays to Z boson pairs.
A study is presented of the mass and spin-parity of the new boson recently observed at the LHC at a mass near 125 GeV. An integrated luminosity of 17.3 fb(-1), collected by the CMS experiment in proton-proton collisions at center-of-mass energies of 7 and 8 TeV, is used. The measured mass in the ZZ channel, where both Z bosons decay to e or μ pairs, is 126.2 ± 0.6(stat) ± 0.2(syst) GeV. The angular distributions of the lepton pairs in this channel are sensitive to the spin-parity of the boson. Under the assumption of spin 0, the present data are consistent with the pure scalar hypothesis, while disfavoring the pure pseudoscalar hypothesis.
122803232
Search for Microscopic Black Hole Signatures at the Large Hadron Collider
A search for microscopic black hole production and decay in pp collisions at a center-of-mass energy of 7 TeV has been conducted by the CMS Collaboration at the LHC, using a data sample corresponding to an integrated luminosity of 35 inverse picobarns. Events with large total transverse energy are analyzed for the presence of multiple high-energy jets, leptons, and photons, typical of a signal expected from a microscopic black hole. Good agreement with the expected standard model backgrounds, dominated by QCD multijet production, is observed for various final-state multiplicities. Limits on the minimum black hole mass are set, in the range 3.5 -- 4.5 TeV, for a variety of parameters in a model with large extra dimensions, along with model-independent limits on new physics in these final states. These are the first direct limits on black hole production at a particle accelerator.
10609473
Precise measurement of the e+e- --> pi+pi-(gamma) cross section with the initial state radiation method at BABAR.
A precise measurement of the cross section of the process e(+)e(-) --> pi(+)pi(-)(gamma) from threshold to an energy of 3 GeV is obtained with the initial state radiation (ISR) method using 232 fb(-1) of data collected with the BABAR detector at e(+)e(-) center-of-mass energies near 10.6 GeV. The ISR luminosity is determined from a study of the leptonic process e(+)e(-) --> mu(+)mu(-)gamma(gamma). The leading-order hadronic contribution to the muon magnetic anomaly calculated using the pipi cross section measured from threshold to 1.8 GeV is (514.1 +/- 2.2(stat) +/- 3.1(syst)) x 10(-10).
110632418
The BABAR detector: Upgrades, operation and performance
The BaBar detector operated successfully at the PEP-II asymmetric e +e- collider at the SLAC National Accelerator Laboratory from 1999 to 2008. This report covers upgrades, operation, and performance of the collider and the detector systems, as well as the trigger, online and offline computing, and aspects of event reconstruction since the beginning of data taking.
118646643
A hybrid model of GeV-TeV gamma ray emission from the Galactic center
The observations of high energy gamma-ray emission from the Galactic center (GC) by HESS, and recently by Fermi, suggest cosmic ray acceleration in the GC and possibly around the supermassive black hole. In this work we propose a lepton-hadron hybrid model to simultaneously explain the GeV-TeV gamma-ray emission. Both electrons and hadronic cosmic rays were accelerated during the previous activity of the GC. These particles would then diffuse outwards and interact with the interstellar gas and background radiation field. The collisions between hadronic cosmic rays with gas are responsible for the TeV gamma-ray emission detected by HESS. With fast cooling in the strong radiation field, the electrons would cool down and radiate GeV photons through inverse Compton scattering off the soft background photons. This scenario provides a natural explanation for the observed GeV-TeV spectral shape of gamma-ray.
123610392
SEARCH FOR NEW MASSIVE PARTICLES IN COSMIC RAYS
In this paper, some unusual cosmic ray events are reviewed. They are the Yunnan event recorded in 1972 using a cloud chamber at Yunnan Cosmic Ray Station (YCRS) near Kunming, the south-west of China; the six exotic events (Kolar events) collected during 1965 to 1975 in the Kolar Gold Mine Field (KGF) in south India; and a double-core event obtained also in KGF in 1979 at a depth different from that where the other six were obtained, In addition, some interesting phenomena were also noticed: the abnormal upward muon flux observed by the MINI collaboration, and several intriguing signals seen in the proton detector in KGF, A careful kinematics analysis has shown that all these exotic events are likely to be related to a kind of heavy and slow-moving (i.e. with a Lorentz factor gamma approximate to 2-5) particles produced from cosmic ray interactions. Besides, the rough flux estimates in these experiments seem to indicate that the event rate does not depend on the depth. Thus a natural hypothesis is that there is a heavy and neutral component in the cosmic rays which might be related with the long-sought weakly interacting massive particle (WIMP) - one of the most promising candidates of the dark matter of our Universe. Moreover, from the tracks seen in these events, there is also a signal of the possible existence of a kind of heavy and charged particles with a relatively long lifetime (say, longer than 10(-9) s) which might be the interacting products of the unknown cosmic ray particles mentioned above. We then turn to the question of how to search for these exotic particles in cosmic rays, and propose to build a dedicated magnetic spectrometer for identifying them.
122785773
XYZ physics at BESIII
In this talk, we present the recent study on the charmonium-like states from the BESIII Collaboration based on large data samples above D ¯ D threshold. The observation of X(3872) from the Y(4260) radiative transition, the study of the Y states from the e + e − → π + π − hc process, and the observation of the charged Zc states are included .
117145668
Attenuation study for Tibet Water Cherenkov Muon Detector Array-A
This work aims at online calibrating the signal attenuation of the long cable used in Tibet Water Cherenkov Muon detector array-A (Tibet MD-A) under the 37 000 m2 Tibet air shower array. Based on the waterproof connection of the PMT (R3600_06) with the signal cable, and the characters of the high voltage divider, terminal reflection method is explored and used for measuring the signal attenuation with a practical way to eliminate the contribution of the pulse baseline (pedestal). Comparison measurement between it and QDC (Charge-to-Digital Conversion) data taking method are carried out by using open-ended cables, confirming that terminal reflection method is a fast and convenient method, and suitable to online calibrate the signal attenuation for Tibet MD-A. At 26\degree C, the measured attenuation coefficient with the 250-m cable, permanently connected to the PMT, is ~13.9%. Also, the cable frequency response is measured by using the sinusoidal signals, which could be used to study the time dispersion of the real signal produced with Tibet MD-A detector via Fourier analysis.
123410881
Test of the hadronic interaction models at around *10 TeV with Tibet EAS core data
A hybrid experiment has been started by ASγ collaboration at Tibet, China, since May 2009, that consists of a burst-detector-grid (YAC, Yangbajing Air shower Core array) and the Tibet air-shower array (Tibet-III). The first step of YAC, called YAC-I, contains 16 detector units and observes high energy electromagnetic particles in air-shower cores within several meters from the shower axis, and Tibet-III array measures the total energy and the arrival direction of air showers. YAC-I is used to check hadronic interaction models currently used for air-shower simulations such as QGSJET, SIBYLL , EPOS etc. through the multi-parameter measurement in air-shower cores. In this paper, we used a data set collected from May 1st 2009 through February 23rd 2010 by the YAC-I. The effective live time used for the present analysis is 169.65 days. The preliminary results of the interaction model checking at *10 TeV energy region is reported in this paper.