52997330
LONG-TERM MONITORING OF THE TeV EMISSION FROM Mrk 421 WITH THE ARGO-YBJ EXPERIMENT
ARGO-YBJ is an air shower detector array with a fully covered layer of resistive plate chambers. It is operated with a high duty cycle and a large field of view. It continuously monitors the northern sky at energies above 0.3 TeV. In this paper, we report a long-term monitoring of Mrk 421 over the period from 2007 November to 2010 February. This source was observed by the satellite-borne experiments Rossi X-ray Timing Explorer and Swift in the X-ray band. Mrk 421 was especially active in the first half of 2008. Many flares are observed in both X-ray and γ-ray bands simultaneously. The γ-ray flux observed by ARGO-YBJ has a clear correlation with the X-ray flux. No lag between the X-ray and γ-ray photons longer than 1 day is found. The evolution of the spectral energy distribution is investigated by measuring spectral indices at four different flux levels. Hardening of the spectra is observed in both X-ray and γ-ray bands. The γ-ray flux increases quadratically with the simultaneously measured X-ray flux. All these observational results strongly favor the synchrotron self-Compton process as the underlying radiative mechanism.
119348940
Detecting the dark matter annihilation at the ground EAS detectors
Abstract In this paper we study the possibility of detecting gamma rays from dark matter annihilation in the subhalos of the Milky Way by the ground based EAS detectors within the frame of the minimal supersymmetric Standard Model. Based on the Monte Carlo simulation we also study the properties of two specific EAS detectors, the ARGO and HAWC, and the sensitivities of these detectors on the detection of dark matter annihilation. We find the ground EAS detectors have the possibility to observe such signals. Conversely if no signal observed we give the constraints on the supersymmetric parameter space, which however depends on the subhalos properties.
124457067
Search for Invisible Decays of eta and eta-prime in the Processes J/psi ---> phi eta and phi eta-prime
Using a data sample of 58x10{sup 6} J/{psi} decays collected with the Beijing Spectrometer II detector at the Beijing Electron Positron Collider, searches for invisible decays of {eta} and {eta}{sup '} in J/{psi} to {phi}{eta} and {phi}{eta}{sup '} are performed. The {phi} signals, which are reconstructed in K{sup +}K{sup -} final states, are used to tag the {eta} and {eta}{sup '} decays. No signals are found for the invisible decays of either {eta} or {eta}{sup '}, and upper limits at the 90% confidence level are determined to be 1.65x10{sup -3} for the ratio (B({eta}{yields}invisible)/B({eta}{yields}{gamma}{gamma})) and 6.69x10{sup -2} for (B({eta}{sup '}{yields}invisible)/B({eta}{sup '}{yields}{gamma}{gamma})). These are the first searches for {eta} and {eta}{sup '} decays into invisible final states.
54761229
Energy spectrum of cosmic protons and helium nuclei by a hybrid measurement at 4300 m a.s.l.
The energy spectrum of cosmic Hydrogen and Helium nuclei has been measured below the so-called "knee" by using a hybrid experiment with a wide field-of-view Cherenkov telescope and the Resistive Plate Chamber (RPC) array of the ARGO-YBJ experiment at 4300 m above sea level. The Hydrogen and Helium nuclei have been well separated from other cosmic ray components by using a multi-parameter technique. A highly uniform energy resolution of about 25% is achieved throughout the whole energy range (100–700 TeV). The observed energy spectrum is compatible with a single power law with index γ=−2.63±0.06.
209869998
Observation of the decay psi(2S) ---> K*(892)anti-K + c.c.
52249775
Medium scale anisotropy in the TeV cosmic ray flux observed by ARGO-YBJ
B. Bartoli, P. Bernardini, X. J. Bi, I. Bolognino, P. Branchini, A. Budano, A.K. Calabrese Melcarne, P. Camarri, Z. Cao, R. Cardarelli, S. Catalanotti, S. Z. Chen, T. L. Chen, P. Creti, S.W. Cui, B. Z. Dai, A. D’Amone, Danzengluobu, I. De Mitri, B. D’Ettorre Piazzoli, T. Di Girolamo, G. Di Sciascio,* C. F. Feng, Zhaoyang Feng, Zhenyong Feng, Q. B. Gou, Y.Q. Guo, H. H. He, Haibing Hu, Hongbo Hu, M. Iacovacci, R. Iuppa, H.Y. Jia, Labaciren, H. J. Li, G. Liguori, C. Liu, J. Liu, M.Y. Liu, H. Lu, X. H. Ma, G. Mancarella, S.M. Mari, G. Marsella, D. Martello, S. Mastroianni, P. Montini, C. C. Ning, M. Panareo, B. Panico, L. Perrone, P. Pistilli, F. Ruggieri, P. Salvini, R. Santonico, S. N. Sbano, P. R. Shen, X.D. Sheng, F. Shi, A. Surdo, Y. H. Tan, P. Vallania, S. Vernetto, C. Vigorito, H. Wang, C. Y. Wu, H. R. Wu, L. Xue, Y.X. Yan, Q.Y. Yang, X. C. Yang, Z. G. Yao, A. F. Yuan, M. Zha, H.M. Zhang, L. Zhang, X.Y. Zhang, Y. Zhang, Zhaxiciren, Zhaxisangzhu, X.X. Zhou, F. R. Zhu, Q.Q. Zhu, and G. Zizzi
122601384
Studies of wire gain and track distortion near the sector edges of the ALEPH time projection chamber
Abstract The materials used to hold the wires at the sector edges in a large Time Projection Chamber (TPC) inrtoduce distortions of the electric drift field near those edges. These distortions degrade tracking information and sometimes cause large changes in wire gain near the edge. We have studied these two problems for the ALEPH TPC and have found that both can be greatly reduced by the addition of two field correction strips held at appropriate voltages.
23122779
Search for new physics in the multijet and missing transverse momentum final state in proton-proton collisions at √s = 7 TeV.
A search for physics beyond the standard model is performed in events with at least three jets and large missing transverse momentum produced in proton-proton collisions at a center-of-mass energy of √s=7 TeV. No significant excess of events above the expected backgrounds is observed in 4.98 fb(-1) of data collected with the CMS detector at the Large Hadron Collider. The results are presented in the context of the constrained minimal supersymmetric extension of the standard model and more generically for simplified models. For the simplified models of gluino-gluino and squark-squark production, gluino masses below 1.0 TeV and squark masses below 0.76 TeV are excluded in case the lightest supersymmetric particle mass is below 200 GeV. These results significantly extend previous searches.
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.
122638974
Centrality dependence of dihadron correlations and azimuthal anisotropy harmonics in PbPb collisions at $\sqrt{s_{NN}}= 2.76\ \mbox{TeV}$
Measurements from the CMS experiment at the LHC of dihadron correlations for charged particles produced in PbPb collisions at a nucleon–nucleon centre-of-mass energy of 2.76 TeV are presented. The results are reported as a function of the particle transverse momenta (pT) and collision centrality over a broad range in relative pseudorapidity (Δη) and the full range of relative azimuthal angle (Δϕ). The observed two-dimensional correlation structure in Δη and Δϕ is characterised by a narrow peak at (Δη,Δϕ)≈(0,0) from jet-like correlations and a long-range structure that persists up to at least |Δη|=4. An enhancement of the magnitude of the short-range jet peak is observed with increasing centrality, especially for particles of pT around 1–2 GeV/c. The long-range azimuthal dihadron correlations are extensively studied using a Fourier decomposition analysis. The extracted Fourier coefficients are found to factorise into a product of single-particle azimuthal anisotropies up to pT≈3–3.5 GeV/c for at least one particle from each pair, except for the second-order harmonics in the most central PbPb events. Various orders of the single-particle azimuthal anisotropy harmonics are extracted for associated particle pT of 1–3 GeV/c, as a function of the trigger particle pT up to 20 GeV/c and over the full centrality range.
119686406
Gating in the ALEPH Time Projection Chamber
The ALEPH TPC at LEP will use a gating grid to prevent distortions caused by space charge buildup in its 2.2 m drift region. Sets of measurements have demonstrated the feasibility of a “synchronous ion trapping” mode of gating, which reduces the positive ion flux through the grid by more than two orders of magnitude. A novel mode of gating will be discussed which would permit static operation of the gate, thereby avoiding the complexity of switching between the open and closed states of the gate. This mode would rely on the dissimilar gate penetration properties of electrons and ions in the presence of a magnetic field, and it may also provide a way to partially compensate for the E × B effect at the sense wires. A combination of these different modes is proposed for the ALEPH TPC.