Simplified SIMPs and the LHC Daci, N.; De Bruyn, I.; Lowette, S. ...
The journal of high energy physics,
11/2015, Letnik:
2015, Številka:
11
Journal Article
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A
bstract
The existence of Dark Matter (DM) in the form of Strongly Interacting Massive Particles (SIMPs) may be motivated by astrophysical observations that challenge the classical Cold DM scenario. ...Other observations greatly constrain, but do not completely exclude, the SIMP alternative. The signature of SIMPs at the LHC may consist of neutral, hadron-like, trackless jets produced in pairs. We show that the absence of charged content can provide a very efficient tool to suppress dijet backgrounds at the LHC, thus enhancing the sensitivity to a potential SIMP signal. We illustrate this using a simplified SIMP model and present a detailed feasibility study based on simulations, including a dedicated detector response parametrization. We evaluate the expected sensitivity to various signal scenarios and tentatively consider the exclusion limits on the SIMP elastic cross section with nucleons.
Spontaneous reduction of 4-nitrobenzene diazonium salt on coal in acetonitrile or HCl aqueous solution permits the strong bonding of aryl groups to its surface as shown by IR spectroscopy. ...Heterogeneous reverse osmosis membranes containing small particles of coal modified with aryldiazonium salts were prepared by the phase inversion process from the casting solutions of cellulose acetate and magnesium perchlorate in acetone water mixture. The weight ratio of cellulose acetate to dispersed coal particles in the casting solution was always 1:1.5. The reverse osmosis performance of the prepared heterogeneous cellulose acetate coal membranes was tested. The membranes containing coal particles modified with aryldiazonium salts for longer time showed the best performance.
One of the subjects of interest in the last years, is to develop new applications of fly ash, produced in growing quantities by burning coal in all coal-fired power stations. In this study, we have ...investigated the possible effects of Kosova lignite fly ash as adsorbent for removal of heavy metal ions in standard solutions, industrial wastewater and the natural water body (Sitnica river). Achieved results showed that 10 minutes of contact time, for standard solutions and natural water body, were appropriate for efficient adsorption of ions reaching the maximum removal to 99.89 wt% and 60 minutes of contact time for industrial wastewater, reaching the maximum removal of 98.12%.
The normalised differential top quark-antiquark production cross section is measured as a function of the jet multiplicity in proton-proton collisions at a centre-of-mass energy of 7 TeV at the LHC ...with the CMS detector. The measurement is performed in both the dilepton and lepton+jets decay channels using data corresponding to an integrated luminosity of 5.0 inverse femtobarns. Using a procedure to associate jets to decay products of the top quarks, the differential cross section of the t t-bar production is determined as a function of the additional jet multiplicity in the lepton+jets channel. Furthermore, the fraction of events with no additional jets is measured in the dilepton channel, as a function of the threshold on the jet transverse momentum. The measurements are compared with predictions from perturbative quantum chromodynamics and no significant deviations are observed.
The t t-bar charge asymmetry in proton-proton collisions at sqrt(s)=7 TeV is measured using the dilepton decay channel (ee, e mu, or mu mu). The data correspond to a total integrated luminosity of ...5.0 inverse femtobarns, collected by the CMS experiment at the LHC. The t t-bar and lepton charge asymmetries, defined as the differences in absolute values of the rapidities between the reconstructed top quarks and antiquarks and of the pseudorapidities between the positive and negative leptons, respectively, are measured to be Ac = -0.010 +/- 0.017 (stat.) +/- 0.008 (syst.) and Aclep = 0.009 +/- 0.010 (stat.) +/- 0.006 (syst). The lepton charge asymmetry is also measured as a function of the invariant mass, rapidity, and transverse momentum of the t t-bar system. All measurements are consistent with the expectations of the standard model.
Azimuthal dihadron correlations of charged particles have been measured in PbPb collisions at sqrt(sNN) = 2.76 TeV by the CMS collaboration, using data from the 2011 LHC heavy-ion run. The data set ...includes a sample of ultra-central (0-0.2% centrality) PbPb events collected using a trigger based on total transverse energy in the hadron forward calorimeters and the total multiplicity of pixel clusters in the silicon pixel tracker. A total of about 1.8 million ultra-central events were recorded, corresponding to an integrated luminosity of 120 inverse microbarns. The observed correlations in ultra-central PbPb events are expected to be particularly sensitive to initial-state fluctuations. The single-particle anisotropy Fourier harmonics, from v2 to v6, are extracted as a function of particle transverse momentum. At higher transverse momentum, the v2 harmonic becomes significantly smaller than the higher-order vn (n greater than or equal to 3). The pt-averaged v2 and v3 are found to be equal within 2%, while higher-order vn decrease as n increases. The breakdown of factorization of dihadron correlations into single-particle azimuthal anisotropies is observed. This effect is found to be most prominent in the ultra-central PbPb collisions, where the initial-state fluctuations play a dominant role. A comparison of the factorization data to hydrodynamic predictions with event-by-event fluctuating initial conditions is also presented.
The inclusive cross section for top-quark pair production measured by the CMS experiment in proton-proton collisions at a center-of-mass energy of 7 TeV is compared to the QCD prediction at ...next-to-next-to-leading order with various parton distribution functions to determine the top-quark pole mass, mtpole, or the strong coupling constant, alphaS. With the parton distribution function set NNPDF2.3, a pole mass of 176.7+3.8-3.4 GeV is obtained when constraining alphaS at the scale of the Z boson mass, mZ, to the current world average. Alternatively, by constraining mtpole to the latest average from direct mass measurements, a value of alphaS(mZ) = 0.1151+0.0033-0.0032 is extracted. This is the first determination of alphaS using events from top-quark production.
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