We present a search for large extra dimensions (ED) in p-pbar collisions at a center-of-mass energy of 1.8 TeV using data collected by the D0 detector at the Fermilab Tevatron in 1994-1996. Data ...corresponding to 78.8 +/- 3.9 pb^-1 are examined for events with large missing transverse energy, one high-p_T jet, and no isolated muons. With no excess beyond the background prediction from the standard model, we place limits on the fundamental Planck scale of 1 TeV (0.6 TeV) for 2 (7) ED.
Using the D0 detector, we have observed events produced in pbar-p collisions that contain W or Z bosons in conjunction with very little energy deposition (``rapidity gaps'') in large forward regions ...of the detector. The fraction of W boson events with a rapidity gap (a signature for diffraction) is 0.89\pm^{0.19}_{0.17}%, and the probability that the non-diffractive background fluctuated to yield the observed diffractive signal is 3 x 10^{-14}, corresponding to a significance of 7.5 sigma. The Z boson sample has a gap fraction of 1.44 \pm^{0.61}_{0.52}%, with a significance of 4.4 sigma. The diffractive events have very similar properties to the more common non-diffractive component.
The High Luminosity LHC (HL-LHC) phase is designed to increase by an order of magnitude the amount of data to be collected by the LHC experiments. The foreseen gradual increase of the instantaneous ...luminosity of up to more than twice its nominal value of \(10\times10^{34}\ {\rm cm}^{-1}{\rm s}^{-2}\) during Phase I and Phase II of the LHC running, presents special challenges for the experiments. The region with high pseudo rapidity (\(\eta\)) region of the forward muon spectrometer (\(2.4 > |\eta| > 1.9\)) is not equipped with RPC stations. The increase of the expected particles rate up to 2 kHz cm\(^{-1}\) ( including a safety factor 3 ) motivates the installation of RPC chambers to guarantee redundancy with the CSC chambers already present. The current CMS RPC technology cannot sustain the expected background level. A new generation of Glass-RPC (GRPC) using low-resistivity glass was proposed to equip the two most far away of the four high \(\eta\) muon stations of CMS. In their single-gap version they can stand rates of few kHz cm\(^{-1}\). Their time precision of about 1 ns can allow to reduce the noise contribution leading to an improvement of the trigger rate. The proposed design for large size chambers is examined and some preliminary results obtained during beam tests at Gamma Irradiation Facility (GIF++) and Super Proton Synchrotron (SPS) at CERN are shown. They were performed to validate the capability of such detectors to support high irradiation environment with limited consequence on their efficiency.
We have performed a search for scalar top quark (stop) pair production in the inclusive electron-muon-missing transverse energy final state, using a sample of $p \bar{p}$ events corresponding to ...108.3 pb$^{-1}$ of data collected with the D{\O}detector at Fermilab. The search is done in the framework of the minimal supersymmetric standard model assuming that the sneutrino is the lightest supersymmetric particle. For the dominant decays of the lightest stop, \bc and \bls, no evidence for signal is found. We derive cross-section limits as a function of stop (\stt), chargino (\ca), and sneutrino (\snu) masses.
Using the DØ detector, we have studied events produced in $\bar{p}p$ collisions that contain large forward regions with very little energy deposition (“rapidity gaps”) and concurrent jet production ...at center-of-mass energies of $\sqrt s$ = 630 and 1800 GeV. The fraction of events with forward or central jets associated with rapidity gaps is compared to predictions for hard diffraction. We also extract the momentum loss for scattered protons in such processes.
We study the radiative corrections induced by the triple Higgs boson coupling \(hhh\) in the three body decay \(h\to ZZ^*\to Zl\bar l\). We show that these corrections are potentially sensitive to ...the specific value of this coupling in the Standard Model and the Two Higgs Doublet Model (2HDM). These effects may induce corrections to the integrated decay width of the three-body decay of order few percent in the 2HDM and thus open a new window to test the Higgs boson self interaction in physics beyond the standard model.
We report a new measurement of the pseudorapidity (eta) and transverse-energy (Et) dependence of the inclusive jet production cross section in pbar b collisions at sqrt(s) = 1.8 TeV using 95 pb**-1 ...of data collected with the DZero detector at the Fermilab Tevatron. The differential cross section d^2sigma/dEt deta is presented up to |eta| = 3, significantly extending previous measurements. The results are in good overall agreement with next-to-leading order predictions from QCD and indicate a preference for certain parton distribution functions.
The DO Collaboration has measured the inclusive jet cross section in proton-antiproton collisions at s**2 = 630 GeV. The results for pseudorapidities -0.5 to 0.5 are combined with our previous ...results at s**2 = 1800 GeV to form a ratio of cross sections with smaller uncertainties than either individual measurement. Next-to-leading-order QCD predictions show excellent agreement with the measurement at 630 GeV; agreement is also satisfactory for the ratio. Specifically, despite a 10% to 15% difference in the absolute normalization, the dependence of the ratio on jet transverse momentum is very similar for data and theory.
We report on a study of the ratio of inclusive three-jet to inclusive two-jet production cross sections as a function of total transverse energy in p-pbar collisions at a center-of-mass energy ...sqrt{s} = 1.8 TeV, using data collected with the D0 detector during the 1992-1993 run of the Fermilab Tevatron Collider. The measurements are used to deduce preferred renormalization scales in perturbative O(alpha_s^3) QCD calculations in modeling soft-jet emission.
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