Double-tag events study with the L3 detector at sqrt(s)=189 GeV

A preliminary study of double tag events using the L3 detector at center of mass energy sqrt{s}=189 GeV has been performed. The cross-section of gamma* gamma* collisions is measured at average =14.5 GeV2. The results are in agreement with predictions based on perturbative QCD, while the Quark Parton Model alone is insufficient to describe the data. The measurements lie below the LO and above the NLO BFKL calculations.Comment: 6 pages, invited talk to be published in the Proceedings of the Photon'99 conferenc

Nagyenergiás fizikai kutatások és fejlesztések a CERN-i LHC gyorsító CMS és a Brookhaven-i RHIC gyorsító PHENIX detektornál = High energy physics research and development at the LHC CMS (LERN) and RHIC PHENIX (BHL) detectors

Az OTKA által támogatott kutatás két területre bontható. I. A BNL RHIC gyorsítójának PHENIX kísérletében a mérésekben és a kísérleti adatok analízisében való részvétel: Csoportunk a PHENIX kollaboráció tagjaként dolgozott, munkája beépült a PHENIX kísérlet közös eredményeibe. Néhány területen a csoport hozzájárulása különösen jelentős volt. Igy kiemelendő a jet-elnyomás jelenségének vizsgálata különböző energiájú nehézion ütközésekben illetve az elektreomágneses kaloriméterrel kapcsolatos szimulációs és kalibrációs tevékenység. II. Részvétel a CERN-i LHC CMS kísérletének építésében, ezen belül a barrel müon kamrák helyzetmeghatározó rendszerének fejlesztése és létrehozása: a pályázati időszak alatt megépítésre került a teljes rendszer, amely lehetővé teszi a CMS barrel müon spektrométerét alkotó 250 nagyméretű driftkamra helyzetének meghatározását szubmilliméteres pontossággal. | The research activity supported by the OTKA fund can be divided in two groups. I. Participation in the measurements and the physics analysis of the PHENIX experiment at the RHIC accelerator in BNL (USA): our group worked in close collaboration with other members of the experiment so its work was integrated in the common results of the whole collaboration. In some areas, however, the contribution was particularly significant. Two areas can be emphasized, the investigation of jet suppression in heavy ion collisions at different energies and the simulation and calibration of the electromagnetic calorimeter. II. Participation in the construction of the CMS experiment to be installed at the LHC accelerator (CERN, Switzerland), development and construction of the barrel muon position monitoring system: the full system has been completed during the period of the OTKA-support. It allowes us to determine the positions of 250 large-scale drift-chambers forming the barrel muon spectrometer with submillimeter accuracy

Efficiency of Finding Muon Track Trigger Primitives in CMS Cathode Strip Chambers

In the CMS Experiment, muon detection in the forward direction is accomplished by cathode strip chambers~(CSC). These detectors identify muons, provide a fast muon trigger, and give a precise measurement of the muon trajectory. There are 468 six-plane CSCs in the system. The efficiency of finding muon trigger primitives (muon track segments) was studied using~36 CMS CSCs and cosmic ray muons during the Magnet Test and Cosmic Challenge~(MTCC) exercise conducted by the~CMS experiment in~2006. In contrast to earlier studies that used muon beams to illuminate a very small chamber area ($< \! 0.01$~m$^2$), results presented in this paper were obtained by many installed CSCs operating {\em in situ} over an area of $\approx \! 23$~m$^2$ as a part of the~CMS experiment. The efficiency of finding 2-dimensional trigger primitives within 6-layer chambers was found to be~$99.93 \pm 0.03\%$. These segments, found by the CSC electronics within $800$~ns after the passing of a muon through the chambers, are the input information for the Level-1 muon trigger and, also, are a necessary condition for chambers to be read out by the Data Acquisition System

Search for top squark pair production using dilepton final states in pp collision data collected at root s=13TeV

A search is presented for supersymmetric partners of the top quark (top squarks) in final states with two oppositely charged leptons (electrons or muons), jets identified as originating from bquarks, and missing transverse momentum. The search uses data from proton-proton collisions at root s = 13 TeV collected with the CMS detector, corresponding to an integrated luminosity of 137 fb(-1). Hypothetical signal events are efficiently separated from the dominant top quark pair production background with requirements on the significance of the missing transverse momentum and on transverse mass variables. No significant deviation is observed from the expected background. Exclusion limits are set in the context of simplified supersymmetric models with pair-produced lightest top squarks. For top squarks decaying exclusively to a top quark and a lightest neutralino, lower limits are placed at 95% confidence level on the masses of the top squark and the neutralino up to 925 and 450 GeV, respectively. If the decay proceeds via an intermediate chargino, the corresponding lower limits on the mass of the lightest top squark are set up to 850 GeV for neutralino masses below 420 GeV. For top squarks undergoing a cascade decay through charginos and sleptons, the mass limits reach up to 1.4 TeV and 900 GeV respectively for the top squark and the lightest neutralino.Peer reviewe

Search for a heavy Higgs boson decaying into two lighter Higgs bosons in the tau tau bb final state at 13 TeV

A search for a heavy Higgs boson H decaying into the observed Higgs boson h with a mass of 125 GeV and another Higgs boson h(S) is presented. The h and h(S) bosons are required to decay into a pair of tau leptons and a pair of b quarks, respectively. The search uses a sample of proton-proton collisions collected with the CMS detector at a center-of-mass energy of 13TeV, corresponding to an integrated luminosity of 137 fb(-1). Mass ranges of 240-3000 GeV for m(H) and 60-2800 GeV for m(hS) are explored in the search. No signal has been observed. Model independent 95% confidence level upper limits on the product of the production cross section and the branching fractions of the signal process are set with a sensitivity ranging from 125 fb (for m(H) = 240 GeV) to 2.7 fb (for m(H) = 1000 GeV). These limits are compared to maximally allowed products of the production cross section and the branching fractions of the signal process in the next-to-minimal supersymmetric extension of the standard model.Peer reviewe

Measurement of the Higgs boson production rate in association with top quarks in final states with electrons, muons, and hadronically decaying tau leptons at s√=13TeV

The rate for Higgs (H) bosons production in association with either one (tH) or two (tt¯H) top quarks is measured in final states containing multiple electrons, muons, or tau leptons decaying to hadrons and a neutrino, using proton–proton collisions recorded at a center-of-mass energy of 13TeV by the CMS experiment. The analyzed data correspond to an integrated luminosity of 137fb−1. The analysis is aimed at events that contain H→WW, H→ττ, or H→ZZ decays and each of the top quark(s) decays either to lepton+jets or all-jet channels. Sensitivity to signal is maximized by including ten signatures in the analysis, depending on the lepton multiplicity. The separation among tH, tt¯H, and the backgrounds is enhanced through machine-learning techniques and matrix-element methods. The measured production rates for the tt¯H and tH signals correspond to 0.92±0.19(stat)+0.17−0.13(syst) and 5.7±2.7(stat)±3.0(syst) of their respective standard model (SM) expectations. The corresponding observed (expected) significance amounts to 4.7 (5.2) standard deviations for tt¯H, and to 1.4 (0.3) for tH production. Assuming that the Higgs boson coupling to the tau lepton is equal in strength to its expectation in the SM, the coupling yt of the Higgs boson to the top quark divided by its SM expectation, κt=yt/ySMt, is constrained to be within −0.9<κt<−0.7 or 0.7<κt<1.1, at 95% confidence level. This result is the most sensitive measurement of the tt¯H production rate to date.SCOAP