arXiv subjects

C. Avila

Publications and source records attributed to C. Avila.

30 records · Page 2Linked to original sources

arXiv2012

CMS Resistive Plate Chamber overview, from the present system to the upgrade phase I

University of Sofia, Faculty of Physics, Atomic Physics Department, 5, James Bourchier Boulevard, BG-1164 Sofia, Bulgaria Ghent University, Department of Physics and Astronomy, Proeftuinstraat 86, BE-9000 Ghent, Belgium Bulgarian Academy of Sciences, Inst. for Nucl. Res. and Nucl. Energy, Tzarigradsko shaussee Boulevard 72, BG-1784 Sofia, Bulgaria Peking University, Department of Technical Physics, CN-100 871 Beijing, China Universidad de Los Andes, Apartado Aéreo 4976, Carrera 1E, no. 18A 10, CO-Bogotá, Colombia Academy of Scientific Research and Technology of the Arab Republic of Egypt, 101 Sharia Kasr El-Ain, Cairo, Egypt Panjab University, Department of Physics, Chandigarh Mandir 160 014, India Universita e INFN, Sezione di Bari, Via Orabona 4, IT-70126 Bari, Italy INFN, Laboratori Nazionali di Frascati, PO Box 13, Via Enrico Fermi 40, IT-00044 Frascati, Italy Universita e INFN, Sezione di Napoli, Complesso Univ. Monte S. Angelo, Via Cintia, IT-80126 Napoli, Italy Universita e INFN, Sezione di Pavia, Via Bassi 6, IT-Pavia, Italy Department of Physics and Korea Detector Laboratory, Korea University, Aman-dong 5-ga, Sungbuk-gu, Seou,l Republic of Korea Sungkyunkwan University, Department of Physics 2066, Seobu-ro, Jangan-gu, Suwon, Gyeonggi-Do, Republic of Korea

physics.ins-det↗

arXiv2012

Measurement of the differential cross section dσ/dt in elastic $p\bar{p}$ scattering at sqrt(s)=1.96 TeV

We present a measurement of the elastic differential cross section $dσ(p\bar{p}\rightarrow p\bar{p})/dt$ as a function of the four-momentum-transfer squared t. The data sample corresponds to an integrated luminosity of $\approx 31 nb^{-1}$ collected with the D0 detector using dedicated Tevatron $p\bar{p} $ Collider operating conditions at sqrt(s) = 1.96 TeV and covers the range $0.26 <|t|< 1.2 GeV^2$. For $|t|<0.6 GeV^2$, dσ/dt is described by an exponential function of the form $Ae^{-b|t|}$ with a slope parameter $ b = 16.86 \pm 0.10(stat) \pm 0.20(syst) GeV^{-2}$. A change in slope is observed at $|t| \approx 0.6 GeV^2$, followed by a more gradual |t| dependence with increasing values of |t|.

hep-ex↗

arXiv2012

Combination of CDF and D0 measurements of the W boson helicity in top quark decays

We report the combination of recent measurements of the helicity of the W boson from top quark decay by the CDF and D0 collaborations, based on data samples corresponding to integrated luminosities of 2.7 - 5.4 fb^-1 of ppbar collisions collected during Run II of the Fermilab Tevatron Collider. Combining measurements that simultaneously determine the fractions of W bosons with longitudinal (f0) and right-handed (f+) helicities, we find f0 = 0.722 \pm 0.081 [\pm 0.062 (stat.) \pm 0.052 (syst.)] and f+ = -0.033 \pm 0.046 [\pm 0.034 (stat.) \pm 0.031 (syst.)]. Combining measurements where one of the helicity fractions is fixed to the value expected in the standard model, we find f0 = 0.682 \pm 0.057 [\pm 0.035 (stat.) \pm 0.046 (syst.)] and f+ = -0.015\pm0.035 [\pm 0.018 (stat.) \pm 0.030 (syst.)]. The results are consistent with standard model expectations.

hep-ex↗

arXiv2012

Search for pair production of the scalar top quark in muon+tau final states

We present a search for the pair production of scalar top quarks ($\tilde{t}_{1}$), the lightest supersymmetric partners of the top quarks, in $p\bar{p}$ collisions at a center-of-mass energy of 1.96 TeV, using data corresponding to an integrated luminosity of {7.3 $fb^{-1}$} collected with the \dzero experiment at the Fermilab Tevatron Collider. Each scalar top quark is assumed to decay into a $b$ quark, a charged lepton, and a scalar neutrino ($\tildeν$). We investigate final states arising from $\tilde{t}_{1} \bar{\tilde{t}_{1}} \rightarrow b\bar{b}μτ\tildeν \tildeν$ and $\tilde{t}_{1} \bar{\tilde{t}_{1}} \rightarrow b\bar{b}ττ\tildeν \tildeν$. With no significant excess of events observed above the background expected from the standard model, we set exclusion limits on this production process in the ($m_{\tilde{t}_{1}}$,$m_{\tildeν}$) plane.

hep-ex↗

arXiv2011

Precise measurement of the top quark mass in the dilepton channel at D0

We measure the top quark mass (mt) in ppbar collisions at a center of mass energy of 1.96 TeV using dilepton ttbar->W+bW-bbar->l+nubl-nubarbbar events, where l denotes an electron, a muon, or a tau that decays leptonically. The data correspond to an integrated luminosity of 5.4 fb-1 collected with the D0 detector at the Fermilab Tevatron Collider. We obtain mt = 174.0 +- 1.8(stat) +- 2.4(syst) GeV, which is in agreement with the current world average mt = 173.3 +- 1.1 GeV. This is currently the most precise measurement of mt in the dilepton channel.

hep-ex↗

arXiv2011

The structure of the strange sea of the proton

In this work we study the strange sea of the proton using a version of the Meson Cloud Model containing both, efective and perturbative degrees of freedom. We construct the $s$ and $\bar{s}$ parton distributions functions at the initial energy scale, $Q_0^2$, where QCD evolution starts. The initial $s$ and $\bar s$ pdfs depend on a number of parameters which we fix by comparison to parameterizations of the strange sea of the nucleon obtained in a recent global fit to experimental data, allowing for a $s-\bar{s}$ asymmetry. We show that the model describes well the strange sea of the proton and argue that it can be a phenomenologically motivated alternative to the usual input parameterizations used in fits to experimental DIS data.

hep-ph↗

arXiv2010

Search for pair production of the scalar top quark in the electron-muon final state

We report the result of a search for the pair production of the lightest supersymmetric partner of the top quark ($\tilde{t}_1$) in $p\bar{p}$ collisions at a center-of-mass energy of 1.96 TeV at the Fermilab Tevatron collider corresponding to an integrated luminosity of 5.4 fb$^{-1}$. The scalar top quarks are assumed to decay into a $b$ quark, a charged lepton, and a scalar neutrino ($\tildeν$), and the search is performed in the electron plus muon final state. No significant excess of events above the standard model prediction is detected, and improved exclusion limits at the 95% C.L. are set in the the ($M_{\tilde{t}_1}$,$M_{\tildeν}$) mass plane.

hep-ex↗

arXiv2010

Determination of the width of the top quark

We extract the total width of the top quark, Gamma_t, from the partial decay width Gamma(t -> W b) measured using the t-channel cross section for single top quark production and from the branching fraction B(t -> W b) measured in ttbar events using up to 2.3 fb^-1 of integrated luminosity collected by the D0 Collaboration at the Tevatron ppbar Collider. The result is Gamma_t = 1.99 +0.69 -0.55 GeV, which translates to a top-quark lifetime of tau_t = (3.3 +1.3 -0.9) x 10^-25 s. Assuming a high mass fourth generation b' quark and unitarity of the four-generation quark-mixing matrix, we set the first upper limit on |Vtb'| < 0.63 at 95% C.L.

hep-ex↗

arXiv2007

On the s-sbar asymmetry of the nucleon sea

We study the $s-\bar s$ asymmetry in the nucleon sea using a model in which the proton wave function includes a Kaon-Hyperon Fock state. Parameters of the model are fixed by fitting the $s-\bar s$ asymmetry obtained from global fits to Deep Inelastic Scattering data. We discuss possible effects of the $s-\bar s$ asymmetry on the measurement of the Weinberg angle by the NuTeV Collaboration.

hep-ph↗

arXiv2006

Charm particle production in hadronic collisions

We study charm particle production in hadron-hadron collisions. After calculating perturbatively the charm quark differential cross section, we study the hadronization mechanisms. It is shown that recombination is the key to understand the so called Leading Particle Effect in charm meson production. For charm baryon production, however, leading particle effects are due to a combination of contributions coming from both, the recombination and the fragmentation mechanisms. We compare our calculations to experimental data on charm hadron production in $π^- N$ and $p N$ interactions from several experiments and show that a consistent description of them can be reached without the aid of other mechanims than recombination and fragmentation.

hep-ph↗

arXiv2002

Pion and kaon parton distribution functions in a meson cloud model

In a model of hadrons in which the hadron wave function at low $Q^2$ is represented by a hadron-like Fock state expansion, we calculate the $π$ and $K$ parton distribution functions by comparing to experimental data. We show that the model gives an accurate description of available data and, in addition, gives a clear prediction of the initial flavors to be considered at the low $Q^2$ scale where perturbative evolution starts

hep-ph↗

arXiv2000

Low $Q^2$ wave-functions of pions and kaons and their parton distribution functions

We study the low $Q^2$ wave-functions of pions and kaons as an expansion in terms of hadron-like Fock state fluctuations. In this formalism, pion and kaon wave-functions are related one another. Consequently, the knowledge of the pion structure allows the determination of parton distributions in kaons. In addition, we show that the intrinsic (low $Q^2$) sea of pions and kaons are different due to their different valence quark structure. Finally, we analize the feasibility of a method to extract kaon's parton distribution functions within this approach and compare with available experimental data.

hep-ph↗