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At least 685 records · Page 38Linked to original sources
arXiv2012

To what extent is Gluon Confinement an empirical fact?

Experimental verifications of Confinement in hadron physics have established the absence of charges with a fraction of the electron's charge by studying the energy deposited in ionization tracks at high energies, and performing Millikan experiments with charged droplets at rest. These experiments test only the absence of particles with fractional charge in the asymptotic spectrum, and thus "Quark" Confinement. However what theory suggests is that Color is confined, that is, all asymptotic particles are color singlets. Since QCD is a non-Abelian theory, the gluon force carriers (indirectly revealed in hadron jets) are colored. We empirically examine what can be said about Gluon Confinement based on the lack of detection of appropriate events, aiming at an upper bound for high-energy free-gluon production.

hep-ph↗
arXiv2013

Measurement of Permanent Electric Dipole Moments of Charged Hadrons in Storage Rings

Permanent Electric Dipole Moments (EDMs) of elementary particles violate two fundamental symmetries: time reversal invariance (T) and parity (P). Assuming the CPT theorem this implies CP-violation. The CP-violation of the Standard Model is orders of magnitude too small to be observed experimentally in EDMs in the foreseeable future. It is also way too small to explain the asymmetry in abundance of matter and anti-matter in our universe. Hence, other mechanisms of CP violation outside the realm of the Standard Model are searched for and could result in measurable EDMs. Up to now most of the EDM measurements were done with neutral particles. With new techniques it is now possible to perform dedicated EDM experiments with charged hadrons at storage rings where polarized particles are exposed to an electric field. If an EDM exists the spin vector will experience a torque resulting in change of the original spin direction which can be determined with the help of a polarimeter. Although the principle of the measurement is simple, the smallness of the expected effect makes this a challenging experiment requiring new developments in various experimental areas. Complementary efforts to measure EDMs of proton, deuteron and light nuclei are pursued at Brookhaven National Laboratory and at Forschungszentrum Juelich with an ultimate goal to reach a sensitivity of 10^{-29} e cm.

hep-ex↗
arXiv2013

Spatial resolution of a μPIC-based neutron imaging detector

We present a detailed study of the spatial resolution of our time-resolved neutron imaging detector utilizing a new neutron position reconstruction method that improves both spatial resolution and event reconstruction efficiency. Our prototype detector system, employing a micro-pattern gaseous detector known as the micro-pixel chamber (μPIC) coupled with a field-programmable-gate-array-based data acquisition system, combines 100μm-level spatial and sub-μs time resolutions with excellent gamma rejection and high data rates, making it well suited for applications in neutron radiography at high-intensity, pulsed neutron sources. From data taken at the Materials and Life Science Experimental Facility within the Japan Proton Accelerator Research Complex (J-PARC), the spatial resolution was found to be approximately Gaussian with a sigma of 103.48 +/- 0.77 μm (after correcting for beam divergence). This is a significant improvement over that achievable with our previous reconstruction method (334 +/- 13 μm), and compares well with conventional neutron imaging detectors and with other high-rate detectors currently under development. Further, a detector simulation indicates that a spatial resolution of less than 60 μm may be possible with optimization of the gas characteristics and μPIC structure. We also present an example of imaging combined with neutron resonance absorption spectroscopy.

physics.ins-det↗
arXiv2013

Characterization of EASIROC as Front-End for the readout of the SiPM at the focal plane of the Cherenkov telescope ASTRI

The Extended Analogue Silicon Photo-multiplier Integrated Read Out Chip, EASIROC, is a chip proposed as front-end of the camera at the focal plane of the imaging Cherenkov ASTRI SST-2M telescope prototype. This paper presents the results of the measurements performed to characterize EASIROC in order to evaluate its compliance with the ASTRI SST-2M focal plane requirements. In particular, we investigated the trigger time walk and the jitter effects as a function of the pulse amplitude. The EASIROC output signal is found to vary linearly as a function of the input pulse amplitude with very low level of electronic noise and cross-talk (<1%). Our results show that it is suitable as front-end chip for the camera prototype, although, specific modifications are necessary to adopt the device in the final version of the telescope.

physics.ins-det↗
arXiv2012

The Magnetic Distortion Calibration System of the LHCb RICH1 Detector

The LHCb RICH1 detector uses hybrid photon detectors (HPDs) as its optical sensors. A calibration system has been constructed to provide corrections for distortions that are primarily due to external magnetic fields. We describe here the system design, construction, operation and performance.

physics.ins-det↗
arXiv2013

Improved Particle Identification Using Cluster Counting in a Full-Length Drift Chamber Prototype

Single-cell prototype drift chambers were built at TRIUMF and tested with a $\sim\unit[210]{MeV/c}$ beam of positrons, muons, and pions. A cluster-counting technique is implemented which improves the ability to distinguish muons and pions when combined with a traditional truncated-mean charge measurement. Several cluster-counting algorithms and equipment variations are tested, all showing significant improvement when combined with the traditional method. The results show that cluster counting is a feasible option for any particle physics experiment using drift chambers for particle identification. The technique does not require electronics with an overly high sampling rate. Optimal results are found with a signal smoothing time of $\sim\unit[5]{ns}$ corresponding to a $\sim\unit[100]{MHz}$ Nyquist frequency.

physics.ins-det↗
arXiv2013

Effect of Temperature and Charged Particle Fluence on the Resistivity of Polycrystalline CVD Diamond Sensors

The resistivity of polycrystalline chemical vapor deposition diamond sensors is studied in samples exposed to fluences relevant to the environment of the High Luminosity Large Hadron Collider. We measure the leakage current for a range of bias voltages on samples irradiated with 800 MeV protons up to 1.6\times 10^{16} p/cm^2. The proton beam at LANSCE, Los Alamos National Laboratory, was applied to irradiate the samples. The devices' resistivity is extracted for temperatures in the -10^\circC to +20^\circC range.

physics.ins-det↗
arXiv2012

Beam Energy Dependence of First and Higher Order Flow Harmonics from the STAR Experiment at RHIC

In these proceedings, we present STAR measurements of directed flow, $v_{1}$, for pions, protons and antiprotons between $\sqrt{s_{NN}} = 7.7$ GeV and 200 GeV. A striking observation is that the $v_1$ slope for net protons as a function of rapidity, $F = dv_1/dy$, which is an estimate of the directed flow contribution from baryon number transported to the midrapidity region, changes sign twice within the lower part of this energy range. We also present the measured beam energy dependence of triangular flow $v_{3}$, and the $n=1$ to $n=5$ flow harmonics for charged particles at 200 GeV.

nucl-ex↗
arXiv2013

Probing the Color Glass Condensate in $pp$ collisions at forward rapidities and very low transverse momenta

The description of the hadron production at very forward rapidities and low transverse momentum is usually made using phenomenological models based on nonperturbative physics. However, at high energies and large rapidities the wave function of one of the projectiles is probed at very small Bjorken $x$, being characterized by a large number of gluons. In this kinematical regime, a new state of matter - the Color Glass Condensate (CGC) - is expected to be formed. One the main characteristics of such system is the presence of a new dynamical momentum scale, the saturation scale $Q_s$, which can assume values very larger than the QCD confinement scale $Λ_{QCD}$ and give the scale of the running coupling constant. In this paper we assume that in particular kinematical region probed by LHC forward (LHCf) experiment the saturation scale can be considered the hard momentum scale present in the process and calculate the forward neutral pion production at very low-$p_T$ using a perturbative approach. We demonstrate that the CGC formalism is able to successfully describe the LHCf data, which can be considered as a compelling indication of the presence of non-linear QCD effects at LHC energies.

hep-ph↗
arXiv2013

Hyperon-nucleon interaction at next-to-leading order in chiral effective field theory

Results for the Lambda N and Sigma N interactions obtained at next-to-leading order in chiral effective field theory are reported. At the order considered there are contributions from one- and two-pseudoscalar-meson exchange diagrams and from four-baryon contact terms without and with two derivatives. SU(3) flavor symmetry is imposed for constructing the hyperon-nucleon interaction while the explicit SU(3) symmetry breaking by the physical masses of the pseudoscalar mesons (pi, K, eta) is taken into account. An excellent description of the hyperon-nucleon system can be achieved at next-to-leading order. It is on the same level of quality as the one obtained by the most advanced phenomenological hyperon-nucleon interaction models.

nucl-th↗
arXiv2013

The Lightest Massive Invisible Particles at the LHC

The observation of new physics events with large missing transverse energy at the LHC would potentially serve as evidence for the direct production of dark matter. A crucial step toward verifying such evidence is the measurement of the would-be dark matter mass. If, for example, the invisible particles are found to have masses consistent with zero, it may prove very challenging to ascertain whether light dark matter or neutrinos are being observed. We assume that new invisible particles are pair-produced in a ttbar-like topology and use two MT2-based methods to measure the masses of the particles associated with the missing energy. Instead of simulating events and backgrounds, we estimate the uncertainty associated with measuring the mass of the invisible particle by assuming a fixed value of the uncertainty associated with the location of the MT2 endpoint. We find that if this uncertainty associated with measuring the MT2 endpoints is, quite optimistically, O(1 GeV), the invisible particles must have masses greater than O(10 GeV) so they can be distinguished from massless ones at 95% CL. If the results from the CoGeNT, DAMA/LIBRA, and CRESST experiments have indeed revealed the existence of light dark matter with mass O(10 GeV), our results suggest that it may be difficult for the LHC to distinguish dark matter from neutrinos solely via mass measurements.

hep-ph↗
arXiv2021

Constraining CP-phases in SUSY: an interplay of muon/electron $g-2$ and electron EDM

The minimal supersymmetric standard model (MSSM) with complex parameters can contribute sizably to muon/electron anomalous magnetic dipole momemnt ($g-2$) and electric dipole moment (EDM). The electron $g-2$ interplays with electron EDM; the muon $g-2$ can also interplay with electron EDM assuming the universality between smuon and selectron masses, either of which can constrain the relevant CP-phases in the MSSM. In this work, we first use such an interplay to derive an approximate analytical upper limit on the relevant CP-phase. Then we extensively scan the parameter space to obtain more accurate upper limits. We obtain the following observations: (i) The muon $g-2$ in the $2σ$ range combined with the electron EDM upper limit (assuming the universality between smuon and selectron masses) typically constrains the relevant CP-phase under $1.9\times 10^{-5} (\text{rad})$; (ii) The electron $g-2$ in the $2σ$ range (Berkeley) interplays with the electron EDM upper limit (without assuming the universality between smuon and selectron masses) constrains the relevant CP-phase under $3.9\times 10^{-6}(\text{rad})$ (also requiring muon $g-2$ in the allowed $2σ$ range). We also find some special cancellations in the parameter space which can relax the constraints by a couple of orders. Such stringent limits on CP-phases may pose a challenge for model building of SUSY, i.e., how to naturally suppress these phases.

hep-ph↗
arXiv2012

Search for a Standard Model Higgs boson in the mass range 200-600 GeV in the H->ZZ->llqq decay channel

A search for a heavy Standard Model Higgs boson decaying via H->ZZ->llqq, where l=e or mu, is presented. The search uses a data set of pp collisions at sqrt(s) = 7 TeV, corresponding to an integrated luminosity of 4.7 fb^-1 collected in 2011 by the ATLAS detector at the CERN LHC. No significant excess of events above the estimated background is found. Upper limits at 95% confidence level on the production cross section of a Higgs boson with a mass in the range between 200 and 600 GeV are derived. A Standard Model Higgs boson with a mass in the range 300 <= mH <= 322 GeV or 353 <= mH <= 410 GeV is excluded at 95% CL. The corresponding expected exclusion range is 351 <= mH <= 404 GeV at 95% CL.

hep-ex↗
arXiv2012

Measurement of the top quark pair cross section with ATLAS in pp collisions at sqrt(s) = 7 TeV using final states with an electron or a muon and a hadronically decaying tau lepton

A measurement of the cross section of top quark pair production in proton-proton collisions recorded with the ATLAS detector at the LHC at a centre-of-mass energy of 7 TeV is reported. The data sample used corresponds to an integrated luminosity of 2.05 fb^-1. Events with an isolated electron or muon and a tau lepton decaying hadronically are used. In addition, a large missing transverse momentum and two or more energetic jets are required. At least one of the jets must be identified as originating from a b quark. The measured cross section, sigma_ttbar = 186+/- 13 (stat) +/- 20 (syst) +/- 7 (lum.) pb is in good agreement with the Standard Model prediction.

hep-ex↗
arXiv2013

Search for direct slepton and gaugino production in final states with two leptons and missing transverse momentum with the ATLAS detector in pp collisions at sqrt(s) = 7 TeV

A search for the electroweak pair production of charged sleptons and weak gauginos decaying into final states with two leptons is performed using 4.7 fb-1 of proton-proton collision data at sqrt(s)=7 TeV recorded with the ATLAS experiment at the Large Hadron Collider. No significant excesses are observed with respect to the prediction from Standard Model processes. In the scenario of direct slepton production, if the sleptons decay directly into the lightest neutralino, left-handed slepton masses between 85 and 195 GeV are excluded at 95% confidence level for a 20 GeV neutralino. Chargino masses between 110 and 340 GeV are excluded in the scenario of direct production of wino-like chargino pairs decaying into the lightest neutralino via an intermediate on-shell charged slepton for a 10 GeV neutralino. The results are also interpreted in the framework of the phenomenological minimal supersymmetric Standard Model.

hep-ex↗
arXiv2012

Search for pair production of heavy top-like quarks decaying to a high-pT W boson and a b quark in the lepton plus jets final state at sqrt(s)=7 TeV with the ATLAS detector

A search is presented for production of a heavy up-type quark (t') together with its antiparticle, assuming a significant branching ratio for subsequent decay into a W boson and a b quark. The search is based on 4.7 fb^-1 of pp collisions at sqrt(s)=7 TeV recorded in 2011 with the ATLAS detector at the CERN Large Hadron Collider. Data are analyzed in the lepton+jets final state, characterized by a high-transverse-momentum isolated electron or muon, large missing transverse momentum and at least three jets. The analysis strategy relies on the substantial boost of the W bosons in the t't'bar signal when mt'>=400 GeV. No significant excess of events above the Standard Model expectation is observed and the result of the search is interpreted in the context of fourth-generation and vector-like quark models. Under the assumption of a branching ratio BR(t'->Wb)=1, a fourth-generation t' quark with mass lower than 656 GeV is excluded at 95% confidence level. In addition, in light of the recent discovery of a new boson of mass ~126 GeV at the LHC, upper limits are derived in the two-dimensional plane of BR(t'->Wb) versus BR(t'->Ht), where H is the Standard Model Higgs boson, for vector-like quarks of various masses.

hep-ex↗