arXiv subjects

Lars Sonnenschein

Publications and source records attributed to Lars Sonnenschein.

At least 19 recordsLinked to original sources

arXiv2014

Recent results of the CMS experiment

The CMS experiment is a multi-purpose detector successfully operated at the LHC where predominantly pp collisions take place at various centre-of-mass energies up to sqrt(s)=8 TeV so far. Several weeks per year also heavy-ion collisions take place leading to interesting studies in Pb-Pb and p-Pb collisions at sqrt(s_(NN))=2.76 TeV and sqrt(s_(NN))=5.02 TeV centre-of-mass energies per nucleon, respectively. The excellent performance of the accelerator and the experiment allows for dedicated physics measurements over a wide range of subjects, starting from particle identification, encompassing forward physics, Standard Model measurements in multijet, boson, heavy flavour and top quark physics, building the basis for new physics searches interpreted within the framework of various models and theories. These pursued pp physics subjects are complemented by a rich heavy ion physics programme.

hep-ex↗

arXiv2012

CMS results and status

The CMS experiment is a multi-purpose detector successfully operated at the LHC where predominantly pp collisions take place at various centre of mass energies up to sqrt(s)=8 TeV at present. Discussed are pp collision results until end of 2011, corresponding to centre of mass energies of up to sqrt(s)=7 TeV. The excellent performance of the accelerator and the experiment allows for dedicated physics measurements over a wide range of subjects, starting from particle identification, encompassing Standard Model measurements in multijet, boson, heavy flavour and top quark physics, building the basis for new physics searches interpreted within the framework of various models and theories.

hep-ex↗

arXiv2012

Searches for New Phenomena at the LHC

Searches for physics beyond the Standard Model (SM) with the CMS and ATLAS experiments in pp collisions at a centre of mass energy of sqrt(s)=7 TeV at the LHC are presented. The discussed results are based on data taken in 2011, making use of integrated luminosities between L=1.1 and 4.9 inv. fb. Various important theories, encompassing TeV scale gravity, quark/lepton compositeness, contact interactions, new heavy vector bosons and other exotic signatures are probed.

hep-ex↗

arXiv2011

Highlights of D0 QCD related analyses

D0 provides a wealth of measurements conceived for probing perturbative and non-perturbative aspects of QCD, giving an accurate experimental account for Standard Model production processes including jets, leptons and photons and improving the sensitivity and the understanding in searches for new physics. Among the most important subjects are inclusive jet production, vector boson plus jet production, direct photon production and measurements in Minimum Bias events and Double Parton Scattering which are discussed here and compared to theory predictions.

hep-ex↗

arXiv2011

Searches in CMS

We discuss the results of searches for various new physics phenomena, including supersymmetry, in pp collisions at 7 TeV delivered by the LHC and collected with the CMS detector. These results demonstrate a good understanding of the detector and backgrounds in a variety of channels and in many cases they set the most stringent limits on these new physics phenomena, surpassing previous experiments.

hep-ex↗

arXiv2011

CMS: Cosmic muons in simulation and measured data

A dedicated cosmic muon Monte-Carlo event generator CMSCGEN has been developed for the CMS experiment. The simulation relies on parameterisations of the muon energy and the incidence angle, based on measured and simulated data of the cosmic muon flux. The geometry and material density of the CMS infrastructure underground and surrounding geological layers are also taken into account. The event generator is integrated into the CMS detector simulation chain of the existing software framework. Cosmic muons can be generated on earth's surface as well as for the detector located 90 m underground. Many million cosmic muon events have been generated and compared to measured data, taken with the CMS detector at its nominal magnetic field of 3.8 T.

hep-ex↗

arXiv2011

Drift velocity and pressure monitoring of the CMS muon drift chambers

The drift velocity in drift tubes of the CMS muon chambers is a key parameter for the muon track reconstruction and trigger. It needs to be monitored precisely in order to detect any deviation from its nominal value. A change in absolute pressure, a variation of the gas admixture or a contamination of the chamber gas by air affect the drift velocity. Furthermore, the temperature and magnetic field influence its value. First data, taken with a dedicated Velocity Drift Chamber (VDC) built by RWTH Aachen IIIA are presented. Another important parameter to be monitored is the pressure inside the muon drift tube chambers. The differential pressure must not exceed a certain value and the absolute pressure has to be kept slightly above ambient pressure to prevent air from entering into the muon drift tube chambers in case of a leak. Latest drift velocity monitoring results are discussed.

physics.ins-det↗

arXiv2011

Algebraic approach to solve $t\bar{t}$ dilepton equations

The set of non-linear equations describing the Standard Model kinematics of the top quark antiqark production system in the dilepton decay channel has at most a four-fold ambiguity due to two not fully reconstructed neutrinos. Its most precise solution is of major importance for measurements of top quark properties like the top quark mass and $t\bar{t}$ spin correlations. Simple algebraic operations allow to transform the non-linear equations into a system of two polynomial equations with two unknowns. These two polynomials of multidegree eight can in turn be analytically reduced to one polynomial with one unknown by means of resultants. The obtained univariate polynomial is of degree sixteen. The number of its real solutions is determined analytically by means of Sturm's theorem, which is as well used to isolate each real solution into a unique pairwise disjoint interval. The solutions are polished by seeking the sign change of the polynomial in a given interval through binary bracketing.

hep-ph↗

arXiv2011

Analytical solution of ttbar dilepton equations

The top quark antiquark production system in the dilepton decay channel is described by a set of equations which is nonlinear in the unknown neutrino momenta. Its most precise and least time consuming solution is of major importance for measurements of top quark properties like the top quark mass and $t\bar{t}$ spin correlations. The initial system of equations can be transformed into two polynomial equations with two unknowns by means of elementary algebraic operations. These two polynomials of multidegree two can be reduced to one univariate polynomial of degree four by means of resultants. The obtained quartic equation is solved analytically.

hep-ph↗

arXiv2010

Measurement of the charge ratio of atmospheric muons with the CMS detector

A measurement is presented of the flux ratio of positive and negative muons from cosmic ray interactions in the atmosphere, using data collected by the CMS detector at ground level and in the underground experimental cavern. The excellent performance of the CMS detector allowed detection of muons in the momentum range from 5GeV/c to 1TeV/c. For muon momenta below 100GeV/c the flux ratio is measured to be a constant 1.2766 +/-0.0032(stat.) +/-0.0032(syst.), the most precise measurement to date. At higher momenta an increase in the charge ratio is observed, in agreement with models of muon production in cosmic ray showers and compatible with previous measurements by deep underground experiments.

hep-ex↗

arXiv2010

W/Z + jet production at the Tevatron

Vector boson plus jet production is interesting for Higgs search, beyond the Standard Model physics and provides standard candles for calibration. This is complementary to inclusive jet production measurements which provide precision tests of perturbative QCD. A multitude of W/Z plus heavy and light flavour jet measurements in ppbar collisions at a centre of mass energy of sqrt{s}=1.96TeV is discussed. Next-to-Leading order perturbative QCD predictions and various models are compared to the measurements.

hep-ex↗

arXiv2010

Determination of the strong coupling constant from inclusive jet cross section in ppbar collisions at sqrt(s)=1.96 TeV with the D0 experiment

The strong coupling constant alpha_s and its dependence on the momentum scale is determined from the p_T dependence of the inclusive jet cross section in ppbar collisions at sqrt(s)=1.96 TeV measured with the D0 experiment. The jet transverse momentum range of 50 < p_T < 145 GeV contributes to the determination. Using perturbative QCD caclulations to order O(alpha_s^3) combined with resummed threshold corrections to order O(alpha_s^4) an alpha_s(M_Z)=0.1161^{+0.0041}_{-0.0048} is obtained. This is the most precise result from a hadron-hadron collider.

hep-ex↗

arXiv2009

CP-conserving and CP-violating properties in semileptonic Bs decays with the D0 experiment

A search for CP violation has been performed in a sample of semileptonic Bs decays corresponding to approximately 5fb^-1 of data collected by the D0 detector in Run II at the Fermilab Tevatron collider. A time-dependent fit to the distributions of Bs candidates yields the flavour-specific asymmetry a^s_fs = [-1.7 +/- 9.1 (stat) +1.2 -2.3 (syst)] x 10^-3, corresponding to the most precise measurement to date for this CP violation parameter. Furthermore a search for the semi-inclusive process Bs to Ds^(*)Ds^(*) has been performed on a data sample of 2.8fb^-1. 26.6 +/- 8.4 signal events are observed with a significance of 3.2 standard deviations above background, leading to a branching ratio of 0.035 +/- 0.010 (stat) +/- 0.011 (syst). Under certain theoretical assumptions, these double-charm final states saturate CP-even eigenstates in the $B_s$ decays, resulting in a width difference of Delta Gamma_s^CP / Gamma_s = 0.072 +/- 0.021 (stat) +/- 0.022 (syst).

hep-ex↗

arXiv2009

Photon + jets at D0

Photon plus jet production has been studied by the D0 experiment in Run II of the Fermilab Tevatron Collider at a centre of mass energy of sqrt{s}=1.96 TeV. Measurements of the inclusive photon, inclusive photon plus jet, photon plus heavy flavour jet cross sections and double parton interactions in photon plus three jet events are presented. They are based on integrated luminosities between 0.4 fb$^-1 and 1.0 fb^-1. The results are compared to perturbative QCD calculations in various approximations.

hep-ex↗

arXiv2009

Heavy flavour jet abundances and tagging rates analytically determined

Heavy flavour jet tagging is widely used in the determination of cross sections including the production of heavy flavoured quarks. This requires the knowledge of heavy and light flavour jet tagging efficiencies and their uncertainties. A system of eight non-linear equations can be used to determine these quantities by means of two different tagging algorithms and two data sets which differ in heavy flavour jet content. The analytical solution of this system of equations, derived by means of resultants is described in detail, including a discussion about its singularities which provide important insights, such as prescriptions to prevent badly chosen sample flavour compositions and working points of the used tagging algorithms. The analytical solution also provides an efficient and transparent way to determine the uncertainties on the solved quantities, taking correlations into account.

physics.comp-ph↗

arXiv2008

Measurement of CP violation phase phi_s and charge asymmetries in B^0_(s) decays at D0

The CP violation phase phi_s and charge asymmetries in B^0_s decays have been measured by the D0 experiment in Run II of the Fermilab Tevatron Collider where proton anti-proton collisions take place at a center of mass energy of sqrt{s}=1.96 TeV. The measurements are based on integrated luminosities between 1.0 fb^-1 and 2.8 fb^-1. A 1.8 sigma deviation from the Standard Model is observed in the measurement of the CP violation phase phi_s=-0.57^{+0.24}_{-0.30} (stat) ^{+0.07}_{-0.02} (syst) rad in the decay channel B^0_s -> J/psi phi. A combination with CDF results yields a 2.2 sigma deviation from the Standard Model.

hep-ex↗

arXiv2008

Photon plus Jet Cross Sections at the Tevatron

Photon plus jet production has been studied by the D0 and CDF experiments in Run II of the Fermilab Tevatron Collider at a center of mass energy of sqrt{s}=1.96 TeV. Measurements of the inclusive photon plus jet, di-photon and photon plus b jet cross section are presented. They are based on integrated luminosities between 0.2 fb^-1 and 1.1 fb^-1. The results are compared to perturbative QCD calculations in various approximations.

hep-ex↗

arXiv2007

Higgs searches at Tevatron

SM and MSSM Higgs Searches at the proton anti-proton collider Tevatron in Run II are presented. The performance of the collider and the two experiments D0 and CDF is shown. No deviation from SM background expectation and no MSSM Higgs signal has been observed.

hep-ex↗