Monte Carlo event generator validation and tuning for the LHC

We summarise the motivation for, and the status of, the tools developed by CEDAR/MCnet for validating and tuning Monte Carlo event generators for the LHC against data from previous colliders. We then present selected preliminary results from studies of event shapes and hadronisation observables from e+e- colliders, and of minimum bias and underlying event observables from the Tevatron, and comment on the approach needed with early LHC data to best exploit the potential for new physics discoveries at the LHC in the next few years.Comment: Prepared for Proceedings of XII Advanced Computing and Analysis Techniques in Physics Research, November 3-7 2008, Erice, Ital

New developments in event generator tuning techniques

Data analyses in hadron collider physics depend on background simulations performed by Monte Carlo (MC) event generators. However, calculational limitations and non-perturbative effects require approximate models with adjustable parameters. In fact, we need to simultaneously tune many phenomenological parameters in a high-dimensional parameter-space in order to make the MC generator predictions fit the data. It is desirable to achieve this goal without spending too much time or computing resources iterating parameter settings and comparing the same set of plots over and over again. We present extensions and improvements to the MC tuning system, Professor, which addresses the aforementioned problems by constructing a fast analytic model of a MC generator which can then be easily fitted to data. Using this procedure it is for the first time possible to get a robust estimate of the uncertainty of generator tunings. Furthermore, we can use these uncertainty estimates to study the effect of new (pseudo-) data on the quality of tunings and therefore decide if a measurement is worthwhile in the prospect of generator tuning. The potential of the Professor method outside the MC tuning area is presented as well.Comment: To appear in the proceedings of the 13th International Workshop on Advanced Computing and Analysis Techniques in Physics Research, ACAT2010, Jaipur, India, February 22-27, 201

Systematic event generator tuning for the LHC

In this article we describe Professor, a new program for tuning model parameters of Monte Carlo event generators to experimental data by parameterising the per-bin generator response to parameter variations and numerically optimising the parameterised behaviour. Simulated experimental analysis data is obtained using the Rivet analysis toolkit. This paper presents the Professor procedure and implementation, illustrated with the application of the method to tunes of the Pythia 6 event generator to data from the LEP/SLD and Tevatron experiments. These tunes are substantial improvements on existing standard choices, and are recommended as base tunes for LHC experiments, to be themselves systematically improved upon when early LHC data is available.Comment: 28 pages. Submitted to European Physical Journal C. Program sources and extra information are available from http://projects.hepforge.org/professor

Overview on Low-flux Detectors

Laboratory based searches for weakly-interacting slim particles (WISPs) of the light-shining-through-a-wall type (LSW) use visible or near-infrared (NIR) laser light. Low-noise and highly efficient detectors are necessary to improve over previous experiments. These requirements overlap with the requirements for single-photon detectors (SPDs) for quantum information (QI) experiments. In this contribution, the sensitivity of several QI SPDs is compared to photo-multiplier tubes (PMTs) and imaging charge-coupled devices (CCDs). It is found that only transition edge sensors (TESs) are viable alternatives to CCDs if the signal can be focussed to a few micro meters

Constraining Weakly Interacting Slim Particles with a Massive Star and in the Laboratory

This doctoral thesis is devoted to constraining the allowed parameter space of weakly interacting slim particles (WISPs). WISPs are predicted by many extensions of the Standard Model of Particle Physics (SM): The Peccei-Quinn solution of the strong CP-problem of quantum chromo dynamics requires the existence of an axion; some embeddings of the SM into string theories predict a large number of axion-like particles (ALPs), the so called axi-verse, and hidden photons (HPs). Cosmological and astrophysical observables are sensitive to the existence of WISPs. Measurements of these observables allow to constrain the allowed WISP parameter space. In addition dedicated laboratory based experiments exist. Although the parameter space excluded by these experiments is generally smaller than the regions excluded by measurements of cosmological or astrophysical observables, the results from these experiment are valuable complements to these measurements because they are less model dependent. In this thesis, I present my work that helps to constrain the WISP parameter space in two ways: First, the existence of ALPs implies their production in stellar cores. The oscillation of ALPs with photons in the galactic magnetic field (GMF) suggest an X-ray flux from red supergiant (RSG) stars. RSGs are expected to emit no X-rays if ALPs do not exist. An upper limit for the X-ray count rate from the nearby RSG -Ori (Betelgeuse) is estimated from observations of -Ori with the Chandra X-ray Telescope. The interior of -Ori is modelled with the “Evolve ZAMS” code. Based on this, the corresponding ALP production rate is calculated. Using current estimates of the value of the regular component of the GMF, the resulting X-ray flux density at Earth from ALP-photon oscillations and the corresponding count rates with the Chandra instruments are calculated. Comparison of this estimate with the upper limit from the Chandra measurements allows to exclude values of the ALP-photon coupling above 2 : 1 10 11 GeV 1 for masses below 2 : 6 10 11 eV. Second, a CCD (PI 1024B) camera is characterized in preparation of the “Any Light Particle Search II” experiment (ALPS-II), which is a “light shining through a wall” experiment searching for WISPs that is currently under prepa- ration at DESY in Hamburg. This characterization includes the measurement of the fixed pattern noise (FPN), the read-out noise and dark count rate. It is found that clock-induced charges cause a spatial variation of the FPN and the read-out noise over the CCD chip area. The dark count rate is found to spatially vary, too, which is caused by a non-uniform thermal load on the CCD chip. In addition the quantum efficiency at 1064 nm, the wavelength used in ALPS-II, is measured to be 1 : 2 %. Based on these results, an analysis algorithm for the CCD data is developed and the sensitivity of ALPS-II if using the CCD is compared to the sensitivity if the experiment uses a transition edge sensor (TES) as detector as planned. I find that the sensitivity with CCD on the ALP-photon coupling is one order of magnitude worse than the sensitivity with TES. This deterioration of the sensitivity is caused in equal parts by the lower quantum efficiency and higher dark count rate of the CCD compared to the TES

Status of ALPS-II at DESY

The light-shining-through-a-wall (LSW) experiment ALPS at DESY provides the current best lab-based bounds for WISP couplings. Based on this success, preparations for ALPS-II have started. The aim is to increase the sensitivity by three orders of magnitude to probe parameter regions with astrophysical hints for the existence of WISPs from white dwarf energy loss and the TeV transparency of the intergalactic medium. To reach this sensitivity, ALPS-II will be considerably longer, making use of 2 x 12 HERA dipole magnets. The laser power in the WISP-production region will be increased and a second optical cavity in the regeneration region will be constructed. Additionally, a very low-noise transition-edge photo-detector is in development. In a pre-experiment, it will be possible to probe the hidden-photon interpretation of the WMAP-7 excess in sterile neutrinos