14063809
One-Loop Gluonic Amplitudes from Single Unitarity Cuts
We show that one-loop amplitudes in massless gauge theories can be determined from single cuts. By cutting a single propagator and putting it on-shell, the integrand of an n-point one-loop integral is transformed into an (n+2)-particle tree level amplitude. The single-cut approach described here is complementary to the double or multiple unitarity cut approaches commonly used in the literature. In common with these approaches, if the cut is taken in four dimensions, one finds only the cut-constructible parts of the amplitude, while if the cut is in D = 4−2 dimensions, both rational and cut-constructible parts are obtained. We test our method by reproducing the known results for the fully rational all-plus and mostly-plus QCD amplitudes, A(1)4(1+, 2+, 3+, 4+) and A(1)5(1+, 2+, 3+, 4+, 5+). We also rederive expressions for the scalar loop contribution to the four-gluon MHV amplitude, A4(1, = 0)(−, −, +, +) which has both cut-constructible and rational contributions, and the fully cut-constructible n-gluon MHV amplitude in = 4 Supersymmetric Yang-Mills, A4(1, = 4)(−, −, +, ..., +).
117588033
Extending the Matrix Element Method to Next-to-Leading Order
We discuss the extension of the matrix element method (MEM) to Next-to-Leading Order (NLO) in perturbation theory. In particular we focus on the production of a Standard Model Higgs boson which decays into four leptons.
119294804
Next-to-Leading Order Predictions for Dark Matter Production at Hadron Colliders
We provide Next-to-Leading Order (NLO) predictions for Dark Matter (DM) production in association with either a jet or a photon at hadron colliders. In particular we study the production of a pair of fermionic DM particles through a mediator which couples to SM via either a vector, axial-vector, scalar, pseudo-scalar, or gluon-induced coupling. Experimental constraints on the scale of new physics associated with these operators are limited by systematics, highlighting the need for NLO signal modeling. We factorize the NLO QCD and the DM parts of the calculation, allowing the possibility of using the results presented here for a large variety of searches in monojet and monophoton nal states. Our results are implemented into the Monte Carlo program MCFM.
118842322
Triphoton production at hadron colliders
We present next-to-leading order predictions for the production of triphoton final states at the LHC and the Tevatron. Our results include the effect of photon fragmentation for the first time and we are able to quantify the impact of different isolation prescriptions. We find that calculations accounting for fragmentation effects at leading order, and those employing a smooth cone isolation where no fragmentation contribution is required, are in reasonable agreement with one another. However, larger differences in the predicted rates arise when higher order corrections to the fragmentation functions are included. In addition we present full analytic results for the $$\gamma\gamma\gamma$$ and $$\gamma\gamma+$$jet one-loop amplitudes. These amplitudes, which are particularly compact, may be useful to future higher-order calculations. Our results are available in the Monte Carlo code MCFM.
73541374
The matrix element method at next-to-leading order
A bstractThis paper presents an extension of the matrix element method to next-to-leading order in perturbation theory, for electro-weak final states. To accomplish this we have developed a method to calculate next-to-leading order weights on an event-by-event basis. This allows for the definition of next-to-leading order likelihoods in exactly the same fashion as at leading order, thus extending the matrix element method to next-to-leading order. A welcome by-product of the method is the straightforward and efficient generation of unweighted next-to-leading order events. As examples of the application of our next-to-leading order matrix element method we consider the measurement of the mass of the Z boson and also the search for the Higgs boson in the four lepton channel.
118200237
Higgs + 2 jets: Compact Analytic Results
This report describes the recent efforts to compute analytic formulae for the Next-to-Leading-Order (NLO) QCD corrections to Higgs plus two jet production at hadron colliders. In these calculations the Higgs boson couples to gluons via a top-quark loop which is integrated out to form an effective vertex. The amplitudes are further simplified by splitting the real Higgs scalar into the sum of two complex scalars phi and phi^dagger. Four-dimensional unitarity is used to construct the cut-containing pieces of the amplitude, while a variety of bootstrap and Feynman diagram techniques are used to construct the rational pieces. The results described here are valid in the limit of a large top quark mass and when the transverse momenta of the jets are less than mt.
119100867
The MIDAS telescope for microwave detection of ultra-high energy cosmic rays
Abstract We present the design, implementation and data taking performance of the MIcrowave Detection of Air Showers (MIDAS) experiment, a large field of view imaging telescope designed to detect microwave radiation from extensive air showers induced by ultra-high energy cosmic rays. This novel technique may bring a tenfold increase in detector duty cycle when compared to the standard fluorescence technique based on detection of ultraviolet photons. The MIDAS telescope consists of a 4.5 m diameter dish with a 53-pixel receiver camera, instrumented with feed horns operating in the commercial extended C-Band (3.4–4.2 GHz). A self-trigger capability is implemented in the digital electronics. The main objectives of this first prototype of the MIDAS telescope – to validate the telescope design, and to demonstrate a large detector duty cycle – were successfully accomplished in a dedicated data taking run at the University of Chicago campus prior to installation at the Pierre Auger Observatory.
115853080
Coulomb instabilities and multifragment decays
118445236
The Air Microwave Yield (AMY) experiment - A laboratory measurement of the microwave emission from extensive air showers
The AMY experiment aims to measure the microwave bremsstrahlung radiation (MBR) emitted by air-showers secondary electrons accelerating in collisions with neutral molecules of the atmosphere. The measurements are performed using a beam of 510 MeV electrons at the Beam Test Facility (BTF) of Frascati INFN National Laboratories. The goal of the AMY experiment is to measure in laboratory conditions the yield and the spectrum of the GHz emission in the frequency range between 1 and 20 GHz. The final purpose is to characterise the process to be used in a next generation detectors of ultra-high energy cosmic rays. A description of the experimental setup and the first results are presented.
23746592
Front-end electronics and data acquisition system for the MIDAS experiment
The MIDAS (MIcrowave Detection of Air Showers) experiment, a prototype detector to characterize the microwave emission of air showers induced by high energy cosmic rays, has been recently commissioned at the University of Chicago. The receivers, 53 feed horns in the 4GHz band, send the signal to fast power detectors which have logarithmic response to the input RF power. The integrated output signal is continuously digitized in custom 14-bit 20 MHz ADC modules. Data are then processed locally with on-board Field Programmable Gate Arrays (FPGAs) where the trigger logic allows discrimination of events. Local trigger pulses are sent out to a Master Board where a system-wise trigger pulse is generated and sent back to the ADC Modules. After each trigger, a 100 us time stream of data is packed and buffered for readout via the VME back plane. A VME GPS module is also used for precise timing information. Design, specifications of the electronic components, a description of the implemented trigger logic, and preliminary test results will be presented in this contribution.
118789728
The MIDAS experiment: A prototype for the microwave emission of Ultra-High Energy Cosmic Rays
Recent measurements suggest that extensive air showers initiated by ultra-high energy cosmic rays (UHECR) emit signals in the microwave band of the electromagnetic spectrum caused by the collisions of the free-electrons with the atmospheric neutral molecules in the plasma produced by the passage of the shower. Such emission is isotropic and could allow the detection of air showers with 100% duty cycle and a calorimetric-like energy measurement, a significant improvement over current detection techniques. We have built MIDAS (MIcrowave Detection of Air Showers), a prototype of microwave detector, which consists of a 4.5 m diameter antenna with a cluster of 53 feed-horns in the 4 GHz range. The details of the prototype and first results will be presented.