120345606
The TOTEM GEM Telescope (T2) at the LHC
The TOTEM T2 telescope will measure inelastically produced charged particles in the forward region of the LHC Interaction Point 5. Each arm of the telescope consists in a set of 20 triple-GEM (Gas Electron Multiplier) detectors with tracking and trigger capabilities. The GEM technology has been considered for the design of TOTEM very forward T2 telescopes thanks to its characteristics: large active areas, good position and timing resolution, excellent rate capability and radiation hardness. Each of the four T2 half arms has been fully assembled and equipped with electronics at CERN and systematically tested in the SPS beam line H8 in 2008/09. After some optimization, the operation of the GEM chambers was fully satisfactory and the T2 telescopes were installed and commissioned in their final positions at the LHC interaction point. During the first LHC run (December 2009) the T2 telescopes have collected data, at 900 GeV and 2.36 TeV. We will present here the performances of the detector and the preliminary results obtained using the data collected.
125690152
The TOTEM experiment at LHC
The TOTEM experiment is dedicated to the measurement of the total proton-proton cross-section with the luminosity-independent method and the study of elastic and diffractive scattering processes. Two tracking telescopes, T1 and T2, integrated in the CMS detector, cover the pseudo-rapidity region between 3.1 and 6.5 on both sides of the interaction point IP5. The Roman Pot (RP) stations are located at distances of ± 147m and ± 220 m with respect to the interaction point to measure the very forward scattered protons at very small angles. During the LHC technical stop in winter 2010/2011, the TOTEM experiment was completed with the installation of the T1 telescope and the RP stations at ± 147 m. In 2011, the LHC machine provided special optics with the large s* = 90 m, allowing TOTEM to measure the elastic scattering differential cross section, down to the four-momentum transfer squared |t| = 2×10−2 GeV2. Using the optical theorem and extrapolation of the differential cross section to t = 0 (optical point), the total p-p cross section at the LHC energy of √v = 7 TeV could be computed for the first time. The status of the experiment, the performance of the detectors with emphasis on the RPs are described and the first physics results are presented.
22796813
Double diffractive cross-section measurement in the forward region at the LHC.
The first double diffractive cross-section measurement in the very forward region has been carried out by the TOTEM experiment at the LHC with a center-of-mass energy of sqrt[s]=7  TeV. By utilizing the very forward TOTEM tracking detectors T1 and T2, which extend up to |η|=6.5, a clean sample of double diffractive pp events was extracted. From these events, we determined the cross section σDD=(116±25)  μb for events where both diffractive systems have 4.7<|η|min<6.5.
44804523
The TOTEM T2 detector at LHC: Track reconstruction algorithm and preliminary measurements
TOTEM is an experiment designed to perform total cross section, elastic scattering, and diffractive dissociation measurements at the LHC. It is made up of elastic detectors set in the tunnel (Roman Pots) and two inelastic telescopes: T1 and T2, located in the same cavern as the CMS experiment.
122038644
The TOTEM T2 telescope based on triple-GEM chambers
Abstract The TOTEM experiment at LHC has chosen the triple Gas Electron Multiplier (GEM) technology for its T2 telescope which will provide charged track reconstruction in the pseudorapidity range 5.3 | η | 6.5 and a fully inclusive trigger for inelastic events. GEMs are gas filled detectors which combine good spatial resolution with very high rate capability and a good resistance to radiation. Preliminary results of cosmic ray tests performed at CERN on final T2 modules before installation are here presented. Comparisons between real and simulated detector performance are also shown.
121659740
The CDF level 2 calorimetric trigger upgrade
Abstract CDF II upgraded the calorimeter trigger to cope with the higher detector occupancy due to the increased Tevatron instantaneous luminosity ( ∼ 2.8 × 10 32 cm - 2 s - 1 ) . While the original system was implemented in custom hardware and provided to the L2 trigger a limited-quality jet clustering performed using a reduced resolution measurement of the transverse energy in the calorimeter trigger towers, the upgraded system provides offline-quality jet reconstruction of the full resolution calorimeter data. This allows to keep better under control the dependence of the trigger rates on the instantaneous luminosity and to improve the efficiency and purity of the trigger selections. The upgraded calorimeter trigger uses the general purpose VME board Pulsar, developed at CDF II and already widely used to upgrade the L2 tracking and L2 decision systems. A battery of Pulsars is used to merge and send the calorimeter data to the L2 CPUs, where software-implemented algorithms perform offline-like clustering. In this paper we review the design and the performance of the upgraded system.
119180749
Heavy-flavor in-medium momentum evolution: Langevin versus Boltzmann approach
The propagation of heavy quarks in the quark-gluon plasma (QGP) has been often treated within the framework of the Langevin equation (LV), i.e. assuming the momentum transfer is small or the scatterings are sufficiently forward peaked, small screening mass $m_D$. We address a direct comparison between the Langevin dynamics and the Boltzmann collisional integral (BM) when a bulk medium is in equilibrium at fixed temperature. We show that unless the cross section is quite forward peaked ($m_D\cong T $) or the mass to temperature ratio is quite large ($M_{HQ}/T \gtrsim 8-10$) there are significant differences in the evolution of the $p-$spectra and consequently on nuclear modification factor $R_{AA}(p_T)$. However for charm quark we find that very similar $R_{AA}(p_T)$ between the LV and BM can be obtained, but with a modified diffusion coefficient by about $\sim 15-50\%$ depending on the angular dependence of the cross section which regulates the momentum transfer. Studying also the momentum spread suffered by a single heavy quarks we see that at temperatures $T\gtrsim \, 250\,\rm MeV$ the dynamics of the scatterings is far from being of Brownian type for charm quarks. In the case of bottom quarks we essentially find no differences in the time evolution of the momentum spectra between the LV and the BM dynamics independently of the angular dependence of the cross section, at least in the range of temperature relevant for ultra-relativistic heavy-ion collisions. Finally, we have shown the possible impact of this study on $R_{AA}(p_T)$ and $v_2(p_T)$ for a realistic simulation of relativistic HIC. For larger $m_D$ the elliptic flow can be about $50\%$ larger for the Boltzmann dynamics with respect to the Langevin. This is helpful for a simultaneous reproduction of $R_{AA}(p_T)$ and $v_2(p_T)$.
118532450
Elliptic flow and shear viscosity of the shattered color glass condensate
In this contribution, we report on our results about the computation of the elliptic flow of the quark-gluon-plasma produced in relativistic heavy ion collisions, simulating the expansion of the fireball by solving the relativistic Boltzmann equation for the parton distribution function tuned at a fixed shear viscosity to entropy density ratio η/s. We emphasize the role of saturation in the initial gluon spectrum modelling the shattering of the color glass condensate, causing the initial distribution to be out of equilibrium. We find that the saturation reduces the efficiency in building-up the elliptic flow, even if the thermalization process is quite fast τtherm ≈ 0.8fm/c. and the pressure isotropization even faster τisotr ≈ 0.3fm/c. The impact of the initial non-equilibrium manifests for non-central collisions and can modify the estimate of the viscosity respect to the assumption of full thermalization in pT-space.
124103629
Elliptic Flow Difference Between Particles and Antiparticles and the EOS of Baryon-rich Matter
Cyclotron Institute and Department of Physics and Astronomy Texas A&M University, College Station, TX 77843, USA Department of Physics, Shanghai Jiao Tong University, Shanghai 200240, China Dipartimento di Fisica e Astronomia, Università di Catania Via S. Sofia 64, 95125 Catania, Italy Department of Physics, East Carolina University C-209 Howell Science Complex, Greenville, NC 27858, USA Shanghai Institute of Applied Physics, Chinese Academy of Sciences Shanghai 201800, China
118127416
Toward a solution to the $R_{AA}$ and $v_2$ puzzle for heavy quarks
The heavy quarks constitutes a unique probe of the quark-gluon plasma properties. Both at RHIC and LHC energies a puzzling relation between the nuclear modification factor $R_{AA}(p_T)$ and the elliptic flow $v_2(p_T)$ has been observed which challenged all the existing models, especially for D mesons. We discuss how the temperature dependence of the heavy quark drag coefficient is responsible for a large part of such a puzzle. In particular, we have considered four different models to evaluate the temperature dependence of drag and diffusion coefficients propagating through a quark gluon plasma (QGP). All the four different models are set to reproduce the same $R_{AA}(p_T)$ observed in experiments at RHIC and LHC energy. We point out that for the same $R_{AA}(p_T)$ one can generate 2-3 times more $v_2$ depending on the temperature dependence of the heavy quark drag coefficient. A non-decreasing drag coefficient as $ T \rightarrow\ T_c \,$ is a major ingredient for a simultaneous description of $R_{AA}(p_T)$ and $v_2(p_T)$.
15747021
Heavy-Quark Kinetics at RHIC and LHC
In ultrarelativistic nuclear collisions heavy quarks are produced out of thermal equilibrium in the very early stage of the reaction and their thermalization time was expected to be considerably larger than that of light quarks. On the other hand, a strongly-interacting QGP can be envisaged in the heavy quark sector due to the presence of heavy-light hadron-like resonances in the QGP for temperatures up to �2TC. We investigate the consequences of such states employing a relativistic Langevin simulation. Hadronization is modeled by a coalescence-fragmentation scheme. We present the predictions for the nuclear modification factor and elliptic flow of D and B mesons at LHC energies and compare the results with the successful predictions of this model for RHIC conditions. We find similar heavy-quark thermalization effects at LHC and RHIC.