Showing papers by "German Martinez published in 2008"

The CMS experiment at the CERN LHC

Abstract: The Compact Muon Solenoid (CMS) detector is described. The detector operates at the Large Hadron Collider (LHC) at CERN. It was conceived to study proton-proton (and lead-lead) collisions at a centre-of-mass energy of 14 TeV (5.5 TeV nucleon-nucleon) and at luminosities up to 10(34)cm(-2)s(-1) (10(27)cm(-2)s(-1)). At the core of the CMS detector sits a high-magnetic-field and large-bore superconducting solenoid surrounding an all-silicon pixel and strip tracker, a lead-tungstate scintillating-crystals electromagnetic calorimeter, and a brass-scintillator sampling hadron calorimeter. The iron yoke of the flux-return is instrumented with four stations of muon detectors covering most of the 4 pi solid angle. Forward sampling calorimeters extend the pseudo-rapidity coverage to high values (vertical bar eta vertical bar <= 5) assuring very good hermeticity. The overall dimensions of the CMS detector are a length of 21.6 m, a diameter of 14.6 m and a total weight of 12500 t.

ATLAS pixel detector electronics and sensors

Abstract: The silicon pixel tracking system for the ATLAS experiment at the Large Hadron Collider is described and the performance requirements are summarized. Detailed descriptions of the pixel detector electronics and the silicon sensors are given. The design, fabrication, assembly and performance of the pixel detector modules are presented. Data obtained from test beams as well as studies using cosmic rays are also discussed.

Heavy-ion collisions at the LHC-Last call for predictions

Abstract: This writeup is a compilation of the predictions for the forthcoming Heavy Ion Program at the Large Hadron Collider, as presented at the CERN Theory Institute 'Heavy Ion Collisions at the LHC - Last Call for Predictions', held from 14th May to 10th June 2007.

Cold nuclear matter effects on J/ψ production as constrained by deuteron-gold measurements at sNN=200 GeV

Abstract: We present a new analysis of J/psi production yields in deuteron-gold collisions at root s(NN) =200 GeV using data taken from the PHENIX experiment in 2003 and previously published in S. S. Adler [Phys. Rev. Lett 96, 012304 (2006)]. The high statistics proton-proton J/psi data taken in 2005 are used to improve the baseline measurement and thus construct updated cold nuclear matter modification factors (R-dAu). A suppression of J/psi in cold nuclear matter is observed as one goes forward in rapidity (in the deuteron-going direction), corresponding to a region more sensitive to initial-state low-x gluons in the gold nucleus. The measured nuclear modification factors are compared to theoretical calculations of nuclear shadowing to which a J/psi (or precursor) breakup cross section is added. Breakup cross sections of sigma(breakup)=2.8(-1.4)(+1.7) (2.2(-1.5)(+1.6)) mb are obtained by fitting these calculations to the data using two different models of nuclear shadowing. These breakup cross-section values are consistent within large uncertainties with the 4.2 +/- 0.5 mb determined at lower collision energies. Projecting this range of cold nuclear matter effects to copper-copper and gold-gold collisions reveals that the current constraints are not sufficient to firmly quantify the additional hot nuclear matter effect.

Design, performance, and calibration of CMS forward calorimeter wedges

Abstract: We report on the test beam results and calibration methods using high energy electrons, pions and muons with the CMS forward calorimeter (HF). The HF calorimeter covers a large pseudorapidity region (\(3\leq|\eta|\leq5\)), and is essential for a large number of physics channels with missing transverse energy. It is also expected to play a prominent role in the measurement of forward tagging jets in weak boson fusion channels in Higgs production. The HF calorimeter is based on steel absorber with embedded fused-silica-core optical fibers where Cherenkov radiation forms the basis of signal generation. Thus, the detector is essentially sensitive only to the electromagnetic shower core and is highly non-compensating (e/h≈5). This feature is also manifest in narrow and relatively short showers compared to similar calorimeters based on ionization. The choice of fused-silica optical fibers as active material is dictated by its exceptional radiation hardness. The electromagnetic energy resolution is dominated by photoelectron statistics and can be expressed in the customary form as \(\frac{a}{\sqrt{E}}\oplus{b}\). The stochastic term a is 198% and the constant term b is 9%. The hadronic energy resolution is largely determined by the fluctuations in the neutral pion production in showers, and when it is expressed as in the electromagnetic case, a = 280% and b = 11%.

Charged hadron multiplicity fluctuations in Au+Au and Cu+Cu collisions from √SNN = 22.5 to 200 GeV

Abstract: A comprehensive survey of event-by-event fluctuations of charged hadron multiplicity in relativistic heavy ions is presented. The survey covers Au+Au collisions at s(NN) =62.4 and 200 GeV, and Cu+Cu collisions at s(NN) =22.5,62.4, and 200 GeV. Fluctuations are measured as a function of collision centrality, transverse momentum range, and charge sign. After correcting for nondynamical fluctuations due to fluctuations in the collision geometry within a centrality bin, the remaining dynamical fluctuations expressed as the variance normalized by the mean tend to decrease with increasing centrality. The dynamical fluctuations are consistent with or below the expectation from a superposition of participant nucleon-nucleon collisions based upon p+p data, indicating that this dataset does not exhibit evidence of critical behavior in terms of the compressibility of the system. A comparison of the data with a model where hadrons are independently emitted from a number of hadron clusters suggests that the mean number of hadrons per cluster is small in heavy ion collisions.

The Dark Energy Camera (DECam)

Abstract: We describe the Dark Energy Camera (DECam), which will be the primary instrument used in the Dark Energy Survey. DECam will be a 3 sq. deg. mosaic camera mounted at the prime focus of the Blanco 4m telescope at the Cerro-Tololo International Observatory (CTIO). DECam includes a large mosaic CCD focal plane, a five element optical corrector, five filters (g,r,i,z,Y), and the associated infrastructure for operation in the prime focus cage. The focal plane consists of 62 2K x 4K CCD modules (0.27"/pixel) arranged in a hexagon inscribed within the roughly 2.2 degree diameter field of view. The CCDs will be 250 micron thick fully-depleted CCDs that have been developed at the Lawrence Berkeley National Laboratory (LBNL). Production of the CCDs and fabrication of the optics, mechanical structure, mechanisms, and control system for DECam are underway; delivery of the instrument to CTIO is scheduled for 2010.

Suppression of High-pTNeutral Pion Production in CentralPb+PbCollisions atsNN=17.3GeVRelative top+Candp+PbCollisions

Abstract: Neutral pion transverse momentum spectra were measured in $p+\mathrm{C}$ and $p+\mathrm{Pb}$ collisions at $\sqrt{{s}_{NN}}=174\text{ }\text{ }\mathrm{GeV}$ at midrapidity ($23\ensuremath{\lesssim}{\ensuremath{\eta}}_{\mathrm{lab}}\ensuremath{\lesssim}30$) over the range $07\ensuremath{\lesssim}{p}_{T}\ensuremath{\lesssim}35\text{ }\text{ }\mathrm{GeV}/c$ The spectra are compared to ${\ensuremath{\pi}}^{0}$ spectra measured in $\mathrm{Pb}+\mathrm{Pb}$ collisions at $\sqrt{{s}_{NN}}=173\text{ }\text{ }\mathrm{GeV}$ in the same experiment For a wide range of $\mathrm{Pb}+\mathrm{Pb}$ centralities (${N}_{\mathrm{part}}\ensuremath{\lesssim}300$), the yield of ${\ensuremath{\pi}}^{0}$'s with ${p}_{T}\ensuremath{\gtrsim}2\text{ }\text{ }\mathrm{GeV}/c$ is larger than or consistent with the $p+\mathrm{C}$ or $p+\mathrm{Pb}$ yields scaled with the number of nucleon-nucleon collisions (${N}_{\mathrm{coll}}$), while for central $\mathrm{Pb}+\mathrm{Pb}$ collisions with ${N}_{\mathrm{part}}\ensuremath{\gtrsim}350$, the ${\ensuremath{\pi}}^{0}$ yield is suppressed

Centrality dependence of charged hadron production in deuteron plus gold and nucleon plus gold collisions at root S-NN=200 GeV

Abstract: We present transverse momentum (p(T)) spectra of charged hadrons measured in deuteron-gold and nucleon-gold collisions at root s(NN)=200 GeV for four centrality classes. Nucleon-gold collisions were selected by tagging events in which a spectator nucleon was observed in one of two forward rapidity detectors. The spectra and yields were investigated as a function of the number of binary nucleon-nucleon collisions, nu, suffered by deuteron nucleons. A comparison of charged particle yields to those in p+p collisions show that yield per nucleon-nucleon collision saturates with nu for high momentum particles. We also present the charged hadron to neutral pion ratios as a function of p(T).

Design, performance, and calibration of the CMS hadron-outer calorimeter

Abstract: The Outer Hadron Calorimeter (HCAL HO) of the CMS detector is designed to measure the energy that is not contained by the barrel (HCAL HB) and electromagnetic (ECAL EB) calorimeters. Due to space limitation the barrel calorimeters do not contain completely the hadronic shower and an outer calorimeter (HO) was designed, constructed and inserted in the muon system of CMS to measure the energy leakage. Testing and calibration of the HO was carried out in a 300 GeV/c test beam that improved the linearity and resolution. HO will provide a net improvement in missing E T measurements at LHC energies. Information from HO will also be used for the muon trigger in CMS.

Front-end electronics for the Dark Energy Camera (DECam)

Abstract: The Dark Energy Survey Camera (DECam), when completed, is going to have one of the largest existing focal planes, equipped with more than 70 CCDs. Due to the large number of CCDs and the tight space on the camera, the DECam electronics group has developed new compact front-end electronics capable of flexibly and rapidly reading out all the focal plane CCDs. The system is based on the existing MONSOON Image Acquisition System designed by the National Optical Astronomy Observatory (NOAO), and it is currently being used for testing and characterization of CCDs. Boards for the new readout are being developed in USA and Spain, with the first prototypes already produced and tested. The next version with some improvements will be tested during 2008 and the system will be ready for production at the beginning of 2009. Custom MONSOON boards and the electronics path will be described.

CCD charge transfer efficiency test with the new DES clock board

Abstract: The Dark Energy Camera will be comprised of 74 CCDs with high efficiency out to a wavelength of 1 micron. The CCDs will be read out by a Monsoon-based system consisting of three boards: Master Control, CCD Acquisition, and Clock boards. The charge transfer efficiency (CTE) is closely related to the clock waveforms provided by the Clock Board (CB). The CB has been redesigned to meet the stringent requirements of the Dark Energy Survey. The number of signals provided by the clock board has been extended from 32 (the number required for 2 CCDs) up to 135 signals (the number required for 9 CCDs). This modification is required to fit the electronics into the limited space available on the imager vessel. In addition, the drivers have been changed to provide more current. The first test result with the new clock board shows a clear improvement in the CTE response when reading out at the higher frequencies required for the guide CCDs.