E. J. Desmond

Versatile spectrometer for experiments using synchrotron radiation at wave-lengths greater than 100 nm

Abstract Most applications of synchrotron radiation (SR) have been in the extreme ultraviolet and X-ray spectral domains, i.e. wave-lengths less than 100 nm. In the spectral region longward of 100 nm, SR may also be superior to other sources for certain experiments. To date, SR above 100 nm has been exploited most extensively by fluorescence lifetime measurements. Experiments such as circular dichroism, magnetic circular dichroism, various emission spectroscopies and photoacoustic spectroscopy can also use to advantage the high intensity, continuous tunability, short term stability and polarization provided by SR. We have constructed a versatile spectrometer capable of performing the experiments mentioned above and suitable for use to wavelengths less than 130 nm. It will be operated at the SURF II (NS) ring pending completion of the NSLS at Brookhaven National Laboratory. In addition, we describe a modular computer system which will be used to control the operation of and collect and process spectral data from this spectrometer system.

Azimuthal Angle Correlations for Rapidity Separated Hadron Pairs in d+Au Collisions at {radical}(s{sub NN})=200 GeV

Deuteron-gold (d+Au) collisions at the Relativistic Heavy Ion Collider provide ideal platforms for testing QCD theories in dense nuclear matter at high energy. In particular, models suggesting strong saturation effects for partons carrying small nucleon momentum fraction (x) predict modifications to jet production at forward rapidity (deuteron-going direction) in d+Au collisions. We report on two-particle azimuthal angle correlations between charged hadrons at forward/backward (deuteron/gold going direction) rapidity and charged hadrons at midrapidity in d+Au and p+p collisions at root s(NN)=200 GeV. Jet structures observed in the correlations are quantified in terms of the conditional yield and angular width of away-side partners. The kinematic region studied here samples partons in the gold nucleus with x similar to 0.1 to similar to 0.01. Within this range, we find no x dependence of the jet structure in d+Au collisions.

Simultaneous measurement of fluorescence and phosphorescence using synchronously gated photon counters

Abstract The fluorescence (prompt emission) and phosphorescence (delayed emission) from a sample can be separated and recorded simultaneously by digital processing of the photon-induced electronic pulses they generate. A single rotating sector wheel (or “chopper”) periodically interrupts the beam of radiation incident upon the sample. Both prompt and delayed emissions from the sample pass through the same optical system to a photomultiplier. The electronic pulses they generate are processed by the same amplifiers and discriminator. Separation of the prompt and delayed components is a two-stage process. Pulses produced while the chopper is blocking the exciting beam are stored in one counter, the contents of which are a measure of the delayed emission. Pulses produced while the chopper is open are stored in another counter. The contents of this counter represent contributions of both prompt and delayed emissions. The contents of both counters are transferred to a computer for postexperimental deconvolution of the fluorescence and phosphorescence. Since the two components are measured simultaneously, the ratio of phosphorescence to fluorescence cannot be affected by changes in the sample as with sequential scans. The optical path, electronic amplification, and gating periods are identical so fluorescence and phosphorescence are measured with equal efficiency. This two-step method of signal processing recovers data which are lost in other arrangements.

Use of CORBA in the PHENIX distributed online computing system

The PHENIX online control system is responsible for the configuration, control and monitoring of the PHENIX detector data acquisition system and ancillary control hardware, and the collection and archiving of the event data. The detector consists of 11 distinct subsystems, which are distributed physically and partitioned logically while ultimately being combined into a single operating unit. The online system consists of a large number of embedded commercial and custom processors as well as custom software processes which are involved in the collection, monitoring and control of the detector and the event data. These processing elements are distributed over a diverse set of computing platforms including VME based Power PC controllers, Pentium based NT systems, and SUN Solaris SPARC processors. CORBA has been adopted as the standard communication mechanism for PHENIX online system. This paper will describe the design, implementation and use of CORBA to achieve a uniform and platform independent control environment while providing for the access, control and monitoring of the online detector elements over the distributed and diverse control environment. Synchronous and asynchronous communication issues will be discussed as well as the development of CORBA compliant components which were developed to achieve client/server isolation and deterministic system behavior. The use and interaction between JAVA based clients and C++ based CORBA servers to further achieve a platform neutral environment will be presented.

The PHENIX Online Computing System

The Online Computing System (ONCS) is responsible for the overall configuration and control of the PHENIX detector system. The experiment is made up of 4 spectrometer arms with a total number of 11 subdetectors, which need to be operated by a single control and monitoring system. This includes the configuration of the individual components of the readout system, as well as the control of the state of the detectors data flow. Furthermore, the ONCS system sets up the environment for the online monitoring of the detectors. The slow control of high voltages and other ancillary devices is also part of the system. The ONCS system is designed around a distributed computing model which relies on CORBA object oriented technology, the ROOT system as the backbone of the online monitoring, and EPICS for the control of the high voltage systems. Issues regarding the use and implementation of these technologies in the ONCS system will be discussed, as well as the methods used to control the state and health of the PHENIX detector.

PHENIX on-line distributed computing system architecture*

Abstract PHENIX is one of the two large experiments at the Relativistic Heavy Ion Collider (RHIC) currently under construction at Brookhaven National Laboratory. The detector consists of 11 subdetectors, that are further subdivided into 29 units (“granules”) that can be operated independently, which includes simultaneous data taking with independent data streams and independent triggers. The detector has 250 000 channels and is read out by front-end modules, where the data is buffered in a pipeline while awaiting the level 1 trigger decision. Zero suppression and calibration is done after the level 1 accept in custom built data collection modules (DCMs) with DSPs before the data is sent to an event builder (design throughput of 2 Gb/sec) and higher level triggers. The On-line Computing Systems Group (ONCS) has two responsibilities. Firstly, it is responsible for receiving the data from the event builder, routing it through a network of workstations to consumer processes and archiving it at a data rate of 20 MB/sec. Secondly, it is also responsible for the overall configuration, control and operation of the detector and data acquisition chain, which comprises the software integration for several thousand custom built hardware modules. The software must furthermore support the independent operation of the above mentioned granules, which includes the coordination of processes that run in 60–100 VME processors and workstations. ONCS has adapted the Shlaer—Mellor Object Oriented Methodology for the design of the top layer software. CORBA is used as communication layer between the distributed objects, which are implemented as asynchronous finite state machines. We will give an overview of the PHENIX online system with the main focus on the system architecture, software components and integration tasks of the On-line Computing group ONCS and report on the status of the current prototypes.

Cold nuclear matter effects on J/{psi} production as constrained by deuteron-gold measurements at {radical}(s{sub NN})=200 GeV

We present a new analysis of J/psi production yields in deuteron-gold collisions at sqrt(s_NN) = 200 GeV using data taken by the PHENIX experiment in 2003 and previously published in [S.S. Adler et al., Phys. Rev. Lett 96, 012304 (2006)]. The high statistics proton-proton J/psi data taken in 2005 is 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) break-up cross-section is added. Breakup cross sections of sigma_breakup = 2.8^[+1.7_-1.4] (2.2^[+1.6_-1.5]) 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.

Single Electrons from Heavy-Flavor Decays in p+p Collisions at {radical}(s)=200 GeV

The invariant differential cross section for inclusive electron production in p+p collisions at [FORMULA: SEE TEXT] has been measured by the PHENIX experiment at the BNL Relativistic Heavy Ion Collider over the transverse momentum range 0.4<or=pT<OR=5.0 GeV/c in the central rapidity region ([FORMULA: SEE TEXT]). The contribution to the inclusive electron spectrum from semileptonic decays of hadrons carrying heavy flavor, i.e., charm quarks or, at high , bottom quarks, is determined via three independent methods. The resulting electron spectrum from heavy-flavor decays is compared to recent leading and next-to-leading order perturbative QCD calculations. The total cross section of charm quark-antiquark pair production is determined to be [FORMULA: SEE TEXT].

Measurement of Identified {pi}{sup 0} and Inclusive Photon Second-Harmonic Parameter v{sub 2} and Implications for Direct Photon Production in {radical}(s{sub NN})=200 GeV Au+Au

The azimuthal distribution of identified pi^0 and inclusive photons has been measured in sqrt{s_{NN}} = 200 GeV Au+Au collisions with the PHENIX experiment at the Relativistic Heavy Ion Collider (RHIC). The second harmonic parameter (v_2) was measured to describe the observed anisotropy of the azimuthal distribution. The measured inclusive photon v_2 is consistent with the value expected for the photons from hadron decay and is also consistent with the lack of direct photon signal over the measured p_T range 1-6 GeV/c. An attempt is made to extract v_2 of direct photons.

Common Suppression Pattern of {eta} and {pi}{sup 0} Mesons at High Transverse Momentum in Au+Au Collisions at {radical}(s{sub NN})=200 GeV

Inclusive transverse momentum spectra of eta mesons have been measured within p(T)=2-10 GeV/c at midrapidity by the PHENIX experiment in Au+Au collisions at root s(NN) = 200 GeV. In central Au+Au the eta yields are significantly suppressed compared to peripheral Au+Au, d+Au, and p+p yields scaled by the corresponding number of nucleon-nucleon collisions. The magnitude, centrality, and p(T) dependence of the suppression is common, within errors, for eta and pi(0). The ratio of eta to pi(0) spectra at high p(T) amounts to 0.40 < R-eta/pi(0)< 0.48 for the three systems, in agreement with the world average measured in hadronic and nuclear reactions and, at large scaled momentum, in e(+)e(-) collisions.