Decays Z' -> \gamma\gamma\gamma{} and Z -> \gamma\gamma\gamma{} in the minimal 331 model

The possibility of a significant effect of exotic particles on the Z'->\gamma\gamma\gamma{} and Z->\gamma\gamma\gamma{} decays is investigated in the context of the minimal 331 model. This model, which is based in the SU_C(3)xSU_L(3)xU_X(1) gauge group, predicts the existence of many exotic charged particles that can significantly enhance the decay widths. It is found that the standard model prediction for the Z->\gamma\gamma\gamma{} decay remains essentially unchanged, as the new physics effects quickly decouples. On the other hand, it is found that the contributions of the new exotic quarks and gauge bosons predicted by this model lead to a branching fraction for the Z'->\gamma\gamma\gamma{} decay of about 10^(-6), which is about three orders of magnitude larger than that of the Z->\gamma\gamma\gamma{} decay.Comment: 20 pages and 20 figure

Electric dipole and magnetic quadrupole moments of the WW boson via a CP-violating HWWHWW vertex in effective Lagrangians

The possibility of nonnegligible $W$ electric dipole ($\widetilde{\mu}_W$) and magnetic quadrupole ($\widetilde{Q}_W$) moments induced by the most general $HWW$ vertex is examined via the effective Lagrangian technique. It is assumed that new heavy fermions induce an anomalous CP-odd component of the $HWW$ vertex, which can be parametrized by an $SU_L(2)\times U_Y(1)$-invariant dimension-six operator. This anomalous contribution, when combined with the standard model CP-even contribution, lead to CP-odd electromagnetic properties of the $W$ boson, which are characterized by the form factors $\Delta \widetilde{\kappa}$ and $\Delta \widetilde{Q}$. It is found that $\Delta \widetilde{\kappa}$ is divergent, whereas $\Delta \widetilde{Q}$ is finite, which reflects the fact that the latter cannot be generated at the one-loop level in any renormalizable theory. Assuming reasonable values for the unknown parameters, we found that $\widetilde{\mu}_W\sim 3-6\times 10^{-21}$ e-cm, which is eight orders of magnitude larger than the SM prediction and close to the upper bound derived from the neutron electric dipole moment. The estimated size of the somewhat less-studied $\widetilde{Q}_W$ moment is of the order of $-10^{-36}$ e-cm^2, which is fifteen orders of magnitude above the SM contribution.Comment: 7 pages, 6 figures, REVTEX styl

NrcR, a new transcriptional regulator of Rhizobium tropici CIAT 899 involved in the Legume root-nodule symbiosis.

The establishment of nitrogen-fixing rhizobium-legume symbioses requires a highly complex cascade of events. In this molecular dialogue the bacterial NodD transcriptional regulators in conjunction with plant inducers, mostly flavonoids, are responsible for the biosynthesis and secretion of Nod factors which are key molecules for successful nodulation. Other transcriptional regulators related to the symbiotic process have been identified in rhizobial genomes, including negative regulators such as NolR. Rhizobium tropici CIAT 899 is an important symbiont of common bean (Phaseolus vulgaris L.), and its genome encompasses intriguing features such as five copies of nodD genes, as well as other possible transcriptional regulators including the NolR protein. Here we describe and characterize a new regulatory gene located in the non-symbiotic plasmid pRtrCIAT899c, that shows homology (46% identity) with the nolR gene located in the chromosome of CIAT 899. The mutation of this gene, named nrcR (nolR-like plasmid c Regulator), enhanced motility and exopolysaccharide production in comparison to the wild-type strain. Interestingly, the number and decoration of Nod Factors produced by this mutant were higher than those detected in the wildtype strain, especially under salinity stress. The nrcR mutant showed delayed nodulation and reduced competitiveness with P. vulgaris, and reduction in nodule number and shoot dry weight in both P. vulgaris and Leucaena leucocephala. Moreover, the mutant exhibited reduced capacity to induce the nodC gene in comparison to the wild-type CIAT 899. The finding of a new nod-gene regulator located in a non-symbiotic plasmid may reveal the existence of even more complex mechanisms of regulation of nodulation genes in R. tropici CIAT 899 that may be applicable to other rhizobial species

Regulatory nodD1 and nodD2 genes of Rhizobium tropici strain CIAT 899 and their roles in the early stages of molecular signaling and host-legume nodulation.

Nodulation and symbiotic nitrogen fixation are mediated by several genes, both of the host legume and of the bacterium. The rhizobial regulatory nodD gene plays a critical role, orchestrating the transcription of the other nodulation genes. Rhizobium tropici strain CIAT 899 is an effective symbiont of several legumes?with an emphasis on common bean (Phaseolus vulgaris)?and is unusual in carrying multiple copies of nodD, the roles of which remain to be elucidated. Results: Phenotypes, Nod factors and gene expression of nodD1 and nodD2 mutants of CIAT 899 were compared with those of the wild type strain, both in the presence and in the absence of the nod-gene-inducing molecules apigenin and salt (NaCl). Differences between the wild type and mutants were observed in swimming motility and IAA (indole acetic acid) synthesis. In the presence of both apigenin and salt, large numbers of Nod factors were detected in CIAT 899, with fewer detected in the mutants. nodC expression was lower in both mutants; differences in nodD1 and nodD2 expression were observed between the wild type and the mutants, with variation according to the inducing molecule, and with a major role of apigenin with nodD1 and of salt with nodD2. In the nodD1 mutant, nodulation was markedly reduced in common bean and abolished in leucaena (Leucaena leucocephala) and siratro (Macroptilium atropurpureum), whereas a mutation in nodD2 reduced nodulation in common bean, but not in the other two legumes. Conclusion: Our proposed model considers that full nodulation of common bean by R. tropici requires both nodD1 and nodD2, whereas, in other legume species that might represent the original host, nodD1 plays the major role. In general, nodD2 is an activator of nod-gene transcription, but, in specific conditions, it can slightly repress nodD1. nodD1 and nodD2 play other roles beyond nodulation, such as swimming motility and IAA synthesis

Density and expansion effects on pion spectra in relativistic heavy-ion collisions

We compute the pion inclusive momentum distribution in heavy-ion collisions at AGS energies, assuming thermal equilibrium and accounting for density and expansion effects at the time of decoupling. We compare to data on mid rapidity charged pions produced in central Au + Au collisions and find a very good agreement. The shape of the distribution at low $m_t-m$ is explained in part as an effect arising from the high mean pion density achieved in these reactions. The difference between the positive and negative pion distributions in the same region is attributed in part to the different average yields of each kind of charged pions.Comment: Minor changes, typo in Fig. 2b corrected, version to appear in Phys. Rev.

Characteristics of the ALICE Silicon Drift Detector

A Silicon Drift Detector (SDD) with an active area of 7.0 x 7.5 cm2 has been designed, produced and tested for the ALICE Inner Tracking System. The development of the SDD has been focussed on the capability of the detector to work without an external support to the integrated high voltage divider. Severalfeatures have been implemented in the design in order to increase the robustness and the long-term electrical stability of the detector. One of the prototypes has been tested in a pion beam at the CERN SPS. Preliminary results on the position resolution are given

Recent Developments on the Silicon Drift Detector readout scheme for the ALICE Inner Tracking System

Proposal of abstract for LEB99, Snowmass, Colorado, 20-24 September 1999Recent developments of the Silicon Drift Detector (SDD) readout system for the ALICE Experiment are presented. The foreseen readout system is based on 2 main units. The first unit consists of a low noise preamplifier, an analog memory which continuously samples the amplifier output, an A/D converter and a digital memory. When the trigger signal validates the analog data, the ADCs convert the samples into a digital form and store them into the digital memory. The second unit performs the zero suppression/data compression operations. In this paper the status of the design is presented, together with the test results of the A/D converter, the multi-event buffer and the compression unit prototype.Summary:In the Inner Tracker System (ITS) of the ALICE experiment the third and the fourth layer of the detectors are SDDs. These detectors provide the measurement of both the energy deposition and the bi-dimensional position of the track. In terms of readout an SDD can be viewed as a matrix, where the rows are the detector anodes and the columns are the samples to be read during the drift time; therefore, a very large amount of data has to be amplified, converted in digital form and preprocessed in order to avoid the storage of non-significatn data.Since the electron mobility is a strong temperature function, detector temperature has to be kept constant; on the other hand, it is not possible to use very efficient cooling systems because the amount of material in this area is very limited, so the power budget for the electronic readout is very low (less than 6 mW/anode).The simplest solution would be to send the analog signals outside the sensitive area immediately after a preamplification; unfortunately, the ratio between the number of channels (around 200 000) and the space available is so high that the simple solution of sending all the SDD anodes output outside teh detector zone after a low-noise amplification is not practically manageable.Abstract:The adopted solution is based on three main units:(i) A front-end chip that performs low noise amplification, fast analog storage and A/D conversion(ii) A multi-event digital buffer for data derandomization(iii) A data compression/zero suppression and system control boardThe first two units are distributed on the ladders near the detectors and have stringent power and space requirements, while the third unit is placed at both ends of the ladders and in boxes placed on both ends of the TPC detector.The first unit is the most critical part of the system. It works as follows: the detector signals are continuously amplified, sampled and stored in the analog memory with a frequency of 40 MSamples/s The L0d trigger signal stops the write operation, while the L1 trigger signal starts the conversion phase. This phase will continue until the event data are stored in the event buffer if the L2y confirm trigger signal is received, or rejected if the L2n abort signal will be issued by the trigger system.Prototypes of the three parts have been designed and tested while the full chip is currently under design. Tests of the A/D converter will be presented.The multi-event buffer purpose is to de-randomize the even data in order to reduce the transmission speed. Preliminary tests of the first prototype will be presented.The board placed at the end of the ladders performs various functions. It reduces the amount of data through various cascaded algorithms with variable parameters and transmits the data to the SIU board. It also controls the test and slow control system for the ladder circuitry. Tests of the FPGA-based prototypes will be presented.Special care has been taken for the test problem. The ASICs designed are provided of a test control port based on teh IEEE 1149.1 JTAG standard. The same protocol is used for downloading configuration information

Test Results of the ALICE SDD Electronic Readout Prototypes

The first prototypes of the front-end electronics of the ALICE silicon driftdetectors have been designed and tested. The integrated circuits have been designed using state of the art technologies and, for the analog parts, with radiation-tolerantdesign techniques. In this paper, the test results of the building blocks of the PASCAL chip and the first prototype of the AMBRA chip are presented. The prototypes fully respect the ALICE requirements; owingto the use of deep-submicron technologies together with radiation-tolerant layout techniques, the prototypes have shown a toleranceto a radiation dose much higher than the one foreseen for the ALICE environment.(Abstract only available, full text to follow)

The Silicon Drift Detector readout scheme for the Inner Tracking System of the ALICE Experiment

Presentation at Quark Matter '99, Torino, Italy, 10-15 May 1999The Silicon Drift Detectors (SDDs) provide, through the measurement of the drift time of the charge deposited by the particle which crosses the detector, information on the impact point and on the energy deposition. The foreseen readout scheme is based on a single chip implementation of an integrated circuit that includes low-noise amplification, fast analog strorage and analog to digital conversion, thus avoiding the problems related to the analog signal transmission. A multi-event buffer that reduces the transmission bandwidth and a data compression/zero suppression unit complete the architecture.Abstract:In this paper, the system components design is described, together with the results of the first prototypes