The ATLAS tau trigger

The ATLAS tau trigger consists of three level trigger systems: the first one (L1) is hardware based and uses FPGAs, while the second (L2) and third levels (EF -Event Filter-) are software based and use commodity computers (2 x Intel Harpertown quad-core 2.5 GHz), running scientific linux 5. In this contribution, we discuss both the physics characteristics of tau leptons and the technical solutions to quick data access and fast algorithms. We show that L1 selects narrow jets in the calorimeter with an overall rejection against QCD jets of 300, whilst L2 and EF (referred together as High Level Trigger -HLT-) use all the detectors with full granularity and apply a typical rejection of 15 within the stringent timing requirements of the LHC. In the HLT there are two complementary approaches: specialized, fast algorithms are used at L2, while more refined and sophisticated algorithms, imported from the offline, are utilized in the EF

Synthesis of optically active half-sandwich complexes with bidentate and tridentate ligands

PN ligands 1 and 2, derived from 2-diphenylphosphanylmethylpyridine, were synthesized, to which in the backbone a tether to a cyclopentadiene system and for comparison an iPr substituent were attached. The chiral compounds were resolved by introduction of a menthoxy substituent into the 2-position of the pyridine system. The tripod ligand 1 contains three different binding sites (Cp, P, and N) connected by a resolved chiral carbon atom. (SC)-Configuration of this tripod ligand enforces (RRh)-configuration at the metal atom in the half-sandwich rhodium complex (LMent,SC,RRh)-4. The opposite metal configuration is inaccessible. Substitution of the chloro ligand in (LMent,SC,RRh)-4 by halide (Br, I) or pseudohalide (N3, CN, SCN) ligands occurs with retention of configuration. However, in the reaction of (LMent,SC,RRh)-4 with PPh3 the pyridine arm of the tripod ligand becomes detached from the metal atom. In the Cp*Rh and CpRh compounds of the bidentate PN ligands 2 and 3 both metal configurations are accessible and they equilibrate fast. The stereochemical assignments are corroborated by 4 X-ray analyses. Treatment of the chiral tripod ligand (LMent,SC)-CpH(PNMent) 1 with (Ph3P)3RuCl2 in ethanol afforded the two chiral-at-metal diastereomers (LMent,SC,RRu)- and (LMent,SC,SRu)-[Cp(PNMent)Ru(PPh3)Cl] (70% de) in which the cyclopentadienyl group and the P atom of the ligand coordinated at the metal center. The (LMent,SC,RRu)-diastereomer was isolated by crystallization from ethanol-pentane and its structure was established by X-ray crystallography. The (LMent,SC,RRu)-diastereomer epimerized in CDCl3 solution at 60 oC in a first-order reaction with a half-life of 56.6 h. In alcoholic solution epimerization occurred at room temperature. Substitution of the chloride ligand in (LMent,SC,RRu)- and (LMent,SC,SRu)- [Cp(PNMent)Ru(PPh3)Cl] by nitriles NCR (R = Me, Ph, CH2Ph) in the presence of NH4PF6 gave mixtures of the diastereomers (LMent,SC,RRu)- and (LMent,SC,SRu)-[Cp(PNMent)Ru(PPh3)NCR]PF6. Treatment of (LMent,SC,RRu)- and (LMent,SC,SRu)-[Cp(PNMent)Ru(PPh3)Cl] with piperidine or morpholine in the presence of NH4PF6 led to the chiral-at-metal diastereomers (LMent,SC,RRu)- and (LMent,SC,SRu)-[Cp(PNMent)Ru(PPh3)NH3]PF6 (6% de). The chiral-at-metal diastereomers (RRu,RC)- and (SRu,RC)-[CpRu(P-P�)Hal], P-P� = (R)-Prophos and (R,R)-Norphos, Hal = Cl, Br, and I, were synthesized, separated, and characterized by X-ray crystallography. In particular, the compounds (RRu,RC)- and (SRu,RC)-[CpRu(Prophos)Cl] were investigated which had been the starting material in the preparation of many new compounds with retention of the Ru-configuration. Erroneously, in the 1980�s these compounds had been considered to be configurationally stable at the metal atom. Halide exchange reactions and epimerization studies were carried out in methanol/chloroform mixtures. The rate determining step in these reactions was the dissociation of the Ru-Hal bond in (RRu,RC)- and (SRu,RC)-[CpRu(P-P�)Hal] forming the 16-electron intermediates (RRu,RC)- and (SRu,RC)-[CpRu(P-P�)]+ which maintain their pyramidal structures. The Hal exchange reactions proceeded at 0 - 20 oC in first-order kinetics with half-lives of minutes/hours and occurred with predominant retention of the metal configuration accompanied by partial epimerization at the metal atom. Interestingly, the thermodynamically less stable (RRu,RC)-diastereomer of [CpRu(Prophos)Cl] reacted about ten times faster then the thermodynamically more stable (SRu,RC)-diastereomer. The change of the metal configuration in the epimerization of (RRu,RC)- and (SRu,RC)-[CpRu(P-P�)Hal] took place in methanol containing solvents about 50 oC in first-order reactions with half-lives of minutes/hours. In CDCl3/CD3OD mixtures the equilibrium composition (RRu,RC)-/(SRu,RC)-[CpRu(Prophos)Cl] was 15:85. The rates of Hal exchange and epimerization increased by a factor of about 10 in going from CDCl3/CD3OD 9:1 to 1:1 due to better solvation of the ions formed in the rate-determining step. Hal exchange reactions and epimerization studies indicated a high pyramidal stability of the 16-electron fragments (RRu,RC)- and (SRu,RC)-[CpRu(P-P�)]+ towards inversion. This is surprising because calculations had shown that 16-electron fragments [CpM(PH3)2]+ with P-M-P angles around 100 o should have planar structures. Obviously, pyramidality of the fragments [CpRu(P-P�)]+ is enforced by the small P-Ru-P angles of 82 - 83 o observed in the X-ray analyses of the chelate compounds (RRu,RC)- and (SRu,RC)-[CpRu(P-P�)Hal]. These small angles resist planarization of the intermediates (RRu,RC)- and (SRu,RC)-[CpRu(P-P�)]+ and thus inversion of the metal configuration. The results are in accord with a basilica-type energy profile which has a relatively high barrier between the pyramidal intermediates (RRu,RC)- and (SRu,RC)-[CpRu(P-P�)]+ (Schemes 4-3 and 4-4)

New Method for Reconstructing Effective Top Quark Spin

We propose a new method for reconstructing an effective spin direction of a semi-leptonically decayed top quark. The method is simple: for instance, it does not require the spin information of the antitop quark in a ttbar event. The reconstructed effective spin is expected to be useful in hadron collider experiments. We demonstrate its usefulness in an analysis of the top decay vertex.Comment: 10 pages, 6 figures; one reference added; version to appear in Phys.Lett.

Search for Anomalous Couplings in Top Decay at Hadron Colliders

We present a quantitative study on sensitivities to the top-decay anomalous couplings, taking into account realistic experimental conditions expected at Tevatron and LHC. A double angular distribution of W and charged lepton in the top decay is analyzed, using ttbar events in the lepton+jets channel. In order to improve sensitivities to the anomalous couplings, we apply two techniques: (1) We use a likelihood fitting method for full kinematical reconstruction of each top event. (2) We develop a new effective spin reconstruction method for leptonically-decayed top quarks; this method does not require spin information of the antitop side. For simplicity, we neglect couplings of right-handed bottom quark as well as CP violating couplings. The 95% C.L. estimated bound on a ratio of anomalous couplings reads -0.81 < f_2/f_1 < -0.70, -0.12<f_2/f_1<0.14 using 1000 reconstructed top events at Tevatron, while -0.74<f_2/f_1<-0.72, -0.01<f_2/f_1<0.01 is expected with 100k reconstructed top events at LHC, where only statistical errors are taken into account. A two-fold ambiguity in the allowed range remains when the number of events exceeds a few hundred.Comment: 21 pages, 15 figure