31218324
First results of an aging test of a full scale MWPC prototype for the LHCb muon system
Abstract Aging studies for a multi-wire proportional chamber of the LHCb muon system have been performed using the CERN Gamma Irradiation Facility. The irradiated four-gap chamber corresponds to a full-size prototype with 1500 cm 2 sensitive area and has been operated with an Ar/CO 2 /CF 4 (40:50:10) gas mixture. A linear charge of ∼0.25 C/cm for 100 m anode wire length has been accumulated over a period of 6 months, which corresponds to the charge collected in 5 LHCb years. The observed aging effects do not prohibit the use of these chambers in the LHCb experiment.
122048635
Time resolution limits of the MWPCs for the LHCb muon system
Abstract Detailed simulations of the timing properties of the Multi-Wire-Proportional-Chambers of the LHCb muon system are compared with actual measurements. The simulated time resolution is in good agreement with the measurement which allows to study the resolution limiting parameters like diffusion, charge deposit fluctuations, cluster position fluctuations, electronics noise, track position and wire spacing to show how they affect the performance of the system. Methods to improve the time resolution of the muon chambers are discussed.
119113679
Search for CP violation in the decay $D^+ \to \pi^-\pi^+\pi^+$
A search for CP violation in the phase space of the decay $D^+\to\pi^-\pi^+\pi^+$ is reported using $pp$ collision data, corresponding to an integrated luminosity of 1.0 fb$^{-1}$, collected by the LHCb experiment at a centre-of-mass energy of 7 TeV. The Dalitz plot distributions for $3.1\times 10^6$ $D^+$ and $D^-$ candidates are compared with binned and unbinned model-independent techniques. No evidence for CP violation is found.
122081812
Study of $\eta-\eta^{\prime}$ mixing from measurement of $B^0_{(s)} \rightarrow J/\psi \eta^{(\prime)}$ decay rates
A study of $B^0$~and $B^0_s$ meson decays into $J/\psi\eta$~and $J/\psi\eta^{\prime}$ final states is performed using a data set of proton-proton collisions at centre-of-mass energies of 7 and 8TeV, collected by the LHCb experiment and corresponding to 3.0fb$^{-1}$ of integrated luminosity. The decay $B^0 \rightarrow J/\psi \eta^{\prime}$ is observed for thefirst time. The following ratios of branching fractions are measured: $$ \frac{\mathcal{B}(B^0 \rightarrow J/\psi \eta^{\prime})}{\mathcal{B}(B^0_s \rightarrow J/\psi \eta^{\prime})} = (2.28\pm0.65\,(stat)\,\pm0.10\,(syst)\,\pm0.13\,(f_{s}/f_{d}))\times10^{-2},$$ $$ \frac{\mathcal{B}(B^0 \rightarrow J/\psi \eta)}{\mathcal{B}(B^0_s \rightarrow J/\psi \eta)} = (1.85\pm0.61\,(stat)\,\pm0.09\,(syst)\,\pm0.11\,(f_{s}/f_{d}))\times10^{-2},$$ where the third uncertainty is related to the present knowledge of $f_{s}/f_{d}$, the ratio between the probabilities for a $b$ quark to form a $B^0_s$ or $B^0$ meson. The branching fraction ratios are used to determine the parameters of $\eta-\eta^{\prime}$ meson mixing. In addition, the first evidence for the decay $B^0_s \rightarrow \psi(2S) \eta^{\prime}$ is reported, and the relative branching fraction is measured, 
$$\frac{\mathcal{B}(B^0_s \rightarrow \psi(2S) \eta^{\prime})}{\mathcal{B}(B^0_s \rightarrow J/\psi \eta^{\prime})} = (38.7\pm9.0\,(stat)\,\pm1.3\,(syst)\,\pm0.9(\mathcal{B}))\times10^{-2},$$ 
where the third uncertainty is due to the limited knowledge of the branching fractions of $J/\psi$ and $\psi(2S)$~mesons.
18491403
Study of beauty hadron decays into pairs of charm hadrons
First observations of the decays Λb 0 → Λc +D(s) - are reported using data corresponding to an integrated luminosity of 3fb-1 collected at 7 and 8 TeV center-of-mass energies in proton-proton collisions with the LHCb detector. In addition, the most precise measurement of the branching fraction B(Bs 0→D+Ds -) is made and a search is performed for the decays B(s) 0→Λc +Λc -. The results obtained are B(Λb 0→Λc +D-)/ B(Λb 0→Λc +D s -)=0.042±0.003(stat)±0.003(syst), [B(Λb 0→Λc +D s -)/B(B0→D+D s -)]/[B(Λb 0→Λ c +π-)/B(B0→D +π-)]=0.96±0.02(stat)±0.06(syst),B(B s 0→D+Ds -)/ B(B0→D+Ds -)=0. 038±0.004(stat)±0.003(syst),B(B0→Λ c +Λc -)/B(B 0→D+Ds -)<0.0022[95%C.L.], B(Bs 0→Λc +Λ c -)/B(Bs 0→D+D s -)<0.30[95%C.L.]. Measurement of the mass of the Λb 0 baryon relative to the B0 meson gives M(Λb 0)-M(B0)=339. 72±0.24(stat)±0.18(syst)MeV/c2. This result provides the most precise measurement of the mass of the Λb 0 baryon to date.
119287240
Searches for Majorana neutrinos in $B^-$ decays
Searches for heavy Majorana neutrinos in B- decays in final states containing hadrons plus a \mu- \mu- pair have been performed using 0.41/fb of data collected with the LHCb detector in proton-proton collisions at a center-of-mass energy of 7 TeV. The D+ \mu- \mu- and D*+ \mu- \mu- final states can arise from the presence of virtual Majorana neutrinos of any mass. Other final states containing \pi+, Ds+, or D0\pi+ can be mediated by an on-shell Majorana neutrino. No signals are found and upper limits are set on Majorana neutrino production as a function of mass, and also on the B- decay branching fractions.
16885865
Studies of aging and HV break down problems during development and operation of MSGC and GEM detectors for the inner tracking system of HERA-B
Abstract The results of 5 years of development of the inner tracking system of the HERA-B experiment and first experience from the data taking period of the year 2000 are reported. The system contains 184 chambers, covering a sensitive area of about (20×20) cm 2 each. The detector is based on microstrip gas counters (MSGCs) with diamond-like coated (DLC) glass wafers and gas electron multipliers (GEMs). The main problems in the development phase were gas discharges in intense hadron beams and aging in a high radiation dose environment. The observation of gas discharges which damage the electrode structure of the MSGC led to the addition of the GEM as a first amplification step. Spurious sparking at the GEM cannot be avoided completely. It does not affect the GEM itself but can produce secondary damage of the MSGC if the electric field between the GEM and the MSGC is above a threshold depending on the operation conditions. We observed that aging does not only depend on the dose but also on the spot size of the irradiated area. Ar–DME mixtures had to be abandoned whereas a mixture of 70% Ar and 30% CO 2 showed no serious aging effects up to about 40 mC /cm deposited charge on the anodes. X-ray measurements indicate that the DLC of the MSGC is deteriorated by the gas amplification process. As a consequence, long-term gain variations are expected. The Inner Tracker has successfully participated in the data taking at HERA-B during summer 2000.
33575635
GRB 011121: A Massive Star Progenitor
Of the cosmological gamma-ray bursts, GRB 011121 has the lowest redshift, z = 0.36. More importantly, the multicolor excess in the afterglow detected in the Hubble Space Telescope (HST) light curves is compelling observational evidence of an underlying supernova. Here we present near-infrared and radio observations of the afterglow, and from our comprehensive afterglow modeling, we find evidence favoring a wind-fed circumburst medium. Lacking X-ray data, we are unable to conclusively measure the mass-loss rate, , but obtain an estimate, ~ 2 × 10-7/vw3 M☉ yr-1, where vw3 is the speed of the wind from the progenitor in units of 103 km s-1. This is similar to that inferred for the progenitor of the Type Ibc supernova SN 1998bw that has been associated with the peculiar burst GRB 980425. Our data, taken in conjunction with the HST results of Bloom et al., provide a consistent picture: the long-duration GRB 011121 had a massive star progenitor that exploded as a supernova at about the same time as the gamma-ray burst event. Finally, we note that the gamma-ray profile of GRB 011121 is similar to that of GRB 980425.
119238071
SkyMapper Filter Set: Design and Fabrication of Large-Scale Optical Filters
ABSTRACT.The SkyMapper Southern Sky Survey will be conducted from Siding Spring Observatory with uu, vv, gg, rr, ii, and zz filters that comprise glued glass combination filters with dimensions of 309 × 309 × 15 mm309×309×15  mm. In this article we discuss the rationale for our bandpasses and physical characteristics of the filter set. The uu, vv, gg, and zz filters are entirely glass filters, which provide highly uniform bandpasses across the complete filter aperture. The ii filter uses glass with a short-wave pass coating, and the rr filter is a complete dielectric filter. We describe the process by which the filters were constructed, including the processes used to obtain uniform dielectric coatings and optimized narrowband antireflection coatings, as well as the technique of gluing the large glass pieces together after coating using UV transparent epoxy cement. The measured passbands, including extinction and CCD QE, are presented.
55842612
A long-term aging study of honeycomb drift tubes for the HERA-B Outer Tracker using a circulated and purified CF4 gas mixture
Abstract The Outer Tracker of HERA-B uses a gas mixture containing CF 4 to obtain high electron drift velocities. The high cost of this gas makes it necessary to circulate the gas mixture which must then be purified to avoid accumulation of air and pollutants. However, the usage of gas purifiers poses the danger of outgassing pollutants from the purifiers themselves into the gas stream. Purifiers could also be attacked chemically by the aggressive products from the cracking of CF 4 molecules in the plasma avalanches of the detector. This could potentially release further harmful pollutants into the gas stream. To test for such effects, a long-term irradiation study of about 3000 h was carried out with the honeycomb drift tubes that are used in the Outer Tracker. This provided a check of the long-term stability of the gas purifiers before putting them into operation for the full-size detector. We report on the experimental setup, procedures and the results obtained.
49382443
EXPERIMENTAL DETERMINATION OF THE TIMING STABILITY OF THE OPTICAL SYNCHRONIZATION SYSTEM AT FLASH
An optical, long-term stable synchronization system with an accuracy of better than 10 fs is presently being installed at the free electron laser FLASH. A periodic laser pulse train from a mode-locked, erbium-doped fiber laser is distributed via length stabilized fiber links. In this paper, we present measurements of the timing stability of the optical distribution system. Two bunch arrival time monitors (BAMs) are used to measure the electron bunch arrival times at two positions in the linac, separated by 60m. Each BAM is supplied with fiber laser pulses by its own fiber link. By correlating the measured arrival times of the same electron bunches, the overall performance of the optical distribution system and the BAMs can be evaluated. A resolution and timing stability of better than 10 fs has been achieved.