281 research outputs found
Inelastic production of J/ψ mesons in photoproduction and deep inelastic scattering at HERA
A measurement is presented of inelastic photo- and electroproduction of J/ψ mesons in ep scattering at HERA. The data were recorded with the H1 detector in the period from 2004 to 2007. Single and double differential cross sections are determined and the helicity distributions of the J/ψ mesons are analysed. The results are compared to theoretical predictions in the colour singlet model and in the framework of non-relativistic QCD. Calculations in the colour singlet model using a k T factorisation ansatz are able to give a good description of the data, while colour singlet model calculations to next-to-leading order in collinear factorisation underestimate the data
Compact Frontend-Electronics and Bidirectional 3.3 Gbps Optical Datalink for Fast Proportional Chamber Readout
The 9600 channels of the multi-wire proportional chamber of the H1 experiment
at HERA have to be read out within 96 ns and made available to the trigger
system. The tight spatial conditions at the rear end flange require a compact
bidirectional readout electronics with minimal power consumption and dead
material.
A solution using 40 identical optical link modules, each transferring the
trigger information with a physical rate of 4 x 832 Mbps via optical fibers,
has been developed and commisioned. The analog pulses from the chamber can be
monitored and the synchronization to the global HERA clock signal is ensured.Comment: 13 pages, 10 figure
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
The results of five 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 cm2 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
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% CO2 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.Comment: 29 pages, 22 figure
New, high statistics measurement of the K+ -> pi0 e+ nu (Ke3) branching ratio
E865 at the Brookhaven National Laboratory AGS collected about 70,000 K+(e3)
events with the purpose of measuring the relative K+(e3) branching ratio. The
pi0 in all the decays was detected using the e+e- pair from pi0 -> e+e-gamma
decay and no photons were required. Using the Particle Data Group branching
ratios for the normalization decays we obtain
BR(K+(e3(gamma))=(5.13+/-0.02(stat)+/-0.09(sys)+/-0.04(norm))%, where
V_{us}$ element of the CKM matrix, and the matrix's
unitarity are discussed.Comment: 4 pages, 5 figures; final version accepted by PR
Search for QCD instanton-induced processes at HERA in the high- domain
Signals of QCD instanton-induced processes are searched for in neutral current deep-inelastic scattering at the electron-proton collider HERA in the kinematic region defined by the Bjorken-scaling variable x > 10−3, the inelasticity 0.2 < y < 0.7 and the photon virtuality 150 < Q2 < 15000 GeV2. The search is performed using H1 data corresponding to an integrated luminosity of 351 pb−1. No evidence for the production of QCD instanton-induced events is observed. Upper limits on the cross section for instanton-induced processes between 1.5 pb and 6 pb, at 95% confidence level, are obtained depending on the kinematic domain in which instantons could be produced. Compared to earlier publications, the limits are improved by an order of magnitude and for the first time are challenging predictions
Precise Measurement of pi+ -> e+ nu Branching Ratio
The PEN Collaboration is conducting a new measurement of the pi+ -> e+ nu
branching ratio at the Paul Scherrer Institute, with the goal uncertainty of
delta B/B(pie2)=5E-4 or lower. At present, the combined accuracy of all
published pie2 decay measurements lags behind the theoretical calculation by a
factor of 40. In this contribution we report on the PEN detector configuration
and its performance during two development runs done in 2007 and 2008.Comment: pdflatex, 11 pages, 5 figures, to be published in "Progress in
High-Energy Physics and Nuclear Safety", NATO Science for Peace Series: B -
Physics and Biophysic
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