HERA-B Experiment Research Articles

The Muon Detector at the HERA-B experiment

The HERA-B experiment is designed to study beauty particle production and decay using the HERA 920 GeV proton beam interactions with an internal target. The Muon detector provides identification for muons having momenta greater than 5 GeV/c and triggering on the muon pair from J/ ψ decay. Three different chamber types are employed for operation in a high-rate environment. The overall design, performance and current status are discussed.

Experience with HERA-B vertexing

The reconstruction of the decay vertices of long-lived particles like B mesons and their separation from the primary interaction is one of the primary tasks at the HERA-B experiment. Using data collected in the year 2000, the design and performance of the silicon vertex detector are reviewed. Results from track and vertex reconstruction are presented.

The electromagnetic calorimeter of the HERA-B experiment

The electromagnetic calorimeter of the HERA-B experiment employs the “shashlik” technology of sampled scintillator/tungsten(lead) sandwiches readout by photomultipliers. In this paper, we present a general overview of the system and the present results on energy and spatial resolution. The performances of the fast electron pre-trigger system are quoted as well.

The Inner Tracker of HERA-B

The Inner Tracker for the HERA-B experiment consists of 136 micro-strip gas chambers (MSGC) with a pre-amplifying device in the gas volume, the gas electron multiplier (GEM). The 102 000 detector channels are read out with the Helix128 ASIC. The HERA-B Inner Tracker is the first large-scale system using this detector technology in a high-rate hadronic environment comparable to LHC conditions.

Status and prospects of the HERA-B experiment

HERA-B is a fixed target experiment at the 920 GeV HERA proton storage ring. The main physics goal of the experiment is the measurement of CP violation in the B-meson system. This article describes the design of the HERA-B experiment, its physics potential and the actual commissioning status.

The HERA-B vertex detector

The design of the vertex detector of the HERA-B experiment at DESY is reviewed, and its components are described. The silicon microstrip detectors were optimized for radiation hardness: results from irradiation tests, reproducing the challenging situation in the experiment, are presented. Since spring 1999, much of the system has been installed and is operational. The detector performance and results from track and vertex reconstruction are presented.

The HERA-B vertex detector system

The HERA-B experiment is being built to measure CP violation in the B-system using internal targets at the HERA proton storage ring at DESY. This paper presents an overview of its vertex detector which – apart from an additional superlayer – is realized by a system of 20 Roman pots containing seven superlayers of double-sided silicon microstrip detectors that are operated at 10 mm distance from the proton beam in a high-radiation environment.

High-P T trigger for HERA-B experiment

The high-P T trigger provides valuable extension for the physics capabilities of HERA-B fixed target experiment. Trigger performs fast and effective selection of various B meson decay modes important for CP violation and B s mixing rate measurements. HERA-B high-P T trigger is built up of three layers of gas detectors placed inside the magnet area. Tests with full-scale detector modules have been done in real conditions. The installation of trigger components in the HERA-B detector is nearly completed.

The HERA-B RICH

The design issues and tests carried out with the ring imaging Cherenkov detector for the HERA-B experiment are reviewed. Results of on-the-bench tests of the employed photomultiplier tubes are reported together with the early commissioning measurements with the HERA proton beam.

Status of the HERA-B vertex detector

The HERA-B experiment is a forward magnetic spectrometer with good particle identification for hadrons and leptons designed to study violation of CP symmetry in the neutral B meson system. The silicon vertex detector operates in a high-rate environment similar to the ones expected at LHC. In this paper we report on our R&D on strip detector design, frontend ASICs, mechanical and thermal engineering, low-mass RF shielding of the HERA proton beam and on the status of our reconstruction software. First experiences with last year's installation are discussed.

The MUON system in the HERA-B experiment

The HERA-B experiment is designed to study CP-violation phenomena in the B-system. B-mesons are produced in interactions of 920 GeV/c beam halo protons with an internal target. The muon system serves to identify muons with momenta greater than 5 GeV/c . Unambiguous muon identification plays a key role for CP violation studies as well as for other important topics of the HERA-B physics program. The overall design of the muon system, the expected and measured performance, and the current status are presented.

Status of the outer tracker for the Hera-B experiment

The outer tracker system of the Hera-B experiment is composed of large size, small diameter drift chambers operated with an Ar–CF 4–CO 2 (65–30–5) gas mixture. The general layout and details of module construction are described. An intensive R&D program has been carried out to ascertain the long-term behaviour of honeycomb modules under irradiation; results of irradiated prototypes are presented. A set of operational conditions, gas mixture, clean assembly materials and adequate production techniques have been found which ensure proper operation of the outer tracker during several years in the harsh Hera-B environment.

HERA-B: trigger system

The HERA-B experiment at DESY, Germany, analyzes interactions of 920 GeV protons with a fixed target to measure CP violation. The production rates of the decays of interest are more than 10 orders of magnitude smaller than the rate of the background interactions. The HERA-B trigger system must be capable to reduce the high event rate of about 10 MHz to an event rate of about 20 Hz, which can be logged to tape. The implementation of the HERA-B trigger is a challenging task. The hardware and software are described, and an update on the progress at the time of the conference in the summer of 1999 is given.

The HERA-B ring imaging Cherenkov system – design and performance

The Ring Imaging Cherenkov detector of the HERA-B experiment at DESY has been completed in January of 1999. Data in its final configuration were taken recently. The HERA-B RICH uses C 4F 10 as radiator gas and a large 24 m 2 spherical mirror for imaging. The photon detector employs 2240 Hamamatsu multi-anode photomultipliers with a total of 27 000 channels. To match anode dimension (4.5 mm) and dispersion error and to solve the PMT packing problem we used a 2 : 1 reducing two-lens telescope in front of each PMT. The design performance of the RICH was fully reached: the average number of photons for a β=1 particle detected in the RICH was found to be 35.4; a single-photon resolution of 0.65 mrad was reached. We used stand-alone ring finding algorithms to measure the angle and β of tracks. With the position information of the target and that of clusters in the electromagnetic calorimeter we were able to identify electrons, pions, kaons and protons.

The electromagnetic calorimeter of the HERA-B experiment

The electromagnetic calorimeter of the HERA-B experiment is described. The main features of the calorimeter calibration procedure are also reported. Finally the first physics signals detected by the calorimeter in recent data taken during the commissioning of the installed HERA-B detector are described.

Multianode photomultipliers as position-sensitive detectors of single photons

Tests of 2300 Hamamatsu multianode photomultipliers (1543 pieces of R5900-M16 and 762 pieces of R5900-M4) have been tested on the bench in order to evaluate their performance for use as position-sensitive photon detectors in the ring imaging Cherenkov counter of the HERA-B experiment.1The groups responsible for the HERA-B RICH comprise: University of Texas at Austin, University of Barcelona, University of Coimbra, Portugal, Northwestern University, University of Houston, J. Stefan Institute and University of Ljubljana, Slovenia, with support from DESY and the University of Hamburg.1 A weak and stable source of photons has been obtained by Cherenkov radiation of electrons from a 90Sr source in a quartz radiator. From measurements of the count rate versus high voltage, optimal high-voltage values have been obtained as well as a parameter (RQE) corresponding to the relative quantum efficiency. Distributions of the number of photomultipliers as a function of the optimal high voltage and as a function of the relative quantum efficiency are presented. The measured parameters are in good correlation with those provided by the manufacturer. The stability of the photomultipliers has also been followed over two years. The observed count rate decrease is consistent with the radioactive decay of 90Sr.

Use of boundary-scan facilities for permanent control of part of the readout electronics of the HERA-B experiment

Special electronic devices which contain boundary-scan facilities that are compatible with the IEEE Standard 1149.1 and which were originally developed to facilitate the test of electronic equipment during board production offer also an excellent tool for permanent control of even large electronic systems. Here the control of a part of the electronics of a complex High-Energy Physics experiment is described.

Double-sided microstrip detectors for the high radiation environment in the HERA-B experiment

The design of the double-sided microstrip detectors for the HERA-B experiment at DESY is discussed, in particular with respect to the strong requirements imposed by the high radiation environment and by the challenging mechanical construction. The detectors are tested with an infrared laser setup and first results from operation in the experiment in 1997 are presented.

The muon pretrigger system of the HERA-B experiment

This paper describes the muon pretrigger system of the HERA-B experiment. The muon pretrigger is designed to detect track candidates for muons in order to generate seeds for the first level trigger (FLT) search algorithm. Muons provide the cleanest event signature in the large amount of hadronic background. In order to achieve the required precision the muon pretrigger system has to cope with an interaction rate of about 40 MHz at the HERA bunch crossing rate of 10.4 MHz. This results in a total input data rate of about 10 Gbyte/s. A total rate reduction by a factor of 200 is aimed at by the complete FLT, including the pretrigger systems (electromagnetic calorimeter, muon and high-p/sub T/), within at most 12 /spl mu/s.

An iterative method for the analysis of Cherenkov rings in the HERA-B RICH

A new method is presented for the analysis of data recorded with a Ring Imaging Cherenkov (RICH) counter. The method, an iterative sorting of hits on the photon detector, is particularly useful for events where rings overlap considerably. The algorithm was tested on simulated data for the HERA-B experiment.