- Email: [email protected]
Data acquisition, monitoring and control for the RICH detectors of LHCb
ARTICLE IN PRESS
Nuclear Instruments and Methods in Physics Research A 572 (2007) 20–21 www.elsevier.com/locate/nima
Data acquisition, monitoring and control for the RICH detectors of LHCb A. Van Lysebetten1 CERN, PH Department, 1211 Geneva 23, Switzerland Available online 29 November 2006
Abstract The Ring Imaging Cherenkov detectors of the LHCb experiment will offer a powerful tool for particle identification in the momentum range from 1 to 100 GeV=c. In order to achieve this, a thorough commissioning phase has now started spanning photon detector integration to offline alignment procedures. This paper will focus on alignment, detector monitoring and control issues, as well as data quality tests. The operation of the photon detectors, readout chain and data acquisition in the experimental environment will be covered. r 2006 Published by Elsevier B.V. PACS: 29.40.Ka Keywords: Ring Imaging Cherenkov detectors; Data acquisition; Monitoring
1. The RICH detectors of LHCb Particle identification is a crucial component of the LHCb experiment. In order to provide precision measurements of CP violation in the B sector, p=Kaon separation has to be efficient over the momentum range from 1 to 100 GeV=c. To provide this coverage over a wide polar angle range, LHCb has chosen a system consisting of two RICH detectors [1] using three different radiators. RICH1, installed upstream of the LHCb dipole magnet, is optimized for low to mid momentum tracks using aerogel and gaseous C4 F10 radiators. RICH2, located further downstream, has a single radiator medium ðCF4 Þ optimised to cover the higher momentum tracks. The main optical components for both RICH detectors have a similar geometry. A track traversing the radiator media will emit Cherenkov photons which are focussed by tilted spherical mirrors. Secondary flat mirrors are used to bring the photons out of the spectrometer acceptance. The design and construction of RICH1 is progressing well. RICH2 is already installed in the experimental area and all
1
E-mail address: [email protected]. On behalf of the LHCb RICH Collaboration.
0168-9002/$ - see front matter r 2006 Published by Elsevier B.V. doi:10.1016/j.nima.2006.10.345
flat and spherical mirrors have been aligned to a precision of 20 and 150 mrad, respectively, well within tolerance. A thorough commissioning phase has now started. This phase comprises validation of the readout chain, detector monitoring system and data-quality monitoring. These topics will be discussed in the next sections. 2. The readout chain The Cherenkov photons produced in the radiator materials are detected by pixel Hybrid Photon Detectors (HPDs) [2]. The HPD is a vacuum tube with a pixelated silicon detector anode assembly. Photoelectrons emitted from the photocathode are accelerated onto the anode assembly by a 20 kV cross-focussing electron optics. The HPDs are mounted on columns with the so-called Level-0 (L0) front-end electronics boards, the Low Voltage and the High Voltage distribution cards. The columns are installed in the magnetic shielding boxes of the two RICH detectors. Fig. 1 shows the column mounting scheme as for RICH2, which has 16 HPDs per column (14 HPDs per column for RICH1). The binary data from a pair of HPDs are transmitted to the corresponding L0 board via flexible kapton cables. The L0 boards receive their triggers and
ARTICLE IN PRESS A. Van Lysebetten / Nuclear Instruments and Methods in Physics Research A 572 (2007) 20–21
21
3. Monitoring the RICH 3.1. The Detector Control System The Detector Control System (DCS) [3] monitors the safe operation of the RICH detectors. The DCS monitors a large number of environmental parameters such as temperature, humidity, pressure and magnetic field. The system also monitors experimental parameters such as LV, HV and the HPD silicon bias voltages, the power supplies, gas and cooling. DCS also supervises the safety interlocks. Quality monitoring includes survey of mirror alignment, the transparency of the gas, and light leaks. 3.2. Data quality monitoring
Fig. 1. The layout of the RICH readout columns showing HPDs, L0 boards and LV and HV distribution cards.
40 MHz clock via the Trigger, Timing and Control (TTC) system. The L0 board, based on FPGA technology, synchronizes the data following a positive trigger decision and transmits the data to the so-called Level-1 (L1) board at 1.6 Gbit/s over optical data fibers. Since the L0 boards are mounted on-detector, the L0 electronics components need to be radiation tolerant. The L1 boards are 100 m away in the control room, hence standard components are used. The L1 boards reformat and zero-suppress the data and transmit at a rate of 1 MHz to the event building network and High Level Trigger. This transfer proceeds via an Ethernet 100 Mbit connection. Prior to data taking, the L0 and L1 boards need to be configured. The HPD pixel chips are configured through the L0 board, e.g. the setting of pixel thresholds and masks, and the timing. The L1 configuration sets the chip readout mode and zero-suppression properties.
Data quality monitoring (DQM) is complementary to the DCS system as a diagnostic tool. The DQM must give a timely feedback on the detector performance in order to allow fast action. The DQM for the RICH detectors includes the status of the 484 HPDs (e.g. the average occupancy and dark count rates), and the real-time reconstruction of refractive indices from ring radii. It is estimated that, with an event rate of 2 kHz at the High Level Trigger, detailed user feedback can be provided in about 100 s. 4. Results and prospects All components of the readout chain (from HPD to L1 boards) as well as a first prototype of the DCS system were tested successfully in the laboratory and in several beam tests [4]. All aspects of integration (e.g. column mounting and cooling) have been addressed. Installation of the populated columns in the experimental area will take place in late autumn 2006, and an in situ commissioning phase, including calibration and alignment, will then start. The RICH detectors will be ready for data-taking in 2007. References [1] [2] [3] [4]
The LHCb Collaboration, CERN/LHCC 2000-0037. M. Alemi, et al., Nucl. Instr. and Meth. A 449 (2000) 49. F. Fontanelli, IEEE NSS Conference Record, vol. 2, 2005, p. 765. T. Blake, these proceedings.
Nuclear Instruments and Methods in Physics Research A 572 (2007) 20–21 www.elsevier.com/locate/nima
Data acquisition, monitoring and control for the RICH detectors of LHCb A. Van Lysebetten1 CERN, PH Department, 1211 Geneva 23, Switzerland Available online 29 November 2006
Abstract The Ring Imaging Cherenkov detectors of the LHCb experiment will offer a powerful tool for particle identification in the momentum range from 1 to 100 GeV=c. In order to achieve this, a thorough commissioning phase has now started spanning photon detector integration to offline alignment procedures. This paper will focus on alignment, detector monitoring and control issues, as well as data quality tests. The operation of the photon detectors, readout chain and data acquisition in the experimental environment will be covered. r 2006 Published by Elsevier B.V. PACS: 29.40.Ka Keywords: Ring Imaging Cherenkov detectors; Data acquisition; Monitoring
1. The RICH detectors of LHCb Particle identification is a crucial component of the LHCb experiment. In order to provide precision measurements of CP violation in the B sector, p=Kaon separation has to be efficient over the momentum range from 1 to 100 GeV=c. To provide this coverage over a wide polar angle range, LHCb has chosen a system consisting of two RICH detectors [1] using three different radiators. RICH1, installed upstream of the LHCb dipole magnet, is optimized for low to mid momentum tracks using aerogel and gaseous C4 F10 radiators. RICH2, located further downstream, has a single radiator medium ðCF4 Þ optimised to cover the higher momentum tracks. The main optical components for both RICH detectors have a similar geometry. A track traversing the radiator media will emit Cherenkov photons which are focussed by tilted spherical mirrors. Secondary flat mirrors are used to bring the photons out of the spectrometer acceptance. The design and construction of RICH1 is progressing well. RICH2 is already installed in the experimental area and all
1
E-mail address: [email protected]. On behalf of the LHCb RICH Collaboration.
0168-9002/$ - see front matter r 2006 Published by Elsevier B.V. doi:10.1016/j.nima.2006.10.345
flat and spherical mirrors have been aligned to a precision of 20 and 150 mrad, respectively, well within tolerance. A thorough commissioning phase has now started. This phase comprises validation of the readout chain, detector monitoring system and data-quality monitoring. These topics will be discussed in the next sections. 2. The readout chain The Cherenkov photons produced in the radiator materials are detected by pixel Hybrid Photon Detectors (HPDs) [2]. The HPD is a vacuum tube with a pixelated silicon detector anode assembly. Photoelectrons emitted from the photocathode are accelerated onto the anode assembly by a 20 kV cross-focussing electron optics. The HPDs are mounted on columns with the so-called Level-0 (L0) front-end electronics boards, the Low Voltage and the High Voltage distribution cards. The columns are installed in the magnetic shielding boxes of the two RICH detectors. Fig. 1 shows the column mounting scheme as for RICH2, which has 16 HPDs per column (14 HPDs per column for RICH1). The binary data from a pair of HPDs are transmitted to the corresponding L0 board via flexible kapton cables. The L0 boards receive their triggers and
ARTICLE IN PRESS A. Van Lysebetten / Nuclear Instruments and Methods in Physics Research A 572 (2007) 20–21
21
3. Monitoring the RICH 3.1. The Detector Control System The Detector Control System (DCS) [3] monitors the safe operation of the RICH detectors. The DCS monitors a large number of environmental parameters such as temperature, humidity, pressure and magnetic field. The system also monitors experimental parameters such as LV, HV and the HPD silicon bias voltages, the power supplies, gas and cooling. DCS also supervises the safety interlocks. Quality monitoring includes survey of mirror alignment, the transparency of the gas, and light leaks. 3.2. Data quality monitoring
Fig. 1. The layout of the RICH readout columns showing HPDs, L0 boards and LV and HV distribution cards.
40 MHz clock via the Trigger, Timing and Control (TTC) system. The L0 board, based on FPGA technology, synchronizes the data following a positive trigger decision and transmits the data to the so-called Level-1 (L1) board at 1.6 Gbit/s over optical data fibers. Since the L0 boards are mounted on-detector, the L0 electronics components need to be radiation tolerant. The L1 boards are 100 m away in the control room, hence standard components are used. The L1 boards reformat and zero-suppress the data and transmit at a rate of 1 MHz to the event building network and High Level Trigger. This transfer proceeds via an Ethernet 100 Mbit connection. Prior to data taking, the L0 and L1 boards need to be configured. The HPD pixel chips are configured through the L0 board, e.g. the setting of pixel thresholds and masks, and the timing. The L1 configuration sets the chip readout mode and zero-suppression properties.
Data quality monitoring (DQM) is complementary to the DCS system as a diagnostic tool. The DQM must give a timely feedback on the detector performance in order to allow fast action. The DQM for the RICH detectors includes the status of the 484 HPDs (e.g. the average occupancy and dark count rates), and the real-time reconstruction of refractive indices from ring radii. It is estimated that, with an event rate of 2 kHz at the High Level Trigger, detailed user feedback can be provided in about 100 s. 4. Results and prospects All components of the readout chain (from HPD to L1 boards) as well as a first prototype of the DCS system were tested successfully in the laboratory and in several beam tests [4]. All aspects of integration (e.g. column mounting and cooling) have been addressed. Installation of the populated columns in the experimental area will take place in late autumn 2006, and an in situ commissioning phase, including calibration and alignment, will then start. The RICH detectors will be ready for data-taking in 2007. References [1] [2] [3] [4]
The LHCb Collaboration, CERN/LHCC 2000-0037. M. Alemi, et al., Nucl. Instr. and Meth. A 449 (2000) 49. F. Fontanelli, IEEE NSS Conference Record, vol. 2, 2005, p. 765. T. Blake, these proceedings.