1. The Backward Silicon Tracker 144 strip detectors (number of readout channels = 92.160) 48 pad detectors (number of trigger channels = 1536) Strip detector (640 strips) Pad detector (32 pads) Detector system Applications: The Backward Silicon Track Trigger for the HERA Experiment H1 Trigger PurposesTrigger Mask Concept Pad detector moduleFront-end ElectronicsPad readout system Test with a Calibration Pulse Beam Test and Calibration BST trigger signalBST veto signal PRO/A readout chip Interface to the H1 DAQ Detector Modules 96 channels Low noise power supply system for the front-end: VME Cards Assembling of the BST Layers Strip detectors Pad detectors Deeply Inelastic Scattering event BST acceptance in the x, Q 2 kinematical plane DIS Measurements with the BST L1 Trigger Elements: - Track trigger; - Back-to-back tracks; - Background veto. L2TT information: - θ and φ of the track; - Hit multiplicity. Sampling phaseReadout phase Plateau width Detector evaluation Radiation background Radiation Monitor for H1Radiation Monitor for HERA BST Collaboration Dose rate measurement with Pads Intense background components: Synchrotron radiation: The radiation monitor rate depends on the vacuum in HERA, therefore for the given conditions the background can be predicted in the first approxi- mation from the current product: Measuring the cumulative dose becomes possible with silicon detectors (besides beam losses when the energy is released in a very short time) as all particles deposit on average the same energy A linear correlation between the radiation monitor rate and the ionization current in the central trackers is used for chambers to control their “turn on” conditions and to explore their high voltage trips. Correlation with scintillation counter rates Reaction to the beam currents Detector smiths A single layer efficiency Raw data analysis: the number of triggered pads is particularly high for the proton scattering off the rest gas molecules or off the beam line optics. Online veto: the multiplicity control helps for early background rejection without affecting events from the eP interaction region. beam collimator Fast response time and reduced sensitivity to a neutral background component make the silicon detectors an important part of the H1 trigger. A track requirement provides further suppression of the beam induced background, the main part of which originates beyond the interaction region. Thus the BST trigger offers a significant data quality improvement for: Calorimeter trigger rate at low energies becomes enormously high because of the photoproduction background. It is kept down by a (hadronic) track requirement in the central tracker that introduces a bias to the inclusive DIS data sample. The track trigger signal from the BST allows for an efficient and unbiased data taking without rate scaling. Energy spectrum in DIS Trigger patterns Influence of a z-vertex spread on the trigger efficiency Influence of a XY-beam offset on the trigger efficiency Track curvature measurement and finding the particle’s momentum; Z-vertex reconstruction and rejection of non-eP tracks and other background. Track trigger for an efficient use of a high luminosity of HERA-II; Inclusive measurements of a scattered electron with a calorimeter and the BST: Event kinematics: Inelastic eP-scattering cross-section: DESY Hamburg Prague Charles University Institute of Physics AS CR Rutherford Appleton Laboratory Max Klein Peter Kostka Thomas Naumann Jan Kretzschmar Tomas Lastovicka Mirek Nozicka Wolfgang Lange Hans Henschel Joachim Meiβner Rainer Wallny Doris Eckstein Vladimir Arkadov Milan Janata Ulrich Harder Wolfgang Eick Wolfgang Philipp Olaf Gräber Ilya Tsurin Bill Haynes H.-C.S-C. Injected charge (8 fC) Multiplexed raw data bit and the trigger signal Multiplexed raw data bit and the radiation monitor Phase switch: sampling / readout Radiation monitor L2TT information: - θ and φ of the track; - Hit multiplicity. Radiation monitor (interrupted during the raw data transmission and then corrected) Raw data output for the L2 topological and neural network trigger Trigger hodoscope: Two outermost detectors with low constant thresholds define a track and the third detector in the middle is being studied with 5 GeV electrons at DESY-II. It also extends an acceptance of the H1 trigger for tracks with a very low P t momentum. The trigger masks allow for selection of tracks which are confined within one azimuthal sector (22.5 degrees) and cross any three detector layers Merging of more than one sector is possible but it complicates the design. F 2 measurements at low Q 2 in the extended x region F L measurements at low Q 2 in the high y region (y = 1 – E’/E) The vertex pointing track trigger is realized by means of a special detector structure when the particles from eP collisions traverse the BST layers firing a predefined combination of the silicon pads. A number of those combinations – the so-called “masks” to cover all possible track angles and curvatures has been found empirically. The detector division in the R-Z plane provides formation of straight roads pointing to the interaction point. With 4 layers and 8 rings this gives 7 basic masks, but the event vertex spread around the nominal interaction point leads to a somewhat larger number of masks. In any case the maximum number of trigger patterns needed is about 60. The trigger efficiency drops for particles whose momentum is below 1 GeV (the Pt in the BST angular acceptance is less than 100 MeV). The PRO/A readout chip was designed in collaboration between DESY Zeuthen and IDE AS (Oslo, Norway) and manufactured in 1.2 um n-well CMOS process by AMS Specifications: 32 channels with digital and analog outputs with controlled ON / OFF function and internal or external trigger thresholds; Individual / subtraction mode choice for channels for the common mode suppression; Dynamic input range 35 dB; Controlled gain 15…30 mV / fC; ENC (noise performance) 570 e; Noise slope 15 e / pF; Shaping time constant 30 ns; Has a calibration pulse mode. 384 channels Manipulating the PRO/A steering codes, setting trigger thresholds; Synchronization of all detector pulses to HERA clock frequency; Track validation with masks and computing the track topology; Accumulating and transmitting the raw data from the silicon pads; The front-end boards for the detector control and the trigger data processing (the ALTERA chip EP20K300E is a core of each board): Monitoring the multiplicity of triggered pads; Auxiliary functions: Monitoring the radiation background; Temperature measurements with a CAN chip. Bipolar voltages for the analog circuits; Bipolar and unipolar voltages for the digital circuits and voltage converters; Bias voltages for the silicon detectors. The system defines a power-ON sequence which is important for the PRO/A readout chip ! Electronics in the VME standard unify all data streams from the front-end and interface them to the level-1 and level-2 of the H1 central trigger system. Threshold scan For each pad of the middle detector a number of trigger pulses was counted as a function of a threshold voltage applied: The plateau width is a measure of a MIP signal and the pedestal FWHM is a noise estimate (the latter was measured with a calibration pulse). The signal-to-noise ratio was control to select good detectors hence the threshold scan was done for all silicon sensors prior to the BST installation. For tracks defined with external scintillation counters the trigger efficiency of assembly of 3 detector modules was (96+/-2)% was measured in H1 during eP-operation of HERA. The particle’s track in the aperture of the silicon pad detector was reconstructed from two space points: an event vertex and a barycenter of the energy cluster in the calorimeter. The high momentum electrons were selected to exclude the background influence. The trigger masks which require a coincidence of any three layers provide the efficiency of up to accordingly to a formula: for the DIS electrons Event Z-vertex as measured with the BST trigger only. No additional cuts are applied Electron energies in the SPACAL: BST L1 trigger only (solid line) Sector validation (dashed line) Luminosity data taken prior to 2003 shutdown Such an event can fulfill randomly any physical trigger or even a combination of several triggers. The synchrotron radiation fan does not enter the H1 facility directly but some part of it scatters from absorbers to- wards the detector and does heat the beam line optics that causes a gas evaporation and worsens the vacuum. In turn this increases a where the latter is the main background component. e-gas scattering P-gas scattering The instantaneous count rate can be helpful for the HERA crew as a feedback from the detector during injection and the beam steering: http://h1lumiserver.desy.de:8080/main/h1mon.html In coincidence with some other counters the radiation monitor can be used for an automatic beam dump in a case of severe radiation load. The trigger algorithm of the pad detector was extended to monitor online the particle flux through the silicon. The multiplicities of triggered pads are summed up within 1 second, during the next second the result obtained is sent out while the next integral is being prepared. One silicon sensor (20 cm 2 ) is taken as an area unit for the radiation monitor. The maximum rate over 48 pad detector modules is being displayed. DESY Zeuthen Simply nice picture :-)