14/02/2008 Michele Bianco 1 G.Chiodini & E.Gorini ATLAS RPC certification with cosmic rays Università del Salento Facoltà di Scienze MM.FF.NN.

14/02/2008 Michele Bianco 2 Outline: The Resistive Plate Chambers (RPC) as muon trigger detector for the ATLAS muon spectrometer. Detector Characterization in Lecce The cosmic ray facility in Lecce Performed Tests Temperature and Pressure calibration RPC performance characterization Working Point definition Conclusions

14/02/2008 Michele Bianco 3 The ATLAS Resistive Plate Chambers Each unit contains 2 layers of gas volume. 2mm gas gap, bakelite resistivity ~ 1-4x10 10  cm  and  read-out copper strips panels, pitch ranging from 26.4 to 37 mm Operated at atmospheric pressure Operated in saturated avalanche regime Gas mixture: C 2 H 2 F % - C 4 H 10 5% - SF 6 0.3% Main ATLAS RPC tasks: Good time resolution for bunch-cross identification (~ 1 ns) High rate capability to substain the high background level 2nd-coordinate measurements with a required resolution of 5-10 mm

14/02/2008 Michele Bianco 4 ATLAS RPC chambers and muon stations An ATLAS muon station is made of two RPC chambers assembled with the MDT chambers. MDT RPC Resistive Plate Chambers will be used as Muon Trigger Detector in the barrel region (-1 <  < 1)

14/02/2008 Michele Bianco 5 The ATLAS RPC test stand facility in Lecce

14/02/2008 Michele Bianco 6 The Lecce Cosmic Ray Test Stand A cosmic ray stand was designed and built in the Lecce laboratory in order to test the ATLAS RPCs 4736 read-out channels. Trigger and tracking performed with 4 ATLAS RPC standard units. Gas system with 20 independent lines. HV, LV system with about 150 channels. Labview based software for the Data Control System and Data Acquisition. DAQ, DCS and Data Analysis program developed in Lecce. Automatic test procedure. Test duration: about 72 hours.

14/02/2008 Michele Bianco 7 The Lecce Cosmic Ray Test Stand C++ Object Oriented framework (read, decodes, checks data integrity, perform time and space clustering, applies the desired geometry). Specific task provide to perform detailed monitoring. Pattern recognition and tracking performed in  and  view. Tracking resolution about 10 mm. Efficiency measurement and monitoring. Environmental data stored in DB and monitored. Automatic data and fit results storage in DB. Off-line Framework and analysis

14/02/2008 Michele Bianco 8 The Lecce Cosmic Ray Test Stand About 220 runs are required for each group of test, for about 3 Gbytes of data per group. Every run header is stored in DB. More than 300 Gbytes of data collected and stored on dedicated server during 18 months of data taking. About 300 fits are performed to characterize each single chamber. About 3000 fits are performed for each group of test and 9000 fit parameters are automatically stored in a dedicated database. A MySQL database made of 17 tables has been implemented. More than entries in about 750 record are stored. DataBase total size of about 60 Mbytes. Data presentation Dedicated dynamic web pages (php+MySQL) have been implemented and built ( Data storage

14/02/2008 Michele Bianco 9 Performed Tests and Parametrizations I-HV Characteristic Cluster Size and Single rate counting vs HV Efficiency curve

14/02/2008 Michele Bianco 10 = Efficiency for infinite HV (top efficiency) = HV per 50% of top efficiency = Diff HV eff 90%-10% Small error on parameter

14/02/2008 Michele Bianco 11 Performed Tests Bidimensional efficiency Historical data trend

14/02/2008 Michele Bianco 12 RPC Characterization with the Lecce test stand facility data

14/02/2008 Michele Bianco 13 High Voltage calibration for Temperature and Pressure variation RPC is a gaseous detector operated at atmospheric pressure, variation of environmental parameters can modify the gas gain and the relative detector response. In order to have comparable test results for measurements performed at different pressure and temperature is necessary to rescale HV applied at gas volume. No correction was applied on-line Correction was performed during data analysis using environmental measurements Ref M. Abbrescia, R. Cardarelli, et al., Nucl. Instr. and Meth. A 359 (1995) K (20 0 C) 1013 mbar

14/02/2008 Michele Bianco 14 V 50 studies as a function of T and P Each single point is related to a test group, usually 5/8 RPC 20/30 gas volume. Many systematic effects are not taken into account in this stage. The standard correction do not make the data independent from T and P. All the Data have been reprocessed without HV correction. This operation takes about one week of CPU time

14/02/2008 Michele Bianco 15 negligible respect to A new calibration formula is needed

14/02/2008 Michele Bianco 16 V 50 behavior for constant T and P V 50 as function of pressure at constant temperature. Empirical formula V 50 as function of temperature at constant pressure.

14/02/2008 Michele Bianco 17 Comparison of calibration formulae Empirical formulaStandard formula Top efficiency parameter do not depend from temperature and     is a difference of two separate values and then almost insensitive

14/02/2008 Michele Bianco 18 Gas Volume Efficiency as function of front-end threshold Gas Volume efficiency distribution for infinite HV Gas volume efficiency as a function of front-end threshold for different applied HV Physical threshold and applied threshold

14/02/2008 Michele Bianco 19 Cluster Size and Single Rate Counting as a function of front-end threshold Cluster Size distribution at HV = 9900 Volts and V th =1000 Cluster Size as function of V th for different HV Noise distribution at HV = 9900 Volts and V th =1000 Noise as function of V th for different HV Each point is the average value of a relative distribution.

14/02/2008 Michele Bianco 20 Current and Single Rate Counting as function of temperature The HV value have been corrected for Temp and Press, nevertheless an evident dependence from temperature is still present Noise map demonstrate that temperature variation induce uniform effect in gas volume Noise rate Vs Exponential current lead to define an average value of each discharge. About 34.5 pC

14/02/2008 Michele Bianco 21 Working Point (V wp ) definition and characterization V wp is a parameter which can define the optimal operating voltage of each detector once fixed the threshold. Choose V wp in the following way: the voltage at which the gas volume reaches a fixed percentage of the top efficiency (i.e. 96%, 97%, 98 %, 99%) Distribution of the V wp (defined at 99% of top efficiency V th =1000 mV), V wp as function of V th and gas volume efficiency at V wp99%

14/02/2008 Michele Bianco 22 Working Point (V wp ) definition and characterization Comparing all results with the ATLAS requirements Gas Volume Efficiency > 96% Cluster Size <1.5 Noise < 2 Hz/cm 2 The average working point at V wp99 is HV=9938 Volts at Vth=1000 mV

14/02/2008 Michele Bianco 23 HV wp distribution for different high voltage correction Distribution of V wp99 not corrected for T and P. RMS is 96Volts due to intrinsically gas volume spread and different T and P Distribution of V wp99 corrected for T e P with standard formula. RMS is 85Volts The average value is increased due to the overcorrection. Distribution of V wp99 corrected for T e P. RMS 72Volts

14/02/2008 Michele Bianco 24 Conclusions A test stand facility for ATLAS RPC characterization has been built. 380 RPC units have been completely characterized and then shipped to CERN. A new empirical formula for Temperature and Pressure calibration has been obtained. Detailed statistical detector characterization has been performed. Temperature performance behavior have been extensively studied. Working point has been defined and characterized. Still lot of very useful information could be extracted from this data. The detectors fulfill the ATLAS requirements