- Email: [email protected]
Status and commissioning of the ATLAS experiment at the LHC
ARTICLE IN PRESS Nuclear Instruments and Methods in Physics Research A 602 (2009) 682–686
Contents lists available at ScienceDirect
Nuclear Instruments and Methods in Physics Research A journal homepage: www.elsevier.com/locate/nima
Status and commissioning of the ATLAS experiment at the LHC A. Di Ciaccio University of Roma Tor Vergata and INFN Tor Vergata, Italy
For the ATLAS Collaboration a r t i c l e in f o
a b s t r a c t
Available online 25 December 2008
The ATLAS experiment (A Toroidal LHC ApparatuS) is one of the two general purpose detectors (CMS is the other) at the Large Hadron Collider, at CERN (Geneva). It is designed to study p–p collision at a pffiffi center of mass energy of s ¼ 14 TeV and at a luminosity of 1034 cm1 s1 . ATLAS with its dimensions, 46 m long, 25 m in diameter and a weight of about 7000 ton is the biggest collider experiment ever built. The project has involved roughly 2000 scientists and engineers of 165 institutions in 35 countries. The installation in the underground cavern is scheduled to be completed in July 2008 to be ready for the pffiffi initial p–p collisions at a center of mass energy of s ¼ 10 TeV by late summer 2008. The detector design has been optimized to cover the largest possible search of new physics at the LHC energy: Higgs bosons and alternative schemes for the spontaneous symmetry-breaking mechanism; supersymmetric particles, new gauge bosons, leptoquarks, quark and lepton compositeness, extra dimensions. At the same time high-precision measurements of Standard Model processes will be performed and this will allow more stringent tests of the present electroweak theory and an indirect search for physics beyond the Standard Model. This paper presents a comprehensive overview of the ATLAS detector prior to the first LHC collisions. & 2009 Elsevier B.V. All rights reserved.
Keywords: ATLAS LHC RPC
1. Introduction The ATLAS detector, shown in the Fig. 1, includes an inner tracking detector inside a 2 T solenoid, electromagnetic and hadronic calorimeters outside the solenoid, and in the outer regions, barrel and end-cap muon chambers inside three superconducting air-core toroidal magnets [1]. It is built to perform precision measurements of photons, electrons, muons and hadrons over a large pseudorapidity range [2]. The complete energy measurement, important for the correct determination of the transverse missing energy, extends over jZjo4:9. The inner tracking detector consists, going from the outer to the most inner part, of straw drift tubes interleaved with transition radiators for robust pattern recognition and electron identification, and several layers of semiconductor strip and pixel detectors providing high-precision space points. The electromagnetic calorimeter is a lead-Liquid Argon sampling calorimeter with an integrated preshower detector and a presampler layer immediately behind the cryostat wall for energy recovery. The end-cap hadronic calorimeters also use Liquid Argon technology, with copper absorber plates. The endcap cryostats house the e.m., hadronic and forward calorimeters
E-mail address: [email protected] 0168-9002/$ - see front matter & 2009 Elsevier B.V. All rights reserved. doi:10.1016/j.nima.2008.12.089
(tungsten-Liquid Argon sampling). The barrel hadronic calorimeter is an iron-scintillating tile sampling calorimeter with longitudinal tile geometry. A barrel and two end-cap muon spectrometers are used to trigger and measure the muon momentum up to jZjo2:7. Eight superconducting coils are used in the barrel region complemented with superconducting end-cap toroids (ECTs) in the forward regions. The toroids are instrumented with Monitored Drift Tubes (MDTs) and with Cathode Strip Chambers (CSCs) at large rapidity where there are high-radiation levels. The muon trigger and second coordinate measurement for muon tracks are provided by Resistive Plate Chambers (RPCs) in the barrel and Thin Gap Chambers (TGCs) in the end-caps. The ATLAS trigger scheme is a three-level trigger and data-acquisition (DAQ) system. The first-level trigger signatures are high-pT muons, electrons, photons, jets and large missing transverse energy. For low-luminosity operation of LHC, a low-pT muon signature will be used in addition. At levels two and three, more complex signatures will be used to select the events to be retained for the analysis [3]. Since some time the production of detector components is completed while the massive underground installation is almost finished. The efforts are now fully concentrated on the rapidly growing detector commissioning activity. The status of the commissioning work on the sub-detectors will be analyzed in the following sections.
ARTICLE IN PRESS A. Di Ciaccio / Nuclear Instruments and Methods in Physics Research A 602 (2009) 682–686
Muon Detectors
Tile Calorimeter
Toroid Magnets
683
Liquid Argon Calorimeter
Solenoid Magnet
SCT Tracker Pixel Detector
TRT Tracker
Fig. 1. A drawing of the ATLAS experiment.
2. Commissioning of the magnet system The ATLAS superconducting magnet system comprises the central solenoid, the barrel toroid (BT), two ECTs and their common services [4]. Both the central solenoid and the BT have been successfully commissioned at full current (plus a small safety margin), and their safety systems have been tested in situ during August and November 2006, respectively. The cryogenics cooling power of the plant at Point 1 was increased, based on this first operation, to cope efficiently with the full system. After installation in summer 2007, both ECTs were cooled down and partially exited in a standalone mode at the end of 2007. These tests were performed with the ECTs not in their final position, and after an unexpected movement of the ECT during the first test, the currents were limited to 75% and 50%, respectively for each side. The complete magnet system will be tested at full current, including some safety margin, in the final closed configuration of the detector, scheduled for May and June 2008, just leading into operation for LHC start-up. An event display of a cosmic muon track, recorded during the test with the BT at the nominal current, is shown in Fig. 2.
3. Commissioning of the inner detector The Inner Detector (ID) combines three concentric sub-system layers, from inside out: the pixel detectors, the Silicon Tracker (SCT) and the Transition Radiation Straw Tracker (TRT). Each of them consists of a barrel and two end-caps (EC side A and EC side C). The detectors are located inside the 2 T magnetic field generated by the central solenoid magnet [5]. The integration work in the clean room facility SR1 at the Point 1 surface has been completed for all sub-systems, and substantial parts of the four integrated large installation components (barrel and two end-cap SCT þ TRT, pixels) have been successfully operated on the surface in cosmic ray tests until early 2007. The installation of the ID services (cables and pipes) has been finished, and the installation and commissioning of the off-detector electronics in the underground control rooms USA15 and US15
Fig. 2. A 3-D event display of a cosmic muon event, showing the path of a muon travelling through three layers of the barrel muon spectrometer. Three of the eight coils of the barrel toroid magnet can be seen in the top half of the drawing. This event has been triggered by the RPC chambers and related trigger electronics.
have been completed according to plans. The installation work, the final cabling and as a consequence, the commissioning work for the ID, were seriously delayed by a problem encountered with the evaporative cooling system used for the SCT and pixels. In a very major effort over the past year this was overcome with refabrication of the failing parts and relocating them into an accessible region in the space between the calorimeter barrel and end-caps. Whereas the commissioning work in situ of the TRT
ARTICLE IN PRESS 684
A. Di Ciaccio / Nuclear Instruments and Methods in Physics Research A 602 (2009) 682–686
Fig. 3. ATLAS pixel detector integrated into the barrel SCT and TRT.
with cosmic rays progressed according to plans, the crucial steps of electrical and cosmic rays commissioning have only been achieved late with the barrel SCT, showing excellent results, and very recently with the end-cap SCT, again with first very encouraging results. The in situ pixel commissioning will only be possible starting in April 2008, just before the closing of the ATLAS detector. The pixel detector integrated into the barrel TRT and SCT is shown in Fig. 3.
Fig. 4. An event display of a comic ray event triggered by the tile calorimeter.
4. Commissioning of the calorimeter system The calorimetry consisting of a barrel electromagnetic and hadronic calorimeter, end-cap calorimeters and forward calorimeters. All of them are constructed and already lowered in the cavern [6]. All three LAr calorimeter cryostats are installed and the main activities concentrate on completing electronics installation and system commissioning in the experimental area. The three cryostats are cold and filled with LAr. During the first ECT test and its unexpected displacement, the vacuum enclosure of a cryogenic feed-line for one of the end-cap LAr calorimeters was damaged, and its liquid argon was emptied as a safety precaution into the storage dewar installed in the cavern. The cryoline has been repaired successfully in situ, and the cryostat has been refilled, and commissioning operation is now resuming again after several months of interruption. Cosmic ray signals in the combined LAr and tile calorimeters have been recorded. An event display of a cosmic ray event triggered by the tile calorimeter is shown in Fig. 4.
5. Commissioning of the muon chambers The muon spectrometer is instrumented with precision chambers for the momentum measurement (MDT chambers, and for a small high-radiation forward area CSCs) and with fast chambers for triggering (RPCs in the barrel and TGCs in the end-caps) [7]. The barrel station installation in the cavern is completed (see Fig. 5) and the chamber commissioning sector by sector ongoing. The end-cap sector pre-assembly and their installation in the cavern are in progress and only one-third of the end-cap end-wall (EO) chambers have still to be installed. The main activity of the past months was concentrated on the assembly and integration of fully tested sectors for the end-cap wheels, including their alignment system and their installation. The so-called ‘Big
Fig. 5. ATLAS side A (with the calorimeter end-cap partially inserted). The barrel calorimeter is visible in the center surrounded by the BT muon spectrometer. The organization of the muon stations in three layers (inner, middle and outer) along the radius and in 16 sectors around the eight coils is also visible.
Wheels’ in the middle station consist of a total of two MDT wheels and six TGC wheels, preassembled in 32 MDT sectors and 72 TGC sectors. The first TGC Big Wheel completed in the underground cavern is shown in Fig. 6, while Fig. 7 is showing a forward arm with the toroid, a ‘Small Wheels’ and a ‘Big Wheels’ installed.
6. Commissioning of the Trigger and DAQ system The level-1 trigger, the High Level Trigger (HLT), the DAQ and the Detector Control System (DCS) have all been field-proven in the combined test beam running and large-scale system tests over the past years. Components of the final system are now being installed at Point 1, both in the underground control room as well as in the surface HLT/DAQ computer room, and they are gradually being used in the commissioning of the ATLAS detector as it gets
ARTICLE IN PRESS A. Di Ciaccio / Nuclear Instruments and Methods in Physics Research A 602 (2009) 682–686
685
Fig. 8. The ATLAS control room.
Fig. 6. The first TGC Big Wheel assembled in the cavern.
Fig. 9. A cosmic ray event triggered by the RPC chambers and crossing the ATLAS detectors.
Fig. 7. A forward arm of the ATLAS detector.
installed. The level-1 trigger system (with the sub-systems calorimeter, muon and central trigger processor, CTP) is fully in production and installation for both hardware and software. The HLT, DAQ and DCS activities proceed according to plans. Major emphasis is put on all aspects of the HLT and DAQ software developments. The HLT and DAQ pre-series system hardware at Point 1 was used successfully in a 10% data flow test already last year. The system installations are now growing according to the needs for detector commissioning work. An important element for
the initial commissioning is the local DAQ capability available to the detector system communities. The operational infrastructure at Point 1 is fully active (central file server and a number of local service machines operational with standard DAQ software, system administration and networking). The Read-Out System (ROS) and the event builders have been demonstrated in a sequence of technical runs to deliver the required performance and data throughput rates. HLT algorithms have been successfully used with physics events pre-loaded in the ROS, and also with cosmic ray muons. Finally, the DCS is operational and available as an important standard tool to all detector system users in the commissioning runs. Apart from its own commissioning, the Trigger and DAQ system is also heavily and routinely used for the commissioning of the overall ATLAS detector.
ARTICLE IN PRESS 686
A. Di Ciaccio / Nuclear Instruments and Methods in Physics Research A 602 (2009) 682–686
The ATLAS Control Room (ACR), shown in Fig. 8, is fully operational. It has become the centre of many prominent activities over the past months, including periods of global commissioning running with collecting cosmic ray events in the cavern. During these so-called ‘milestone weeks’ gradually all detector components, and increasingly larger fractions of given sub-systems, are integrated into the full chain from the detector to the remote offline analysis. A cosmic ray event, triggered by the RPC chambers and traversing the detector is shown in Fig. 9. The data flow includes the operation of the trigger system, the DAQ chain, transfer to the Tier-0 and distribution over the WLCG backbone to all 10 ATLAS Tier-1 and most Tier-2 centres. Concurrent with the cosmics running, monitoring (online and offline) and data preparation tasks are exercised. The collected data is used for debugging the detector systems as well as for early calibration and alignment studies.
7. Conclusions The ATLAS experiment [8] has concluded successfully the construction and the massive installation phase and is currently under the heavy commissioning work of the different
detectors. The commissioning with cosmic rays data is proceeding well. The main goal is to debug the detector, computing and software and to gain, as efficiently as possible, an excellent understanding of the detector performance to ensure the best quality of the data when the first collisions will start. The present installation schedule foresees the detector ready for physics at the start of the first LHC collisions in late summer 2008. References [1] ATLAS Collaboration, Technical Proposal, CERN/LHCC/94-93, LHCC/P2, 15 December 1998. [2] ATLAS Collaboration, Detector and Physics Performance Technical Design Report, CERN/LHCC/99-14, 23 May 1999. [3] ATLAS Collaboration, Trigger Performance Design Report, CERN/LHCC/98-15, 25 August 1998. [4] ATLAS Collaboration, Magnet System Technical Design Report, CERN/LHCC/9718, 30 April 1997. [5] ATLAS Collaboration, Inner Detector Technical Design Report, CERN/LHCC/9716, CERN/LHCC/97-17, 30 April 1997. [6] ATLAS Collaboration, Calorimeter Performance Technical Design Report, CERN/ LHCC/96-40, 15 December 1996. [7] ATLAS Collaboration, Muon Technical Design Report, CERN/LHCC/97-22, 31 May 1997. [8] ATLAS Collaboration, G. Aad et al., The ATLAS experiment at the CERN Large Hadron Collider, 2008 JINST 3 S08003.
Contents lists available at ScienceDirect
Nuclear Instruments and Methods in Physics Research A journal homepage: www.elsevier.com/locate/nima
Status and commissioning of the ATLAS experiment at the LHC A. Di Ciaccio University of Roma Tor Vergata and INFN Tor Vergata, Italy
For the ATLAS Collaboration a r t i c l e in f o
a b s t r a c t
Available online 25 December 2008
The ATLAS experiment (A Toroidal LHC ApparatuS) is one of the two general purpose detectors (CMS is the other) at the Large Hadron Collider, at CERN (Geneva). It is designed to study p–p collision at a pffiffi center of mass energy of s ¼ 14 TeV and at a luminosity of 1034 cm1 s1 . ATLAS with its dimensions, 46 m long, 25 m in diameter and a weight of about 7000 ton is the biggest collider experiment ever built. The project has involved roughly 2000 scientists and engineers of 165 institutions in 35 countries. The installation in the underground cavern is scheduled to be completed in July 2008 to be ready for the pffiffi initial p–p collisions at a center of mass energy of s ¼ 10 TeV by late summer 2008. The detector design has been optimized to cover the largest possible search of new physics at the LHC energy: Higgs bosons and alternative schemes for the spontaneous symmetry-breaking mechanism; supersymmetric particles, new gauge bosons, leptoquarks, quark and lepton compositeness, extra dimensions. At the same time high-precision measurements of Standard Model processes will be performed and this will allow more stringent tests of the present electroweak theory and an indirect search for physics beyond the Standard Model. This paper presents a comprehensive overview of the ATLAS detector prior to the first LHC collisions. & 2009 Elsevier B.V. All rights reserved.
Keywords: ATLAS LHC RPC
1. Introduction The ATLAS detector, shown in the Fig. 1, includes an inner tracking detector inside a 2 T solenoid, electromagnetic and hadronic calorimeters outside the solenoid, and in the outer regions, barrel and end-cap muon chambers inside three superconducting air-core toroidal magnets [1]. It is built to perform precision measurements of photons, electrons, muons and hadrons over a large pseudorapidity range [2]. The complete energy measurement, important for the correct determination of the transverse missing energy, extends over jZjo4:9. The inner tracking detector consists, going from the outer to the most inner part, of straw drift tubes interleaved with transition radiators for robust pattern recognition and electron identification, and several layers of semiconductor strip and pixel detectors providing high-precision space points. The electromagnetic calorimeter is a lead-Liquid Argon sampling calorimeter with an integrated preshower detector and a presampler layer immediately behind the cryostat wall for energy recovery. The end-cap hadronic calorimeters also use Liquid Argon technology, with copper absorber plates. The endcap cryostats house the e.m., hadronic and forward calorimeters
E-mail address: [email protected] 0168-9002/$ - see front matter & 2009 Elsevier B.V. All rights reserved. doi:10.1016/j.nima.2008.12.089
(tungsten-Liquid Argon sampling). The barrel hadronic calorimeter is an iron-scintillating tile sampling calorimeter with longitudinal tile geometry. A barrel and two end-cap muon spectrometers are used to trigger and measure the muon momentum up to jZjo2:7. Eight superconducting coils are used in the barrel region complemented with superconducting end-cap toroids (ECTs) in the forward regions. The toroids are instrumented with Monitored Drift Tubes (MDTs) and with Cathode Strip Chambers (CSCs) at large rapidity where there are high-radiation levels. The muon trigger and second coordinate measurement for muon tracks are provided by Resistive Plate Chambers (RPCs) in the barrel and Thin Gap Chambers (TGCs) in the end-caps. The ATLAS trigger scheme is a three-level trigger and data-acquisition (DAQ) system. The first-level trigger signatures are high-pT muons, electrons, photons, jets and large missing transverse energy. For low-luminosity operation of LHC, a low-pT muon signature will be used in addition. At levels two and three, more complex signatures will be used to select the events to be retained for the analysis [3]. Since some time the production of detector components is completed while the massive underground installation is almost finished. The efforts are now fully concentrated on the rapidly growing detector commissioning activity. The status of the commissioning work on the sub-detectors will be analyzed in the following sections.
ARTICLE IN PRESS A. Di Ciaccio / Nuclear Instruments and Methods in Physics Research A 602 (2009) 682–686
Muon Detectors
Tile Calorimeter
Toroid Magnets
683
Liquid Argon Calorimeter
Solenoid Magnet
SCT Tracker Pixel Detector
TRT Tracker
Fig. 1. A drawing of the ATLAS experiment.
2. Commissioning of the magnet system The ATLAS superconducting magnet system comprises the central solenoid, the barrel toroid (BT), two ECTs and their common services [4]. Both the central solenoid and the BT have been successfully commissioned at full current (plus a small safety margin), and their safety systems have been tested in situ during August and November 2006, respectively. The cryogenics cooling power of the plant at Point 1 was increased, based on this first operation, to cope efficiently with the full system. After installation in summer 2007, both ECTs were cooled down and partially exited in a standalone mode at the end of 2007. These tests were performed with the ECTs not in their final position, and after an unexpected movement of the ECT during the first test, the currents were limited to 75% and 50%, respectively for each side. The complete magnet system will be tested at full current, including some safety margin, in the final closed configuration of the detector, scheduled for May and June 2008, just leading into operation for LHC start-up. An event display of a cosmic muon track, recorded during the test with the BT at the nominal current, is shown in Fig. 2.
3. Commissioning of the inner detector The Inner Detector (ID) combines three concentric sub-system layers, from inside out: the pixel detectors, the Silicon Tracker (SCT) and the Transition Radiation Straw Tracker (TRT). Each of them consists of a barrel and two end-caps (EC side A and EC side C). The detectors are located inside the 2 T magnetic field generated by the central solenoid magnet [5]. The integration work in the clean room facility SR1 at the Point 1 surface has been completed for all sub-systems, and substantial parts of the four integrated large installation components (barrel and two end-cap SCT þ TRT, pixels) have been successfully operated on the surface in cosmic ray tests until early 2007. The installation of the ID services (cables and pipes) has been finished, and the installation and commissioning of the off-detector electronics in the underground control rooms USA15 and US15
Fig. 2. A 3-D event display of a cosmic muon event, showing the path of a muon travelling through three layers of the barrel muon spectrometer. Three of the eight coils of the barrel toroid magnet can be seen in the top half of the drawing. This event has been triggered by the RPC chambers and related trigger electronics.
have been completed according to plans. The installation work, the final cabling and as a consequence, the commissioning work for the ID, were seriously delayed by a problem encountered with the evaporative cooling system used for the SCT and pixels. In a very major effort over the past year this was overcome with refabrication of the failing parts and relocating them into an accessible region in the space between the calorimeter barrel and end-caps. Whereas the commissioning work in situ of the TRT
ARTICLE IN PRESS 684
A. Di Ciaccio / Nuclear Instruments and Methods in Physics Research A 602 (2009) 682–686
Fig. 3. ATLAS pixel detector integrated into the barrel SCT and TRT.
with cosmic rays progressed according to plans, the crucial steps of electrical and cosmic rays commissioning have only been achieved late with the barrel SCT, showing excellent results, and very recently with the end-cap SCT, again with first very encouraging results. The in situ pixel commissioning will only be possible starting in April 2008, just before the closing of the ATLAS detector. The pixel detector integrated into the barrel TRT and SCT is shown in Fig. 3.
Fig. 4. An event display of a comic ray event triggered by the tile calorimeter.
4. Commissioning of the calorimeter system The calorimetry consisting of a barrel electromagnetic and hadronic calorimeter, end-cap calorimeters and forward calorimeters. All of them are constructed and already lowered in the cavern [6]. All three LAr calorimeter cryostats are installed and the main activities concentrate on completing electronics installation and system commissioning in the experimental area. The three cryostats are cold and filled with LAr. During the first ECT test and its unexpected displacement, the vacuum enclosure of a cryogenic feed-line for one of the end-cap LAr calorimeters was damaged, and its liquid argon was emptied as a safety precaution into the storage dewar installed in the cavern. The cryoline has been repaired successfully in situ, and the cryostat has been refilled, and commissioning operation is now resuming again after several months of interruption. Cosmic ray signals in the combined LAr and tile calorimeters have been recorded. An event display of a cosmic ray event triggered by the tile calorimeter is shown in Fig. 4.
5. Commissioning of the muon chambers The muon spectrometer is instrumented with precision chambers for the momentum measurement (MDT chambers, and for a small high-radiation forward area CSCs) and with fast chambers for triggering (RPCs in the barrel and TGCs in the end-caps) [7]. The barrel station installation in the cavern is completed (see Fig. 5) and the chamber commissioning sector by sector ongoing. The end-cap sector pre-assembly and their installation in the cavern are in progress and only one-third of the end-cap end-wall (EO) chambers have still to be installed. The main activity of the past months was concentrated on the assembly and integration of fully tested sectors for the end-cap wheels, including their alignment system and their installation. The so-called ‘Big
Fig. 5. ATLAS side A (with the calorimeter end-cap partially inserted). The barrel calorimeter is visible in the center surrounded by the BT muon spectrometer. The organization of the muon stations in three layers (inner, middle and outer) along the radius and in 16 sectors around the eight coils is also visible.
Wheels’ in the middle station consist of a total of two MDT wheels and six TGC wheels, preassembled in 32 MDT sectors and 72 TGC sectors. The first TGC Big Wheel completed in the underground cavern is shown in Fig. 6, while Fig. 7 is showing a forward arm with the toroid, a ‘Small Wheels’ and a ‘Big Wheels’ installed.
6. Commissioning of the Trigger and DAQ system The level-1 trigger, the High Level Trigger (HLT), the DAQ and the Detector Control System (DCS) have all been field-proven in the combined test beam running and large-scale system tests over the past years. Components of the final system are now being installed at Point 1, both in the underground control room as well as in the surface HLT/DAQ computer room, and they are gradually being used in the commissioning of the ATLAS detector as it gets
ARTICLE IN PRESS A. Di Ciaccio / Nuclear Instruments and Methods in Physics Research A 602 (2009) 682–686
685
Fig. 8. The ATLAS control room.
Fig. 6. The first TGC Big Wheel assembled in the cavern.
Fig. 9. A cosmic ray event triggered by the RPC chambers and crossing the ATLAS detectors.
Fig. 7. A forward arm of the ATLAS detector.
installed. The level-1 trigger system (with the sub-systems calorimeter, muon and central trigger processor, CTP) is fully in production and installation for both hardware and software. The HLT, DAQ and DCS activities proceed according to plans. Major emphasis is put on all aspects of the HLT and DAQ software developments. The HLT and DAQ pre-series system hardware at Point 1 was used successfully in a 10% data flow test already last year. The system installations are now growing according to the needs for detector commissioning work. An important element for
the initial commissioning is the local DAQ capability available to the detector system communities. The operational infrastructure at Point 1 is fully active (central file server and a number of local service machines operational with standard DAQ software, system administration and networking). The Read-Out System (ROS) and the event builders have been demonstrated in a sequence of technical runs to deliver the required performance and data throughput rates. HLT algorithms have been successfully used with physics events pre-loaded in the ROS, and also with cosmic ray muons. Finally, the DCS is operational and available as an important standard tool to all detector system users in the commissioning runs. Apart from its own commissioning, the Trigger and DAQ system is also heavily and routinely used for the commissioning of the overall ATLAS detector.
ARTICLE IN PRESS 686
A. Di Ciaccio / Nuclear Instruments and Methods in Physics Research A 602 (2009) 682–686
The ATLAS Control Room (ACR), shown in Fig. 8, is fully operational. It has become the centre of many prominent activities over the past months, including periods of global commissioning running with collecting cosmic ray events in the cavern. During these so-called ‘milestone weeks’ gradually all detector components, and increasingly larger fractions of given sub-systems, are integrated into the full chain from the detector to the remote offline analysis. A cosmic ray event, triggered by the RPC chambers and traversing the detector is shown in Fig. 9. The data flow includes the operation of the trigger system, the DAQ chain, transfer to the Tier-0 and distribution over the WLCG backbone to all 10 ATLAS Tier-1 and most Tier-2 centres. Concurrent with the cosmics running, monitoring (online and offline) and data preparation tasks are exercised. The collected data is used for debugging the detector systems as well as for early calibration and alignment studies.
7. Conclusions The ATLAS experiment [8] has concluded successfully the construction and the massive installation phase and is currently under the heavy commissioning work of the different
detectors. The commissioning with cosmic rays data is proceeding well. The main goal is to debug the detector, computing and software and to gain, as efficiently as possible, an excellent understanding of the detector performance to ensure the best quality of the data when the first collisions will start. The present installation schedule foresees the detector ready for physics at the start of the first LHC collisions in late summer 2008. References [1] ATLAS Collaboration, Technical Proposal, CERN/LHCC/94-93, LHCC/P2, 15 December 1998. [2] ATLAS Collaboration, Detector and Physics Performance Technical Design Report, CERN/LHCC/99-14, 23 May 1999. [3] ATLAS Collaboration, Trigger Performance Design Report, CERN/LHCC/98-15, 25 August 1998. [4] ATLAS Collaboration, Magnet System Technical Design Report, CERN/LHCC/9718, 30 April 1997. [5] ATLAS Collaboration, Inner Detector Technical Design Report, CERN/LHCC/9716, CERN/LHCC/97-17, 30 April 1997. [6] ATLAS Collaboration, Calorimeter Performance Technical Design Report, CERN/ LHCC/96-40, 15 December 1996. [7] ATLAS Collaboration, Muon Technical Design Report, CERN/LHCC/97-22, 31 May 1997. [8] ATLAS Collaboration, G. Aad et al., The ATLAS experiment at the CERN Large Hadron Collider, 2008 JINST 3 S08003.