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First cosmic ray results of the RPC commissioning in the ATLAS cavern
Nuclear Physics B (Proc. Suppl.) 177–178 (2008) 335–338 www.elsevierphysics.com
First cosmic ray results of the RPC commissioning in the ATLAS cavern E.Solfarolia, G.Aiellib , A.Aloisioc , M.Alviggic , S.Antonellid , L.Bellagambad, M.Biancoe , M.Bigliettic , D.Boscherinid, A.Brunid , G.Brunid , S.Budahf , P.Camarria, V.Canalec , R.Cardarellia, G.Carlinoc , G.Cattania , G.Chiodinie , G.Ciapettig , M.R.Colucciae , S.Constantinf , F.Conventic , R.De Asmundisc , M.Della Pietrac , D.Della Volpec , D.De Pedisg , A.Di Ciaccioa , A.Di Girolamog , A.Di Mattiag , R.Di Nardoa , M.Dogaruf , P.Giustid , E.Gorini e , F.Grancagnoloe, G.Iacobuccid , P.Iengoh, V.Izzoc , B.Libertia , C.Lucig , F.Marchesea , A.Migliaccioc , A.Nisatig , A.Polinid , E.Pasqualuccig , F.Pastoreg , S.Patricellic, M.Pectuf , R.Perrinoe, E.Petrolog, M.Primaverae, S.Rosatig , A.Salamona , R.Santonicoa , G.Sekhniaidzec , S.Spagnoloe, F.Spilag , R.Varig , S.Venezianog , L.Zanellog a
INFN Sezione di Roma Tor Vergata and Universit` a di Roma “Tor Vergata” - Italy
b
INFN Sezione di Roma Tor Vergata and ENEA Frascati - Italy
c
INFN Sezione di Napoli and Universit` a di Napoli “Federico II” - Italy
d e f
INFN Sezione di Bologna and Universit` a di Bologna - Italy
INFN Sezione di Lecce and Universit`a del Salento - Italy
NIPNE-HH, Bucarest, Romania
g
INFN Roma and Universit` a di Roma “La Sapienza” - Italy
h
CERN, Geneva - Switzerland
The first commissioning test of three muon towers of the ATLAS Muon Spectrometer, installed in the cavern, was carried out. The stations under test belong to the barrel sector 13, which is a large sector. A muon tower consists of three stations: the Inner, the Middle and the Outer, starting from the interaction point. The Barrel Inner Large (BIL) stations are constituted by MDT chambers; the Barrel Middle Large (BML) stations by MDTs assembled between two RPC chambers; and the Barrel Outer Large (BOL) stations by MDTs with only one RPC mounted downstream. Specific Level-1 trigger algorithms have been studied to trigger on cosmic rays and implemented to commission the muon stations. Comparison between the measured trigger rate and the simulated results will be presented. Moreover, the RPC performances have been studied by comparing the MDT track extrapolations with the firing RPC readout strips. The RPC detection efficiency is evaluated in the eta measuring view, resulting as a combination of gas volume efficiency and Front-End efficiency.
1. Simulation of the LVL-1 trigger rate in the barrel with cosmic muons The ATLAS [1] LVL-1 trigger system [2] layout is optimized for muons coming from the interaction point. However the trigger acceptance is adjustable by programming the Coincidence Matrices [3] with a set of appropriate thresholds.They have been optimized for the cosmic rays selection during the commissioning test. Three LVL-1 con0920-5632/$ – see front matter © 2007 Elsevier B.V. All rights reserved. doi:10.1016/j.nuclphysbps.2007.11.152
figurations have been studied using a dedicated simulation [4] of the detector performance. The cosmic muon rate simulated in the ATLAS cavern is 2.2 kHz [5]. Muons with energy below 30 GeV at ground level reach the cavern, only if they pass through the two shafts. The trigger rates computed for the cosmic muons using the ATLAS standard LVL-1 trigger logic, together with the values expected for the p-p collisions, are listed in table 1. Since these
336
E. Solfaroli et al. / Nuclear Physics B (Proc. Suppl.) 177–178 (2008) 335–338
Table 1 Trigger rates due to cosmic muons in the standard LVL-1 configuration. The values expected [2] for the p-p collisions at low (low-pT 6 GeV ) and high (High-pT 20 GeV ) luminosity are also indicated. LVL-1 trigger cosmic rays p-p collisions Low-pT 6 GeV 214 Hz ∼ 9.3 kHz Low-pT 10 GeV 141 Hz High-pT 20 GeV 21 Hz ∼ 1.4 kHz 18 Hz High-pT 40 GeV
values are not sufficient to ensure a high acquisition rate during the commissioning phase, two different schemes for the low-pT trigger have been considered: 1. Low-pT trigger with fully open coincidence window: no coincidence window is imposed except the limit due to the cabling. 2. Low-pT trigger coincidence between two adjacent detecting planes in the RPC pivot: this configuration allow a larger acceptance on cosmic ray flight direction, since the constraint on the interaction point has been removed.
Table 3 Trigger rates for three muon stations of the barrel sector 13, resulting from the low-pT trigger with fully open coincidence window in the phi measuring view. Data are compared with the simulation results. Trigger Sector 55 Trigger Sector 56 Tower Data Simulation Data Simulation 1 8Hz 5.3Hz 4Hz 5.7Hz 2 16Hz 9.0Hz 9Hz 8.8Hz 3 23Hz 8.7Hz 16Hz 8.6Hz
detector was simulated, whereas during the test a significant part of the detector was not yet installed, corresponding to a different cosmic muon absorption. 2. Sector 13 commissioning test: RPC efficiency study The first commissioning test was carried out on three muon towers of the ATLAS barrel sector 13. An event display is shown in figure 1. The
The simulated trigger rates resulted from these special trigger configurations are summarized in table 2.
Table 2 Simulated trigger rates of the two special configurations for the low-pT trigger optimizing the cosmic muon selection. Low-pT trigger Rate Fully open coincidence window 607 Hz Only pivot doublet 1107 Hz
In summer 2006 a first commissioning test of three muon towers in the ATLAS cavern made possible a comparison between the simulated results with the data (table 3). The data agree with the simulation within a factor 3. A possible explanation could be that the entire ATLAS
Figure 1. Event display of a cosmic muon in the ATLAS barrel sector 13.
RPC detection efficiency has been studied using the extrapolation of the track segments reconstructed with the MDT chambers (this method
337
E. Solfaroli et al. / Nuclear Physics B (Proc. Suppl.) 177–178 (2008) 335–338
In figure 3 the RPC efficiency is plotted as a function of the applied high voltage to the RPC gas volume. At 10 kV the RPCs are fully efficient.
Muon Tower Eta Sector 2 Efficiency
was already used to calculated the RPC efficiency for the H8 RPC test-beam data). The detector plane is declared efficient if a RPC hit is found within two strips from the extrapolated point. In figure 2 the correlation of the MDT track extrapolation and the RPC hit is shown.
1
0.9
RPC Strips - Eta view
St.Phi7 Eta3 - BML Confirm DZ1 DPhi2 Gap1 Eta
0.8
BML Confirm
BOL Confirm
0.7
30 0.6
MDT Tracking RPC Self-Tracking
25 0.5
RPC Plane
20 15 10 5 0 0
5 10 15 20 25 30 Eta strip expected by MDT reconstruction
Figure 2. RPC and MDT hit correlation at the commissioning test (RPC: high voltage HV = 9.8 kV , FE electronics threshold Vth = 1 V ; MDT: HV = 3.1 kV , Vth = −40mV ).
Efficiency
Plateau Curve - St.Phi7 Eta2 - BOL Confirm DZ2 DPhi2 Gap1 Eta
1
0.8
0.6
0.4
0.2
0 8.6
8.8
9
9.2
9.4
9.6
9.8
10 HV (kV)
Figure 3. RPC efficiency (using MDT tracks) as a function of the applied high voltage (RPC: Vth = 1 V ).
Figure 4. The RPC efficiency results for two muon stations of sector 13 using MDT tracks and stand-alone RPC tracks are compared.
Also a stand-alone tracking algorithm, using only RPC hits, was used to reconstruct cosmic muon tracks [6]. In figure 4 the efficiency results for two muon stations obtained using the MDT tracks are compared with the results produced with the stand-alone RPC tracks.
338
E. Solfaroli et al. / Nuclear Physics B (Proc. Suppl.) 177–178 (2008) 335–338
REFERENCES 1. ATLAS Collaboration “ATLAS Letter of Intent for a General-Purpose pp Experiment at the Large Hadron Collider at CERN ”, CERN/LHCC/92-4. 2. ATLAS Level-1 Trigger Group “ATLAS First-Level Trigger Technical Design Report”, CERN/LHCC 97-22 (1998). 3. V. Bocci, E. Petrolo, A. Salamon, R. Vari, S. Veneziano “The Coincidence Matrix ASIC of the Level-1 Muon Barrel Trigger of the ATLAS Experiment”, IEEE Transactions on Nuclear Science, (2003) Issue vol.50, no.4. 4. A.Dell’Acqua, A.Rimoldi, V.Vercesi: “Level1 Muon Trigger Simulation in the Barrel Region”, ATLAS Internal Note ATL-MUON-94067, ATL-M-PN-67. 5. E. Solfaroli “The ATLAS muon trigger detector in the barrel: performance simulation and cosmic ray tests”, PhD Thesis. 6. G. Chiodini et al. “RPC cosmic ray tests in the ATLAS experiment”, talk presented at the XIth Vienna Conference on Instrumentation 2007.
First cosmic ray results of the RPC commissioning in the ATLAS cavern E.Solfarolia, G.Aiellib , A.Aloisioc , M.Alviggic , S.Antonellid , L.Bellagambad, M.Biancoe , M.Bigliettic , D.Boscherinid, A.Brunid , G.Brunid , S.Budahf , P.Camarria, V.Canalec , R.Cardarellia, G.Carlinoc , G.Cattania , G.Chiodinie , G.Ciapettig , M.R.Colucciae , S.Constantinf , F.Conventic , R.De Asmundisc , M.Della Pietrac , D.Della Volpec , D.De Pedisg , A.Di Ciaccioa , A.Di Girolamog , A.Di Mattiag , R.Di Nardoa , M.Dogaruf , P.Giustid , E.Gorini e , F.Grancagnoloe, G.Iacobuccid , P.Iengoh, V.Izzoc , B.Libertia , C.Lucig , F.Marchesea , A.Migliaccioc , A.Nisatig , A.Polinid , E.Pasqualuccig , F.Pastoreg , S.Patricellic, M.Pectuf , R.Perrinoe, E.Petrolog, M.Primaverae, S.Rosatig , A.Salamona , R.Santonicoa , G.Sekhniaidzec , S.Spagnoloe, F.Spilag , R.Varig , S.Venezianog , L.Zanellog a
INFN Sezione di Roma Tor Vergata and Universit` a di Roma “Tor Vergata” - Italy
b
INFN Sezione di Roma Tor Vergata and ENEA Frascati - Italy
c
INFN Sezione di Napoli and Universit` a di Napoli “Federico II” - Italy
d e f
INFN Sezione di Bologna and Universit` a di Bologna - Italy
INFN Sezione di Lecce and Universit`a del Salento - Italy
NIPNE-HH, Bucarest, Romania
g
INFN Roma and Universit` a di Roma “La Sapienza” - Italy
h
CERN, Geneva - Switzerland
The first commissioning test of three muon towers of the ATLAS Muon Spectrometer, installed in the cavern, was carried out. The stations under test belong to the barrel sector 13, which is a large sector. A muon tower consists of three stations: the Inner, the Middle and the Outer, starting from the interaction point. The Barrel Inner Large (BIL) stations are constituted by MDT chambers; the Barrel Middle Large (BML) stations by MDTs assembled between two RPC chambers; and the Barrel Outer Large (BOL) stations by MDTs with only one RPC mounted downstream. Specific Level-1 trigger algorithms have been studied to trigger on cosmic rays and implemented to commission the muon stations. Comparison between the measured trigger rate and the simulated results will be presented. Moreover, the RPC performances have been studied by comparing the MDT track extrapolations with the firing RPC readout strips. The RPC detection efficiency is evaluated in the eta measuring view, resulting as a combination of gas volume efficiency and Front-End efficiency.
1. Simulation of the LVL-1 trigger rate in the barrel with cosmic muons The ATLAS [1] LVL-1 trigger system [2] layout is optimized for muons coming from the interaction point. However the trigger acceptance is adjustable by programming the Coincidence Matrices [3] with a set of appropriate thresholds.They have been optimized for the cosmic rays selection during the commissioning test. Three LVL-1 con0920-5632/$ – see front matter © 2007 Elsevier B.V. All rights reserved. doi:10.1016/j.nuclphysbps.2007.11.152
figurations have been studied using a dedicated simulation [4] of the detector performance. The cosmic muon rate simulated in the ATLAS cavern is 2.2 kHz [5]. Muons with energy below 30 GeV at ground level reach the cavern, only if they pass through the two shafts. The trigger rates computed for the cosmic muons using the ATLAS standard LVL-1 trigger logic, together with the values expected for the p-p collisions, are listed in table 1. Since these
336
E. Solfaroli et al. / Nuclear Physics B (Proc. Suppl.) 177–178 (2008) 335–338
Table 1 Trigger rates due to cosmic muons in the standard LVL-1 configuration. The values expected [2] for the p-p collisions at low (low-pT 6 GeV ) and high (High-pT 20 GeV ) luminosity are also indicated. LVL-1 trigger cosmic rays p-p collisions Low-pT 6 GeV 214 Hz ∼ 9.3 kHz Low-pT 10 GeV 141 Hz High-pT 20 GeV 21 Hz ∼ 1.4 kHz 18 Hz High-pT 40 GeV
values are not sufficient to ensure a high acquisition rate during the commissioning phase, two different schemes for the low-pT trigger have been considered: 1. Low-pT trigger with fully open coincidence window: no coincidence window is imposed except the limit due to the cabling. 2. Low-pT trigger coincidence between two adjacent detecting planes in the RPC pivot: this configuration allow a larger acceptance on cosmic ray flight direction, since the constraint on the interaction point has been removed.
Table 3 Trigger rates for three muon stations of the barrel sector 13, resulting from the low-pT trigger with fully open coincidence window in the phi measuring view. Data are compared with the simulation results. Trigger Sector 55 Trigger Sector 56 Tower Data Simulation Data Simulation 1 8Hz 5.3Hz 4Hz 5.7Hz 2 16Hz 9.0Hz 9Hz 8.8Hz 3 23Hz 8.7Hz 16Hz 8.6Hz
detector was simulated, whereas during the test a significant part of the detector was not yet installed, corresponding to a different cosmic muon absorption. 2. Sector 13 commissioning test: RPC efficiency study The first commissioning test was carried out on three muon towers of the ATLAS barrel sector 13. An event display is shown in figure 1. The
The simulated trigger rates resulted from these special trigger configurations are summarized in table 2.
Table 2 Simulated trigger rates of the two special configurations for the low-pT trigger optimizing the cosmic muon selection. Low-pT trigger Rate Fully open coincidence window 607 Hz Only pivot doublet 1107 Hz
In summer 2006 a first commissioning test of three muon towers in the ATLAS cavern made possible a comparison between the simulated results with the data (table 3). The data agree with the simulation within a factor 3. A possible explanation could be that the entire ATLAS
Figure 1. Event display of a cosmic muon in the ATLAS barrel sector 13.
RPC detection efficiency has been studied using the extrapolation of the track segments reconstructed with the MDT chambers (this method
337
E. Solfaroli et al. / Nuclear Physics B (Proc. Suppl.) 177–178 (2008) 335–338
In figure 3 the RPC efficiency is plotted as a function of the applied high voltage to the RPC gas volume. At 10 kV the RPCs are fully efficient.
Muon Tower Eta Sector 2 Efficiency
was already used to calculated the RPC efficiency for the H8 RPC test-beam data). The detector plane is declared efficient if a RPC hit is found within two strips from the extrapolated point. In figure 2 the correlation of the MDT track extrapolation and the RPC hit is shown.
1
0.9
RPC Strips - Eta view
St.Phi7 Eta3 - BML Confirm DZ1 DPhi2 Gap1 Eta
0.8
BML Confirm
BOL Confirm
0.7
30 0.6
MDT Tracking RPC Self-Tracking
25 0.5
RPC Plane
20 15 10 5 0 0
5 10 15 20 25 30 Eta strip expected by MDT reconstruction
Figure 2. RPC and MDT hit correlation at the commissioning test (RPC: high voltage HV = 9.8 kV , FE electronics threshold Vth = 1 V ; MDT: HV = 3.1 kV , Vth = −40mV ).
Efficiency
Plateau Curve - St.Phi7 Eta2 - BOL Confirm DZ2 DPhi2 Gap1 Eta
1
0.8
0.6
0.4
0.2
0 8.6
8.8
9
9.2
9.4
9.6
9.8
10 HV (kV)
Figure 3. RPC efficiency (using MDT tracks) as a function of the applied high voltage (RPC: Vth = 1 V ).
Figure 4. The RPC efficiency results for two muon stations of sector 13 using MDT tracks and stand-alone RPC tracks are compared.
Also a stand-alone tracking algorithm, using only RPC hits, was used to reconstruct cosmic muon tracks [6]. In figure 4 the efficiency results for two muon stations obtained using the MDT tracks are compared with the results produced with the stand-alone RPC tracks.
338
E. Solfaroli et al. / Nuclear Physics B (Proc. Suppl.) 177–178 (2008) 335–338
REFERENCES 1. ATLAS Collaboration “ATLAS Letter of Intent for a General-Purpose pp Experiment at the Large Hadron Collider at CERN ”, CERN/LHCC/92-4. 2. ATLAS Level-1 Trigger Group “ATLAS First-Level Trigger Technical Design Report”, CERN/LHCC 97-22 (1998). 3. V. Bocci, E. Petrolo, A. Salamon, R. Vari, S. Veneziano “The Coincidence Matrix ASIC of the Level-1 Muon Barrel Trigger of the ATLAS Experiment”, IEEE Transactions on Nuclear Science, (2003) Issue vol.50, no.4. 4. A.Dell’Acqua, A.Rimoldi, V.Vercesi: “Level1 Muon Trigger Simulation in the Barrel Region”, ATLAS Internal Note ATL-MUON-94067, ATL-M-PN-67. 5. E. Solfaroli “The ATLAS muon trigger detector in the barrel: performance simulation and cosmic ray tests”, PhD Thesis. 6. G. Chiodini et al. “RPC cosmic ray tests in the ATLAS experiment”, talk presented at the XIth Vienna Conference on Instrumentation 2007.