- Email: [email protected]
Particle identification for the P¯ANDA detector
Nuclear Instruments and Methods in Physics Research A 639 (2011) 169–172
Contents lists available at ScienceDirect
Nuclear Instruments and Methods in Physics Research A journal homepage: www.elsevier.com/locate/nima
Particle identification for the PANDA detector b f ¨ ¨ C. Schwarz a,, G. Ahmed b, A. Britting c, P. Buhler , E. Cowie d, V.Kh. Dodokhov e, M. Duren , D. Dutta a,1, c f g f d a c ¨ , D.I. Glazier , A. Hayrapetyan , M. Hoek , R. Hohler , A. Lehmann , D. Lehmann a, W. Eyrich , K. Fohl d d ¨ f, J. Marton b, O. Merle f, R. Montgomery d, K. Peters a, S. Reinicke c, R. Kaiser , T. Keri , P. Koch f, B. Krock d a,1 a G. Rosner , B. Roy , G. Schepers , L. Schmitt a, J. Schwiening a, B. Seitz d, C. Sfienti a,2, K. Suzuki b, F. Uhlig c, A.S. Vodopianov e, D.P. Watts g, W. Yu f a
GSI Helmholtzzentrum f¨ ur Schwerionenforschung GmbH, Planckstrasse 1, 64291 Darmstadt, Germany Stefan Meyer Institut f¨ ur subatomare Physik, Austrian Academy of Sciences, A-1090 Vienna, Austria Physikalisches Institut Abteilung IV, University of Erlangen-Nuremberg, D-91058 Erlangen, Germany d Department of Physics & Astronomy, Kelvin Building, University of Glasgow, Glasgow G12 8QQ, United Kingdom e Laboratory of High Energies, Joint Institute for Nuclear Research,141980 Dubna, Russia f II. Physikalisches Institut, University of Giessen, D-35392 Giessen, Germany g School of Physics, University of Edinburgh, Edinburgh EH9 3JZ, United Kingdom b c
a r t i c l e in f o
abstract
Available online 12 November 2010
Cooled antiproton beams of unprecedented intensities in the momentum range of 1.5–15 GeV/c will be used for the PANDA experiment at FAIR to perform high precision experiments in the charmed quark sector. The proposed PANDA detector is a 4p internal target spectrometer at the HESR allowing the detection and identification of neutral and charged particles generated within the total energy range of the antiproton annihilation products. The detector is divided in a forward spectrometer and a target spectrometer. The charged particle identification in the latter is performed by ring imaging Cherenkov counters employing the DIRC principle. & 2010 Elsevier B.V. All rights reserved.
Keywords: Particle identification Cherenkov counter Ring imaging RICH DIRC Fused silica radiator
1. Introduction The plans for the international Facility for Antiproton and Ion Research (FAIR) [1,2] at GSI currently get realized. A 30 GeV proton synchrotron will provide secondary beams with unsurpassed quality to many experiments. Antiprotons abundantly produced at a rate of 107 s 1 will be accumulated and transferred into the High Energy Storage Ring (HESR). The design parameters encompass the momentum range of 1.5–15 GeV/c with momentum resolution as good as 2 105 when cooled either stochastically or by magnetized electron cooling. At the interaction point of the PANDA detector (antiProton ANnihilations at DArmstadt) this antiproton beam crosses a dense internal target such that the average luminosity reaches 2 1032 cm2 s1 [3]. The interaction rate is 20 MHz on average, but can reach up to 50 MHz due to the filling scheme of the storage ring and fluctuations introduced by the target system. Two target systems are foreseen. A hydrogen cluster
Corresponding author.
E-mail address: [email protected] (C. Schwarz). Present address: Nuclear Physics Division, Bhabha Atomic Research Centre, Mumbai 400085, India. 2 ¨ Kernphysik, University of Mainz, D-55128 Mainz, Present address: Institut fur Germany. 1
0168-9002/$ - see front matter & 2010 Elsevier B.V. All rights reserved. doi:10.1016/j.nima.2010.10.116
target with a steady target density in time and a pellet target with the capability to determine the primary interaction vertex. The major physical research topics are: High precision spectroscopy of resonances in the energy region of charmonium and above; the exact knowledge about masses, widths, and branching ratios provides information about the mechanisms of quark confinement; in-medium effects of open and hidden charm and their relationship to the chiral symmetry breaking addressing especially the origin of hadron mass; so-called glueballs, predicted by QCD, need a firm experimental establishment in our picture of strong interactions; also hybrid meson states, so-called excited glue, in the mass range between 3 and 5 GeV/c2 are predicted to be rather narrow without mixing into neighboring resonances; hypernuclei, when abundantly produced, and examined with the next generation of gdetectors, will revive the physics with single and double hypernuclei. This will improve our modest knowledge on their structure and yield information on the interaction of hyperons with nucleons as well as hyperon–hyperon interaction. The detector (Fig. 1) is divided into a forward spectrometer with a dipole magnet and a target spectrometer with a solenoid magnet [5]. The Cherenkov counters within the target spectrometer take care of the charged particle identification. They are positioned between tracking detectors and an electromagnetic calorimeter consisting of PbWO4. In order to keep the latter small in size the
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C. Schwarz et al. / Nuclear Instruments and Methods in Physics Research A 639 (2011) 169–172
Fig. 1. The PANDA detector consists of a target and a forward magnetic spectrometer. The figure shows the subdetectors within the solenoid and subdetectors inside and behind the dipole magnet of the forward spectrometer. The DIRC detectors in the target spectrometer are drawn in light colors. The beam comes from the left as indicated by the arrow. (For interpretation of the references to color in this figure legend, the reader is referred to the web version of this article.)
Fig. 3. The PANDA Barrel DIRC with small photon detector box at the upstream side.
Fig. 2. Kaons from the radiative decay J=c-gK þ K [4]. The rectangular boxes denote the acceptance of the Barrel DIRC and Endcap DIRC. The lower momentum threshold is the threshold for Cherenkov light generation.
Cherenkov detectors cannot consume too much space [6]. Therefore, the DIRC principle was chosen for which the BaBar collaboration [7] has demonstrated an excellent performance. The target spectrometer houses a Barrel DIRC [9] covering polar angles from 1401 down to 221 and an Endcap DIRC covering the angles from 221 down to 101 and 51 in the horizontal and vertical direction, respectively. For the Endcap DIRC two options exist, a Focussing Disc DIRC and a Time Of Propagation DIRC. The acceptance of both devices are shown in Fig. 2. All DIRCs use synthetic fused silica radiators to meet the radiation hardness requirements [8].
2. The barrel DIRC A schematic view of the Barrel DIRC is shown in Fig. 3. The beam comes from the left as indicated by the arrow. On the right the radiator barrel is crossed vertically by the target pipe of a cluster-jet or a pellet target. Therefore, two radiator bars are missing at the top and at the bottom. Centered within the barrel a piece of the beam pipe is visible. In the forward direction the ends of the radiators are covered with a mirror reflecting the Cherenkov light back towards the photon detector. On the left the photon detector box is shown. We simulated the response of the Barrel DIRC with reaction
Fig. 4. The probability to misidentify a pion as a kaon as a function of the particle momentum (closed circles, left ordinate scale) and the efficiency to identify a kaon (open circles, right ordinate scale).
products coming from p þ p-J=c þ f with an older version of the geometry, which had the same angular resolution. The efficiency for the DIRC to identify a kaon has been investigated, and it is plotted as a function of momentum (open circles, ordinate scale on the right) in Fig. 4 for kaons in the mass region of 450–550 MeV/c2. The corresponding probability that a pion is incorrectly identified as a kaon is presented as the full circles (ordinate scale on the left) for the same mass region. The efficiency to detect kaons is close to 100% over a wide momentum range with a pion misidentification at the level of 1–2%. The loss of efficiency at low momenta is due to the kaon threshold. Operating the detectors in the veto mode, all low momentum tracks are considered to be kaons except those with Cherenkov signals. The purity of the kaon sample in this mode, however, depends on the detailed composition of the background. Currently a fast reconstruction method is developed [10] to operate the DIRC within the online event selection. The current design with an expansion volume extending 300 mm along the beam axis and a pixel size of 6:5 6:5 mm2 yields a single photon Cherenkov angle resolution of 6.3 mrad.
C. Schwarz et al. / Nuclear Instruments and Methods in Physics Research A 639 (2011) 169–172
171
The chromatic angular resolution is approximately 5 mrad. These values dominate the combined single photon resolution of about 8–9 mrad. For 20 photons and a track angular resolution of 1 mrad an overall Cherenkov resolution of 2–2.5 mrad is achieved. This allows the separation of pions and kaons with more than three standard deviations for the full momentum range up to 3.5 GeV/c. Further details about the setup and geometry options can be found in Ref. [11].
3. The endcap DIRC Two options of the Endcap DIRC are being considered. One is a Focusing Disc DIRC (FDD) using a two-dimensional pixel readout and the timing for background rejection [12,13]. The other emerged from a pure Time of Propagation (ToP) DIRC [14], to a so-called hybrid solution, where a two-dimensional spatial readout is combined with the time of arrival of the photons [15,16]. Both designs are adapted to the tight spatial requirements in the spectrometer and use a hardware dispersion correction. The FDD uses a LiF prism to correct for dispersion, the ToP-based design utilizes dichroic mirrors as selection for different wavelength bins. The Focusing Disc DIRC will house about 120 individual readout elements around an amorphous fused silica Cherenkov radiator plate (Fig. 5, left side). The detector measures the azimuthal angle of a photon at the rim, and the position on the focal plane in beam direction. The Lithium Fluoride prism corrects the dispersion. In Fig. 6 the focussing element with the LiF prism volume is shown. The simulated pion–kaon separation power of this option is shown in Fig. 7. The ToP-based design is shown in Fig. 5, right side. Together with the position around the rim the time of arrival of the photon is measured. A time resolution in the order of s ¼ 50 ps is needed. The wavelength bin of the photon is known due to blue or green transmitting dichroic mirrors in front of the photon detector. A green photon which is reflected from a blue transmitting dichroic mirror is not lost but measured as soon it hits a green transmitting dichroic mirror [15,16].
Fig. 6. The refraction of photons within a LiF-volume of the FDD allows to minimize dispersive blurring of the Cherenkov image. The curves show the effect of the correction. The uncorrected dashed lines with wavelengths of 300, 400, and 500 nm from top to bottom lie on one single solid line after correction.
Fig. 7. Simulated pion–kaon separation power of the Focusing Disc DIRC option.
Fig. 5. Left side: The Focusing Disc DIRC (FDD) option with a two dimensional readout. The timing information helps to reject background events. Right side: The ToP based design of the Endcap DIRC. Dichroic mirrors in front of the photon detectors either transmit the photons of a certain wavelength bin or reflect them towards another photon detector increasing the time of flight.
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C. Schwarz et al. / Nuclear Instruments and Methods in Physics Research A 639 (2011) 169–172
The ToP DIRC changed recently to a more robust hybrid design. It combines the advantages of the FDD with those of the ToP design. The added spatial photon hit coordinate in z-direction allows to separate the signal photons generated by the charged particle from the background photons generated by the delectrons. These delectrons produce Cherenkov photons with arrival times similar to the Cherenkov photons of the charged particle but uncorrelated in space. Since the radiator disc cannot be made as a single synthetic fused silica plate, several pieces need to be used. In the case of the FDD an open question is the partial reflection of photons at the glue joints. The ToP-based hybrid solution currently investigates the usage of unconnected radiator pieces. Both designs currently plan to use MCP-PMTs as photon detectors. However, due to a thicker radiator and a smaller photon detector area the aging of the photon detector places more severe constraints on its lifetime compared to the photon detector of the Barrel DIRC [17,18]. Therefore, also the usage of Geiger mode APDs is being investigated [19].
4. Conclusion For experiments with cooled antiproton beams in a storage ring on an internal target the PANDA experiment will be realized within the FAIR project at GSI/Darmstadt. It consists of a solenoid as target spectrometer, containing tracking detectors and Cherenkov detectors for particle identification for charged particles as well as an electromagnetic calorimeter. The charged PID is based on two Cherenkov counters using the DIRC principle. At large angles a
Barrel DIRC is foreseen and in forward direction an Endcap DIRC measures the charged particles. For the latter two options are investigated, a Focusing Disc DIRC (FDD) and a ToP-based hybrid solution.
Acknowledgments Work supported by EU6 Grant, contract number 515873, DIRACsecondary-Beams, and EU FP7 Grant, contract number 227431, HadronPhysics2. References [1] W.F. Henning, J. Phys. G Nucl. Part. Phys. 34 (2007) S551. [2] P. Spiller, G. Franchetti, Nucl. Instr. and Meth. A 561 (2006) 305. [3] M. Kotulla, et al., [PANDA Collaboration], /http://www.slac.stanford.edu/ spires/find/hep/www?irn=6280412S. [4] M. Chanowitz, R. Sharpe, Phys. Lett. B 132 (1983) 413. [5] W. Erni, et al., /http://arxiv.org/pdf/0903.3905S. ¨ [6] K. Fohl, et al., Nucl. Instr. and Meth. A 595 (2008) 88. [7] R. Aleksan, et al., Nucl. Instr. and Meth. A 538 (2005) 281. [8] M. Hoek, et al., this issue. [9] C. Schwarz, et al., Nucl. Instr. and Meth. A 595 (2008) 112. [10] D. Dutta, et al., this issue. [11] J. Schwiening, et al., this issue. [12] M. Hoek, et al., J. Instr. 4 (2008) P09008. [13] E. Cowie, et al., this issue. [14] M. Akazu, et al., Nucl. Instr. and Meth. A 440 (2000) 124. ¨ [15] P. Schonmeier, et al., Nucl. Instr. and Meth. A 595 (2008) 108. [16] O. Merle, et al., J. Instr. 4 (2009) P09008. [17] A. Lehmann, et al., Nucl. Instr. and Meth. A 595 (2008) 173. [18] A. Lehmann, et al., this issue. [19] H. Marton, et al., this issue.
Contents lists available at ScienceDirect
Nuclear Instruments and Methods in Physics Research A journal homepage: www.elsevier.com/locate/nima
Particle identification for the PANDA detector b f ¨ ¨ C. Schwarz a,, G. Ahmed b, A. Britting c, P. Buhler , E. Cowie d, V.Kh. Dodokhov e, M. Duren , D. Dutta a,1, c f g f d a c ¨ , D.I. Glazier , A. Hayrapetyan , M. Hoek , R. Hohler , A. Lehmann , D. Lehmann a, W. Eyrich , K. Fohl d d ¨ f, J. Marton b, O. Merle f, R. Montgomery d, K. Peters a, S. Reinicke c, R. Kaiser , T. Keri , P. Koch f, B. Krock d a,1 a G. Rosner , B. Roy , G. Schepers , L. Schmitt a, J. Schwiening a, B. Seitz d, C. Sfienti a,2, K. Suzuki b, F. Uhlig c, A.S. Vodopianov e, D.P. Watts g, W. Yu f a
GSI Helmholtzzentrum f¨ ur Schwerionenforschung GmbH, Planckstrasse 1, 64291 Darmstadt, Germany Stefan Meyer Institut f¨ ur subatomare Physik, Austrian Academy of Sciences, A-1090 Vienna, Austria Physikalisches Institut Abteilung IV, University of Erlangen-Nuremberg, D-91058 Erlangen, Germany d Department of Physics & Astronomy, Kelvin Building, University of Glasgow, Glasgow G12 8QQ, United Kingdom e Laboratory of High Energies, Joint Institute for Nuclear Research,141980 Dubna, Russia f II. Physikalisches Institut, University of Giessen, D-35392 Giessen, Germany g School of Physics, University of Edinburgh, Edinburgh EH9 3JZ, United Kingdom b c
a r t i c l e in f o
abstract
Available online 12 November 2010
Cooled antiproton beams of unprecedented intensities in the momentum range of 1.5–15 GeV/c will be used for the PANDA experiment at FAIR to perform high precision experiments in the charmed quark sector. The proposed PANDA detector is a 4p internal target spectrometer at the HESR allowing the detection and identification of neutral and charged particles generated within the total energy range of the antiproton annihilation products. The detector is divided in a forward spectrometer and a target spectrometer. The charged particle identification in the latter is performed by ring imaging Cherenkov counters employing the DIRC principle. & 2010 Elsevier B.V. All rights reserved.
Keywords: Particle identification Cherenkov counter Ring imaging RICH DIRC Fused silica radiator
1. Introduction The plans for the international Facility for Antiproton and Ion Research (FAIR) [1,2] at GSI currently get realized. A 30 GeV proton synchrotron will provide secondary beams with unsurpassed quality to many experiments. Antiprotons abundantly produced at a rate of 107 s 1 will be accumulated and transferred into the High Energy Storage Ring (HESR). The design parameters encompass the momentum range of 1.5–15 GeV/c with momentum resolution as good as 2 105 when cooled either stochastically or by magnetized electron cooling. At the interaction point of the PANDA detector (antiProton ANnihilations at DArmstadt) this antiproton beam crosses a dense internal target such that the average luminosity reaches 2 1032 cm2 s1 [3]. The interaction rate is 20 MHz on average, but can reach up to 50 MHz due to the filling scheme of the storage ring and fluctuations introduced by the target system. Two target systems are foreseen. A hydrogen cluster
Corresponding author.
E-mail address: [email protected] (C. Schwarz). Present address: Nuclear Physics Division, Bhabha Atomic Research Centre, Mumbai 400085, India. 2 ¨ Kernphysik, University of Mainz, D-55128 Mainz, Present address: Institut fur Germany. 1
0168-9002/$ - see front matter & 2010 Elsevier B.V. All rights reserved. doi:10.1016/j.nima.2010.10.116
target with a steady target density in time and a pellet target with the capability to determine the primary interaction vertex. The major physical research topics are: High precision spectroscopy of resonances in the energy region of charmonium and above; the exact knowledge about masses, widths, and branching ratios provides information about the mechanisms of quark confinement; in-medium effects of open and hidden charm and their relationship to the chiral symmetry breaking addressing especially the origin of hadron mass; so-called glueballs, predicted by QCD, need a firm experimental establishment in our picture of strong interactions; also hybrid meson states, so-called excited glue, in the mass range between 3 and 5 GeV/c2 are predicted to be rather narrow without mixing into neighboring resonances; hypernuclei, when abundantly produced, and examined with the next generation of gdetectors, will revive the physics with single and double hypernuclei. This will improve our modest knowledge on their structure and yield information on the interaction of hyperons with nucleons as well as hyperon–hyperon interaction. The detector (Fig. 1) is divided into a forward spectrometer with a dipole magnet and a target spectrometer with a solenoid magnet [5]. The Cherenkov counters within the target spectrometer take care of the charged particle identification. They are positioned between tracking detectors and an electromagnetic calorimeter consisting of PbWO4. In order to keep the latter small in size the
170
C. Schwarz et al. / Nuclear Instruments and Methods in Physics Research A 639 (2011) 169–172
Fig. 1. The PANDA detector consists of a target and a forward magnetic spectrometer. The figure shows the subdetectors within the solenoid and subdetectors inside and behind the dipole magnet of the forward spectrometer. The DIRC detectors in the target spectrometer are drawn in light colors. The beam comes from the left as indicated by the arrow. (For interpretation of the references to color in this figure legend, the reader is referred to the web version of this article.)
Fig. 3. The PANDA Barrel DIRC with small photon detector box at the upstream side.
Fig. 2. Kaons from the radiative decay J=c-gK þ K [4]. The rectangular boxes denote the acceptance of the Barrel DIRC and Endcap DIRC. The lower momentum threshold is the threshold for Cherenkov light generation.
Cherenkov detectors cannot consume too much space [6]. Therefore, the DIRC principle was chosen for which the BaBar collaboration [7] has demonstrated an excellent performance. The target spectrometer houses a Barrel DIRC [9] covering polar angles from 1401 down to 221 and an Endcap DIRC covering the angles from 221 down to 101 and 51 in the horizontal and vertical direction, respectively. For the Endcap DIRC two options exist, a Focussing Disc DIRC and a Time Of Propagation DIRC. The acceptance of both devices are shown in Fig. 2. All DIRCs use synthetic fused silica radiators to meet the radiation hardness requirements [8].
2. The barrel DIRC A schematic view of the Barrel DIRC is shown in Fig. 3. The beam comes from the left as indicated by the arrow. On the right the radiator barrel is crossed vertically by the target pipe of a cluster-jet or a pellet target. Therefore, two radiator bars are missing at the top and at the bottom. Centered within the barrel a piece of the beam pipe is visible. In the forward direction the ends of the radiators are covered with a mirror reflecting the Cherenkov light back towards the photon detector. On the left the photon detector box is shown. We simulated the response of the Barrel DIRC with reaction
Fig. 4. The probability to misidentify a pion as a kaon as a function of the particle momentum (closed circles, left ordinate scale) and the efficiency to identify a kaon (open circles, right ordinate scale).
products coming from p þ p-J=c þ f with an older version of the geometry, which had the same angular resolution. The efficiency for the DIRC to identify a kaon has been investigated, and it is plotted as a function of momentum (open circles, ordinate scale on the right) in Fig. 4 for kaons in the mass region of 450–550 MeV/c2. The corresponding probability that a pion is incorrectly identified as a kaon is presented as the full circles (ordinate scale on the left) for the same mass region. The efficiency to detect kaons is close to 100% over a wide momentum range with a pion misidentification at the level of 1–2%. The loss of efficiency at low momenta is due to the kaon threshold. Operating the detectors in the veto mode, all low momentum tracks are considered to be kaons except those with Cherenkov signals. The purity of the kaon sample in this mode, however, depends on the detailed composition of the background. Currently a fast reconstruction method is developed [10] to operate the DIRC within the online event selection. The current design with an expansion volume extending 300 mm along the beam axis and a pixel size of 6:5 6:5 mm2 yields a single photon Cherenkov angle resolution of 6.3 mrad.
C. Schwarz et al. / Nuclear Instruments and Methods in Physics Research A 639 (2011) 169–172
171
The chromatic angular resolution is approximately 5 mrad. These values dominate the combined single photon resolution of about 8–9 mrad. For 20 photons and a track angular resolution of 1 mrad an overall Cherenkov resolution of 2–2.5 mrad is achieved. This allows the separation of pions and kaons with more than three standard deviations for the full momentum range up to 3.5 GeV/c. Further details about the setup and geometry options can be found in Ref. [11].
3. The endcap DIRC Two options of the Endcap DIRC are being considered. One is a Focusing Disc DIRC (FDD) using a two-dimensional pixel readout and the timing for background rejection [12,13]. The other emerged from a pure Time of Propagation (ToP) DIRC [14], to a so-called hybrid solution, where a two-dimensional spatial readout is combined with the time of arrival of the photons [15,16]. Both designs are adapted to the tight spatial requirements in the spectrometer and use a hardware dispersion correction. The FDD uses a LiF prism to correct for dispersion, the ToP-based design utilizes dichroic mirrors as selection for different wavelength bins. The Focusing Disc DIRC will house about 120 individual readout elements around an amorphous fused silica Cherenkov radiator plate (Fig. 5, left side). The detector measures the azimuthal angle of a photon at the rim, and the position on the focal plane in beam direction. The Lithium Fluoride prism corrects the dispersion. In Fig. 6 the focussing element with the LiF prism volume is shown. The simulated pion–kaon separation power of this option is shown in Fig. 7. The ToP-based design is shown in Fig. 5, right side. Together with the position around the rim the time of arrival of the photon is measured. A time resolution in the order of s ¼ 50 ps is needed. The wavelength bin of the photon is known due to blue or green transmitting dichroic mirrors in front of the photon detector. A green photon which is reflected from a blue transmitting dichroic mirror is not lost but measured as soon it hits a green transmitting dichroic mirror [15,16].
Fig. 6. The refraction of photons within a LiF-volume of the FDD allows to minimize dispersive blurring of the Cherenkov image. The curves show the effect of the correction. The uncorrected dashed lines with wavelengths of 300, 400, and 500 nm from top to bottom lie on one single solid line after correction.
Fig. 7. Simulated pion–kaon separation power of the Focusing Disc DIRC option.
Fig. 5. Left side: The Focusing Disc DIRC (FDD) option with a two dimensional readout. The timing information helps to reject background events. Right side: The ToP based design of the Endcap DIRC. Dichroic mirrors in front of the photon detectors either transmit the photons of a certain wavelength bin or reflect them towards another photon detector increasing the time of flight.
172
C. Schwarz et al. / Nuclear Instruments and Methods in Physics Research A 639 (2011) 169–172
The ToP DIRC changed recently to a more robust hybrid design. It combines the advantages of the FDD with those of the ToP design. The added spatial photon hit coordinate in z-direction allows to separate the signal photons generated by the charged particle from the background photons generated by the delectrons. These delectrons produce Cherenkov photons with arrival times similar to the Cherenkov photons of the charged particle but uncorrelated in space. Since the radiator disc cannot be made as a single synthetic fused silica plate, several pieces need to be used. In the case of the FDD an open question is the partial reflection of photons at the glue joints. The ToP-based hybrid solution currently investigates the usage of unconnected radiator pieces. Both designs currently plan to use MCP-PMTs as photon detectors. However, due to a thicker radiator and a smaller photon detector area the aging of the photon detector places more severe constraints on its lifetime compared to the photon detector of the Barrel DIRC [17,18]. Therefore, also the usage of Geiger mode APDs is being investigated [19].
4. Conclusion For experiments with cooled antiproton beams in a storage ring on an internal target the PANDA experiment will be realized within the FAIR project at GSI/Darmstadt. It consists of a solenoid as target spectrometer, containing tracking detectors and Cherenkov detectors for particle identification for charged particles as well as an electromagnetic calorimeter. The charged PID is based on two Cherenkov counters using the DIRC principle. At large angles a
Barrel DIRC is foreseen and in forward direction an Endcap DIRC measures the charged particles. For the latter two options are investigated, a Focusing Disc DIRC (FDD) and a ToP-based hybrid solution.
Acknowledgments Work supported by EU6 Grant, contract number 515873, DIRACsecondary-Beams, and EU FP7 Grant, contract number 227431, HadronPhysics2. References [1] W.F. Henning, J. Phys. G Nucl. Part. Phys. 34 (2007) S551. [2] P. Spiller, G. Franchetti, Nucl. Instr. and Meth. A 561 (2006) 305. [3] M. Kotulla, et al., [PANDA Collaboration], /http://www.slac.stanford.edu/ spires/find/hep/www?irn=6280412S. [4] M. Chanowitz, R. Sharpe, Phys. Lett. B 132 (1983) 413. [5] W. Erni, et al., /http://arxiv.org/pdf/0903.3905S. ¨ [6] K. Fohl, et al., Nucl. Instr. and Meth. A 595 (2008) 88. [7] R. Aleksan, et al., Nucl. Instr. and Meth. A 538 (2005) 281. [8] M. Hoek, et al., this issue. [9] C. Schwarz, et al., Nucl. Instr. and Meth. A 595 (2008) 112. [10] D. Dutta, et al., this issue. [11] J. Schwiening, et al., this issue. [12] M. Hoek, et al., J. Instr. 4 (2008) P09008. [13] E. Cowie, et al., this issue. [14] M. Akazu, et al., Nucl. Instr. and Meth. A 440 (2000) 124. ¨ [15] P. Schonmeier, et al., Nucl. Instr. and Meth. A 595 (2008) 108. [16] O. Merle, et al., J. Instr. 4 (2009) P09008. [17] A. Lehmann, et al., Nucl. Instr. and Meth. A 595 (2008) 173. [18] A. Lehmann, et al., this issue. [19] H. Marton, et al., this issue.