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 PANDA detector will investigate antiproton annihilations with beams in the momentum range of 1.5 GeV/c to 15 GeV/c on a fixed target. An almost 4π acceptance double spectrometer 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

A Britting

A Hayrapetyan

A Lehmann

A S Vodopianov

B Kröck

B Lewandowski

B Seitz

C Schwarz

C Sfienti

D Lehmann

E Cowie

E Widmann

F Uhlig

G Kalicy

G Rosner

G Schepers

J Marton

J Schwiening

K Föhl

K Peters

K Suzuki

L Gruber

L Schmitt

M Düren

M Hoek

M Patsyuk

M. Patsyuk .

O Merle

P Bühler

P Koch

PANDA collaboration

R Hohler

R Montgomery

S. Spataro .

T Keri

V Kh Dodokhov

W Eyrich

W.F. Henning

English

Schwarz, C.

Britting, A.

Bühler, P.

Cowie, E.

Dodokhov, V.K.

Düren, M.

Eyrich, W.

Föhl, K.

Gruber, L.

Hayrapetyan, A.

Hoek, M.

Hohler, R.

Kalicy, G.

Keri, T.

Koch, P.

Kröck, B.

Lehmann, A.

Lehmann, D.

Lewandowski, B.

Marton, J.

Merle, O.

Montgomery, R.

Patsyuk, M.

Peters, K.

Rosner, G.

Schepers, G.

Schmitt, L.

Schwiening, J.

Seitz, B.

Sfienti, C.

Suzuki, K.

Uhlig, F.

Vodopianov, A.S.,

Widmann, E.

Enlighten

    Schwarz, C. et al. (2012) The barrel DIRC of PANDA. Journal of Instrumentation, 7(2), C02008.   Copyright © 2012 IOP Publishing Ltd and SISSA   Version: Published       http://eprints.gla.ac.uk/85255    Deposited on:  02 July 2015              Enlighten – Research publications by members of the University of Glasgow http://eprints.gla.ac.uk  This content has been downloaded from IOPscience. Please scroll down to see the full text.Download details:IP Address: 130.209.115.202This content was downloaded on 02/07/2015 at 11:39Please note that terms and conditions apply. The Barrel DIRC of PANDAView the table of contents for this issue, or go to the journal homepage for more2012 JINST 7 C02008(http://iopscience.iop.org/1748-0221/7/02/C02008)Home Search Collections Journals About Contact us My IOPscience2012 JINST 7 C02008PUBLISHED BY IOP PUBLISHING FOR SISSARECEIVED: October 16, 2011ACCEPTED: January 5, 2012PUBLISHED: February 7, 2012WORKSHOP ON FAST CHERENKOV DETECTORS - PHOTON DETECTION,DIRC DESIGN AND DAQAPRIL 4–6, 2011, GIESSEN, GERMANYThe Barrel DIRC of PANDAC. Schwarz,a,1 A. Britting,b P. Bu¨hler,c E. Cowie,d V.Kh. Dodokhov,e M. Du¨ren, fW. Eyrich,b K. Fo¨hl, f L. Gruber,c A. Hayrapetyan, f M. Hoek,d R. Hohler,a G. Kalicy,aT. Keri,d P. Koch, f B. Kro¨ck, f A. Lehmann,b D. Lehmann,a B. Lewandowski,aJ. Marton,c O. Merle, f R. Montgomery,d M. Patsyuk,a K. Peters,a G. Rosner,dG. Schepers,a L. Schmitt,a J. Schwiening,a B. Seitz,d C. Sfienti,g K. Suzuki,cF. Uhlig,b A.S. Vodopianove and E. WidmanncaGSI Helmholtzzentrum fu¨r Schwerionenforschung GmbH,Planckstrasse 1, 64291 Darmstadt, GermanybPhysikalisches Institut Abteilung IV, University of Erlangen-Nuremberg,D-91058 Erlangen, GermanycStefan Meyer Institut fu¨r subatomare Physik, Austrian Academy of Sciences,A-1090 Vienna, AustriadSUPA School of Physics & Astronomy, Kelvin Building, University of Glasgow,Glasgow G12 8QQ, U.K.eLaboratory of High Energies, Joint Institute for Nuclear Research,141980 Dubna, Russiaf II. Physikalisches Institut, University of Giessen,D-35392 Giessen, GermanygInstitut fu¨r Kernphysik, University of Mainz,D-55128 Mainz, GermanyE-mail: C.Schwarz@gsi.deABSTRACT: 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 experimentsin the charmed quark sector. The PANDA detector will investigate antiproton annihilations withbeams in the momentum range of 1.5 GeV/c to 15 GeV/c on a fixed target. An almost 4pi acceptancedouble spectrometer is divided in a forward spectrometer and a target spectrometer. The chargedparticle identification in the latter is performed by ring imaging Cherenkov counters employing theDIRC principle.KEYWORDS: Particle identification methods; Cherenkov detectors1Corresponding author.c© 2012 IOP Publishing Ltd and SISSA doi:10.1088/1748-0221/7/02/C020082012 JINST 7 C02008Contents1 Introduction 12 Barrel DIRC 23 Performance 34 Outlook 41 IntroductionThe international Facility for Antiproton and Ion Research (FAIR) [1, 2] at GSI currently gets real-ized. A 30 GeV proton synchrotron will provide secondary beams with unsurpassed quality to manyexperiments. Antiprotons abundantly produced at a rate of 2× 107 s−1 will be accumulated andtransferred into the High Energy Storage Ring (HESR). The design parameters cover the momen-tum range of 1.5 to 15 GeV/c with momentum resolution as good as 2×10−5 when cooled eitherstochastically or by magnetized electron cooling. At the interaction point of the PANDA detector(antiProton ANnihilations at DArmstadt), shown in figure 1, this antiproton beam crosses a denseinternal target such that the average luminosity reaches 2×1032 cm−2s−1 [3]. The interaction rateis 20 MHz on average, but can reach up to 50 MHz due to the filling scheme of the storage ring andfluctuations introduced by the target system. Two target systems are foreseen. A hydrogen clustertarget with a steady target density in time and a pellet target with the capability to determine theprimary interaction vertex.The physics program of PANDA covers a wide range of subjects: High precision spectroscopyof 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 breakingaddressing especially the origin of hadron mass; glueballs, predicted by QCD, need a firm experi-mental establishment in the current picture of strong interactions; hybrid meson states, also knownas excited glue, in the mass range between 3 and 5 GeV/c2 are predicted to be rather narrow with-out mixing into neighboring resonances; hypernuclei, when abundantly produced, and examinedwith the next generation of γ-detectors, will revive the physics with single and double hypernuclei.This will improve the currently modest knowledge on their structure and yield information on theinteraction of hyperons with nucleons as well as hyperon-hyperon interaction.With the novel design of the detector as well as of the readout PANDA faces the challengesof the necessary momentum resolution (1%), high dynamic range for γ-detection (few MeV to10 GeV) and high-range charged-particle identification capability (several hundred MeV to someGeV for electrons, muons, pions, kaons, and protons). For the operation at the high interaction rate– 1 –2012 JINST 7 C02008Figure 1. The PANDA detector comprises a target and a forward magnetic spectrometer. The figure showsthe subdetectors within the solenoid and subdetectors inside and behind the dipole magnet of the forwardspectrometer. The DIRC detectors in the target spectrometer are drawn in light colors. The beam comesfrom the left as indicated by the arrow.of 2×107 s−1 a self-triggering readout scheme for different physical topologies is discussed wherethe frontend continuously processes the detector data and autonomously finds valid hits.The detector, shown in figure 1, is divided into a forward spectrometer with a dipole magnetand a target spectrometer with a solenoid magnet [5]. The Cherenkov counters within the targetspectrometer take care of the charged particle identification. They are positioned between trackingdetectors and an electromagnetic calorimeter consisting of PbWO4. In order to keep the latter smallin size the Cherenkov detectors cannot occupy too much space [6, 9]. Therefore, the DIRC princi-ple was chosen for which the BaBar collaboration [7] has demonstrated an excellent performance.The target spectrometer houses a Barrel DIRC [8, 9] covering polar angles from 140o down to 22oand an Endcap DIRC, called the 3D Disc-DIRC, covering the angles from 22o down to 10o and 5oin the horizontal and vertical directions, respectively (figure 2).2 Barrel DIRCWhen a charged particle traverses a radiator of refractive index n with a velocity β = v/c > 1/n itemits Cherenkov photons on a cone with a half opening angle cos(θC)= 1/(βn). For particle tracksof β ≈ 1 in radiators of refractive index n>√2 some photons are always totally internally reflected.The magnitude of the Cherenkov angle is conserved during the internal reflections provided adja-cent and opposite optical surfaces are perpendicular and parallel to each other, respectively. The– 2 –2012 JINST 7 C02008Figure 2. Polar angle distribution of kaons from the radiative decay J/ψ → γK+K− [4]. The rectangularboxes denote the acceptance of the Barrel DIRC and Endcap DIRC. The lower momentum threshold is thethreshold for Cherenkov light generation.efficiency for the DIRC to identify a kaon has been investigated with an downscaled setup of theBaBar [7] version for kaons in the mass region 450−550 MeV/c2. The efficiency to detect kaons isclose to 100% with a pion misidentification at the level of 1-2 %. Operating the detectors in the vetomode, all low momentum tracks with momenta below the kaon threshold are considered to be kaonsexcept those with Cherenkov signals. The purity of the kaon sample in this mode, however, dependson the detailed composition of the background. Currently the simulation of an improved design asshown in figure 1 is developed. In this design, a smaller photon expansion volume within the yokeof the solenoid magnet is used. Focussing lenses at the end of the radiator bars provide a sufficientsharp image on the photon detector plane. A the same time a fast reconstruction method is devel-oped [10] to operate the DIRC within the online event selection. The simulation of a single chargedparticle within the PandaRoot framework [11] is shown in figure 3. The produced photons are inter-nally reflected and guided towards the expansion box. Photons propagating towards the other endare reflected off a mirror. Depending on their direction, the photons reach different positions on thebackside of the expansion box where they are recorded by photon detectors. From the hit positionthe initial photon direction can be calculated if the hit radiator is know (tracking detectors).3 PerformanceThe current design is based on 2500× 17× 35mm3 radiator bars made of synthetical fused silica.Five bars form one bar box and 16 bar boxes make up a barrel of 50 cm radius around the beam line.Two gaps, one on the top and one at the bottom of the barrel are foreseen for the vertical beam pipe,whereas all bar boxes are identical. The expansion box has a depth of 300mm and the pixel size of– 3 –2012 JINST 7 C02008Figure 3. Upstream view of the PANDA Barrel DIRC. The internallly reflecting photons propagate alongthe radiator until they hit the backside of the expansion box. Here, they are recorded by pixelized photondetectors.the photon detectors is 6.5× 6.5mm2 [13]. The expansion box is filled with Marcol82 oil [12] toreduce image distortions. Between radiator and expansion volume a focusing lens ensures a sharpimage of the Cherenkov photons. The pixel size adds 6.3 mrad to the single photon Cherenkov an-gle resolution. The chromatic angular resolution contributes for 5 mrad. These values dominate thecombined single photon resolution that amounts to 8−9 mrad. For 20 photons and a track angularresolution of 1 mrad an overall Cherenkov resolution of 2−2.5 mrad is achieved. This allows theseparation of pions and kaons with more than 3 standard deviations for the full momentum rangeup to 3.5 GeV/c. Further details about the setup and geometry options can be found in ref. [14].4 OutlookThe number of critical parameters of the current design are not yet optimized and several designoptions need to be investigated. The influence of these options on the performance of the DIRC,estimated in terms of single photon Cherenkov angle resolution and photon yield per particle, needsto be studies within the PANDARoot simulation framework. One of the design options is the crosssection of the radiator which could be in the extreme case a plate. Another option is a differentfocussing system with a focussing mirror at the downstream end of the radiator. Most photons will– 4 –2012 JINST 7 C02008hit this mirror since the angular distribution of the charged particles in a fixed target experiment isforward peaked.AcknowledgmentsThis work is supported by EU6 grant, contract number 515873, DIRACsecondary-Beams, and EUFP7 grant, contract number 227431, HadronPhysics2.References[1] W.F. Henning, FAIR and its experimental program, J. Phys. G 34 (2007) S551.[2] P. Spiller and G. Franchetti, The FAIR accelerator project at GSI, Nucl. Instrum. Meth. A 561 (2006)305.[3] PANDA collaboration, M. Kotulla et al., Strong interaction studies with antiprotons, letter of intentfor PANDA (Antiproton Annihilations at Darmstadt), http://inspirehep.net/record/671592.[4] M.S. Chanowitz and S.R. Sharpe, Glueballs and Meiktons which decay to multi-kaon final states,Phys. Lett. B 132 (1983) 413.[5] PANDA collaboration, M.F.M. Lutz et al., Physics performance report for PANDA: stronginteraction studies with antiprotons, arXiv:0903.3905.[6] K. Fo¨hl et al., The DIRC detectors of the PANDA experiment at FAIR, Nucl. Instrum. Meth. A 595(2008) 88.[7] BABAR-DIRC collaboration, I. Adam et al., The DIRC particle identification system for the BaBarexperiment, Nucl. Instrum. Meth. A 538 (2005) 281.[8] C. Schwarz et al., The Barrel DIRC of the PANDA experiment, Nucl. Instrum. Meth. A 595 (2008)112.[9] C. Schwarz et al., Particle identification for the PANDA detector, Nucl. Instrum. Meth. A 639 (2011)169.[10] M. Patsyuk et al., Simulation and reconstruction of the PANDA Barrel DIRC detector, 2011 JINST 6C11015.[11] S. Spataro et al., Simulation and event reconstruction inside the PandaRoot framework, J. Phys. Conf.Ser. 119 (2008) 032035.[12] Exxon Mobil Corporation webpage, http://www.exxonmobil.com/.[13] Burle-Planacon MCP-PMT, http://www.photonis.com/, http://www.burle.com/.[14] PANDA CHERENKOV collaboration, J. Schwiening, The Barrel DIRC detector for the PANDAexperiment at FAIR, Nucl. Instrum. Meth. A 639 (2011) 315.– 5 –

The barrel DIRC of PANDA

Schwarz, C

Britting, A

Hoek, M

Hohler, R

Kalicy, G

Keri, T

Koch, P

Kröck, B

Lehmann, A

Lehmann, D

Lewandowski, B

Marton, J

Bühler, P

Merle, O

Montgomery, R

Patsyuk, M

Peters, K

Rosner, G

Schepers, G

Schmitt, L

Schwiening, J

Seitz, B

Sfienti, C

Cowie, E

Suzuki, K

Uhlig, F

Vodopianov, A S

Widmann, E

Dodokhov, V Kh

Düren, M

Eyrich, W

Föhl, K

Gruber, L

Hayrapetyan, A

GSI Repository

The Barrel DIRC of PANDA

Enlighten: Publications

  
 
 
Schwarz, C. et al. (2012) The barrel DIRC of PANDA. Journal of 
Instrumentation, 7(2), C02008. 
 
 
Copyright © 2012 IOP Publishing Ltd and SISSA 
 
 
Version: Published 
 
 
 
 
 
 
http://eprints.gla.ac.uk/85255 
 
 
 
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http://eprints.gla.ac.uk 
 
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 The Barrel DIRC of PANDA
View the table of contents for this issue, or go to the journal homepage for more
2012 JINST 7 C02008
(http://iopscience.iop.org/1748-0221/7/02/C02008)
Home Search Collections Journals About Contact us My IOPscience
2012 JINST 7 C02008
PUBLISHED BY IOP PUBLISHING FOR SISSA
RECEIVED: October 16, 2011
ACCEPTED: January 5, 2012
PUBLISHED: February 7, 2012
WORKSHOP ON FAST CHERENKOV DETECTORS - PHOTON DETECTION,
DIRC DESIGN AND DAQ
APRIL 4–6, 2011, GIESSEN, GERMANY
The Barrel DIRC of PANDA
C. Schwarz,a,1 A. Britting,b P. Bu¨hler,c E. Cowie,d V.Kh. Dodokhov,e M. Du¨ren, f
W. Eyrich,b K. Fo¨hl, f L. Gruber,c A. Hayrapetyan, f M. Hoek,d R. Hohler,a G. Kalicy,a
T. Keri,d P. Koch, f B. Kro¨ck, f A. Lehmann,b D. Lehmann,a B. Lewandowski,a
J. Marton,c O. Merle, f R. Montgomery,d M. Patsyuk,a K. Peters,a G. Rosner,d
G. Schepers,a L. Schmitt,a J. Schwiening,a B. Seitz,d C. Sfienti,g K. Suzuki,c
F. Uhlig,b A.S. Vodopianove and E. Widmannc
aGSI Helmholtzzentrum fu¨r Schwerionenforschung GmbH,
Planckstrasse 1, 64291 Darmstadt, Germany
bPhysikalisches Institut Abteilung IV, University of Erlangen-Nuremberg,
D-91058 Erlangen, Germany
cStefan Meyer Institut fu¨r subatomare Physik, Austrian Academy of Sciences,
A-1090 Vienna, Austria
dSUPA School of Physics & Astronomy, Kelvin Building, University of Glasgow,
Glasgow G12 8QQ, U.K.
eLaboratory of High Energies, Joint Institute for Nuclear Research,
141980 Dubna, Russia
f II. Physikalisches Institut, University of Giessen,
D-35392 Giessen, Germany
gInstitut fu¨r Kernphysik, University of Mainz,
D-55128 Mainz, Germany
E-mail: C.Schwarz@gsi.de
ABSTRACT: 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 PANDA detector will investigate antiproton annihilations with
beams in the momentum range of 1.5 GeV/c to 15 GeV/c on a fixed target. An almost 4pi acceptance
double spectrometer 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.
KEYWORDS: Particle identification methods; Cherenkov detectors
1Corresponding author.
c© 2012 IOP Publishing Ltd and SISSA doi:10.1088/1748-0221/7/02/C02008
2012 JINST 7 C02008
Contents
1 Introduction 1
2 Barrel DIRC 2
3 Performance 3
4 Outlook 4
1 Introduction
The international Facility for Antiproton and Ion Research (FAIR) [1, 2] at GSI currently gets real-
ized. A 30 GeV proton synchrotron will provide secondary beams with unsurpassed quality to many
experiments. Antiprotons abundantly produced at a rate of 2× 107 s−1 will be accumulated and
transferred into the High Energy Storage Ring (HESR). The design parameters cover the momen-
tum range of 1.5 to 15 GeV/c with momentum resolution as good as 2×10−5 when cooled either
stochastically or by magnetized electron cooling. At the interaction point of the PANDA detector
(antiProton ANnihilations at DArmstadt), shown in figure 1, this antiproton beam crosses a dense
internal target such that the average luminosity reaches 2×1032 cm−2s−1 [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
target with a steady target density in time and a pellet target with the capability to determine the
primary interaction vertex.
The physics program of PANDA covers a wide range of subjects: 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; glueballs, predicted by QCD, need a firm experi-
mental establishment in the current picture of strong interactions; hybrid meson states, also known
as excited glue, in the mass range between 3 and 5 GeV/c2 are predicted to be rather narrow with-
out mixing into neighboring resonances; hypernuclei, when abundantly produced, and examined
with the next generation of γ-detectors, will revive the physics with single and double hypernuclei.
This will improve the currently modest knowledge on their structure and yield information on the
interaction of hyperons with nucleons as well as hyperon-hyperon interaction.
With the novel design of the detector as well as of the readout PANDA faces the challenges
of the necessary momentum resolution (1%), high dynamic range for γ-detection (few MeV to
10 GeV) and high-range charged-particle identification capability (several hundred MeV to some
GeV for electrons, muons, pions, kaons, and protons). For the operation at the high interaction rate
– 1 –
2012 JINST 7 C02008
Figure 1. The PANDA detector comprises 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.
of 2×107 s−1 a self-triggering readout scheme for different physical topologies is discussed where
the frontend continuously processes the detector data and autonomously finds valid hits.
The detector, shown in figure 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 Cherenkov detectors cannot occupy too much space [6, 9]. Therefore, the DIRC princi-
ple was chosen for which the BaBar collaboration [7] has demonstrated an excellent performance.
The target spectrometer houses a Barrel DIRC [8, 9] covering polar angles from 140o down to 22o
and an Endcap DIRC, called the 3D Disc-DIRC, covering the angles from 22o down to 10o and 5o
in the horizontal and vertical directions, respectively (figure 2).
2 Barrel DIRC
When a charged particle traverses a radiator of refractive index n with a velocity β = v/c > 1/n it
emits Cherenkov photons on a cone with a half opening angle cos(θC)= 1/(βn). For particle tracks
of β ≈ 1 in radiators of refractive index n>√2 some photons are always totally internally reflected.
The magnitude of the Cherenkov angle is conserved during the internal reflections provided adja-
cent and opposite optical surfaces are perpendicular and parallel to each other, respectively. The
– 2 –
2012 JINST 7 C02008
Figure 2. Polar angle distribution of kaons from the radiative decay J/ψ → γK+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.
efficiency for the DIRC to identify a kaon has been investigated with an downscaled setup of the
BaBar [7] version for kaons in the mass region 450−550 MeV/c2. The efficiency to detect kaons is
close to 100% with a pion misidentification at the level of 1-2 %. Operating the detectors in the veto
mode, all low momentum tracks with momenta below the kaon threshold 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 the simulation of an improved design as
shown in figure 1 is developed. In this design, a smaller photon expansion volume within the yoke
of the solenoid magnet is used. Focussing lenses at the end of the radiator bars provide a sufficient
sharp image on the photon detector plane. A the same time a fast reconstruction method is devel-
oped [10] to operate the DIRC within the online event selection. The simulation of a single charged
particle within the PandaRoot framework [11] is shown in figure 3. The produced photons are inter-
nally reflected and guided towards the expansion box. Photons propagating towards the other end
are reflected off a mirror. Depending on their direction, the photons reach different positions on the
backside of the expansion box where they are recorded by photon detectors. From the hit position
the initial photon direction can be calculated if the hit radiator is know (tracking detectors).
3 Performance
The current design is based on 2500× 17× 35mm3 radiator bars made of synthetical fused silica.
Five bars form one bar box and 16 bar boxes make up a barrel of 50 cm radius around the beam line.
Two gaps, one on the top and one at the bottom of the barrel are foreseen for the vertical beam pipe,
whereas all bar boxes are identical. The expansion box has a depth of 300mm and the pixel size of
– 3 –
2012 JINST 7 C02008
Figure 3. Upstream view of the PANDA Barrel DIRC. The internallly reflecting photons propagate along
the radiator until they hit the backside of the expansion box. Here, they are recorded by pixelized photon
detectors.
the photon detectors is 6.5× 6.5mm2 [13]. The expansion box is filled with Marcol82 oil [12] to
reduce image distortions. Between radiator and expansion volume a focusing lens ensures a sharp
image of the Cherenkov photons. The pixel size adds 6.3 mrad to the single photon Cherenkov an-
gle resolution. The chromatic angular resolution contributes for 5 mrad. These values dominate the
combined single photon resolution that amounts to 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 3 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. [14].
4 Outlook
The number of critical parameters of the current design are not yet optimized and several design
options need to be investigated. The influence of these options on the performance of the DIRC,
estimated in terms of single photon Cherenkov angle resolution and photon yield per particle, needs
to be studies within the PANDARoot simulation framework. One of the design options is the cross
section of the radiator which could be in the extreme case a plate. Another option is a different
focussing system with a focussing mirror at the downstream end of the radiator. Most photons will
– 4 –
2012 JINST 7 C02008
hit this mirror since the angular distribution of the charged particles in a fixed target experiment is
forward peaked.
Acknowledgments
This work is supported by EU6 grant, contract number 515873, DIRACsecondary-Beams, and EU
FP7 grant, contract number 227431, HadronPhysics2.
References
[1] W.F. Henning, FAIR and its experimental program, J. Phys. G 34 (2007) S551.
[2] P. Spiller and G. Franchetti, The FAIR accelerator project at GSI, Nucl. Instrum. Meth. A 561 (2006)
305.
[3] PANDA collaboration, M. Kotulla et al., Strong interaction studies with antiprotons, letter of intent
for PANDA (Antiproton Annihilations at Darmstadt), http://inspirehep.net/record/671592.
[4] M.S. Chanowitz and S.R. Sharpe, Glueballs and Meiktons which decay to multi-kaon final states,
Phys. Lett. B 132 (1983) 413.
[5] PANDA collaboration, M.F.M. Lutz et al., Physics performance report for PANDA: strong
interaction studies with antiprotons, arXiv:0903.3905.
[6] K. Fo¨hl et al., The DIRC detectors of the PANDA experiment at FAIR, Nucl. Instrum. Meth. A 595
(2008) 88.
[7] BABAR-DIRC collaboration, I. Adam et al., The DIRC particle identification system for the BaBar
experiment, Nucl. Instrum. Meth. A 538 (2005) 281.
[8] C. Schwarz et al., The Barrel DIRC of the PANDA experiment, Nucl. Instrum. Meth. A 595 (2008)
112.
[9] C. Schwarz et al., Particle identification for the PANDA detector, Nucl. Instrum. Meth. A 639 (2011)
169.
[10] M. Patsyuk et al., Simulation and reconstruction of the PANDA Barrel DIRC detector, 2011 JINST 6
C11015.
[11] S. Spataro et al., Simulation and event reconstruction inside the PandaRoot framework, J. Phys. Conf.
Ser. 119 (2008) 032035.
[12] Exxon Mobil Corporation webpage, http://www.exxonmobil.com/.
[13] Burle-Planacon MCP-PMT, http://www.photonis.com/, http://www.burle.com/.
[14] PANDA CHERENKOV collaboration, J. Schwiening, The Barrel DIRC detector for the PANDA
experiment at FAIR, Nucl. Instrum. Meth. A 639 (2011) 315.
– 5 –


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