The GlueX DIRC Program
A. Ali, F. Barbosa, J. Bessuille, E. Chudakov, R. Dzhygadlo, C. Fanelli, J. Frye, J. Hardin, A. Hurley, G. Kalicy, J. Kelsey, W. Li, M. Patsyuk, C. Schwarz, J. Schwiening, M. Shepherd, J. R. Stevens, T. Whitlatch, M. Williams, Y. Yang
PPrepared for submission to JINST
International Workshop on Fast Cherenkov Detectors - Photon detection, DIRCdesign and DAQ11 - 13 September 2019,Castle Rauischholzhausen, Justus-Liebig-University Giessen, Germany
The GlueX DIRC program
A. Ali, b F. Barbosa, d J. Bessuille, e E. Chudakov, d R. Dzhygadlo, b C. Fanelli, d , e J. Frye, c J.Hardin, e A. Hurley, f G. Kalicy, a J. Kelsey, e W. Li, f M. Patsyuk, e C. Schwarz, b J.Schwiening, b M. Shepherd, c J. R. Stevens, f , T. Whitlatch, d M. Williams, e Y. Yang, e a Catholic University of AmericaWashington DC, United States b GSI Helmholtzzentrum für Schwerionenforschung GmbH,Darmstadt, Germany c Indiana University,Bloomington, IN, United States d Jefferson Lab,Newport News, VA, United States e Massachusetts Institute of Technology,Cambridge, MA, United States f William & MaryWilliamsburg, VA, United States
E-mail: [email protected]
Abstract: The GlueX experiment is located in experimental Hall D at Jefferson Lab (JLab)and provides a unique capability to search for hybrid mesons in high-energy photoproduction,utilizing a ∼ Corresponding author. a r X i v : . [ phy s i c s . i n s - d e t ] M a r ontents The GlueX experiment, shown schematically in Fig. 1 and located in Jefferson Lab’s Hall D,utilizes a tagged photon beam derived from the electron beam’s coherent bremsstrahlung radiationfrom a thin diamond wafer. The primary goal of the experiment is to search for and ultimatelystudy an unconventional class of mesons, known as hybrids mesons, which contain an intrinsicgluonic component to their wave functions [1–3]. Hybrid meson states are predicted by LatticeQCD calculations [4], and provide an opportunity to quantitatively test our understanding of thestrong nuclear force in this non-perturbative regime.
Figure 1 . A schematic of the Hall D beamline and GlueX detector at Jefferson Laboratory. The DIRCdetector is installed directly upstream of the time-of-flight detector in the forward region.
Construction and installation of the baseline GlueX detector were completed in 2014, with firstphysics-quality photon beams delivered in Spring 2016 [5]. The low-intensity phase of the physics– 1 –rogram with the baseline GlueX detector then ran from 2017-2018. The particle identification(PID) capabilities have been studied with this data, and in the forward region the time-of-flight(TOF) detector performance has reached its design specifications for providing π / K separation upto p ∼ / c . An initial physics program to search for and study hybrid mesons which decay tonon-strange final state particles is underway. An upgrade to the PID capabilities is needed to fullyexploit the discovery potential of the GlueX experiment by studying the quark flavor content ofthe potential hybrid states. The DIRC upgrade for GlueX, described in detail in Ref. [6], utilizesone-third of the fused silica radiators from the BaBar DIRC (Detection of Internally ReflectedCherenkov light) detector [7], with two new, compact expansion volumes. These proceedingsdescribe the installation of the GlueX DIRC and the analysis of initial commissioning data. The first major milestone of the GlueX DIRC installation was successfully transporting four ofthe DIRC “bar boxes" from SLAC to JLab in 2018, which each are recycled components from theBaBar detector consisting of ∼ Figure 2 . Four BaBar bar boxes transported to JLab and installed in the GlueX detector on the DIRC supportstructure in Hall D.
The remaining optical components for the DIRC, known as the Optical Box (OB), consists ofmultiple flat mirrors, immersed in water, that reflect the Cherenkov photons through a fused silicawindow to a plane of Multi-Anode PMTs (MAPMTs) as shown in Fig. 3. The front surface flatmirrors were characterized for their reflectivity vs wavelength to be utilized in simulation. Thecharacterization and calibration of the 64-channel Hamamatsu H12700 MAPMTs and readoutelectronics modules was done at JLab, including a battery of tests using a dedicated laser testsetup which illuminates the MAPMTs to measure the single photoelectron response for each pixelindividually to determine the gain and efficiency, following the procedure described in Ref. [10]. https://firstsurfacemirror.com – 2 – igure 3 . Optical Box design and components (left), mirror components installed in optical box (center),and fused silica window with installed MAPMT modules (right). In preparation for the first commissioning beamtime, half of the assembled and tested MAPMTmodules were then installed for one of the Optical Boxes, as shown in Fig. 4 (left). The MAPMTsare coupled to the fused silica window of the OB by a silicone cookie and compressed by the blackbracket seen in the figure [9]. Each module has its own low and high voltage as well as opticalfiber, which were installed and routed through the dark box as seen in Fig. 4 (right). The fully-instrumented OB was coupled to the bar boxes with a water-tight gasket, followed by a complete testof the readout electronics prior to the commissioning beamtime, using the LED calibration system.
Figure 4 . Installation of DIRC MAPMT modules on fused silica window of the Optical Box (left) andcabling of modules to complete the installation (right).
Over a ten-day period in February 2019, half of the GlueX DIRC was commissioned by operatingthe nominal GlueX experiment with the addition of one Optical Box readout with the standard– 3 –AQ system with an open trigger provided by coincidence of minimal energy deposits in theforward and barrel calorimeters. The nominal GlueX experiment provided the trigger and finalstate particle reconstruction, yielding high statistics samples of exclusive γ p → ρ p , ρ → π + π − and γ p → φ p , φ → K + K − events as shown by the invariant mass distributions in Fig. 5 (left) and(right), respectively. These event samples provided pure samples of π ± and K ± track samples totest the DIRC reconstruction algorithms and particle identification performance. Figure 5 . Invariant mass of exclusively produced π + π − (left) and K + K − (right) showing clear ρ and φ peaksselected to study the DIRC detector performance. The occupancy of the MAPMT pixels form a 2-dimensional array (48 columns by 144 rows)where the Cherenkov photons from the DIRC radiators are imaged as shown in Fig. 6 for a sampleof selected π + tracks. The tracks from the data (described above) are shown on the top panel ofFig. 6 while the bottom panel shows the analogous distribution from a GEANT simulation sampleof selected π + tracks. These occupancy distributions were obtained in nearly real-time during thecommissioning, and their consistency was critical to confirm the validity of the data being recordedas well as the implementation of the simulated detector geometry. - · - · Figure 6 . DIRC Cherenkov photon hit unnormalized hit intensity over MAPMT plane for identified π + tracks, comparing data (top) with expected distribution from GEANT MC simulation (bottom). Particle identification with the DIRC is performed by comparing the observed Cherenkovphoton pattern for a single track to the expected Cherenkov angles for a π and K mass hypothesis,– 4 –nd computing the likelihood for each hypothesis assuming a Gaussian resolution on the Cherenkovangle. The measured Cherenkov angles per photon for charged pions and kaons are shown in Fig. 7for p > . c identified through the ρ and φ reactions described above for beam data (left)and simulation (right). The results shown here are from a limited range of the available polarangles, which show a good agreement between the observed mean Cherenkov angle θ C and singlephoton resolution ( σ C ) for the data and simulation. The average number of detected photons pertrack ranges from 15 to 35, depending on the track incident angle, which is consistent with theobserved photon yield at BaBar. These results utilize preliminary calibration and alignment, whichare currently under study and improvements are expected before the final performance of the DIRCcan be quantified over the full available phase space. [rad] C q [ ] m a x en t r i e s / N = 0.8240 rad p c q = 0.8173 rad Kc q = 8.0 mrad p c s = 8.0 mrad Kc s pionskaons [rad] C q [ ] m a x en t r i e s / N = 0.8239 rad p c q = 0.8178 rad Kc q = 8.3 mrad p c s = 7.8 mrad Kc s pionskaons Figure 7 . Cherenkov angle θ C distribution for identified pions (blue) and kaons (red) with p > . c identified through the ρ and φ reactions described above for beam data (left) and simulation (right). After the Spring 2019 commissioning run the water was drained from the optical box to inspect theoptical components. The mirrors which had been immersed in water for ∼ Acknowledgments
We would like to acknowledge the outstanding efforts of the staff of the Accelerator and the PhysicsDivisions at Jefferson Lab that made the experiment possible. This work is supported by theU.S. Department of Energy, Office of Science, Office of Nuclear Physics under contracts DE-AC05-06OR23177, DE-FG02-05ER41374 and Early Career Award contract DE-SC0018224 andthe German Research Foundation, GSI Helmholtzzentrum für Schwerionenforschung GmbH.– 5 – eferences [1] GlueX Collaboration, “Mapping the spectrum of light quark Mesons and gluonic excitations withlinearly polarized protons," Jefferson Lab PAC 30 Proposal (2006), Available at: [2] A. AlekSejevs et al. (GlueX Collaboration), “An initial study of mesons and baryons containing strangequarks with GlueX,” Jefferson Lab PAC 40 Proposal (2013), arXiv:1305.1523 [nucl-ex].[3] M. Dugger et al. (GlueX Collaboration), “A study of decays to strange final states with GlueX in Hall Dusing components of the BaBar DIRC,” Jefferson Lab PAC 42 Proposal (2014) arXiv:1408.0215[physics.ins-det].[4] J. J. Dudek et al. , “Toward the excited isoscalar meson spectrum from lattice QCD,” Phys. Rev. D ,094505 (2013), arXiv:1309.2608 [hep-lat].[5] H. Al Ghoul et al. (GlueX Collaboration), “First Results from The GlueX Experiment,” AIP Conf.Proc. , 020001 (2016), arXiv:1512.03699 [nucl-ex].[6] GlueX Collaboration, “GlueX DIRC Technical Design Report," (2015), Available at: https://halldweb.jlab.org/DocDB/0028/002809/003/dirc_tdr.pdf [7] I. Adam et al. (BaBar DIRC Collaboration), “The DIRC particle identification system for the BaBarexperiment,” Nucl. Instrum. Meth. A , 281 (2005).[8] B. Dey et al. , “Design and performance of the Focusing DIRC detector,” Nucl. Instrum. Meth. A ,112 (2015), arXiv:1410.0075 [physics.ins-det].[9] M. Patsyuk et al. , “Status of the GlueX DIRC,” Nucl. Instrum. Meth. A , 161756 (2020).[10] M. Contalbrigo et al. , “Single photon detection with the multi-anode CLAS12 RICH detector,” Nucl.Instrum. Meth. A , 162123 (2020)., 162123 (2020).