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Particle identification system for the Super Charm–Tau Factory at Novosibirsk
Nuclear Inst. and Methods in Physics Research, A xxx (xxxx) xxx
Contents lists available at ScienceDirect
Nuclear Inst. and Methods in Physics Research, A journal homepage: www.elsevier.com/locate/nima
Particle identification system for the Super Charm–Tau Factory at Novosibirsk A.Yu. Barnyakov a,b,d ,∗, M.Yu. Barnyakov a,d , V.S. Boborovnikov a,b , A.R. Buzykaev a,b , A.V. Bykov a , A.F. Danilyuk c,b , A.A. Katcin a,b , S.A. Kononov a,b , D.V. Korda a,b , E.A. Kravchenko a,b , I.A. Kuyanov a,b , A.P. Onuchin a,b , I.V. Ovtin a,b , N.A. Podgornov a,b , V.V. Porosev a,b , G.P. Razuvaev a,b , V.A. Rodiakin a,b , K.Yu. Todyshev a,b , V.S. Vorobyev a,b,e a
Budker Institute of Nuclear Physics, Acad. Lavrentiev Prospect 11, Novosibirsk 630090, Russia Novosibirsk State University, St. Pirogova 2, Novosibirsk 630090, Russia c Boreskov Institute of Catalysis, Acad. Lavrentiev Prospect 5, Novosibirsk 630090, Russia d Novosibirsk State Technical University, Karl Marks Prospect 20, Novosibirsk 630073, Russia e P.N. Lebedev Physical Institute of the Russian Academy of Sciences, Leninskii pr. 53, 119991, Moscow, Russia b
ARTICLE Keywords: Aerogel RICH ToF TOP Shifter ASHIPH PID system Particle separation
INFO
ABSTRACT The Super Charm–Tau (SCT) Factory is a proposed electron–positron collider in Novosibirsk with a peak luminosity of 1035 cm−1 s−1 operating in the energy range between 2and 6 GeV. The interaction region should be equipped by an excellent universal particle detector meeting the requirements of broad physics program of the experiment. Research and development for all detector subsystems is currently underway. Particle identification (PID) system of the detector is required to provide the state-of-the-art level of 𝜇/𝜋 separation for the particle momenta up to 1.2 GeV∕c. The following options for the PID system are considered in this paper: focusing aerogel ring imaging Cherenkov (FARICH) detector composed of 4-layer aerogel tiles, threshold Cherenkov counters based on aerogel shifter photomultiplier (ASHIPH), and time-of-flight (ToF) detector combined with the time-of-propagation (ToP) approach providing a time resolution better than 30 ps. Assessment of the charged particle separation performance for these options based on simulation and prototype tests results is presented.
1. Introduction The SCT Factory project [1] is being developed at Budker Institute of Nuclear Physics (BINP). It is a symmetric 𝑒+ 𝑒− collider with luminosity of 1035 cm−2 s−1 operating in the energy range between 2 and 6 GeV. Longitudinal polarization of the electrons at the interaction region is foreseen in the project. The experiment has extensive and rich physics program devoted to the measurements of charm quark and tau lepton. It includes precision tests of the standard model (SM) in the electro-weak sector (lepton flavour universality tests, measurement of the CKM matrix elements, measurements of the weak charged current structure in tau decays), QCD measurements in the non-perturbative region (hadronic cross sections, spectroscopy, dynamics of the hadronic decays of the charmed hadrons and tau lepton), and searches for the beyond SM phenomena (lepton flavour violating decays and other forbidden or highly suppressed in the SM processes). Data sample to be collected at SCT exceed the currently available samples in this energy range by 2 orders of magnitudes. Operation in
the conditions of very high luminosity and goals of the physics program impose high requirements on the universal magnetic detector to be installed in the interaction region. An excellent PID system is one of the key requirements. For instance, nearly perfect 𝜇/𝜋 separation is needed for search of the 𝜏 → 𝜇𝛾 decay. The PID system should satisfy the following operation conditions: • To sustain the event rate up to 300 kHz; • To sustain the annual neutron-equivalent dose of 2 ⋅ 109 neq ∕cm2 for the barrel part and 1010 neq ∕cm2 for the endcap part [2]; • To fit in the limited space of about 25 cm in the gap between electromagnetic calorimeter and drift chamber [1]. 2. Aerogel Cherenkov counters 2.1. Aerogel Production of the aerogel based on SiO2 in Novosibirsk was started in 1986. Refractive index of the aerogel produced in Novosibirsk can
∗ Corresponding author at: Budker Institute of Nuclear Physics, Acad. Lavrentiev Prospect 11, Novosibirsk 630090, Russia. E-mail address: [email protected] (A.Yu. Barnyakov).
https://doi.org/10.1016/j.nima.2019.162352 Received 1 April 2019; Received in revised form 3 July 2019; Accepted 4 July 2019 Available online xxxx 0168-9002/© 2019 Elsevier B.V. All rights reserved.
Please cite this article as: A.Yu. Barnyakov, M.Yu. Barnyakov, V.S. Boborovnikov et al., Particle identification system for the Super Charm–Tau Factory at Novosibirsk, Nuclear Inst. and Methods in Physics Research, A (2019) 162352, https://doi.org/10.1016/j.nima.2019.162352.
A.Yu. Barnyakov, M.Yu. Barnyakov, V.S. Boborovnikov et al.
Nuclear Inst. and Methods in Physics Research, A xxx (xxxx) xxx
Fig. 1. The Focusing Aerogel RICH concept.
Fig. 2. Scheme of the FARICH system for SCT detector.
be adjusted within a wide range from 𝑛 = 1.006 to 𝑛 = 1.13. The very good optical properties achieved [3] provided the wide use of aerogel in various threshold and ring imaging Cherenkov detectors: KEDR [4] and SND [5] (BINP, Novosibirsk, Russia), LHCb [6] (CERN, Switzerland), AMS-02 [7] (ISS), CLAS12 [8] (J-Lab,Newport, USA). 2.2. Focusing aerogel RICH 2.2.1. The FARICH technique The FARICH concept emerged in 2004 as improvement of the proximity focusing aerogel RICH detector [9,10]. The general idea of FARICH is to arrange several aerogel layers with different refractive indices so that the Cherenkov rings from different layers overlap at the photon detector plane (Fig. 1). The FARICH technique enables to increase the number of photoelectrons by increasing the radiator thickness without degradation of the Cherenkov angle resolution. There are two approaches to compose a multilayer aerogel radiator: stack several aerogel blocks as in the Belle II ARICH system [11] or produce a monolithic multiple layer block. The second approach was suggested for the FARICH endcap system of the Super B (LNF, Italy) [12] and SCT projects [13]. The FARICH detector satisfies almost all requirements for the particle separation in the SCT experiment, as shown with simulations and the prototype beam test at CERN in 2012 [14,15]. It makes the FARICH system the base option of the PID system for the SCT detector.
Fig. 3. Scheme of the ASHIPH counter.
2.3. Threshold aerogel counters ASHIPH The ASHIPH method was proposed at BINP in 1991 [4]. Light collection in such counters is performed using wavelength shifters (WLS), which are designed as light guides. The Cherenkov light from aerogel is reemitted and partially appears in conditions of total internal reflection. This part of the reemitted light is transported to the photomultiplier and then recorded. The absorption length of the reemitted light is tens of centimetres and so the longitudinal size of the counter can reach 50 cm or more. Schematically the ASHIPH counter is shown in Fig. 3. Today the ASHIPH systems are used in the KEDR detector [16] at VEPP-4M e+ e− -collider and in the SND detector [17,18] at VEPP-2000 e+ e− -collider. 2.3.1. The ASHIPH system for the SCT detector Aerogel with refractive index n=1.030 could be used for 𝜋/𝐾separation from 0.6 up to 2 GeV/c and 𝜇/𝜋-separation from 0.4 up to 0.6 GeV/c. To extend the region of 𝜇/𝜋-separation the additional ASHIPH system based on aerogel with n=1.015 was considered. The aerogel with such refractive index could extend 𝜇/𝜋-separation up to 0.8 GeV/𝑐. In the region above the threshold momentum we can separate particles by using variable threshold depending on the particle momentum if the difference in the number of detected photons from different particles will be noticeable. It could help us to extend momentum range with good 𝜇/𝜋-separation up to 0.9 GeV/𝑐 (see Section 4). The main parameters of the proposed system:
2.2.2. FARICH system for the SCT detector A sketch of the proposed system is shown in Fig. 2. Its main parameters are: • Hermeticity: the system consists of two endcap and one barrel parts and covers nearly 4𝜋 solid angle; • The total surface area of the 4-layer aerogel Cherenkov radiator with 𝑛max =1.07 and thickness of 35 mm is 17 m2 ; • The distance between the inner surface of the radiator and the photon detector is 20 cm; • The total area of position sensitive photon detectors with pixel size of 3 × 3 mm2 is 21 m2 ; • About 1.8 × 106 readout electronics channels; • The material budget within the range of 0.15𝑋0 and 0.30𝑋0 depending on the photon detectors technology.
• 3 layer system: 1 layer with n1 =1.03 (2000 litres) and 2 layers with n2 =1.015 (4000 litres); • counter dimensions are 18 × 30 × 8 cm3 ; • WLS dimensions are 0.3 × 28 × 6 cm3 ; • silicon photomultipliers (SiPMs) area per counter is 180 mm2 ; • material budget is 0.14𝑋0 ;
Recent results on the FARICH prototyping and beam tests are reported in Ref. [2]. 2
Please cite this article as: A.Yu. Barnyakov, M.Yu. Barnyakov, V.S. Boborovnikov et al., Particle identification system for the Super Charm–Tau Factory at Novosibirsk, Nuclear Inst. and Methods in Physics Research, A (2019) 162352, https://doi.org/10.1016/j.nima.2019.162352.
A.Yu. Barnyakov, M.Yu. Barnyakov, V.S. Boborovnikov et al.
Nuclear Inst. and Methods in Physics Research, A xxx (xxxx) xxx
• number of counters in the system is 1400, number of SiPMs in the system is 28000; • system for SiPMs cooling to −40 ◦ C. According to our estimations based on our experience of the ASHIPH system developing and operation in the KEDR detector and in the SND detector, about 24 detected Cherenkov photons could be expected in the proposed system for relativistic particles (𝛽 ≈ 1) in each subsystem: with n1 =1.030 (8 cm thick) and with n2 =1.015 (16 cm thick). The main contributions to subthreshold detection efficiency were estimated as the following:
Fig. 4. A sketch of the barrel segment of the ToF system for SCT detector.
• 𝛿-electrons production ∼5% (n1 =1.030, 8 cm path) and ∼3.3% (n2 =1.015, 16 cm path) • accidental coincidence with SiPM noise ∼0.7% (n1 =1.030), ∼1.4% (n2 =1.015), matching time 𝛥t = 100 ns. The advantages of the such system in comparison with the FARICH approach are well known production technology, less number of photon sensors, electronics channels and consequently less cost of the system.
3. ‘‘ToF + ToP’’ approach
Fig. 5. 𝜋/𝐾-separation in terms of the standard deviation (𝜎) for several PID options obtained with parametric simulation: FARICH (•), ASHIPH with 𝑛1 = 1.030 (▴), ASHIPH with 𝑛2 = 1.015 (▾) and ToF (■).
The proposed aerogel Cherenkov counters are not able to provide 𝜇/𝜋-separation in momentum range below 0.3 GeV/𝑐 (FARICH) and 0.4 GeV/𝑐 (ASHIPH). 𝜇/𝜋-separation in this region could be especially useful for study of semi-leptonic D-mesons decays. At the SCT Factory operation energies approximately half of muons in such processes have the momenta below 0.4 GeV/𝑐. The ‘‘ToF+ToP’’ (Time of Flight and Time of Propagation) technique is considered as extension of the 𝜇/𝜋-separation capability for one of the proposed system based on aerogel.
4. Parametric simulation of the particle separation A parametric model of the SCT detector is used to compare different PID options. Muons, pions and kaons with momenta from 0 to 3.5 GeV∕𝑐 distributed uniformly in the full solid angle were generated. The same geometry layout is adopted for all PID options: barrel radial and longitudinal sizes are 80 cm and ±100 cm, respectively. The following parameters define the systems response:
The best accuracy of ToF measurement achieved in currently operating colliding beam experiments is about 80 ps [19,20]. The time resolution of about 30 ps is considered for future upgrade of the CMS detector [21]. The time resolution of about 15 ps is the aim of TORCH project — a time-of-flight detector for upgrade of the LHCb experiment [22]. In work [23] the 5 ps time resolution was achieved with a detector composed of a small quartz Cherenkov radiator coupled with microchannel plate photomultiplier tube (MCP-PMT).
• The momentum resolution according to the SCT conceptual design report [1] 𝜎𝑝𝑇 = (0.13 ± 0.01)% ⋅ 𝑝𝑇 + (0.45 ± 0.03)%; (1) 𝑝𝑇 • The uniform axial magnetic field in the detector of 1 T; • The dependence of the particle velocity resolution on 𝛽𝛾 (𝜎𝛽 (𝛽𝛾)) taken from a stand-alone simulation of the FARICH detector [1]; • Parameters of the ASHIPH system: number of the detected pho⟂ ) and subthreshold efficiencies (Eff⟂ tons (𝑁ph ) for the pers.thr. pendicular crossing particles (see Section 2.3.1) recalculated for different track lengths inside the system as a function of the track polar angle, momentum and detector magnetic field. The values obtained are following: ⟂ = 24 and Eff – For 𝑛1 = 1.030: 𝑁ph s.thr. = 0.06;
Recent progress in time-of-flight technique allows us to consider the ToF system with intrinsic time resolution better than 30 ps. The resulting time resolution also depends on accelerator uncertainties in time of the beam interaction (bunch length) and electronics synchronization jitter.
3.1. ToF + ToP system
⟂ = 24 and Eff – For 𝑛2 = 1.015: 𝑁ph s.thr. = 0.05.
The conceptual design of the ToF system for SCT detector is shown in Fig. 4 The barrel part of the system consists of 10000 quartz bars (5 × 5 × 250 mm3 ) and 1648 multi-anode MCP-PMTs with rectangular shape 40 × 20 mm. The estimated material budget is about 0.07𝑋0 . There are two components of measured time in such system: ToF and ToP.
• The time resolution of 𝜎𝑡 = 36 ps is adopted for the ToF option. This value accounts for the two effects: the counters time resolution (30 ps) and timing uncertainty of the bunch crossing (20 ps). Electronics synchronization jitter is not considered. The polar angle acceptance interval adopted in simulation is −75◦ ⩽ 𝛩 ⩽ 75◦ . The 𝜋/𝐾 and 𝜇/𝜋-separation in terms of the standard deviations (𝜎) as a function of particle momentum is shown in Figs. 5 and 6. The following PID options are considered: FARICH (•), ASHIPH with 𝑛1 = 1.030 (▴), ASHIPH with 𝑛2 = 1.015 (▾) and ToF (■). Both the ASHIPH detector based on aerogel with two refractive indices (1.030 and 1.015) and the FARICH detector provide 𝜋/𝐾 separation at the level of 3𝜎 in the momentum range from 0.5 to 2.5 GeV∕𝑐. The ToF detector provides the same separation level only up to 1.5 GeV∕𝑐.
With the ToF + ToP approach the time difference between muons and pions with the same momenta will be increased and consequently the momentum range for reliable 𝜇/𝜋 and 𝜋/𝐾-separation will be extended. According to Monte-Carlo simulation the difference in ToP for muon and pion with momentum 0.3 GeV/c is about 85 ps for 250 mm bar length. The similar approach was considered in DIRClike-ToF (or FTOF) PID system proposed for the forward region of the Super B Factory detector [24]. 3
Please cite this article as: A.Yu. Barnyakov, M.Yu. Barnyakov, V.S. Boborovnikov et al., Particle identification system for the Super Charm–Tau Factory at Novosibirsk, Nuclear Inst. and Methods in Physics Research, A (2019) 162352, https://doi.org/10.1016/j.nima.2019.162352.
A.Yu. Barnyakov, M.Yu. Barnyakov, V.S. Boborovnikov et al.
Nuclear Inst. and Methods in Physics Research, A xxx (xxxx) xxx
The physics case feasibility studies with full simulation of the SCT detector are necessary to optimize the parameters of PID and other subsystems. Activities related to the full SCT detector simulation are currently in progress. Prototyping and beam tests of the considered approaches are carried out in BINP. References [1] Super Charm Tau Factory, Conceptual Design Report, vol. 1, BINP SB RAS, Novosibirsk, 2018, https://ctd.inp.nsk.su/wiki/images/4/47/CDR2_ScTau_ en_vol1pdf. [2] A.Yu. Barnyakov, et al., PID System based on Focusing Aerogel RICH for the super c-𝜏 factory, Nucl. Instrum. Methods Phys. Res. A (2019) http://dx.doi.org/ 10.1016/j.nima.2019.05.088. [3] A.F. Danilyuk, et al., Phys.-Usp. 58 (2015) 503–511. [4] A. Onuchin, et al., Nucl. Instrum. Methods Phys. Res. A 315 (1992) 517. [5] K.I. Beloborodov, et al., Nucl. Instrum. Methods Phys. Res. A 494 (2002) 487. [6] C. Matteuzzi, (for the LHCb Collab.), Nucl. Instrum. Methods Phys. Res. A 494 (2002) 409. [7] M. Buenerd, (for the AMS-RICH Collab.), Nucl. Instrum. Methods Phys. Res. A 553 (2005) 264. [8] M. Contralbrigo, et al., Nucl. Instrum. Methods Phys. Res. A 876 (2017) 168–172. [9] T. Iijima, et al., Nucl. Instrum. Methods Phys. Res. A 548 (2005) 383–390. [10] A.Yu. Barnyakov, et al., Nucl. Instrum. Methods Phys. Res. A 553 (2005) 70–75. [11] S. Nishida, et al., Nucl. Instrum. Methods Phys. Res. A 766 (2014) 28–31. [12] A.Yu. Barnyakov, et al., Nucl. Instrum. Methods Phys. Res. A 598 (2009) 169–172. [13] A.Yu. Barnyakov, et al., Nucl. Instrum. Methods Phys. Res. A 639 (2011) 290–293. [14] A.Yu. Barnyakov, et al., Nucl. Instrum. Methods Phys. Res. A 732 (2013) 352–356. [15] A.Yu. Barnyakov, et al., Nucl. Instrum. Methods Phys. Res. A 766 (2014) 88–91. [16] A.Yu. Barnyakov, et al., Nucl. Instrum. Methods Phys. Res. A 824 (2016) 79. [17] A.Yu. Barnyakov, et al., Nucl. Instrum. Methods Phys. Res. A 732 (2013) 330. [18] A.Yu. Barnyakov, et al., Instrum. Exp. Tech. 58 (2015) 30–35. [19] M. Ablikim, et al., Nucl. Instrum. Methods Phys. Res. A 614 (2010) 345–399. [20] A. Alici, Nucl. Instrum. Methods Phys. Res. A 706 (2013) 29. [21] M. Lucchini, Development of the CMS MIP timing detector, Nucl. Instrum. Methods Phys. Res. A (2019) http://dx.doi.org/10.1016/j.nima.2019.04.044. [22] N. Harnew, et al., Nucl. Instrum. Methods Phys. Res. A 936 (2019) 595. [23] K. Inami, et al., Nucl. Instrum. Methods Phys. Res. A 560 (2006) 303. [24] L. Burmistrov, et al., Nucl. Instrum. Methods Phys. Res. A 695 (2012) 83–86.
Fig. 6. 𝜇/𝜋-separation in terms of standard deviation (𝜎) for several PID options obtained with parametric simulation: FARICH (•), ASHIPH with 𝑛1 = 1.030 (▴), ASHIPH with 𝑛2 = 1.015 (▾) and ToF (■).
The 𝜇/𝜋 separation at the level of 3𝜎 can be obtained with the ASHIPH detector in the momentum range from 0.5 to 0.9 GeV∕𝑐, with the FARICH detector in the range from 0.45 to 1.3 GeV∕𝑐, and with the ToF detector for the particle momenta below 0.3 GeV∕𝑐. Performance of the ToF option can be reinforced with the ‘‘ToF+ToP’’ approach. A study of this solution with parametric model of the SCT detector is planned. 5. Summary Superior particle identification in the full momentum range of the SCT experiment requires the use of all detector subsystems. A dedicated PID system is necessary to separate kaons and pions above 0.6 GeV∕𝑐 and muons and pions from 0.2 to 1.2 GeV∕𝑐. Each of the three considered PID techniques provides a good enough 𝜋/𝐾 separation between 0.6 and 2 GeV∕𝑐, while the 𝜇/𝜋 separation from 0.2 to 1.2 GeV∕𝑐 requires a combination of several techniques.
4
Please cite this article as: A.Yu. Barnyakov, M.Yu. Barnyakov, V.S. Boborovnikov et al., Particle identification system for the Super Charm–Tau Factory at Novosibirsk, Nuclear Inst. and Methods in Physics Research, A (2019) 162352, https://doi.org/10.1016/j.nima.2019.162352.
Contents lists available at ScienceDirect
Nuclear Inst. and Methods in Physics Research, A journal homepage: www.elsevier.com/locate/nima
Particle identification system for the Super Charm–Tau Factory at Novosibirsk A.Yu. Barnyakov a,b,d ,∗, M.Yu. Barnyakov a,d , V.S. Boborovnikov a,b , A.R. Buzykaev a,b , A.V. Bykov a , A.F. Danilyuk c,b , A.A. Katcin a,b , S.A. Kononov a,b , D.V. Korda a,b , E.A. Kravchenko a,b , I.A. Kuyanov a,b , A.P. Onuchin a,b , I.V. Ovtin a,b , N.A. Podgornov a,b , V.V. Porosev a,b , G.P. Razuvaev a,b , V.A. Rodiakin a,b , K.Yu. Todyshev a,b , V.S. Vorobyev a,b,e a
Budker Institute of Nuclear Physics, Acad. Lavrentiev Prospect 11, Novosibirsk 630090, Russia Novosibirsk State University, St. Pirogova 2, Novosibirsk 630090, Russia c Boreskov Institute of Catalysis, Acad. Lavrentiev Prospect 5, Novosibirsk 630090, Russia d Novosibirsk State Technical University, Karl Marks Prospect 20, Novosibirsk 630073, Russia e P.N. Lebedev Physical Institute of the Russian Academy of Sciences, Leninskii pr. 53, 119991, Moscow, Russia b
ARTICLE Keywords: Aerogel RICH ToF TOP Shifter ASHIPH PID system Particle separation
INFO
ABSTRACT The Super Charm–Tau (SCT) Factory is a proposed electron–positron collider in Novosibirsk with a peak luminosity of 1035 cm−1 s−1 operating in the energy range between 2and 6 GeV. The interaction region should be equipped by an excellent universal particle detector meeting the requirements of broad physics program of the experiment. Research and development for all detector subsystems is currently underway. Particle identification (PID) system of the detector is required to provide the state-of-the-art level of 𝜇/𝜋 separation for the particle momenta up to 1.2 GeV∕c. The following options for the PID system are considered in this paper: focusing aerogel ring imaging Cherenkov (FARICH) detector composed of 4-layer aerogel tiles, threshold Cherenkov counters based on aerogel shifter photomultiplier (ASHIPH), and time-of-flight (ToF) detector combined with the time-of-propagation (ToP) approach providing a time resolution better than 30 ps. Assessment of the charged particle separation performance for these options based on simulation and prototype tests results is presented.
1. Introduction The SCT Factory project [1] is being developed at Budker Institute of Nuclear Physics (BINP). It is a symmetric 𝑒+ 𝑒− collider with luminosity of 1035 cm−2 s−1 operating in the energy range between 2 and 6 GeV. Longitudinal polarization of the electrons at the interaction region is foreseen in the project. The experiment has extensive and rich physics program devoted to the measurements of charm quark and tau lepton. It includes precision tests of the standard model (SM) in the electro-weak sector (lepton flavour universality tests, measurement of the CKM matrix elements, measurements of the weak charged current structure in tau decays), QCD measurements in the non-perturbative region (hadronic cross sections, spectroscopy, dynamics of the hadronic decays of the charmed hadrons and tau lepton), and searches for the beyond SM phenomena (lepton flavour violating decays and other forbidden or highly suppressed in the SM processes). Data sample to be collected at SCT exceed the currently available samples in this energy range by 2 orders of magnitudes. Operation in
the conditions of very high luminosity and goals of the physics program impose high requirements on the universal magnetic detector to be installed in the interaction region. An excellent PID system is one of the key requirements. For instance, nearly perfect 𝜇/𝜋 separation is needed for search of the 𝜏 → 𝜇𝛾 decay. The PID system should satisfy the following operation conditions: • To sustain the event rate up to 300 kHz; • To sustain the annual neutron-equivalent dose of 2 ⋅ 109 neq ∕cm2 for the barrel part and 1010 neq ∕cm2 for the endcap part [2]; • To fit in the limited space of about 25 cm in the gap between electromagnetic calorimeter and drift chamber [1]. 2. Aerogel Cherenkov counters 2.1. Aerogel Production of the aerogel based on SiO2 in Novosibirsk was started in 1986. Refractive index of the aerogel produced in Novosibirsk can
∗ Corresponding author at: Budker Institute of Nuclear Physics, Acad. Lavrentiev Prospect 11, Novosibirsk 630090, Russia. E-mail address: [email protected] (A.Yu. Barnyakov).
https://doi.org/10.1016/j.nima.2019.162352 Received 1 April 2019; Received in revised form 3 July 2019; Accepted 4 July 2019 Available online xxxx 0168-9002/© 2019 Elsevier B.V. All rights reserved.
Please cite this article as: A.Yu. Barnyakov, M.Yu. Barnyakov, V.S. Boborovnikov et al., Particle identification system for the Super Charm–Tau Factory at Novosibirsk, Nuclear Inst. and Methods in Physics Research, A (2019) 162352, https://doi.org/10.1016/j.nima.2019.162352.
A.Yu. Barnyakov, M.Yu. Barnyakov, V.S. Boborovnikov et al.
Nuclear Inst. and Methods in Physics Research, A xxx (xxxx) xxx
Fig. 1. The Focusing Aerogel RICH concept.
Fig. 2. Scheme of the FARICH system for SCT detector.
be adjusted within a wide range from 𝑛 = 1.006 to 𝑛 = 1.13. The very good optical properties achieved [3] provided the wide use of aerogel in various threshold and ring imaging Cherenkov detectors: KEDR [4] and SND [5] (BINP, Novosibirsk, Russia), LHCb [6] (CERN, Switzerland), AMS-02 [7] (ISS), CLAS12 [8] (J-Lab,Newport, USA). 2.2. Focusing aerogel RICH 2.2.1. The FARICH technique The FARICH concept emerged in 2004 as improvement of the proximity focusing aerogel RICH detector [9,10]. The general idea of FARICH is to arrange several aerogel layers with different refractive indices so that the Cherenkov rings from different layers overlap at the photon detector plane (Fig. 1). The FARICH technique enables to increase the number of photoelectrons by increasing the radiator thickness without degradation of the Cherenkov angle resolution. There are two approaches to compose a multilayer aerogel radiator: stack several aerogel blocks as in the Belle II ARICH system [11] or produce a monolithic multiple layer block. The second approach was suggested for the FARICH endcap system of the Super B (LNF, Italy) [12] and SCT projects [13]. The FARICH detector satisfies almost all requirements for the particle separation in the SCT experiment, as shown with simulations and the prototype beam test at CERN in 2012 [14,15]. It makes the FARICH system the base option of the PID system for the SCT detector.
Fig. 3. Scheme of the ASHIPH counter.
2.3. Threshold aerogel counters ASHIPH The ASHIPH method was proposed at BINP in 1991 [4]. Light collection in such counters is performed using wavelength shifters (WLS), which are designed as light guides. The Cherenkov light from aerogel is reemitted and partially appears in conditions of total internal reflection. This part of the reemitted light is transported to the photomultiplier and then recorded. The absorption length of the reemitted light is tens of centimetres and so the longitudinal size of the counter can reach 50 cm or more. Schematically the ASHIPH counter is shown in Fig. 3. Today the ASHIPH systems are used in the KEDR detector [16] at VEPP-4M e+ e− -collider and in the SND detector [17,18] at VEPP-2000 e+ e− -collider. 2.3.1. The ASHIPH system for the SCT detector Aerogel with refractive index n=1.030 could be used for 𝜋/𝐾separation from 0.6 up to 2 GeV/c and 𝜇/𝜋-separation from 0.4 up to 0.6 GeV/c. To extend the region of 𝜇/𝜋-separation the additional ASHIPH system based on aerogel with n=1.015 was considered. The aerogel with such refractive index could extend 𝜇/𝜋-separation up to 0.8 GeV/𝑐. In the region above the threshold momentum we can separate particles by using variable threshold depending on the particle momentum if the difference in the number of detected photons from different particles will be noticeable. It could help us to extend momentum range with good 𝜇/𝜋-separation up to 0.9 GeV/𝑐 (see Section 4). The main parameters of the proposed system:
2.2.2. FARICH system for the SCT detector A sketch of the proposed system is shown in Fig. 2. Its main parameters are: • Hermeticity: the system consists of two endcap and one barrel parts and covers nearly 4𝜋 solid angle; • The total surface area of the 4-layer aerogel Cherenkov radiator with 𝑛max =1.07 and thickness of 35 mm is 17 m2 ; • The distance between the inner surface of the radiator and the photon detector is 20 cm; • The total area of position sensitive photon detectors with pixel size of 3 × 3 mm2 is 21 m2 ; • About 1.8 × 106 readout electronics channels; • The material budget within the range of 0.15𝑋0 and 0.30𝑋0 depending on the photon detectors technology.
• 3 layer system: 1 layer with n1 =1.03 (2000 litres) and 2 layers with n2 =1.015 (4000 litres); • counter dimensions are 18 × 30 × 8 cm3 ; • WLS dimensions are 0.3 × 28 × 6 cm3 ; • silicon photomultipliers (SiPMs) area per counter is 180 mm2 ; • material budget is 0.14𝑋0 ;
Recent results on the FARICH prototyping and beam tests are reported in Ref. [2]. 2
Please cite this article as: A.Yu. Barnyakov, M.Yu. Barnyakov, V.S. Boborovnikov et al., Particle identification system for the Super Charm–Tau Factory at Novosibirsk, Nuclear Inst. and Methods in Physics Research, A (2019) 162352, https://doi.org/10.1016/j.nima.2019.162352.
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• number of counters in the system is 1400, number of SiPMs in the system is 28000; • system for SiPMs cooling to −40 ◦ C. According to our estimations based on our experience of the ASHIPH system developing and operation in the KEDR detector and in the SND detector, about 24 detected Cherenkov photons could be expected in the proposed system for relativistic particles (𝛽 ≈ 1) in each subsystem: with n1 =1.030 (8 cm thick) and with n2 =1.015 (16 cm thick). The main contributions to subthreshold detection efficiency were estimated as the following:
Fig. 4. A sketch of the barrel segment of the ToF system for SCT detector.
• 𝛿-electrons production ∼5% (n1 =1.030, 8 cm path) and ∼3.3% (n2 =1.015, 16 cm path) • accidental coincidence with SiPM noise ∼0.7% (n1 =1.030), ∼1.4% (n2 =1.015), matching time 𝛥t = 100 ns. The advantages of the such system in comparison with the FARICH approach are well known production technology, less number of photon sensors, electronics channels and consequently less cost of the system.
3. ‘‘ToF + ToP’’ approach
Fig. 5. 𝜋/𝐾-separation in terms of the standard deviation (𝜎) for several PID options obtained with parametric simulation: FARICH (•), ASHIPH with 𝑛1 = 1.030 (▴), ASHIPH with 𝑛2 = 1.015 (▾) and ToF (■).
The proposed aerogel Cherenkov counters are not able to provide 𝜇/𝜋-separation in momentum range below 0.3 GeV/𝑐 (FARICH) and 0.4 GeV/𝑐 (ASHIPH). 𝜇/𝜋-separation in this region could be especially useful for study of semi-leptonic D-mesons decays. At the SCT Factory operation energies approximately half of muons in such processes have the momenta below 0.4 GeV/𝑐. The ‘‘ToF+ToP’’ (Time of Flight and Time of Propagation) technique is considered as extension of the 𝜇/𝜋-separation capability for one of the proposed system based on aerogel.
4. Parametric simulation of the particle separation A parametric model of the SCT detector is used to compare different PID options. Muons, pions and kaons with momenta from 0 to 3.5 GeV∕𝑐 distributed uniformly in the full solid angle were generated. The same geometry layout is adopted for all PID options: barrel radial and longitudinal sizes are 80 cm and ±100 cm, respectively. The following parameters define the systems response:
The best accuracy of ToF measurement achieved in currently operating colliding beam experiments is about 80 ps [19,20]. The time resolution of about 30 ps is considered for future upgrade of the CMS detector [21]. The time resolution of about 15 ps is the aim of TORCH project — a time-of-flight detector for upgrade of the LHCb experiment [22]. In work [23] the 5 ps time resolution was achieved with a detector composed of a small quartz Cherenkov radiator coupled with microchannel plate photomultiplier tube (MCP-PMT).
• The momentum resolution according to the SCT conceptual design report [1] 𝜎𝑝𝑇 = (0.13 ± 0.01)% ⋅ 𝑝𝑇 + (0.45 ± 0.03)%; (1) 𝑝𝑇 • The uniform axial magnetic field in the detector of 1 T; • The dependence of the particle velocity resolution on 𝛽𝛾 (𝜎𝛽 (𝛽𝛾)) taken from a stand-alone simulation of the FARICH detector [1]; • Parameters of the ASHIPH system: number of the detected pho⟂ ) and subthreshold efficiencies (Eff⟂ tons (𝑁ph ) for the pers.thr. pendicular crossing particles (see Section 2.3.1) recalculated for different track lengths inside the system as a function of the track polar angle, momentum and detector magnetic field. The values obtained are following: ⟂ = 24 and Eff – For 𝑛1 = 1.030: 𝑁ph s.thr. = 0.06;
Recent progress in time-of-flight technique allows us to consider the ToF system with intrinsic time resolution better than 30 ps. The resulting time resolution also depends on accelerator uncertainties in time of the beam interaction (bunch length) and electronics synchronization jitter.
3.1. ToF + ToP system
⟂ = 24 and Eff – For 𝑛2 = 1.015: 𝑁ph s.thr. = 0.05.
The conceptual design of the ToF system for SCT detector is shown in Fig. 4 The barrel part of the system consists of 10000 quartz bars (5 × 5 × 250 mm3 ) and 1648 multi-anode MCP-PMTs with rectangular shape 40 × 20 mm. The estimated material budget is about 0.07𝑋0 . There are two components of measured time in such system: ToF and ToP.
• The time resolution of 𝜎𝑡 = 36 ps is adopted for the ToF option. This value accounts for the two effects: the counters time resolution (30 ps) and timing uncertainty of the bunch crossing (20 ps). Electronics synchronization jitter is not considered. The polar angle acceptance interval adopted in simulation is −75◦ ⩽ 𝛩 ⩽ 75◦ . The 𝜋/𝐾 and 𝜇/𝜋-separation in terms of the standard deviations (𝜎) as a function of particle momentum is shown in Figs. 5 and 6. The following PID options are considered: FARICH (•), ASHIPH with 𝑛1 = 1.030 (▴), ASHIPH with 𝑛2 = 1.015 (▾) and ToF (■). Both the ASHIPH detector based on aerogel with two refractive indices (1.030 and 1.015) and the FARICH detector provide 𝜋/𝐾 separation at the level of 3𝜎 in the momentum range from 0.5 to 2.5 GeV∕𝑐. The ToF detector provides the same separation level only up to 1.5 GeV∕𝑐.
With the ToF + ToP approach the time difference between muons and pions with the same momenta will be increased and consequently the momentum range for reliable 𝜇/𝜋 and 𝜋/𝐾-separation will be extended. According to Monte-Carlo simulation the difference in ToP for muon and pion with momentum 0.3 GeV/c is about 85 ps for 250 mm bar length. The similar approach was considered in DIRClike-ToF (or FTOF) PID system proposed for the forward region of the Super B Factory detector [24]. 3
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The physics case feasibility studies with full simulation of the SCT detector are necessary to optimize the parameters of PID and other subsystems. Activities related to the full SCT detector simulation are currently in progress. Prototyping and beam tests of the considered approaches are carried out in BINP. References [1] Super Charm Tau Factory, Conceptual Design Report, vol. 1, BINP SB RAS, Novosibirsk, 2018, https://ctd.inp.nsk.su/wiki/images/4/47/CDR2_ScTau_ en_vol1pdf. [2] A.Yu. Barnyakov, et al., PID System based on Focusing Aerogel RICH for the super c-𝜏 factory, Nucl. Instrum. Methods Phys. Res. A (2019) http://dx.doi.org/ 10.1016/j.nima.2019.05.088. [3] A.F. Danilyuk, et al., Phys.-Usp. 58 (2015) 503–511. [4] A. Onuchin, et al., Nucl. Instrum. Methods Phys. Res. A 315 (1992) 517. [5] K.I. Beloborodov, et al., Nucl. Instrum. Methods Phys. Res. A 494 (2002) 487. [6] C. Matteuzzi, (for the LHCb Collab.), Nucl. Instrum. Methods Phys. Res. A 494 (2002) 409. [7] M. Buenerd, (for the AMS-RICH Collab.), Nucl. Instrum. Methods Phys. Res. A 553 (2005) 264. [8] M. Contralbrigo, et al., Nucl. Instrum. Methods Phys. Res. A 876 (2017) 168–172. [9] T. Iijima, et al., Nucl. Instrum. Methods Phys. Res. A 548 (2005) 383–390. [10] A.Yu. Barnyakov, et al., Nucl. Instrum. Methods Phys. Res. A 553 (2005) 70–75. [11] S. Nishida, et al., Nucl. Instrum. Methods Phys. Res. A 766 (2014) 28–31. [12] A.Yu. Barnyakov, et al., Nucl. Instrum. Methods Phys. Res. A 598 (2009) 169–172. [13] A.Yu. Barnyakov, et al., Nucl. Instrum. Methods Phys. Res. A 639 (2011) 290–293. [14] A.Yu. Barnyakov, et al., Nucl. Instrum. Methods Phys. Res. A 732 (2013) 352–356. [15] A.Yu. Barnyakov, et al., Nucl. Instrum. Methods Phys. Res. A 766 (2014) 88–91. [16] A.Yu. Barnyakov, et al., Nucl. Instrum. Methods Phys. Res. A 824 (2016) 79. [17] A.Yu. Barnyakov, et al., Nucl. Instrum. Methods Phys. Res. A 732 (2013) 330. [18] A.Yu. Barnyakov, et al., Instrum. Exp. Tech. 58 (2015) 30–35. [19] M. Ablikim, et al., Nucl. Instrum. Methods Phys. Res. A 614 (2010) 345–399. [20] A. Alici, Nucl. Instrum. Methods Phys. Res. A 706 (2013) 29. [21] M. Lucchini, Development of the CMS MIP timing detector, Nucl. Instrum. Methods Phys. Res. A (2019) http://dx.doi.org/10.1016/j.nima.2019.04.044. [22] N. Harnew, et al., Nucl. Instrum. Methods Phys. Res. A 936 (2019) 595. [23] K. Inami, et al., Nucl. Instrum. Methods Phys. Res. A 560 (2006) 303. [24] L. Burmistrov, et al., Nucl. Instrum. Methods Phys. Res. A 695 (2012) 83–86.
Fig. 6. 𝜇/𝜋-separation in terms of standard deviation (𝜎) for several PID options obtained with parametric simulation: FARICH (•), ASHIPH with 𝑛1 = 1.030 (▴), ASHIPH with 𝑛2 = 1.015 (▾) and ToF (■).
The 𝜇/𝜋 separation at the level of 3𝜎 can be obtained with the ASHIPH detector in the momentum range from 0.5 to 0.9 GeV∕𝑐, with the FARICH detector in the range from 0.45 to 1.3 GeV∕𝑐, and with the ToF detector for the particle momenta below 0.3 GeV∕𝑐. Performance of the ToF option can be reinforced with the ‘‘ToF+ToP’’ approach. A study of this solution with parametric model of the SCT detector is planned. 5. Summary Superior particle identification in the full momentum range of the SCT experiment requires the use of all detector subsystems. A dedicated PID system is necessary to separate kaons and pions above 0.6 GeV∕𝑐 and muons and pions from 0.2 to 1.2 GeV∕𝑐. Each of the three considered PID techniques provides a good enough 𝜋/𝐾 separation between 0.6 and 2 GeV∕𝑐, while the 𝜇/𝜋 separation from 0.2 to 1.2 GeV∕𝑐 requires a combination of several techniques.
4
Please cite this article as: A.Yu. Barnyakov, M.Yu. Barnyakov, V.S. Boborovnikov et al., Particle identification system for the Super Charm–Tau Factory at Novosibirsk, Nuclear Inst. and Methods in Physics Research, A (2019) 162352, https://doi.org/10.1016/j.nima.2019.162352.