- Email: [email protected]
Detectors and physics at VEPP-2000
Nuclear Instruments and Methods in Physics Research A 623 (2010) 353–355
Contents lists available at ScienceDirect
Nuclear Instruments and Methods in Physics Research A journal homepage: www.elsevier.com/locate/nima
Detectors and physics at VEPP-2000 B.I. Khazin ,1 a r t i c l e in fo
abstract
Available online 3 March 2010
A new electron–positron collider VEPP-2000 is now under commission at the Budker Institute of Nuclear Physics. The high luminosity and its center-of-mass energy extended up to 2 GeV open up new possibilities in precision studies of the electron–positron annihilation into hadrons. To perform experiments with this new collider, two detectors—SND and CMD-3—are now being installed at the VEPP-2000 experimental hall. The physics program and results of the tests of the major detector subsystems are reported. & 2010 Elsevier B.V. All rights reserved.
Keywords: Electron–positron colliders Particle detectors
1. Introduction
2. SND and CMD-3 detectors
A long set of experiments at the VEPP-2M [1] collider in Novosibirsk produced a lot of detailed and precise data concerning processes of the electron–positron annihilation at the center of mass energy ranging from the threshold of two pion production up to 1.4 GeV. The relevance of detailed and precise low energy data and existence of rather poorly studied data in the center-of-mass energy between 1.4 and 2 GeV were the motivation for the construction at Budker Institute of Nuclear Physics of the electron–positron collider VEPP-2000 with the c.m. energy up to 2 GeV and luminosity up to 1032 cm 2 s 1 [2]. The physics program of future experiments will be a natural continuation of the program performed at VEPP-2M including precision measurements of hadronic cross-sections, studies of light vector meson recurrences, and measurements of nucleon electromagnetic form-factors near threshold. Taking into account the requirements of this program, two detectors—the upgraded Spherical Neutral Detector (SND) and the newly constructed Cryogenic Magnetic Detector (CMD-3)— are now being installed at the experimental hall of VEPP-2000. Some details of the detectors are described in Ref. [3]. Both detectors have the improved tracking system, electromagnetic calorimeter, particle identification capability and new, much faster data acquisition system including both the hardware and software. The results of latest tests of some detector subsystems are described below.
2.1. SND
Tel.: + 7 383 333 4920; fax: +7 383 330 7163.
E-mail address: [email protected] On behalf of CMD-3 and SND Collaborations.
1
0168-9002/$ - see front matter & 2010 Elsevier B.V. All rights reserved. doi:10.1016/j.nima.2010.02.246
The layout of SND is shown in Fig. 1. The vacuum tube of 40 mm in diameter and with the wall thickness of 0.75 mm is made of beryllium. It is surrounded by cylindrical drift chamber that measures the charged particle direction of flight. The system of aerogel counters is placed just outside the DC. All the detector subsystems are housed inside the spherically shaped electromagnetic calorimeter, made of three layers of NaI(Tl) crystals with the readout vacuum phototriodes [4]. The total number of crystals is 1632 and the thicknesses of the layers are 2.9X0, 4.8X0 and 5.7X0 respectively. The angular dimensions of the calorimeter are 183 r y r 1623 and 03 r f r 3603 . Outside the calorimeter a 12 cm-thick iron absorber, muon detection system containing double layers of streamer tubes and plastic scintillator counters are placed. 2.2. CMD-3 The layout of the CMD-3 detector is shown in Fig. 2. Electrons and positrons collide at the center of the vacuum chamber. The coordinates, angles and momenta of charged particles are measured by the cylindrical drift chamber (DC). The Z-chamber surrounding the DC measures track coordinate along the beam direction (Z-coordinate) with high resolution and produces the fast signal starting trigger electronics. DC and Z-chamber are placed inside the very thin (0.18X0) superconductive solenoid with a magnetic field of 1.35 T. The position and energy of photons are measured by the system of barrel calorimeters based on the liquid Xe and CsI crystals and endcap calorimeter based on BGO crystals. The barrel and endcap calorimeters cover a solid angle of 0:94 4p steradians. The system of range measurement with plastic scintillators is located outside the flux return yoke. TOF counters made of BC-408 plastic scintillators with
354
B.I. Khazin / Nuclear Instruments and Methods in Physics Research A 623 (2010) 353–355
μ+ 3 7 5 e-
e+
σ, mkm
8
6-layer
350
4-layer
300
3-layer
250 200
100
6
2 4
400
150
10
1
SND Drift Chamber Resolution abs(delta6):abs(rho6)
450
50
9
0
μ− 0 20 40 60 80 100 cm Fig. 1. Cross-section of SND. 1—VEPP-2000 vacuum chamber; 2—tracking system; 3—aerogel counters; 4—NaI(Tl) electromagnetic calorimeter; 5—vacuum phototriodes; 6—iron absorber; 7–9—muon system; 10—VEPP-2000 focusing solenoid.
0.1
0.2
0.3 0.4 0.5 Drift distance
0.6
0.7 ρ, cm
Fig. 3. Spatial resolution of SND DC in the R2j plane of the 3rd, 4th and 6th layers versus the drift distance.
70
σMC = 0.53±0.02
60
σ EXP = 1.63±0.08
50 40 30 20 10 0
-8
-6
-4
-2
0
2
4
6 Z, xmm
Fig. 4. SND DC resolution along the sense wires. Data (points with errors) and simple simulation (open histogram) with fitted curves are shown.
Fig. 2. Cross-section of CMD-3. 1—interaction point; 2—drift chamber; 3—end cap BGO electromagnetic calorimeter; 4—Z-chamber; 5—superconductive solenoid; 6—liquid xenon electromagnetic calorimeter; 7—CsI electromagnetic calorimeter; 8—yoke; 9—VEPP-2000 focusing solenoid.
microchannel PMT readout are placed in a 10 mm gap between the liquid Xe calorimeter and the CsI crystals.
obtained with a few percent non-uniformity throughout the detector volume. No detection inefficiency was observed. Spatial resolutions in drift plane and along the sense wires are presented in Figs. 3 and 4, respectively. They are in reasonable agreement with the design values. Now the drift chamber is completely assembled and is ready for data taking at VEPP-2000.
3. Subsytems 3.1. SND drift chamber
3.2. Liquid Xe calorimeter of CMD-3
The SND drift chamber [5] consists of 24 radial jet-type cells each containing nine gold-plated tungsten sense wires of 15 mm in diameter. The hit coordinate along the wire is measured by charge division. Near the outer cylindrical fiber/epoxy shell the proportional chamber with a 3 mm wire spacing is placed. The cathode strips with 6 mm pitch in the Z direction on the inner and outer cylindrical shells are used for additional improvement of Z-coordinate measurement precisely defining the fiducial volume. The tracking system operates with Ar:CO2 (80:20) gas mixture. During tests with cosmic-ray muons, the operational conditions were optimized and main parameters of the system were measured. As a result of tests, the design gas gain of 5 105 was
The liquid Xe (LXe) calorimeter of the CMD-3 [6] is a set of 14 consecutive cylindrical gaps of ionization chambers with copper plated G-10 electrodes. The gap width is 10.2 mm. The copper coverage on both sides of odd (anode) electrodes is subdivided into rectangular pads, whose size depends on the electrode radii and roughly equals to 80 80 mm2. The radially consecutive pads are combined to a tower for energy measurement. The copper lamination on both sides of cathode electrodes is subdivided into the mutually perpendicular strips going at an angle of 451 relative to the cylinder moving line. The hit coordinate is measured by the center of gravity of charges induced on these strips.
B.I. Khazin / Nuclear Instruments and Methods in Physics Research A 623 (2010) 353–355
3
180
lxe dr resolution by layers
160
2.5
140
FWHM ≈ 4.8 ns
120
2
Events
resolution, mm
355
1.5
100 80 60
1
40 20
0.5
0 -10
-5
0 1
2
3
5 4 layer number
6
7
80 70 60 events
50 40 30 20 10 0
5
10
15 signal, ph.e.
20
25
5
10 t, ns
15
20
25
30
Fig. 7. Time resolution of the aerogel Cherenkov counter.
Fig. 5. LXe calorimeter spatial resolution as a function of layer number.
0
0
30
Fig. 6. Charge spectrum for cosmic muons with p Z 1 GeV=c in units of the mean single photoelectron pulse charge. Points with error bar are experimental data, the curve is a fit by convolution of the single-electron charge spectrum and Poisson distribution.
The LXe calorimeter was installed into CMD-3 and the study of its parameters with the help of cosmic-ray particles were started. About 3 106 cosmic-ray events were recorded on tapes. The performed tests show the sufficient stability of electronics. The obtained spatial resolution shown in Fig. 5 varies from 0.7 to 1.4 mm depending on the layer number. 3.3. Aerogel Cherenkov counters of SND The main task of Cherenkov counters in SND is p=K separation in the particle momentum region 300 MeV=c r p r870 MeV=c. The aerogel counters system of 255 mm long and with the inner radius of 103 mm and the outer radius of 139 mm is made of three separate pieces comprising a cylinder surrounding the tracking part of the detector. The aerogel radiator of each piece is piled up from aerogel blocks. The total number of blocks in a counter is 39, resulting in 351 in the whole system. The light collection is done with the help of 3 17.5 mm2 BBQ doped polymethylmetacrylat shifter. The photomultipliers with multi-channel plates, having a photocathode of
18 mm in diameter, are used for the light readout. To ensure the reliable p=K separation in the energy range below 2 GeV, the aerogel refraction index was chosen to be equal to 1.13. The tests were carried out with one full-size counter. The main goal of the tests was to measure the mean signal magnitude m for relativistic charged particles which radiate the Cherenkov light with an intensity close to its maximum. The cosmic-ray muons with the momentum p Z 1 GeV=c, five times the Cherenkov threshold momentum for muons in n ¼1.13 aerogel, were used. A typical spectrum of the total signal charge for cosmic-ray muons is shown in Fig. 6. The horizontal scale is in units of an average single photoelectron pulse charge (ph.e.). The drop-out points at about 25 ph.e. are due to preamplifier saturation. The time distribution of signals measured with cosmic-ray muons with the momentum p Z 1 GeV=c is shown in Fig. 7. The obtained time resolution is consistent with the estimation tBBQ =nph:e: ¼ 2 ns, where tBBQ ¼ 15 ns is the decay time of BBQ [7] and nph:e: ¼ 7:5 ph.e. is an average signal during the measurements.
4. Conclusions The upgrade of detectors for the VEPP-2000 collider is close to completion. Tests of subsystems performed with the help of cosmic-ray particles show that all parameters are close to the expected ones, convincing that new physical requirements provided by an increase in energy and luminosity of the new collider will be fully satisfied.
Acknowledgments This work is supported in part by Grants RFBR 07-02-00104, 0802-08082, 08-02-00328, 08-02-00634, 08-02-00660, 09-02-00276-a, 09-02-00643-a, Sci. School-5655.2008.2, Sci. School-4837.2008.2. References [1] A.N. Skrinsky, in: Proceedings of Workshop on Physics and Detectors for DAFNE, Frascati, Italy, April 4–7, 1995, p. 3. [2] I. Koop, Nucl. Phys. B (Proc. Suppl.) 181–182 (2008) 371. [3] B. Khazin, Nucl. Phys. B (Proc. Suppl.) 162 (2006) 327. [4] M.N. Achasov, et al., Nucl. Instr. and Meth. A 449 (2000) 125. [5] V.M. Aulchenko, et al., Nucl. Instr. and Meth. A 494 (2002) 246. [6] A.A. Grebenuk, Nucl. Instr. and Meth. A 379 (1996) 488. [7] E.A. Kravchenko, et al., Nucl. Instr. and Meth. A 494 (2002) 424.
Contents lists available at ScienceDirect
Nuclear Instruments and Methods in Physics Research A journal homepage: www.elsevier.com/locate/nima
Detectors and physics at VEPP-2000 B.I. Khazin ,1 a r t i c l e in fo
abstract
Available online 3 March 2010
A new electron–positron collider VEPP-2000 is now under commission at the Budker Institute of Nuclear Physics. The high luminosity and its center-of-mass energy extended up to 2 GeV open up new possibilities in precision studies of the electron–positron annihilation into hadrons. To perform experiments with this new collider, two detectors—SND and CMD-3—are now being installed at the VEPP-2000 experimental hall. The physics program and results of the tests of the major detector subsystems are reported. & 2010 Elsevier B.V. All rights reserved.
Keywords: Electron–positron colliders Particle detectors
1. Introduction
2. SND and CMD-3 detectors
A long set of experiments at the VEPP-2M [1] collider in Novosibirsk produced a lot of detailed and precise data concerning processes of the electron–positron annihilation at the center of mass energy ranging from the threshold of two pion production up to 1.4 GeV. The relevance of detailed and precise low energy data and existence of rather poorly studied data in the center-of-mass energy between 1.4 and 2 GeV were the motivation for the construction at Budker Institute of Nuclear Physics of the electron–positron collider VEPP-2000 with the c.m. energy up to 2 GeV and luminosity up to 1032 cm 2 s 1 [2]. The physics program of future experiments will be a natural continuation of the program performed at VEPP-2M including precision measurements of hadronic cross-sections, studies of light vector meson recurrences, and measurements of nucleon electromagnetic form-factors near threshold. Taking into account the requirements of this program, two detectors—the upgraded Spherical Neutral Detector (SND) and the newly constructed Cryogenic Magnetic Detector (CMD-3)— are now being installed at the experimental hall of VEPP-2000. Some details of the detectors are described in Ref. [3]. Both detectors have the improved tracking system, electromagnetic calorimeter, particle identification capability and new, much faster data acquisition system including both the hardware and software. The results of latest tests of some detector subsystems are described below.
2.1. SND
Tel.: + 7 383 333 4920; fax: +7 383 330 7163.
E-mail address: [email protected] On behalf of CMD-3 and SND Collaborations.
1
0168-9002/$ - see front matter & 2010 Elsevier B.V. All rights reserved. doi:10.1016/j.nima.2010.02.246
The layout of SND is shown in Fig. 1. The vacuum tube of 40 mm in diameter and with the wall thickness of 0.75 mm is made of beryllium. It is surrounded by cylindrical drift chamber that measures the charged particle direction of flight. The system of aerogel counters is placed just outside the DC. All the detector subsystems are housed inside the spherically shaped electromagnetic calorimeter, made of three layers of NaI(Tl) crystals with the readout vacuum phototriodes [4]. The total number of crystals is 1632 and the thicknesses of the layers are 2.9X0, 4.8X0 and 5.7X0 respectively. The angular dimensions of the calorimeter are 183 r y r 1623 and 03 r f r 3603 . Outside the calorimeter a 12 cm-thick iron absorber, muon detection system containing double layers of streamer tubes and plastic scintillator counters are placed. 2.2. CMD-3 The layout of the CMD-3 detector is shown in Fig. 2. Electrons and positrons collide at the center of the vacuum chamber. The coordinates, angles and momenta of charged particles are measured by the cylindrical drift chamber (DC). The Z-chamber surrounding the DC measures track coordinate along the beam direction (Z-coordinate) with high resolution and produces the fast signal starting trigger electronics. DC and Z-chamber are placed inside the very thin (0.18X0) superconductive solenoid with a magnetic field of 1.35 T. The position and energy of photons are measured by the system of barrel calorimeters based on the liquid Xe and CsI crystals and endcap calorimeter based on BGO crystals. The barrel and endcap calorimeters cover a solid angle of 0:94 4p steradians. The system of range measurement with plastic scintillators is located outside the flux return yoke. TOF counters made of BC-408 plastic scintillators with
354
B.I. Khazin / Nuclear Instruments and Methods in Physics Research A 623 (2010) 353–355
μ+ 3 7 5 e-
e+
σ, mkm
8
6-layer
350
4-layer
300
3-layer
250 200
100
6
2 4
400
150
10
1
SND Drift Chamber Resolution abs(delta6):abs(rho6)
450
50
9
0
μ− 0 20 40 60 80 100 cm Fig. 1. Cross-section of SND. 1—VEPP-2000 vacuum chamber; 2—tracking system; 3—aerogel counters; 4—NaI(Tl) electromagnetic calorimeter; 5—vacuum phototriodes; 6—iron absorber; 7–9—muon system; 10—VEPP-2000 focusing solenoid.
0.1
0.2
0.3 0.4 0.5 Drift distance
0.6
0.7 ρ, cm
Fig. 3. Spatial resolution of SND DC in the R2j plane of the 3rd, 4th and 6th layers versus the drift distance.
70
σMC = 0.53±0.02
60
σ EXP = 1.63±0.08
50 40 30 20 10 0
-8
-6
-4
-2
0
2
4
6 Z, xmm
Fig. 4. SND DC resolution along the sense wires. Data (points with errors) and simple simulation (open histogram) with fitted curves are shown.
Fig. 2. Cross-section of CMD-3. 1—interaction point; 2—drift chamber; 3—end cap BGO electromagnetic calorimeter; 4—Z-chamber; 5—superconductive solenoid; 6—liquid xenon electromagnetic calorimeter; 7—CsI electromagnetic calorimeter; 8—yoke; 9—VEPP-2000 focusing solenoid.
microchannel PMT readout are placed in a 10 mm gap between the liquid Xe calorimeter and the CsI crystals.
obtained with a few percent non-uniformity throughout the detector volume. No detection inefficiency was observed. Spatial resolutions in drift plane and along the sense wires are presented in Figs. 3 and 4, respectively. They are in reasonable agreement with the design values. Now the drift chamber is completely assembled and is ready for data taking at VEPP-2000.
3. Subsytems 3.1. SND drift chamber
3.2. Liquid Xe calorimeter of CMD-3
The SND drift chamber [5] consists of 24 radial jet-type cells each containing nine gold-plated tungsten sense wires of 15 mm in diameter. The hit coordinate along the wire is measured by charge division. Near the outer cylindrical fiber/epoxy shell the proportional chamber with a 3 mm wire spacing is placed. The cathode strips with 6 mm pitch in the Z direction on the inner and outer cylindrical shells are used for additional improvement of Z-coordinate measurement precisely defining the fiducial volume. The tracking system operates with Ar:CO2 (80:20) gas mixture. During tests with cosmic-ray muons, the operational conditions were optimized and main parameters of the system were measured. As a result of tests, the design gas gain of 5 105 was
The liquid Xe (LXe) calorimeter of the CMD-3 [6] is a set of 14 consecutive cylindrical gaps of ionization chambers with copper plated G-10 electrodes. The gap width is 10.2 mm. The copper coverage on both sides of odd (anode) electrodes is subdivided into rectangular pads, whose size depends on the electrode radii and roughly equals to 80 80 mm2. The radially consecutive pads are combined to a tower for energy measurement. The copper lamination on both sides of cathode electrodes is subdivided into the mutually perpendicular strips going at an angle of 451 relative to the cylinder moving line. The hit coordinate is measured by the center of gravity of charges induced on these strips.
B.I. Khazin / Nuclear Instruments and Methods in Physics Research A 623 (2010) 353–355
3
180
lxe dr resolution by layers
160
2.5
140
FWHM ≈ 4.8 ns
120
2
Events
resolution, mm
355
1.5
100 80 60
1
40 20
0.5
0 -10
-5
0 1
2
3
5 4 layer number
6
7
80 70 60 events
50 40 30 20 10 0
5
10
15 signal, ph.e.
20
25
5
10 t, ns
15
20
25
30
Fig. 7. Time resolution of the aerogel Cherenkov counter.
Fig. 5. LXe calorimeter spatial resolution as a function of layer number.
0
0
30
Fig. 6. Charge spectrum for cosmic muons with p Z 1 GeV=c in units of the mean single photoelectron pulse charge. Points with error bar are experimental data, the curve is a fit by convolution of the single-electron charge spectrum and Poisson distribution.
The LXe calorimeter was installed into CMD-3 and the study of its parameters with the help of cosmic-ray particles were started. About 3 106 cosmic-ray events were recorded on tapes. The performed tests show the sufficient stability of electronics. The obtained spatial resolution shown in Fig. 5 varies from 0.7 to 1.4 mm depending on the layer number. 3.3. Aerogel Cherenkov counters of SND The main task of Cherenkov counters in SND is p=K separation in the particle momentum region 300 MeV=c r p r870 MeV=c. The aerogel counters system of 255 mm long and with the inner radius of 103 mm and the outer radius of 139 mm is made of three separate pieces comprising a cylinder surrounding the tracking part of the detector. The aerogel radiator of each piece is piled up from aerogel blocks. The total number of blocks in a counter is 39, resulting in 351 in the whole system. The light collection is done with the help of 3 17.5 mm2 BBQ doped polymethylmetacrylat shifter. The photomultipliers with multi-channel plates, having a photocathode of
18 mm in diameter, are used for the light readout. To ensure the reliable p=K separation in the energy range below 2 GeV, the aerogel refraction index was chosen to be equal to 1.13. The tests were carried out with one full-size counter. The main goal of the tests was to measure the mean signal magnitude m for relativistic charged particles which radiate the Cherenkov light with an intensity close to its maximum. The cosmic-ray muons with the momentum p Z 1 GeV=c, five times the Cherenkov threshold momentum for muons in n ¼1.13 aerogel, were used. A typical spectrum of the total signal charge for cosmic-ray muons is shown in Fig. 6. The horizontal scale is in units of an average single photoelectron pulse charge (ph.e.). The drop-out points at about 25 ph.e. are due to preamplifier saturation. The time distribution of signals measured with cosmic-ray muons with the momentum p Z 1 GeV=c is shown in Fig. 7. The obtained time resolution is consistent with the estimation tBBQ =nph:e: ¼ 2 ns, where tBBQ ¼ 15 ns is the decay time of BBQ [7] and nph:e: ¼ 7:5 ph.e. is an average signal during the measurements.
4. Conclusions The upgrade of detectors for the VEPP-2000 collider is close to completion. Tests of subsystems performed with the help of cosmic-ray particles show that all parameters are close to the expected ones, convincing that new physical requirements provided by an increase in energy and luminosity of the new collider will be fully satisfied.
Acknowledgments This work is supported in part by Grants RFBR 07-02-00104, 0802-08082, 08-02-00328, 08-02-00634, 08-02-00660, 09-02-00276-a, 09-02-00643-a, Sci. School-5655.2008.2, Sci. School-4837.2008.2. References [1] A.N. Skrinsky, in: Proceedings of Workshop on Physics and Detectors for DAFNE, Frascati, Italy, April 4–7, 1995, p. 3. [2] I. Koop, Nucl. Phys. B (Proc. Suppl.) 181–182 (2008) 371. [3] B. Khazin, Nucl. Phys. B (Proc. Suppl.) 162 (2006) 327. [4] M.N. Achasov, et al., Nucl. Instr. and Meth. A 449 (2000) 125. [5] V.M. Aulchenko, et al., Nucl. Instr. and Meth. A 494 (2002) 246. [6] A.A. Grebenuk, Nucl. Instr. and Meth. A 379 (1996) 488. [7] E.A. Kravchenko, et al., Nucl. Instr. and Meth. A 494 (2002) 424.