- Email: [email protected]
The future CESR–CLEO program
Nuclear Instruments and Methods in Physics Research A 446 (2000) 92}96
The future CESR}CLEO program Karl Berkelman Laboratory of Nuclear Studies, Cornell University, Ithaca, NY 14853, USA
Abstract After the completion of this year's upgrade installation, CLEO will be able to run at luminosities in excess of 10/cms with improved tracking and particle identi"cation. Plans are underway for a future upgrade to bring CESR luminosity to the level of 3;10. Such luminosities will be required for a full understanding of CP violation in B decays. 2000 Elsevier Science B.V. All rights reserved. PACS: 13.65.#i; 29.20.Dh
1. The present upgrade 1.1. CESR The Cornell electron}positron storage ring is being upgraded to increase the peak luminosity from the present L"8;10 cm\s\ to L51.7;10 cm\s\. Assuming #at beams of equal energy E in GeV, we can write luminosity as L"2.17;10mEeN f/bH. The upgraded CESR parameters are bunch number N "9 trains ;5 bunches/train, beam current I"eN f5500 mA, depth of focus bH"1.8 cm, tune shift m50.04. To accomplish this we are now completing the installation of four superconducting rf cavities, upgrades of the injection linac and the positron
E-mail address: [email protected] (K. Berkelman).
production target, upgraded vacuum components, and improved multibunch beam feedback systems. Within the next year we expect also to upgrade the interaction region focus system with superconducting quadrupoles now under construction. 1.2. CLEO The de"nitive study of rare B decay modes such as BPpp and BPKp requires better high-momentum p}K separation than is provided by the present CLEO dE/dx and time-of-#ight systems. This, plus the fact that the new CESR interaction region quadrupoles impinge on the space occupied by the CLEO main drift chamber, obliges us to upgrade the inner core of the CLEO detector. The new components with their radii relative to the beam line, are 80}100 cm.
Ring imaging Cherenkov with LiF radiator and TEA photon converter,
Georg Viehhauser's talk for more details Ref. [1].
0168-9002/00/$ - see front matter 2000 Elsevier Science B.V. All rights reserved. PII: S 0 1 6 8 - 9 0 0 2 ( 0 0 ) 0 0 0 3 8 - 3
K. Berkelman / Nuclear Instruments and Methods in Physics Research A 446 (2000) 92}96
New main drift chamber with stepped end plates, 2.5}10.0 cm. New four-layer double-sided Si strip tracker. 12}80 cm.
The triggering and readout electronics are also being upgraded in order to handle the higher expected event rates. Although the new drift chamber is smaller, the momentum resolution will be the same as before, because of the decreased multiple scattering resulting from the more sophisticated low-mass design. Starting in late 1999 the upgrade will enable CLEO to run with over twice the previous data rate, recording at least 12 million BBM events per year. K's and p's will be identi"ed with better than three standard deviation separation at all momenta. This will make possible improved accuracy in all past CLEO measurements in b, c, q, B, and two-c physics. We will be making more sensitive searches for nonstandard physics, measuring branching fractions for rare B decays at the 10\}10\ level, and if nature is kind, observing direct CP violation. 2. CP violation at CESR 2.1. CP observables In order to understand CP violation in B decays and determine whether there are any non-standard model sources, one will have to measure as many independent CP asymmetries as possible. An important goal is to measure in as many independent ways as possible the three angles a, b, and c of the unitarity triangle de"ned by the standard model orthogonality relation between the "rst and third rows of the CKM matrix, then check consistency with the lengths of the sides of the triangle. E The time-dependent asymmetry A(t !t ) in mixing-mediated bPc processes like BPwK 1 yields a measurement of the mixing phase b"arg(<
93
E A(t !t ) in mixing-mediated bPu processes like BPp>p\ depends on the mixing phase and the phase of < (in the standard model) but is complicated by interference from penguin amplitudes. Here again, the experiment is easier in the boosted frame, and is not likely to be done "rst at CESR. E The direct, time-independent A in decays like BPK!p measures the phase between the interfering tree (bPu) and penguin (bPc,tPs) amplitudes, which in the standard model is c"arg(<
SECTION II.
94
K. Berkelman / Nuclear Instruments and Methods in Physics Research A 446 (2000) 92}96
Table 1 Branching ratios, asymmetries, and CP violation signi"cance factor for several interesting rare B decay modes. Data with $ errors are from CLEO, otherwise speculation BA A
Mode
B 10\
"A" %
R" \ 10\
K\p K\g K\g K\u KM p\ p\p p\g p\g p\u o\u K\p> KH\p> p\p>
15$5 0.1}5 74$15 1.5}4 14$5 1.3}11 5 6}17 4}11 13}25 14$4 22$8 2}12
1}18 6}65 1}3 3 0}1 0.4}70 33 16}22 4 4 1}22 2 1}6
0.1}40 0.1}70 0.5}10 0.1}0.4 0}0.2 0}130 60 15}80 0.6}2 4 0.4}60 1 0.2}3
the form !2 sin c sin
A" , R#1/R#2 cos c cos
where R is the absolute value of the ratio of penguin and tree amplitudes. Since and R are a priori unknown, we will need more experimental data on tree and penguin amplitudes in order to extract c. Isospin and SU(3) relations allow one to extract such information by comparing branching ratios of related decay modes [2]. For example, the BPK!p amplitude can be related to the amplitudes for pure penguin and pure tree processes: "pK>2"!(1/(2)"p>K2#j(f /f )"p>p2 ) p "pK\2"!(1/(2)"p\KM 2#j(f /f )"p\p2. ) p Measurement of all of the relevant rates allows one to extract c as well as R and . Smaller electroweak penguin and "nal state interaction contributions can be accounted for by comparing more modes. Table 1 shows measured or predicted rates and predicted CP asymmetries for some potentially interesting modes. The last column lists the function R of branching ratio B and asymmetry A that determines the number of standard
deviations of statistical signi"cance in the measurement of A: A/dA"(eN M ;(R. For example, if N M "10BBM events and e$ciency e&, as we might expect in the next few years from the upgraded CLEO, then CP asymmetries will be more than four-standard-deviation signi"cant for modes with R'60;10\. The table shows a few cases for which that might be possible, but for a complete understanding of the origin of CP violation in B decays, we will clearly need a data sample of much more than 100 million BBM events. 3. Looking 5ve years ahead By 2002, or soon after, we can expect that E CLEO, BaBar, and BELLE will be seeing tens of millions of BBM per year; E b, and perhaps a, will be measured by BaBar, BELLE, HERA-B, CDF, and/or D"; E direct CP violation might be seen in Kp or some such mode by CLEO, BaBar, and/or BELLE; E we will still be crying for more BBM events to understand CP violation and test the standard model. Of course, more B's are expected at the hadron experiments, HERA-B, CDF, D", BTeV, ATLAS, CMS, LHC-B, but in a di$cult background environment and mainly in all-charged "nal states. What can we do to get more e>e\PB(4S) PBBM ? The existing e>e\ rings will be limited to peak luminosities of the order of L&3;10. Is 3;10 possible? If so, we could get 200 million BBM per year? What do we need? E Either the beam current has to be increased by storing more bunches, or the beam}beam tune shift parameter has to be increased, perhaps by using round beams instead of #at beams. The two beams have to be in separate channels in order to have enough physical aperture, and to avoid destablizing long-range beam}beam interactions.
K. Berkelman / Nuclear Instruments and Methods in Physics Research A 446 (2000) 92}96
95
Fig. 1. Cross section of a dual-aperture dipole magnet and vacuum chamber.
Fig. 2. Cross section of a dual-aperture superconducting quadrupole.
E Equal e> and e\ energies is an advantage. Energy symmetry imposes fewer constraints on the IR focusing design, and less serious beam}beam interaction limitation on the luminosity. The
lower E implies fewer RF cavities and better
beam stability. The smaller orbit radius that comes with lower E makes the collider less
expensive to upgrade.
SECTION II.
96
K. Berkelman / Nuclear Instruments and Methods in Physics Research A 446 (2000) 92}96
more compact than the present CESR magnets and could be installed above the present synchrotron injector in the CESR tunnel (Fig. 3). We have already tested a prototype quadrupole, and prototypes of the dipoles and corrector magnets are proceeding.
4. Conclusions
Fig. 3. Cross section of the CESR tunnel showing the existing CESR magnet (left), the synchrotron injector (right), and the proposed dual-aperture ring above the synchrotron.
E CESR also has other advantages for luminosity upgrading: the beam crossing angle allows for more circulating bunches than the head-on con"guration; superconducting RF can handle higher beam currents; and there are no competing laboratory priorities. We have a plan for a dual-channel replacement of the CESR arc magnets that can be made for ($40 million. We would keep the present superconducting RF system (adding some more cavities), the present interaction region components, and the CLEO detector. The dipoles (Fig. 1) and superconducting quadrupoles (Fig. 2) would be considerably
1. CLEO is now exploring rare, charmless B decays: Cabibbo suppressed bPu decays, and e!ective #avor-changing neutral current bPs decays. 2. CESR and CLEO will continue to be productive in the next "ve years exploiting the present upgrade: rare B decays, observation of direct CP violation, tests of the standard model, and exploring new physics. 3. B physics will then require L53;10 cm\s, in order to carry out the de"nitive study of CP in many decay modes, investigate rare decay at the level of 10, and understand #avor physics. 4. We are planning such an upgrade to CESR. 5. CLEO is inviting new collaborators.
References [1] G. Viehhauser, Nucl. Instr. and Meth. A 446 (2000) 97, These Proceedings. [2] M. Gronau, J. Rosner, D. London, Phys. Rev. Lett. B 425 (1004) 21.
The future CESR}CLEO program Karl Berkelman Laboratory of Nuclear Studies, Cornell University, Ithaca, NY 14853, USA
Abstract After the completion of this year's upgrade installation, CLEO will be able to run at luminosities in excess of 10/cms with improved tracking and particle identi"cation. Plans are underway for a future upgrade to bring CESR luminosity to the level of 3;10. Such luminosities will be required for a full understanding of CP violation in B decays. 2000 Elsevier Science B.V. All rights reserved. PACS: 13.65.#i; 29.20.Dh
1. The present upgrade 1.1. CESR The Cornell electron}positron storage ring is being upgraded to increase the peak luminosity from the present L"8;10 cm\s\ to L51.7;10 cm\s\. Assuming #at beams of equal energy E in GeV, we can write luminosity as L"2.17;10mEeN f/bH. The upgraded CESR parameters are bunch number N "9 trains ;5 bunches/train, beam current I"eN f5500 mA, depth of focus bH"1.8 cm, tune shift m50.04. To accomplish this we are now completing the installation of four superconducting rf cavities, upgrades of the injection linac and the positron
E-mail address: [email protected] (K. Berkelman).
production target, upgraded vacuum components, and improved multibunch beam feedback systems. Within the next year we expect also to upgrade the interaction region focus system with superconducting quadrupoles now under construction. 1.2. CLEO The de"nitive study of rare B decay modes such as BPpp and BPKp requires better high-momentum p}K separation than is provided by the present CLEO dE/dx and time-of-#ight systems. This, plus the fact that the new CESR interaction region quadrupoles impinge on the space occupied by the CLEO main drift chamber, obliges us to upgrade the inner core of the CLEO detector. The new components with their radii relative to the beam line, are 80}100 cm.
Ring imaging Cherenkov with LiF radiator and TEA photon converter,
Georg Viehhauser's talk for more details Ref. [1].
0168-9002/00/$ - see front matter 2000 Elsevier Science B.V. All rights reserved. PII: S 0 1 6 8 - 9 0 0 2 ( 0 0 ) 0 0 0 3 8 - 3
K. Berkelman / Nuclear Instruments and Methods in Physics Research A 446 (2000) 92}96
New main drift chamber with stepped end plates, 2.5}10.0 cm. New four-layer double-sided Si strip tracker. 12}80 cm.
The triggering and readout electronics are also being upgraded in order to handle the higher expected event rates. Although the new drift chamber is smaller, the momentum resolution will be the same as before, because of the decreased multiple scattering resulting from the more sophisticated low-mass design. Starting in late 1999 the upgrade will enable CLEO to run with over twice the previous data rate, recording at least 12 million BBM events per year. K's and p's will be identi"ed with better than three standard deviation separation at all momenta. This will make possible improved accuracy in all past CLEO measurements in b, c, q, B, and two-c physics. We will be making more sensitive searches for nonstandard physics, measuring branching fractions for rare B decays at the 10\}10\ level, and if nature is kind, observing direct CP violation. 2. CP violation at CESR 2.1. CP observables In order to understand CP violation in B decays and determine whether there are any non-standard model sources, one will have to measure as many independent CP asymmetries as possible. An important goal is to measure in as many independent ways as possible the three angles a, b, and c of the unitarity triangle de"ned by the standard model orthogonality relation between the "rst and third rows of the CKM matrix, then check consistency with the lengths of the sides of the triangle. E The time-dependent asymmetry A(t !t ) in mixing-mediated bPc processes like BPwK 1 yields a measurement of the mixing phase b"arg(<
93
E A(t !t ) in mixing-mediated bPu processes like BPp>p\ depends on the mixing phase and the phase of < (in the standard model) but is complicated by interference from penguin amplitudes. Here again, the experiment is easier in the boosted frame, and is not likely to be done "rst at CESR. E The direct, time-independent A in decays like BPK!p measures the phase between the interfering tree (bPu) and penguin (bPc,tPs) amplitudes, which in the standard model is c"arg(<
SECTION II.
94
K. Berkelman / Nuclear Instruments and Methods in Physics Research A 446 (2000) 92}96
Table 1 Branching ratios, asymmetries, and CP violation signi"cance factor for several interesting rare B decay modes. Data with $ errors are from CLEO, otherwise speculation BA A
Mode
B 10\
"A" %
R" \ 10\
K\p K\g K\g K\u KM p\ p\p p\g p\g p\u o\u K\p> KH\p> p\p>
15$5 0.1}5 74$15 1.5}4 14$5 1.3}11 5 6}17 4}11 13}25 14$4 22$8 2}12
1}18 6}65 1}3 3 0}1 0.4}70 33 16}22 4 4 1}22 2 1}6
0.1}40 0.1}70 0.5}10 0.1}0.4 0}0.2 0}130 60 15}80 0.6}2 4 0.4}60 1 0.2}3
the form !2 sin c sin
A" , R#1/R#2 cos c cos
where R is the absolute value of the ratio of penguin and tree amplitudes. Since and R are a priori unknown, we will need more experimental data on tree and penguin amplitudes in order to extract c. Isospin and SU(3) relations allow one to extract such information by comparing branching ratios of related decay modes [2]. For example, the BPK!p amplitude can be related to the amplitudes for pure penguin and pure tree processes: "pK>2"!(1/(2)"p>K2#j(f /f )"p>p2 ) p "pK\2"!(1/(2)"p\KM 2#j(f /f )"p\p2. ) p Measurement of all of the relevant rates allows one to extract c as well as R and . Smaller electroweak penguin and "nal state interaction contributions can be accounted for by comparing more modes. Table 1 shows measured or predicted rates and predicted CP asymmetries for some potentially interesting modes. The last column lists the function R of branching ratio B and asymmetry A that determines the number of standard
deviations of statistical signi"cance in the measurement of A: A/dA"(eN M ;(R. For example, if N M "10BBM events and e$ciency e&, as we might expect in the next few years from the upgraded CLEO, then CP asymmetries will be more than four-standard-deviation signi"cant for modes with R'60;10\. The table shows a few cases for which that might be possible, but for a complete understanding of the origin of CP violation in B decays, we will clearly need a data sample of much more than 100 million BBM events. 3. Looking 5ve years ahead By 2002, or soon after, we can expect that E CLEO, BaBar, and BELLE will be seeing tens of millions of BBM per year; E b, and perhaps a, will be measured by BaBar, BELLE, HERA-B, CDF, and/or D"; E direct CP violation might be seen in Kp or some such mode by CLEO, BaBar, and/or BELLE; E we will still be crying for more BBM events to understand CP violation and test the standard model. Of course, more B's are expected at the hadron experiments, HERA-B, CDF, D", BTeV, ATLAS, CMS, LHC-B, but in a di$cult background environment and mainly in all-charged "nal states. What can we do to get more e>e\PB(4S) PBBM ? The existing e>e\ rings will be limited to peak luminosities of the order of L&3;10. Is 3;10 possible? If so, we could get 200 million BBM per year? What do we need? E Either the beam current has to be increased by storing more bunches, or the beam}beam tune shift parameter has to be increased, perhaps by using round beams instead of #at beams. The two beams have to be in separate channels in order to have enough physical aperture, and to avoid destablizing long-range beam}beam interactions.
K. Berkelman / Nuclear Instruments and Methods in Physics Research A 446 (2000) 92}96
95
Fig. 1. Cross section of a dual-aperture dipole magnet and vacuum chamber.
Fig. 2. Cross section of a dual-aperture superconducting quadrupole.
E Equal e> and e\ energies is an advantage. Energy symmetry imposes fewer constraints on the IR focusing design, and less serious beam}beam interaction limitation on the luminosity. The
lower E implies fewer RF cavities and better
beam stability. The smaller orbit radius that comes with lower E makes the collider less
expensive to upgrade.
SECTION II.
96
K. Berkelman / Nuclear Instruments and Methods in Physics Research A 446 (2000) 92}96
more compact than the present CESR magnets and could be installed above the present synchrotron injector in the CESR tunnel (Fig. 3). We have already tested a prototype quadrupole, and prototypes of the dipoles and corrector magnets are proceeding.
4. Conclusions
Fig. 3. Cross section of the CESR tunnel showing the existing CESR magnet (left), the synchrotron injector (right), and the proposed dual-aperture ring above the synchrotron.
E CESR also has other advantages for luminosity upgrading: the beam crossing angle allows for more circulating bunches than the head-on con"guration; superconducting RF can handle higher beam currents; and there are no competing laboratory priorities. We have a plan for a dual-channel replacement of the CESR arc magnets that can be made for ($40 million. We would keep the present superconducting RF system (adding some more cavities), the present interaction region components, and the CLEO detector. The dipoles (Fig. 1) and superconducting quadrupoles (Fig. 2) would be considerably
1. CLEO is now exploring rare, charmless B decays: Cabibbo suppressed bPu decays, and e!ective #avor-changing neutral current bPs decays. 2. CESR and CLEO will continue to be productive in the next "ve years exploiting the present upgrade: rare B decays, observation of direct CP violation, tests of the standard model, and exploring new physics. 3. B physics will then require L53;10 cm\s, in order to carry out the de"nitive study of CP in many decay modes, investigate rare decay at the level of 10, and understand #avor physics. 4. We are planning such an upgrade to CESR. 5. CLEO is inviting new collaborators.
References [1] G. Viehhauser, Nucl. Instr. and Meth. A 446 (2000) 97, These Proceedings. [2] M. Gronau, J. Rosner, D. London, Phys. Rev. Lett. B 425 (1004) 21.