- Email: [email protected]
Experience at PETRA
The MARK.I collaboration, Physics with high energy electron-positron colliding beams
341
of hard non-collinear gluons, and the determination of the strong coupling constant a~, are also discussed. Section 5 closes the report with a summary of the physics conclusions.
2. Experience at PETRA PETRA [1] (l?ositron E lektron Tandem Ringbeschleuniger Anlage) began operation in the fall of 1978 as the world's highest energy e+e - colliding beam machine. Since its commissioning, PETRA beams have been available for physics runs 60% of the time, with the remaining time being devoted to machine development and maintenance periods [2]. The ring, with a circumference of 2.3 kilometers, has eight long straight sections of which two are reserved for the RF accelerating cavities. At present only four of the experimemal areas are occupied. The remaining two experimental areas are reserved for second generation experiments. The original injection scheme utilized both of the existing DESY facilities, DESY and DORIS. Electrons, initially accelerated in LINAC I (see fig. 1) are injected into DESY (Deutsches E lektronen Synchrotron) where they are further accelerated to 6 GeV and injected into PETRA. Positrons follow a ~mewhat more complicated path: after initial acceleration in LINAC II, positrons are injected via DESY into DORIS (DoppeI-Ring-Speicher), where they are accumulated at an energy of 2.2 GeV. Stored positron bunches in DORIS are then transferred back to DESY for further acceleration to 6 GeV, the minimum PETRA injection energy. With the discovery of the upsilon (Y) resoaance in 1977 at FNAL [3] and the confirmation in e ÷einteractions [4], the need! to operate DORIS as a storage ring independent of PETRA was realized. Consequently, in the fall of 1977 the decision was made to construct a Positron Intensity Accumulator (PIA) [5] to free DORIS for physics runs. In this new injection scheme, positrons are accumulated in PIA after acceleration in LINAC II. Twenty successive LINAC bunches are injected into PIA, compressed in phase space, and transferred to DESY for acceleration and injection into PETRA. PIA was assembled in record time and since the summer of 1979 has served as the injector for both DORIS and PETRA. The average luminosity is 2 x 10~ cm -2 sec-1 at beam energies of 15 GeV. It is expected that the luminosity will increase in the near future with more operatienal experience.
N
Rt HALLS
Y*SEHALL
IMARK|1 Fig. 1. The layout of PETRA e+e- Storage Ring at DESY, showing the location of the MARK J detector. The other major detectors referred to in the text are respectively located in the SE Hall (Tasso), the NE Hall (Pluto now replaced by CELLO) and the NW Hall (JADE).
?.42
The MARK I collaboration, Physics with high energy electron-positron colliding beams
In the first year of operation, PETRA has run from an energy of 12 GeV to 36 GeV. It has run reliably with very little failures. The stability of the machine was the major reason why all groups at PETRA have been able to perform their experiments satisfactorily.
3. The MARK J experiment
&l. Physics obiectives The MARK J detecte" [6], which identifies and measures the energy and direction of muons, e!ectrons, charged and neutral hadrons with close to uniform efficiency and with ---4~" acceptance, is capable of fulfilling a broad range of physics objectives. Some of the prime physics goals of the experiment are: (1) To study the various QED processes shown in fig. 2 and to study the universality of the known charged leptons in their electromagnetic interactions. At PETRA the available c.m. energy is V~s = GeV (q" up to 1300 GeV2). Since first order QED processes exhibit a s -t cross section dependence the MARK J can probe the validity of QED with an order of magnitude greater sensitivity than that previously available in earlier colliding beam experiments performed at storage rings at SLAC, DESY, ADONE and CEA in the range of q2< 50 GeV 2. (2) To search for new quark flavor's by studying the energy and angular distributions of inclusive muon production in hadronic events (fig. 3a). (3) Using the distributions of I~e and I~h final states shown in fig. 3b to search for the existence of new charged leptons heavier than the tau. (4) To measore the total laadronic cross section (fig. 4) and thereby the structure and energy dependence of the total cross section, in order to search for new thresholds in the hadronic final state continuum, and to search directly for more J-like particles which appear as sharp resonances. (5) To study the topology of hadronic events by measuring the direction and energy of charged and neutral particles. In particular, at PETRA energies, the fragmentation of hard gluons emitted in e-
e-
e+
(~
(a)
e÷
e"
~'-
--'<% "k
q
~(~1
,vI
v(q)
(b)
e"
e+/j.,+ T +
Fig 2. Electron. muon and tau pair production in lowest order.
e-
L-
Fig. 3. (a) Diagram for production and deca~ of heavy quarks in e 'eannihilation. (b) Diagram for production and decay of heavy leptons in e+e - annihilation.
341
of hard non-collinear gluons, and the determination of the strong coupling constant a~, are also discussed. Section 5 closes the report with a summary of the physics conclusions.
2. Experience at PETRA PETRA [1] (l?ositron E lektron Tandem Ringbeschleuniger Anlage) began operation in the fall of 1978 as the world's highest energy e+e - colliding beam machine. Since its commissioning, PETRA beams have been available for physics runs 60% of the time, with the remaining time being devoted to machine development and maintenance periods [2]. The ring, with a circumference of 2.3 kilometers, has eight long straight sections of which two are reserved for the RF accelerating cavities. At present only four of the experimemal areas are occupied. The remaining two experimental areas are reserved for second generation experiments. The original injection scheme utilized both of the existing DESY facilities, DESY and DORIS. Electrons, initially accelerated in LINAC I (see fig. 1) are injected into DESY (Deutsches E lektronen Synchrotron) where they are further accelerated to 6 GeV and injected into PETRA. Positrons follow a ~mewhat more complicated path: after initial acceleration in LINAC II, positrons are injected via DESY into DORIS (DoppeI-Ring-Speicher), where they are accumulated at an energy of 2.2 GeV. Stored positron bunches in DORIS are then transferred back to DESY for further acceleration to 6 GeV, the minimum PETRA injection energy. With the discovery of the upsilon (Y) resoaance in 1977 at FNAL [3] and the confirmation in e ÷einteractions [4], the need! to operate DORIS as a storage ring independent of PETRA was realized. Consequently, in the fall of 1977 the decision was made to construct a Positron Intensity Accumulator (PIA) [5] to free DORIS for physics runs. In this new injection scheme, positrons are accumulated in PIA after acceleration in LINAC II. Twenty successive LINAC bunches are injected into PIA, compressed in phase space, and transferred to DESY for acceleration and injection into PETRA. PIA was assembled in record time and since the summer of 1979 has served as the injector for both DORIS and PETRA. The average luminosity is 2 x 10~ cm -2 sec-1 at beam energies of 15 GeV. It is expected that the luminosity will increase in the near future with more operatienal experience.
N
Rt HALLS
Y*SEHALL
IMARK|1 Fig. 1. The layout of PETRA e+e- Storage Ring at DESY, showing the location of the MARK J detector. The other major detectors referred to in the text are respectively located in the SE Hall (Tasso), the NE Hall (Pluto now replaced by CELLO) and the NW Hall (JADE).
?.42
The MARK I collaboration, Physics with high energy electron-positron colliding beams
In the first year of operation, PETRA has run from an energy of 12 GeV to 36 GeV. It has run reliably with very little failures. The stability of the machine was the major reason why all groups at PETRA have been able to perform their experiments satisfactorily.
3. The MARK J experiment
&l. Physics obiectives The MARK J detecte" [6], which identifies and measures the energy and direction of muons, e!ectrons, charged and neutral hadrons with close to uniform efficiency and with ---4~" acceptance, is capable of fulfilling a broad range of physics objectives. Some of the prime physics goals of the experiment are: (1) To study the various QED processes shown in fig. 2 and to study the universality of the known charged leptons in their electromagnetic interactions. At PETRA the available c.m. energy is V~s = GeV (q" up to 1300 GeV2). Since first order QED processes exhibit a s -t cross section dependence the MARK J can probe the validity of QED with an order of magnitude greater sensitivity than that previously available in earlier colliding beam experiments performed at storage rings at SLAC, DESY, ADONE and CEA in the range of q2< 50 GeV 2. (2) To search for new quark flavor's by studying the energy and angular distributions of inclusive muon production in hadronic events (fig. 3a). (3) Using the distributions of I~e and I~h final states shown in fig. 3b to search for the existence of new charged leptons heavier than the tau. (4) To measore the total laadronic cross section (fig. 4) and thereby the structure and energy dependence of the total cross section, in order to search for new thresholds in the hadronic final state continuum, and to search directly for more J-like particles which appear as sharp resonances. (5) To study the topology of hadronic events by measuring the direction and energy of charged and neutral particles. In particular, at PETRA energies, the fragmentation of hard gluons emitted in e-
e-
e+
(~
(a)
e÷
e"
~'-
--'<% "k
q
~(~1
,vI
v(q)
(b)
e"
e+/j.,+ T +
Fig 2. Electron. muon and tau pair production in lowest order.
e-
L-
Fig. 3. (a) Diagram for production and deca~ of heavy quarks in e 'eannihilation. (b) Diagram for production and decay of heavy leptons in e+e - annihilation.