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It Was Deemed Appropriate to Start the Summer Study at Les Houches with Extensive Presentations of the PETRA and PEP Programmes

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It Was Deemed Appropriate to Start the Summer Study at Les Houches with Extensive Presentations of the PETRA and PEP Programmes - 390 - It was deemed appropriate to start the Summer Study at Les Houches with extensive presentations of the PETRA and PEP programmes. These presentations were given by G. Wolf and R. Schwitters, respectively. This paper is written from their transparencies. The reviewer (M. Jacob) is entirely responsible for pos• sible inaccuracies and omissions. 1. The PETRA Programme 1.1 Foreword PETRA is an acrostic for Positron-Elektron-Tandem Ring Anlage. The cir• cumference of the machine is 2.3 Km. The energy range extends from 10 to 38 GeV (5 to 19 GeV beam energy) but the beam energy could be increased to 23 GeV at a later stage. The design luminosity at 15 GeV is 1032 cm-2 s-1. Construction started in December 1975. Beams were stored for the first time in July 1978*. Figure 1 gives the general layout on the DESY site. 1.2 Physics with PETRA At present, one can classify physics research at PETRA along different lines. They are as follows: a) T (bb) spectroscopy and study of the bq (Eq) states. This corresponds to the lower end of the energy range. b) Search for new narrow states (new quarks) and related spectroscopy. c) Jet studies with a possible différenciation between quark jets and gluon jets. d) Search for heavy leptons. e) Study of yy processes. f) Study of weak-electromagnetic interference with possible hints at the weak boson(s). The present review follows them sequentially. The T Family In connection with b quark physics a look at the present (experiments at DORIS) is worthwhile. Figure 2.a) gives the T peak as observed in 3 different experiments: DESY-Dortmund-Heidelberg-Lund, in DASP, DESY-Heidelberg-Munich and Aachen-DESY-Hamburg-Seigen-Wuppertal in PLUTO. The value of R off resonance is 5.2 ± 1. G. Voss presented the machine and discussed its performance by September 1978 in his talk at Les Houches - 391 - N ^ N E expérimentai hail \ vOORIS \ qccess tunnels c» Icnq £trr.ïiî.lt ¥ u S,/ short çtraight AV. sw ftf halls A»? SE i I I Figure 1 : The PETRA machine. General layout. - 392 - The parameters of the resonance are obtained in a (by now) standard way. The three experiments report respectively: PLUTO DASP 2 1 DESY-HD M(GeV) 9.46 ± 0.01 9.46 ± 0.01 9.46 ± 0.01 Tee(KeV) 1.3 ± 0.4 1.5 + 0.4 1.1 ± 0.3 + 34 1 2 2.7 ± 2.0 2.5 ± 2.1 i Buu(10~ ) -° -í:o i rtot(KeV) > 20 > 20 > 15 The mean values, as presented at the Tokyo Conference by G. Flügge are -2 I" ; 50 KeV, Tee = 1.3 ± 0.2 KeV, Blm = (2.6 ± 1.4) x 10 . Cot MM A prominent and very recent result has been the observation of the T*. The variation of the cross-section over the resonance peak is shown in Figure 2.b). The parameters, as reported by the two different groups, are as follows: i D-HD-M DASP 2 M(GeV) 10.016 ± 0.01 10.012 ± 0.01 AM(MeV) 557 ± 5 555 ± 3 ree(KeV) 0.32 ±0.10 0.5 ± 0.2 r T r (T 3.4 ± 0.9 = 3 ee( )/ ee "> The mass difference AM between the T' and the T (556 ± 3) is definitely smaller than the one observed in the '0 family, namely 591 ± 1 MeV. The observed values for the ' r" partial width, for both the T and the T' clearly favours Q = 1/3, or the b qua-; assignment. Tt is then interesting to note that this is an assignment which gives a constant value for the quantity 2 3s ree/|Ec¿Q¿| for all l i vector states. This is shown in Figure 2.c). The spectroscopy of the J/I)J family is displayed in Figure 3.a). The established states and the still expected ones are shown as solid and dashed lines respectively. The T family should show a similar pattern. Figure 3.b) gives the excitation energies as measured for the J/i[> family and calculated by the Cornell group for the T family. Next to the T family, states with b quarks should be produced in pairs. They correspond to the quark assignments B" = bü B° = bd B| = bl B" = be They will decay weakly. - 393 - Figure 2.a) : The T as observed at DORIS - 394 - —Nal lead giass detector '-4~ DASP -2 T DESY( doris) preliminary J l I i 9.96 1000 10.04 10.08 Ys (GeV) Figure 2.b) : The T1 as observed at DESY - 395 - lo Y .J/v o 1 iil 2 .3 S" lo 2 Figure 2.c) : The quantity Tvee/IEC^Q^¡ (in KeV) for the vector mesons corres• ponding to the fundamental 3S^ states - 396 - - 397 - Figure 3.b) : Excitación energies (in MeV) for a qq system as functions of the quark mass M - 398 - The weak coupling at the quark level is defined through a Cabibbo matrix which is written as follows: se s,s „ 13 13 c c c - s s e*-5 ces, + see'1"'3 123 23 123 23 -esc - c se ifi -c,s.c +^ c_c,e iSj 123 23 123 23 with c^ = cos9^ s. = sinB^ The Cabibbo angle proper corresponds to 6C = Arg cosSj. The values of 9 and 6, are bounded by 20° and 16° respectively, when 8 = 13°. The CP viola- 2 3 c ting phase 6 is such that sinö > 5 x 10-3. The weak coupling induces second order transitions between the B° and BQ states. As a result a B°B° primordial configuration, which should lead through semi-leptonic decays to final states of the type (e+vX) (e~\5X') , with yields + referred to as N"1-^ ) should, through B0B° mixing, also give final state confi• gurations of the type (e+vX)(e~vX') and (e~vX)(e~vX'), with yields referred to as N++ and N . It will be important to study such a mixing, measuring ++ ++ + _+ Y2 = (N + N~~)/(N + N~~ + N ~ + K ) for which theoretical estimates (Ellis et al., Ali et al.,) are at the level of Y2 = 0.1 (non strange) and y » 0.5 (strange). The N++ and N yields should actually differ. This is a CP violating effect associated with the phase S. The asymmetry is given by N++ - N a 4 26 = N++ + I" = Estimates for the asymmetry a are at the level of 5 x 10-3 (non strange) and 2 x 10-3 (strange). Similar effects, but now associated with closed loops with Higgs bosons, could possibly be one order of magmtude larger. This is however very model depen• dent . Search for New Quarks The first approach is to look for narrow states. The cross-section at the peak depends directly on the energy resolution of the beam AE. It increases as S at fixed radius and decreases as p-^, where p is the magnetic radius. The 12TI Tee cross-section at the peak is given in practice by a = —=— —r=r o AE One may then compare the resolution at PETRA and at DORIS, giving also the corresponding value for a LEP machine (at 100 GeV per beam). - 399 - DORIS PETRA LEP 100 P (m) 12 192 2900 AE (MeV) 0.3 S 0.08 S 0.02 S where S is in (GeV)2. The signal over noise ratio can then be estimated (taking Q = 2/3 and T =5 KeV) as a function of the mass of the resonance. This gives for the vee PETRA range M,, (GeV) Integrated : Signal over E-vents/day cross section Noise ratio (L = 1031) (nb GeV) (PETRA) 15 0.44 16 32 x 103 20 0.24 8 8 x 103 30 0.11 4 2 x 103 This is manageable but one is far below the values which are typical of J/ty spec• troscopy. A schematic picture for the variation of parameter R as a function of the centre-of-mass energy is given in Figure 4. Next to bb states one should expect tt states (Q = 2/3). There is however no solid prediction for the t mass. The expected precision on R should be at the level of 0.1. The increase associa• ted with the bb threshold (Q = 1/3) may then be hardly detectable. Jet Studies As first shown by the SLAC-LBL study in the 3 - 7.4 GeV range, the final state hadrons organized themselves into two jets, as expected from a pri• mordial quark anti-quark system. This leads to a decrease of the sphericity with increasing energy as the jet structure becomes more and more pronounced. As is now well known, the jets follow the 1 + cos2Ö distribution associated with the primordial quarks of spin \. PLUTO, at DORIS, has now extended this analysis up to 9.5 GeV. The jet picture has thus been further confirmed. Also, the jet axis, whether defined from charged particles or neutrals, is found to be the same. The variation of the mean observed sphericity as a function of energy is shown in Figure 5. It combines SLAC results (open dots) and DORIS results (full dots). There is an obvious departure from the phase space model which matches data as well as the jet model at 3 GeV, and full agreement with the jet model. At 5 GeV half of the energy is found within a cone of 33°. At 9.4 GeV it is within a cone of 28° only. Going further in energy is of great potential interest.
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