e+ e- INTERACTIONS AT HIGH ENERGY. EXPERIMENTAL RESULTS WITH ADONE

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e+ e- INTERACTIONS AT HIGH ENERGY.

EXPERIMENTAL RESULTS WITH ADONE

V. Silvestrini

To cite this version:

V. Silvestrini. e+ e- INTERACTIONS AT HIGH ENERGY. EXPERIMENTAL RESULTS WITH ADONE. Journal de Physique Colloques, 1971, 32 (C3), pp.C3-87-C3-91. �10.1051/jphyscol:1971312�.

�jpa-00214593�

JOURNAL

DE

Colloque C3, supplkment au no 10, Tome 32, Octobre 1971, page C3-87

e+ e - INTERACTIONS AT HIGH ENERGY.

EXPERIMENTAL RESULTS WITH ADONE

V. SILVESTRINI

Laboratori Nazionali del CNEN, Frascati, Italy

Rksumk. - La situation des groupes d'expkrimentateurs qui travaillent actuellement sur ADONE est esquissee. On prksente des resultats preliminaires en se referant a la fois aux tests de QED (e+ e=

; e+ e-

e+ e- ; e+ e-

p-) et A la production hadronique et multiple. Dans toutes les experiences les rksultats experimentaux et la prediction de QED concordent, avec une marge d'erreur de 10 %. La section efficace de la production des hadrons est de l'ordre de

cm2 dans le systZme du centre de masse se situant entre 1,4 et 2,4 GeV.

Abstract. - The situation of the experimental groups presently working at ADONE is outlined.

Preliminary experimental results are presented, referring both to tests of QED (e+ e-

; e+ e-

e+ e- ; e+ e-

and to the hadronic and multiple production.

In all the experiments agreement is found between experimental results and QED prediction, within an error of - ^{f 10 %.} The cross section for production of hadrons is of the order of 10-32 cm2, in a center of mass energy region between 1.4 and 2.4 GeV.

1 am going to present the experimental situation of the five experimental groups presently on the floor at Adone.

First of all a few words about the machine. As you know, Adone is an e+ e- storage ring (Fig. l), whose maximum energy is 1.5 GeV per beam. Up to now, only two of the four radiofrequency cavities are instal- ed, allowing to reach an energy of 1.2 GeV/beam. The complete radiofrequency system is being installed just in these days : runs at the maximum energy of 2 x 1.5 GeV are scheduled for may.

The energy range in which we runned up to now for experiments is between 0.7 and 1.2 GeV/beam. The machine operation is quite reliable, with head-on collision of the two beams. The transverse dimens~ons of the two beams are - ^{1 x} 1 mm2. Longitudinally, the interaction region is gaussian shaped, with a o of (22 cm) E ~ / ~ , where E is the energy of the machine expressed in GeV. The typical luminosity is - cm2/h after injection at 1 GeV (typical currents of 40-50 mA/beam), and varies proportionally to E - ~ . It takes - 30 minutes to inject, the half life of the luminosity being 6-12 hours depending on the energy. About 40 12-hour shifts are scheduled for

experiments each month.

The experiments on the floor are the following :

Group Authors

- -

E.mn G. Barbiellini, B. Borgia, F. Cera-

dini, M. Conversi, F. Grianti, M. Grilli, A. Mulachi&, G. Nico- letti, M. Nigro, L. Paoluzi, R. Santonico, W. Scandale P. Spillantini, R. Visentjn, G.

T. Zorn

Group Authors

-

BCF V. Alles-Borelli, M. Bernardini, (Bologna- Bollini, T. Massam, L. Mona- Cern-Frascati) ri, F. Palmonari, A. Zichichi

YY C. Bacci, R. Baldini Celio, G.

Capon, C. Mencuccini, G. P.

Murtas, G. Penso, A. Reale, G. Salvini, M. Spinetti, B. Stella Boson B. Bartoli, B. ~ o l u z z i , F. Feli- cetti, G. Goggi, G. Marini, F. Massa, A. Nigro, H. Ogren, D. Scannicchio, V. Silvestrini) N. Spinelli, F. Vanoli

PP -- G. Di Giugno, J. W. Hunfrey, I. Peruzzi, E. Sassi, U. Troia, G. Troise, S. Vitale

The first three groups are permanently at the macinhe (Adone has four experimental sections, see Fig. 1) while the Boson and pp groups interchange with each other at the fourth experimental section.

All the experimental apparatus are build up with spark chambers and scintillation counters, and are quite standard. Schematic drawings of four of them are shown in figures 2, 3, 4, 5, 6 and 7.

The main reactions explored by each group are summarized in table 1.

Search for heavy leptons has also been performed by the BCF group, and the results are published on Lettere a1 Nuovo Cimento, 4, 1156 (1970).

Article published online by EDP Sciences and available at http://dx.doi.org/10.1051/jphyscol:1971312

V. SILVESTRINI

k ^{180 sm} -.

I

- -- -. . .. . .

FIG. 3. - Schematic drawing of the <enlonitor

apparatus of the pz group. It detects the ei e- elastic scattering at small angles (3.5O < 8 < 60). In each telescope TI, P6 Gi are scintillation counters and Si are shower detectors. The average of the coinci- dences TI T 3 and Tz T4 does not depend - in first approxima- tion - on the position of the source. Background from single

beam is eliminated through time-of-flight measurements.

FIG. 1. - Schematic drawing of Adone. Injection occurs at the left. There are 12 straight sections (in the drawing, sections 1, 4, 6 and 8 are labelled with the corresponding number). On the odd ones the beams intersect. On section 7 there are two radiofre- quency cavities, and two others are being placed on section 7.

Sections 3, 5, 9, 11 are used for experiments.

Group

-

BCF Boson YY _-

PP

yes no yes no no yes no no no no

+-,

C4 Fe

C3C2

FIG. 2. - Schematic drawing of the

experimental appara- tus. The two telescopes are built-up with scintillation counters and spark-chambers. Total solid angle

( ~ 3 ) 4 n. One of

the

s from e+ e-

p- is stopped in C4.

FIG. 4. - Schematic drawing of the apparatus of the BCF group. Again two telescopes of scintillation counters and spark

chambers. Total solid angle - ^{0.3(4 z).}

S E C T I O N A A

FIG. 5. - Schematic drawing of the cc Boson

apparatus, consisting of scintillation counters and wire n~agnetostrictive spark chambers. A detailed description can be found in

Nuovo Cirnento, 1970,70A, 603.

e + e = INTERACTIONS AT HIGH ENERGY. EXPERIMENTAL RESULTS WITH ADONE C3 - 89

- - L e a d or i r o n S c i n t i l l a t o r l a y e r

0

S p a r k c h a m b e r

FIG. 6, 7. - Schematic drawings of the yy-apparatus. It consists of four telescopes of scintillation counters, spark chambers and

shower converters. The total solid angle is - 0.25(4 n).

Tests of the validity of quantum electrodynamics

The experimental results of the different groups - most of them are still preliminary - are shown in figures 8, 9, 10, 11, 12 and 13.

FIG. 8. - Experimental results of the pn group for the reaction e+ e-

e+ e-. The results are expressed in terms of

as a function of the total C. M. energy 2 E.

FIG. 9. - Experimental results of the BCF group for the reac- tion e+ e-

e+ e-, as compared with the predictions of QED.

[Radiative Corrations included (peaking approximation)]

(OED). . -

- The first three reactions of table I are r>ure ^{FIG. 10.} - Experimental results of the Boson group for the

QED reactions, and allow to test the validity of QED reaction e+ e-

e+ e-. The results are expressed in terms of the ratio of wide angle scattering events (65O <

< 1 1 5 O ) to the

in different regions' This is obtained angle << monitor

events. The average value of the momen-

measuring angular distributions and/or absolute cross tum transfer to the virtual vhoton is given in the uvaer scale .

sections. further details see ~ a o v o ~ i m e n f o , 1970, ^ ~ o A , 60;.

C3-90 V. SILVESTRINI

EXPERIMENT

THEORY (o.E.D)

FIG. 11. - Experimental results of the BCF group for the reaction e+ e- +

Very similar results are obtained also by

the

group.

FIG. 12. -Experimental results of the

group for the reaction e+ e-

(Ratio of the experimental to the theore-

tical cross-sections.)

FIG. 13. - Experimental results of the

group for the reaction eC e-

(angular distribution). The ordinates are number of events (a total of 350 events). The events come from runs at different c. m. energies around 2 GeV (see Fig. 12).

1 0 -

The reaction ei e-

e+ e- explores essentially the kinematical regions in which a space-like momentum is transferred to the virtual photon ; e + e- -+ p+ p- time-like momentum to the virtual photon ; ei e-

y y space-like momenta to the virtual lepton.

All the results are in good agreement with the pre-

QE,

8,

dictions of QED within the experimental - mostly systematic - error of the order of f 10 %. These results refer to data collected up to the 1970 summer.

The analysis of further data is in progress.

23 29 35 41 L7 53 59 65 71 77 83 89 95 101 H)7113 DEGREES

e+ e-

BB reactions (BB stands for n+ n- + K + K-). - The (preliminary) results of the pn and BCF groups - referring to the analysis of data collected before the Kiev conference are the following :

Number of

Group events

- - -

PP 14 0.5 + ^0.18

BCF -- 20 0.49 _+ 0.1 5 The results are expressed in ternis of

where F ; ( Z ) is the square of the pion (kaon) form factor for

(The data where collected at a total c. m. energy ranging from 1.6 to 2 GeV).

ei e- -, multiple. - e+ e- interactions giving rise to more than two particles in the final state are observed by the pn, BCF, y y and Boson groups. The evaluation of cross-section is rather difficult, since the efficiency of the experimental apparatus depend on the kine- matical features (in particular multiplicity) of the reaction observed. In turn the multiplicity is very difficult to be evaluated with the present apparatuses, which have a rather small solid angle and were not designed to observe reactions of this kind.

Due to these limitations, the results I am going to present in the following are to be considered, in my opinion, as a preliminary qualitative exploration, whose quality is going to really improve only with the second generation experiments.

pn group. - The results referring to -- 40 events with more than two charged particles observed in the final state have been presented to the 1970 Kiev Conference. The resulting cross section - correspond- ing to a c. m. energy interval 1.6-2.0 GeV - has been quoted as

o , = a (e+ e-

4 charged particles + possible neu- trals) = (3 ^$. 1) x cmZ .

The number of events of this type analyzed are now - ^70.

The behaviour of the particles observed allows to exclude that they are high energy electrons. However, it is not possible for the moment to exclude that part of them are low energy electrons (150-200 MeV).

The group is working at this problem.

e + e- INTERACTIONS AT HIGH ENERGY. EXPERIMENTAL RESULTS WITH ADONE C3-91

Boson group. - Preliminary results - referring to

N

240 events - have already been published (Nuovo Cinzento, 1970,70A, 615). The results are expressed in terms of ko,, were

and

o, = o (e' e- -, n charged particles +possible neutrals).

The energy behaviour of k4 is rather constant in the energy range 1.4 < ,. ,. < 2.4 GeV (see Fig. 14). The value of ko, is - ^{3 x} with an overall uncertainty of - ^{_+ 30 %.} The pulse height distribution of the observed charged particles allows to exclude that they are high energy electrons. However, it is again compa- tible with the experimental information that at least part of them are low energy electrons. The Aq distribu- tion (Aq = q i - qj, where qj is the azimuthal angle of the ith charged emitted particle, z-axis along the beam) extends up to values of Ap = 1800.

FIG. 14. -Experimental results of the Boson group for the reaction e+ e-

multiple

280 non-coplanar events analyzed out of a total of - 800 collected). Already a first look to the additional data available at 1 850 MeV shows that also this point

will rise at the same level of the others.

yy group. - They trigger when at least three particles enter the different telescopes. The above particles may be either charged particles or y-rays.

On the basis of 21 events, they quote a total cross section around 2 x cm2. For the events with at least three charged particles observed, the correspond-

ing cross section is at most (0.7 & 0.3) x The detected charged particles show nuclear interactions typical of hadrons.

BCF group. - For events with at least three observed charged particles - recognized as hadrons - the cross section is similar to that obtained by the YY group.

As we see, also considering the low statistics and large errors, the results of the different groups are in fair agreement. If we believe that all of the group are working correctly, one of the following - and may be other - hypothesis can be made.

1) The angular distribution - not yet experimen- tally determined - of the emitted staff is not correctly taken into account in the models used for the evalua- tion of efficiencies.

2) The multiplicity of the events varies rapidly with the energy. The energy range explored is in fact differently weighted in result of the different experi- ments.

3) There is a considerable contribution of evcnts with low energy electrons in the final state. Since the A q distribution is quite smooth, it is however hard to think of usual QED reaction from which these electron could come.

As we see, a lot of further work, especially with more sophisticated apparatuses, is needed. In particular, good quality information are expected from the magnetic detector which is under construction.

Reaction e + e -

pp. - This reaction is being studied by the pp group. Data have been collected during 4 month of machine time (Total integrated luminosity 2.5 x lo3' cmP2). This group expects to have enough sensitivity to lower the present limit of the proton form factor in the time-like region as obtained from the inverse reaction pp -, ef e-.

The preliminary analysis of a partial sample

(0.4 x lo3' cm-2 of integrated luminosity) already

gives an upper limit on oCef e- -+pIj) of

(4 : 8) x cm2 at a total c. m. energy of 2.1 GeV.