• Abstract and Figures
• Public Full-text

ilanarity of High Energy Collisions Aachen - Berlin - Bonn - CiiHN - Cracow - Heidelberg - Warsaw - Collabdration"Cprosented by H. Schiller) I.) Introduction In the last years there was an increasing interea • in the study of new kinematical variables. These new'-'y^labies'-eh^^^'help to understand the dynamics of multiparticle production in strong interaction. They were constructed in a way to be more sensitive to at least some aspects of the expected underlying dynamical mechanisms. In this ряпег we report about the results of a search for plana- rity of interactions at medium energies* By planarity we mean the alignment of f inial state particles - an alignment in such a way that the events appear flat* To study the effect of planarity-one obviously needs a variable which is "global" in the sense of taking into account all par­ ticles of a Given interaction, conseauently a multiparticle vari­ able. To separate the effect of planarity from the mechanism which reflects themselves mainly in the longitudinal momenta we look for an alignment in the planes perpendicular to the beam or to the principal axis of the jet, reeoectively* It is reasonable to assume that this alignment is caused by the high angular momentum in the intial state* Indeed in 16 GeV/c interactions and for an impact parameter of 1 fermi we find an angular momentum of <"" 14 n. We used the method suggested inflj. Additionally we applied this method in the principal axis frame. 4C events In the energy range from 4 to 25 GeV/c from ftp interactions were studied* In section II we give a short description of the methods used for analyzing the planarity. Section III contains the discussion of the experimental results, the dependences of multiplicity, energy and resonance production. In Section IV are summarized the conclusions. II. Method and Definitions Starting from the system (x,y,z) where x is parallel to the beam* we obtain for each event a new coordinate system (x'.y'.z') by the requirement that the rotation around the (x'= x)-axis gives 2 £ (pjy.) = MIN. all particles (1) In fig* 1 are illuetred the old and the new coordinate systems. In the rotated system (x'^r, y*f z') one defines the relative thickness of one event от T- ' ty1 ElpizJ A complete alignment gives T=0. Similar quantities were defined by Glasser 0*3 and by Foster, Friedman and Nussinov £з1. We have calculate the relative thickness in two different systems 1. in CMS ( marked by ж ) 2. in the Principal Axis system QQ (marked by PA) In this system is the x - axis defined as the direction of that group of particles which has the biggest momentum in the CHS i.e. 1г^Ц PIA. (R~A.J2? max (I Vj)2 o) all сотЫ- ' nations «#PA |Д*Л with, i = number of the given combination; y™ and г are perpendicular to and to each other. The analysis in terms of T consists in a systematic comparison between the experimental values of <T> with those f rom Monte Carlo calculations. We used the following variables 165 <ТИС>-<ТЕХР> ;: <ТМС * ' '-х-;^П®У^:+ ,„ In the Monte Carlo calculations we used for weigHting eyente a matrix elorarit which is obtained from Cylindrical -ftaw Space including leading particle effects: 2 |ll| *exp C-A-DJ (proton)-B.p£(all рЮпв)-»^-!)^^ Jr») The coefficents Л, В, С and D were adjusted to reproduce the 4, D,Cproton)> , ^Px^all^ and *t>t>dis *riQU*ions» ^be values of the coefficents are listed in table 1. The foia of the natrix element was chosen to assure the observed deviations between experimental and KonteCarlo values of ^T^i beinc caused neither by the strong dumping of transverse momenta nor by the existence of leading particles. However it was chocked that a change of the coefficents Л, В, С, Ь within reasonable limits effects <T> very weakly. As shown in fin. 2» the energy dependence of the relative thick­ ness of lionte Carlo events turned out to be rather weak. ЯЪе Т values of LTonte Carlo events are essentially constant for a given multiplicity already at moderate energies. Ill» BCTerimental Results The values T°*<^q>»2<^ calculated for the reactions sumarized in table 2. ^ei8 and 16 GeV/c experiments were done by the:..^BBCt^^-^vColiaDbratiph. The data of 25 GeV/c come-from ah experipe^ ^ x of Wisconsin 't the data of 4 GeV/c from the АВШШ- Collaboration. xy '': . r,:~'»...::~:'.. y We are very ihdepted to A.R. Erwin and \7.D. Walker for the ' permission to use some of their data -fsom the "*p experiment "at 25 GeV/c. tee To look for a possible systematical error we checked the iaotropy of the 0 = A(y, y*) angle distribution, Tfce worst case has a %2-probaoility of 16 %. The result for the CMS and the P. A. system aark<-1 by *> and I'. A. resoeatively, are listed in table 3* It could be seen that for four particle final states {#*> is always smaller in the experiment than in the corresponding Monte Carlo sample, that means that the experimental events are more planar in average. In the six particle final states planarity becomes developed for pj^B 3» 16 GeV/c and the effect is not observed in eight particle final state In energy range studied* We havelooked for^planarl^ in the P.A. system, trying to check If thiseffeot Is due to the existence of flattened aets. The results show that the majority ofthe experimental points lie close toi the points obtained from the Monte Curio sample.As is shown In the lower part of fig. 3 the deviations are consistent with zero. The energy variation of the effect in the G»M. system can be seen at the left side of the upper part of fig. 3 tor reactions £ p -•> p3Jtv The effect is increasing with energy* On the other hand if we have fixed the energy and looked for the multiplicity dependence we found a rapidly decreasing of the planarity with Increasing multiplicity* In the right part of fig* 2 the typical behaviour Is shown for some 16 GeV/oflti reactions* It was interesting to check if the observed effect is caused by resonanoe' production* It is known that the production of reso­ nances covers the few particle final states and that's way it can contribute to the planarity* For this analysis we have chosen the reaction 3t*p —» рЖ+*+Ж~ at 8 and 16 GeY/c* The 4 GeV/o data were excluded due to -the smallness of the effect at this low energy* Since it is Impossible to find a reasonable large sample o;Z events without resonanoe production in the available reaction channels, the only possibility is to check whether the effect shows a struc­ ture at the reasonanoes region* 167 Fur several particle: combinations we '"calculated \^^0^!Ш&^(^^ as а Г unction of their invariant 13ass.es)* The generali ohseryatlpn is that the :>laaarity effect is in no case greater in the reaso- nance and difi'ractive bump region than in the other* is exanoles are shown in fig. 4a - 4d the results for the two particle soabinatiuhs CpJr+) and (JST'*'3fc'"')« ..e have chosen them because of finding there the largest effest in the corresponding resonance renion* The shaoe of the К^хсУ values (denoted bv a cross) as a function of the invariant laass is quite similar to the shape of {Ч&гт,} (denoted by a point). It could be seen that there is no structure in the relative deviations of the \^(а)Х values itfiich can be correlated with the resonance production» Additional we have found that К^хрУ is "in tixc resonance region larger than the, overall value of К^шрУ * that means that events outside the resonance region are more planar and they are respon­ sible for the ^"jxp^ being less than <CI%Q) * Smother argument nGainst the interpretation of the effect as a consequence of resonance production i3 the fact that the plana- rity increases with enerey for fixed multiplicity» To understand the observed effect one could speculate that the hi^h angular momentum of the initial state causes an alignment of the final otate particles* In this case one can expect the par­ ticles to be emitted preferentially close to the Plane perpendi­ cular to the total annular Koientum - the events become planar* In the case of (х,у,г) beinn thevCiil. system an alignments due to high angular momentum will closely relate the (yVz'^lahe to the plane containing the.beam and thelimpact parameter b^^the interaction. It seems reasonable-to expect sucti an>alx{5hn.ent,since classically, an interaction at 16 GeV/c( «nd with an impact parame­ ter of 1 fermi has an angular momentum of about 14.45* jy^. Conclusion - Using a nglobaiH •reiable we; nave found a special type of corre­ lations of the secondary particles in interactions at medium energies. - We have shown that this alignment of final state particles, which we called planarity, is neither the reflection of the cut off of the transverse momenta nor of the existence of lea­ ding particles. - We found that the effect increases with the energy and decrea­ ses with the multiplicity. If either the energy is too low or the multiplicity is too high ths planarity effect vanishes* - There is no indication that the planarity is caused by resonance production and possible existence of flattened jets. - The obtained results are consistent with the speculation that the planarity is a oonsequence of the high angular momentum of the interaction.

Load more

  16

Copy Link