Sistema de control de los sistemas de limpieza

T his thesis has been a study of th e d a ta th a t were recorded by th e ZEUS detector in th e sum m er of 1992, at DESY. A technical study was carried out on the m atching of hits in th e FADC system and Z-by-Tim ing (ZbyT) system . There after we have concentrated on the Hadronic final states of th e events, which depend crucially on how th e proton is treated in QCD models.

• We have studied hits from the ZEUS C entral Tracking D etector using the FADC and Z-by-Tim ing systems (see chapter-2). The hits m atch very well betw een th e two system s which together m easure drift tim e, z position and pulse height. We find th a t m atching hits is a powerful m ethod, independent of track reconstruction, for studying the perform ance of th e cham ber and its readout. The inefficiencies and noise tend to occur at large drift tim es

and low pulse heights (see section 2.1 1).

— T here is a ZbyT hit inefficiency of 3% up to about drift tim es of order 350ns. The inefficiency at large pulses is less th en 1%.

— T here is a FADC hit inefficiency of 2% up to about drift tim es of order

350ns.

We have com pared th ree most successful p ertu rb ativ e QCD -f fragm en­

ta tio n m odels in previous Deep Inelastic Scattering experim ents, w ith ep

134 C H A P T E R ? . CO NCLUSI ONS A N D O U T L O O K

n eu tral current events recorded in the first year of d a ta taking, at a centre of m ass energy 295 GeV. T he three types of models were:

— M atrix E lem ent + P arto n Shower (M E-fPS)

— P a rto n Shower w ith two types of v irtuality scales for th e shower de­ velopm ent: P S (iy ^ ) and PS(Q^)

— Colour Dipole M odel (CDM)

Already, w ith this in itial d a ta it is has been possible to exclude two QCD

models, PS(VE^) and PS(Q^) for describing th e ep n eu tral current d ata (see

ch ap ter-6). PS(VE^) has an excess of Et over th e d a ta while PS(Q^) predicts

a deficiency as com pared w ith data. We cannot account for these differences in th e predicted and m easured E / s by varying th e fragm entation param ­ eters or using different p arto n density param etrisations. The best overall description of th e d a ta was given by th e ME-j-PS and CDM models. It is expected th a t a fu rth er analysis, w ith more d ata, will be able to distinguish which of these two rem aining QCD models best describes th e data.

• A prelim inary analysis was carried out using energy clustering in th e cal­ orim eter em ploying th e condensate algorithm (see chapter-5). Firstly, a M onte-C arlo com parison between final state particles and calorim eter cell clusters (condensates) was presented. For this analysis the event variables were com puted in th e hadronic centre of mass fram e (HCM) (section 5.3.4). S ystem atic effects introduced by th e boost to this HCM fram e were th en discussed (section 5.3). From this study we conclude th a t single particles are well represented by condensates in th e restricted kinem atical region:

— W Ia > 1600 GeV^

— 10° < 0 < 175°, cut on the polar angle for each condensate

— Ecconsa > 400 MeV, th e m inim um energy threshold for condensate

Finally, we com pared th e d a ta and the M onte-Carlo for some of the shape variables in th e HCM (section 5.5). N either the M E-f PS nor the CDM-|-BGF

135

m odels fit th e m easured < S > and < 1 — T > , b o th as functions of th e

invariant mass squared distributions and we see no dependence on th e

p aram etrisatio n of th e stru ctu re functions used in these M onte-Carlos. It will be possible to do this analysis m ore fully once tracking inform ation becomes available and charged particles can be boosted to the HCM frame. • Lastly, we looked at the unfolding of th e distributions of < S' > and <

1 — T > w ith in th e HCM fram e (see A ppendix-B ), T he M onte-Carlos,

ME-I-PS and CDM -f E O F , do not describe th e corrected d a ta very well and it is hoped th e tracking inform ation th a t will be available in th e future will allow a m ore com plete analysis and b e tte r agreem ent.

P art I