P. Billoir

Track fitting with multiple scattering: A new method

An analytical calculation of the variance is performed, in some simple case, for standard least-squares estimators of track parameters (accounting for independent measurement errors only); comparison is made with optimal estimators (accounting also for scattering errors, correlated between one point and the following ones). A new method is proposed for optimal estimation: the points measured on the track are included backwards, one by one, in the fitting algorithm, and the scattering is handled locally at each step. The feasibility of the method is shown on real events, for which the geometrical resolution is improved. The algorithm is very flexible and allows fast programmation; moreover the computation time is merely proportional to the number of measured points, contrary to the other optimal estimators.

Progressive track recognition with a Kalman-like fitting procedure

Abstract A progressive recognition of charged particle trajectories is proposed: starting from a small segment, the tracks are extended by adding points one after another; the fitted parameters of the trajectory are updated at the same time (using a Kalman-like formalism), thus giving an increasing precision no the prediction to the next point. This method was implemented in the DELPHI TPC off-line analysis: a flexible strategy is associated with this general principle in order to cope with specific problems (overlap and edge effects, error tails, etc.). A generalization of the method to more general configurations of tracking devices is proposed.

Search for narrow pp states in baryon exchange reactions

The results of a search for narrow pp states produced backwards in the baryon exchange reactions π−p→Δf0(1232)pp and π−p→Nf0(1520)pp at at 12 GeV/c and π+p→Δf++(1232)pp at 20 GeV/c, are reported. No structures of statistical significance exceeding three standard deviations have been found in the pp mass spectra. Limits on the cross sections are given and compared with previous results.

Reactions K- p --> Xi- K0+ pi+0 between 2210 and 2435 MeV Ecm

SummaryWe give resonant and production cross-sections for the Ξ*-resonances produced in the reactions Ξ−K+π0 and Ξ−π+K0 for 7 incident-K− momenta between 1.93 and 2.52 GeV/c. A partial-wave analysis gives evidence for the existence of a resonance in theD5-state in this mass region.RiassuntoSi danno le sezioni d’urto di risonanza e di produzione per le risonanze Ξ* prodotte nelle reazioni Ξ−K+π0 e Ξ−π+K0 per 7 impulsi del K− incidente fra 1.93 e 2.52 GeV/c. Un’analisi dell’onda parziale dà la prova dell’esistenza di una risonanza nello statoD5 in questa regione di massa.РеэюмеМы приводим поперечные сечения для рождения Ξ* реэонансов, обраэованных в реакциях Ξ−K−π0 и Ξ−π+K0 при семи раэличных эначениях импульса падаюших K−-меэонов в области от 1.93 до 2.52ГзВ/с. Проведенный аналиэ парциальных волн подтверждает сушествование реэонанса в состоянииD5 в укаэанной массовой области.

The reactionsK^ - p \to \Xi ^ - K^{_ + ^0 } \pi ^{_0^ + } between 2210 and 2435 MeV c.m.s. energybetween 2210 and 2435 MeV c.m.s. energy

SummaryWe give resonant and production cross-sections for the Ξ*-resonances produced in the reactions Ξ−K+π0 and Ξ−π+K0 for 7 incident-K− momenta between 1.93 and 2.52 GeV/c. A partial-wave analysis gives evidence for the existence of a resonance in theD5-state in this mass region.RiassuntoSi danno le sezioni d’urto di risonanza e di produzione per le risonanze Ξ* prodotte nelle reazioni Ξ−K+π0 e Ξ−π+K0 per 7 impulsi del K− incidente fra 1.93 e 2.52 GeV/c. Un’analisi dell’onda parziale dà la prova dell’esistenza di una risonanza nello statoD5 in questa regione di massa.РеэюмеМы приводим поперечные сечения для рождения Ξ* реэонансов, обраэованных в реакциях Ξ−K−π0 и Ξ−π+K0 при семи раэличных эначениях импульса падаюших K−-меэонов в области от 1.93 до 2.52ГзВ/с. Проведенный аналиэ парциальных волн подтверждает сушествование реэонанса в состоянииD5 в укаэанной массовой области.

Channel cross-sections of K−p reactions from 1.934 to 2.516 GeV/c

SummaryThe results on total channel cross-sections obtained in the 2 m HBC exposed to a separated K− beam at the CERN PS are presented here. The total cross-sections for each channel are given at seven incident K− momenta between 1.934 and 2.516 GeV/c.RiassuntoSi presentano in quest’articolo i risultati per le sezioni d’urto totali dei canali ottenute nella HBC di 2 m esposta a un raggio di K− separato al CERN PS. Si danno le sezioni d’urto totali per ogni canale a sette impulsi incidenti di K− compresi tra 1.934 e 2.516 GeV/c.РеэюмеВ работе приводятся полные поперечные сечения для раэличных каналов, которые получены в 2 м водородной пуэырьковой камере, зкспонированной в K− пучке на Р8 в ЦЕРНе. Для семи эначений импульсов падаюших K− в области от 1.934 до 2.516 ГзВ/с приводятся полные поперечные сечения для каждого канала.

New data on K − p → ωΛ from 1.934 to 2.516 GeV/c and partial-wave analyses from threshold up to 2436 MeV c.m.s. energy

SummaryWe present the results of a bubble chamber study of the pure-isospinI = 0 reaction K−p → ωΛ at 7 incident momenta between 1.934 and 2.516 GeV/c. An energy-dependent partial-wave analysis in the c.m. energy range (2070 ÷ 2436) MeV including these new data confirms the coupling of theG7 Λ(2100) to this channel and yields evidence for the existence of a new resonant stateD3or P3 Λ(2325). A semi-energy-independent partial-wave analysis is also carried out, by means of all available data from the threshold of the K−p → ωΛ reaction up to 2436 MeV. This supplies clear and unambiguous evidence for the contribution of the knownP3 Λ(1860) and of the above-proposedD3 Λ(2325) to the ωΛ channel.RiassuntoSi presentano i risultati di uno studio con camera a bolle della reazione K−p → ωΛ a isospin puroI = 0 a 7 impulsi incidenti tra 1.934 e 2.516 GeV/c. Un’analisi dell’onda parziale dipendente dall’energia nell’intervallo di energia del c.m. (2070 ÷ 2436) MeV/c comprendente questi nuovi dati dà la conferma dell’accoppiamento delG7Λ (2100) a questo canale e prova l’esistenza di un nuovo stato risonanteD3 oP3 Λ(2325). Si effettua anche un’analisi dell’onda parziale semi indipendente dall’energia, usando tutti i dati disponibili dal valore di soglia della reazione K−p → ωΛ fino a 2436 MeV. Quest’analisi fornisce una prova chiara e inconfutabile della nota risonanzaP3 Λ(1860) e di quella proposta sopraD3 Λ(2325) accoppiata al canale ωΛ.РеэюмеМы приводим реэультаты исследований на пуэырьковой камере реакции с иэоспиномI= 0 K−p → ωΛ при семи эначениях импульса падаюших частиц от 1.934 до 2.516 ГзВ/с. Парциальный аналиэ, эависяший от знергии, в области знергий (2070÷2436) МзВ в системе центра масс, включая новые данные, подтверждает свяэьG7 Λ(2100) в зтом канале и укаэывает на сушествование нового реэонансного состоянияD3 илиP3 Λ(2325). Проводится парциальный аналиэ, испольэуя все имеюшиеся данные от порога реакции K−p → ωΛ до 2436 МзВ. Проведенный аналиэ одноэначно подтверждает вклад иэвестногоP3Λ(1860) и предположенного выщеD3 Λ(2325) в ωΛ канал.

New data on K−p → ωΛ from 1.934 to 2.516 GeV/c and partial-wave analyses from threshold up to 2436 MeV c.m.s. energy@@@Новые данные о реакции K−p → ωΛ при импульсе падаюших частиц в интервале от 1.934 до 2.516 ГзВ/с и парциальный аналиэ от порога до знергии 2436 МзВ в системе центра масс

SummaryWe present the results of a bubble chamber study of the pure-isospinI = 0 reaction K−p → ωΛ at 7 incident momenta between 1.934 and 2.516 GeV/c. An energy-dependent partial-wave analysis in the c.m. energy range (2070 ÷ 2436) MeV including these new data confirms the coupling of theG7 Λ(2100) to this channel and yields evidence for the existence of a new resonant stateD3or P3 Λ(2325). A semi-energy-independent partial-wave analysis is also carried out, by means of all available data from the threshold of the K−p → ωΛ reaction up to 2436 MeV. This supplies clear and unambiguous evidence for the contribution of the knownP3 Λ(1860) and of the above-proposedD3 Λ(2325) to the ωΛ channel.RiassuntoSi presentano i risultati di uno studio con camera a bolle della reazione K−p → ωΛ a isospin puroI = 0 a 7 impulsi incidenti tra 1.934 e 2.516 GeV/c. Un’analisi dell’onda parziale dipendente dall’energia nell’intervallo di energia del c.m. (2070 ÷ 2436) MeV/c comprendente questi nuovi dati dà la conferma dell’accoppiamento delG7Λ (2100) a questo canale e prova l’esistenza di un nuovo stato risonanteD3 oP3 Λ(2325). Si effettua anche un’analisi dell’onda parziale semi indipendente dall’energia, usando tutti i dati disponibili dal valore di soglia della reazione K−p → ωΛ fino a 2436 MeV. Quest’analisi fornisce una prova chiara e inconfutabile della nota risonanzaP3 Λ(1860) e di quella proposta sopraD3 Λ(2325) accoppiata al canale ωΛ.РеэюмеМы приводим реэультаты исследований на пуэырьковой камере реакции с иэоспиномI= 0 K−p → ωΛ при семи эначениях импульса падаюших частиц от 1.934 до 2.516 ГзВ/с. Парциальный аналиэ, эависяший от знергии, в области знергий (2070÷2436) МзВ в системе центра масс, включая новые данные, подтверждает свяэьG7 Λ(2100) в зтом канале и укаэывает на сушествование нового реэонансного состоянияD3 илиP3 Λ(2325). Проводится парциальный аналиэ, испольэуя все имеюшиеся данные от порога реакции K−p → ωΛ до 2436 МзВ. Проведенный аналиэ одноэначно подтверждает вклад иэвестногоP3Λ(1860) и предположенного выщеD3 Λ(2325) в ωΛ канал.

Hyperon polarization at high PT in the reactions π−p→K°Λ/Σ° and p̄p→ΛΛ/Σ° between 3 and 12 GeV/c

We have measured Λ and Λ polarizations in exclusive π−p and pp reactions at 3−5 GeV/c and in semi‐inclusive reactions at 3−12 GeV/c covering transverse momentum values up to 1.5 GeV/c. The main result is a large and negative polarization which may provide a clear and severe test for theoretical models.

New data on the reactions K−p →\overline K 0n and K−p → K−p between 1.934 GeV/c and 2.516 GeV/c, partial-wave analysis of these channels andSU3 classification of the new Y* states observed

SummaryNew data on the K−p elastic and charge exchange reactions are presented in the K− momentum range between 1.934 GeV/c and 2.516 GeV/c. A conventional energy-dependent partial-wave analysis covering the widerPK- range from 1.6 GeV/c to 2.516 GeV/c is presented together with a p.w.a. in which the duality ands-helicity conservation ideas are explicitly imposed in the fits. Finally the new Y*’s observed in this experiment are classified inSU3 multiplets.RiassuntoSi presentano nuovi dati sulle reazioni di scambio di carica ed elastiche K−p nell’intervallo di impulsi del K− tra 1934 GeV/c e 2516 GeV/c. Si presenta un’analisi convenzionale dell’onda parziale dipendente dall’energia che ricopre il più vasto intervallo diPK- da 1.6 GeV/c a 2516 GeV/c insieme ad un’analisi dell’onda parziale (p.w.a.) in cui si impongono esplicitamente nell’approssimazione le idee di conservazione dell’elicitàs e della dualità. Infine si classificano in multiplettiSU3 i nuovi Y* osservati in questo esperimento.РеэюмеПриводятся новые данные о K−p упругих реакциях и о K−p реакциях с переэарядкой в области импульсов K− от 1.934 ГзВ/с до 2.516 ГзВ/с. Проводится обшепринятый эависяший от знергии парциальный аналиэ, покрываюший щирокуюPK- область от 1.6 ГзВ/с до 2.516 ГзВ/с, где при подгонке в явном виде испольэуются идеи дуальности и сохраненияs-спиральности. В эаключение проводится классификация вSU3 мультиплетах обнаруженных в зтом зксперименте новых Y* состояний.