56098294
Review of measurements of the angles of the CKM matrix from the BaBar experiment
Experimental results on CP violation measurements in the B meson system from the BABAR experiment at the PEP-II asymmetric B Factory are reviewed.
52216370
Measuring propagation speed of Coulomb fields
The problem of gravity propagation has been subject of discussion for quite a long time: Newton, Laplace and, in relatively more modern times, Eddington pointed out that, if gravity propagated with finite velocity, planet motion around the sun would become unstable due to a torque originating from time lag of the gravitational interactions. Such an odd behavior can be found also in electromagnetism, when one computes the propagation of the electric fields generated by a set of uniformly moving charges. As a matter of fact the Liénard–Weichert retarded potential leads to the same formula as the one obtained assuming that the electric field propagate with infinite velocity. The Feynman explanation for this apparent paradox was based on the fact that uniform motions last indefinitely. To verify such an explanation, we performed an experiment to measure the time/space evolution of the electric field generated by an uniformly moving electron beam. The results we obtain, on a finite lifetime kinematical state, are compatible with an electric field rigidly carried by the beam itself.
110466342
Performance and Aging Studies of BaBar Resistive Plate Chambers
The BaBar detector is currently operating nearly 200 Resistive Plate Chambers (RPCs), constructed as part of an upgrade of the forward endcap muon detector in 2002. Although the average RPC efficiency remains high, numerous changes in the RPC performance (increased currents and rates) have been observed. A few of the highest rate RPCs have suffered efficiency losses of more than 15%. Several types of efficiency loss have been observed. Tests with humidified gas have shown that some of the lost efficiency is recoverable. However, efficiency losses in the highest rate regions have not yet improved with humid gases.
109329842
Improved Particle Identification Using Cluster Counting in a Full-Length Drift Chamber Prototype
Single-cell prototype drift chambers were built at TRIUMF and tested with a ~210MeV/c beam of positrons, muons, and pions. A cluster-counting technique is implemented which improves the ability to distinguish muons and pions when combined with a traditional truncated-mean charge measurement. Several cluster-counting algorithms and equipment variations are tested, all showing significant improvement when combined with the traditional method. The results show that cluster counting is a feasible option for any particle physics experiment using drift chambers for particle identification. The technique does not require electronics with an overly high sampling rate. Optimal results are found with a signal smoothing time of ~5ns corresponding to a ~100MHz Nyquist frequency.
16601897
Mechanisms affecting performance of the BaBar resistive plate chambers and searches for remediation
The BaBar experiment at PEPII relies on the instrumentation of the flux return (IFR) for both muon identification and KL detection. The active detector is composed of resistive plate chambers (RPCs) operated in streamer mode. Since the start of operation the RPCs have suffered persistent efficiency deterioration and dark current increase problems. The ‘‘autopsy’’ of bad BaBar RPCs revealed that in many cases uncured linseed oil droplets had formed on the inner surface of the Bakelite plates, leading to current paths from oil ‘‘stalagmites’’ bridging the 2mm gap. In this paper, a possible model of this ‘‘stalagmite’’ formation and its effect on the dark current and efficiency of RPC chambers is presented. Laboratory test results strongly support this model. ARTICLE IN PRESS *Corresponding author. Tel.: +1-609-258-4391; fax: +1-609-258-6360. E-mail address: changguo@princeton.edu (C. Lu). 0168-9002/03/$ see front matter r 2003 Elsevier Science B.V. All rights reserved. doi:10.1016/S0168-9002(03)01292-0 Based upon this model we are searching for solutions to eliminate the unfavorable effect of the oil stalagmites. The lab tests show that the stalagmite resistivity increases dramatically if exposed to the air, an observation that points to a possible way to remedy the damage and increase the efficiency. We have seen that flowing an oxygen gas mixture into the chamber helps to polymerize the uncured linseed oil. Consequently, the resistivity of the bridged oil stalagmites increases, as does that of the oil coating on the frame edges and spacers, significantly reducing the RPC dark currents and low-efficiency regions. We have tested this idea on two chambers removed from BaBar because of their low efficiency and high dark current. These test results are reported in the paper, and two other remediation methods also mentioned. We continue to study this problem, and try to find new treatments with permanent improvement. r 2003 Elsevier Science B.V. All rights reserved.
63620607
The new BaBar Analysis Model
As part of a general Computing Model upgrade, BaBar has deployed a new analysis model. The new analysis model was designed to overcome the major shortcomings of the previous analysis model. In particular, the new analysis model consolidates several redundant data formats, allows users to customize the data format for their analysis, and provides a wider range of data access options than the old model, while maintaining backwards compatibility with BaBar’s existing analysis interface and analysis code base. The new analysis model was used in roughly half the analyses submitted to the recent ICHEP 2004 conference, and has been enthusiastically welcomed by the BaBar analysis community.
120513565
Measurement of inclusive two-particle rapidity correlations at the ISR
Abstract We present data on two-particle distributions in the approximate rapidity variable η = −1n tan θ /2 for secondaries produced in proton-proton collisions at the CERN Intersecting Storage Rings (ISR). The data at centre-of-mass energies of 23 and 62 GeV show the existence of energy-independent positive, short-range correlations between secondaries within the central region. Deviations from short-range correlation exist when one (or both) of the particles is near the boundary of the available phase space. In part, such deviations are interpreted as the effect of a diffractive-like component in multiparticle production.
118729839
Measurement of two-particle semi-inclusive rapidity distributions at the CERN ISR
SummaryWe present data on the semi-inclusive distributions of rapidities of secondary particles produced in pp collisions at very high energies. Our experiment was performed at the CERN Intersecting Storage Rings (ISR). The data given here, at centre-of-mass energies of √s=23 and 62 GeV, include the single-particle distributions and two-particle correlations. The semi-inclusive correlations show pronounced short-range correlation effects which have a width considerably narrower than in the case of inclusive correlations. We show that these short-range effects can be understood empirically in terms of three parameters whose energy and multiplicity dependence are studied. The data support the picture of multiparticle production in which clusters of small multiplicity and small dispersion are emitted with subsequent decay into hadrons.RiassuntoVengono presentati dati sulle distribuzioni inclusive in rapidità dei secondari carichi prodotti nelle collisioni protone-protone ad altissime energie. L’esperimento è stato eseguito agli Anelli ad Intersezione (ISR) del CERN. I dati, ad una energia √s=23 e 62 GeV nel centro di massa, comprendono le distribuzioni di particella singola e le correlazioni a due particelle per fissa molteplicità carica, come anche le correlazioni inclusive a due particelle. Le correlazioni semi inclusive mostrano forti effetti di correlazione a breve distanza, che hanno una larghezza molto più piccola che nel caso delle correlazioni inclusive. Nel lavoro si fa vedere che questi effetti a breve distanza possono essere capiti empiricamente in funzione di tre parametri di cui si studia la dipendenza dall’energia e dalla molteplicità. I dati favoriscono la descrizione della produzione a molti corpi in cui vengono emessi agglomerati di piccola molteplicità e piccola dispersione, che successivamente decadono in adroni.РеэюмеВ работе приводятся данные для полуинклюэивных распределений вторичных частиц, рожденных в рр соударениях при очень высоких знергиях. Нащ зксперимент был проиэведен на встречных накопительных кольцах в ЦЕРНе. Полученные в работе данные при знергиях в системе центра масс √s=23 и 62 ГзВ включают одночастичные распределения и двухчастичные корреляции при фиксированной множественности эаряженных частиц п, а также инклюэивные двухчастичные корреляции. Полуинклюэивные корреляции обнаруживают явно выраженные зффекты короткодействуюших корреляций, которые обладают щириной эначительно меньщей, чем в случае инклюэивных корреляций. Мы покаэываем, что зти короткодействуюшие зффекты могут быть общяснены змпрически в терминах трех параметров. Обсуждается эависимость зтих параметров от знергии и множественности. Полученные данные подтверждают картину множественного рождения, в которой испускаются кластеры с малой множественностью и малой дисперсией с последуюшим распадом в адроны.
110772906
The use of waveform digitizers with drift chambers for D0
Abstract A prototype drift chamber cell with good space resolution, d E d x , and two particle separation has been constructed. A 100 MHz, 11 bit waveform digitizer readout scheme has been used for the tests.
121517669
Measurement of charged particle multiplicities associated with large transverse momentum photons in proton-proton collisions
Abstract We have measured the behaviour or charged-particle multiplicities as a function of the transverse momentum of photons produced at 90° in proton-proton collisions. The data were obtained at the CERN Intersecting Storage Rings (ISR) at a centre-of-mass energy of 53 GeV and cover the transverse momentum range 0 p ⊥ c . The total associated charge multiplicity increases with p ⊥ and most of the increase is found in a very wide cone opposite the detected photons. Partial multiplicities in the direction of the photons vary only slightly with p ⊥ . However, multiplicities at small angles with respect to the beams decrease sharply with increasing p ⊥ .
120228621
Observation of the Transition $\Upsilon^\prime \to \Upsilon \pi^+ \pi^- \to e^+ e^- \pi^+ \pi^-$