Luc Pape

K+p elastic scattering at 3.0 GeV/c

SummaryIn the course of a systematic study of K+p interactions at 3.0 GeV/c, the elastic-scattering reaction has been investigated. A total of 1720 events were identified as elastic scatters, giving a cross-section of (4.8±0.4) mb. The angular distribution shows characteristic diffraction peaking and was fitted using dσ/d|t|=(dσ/d|t|)0 exp [αt+βt2], in the momentum-transfer region (0.05÷1.14) (GeV/c)2. The best fit gaveα=(4.55±0.39) (GeV/c)−2 andβ=(0.64±0.42)(GeV/c)−4. The extrapolated experimental cross-section at 0°, (dσ/dt)0, is found to be (19.5±2.3) mb/(GeV/c)2, and exceeds the optical-theorem prediction by (3.8±2.3) mb/(GeV/c)2, implying that there is a contribution from the real part of the K+p scattering amplitude at 3.0 GeV/c.RiassuntoNel corso di uno studio sistematico delle interazioni K+p di 3.0 GeV/c si è esaminata la reazione di scattering elastico. Un totale di 1720 eventi è stato identificato come scattering elastici che danno una sezione d’urto di (4.8±0.4) mb. La distribuzione angolare presenta un caratteristico picco di diffrazione ed è stata approssimata da dσ/d|t|=(dσ/d|t|)0 exp[αt+βt2] nella regione dei momenti trasferiti (0.05÷1.14)(GeV/c)2. Un calcolo di « best fit » dàα=(4.55±0.39)(GeV/c)−2 eβ=(0.64±0.42)(GeV)−4. Si trova che la sezione d’urto sperimentale estrapolata a 0°, (dσ/d)0, è (19.5±2.5) mb/(GeV/c)2, e supera le predizioni del teorema ottico di (3.8±2.3) mb/(GeV/c)2, implicando che si ha un contributo della parte reale dell’ampiezza di scattering K+p a 3.0 GeV/c.

On-shell constrained M 2 variables with applications to mass measurements and topology disambiguation

A bstractWe consider a class of on-shell constrained mass variables that are 3+1 dimensional generalizations of the Cambridge MT2 variable and that automatically incorporate various assumptions about the underlying event topology. The presence of additional on-shell constraints causes their kinematic distributions to exhibit sharper endpoints than the usual MT2 distribution. We study the mathematical properties of these new variables, e.g., the uniqueness of the solution selected by the minimization over the invisible particle 4-momenta. We then use this solution to reconstruct the masses of various particles along the decay chain. We propose several tests for validating the assumed event topology in missing energy events from new physics. The tests are able to determine: 1) whether the decays in the event are two-body or three-body, 2) if the decay is two-body, whether the intermediate resonances in the two decay chains are the same, and 3) the exact sequence in which the visible particles are emitted from each decay chain.

Improving the sensitivity of stop searches with on-shell constrained invariant mass variables

A bstractThe search for light stops is of paramount importance, both in general as a promising path to the discovery of beyond the standard model physics and more specifically as a way of evaluating the success of the naturalness paradigm. While the LHC experiments have ruled out much of the relevant parameter space, there are “stop gaps”, i.e., values of sparticle masses for which existing LHC analyses have relatively little sensitivity to light stops. We point out that techniques involving on-shell constrained M2 variables can do much to enhance sensitivity in this region and hence help close the stop gaps. We demonstrate the use of these variables for several benchmark points and describe the effect of realistic complications, such as detector effects and combinatorial backgrounds, in order to provide a useful toolkit for light stop searches in particular, and new physics searches at the LHC in general.

Spin, branching ratios and production characteristics of the K∗(1420)

Abstract The reactions (1) K + p → K ∗ (1420) p and (2) K + p → K ∗ (1420) N ∗ (1236) are studied at 5 GeV/c incident K+ momentum. The simultaneous fitting of the K π and K ∗ (892)π decayy modes of the K∗ (1420) in the same production reaction makes it possible to eliminate 1− as the spin of the K∗(1420). The most likely K∗(1420) spin-parity assignment is 2+ although 3− cannot be excluded. The various decay branching ratios of the K∗(1420) are determined. The ratio of the K ∗ (892)π to the Kπ decay modes is found to be 0.9 ± 0.2. The peripheral production of the K∗(1420) seems to be due predominantly to vector-meson exchange in reaction (1) and to pion exchange in reaction (2).

Evidence for three Kππ resonant states below 1.4 GeV in K+p reactions at 5 GeV/c

Abstract The study of K+p reactions at an incident momentum of 4.97 GeV/c suggests that the wide enhancement in the (Kππ)+ mass spectrum may be split into several resonant states. In particular, examination of the K ∗ (892)π decay mode indicates the existence of the states K∗(1230), K∗(1280) and K∗(1320), in addition to the well known K∗(1420). The K∗(1230) and K∗(1320) have the properties expected from 1+ states produced by 0+ exchange.

Study of multi-body final states in K+p reactions at an incident momentum of 5 GeV/c

Abstract Results are given on the comparison of the predictions of the multiperipheral model of Chan, Loskiewicz and allison with the experimental data obtained from a study of the interactions of 5 GeV/c K+ mesons with protons. Comparisons have been made in the three-, four-, five- and six-body final states containing a proton, kaon and pions. With the addition of resonance production to the model, adequate predictions of experimental distributions are obtained. An attempt is made to describe the energy variation of the three- and four-body final-state cross sections.

Study of the reaction K+p→ K*0 (890) Δ++ from 4.6-16.0 GeV/c

Abstract A systematic analysis is presented on the reaction K + p → K ∗0 (890) Δ ++ for nine incident momenta between 4.6–16.0 GeV/ c . Cross sections, differential cross sections and vector meson single density matrix elements are given. As a function of energy, little if any change is observed in either the shapes of the differential cross sections or in the values of the density matrix elements. The data are interpreted in terms of current ideas on t -channel exchange mechanisms.

Prompt Neutrino Production in 400-{GeV} Proton Copper Interactions

Abstract The prompt electron neutrino and muon neutrino fluxes from proton copper interactions at 400 GeV/ c proton momentum have been measured. The asymmetry between the prompt electron (anti) neutrino and the prompt muon (anti) neutrino event rates above 20 GeV is A e μ = (N e − N μ (N c + N μ ) = 0.07 ± 0.08 corresponding to an N e / N μ ratio of 1.14 −0.16 −0.19 . The cross section weighted charge asymmetry for electrons and muons combined is A ν ν = 0.15 ± 0.08 . The number of D decays into ν e and ν μ is (4.1 ± 0.9) × 10 −4 per incident proton. No evidence for ν τ interactions was found.

Study of the exchange mechanism in K+p → K+π-N*++ at 5 GeV/c incoming K+ momentum

We present results on the analysis of the quasi three-body reaction K+p → K+π-N*++ obtained from bubble chamber exposures at 5 GeV/c incident K+ momentum. We have applied a method of analysis based on the study of the longitudinal phase space plot recently proposed by Van Hove. Evidence for the existence of π- mesons with a four-momentum transfer peaked at small values is shown. (Events contributing to this peak correspond to the cross section of about 80 μb.) The difficulties in explaining this result in terms of the double-particle exchange model are discussed.

A comparison of the production of K∗ (890) in K+p and K−p interactions

Abstract Results are presented on an analysis of the reaction K + p → K ∗+ (890) p at 16 GeV/ c and compared with data at lower incident momenta and with corresponding results for the reaction K − p → K ∗− (890) p. It is found for both reactions that the energy dependence of the cross section exhibits a simple ( p − n lab behaviour.