A study of charged charm production is made at 400 GeV incident energy of protons in nuclear emulsion. A total of 7005 primary stars have been scrutinized to look for charm particle decays in the forward cone within a decay distance of 100–1,000 μm (3,056 stars) and 100–2,000 μm (3,949 stars). In all 10 charm candidates decaying to 3 charged particles plus neutrals have been observed. Background due to secondary interactions for events of such topology is estimated to be ≈3. Background due to strange particle decays is estimated to be negligible. The rest of the events are attributed toΛc+ andD± decays. This leads to a value of 91±35 μb/nucleon for the total charged charm production cross section. Using production cross section forD± from other experiments we obtainΛc+ production cross section as 62±27 μb/nucleon. Two cases of pair production of charm have been seen.
Axis error includes +- 0.0/0.0 contribution (NOT GIVENDECAY-BR(BRN=D+ --> 3CHARGED (NEUTRALS), BR=0.5)//DECAY-BR(BRN=D- --> 3CHARGED (NEUTRALS), BR=0.5)//DECAY-BR(BRN=LAMBDA/C+ --> 3CHARGED (NEUTRALS), BR=0.6)).
Axis error includes +- 0.0/0.0 contribution (NOT GIVENDECAY-BR(BRN=D+ --> 3CHARGED (NEUTRALS), BR=0.5)//DECAY-BR(BRN=D- --> 3CHARGED (NEUTRALS), BR=0.5)//DECAY-BR(BRN=LAMBDA/C+ --> 3CHARGED (NEUTRALS), BR=0.6)).
Narrow states observable through the emission of monoenergetic charged pions have been searched for in p p annihilation at rest in a gaseous hydrogen target where annihilation from atomic angular momentum L = 1 states dominates. No structure is observed. The 5σ upper limit for the production of narrow states in the mass range 1100–1670 MeV is 2 × 10 −3 of all annihilations.
X means a narrow state.
We have obtained the branching ratios for p p annihilation at rest into π + π − and K + K − in a pure p p initial angular momentum state L = 1. A gaseous hydrogen target at normal pressure and temperature was used and events associated with transitions of the antiprotonic atom to the 2p level were selected by detecting the Balmer X-ray series. The branching ratios for p p annihilation into π + π − and K + K − from the 2p state are (4.81 ± 0.49) × 10 −3 and (2.87 ± 0.51) × 10 −4 , respect The pion yield is slightly larger than in liquid hydrogen, where L = 0 annihilation dominates, while the kaon yield is suppressed by a factor of four. Using these and previous data, we derive the branching ratios for pp annihilation into all ππ and K K modes from S and P states. A measurement in gaseous hydrogen, without X-ray requirement, yields the branching ratios (4.30 ± 0.14) × 10 −3 and (6.92 ± 0.41) × 10 −4 . With the known branching ratios of (3.33 ± 0.17) × 10 −3 and (1.01 ± 0.05) × 10 −3 in liquid hydrogen, we find that (50.3 ± 6.4)% of all annihilations in gas at NTP occur in the initial angular momentum state L = 1.
Axis error includes +- 0.0/0.0 contribution (?////).
Axis error includes +- 0.0/0.0 contribution (?////).
If quarks are composite particles then excited states are expected. We have searched in pp¯ collisions for excited quarks (q*) which decay to common quarks by emitting a W boson (q*→qW) or a photon (q*→qγ). The simplest model of excited quarks has been excluded for mass M*<540 GeV/c2 at 95% confidence level.
No description provided.
No description provided.
No description provided.
We present the results of a search for the top quark in 19.3 pb−1 of p¯p collisions at √s =1.8 TeV. The data were collected at the Fermilab Tevatron collider using the Collider Detector at Fermilab (CDF). The search includes standard model tt¯ decays to final states eeνν¯, eμνν¯, and μμνν¯ as well as e+ν+jets or μ+ν+jets. In the (e,μ)+ν+jets channel we search for b quarks from t decays via secondary vertex identification and via semileptonic decays of the b and cascade c quarks. In the dilepton final states we find two events with a background of 0.56−0.13+0.25 events. In the e,μ+ν+jets channel with a b identified via a secondary vertex, we find six events with a background of 2.3±0.3. With a b identified via a semileptonic decay, we find seven events with a background of 3.1±0.3. The secondary vertex and semileptonic-decay samples have three events in common. The probability that the observed yield is consistent with the background is estimated to be 0.26%. The statistics are too limited to firmly establish the existence of the top quark; however, a natural interpretation of the excess is that it is due to tt¯ production. We present several cross-checks. Some support this hypothesis; others do not. Under the assumption that the excess yield over background is due to tt¯, constrained fitting on a subset of the events yields a mass of 174±10−12+13 GeV/c2 for the top quark. The tt¯ cross section, using this top quark mass to compute the acceptance, is measured to be 13.9−4.8+6.1 pb.
Cross section refers to top quark mass equals 174 +- 10 +13 - 12 GeV. Two events in the dilepton final states and six events in the electron or muon nu jets final states.
We summarize a search for the top quark with the Collider Detector at Fermilab (CDF) in a sample of $\bar{p}p$ collisions at $\sqrt{s}$= 1.8 TeV with an integrated luminosity of 19.3pb$~{-1}$. We find 12 events consistent with either two $W$ bosons, or a $W$ boson and at least one $b$ jet. The probability that the measured yield is consistent with the background is 0.26\%. Though the statistics are too limited to establish firmly the existence of the top quark, a natural interpretation of the excess is that it is due to $t\bar{t}$ production. Under this assumption, constrained fits to individual events yield a top quark mass of $174 \pm 10~{+13}_{-12}$ GeV/c$~2$. The $t\bar{t}$ production cross section is measured to be $13.9~{+6.1}_{-4.8}$pb. (Submitted to Physical Review Letters on May 16, 1994).
No description provided.
We present an analysis of data from p p¯ collisions at a center-of-mass energy of √s =1800 GeV. A measurement is made of the ratio R≡σB(p p¯→W→eν)/σB(p p¯→Z0→ee). The data represent 19.6 pg−1 collected by the Collider Detector at Fermilab during the 1992–1993 collider run of the Fermilab Tevatron. We find R=10.90±0.32(stat)±0.29(syst), and from this value we extract a measurement of the W→eν branching ratio Γ(W→eν)/Γ(W)=0.1094±0.0033(stat)±0.0031(syst). From this branching ratio we set a limit on the top quark mass of mt>62 GeV/c2 at the 95% confidence level. In contrast with direct searches for the top quark, this limit makes no assumptions about the allowed decay modes of the top quark. In addition, we use a calculation of the leptonic width Γ(W→eν) to obtain a value for the W total decay width: Γ(W)=2.064±0.060(stat)±0.059(syst) GeV.
The cross section ratio contains the branching ratio of W --> E NU and Z0 --> E+ E-. RE = PBAR P --> W+ X.
We report the first observation of the associated production of a W boson and a Z boson. This result is based on 1.1 fb-1 of integrated luminosity from ppbar collisions at sqrt{s} = 1.96 TeV collected with the CDF II detector at the Fermilab Tevatron. We observe 16 WZ candidates passing our event selection with an expected background of 2.7 +/- 0.4 events. A fit to the missing transverse energy distribution indicates an excess of events compared to the background expectation corresponding to a significance equivalent to six standard deviations. The measured cross section is sigma(ppbar -> WZ) = 5.0^{+1.8}_{-1.6} pb, consistent with the standard model expectation.
Measured cross section.
We report a measurement of the single top quark production cross section in 2.2 ~fb-1 of p-pbar collision data collected by the Collider Detector at Fermilab at sqrt{s}=1.96 TeV. Candidate events are classified as signal-like by three parallel analyses which use likelihood, matrix element, and neural network discriminants. These results are combined in order to improve the sensitivity. We observe a signal consistent with the standard model prediction, but inconsistent with the background-only model by 3.7 standard deviations with a median expected sensitivity of 4.9 standard deviations. We measure a cross section of 2.2 +0.7 -0.6(stat+sys) pb, extract the CKM matrix element value |V_{tb}|=0.88 +0.13 -0.12 (stat+sys) +- 0.07(theory), and set the limit |V_{tb}|>0.66 at the 95% C.L.
Combined measured single top quark cross section in the s and t channels. The error is combined statistics and systematics.
We present a measurement of the $\ttbar$ production cross section in $\ppbar$ collisions at $\sqrt{s}=1.96$ TeV using events containing a high transverse momentum electron or muon, three or more jets, and missing transverse energy. Events consistent with $\ttbar$ decay are found by identifying jets containing candidate heavy-flavor semileptonic decays to muons. The measurement uses a CDF Run II data sample corresponding to $2 \mathrm{fb^{-1}}$ of integrated luminosity. Based on 248 candidate events with three or more jets and an expected background of $79.5\pm5.3$ events, we measure a production cross section of $9.1\pm 1.6 \mathrm{pb}$.
Measured cross section assuming a top quark mass of 175 GeV. The second systematic error is the uncertainty on the luminosity.
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