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Search for exclusive decays of the Λb baryon and measurement of its mass

Physics Letters, Section B: Nuclear, Elementary Particle and High-Energy Physics 374:4 (1996) 351-361

Authors:

P Abreu, W Adam, T Adye, E Agasi, I Ajinenko, R Aleksan, GD Alekseev, R Alemany, PP Allport, S Almehed, U Amaldi, S Amato, A Andreazza, ML Andrieux, P Antilogus, WD Apel, Y Arnoud, B Åsman, JE Augustin, A Augustinus, P Baillon, P Bambade, F Barao, R Barate, M Barbi, DY Bardin, A Baroncelli, O Barring, JA Barrio, W Bartl, MJ Bates, M Battaglia, M Baubillier, J Baudot, KH Becks, M Begalli, P Beilliere, Y Belokopytov, AC Benvenuti, M Berggren, D Bertrand, F Bianchi, M Bigi, MS Bilenky, P Billoir, D Bloch, M Blume, S Blyth, T Bolognese, M Bonesini, W Bonivento, PSL Booth, G Borisov, C Bosio, S Bosworth, O Botner, E Boudinov, B Bouquet, C Bourdarios, TJV Bowcock, M Bozzo, P Branchini, KD Brand, T Brenke, RA Brenner, C Bricman, L Brillault, RCA Brown, P Bruckman, JM Brunet, L Bugge, T Buran, T Burgsmueller, P Buschmann, A Buys, S Cabrera, M Caccia, M Calvi, A Camacho Rozas, T Camporesi, V Canale, M Canepa, K Cankocak, F Cao, F Carena, L Carroll, C Caso, MV Castillo Gimenez, A Cattai, FR Cavallo, L Cerrito, V Chabaud, M Chapkin, P Charpentier, L Chaussard, J Chauveau, P Checchia, GA Chelkov, M Chen, R Chierici

Abstract:

A search for fully reconstructed Λ0b beauty baryons is performed using about 3 million Ζ decays collected with the DELPHI detector at LEP. The analysis relies on the combined use of the accurate tracking and of the hadron identification capabilities of DELPHI. A total of four events has been found, three in the Λ+cπ- channel and one in the Λ+ca-1 channel over a small background. The Λ0b beauty baryon mass is measured to be (5668 ± 16 (stat.) ± 8 (syst.)) MeV/c2.
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Charged particle multiplicity in e+e- interactions at √s = 130 GeV

Physics Letters, Section B: Nuclear, Elementary Particle and High-Energy Physics 372:1-2 (1996) 172-180

Authors:

P Abreu, W Adam, T Adye, E Agasi, I Ajinenko, R Aleksan, GD Alekseev, R Alemany, PP Allport, S Almehed, U Amaldi, S Amato, A Andreazza, ML Andrieux, P Antilogus, WD Apel, Y Arnoud, B Åsman, JE Augustin, A Augustinus, P Baillon, P Bambade, F Barao, R Barate, M Barbi, DY Bardin, A Baroncelli, O Barring, JA Barrio, W Bartl, MJ Bates, M Battaglia, M Baubillier, J Baudot, KH Becks, M Begalli, P Beilliere, Y Belokopytov, K Belous, AC Benvenuti, M Berggren, D Bertrand, F Bianchi, M Bigi, MS Bilenky, P Billoir, D Bloch, M Blume, S Blyth, T Bolognese, M Bonesini, W Bonivento, PSL Booth, G Borisov, C Bosio, S Bosworth, O Botner, E Boudinov, B Bouquet, C Bourdarios, TJV Bowcock, M Bozzo, P Branchini, KD Brand, T Brenke, RA Brenner, C Bricman, L Brillault, RCA Brown, P Bruckman, JM Brunet, L Bugge, T Buran, T Burgsmueller, P Buschmann, A Buys, S Cabrera, M Caccia, M Calvi, AJ Camacho Rozas, T Camporesi, V Canale, M Canepa, K Cankocak, F Cao, F Carena, L Carroll, C Caso, MV Castillo Gimenez, A Cattai, FR Cavallo, L Cerrito, V Chabaud, P Charpentier, L Chaussard, J Chauveau, P Checchia, GA Chelkov, M Chen, R Chierici

Abstract:

From the data collected by DELPHI at LEP in autumn 1995, the multiplicity of charged particles at a hadronic energy of 130 GeV has been measured to be 〈nch〉 = 23.84 ± 0.51 (stat) ± 0.52(syst). When compared to lower energy data, the value measured is consistent with the evolution predicted by QCD with corrections at next-to-leading order, for a value αs(130 GeV) = 0.105 ± 0.003(stat) ± 0.008(syst).
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Rapidity gaps between jets in photoproduction at HERA

Physics Letters, Section B: Nuclear, Elementary Particle and High-Energy Physics 369:1 (1996) 55-68

Authors:

M Derrick, D Krakauer, S Magill, D Mikunas, B Musgrave, J Repond, R Stanek, RL Talaga, H Zhang, G Bari, M Basile, L Bellagamba, D Boscherini, A Bruni, G Bruni, R Bruni, G Cara Romeo, G Castellini, M Chiarini, L Cifarelli, F Cindolo, A Contin, M Corradi, I Gialas, R Giusti, G Iacobucci, G Laurenti, G Levi, A Margotti, T Massam, R Nania, C Nemoz, F Palmonari, A Polini, G Sartorelli, R Timellini, Y Zamora Garcia, A Zichichi, A Bornheim, J Crittenden, K Desch, B Diekmann, T Doeker, M Eckert, L Feld, A Frey, M Geerts, M Grothe, H Hartmann, K Heinloth, L Heinz, E Hilger, HP Jakob, UF Katz, S Mengel, J Mollen, E Paul, M Pfeiffer, C Rembser, D Schramm, J Stamm, R Wedemeyer, S Campbell-Robson, A Cassidy, WN Cottingham, N Dyce, B Foster, S George, ME Hayes, GP Heath, HF Heath, CJS Morgado, JA O'Mara, D Piccioni, DG Roff, RJ Tapper, R Yoshida, RR Rau, M Arneodo, R Ayad, M Capua, A Garfagnini, L Iannotti, M Schioppa, G Susinno, A Bernstein, A Caldwell, N Cartiglia, JA Parsons, S Ritz, F Sciulli, PB Straub, L Wai, S Yang, Q Zhu, P Borzemski, J Chwastowski, A Eskreys, K Piotrzkowski, M Zachara

Abstract:

Photoproduction events which have two or more jets have been studied in the Wγp range 135 GeV < Wγp < 280 GeV with the ZEUS detector at HERA. A class of events is observed with little hadronic activity between the jets. The jets are separated by pseudorapidity intervals (Δη) of up to four units and have transverse energies greater than 6 GeV. A gap is defined as the absence between the jets of particles with transverse energy greater than 300 MeV. The fraction of events containing a gap is measured as a function of Δη. It decreases exponentially as expected for processes in which colour is exchanged between the jets, up to a value of Δη ∼ 3, then reaches a constant value of about 0.1. The excess above the exponential fall-off can be interpreted as evidence for hard diffractive scattering via a strongly interacting colour singlet object.
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A precise measurement of the tau lepton lifetime

Physics Letters, Section B: Nuclear, Elementary Particle and High-Energy Physics 365:1-4 (1996) 448-460

Authors:

P Abreu, W Adam, T Adye, E Agasi, I Ajinenko, R Aleksan, GD Alekseev, PP Allport, S Almehed, SJ Alvsvaag, U Amaldi, S Amato, A Andreazza, ML Andrieux, P Antilogus, WD Apel, Y Arnoud, B Åsman, JE Augustin, A Augustinus, P Baillon, P Bambade, F Barao, R Barate, DY Bardin, GJ Barker, A Baroncelli, O Barring, JA Barrio, W Bartl, MJ Bates, M Battaglia, M Baubillier, J Baudot, KH Becks, M Begalli, P Beilliere, Y Belokopytov, AC Benvenuti, M Berggren, D Bertrand, F Bianchi, M Bigi, MS Bilenky, P Billoir, D Bloch, M Blume, S Blyth, V Bocci, T Bolognese, M Bonesini, W Bonivento, PSL Booth, G Borisov, C Bosio, S Bosworth, O Botner, B Bouquet, C Bourdarios, TJV Bowcock, M Bozzo, P Branchini, KD Brand, T Brenke, RA Brenner, C Bricman, L Brillault, RCA Brown, P Bruckman, JM Brunet, L Bugge, T Buran, T Burgsmueller, P Buschmann, A Buys, M Caccia, M Calvi, AJ Camacho Rozas, T Camporesi, V Canale, M Canepa, K Cankocak, F Cao, F Carena, P Carrilho, L Carroir, C Caso, MV Castillo Gimenez, A Cattai, FR Cavallo, L Cerrito, V Chabaud, P Charpentier, L Chaussard, J Chauveau, P Checchia, GA Chelkov, R Chierici, P Chliapnikov, P Chochula

Abstract:

The tau lepton lifetime has been measured using three different methods with the DELPHI detector. Two measurements of one-prong decays are combined, accounting for correlations, giving a result ofττ = 291.8 ± 3.3 (stat.) ± 2.0(sys.) fs while the decay length distribution of three-prong decays gives the result ττ = 286.7 ± 4.9 (stat.) ± 3.3 (sys.) fs. Combining the results presented here with previous DELPHI measurements, we get ττ = 291.4 ± 3.0 fs and find that the ratio of the coupling constant for tau decay relative to that for muon decay is 0.990 ± 0.009, compatible with lepton universality.
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Determination of the average lifetime of b-baryons

Zeitschrift fur Physik C-Particles and Fields 71:2 (1996) 199-210

Authors:

P Abreu, W Adam, T Adye, E Agasi, I Ajinenko, R Aleksan, GD Alekseev, R Alemany, PP Allport, S Almehed, U Amaldi, S Amato, A Andreazza, ML Andrieux, P Antilogus, WD Apel, Y Amoud, B Åsman, JE Augustin, A Augustinus, P Baillon, P Bambade, F Barao, R Barate, M Barbi, DY Bardin, A Baroncelli, O Barring, JA Barrio, W Bartl, MJ Bates, M Battaglia, M Baubillier, J Baudot, KH Becks, M Begalli, P Beilliere, Y Belokopytov, K Belous, AC Benvenuti, M Berggren, D Bertrand, F Bianchi, M Bigi, MS Bilenky, P Billoir, D Bloch, M Blume, S Blyth, T Bolognese, M Bonesini, W Bonivento, PSL Booth, G Borisov, C Bosio, S Bosworth, O Botner, E Boudinov, B Bouquet, C Bourdarios, TJV Bowcock, M Bozzo, P Branchini, KD Brand, T Brenke, RA Brenner, C Bricman, L Brillault, RCA Brown, P Bruckman, JM Brunet, L Bugge, T Buran, T Burgsmueller, P Buschmann, A Buys, S Cabrera, M Caccia, M Calvi, AJ Camacho Rozas, T Camporesi, V Canale, M Canepa, K Cankocak, F Cao, F Carena, L Carroll, C Caso, MV Castillo Gimenez, A Cattai, FR Cavallo, L Cerrito, V Chabaud, M Chapkin, P Charpentier, L Chaussard, J Chauveau, P Checchia, GA Chelkov, M Chen

Abstract:

The average lifetime of b-baryons has been studied using 3 × 106 hadronic Z0 decays collected by the DEL-PHI detector at LEP. Three methods have been used, based on the measurement of different observables: the proper decay time distribution of 206 vertices reconstructed with a Λ, a lepton and an oppositely charged pion; the impact parameter distribution of 441 muons with high transverse momentum accompanied by a Λ in the same jet; and the proper decay time distribution of 125 Λc-lepton decay vertices with the Λc exclusively reconstructed through its pKπ, pK0 and Λ3π decay modes. The combined result is: τ(b-baryon) = (1.254-0.109+0.121(stat) ±0.04(syst)-0.05+0.03(syst)) ps where the first systematic error is due to experimental uncertainties and the second to the uncertainties in the modelling of the b-baryon production and semi-leptonic decay. Including the measurement recently published by DELPHI based on a sample of proton-muon vertices, the average b-baryon lifetime is : τ(b-baryon) = (1.255-0.102+0.115(stat) ±0.05) ps. © Springer-Verlag 1996.
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