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Observation of short range three-particle correlations in e+e- annihilations at LEP energies

Physics Letters B 355:1-2 (1995) 415-424

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, G Barbiellini, 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, K Blous, 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, RA Brenner, C Bricman, L Brillault, RCA Brown, P Bruckman, JM Brunet, L Bugge, T Buran, A Buys, M Caccia, M Calvi, AJ Camacho Rozas, T Camporesi, V Canale, M Canepa, K Cankocak, F Cao, F Carena, P Carrilho, 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, R Chierici, P Chochula, V Chorowicz, V Cindro

Abstract:

Measurements are presented of short range three-particle correlations in e+e- annihilations at LEP using data collected by the DELPHI detector. At small values of the four-momentum difference, strong three-particle correlations are observed for like-sign (+++ and ---) and for unlike-sign (++- and +--) pion combinations which are not a consequence of two-particle correlations. A possible explanation of the observed effects in like-sign combinations is the existence of higher order Bose-Einstein interference, which significantly changes the particle distributions in jets. © 1995.
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Study of the photon remnant in resolved photoproduction at HERA

Physics Letters B 354:1-2 (1995) 163-177

Authors:

M Derrick, D Krakauer, S Magill, D Mikunas, B Musgrave, J Repond, R Stanek, RL Talaga, H Zhang, R Ayad, G Bari, M Basile, L Bellagamba, D Boscherini, A Bruni, G Bruni, P Bruni, G Cara Romeo, G Castellini, M Chiarini, L Cifarelli, F Cindolo, A Contin, M Corradi, I Gialas, P 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 Bargende, J Crittenden, K Desch, B Diekmann, T Doeker, M Eckert, L Feld, A Frey, M Geerts, G Geitz, M Grothe, T Haas, H Hartmann, K Heinloth, E Hilger, HP Jakob, UF Katz, SM Mari, A Mass, S Mengel, J Mollen, E Paul, C Rembser, D Schramm, J Stamm, R Wedemeyer, S Campbell-Robson, A Cassidy, N Dyce, B Foster, S George, R Gilmore, GP Heath, HF Heath, TJ Llewellyn, CJS Morgado, DJP Norman, JA O'Mara, RJ Tapper, SS Wilson, R Yoshida, RR Rau, M Arneodo, 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 at HERA is studied in ep collisions, with the ZEUS detector, for γp centre-of-mass energies ranging from 130-270 GeV. A sample of events with two high-pTjets (pT> 6 GeV, η < 1.6) and a third cluster in the approximate direction of the electron beam is isolated using a clustering algorithm. These events are mostly due to resolved photoproduction. The third cluster is identified as the photon remnant. Its properties, such as the transverse and longitudinal energy flows around the axis of the cluster, are consistent with those commonly attributed to jets, and in particular with those found for the two jets in these events. The mean value of the photon remnant pTwith respect to the beam axis is measured to be 2.1 ± 0.2 GeV, which demonstrates substantial mean transverse momenta for the photon remnant. © 1995.
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Inclusive measurements of the K± and p/p production in hadronic Z0 decays

Nuclear Physics, Section B 444:1-2 (1995) 3-26

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, K Belous, AC Benvenuti, M Berggren, D Bertrand, F Bianchi, M Bigi, MS Bilenky, P Billoir, J Bjarne, D Bloch, M Blume, S Blyth, V Bocci, T Bolognese, M Bonesini, W Bonivento, PSL Booth, G Borisov, C Bosio, B Bostjancic, S Bosworth, O Botner, E Boudinov, B Bouquet, C Bourdarios, TJV Bowcock, M Bozzo, P Branchini, KD Brand, RA Brenner, C Bricman, L Brillault, RCA Brown, P Bruckman, JM Brunet, L Bugge, T Buran, A Buys, M Caccia, M Calvi, AJ Camacho Rozas, T Camporesi, V Canale, M Canepa, K Cankocak, F Cao, F Carena, P Carrilho, L Carroll, C Caso, V Cassio, MV Castillo Gimenez, A Cattai, FR Cavallo, L Cerrito, V Chabaud, P Charpentier, L Chaussard, J Chauveau, P Checchia, GA Chelkov, P Chliapnikov

Abstract:

This analysis, based on a sample of 170000 hadronic Z0 decays, provides a measurement of the K± and p/p differential cross sections which is compared to string- and cluster fragmentation models. The total multiplicities for K± and p/p per hadronic event were found to be: NK = 2.26 ± 0.18 and Np = 1.07 ± 0.14. The positions ξ* of the maxima of the differential cross sections as a function of ξ = ln(1/xp) for K± and p/p were determined to be 2.63 ± 0.07 and 2.96 ± 0.16 respectively. A comparison of the ξ* values for various identified particles measured at LEP with the prediction of the Modified Leading Logarithm Approximation with Local Parton Hadron Duality model has been performed. The measured ξ* position as a function of the hadron mass, after corrections due to particle decays, is in agreement with the model calculation. © 1995.
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Inclusive transverse momentum distributions of charged particles in diffractive and non-diffractive photoproduction at HERA

Zeitschrift für Physik C Particles and Fields 67:2 (1995) 227-237

Authors:

M Derrick, D Krakauer, S Magill, D Mikunas, B Musgrave, J Repond, R Stanek, RL Talaga, H Zhang, R Ayad, G Bari, M Basile, L Bellagamba, D Boscherini, A Bruni, G Bruni, P Bruni, GC Romeo, G Castellini, M Chiarini, L Cifarelli, F Cindolo, A Contin, M Corradi, I Gialas, P Giusti, G Iacobucci, G Laurenti, G Levi, A Margotti, T Massam, R Nania, C Nemoz, F Palmonari, A Polini, G Sartorelli, R Timellini, YZ Garcia, A Zichichi, A Bargende, J Crittenden, K Desch, B Diekmann, T Doeker, M Eckert, L Feld, A Frey, M Geerts, G Geitz, M Grothe, T Haas, H Hartmann, D Haun, K Heinloth, E Hilger, HP Jakob, UF Katz, SM Mari, A Mass, S Mengel, J Mollen, E Paul, C Rembser, R Schattevoy, D Schramm, J Stamm, R Wedemeyer, S Campbell-Robson, A Cassidy, N Dyce, B Foster, S George, R Gilmore, GP Heath, HF Heath, TJ Llewellyn, CJS Morgado, DJP Norman, JA O'Mara, RJ Tapper, SS Wilson, R Yoshida, RR Rau, M Arneodo, 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

Abstract:

Inclusive transverse momentum spectra of charged particles in photoproduction events in the laboratory pseudorapidity range -1.2<η<1.4 have been measured up to pT=8 GeV usign the ZEUS detector. Diffractive and non-diffractive reactions have been selected with an average γp centre of mass (c.m.) energy of 〈W〉=180 GeV. For diffractive reactions, the pT spectra of the photon dissociation events have been measured in two intervals of the dissociated photon mass with mean values 〈MX〉=5 GeV and 10 GeV. The inclusive transverse momentum spectra fall exponentially in the low pT region. The non-diffractive data show a pronounced high pT tail departing from the exponential shape. The pT distributions are compared to lower energy photoproduction data and to hadron-hadron collisions at a similar c.m. energy. The data are also compared to the results of a next-to-leading order QCD calculation. © 1995 Springer-Verlag.
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Measurements of the τ polarisation in Z0 decays

Zeitschrift für Physik C Particles and Fields 67:2 (1995) 183-201

Authors:

P Abreu, W Adam, T Adye, E Agasi, I Ajinenko, R Aleksan, GD Alekseev, PP Allport, S Almehed, FML Almeida, 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, G Barbiellini, 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, P Beltran, AC Benvenuti, M Berggren, D Bertrand, F Bianchi, M Bigi, MS Bilenky, P Billoir, J Bjarne, D Bloch, M Blume, S Blyth, V Bocci, T Bolognese, M Bonesini, W Bonivento, PSL Booth, G Borisov, C Bosio, B Bostjancic, S Bosworth, O Botner, E Boudinov, B Bouquet, C Bourdarios, TJV Bowcock, M Bozzo, P Branchini, KD Brand, RA Brenner, C Bricman, L Brillault, RCA Brown, P Bruckman, JM Brunet, L Bugge, T Buran, A Buys, M Caccia, M Calvi, AJ Camacho Rozas, T Camporesi, V Canale, M Canepa, K Cankocak, F Cao, F Carena, P Carrilho, L Carroll, C Caso, V Cassio, MV Castillo Gimenez, A Cattai, FR Cavallo, L Cerrito, V Chabaud, P Charpentier, L Chaussard, J Chauveau, P Checchia

Abstract:

A sample of Z0→τ+τ- events observed in the DELPHI detector at LEP in 1991 and 1992 is analysed to measure the τ polarisation in the exclusive decay channels {Mathematical expression}, {Mathematical expression}, πν, ρν and a1ν. The τ polarisation is also measured with an inclusive hadronic analysis which benefits from a higher efficiency and a better systematic precision than the use of the exclusive decay modes. The results have been combined with those published on the 1990 data. A measurement of the τ polarisation as a function of production angle yields the values for the mean τ polarisation 〈P〉τ=-0.148±0.022 and for the Z0 polarisation PZ=-0.136±0.027. These results are used to determine the ratio of vector to axial-vector effective couplings for taus {Mathematical expression}, and for electrons {Mathematical expression}, compatible with e-τ universality. With the assumption of lepton universality, the ratio of vector to axial-vector effective couplings for leptons {Mathematical expression} is obtained, implying a value of the effective weak mixing angle sin2θefflept=0.2320±0.0021 . © 1995 Springer-Verlag.
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