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Observation of jet production in deep inelastic scattering with a large rapidity gap at HERA

Physics Letters B 332:1-2 (1994) 228-243

Authors:

M Derrick, D Krakauer, S Magill, B Musgrave, J Repond, J Schlereth, R Stanek, RL Talaga, J Thron, F Arzarello, 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, F Ciralli, A Contin, S D'Auria, C Del Papa, F Frasconi, P Giusti, G Iacobucci, G Laurenti, G Levi, G Maccarrone, A Margotti, T Massam, R Nania, C Nemoz, F Palmonari, G Sartorelli, R Timellini, YZ Garcia, A Zichichi, A Bargende, J Crittenden, K Desch, B Diekmann, T Doeker, L Feld, A Frey, M Geerts, G Geitz, H Hartmann, D Haun, K Heinloth, E Hilger, HP Jakob, UF Katz, S Kramarczyk, A Mass, S Mengel, J Mollen, E Paul, C Rembser, R Schattevoy, JL Schneider, 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, M Schioppa, G Susinno, A Bernstein, A Caldwell, I Gialas, JA Parsons, S Ritz, F Sciulli, PB Straub, L Wai, S Yang, P Borzemski, J Chwastowski, A Eskreys, K Piotrzkowski

Abstract:

Events with a large rapidity gap in deep inelastic scattering with Q2 ≥ 10 GeV2 have been studied in the ZEUS detector. The properties of these events with W > 140 GeV are consistent with a leading twist diffractive production mechanism. In the laboratory frame, with ETjet ≥ 4 GeV, 15% of the events are of the 1-jet type with negligible 2-jet production. The single jet is back-to-back in azimuth with the scattered electron. No energy flow is observed between the jet and the proton direction. With a lower jet transverse energy cut 2-jet production is observed both in the laboratory and the γ* p centre-of-mass systems, demonstrating the presence of hard scattering in the virtual photon proton interactions that give rise to large rapidity gap events. © 1994.
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Search for the standard model Higgs boson in Z0 decays

Nuclear Physics, Section B 421:1 (1994) 3-37

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, A Andreazza, P Antilogus, WD Apel, RJ Apsimon, 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, KH Becks, M Begalli, P Beilliere, P Beltran, AC Benvenuti, M Berggren, D Bertrand, F Bianchi, M Bigi, MS Bilenky, P Billoir, J Bjarne, D Bloch, J Blocki, S Blyth, V Bocci, PN Bogolubov, 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, S Braibant, P Branchini, KD Brand, RA Brenner, H Briand, C Bricman, L Brillault, RCA Brown, JM Brunet, L Bugge, T Buran, A Buys, JAMA Buytaert, M Caccia, M Calvi, AJ Camacho Rozas, R Campion, T Camporesi, V Canale, K Cankocak, F Cao, F Carena, P Carrilho, L Carroll, R Cases, C Caso, MV Castillo Gimenez, A Cattai, FR Cavallo, L Cerrito, V Chabaud, A Chan, M Chapkin, P Charpentier, J Chauveau

Abstract:

A search for the Standard Model Higgs boson was performed in the data sample of around 1 million hadronic Z0 decays recorded in 1991 and 1992 with the DELPHI detector at LEP. The Higgs boson was searched for through its production in association with either neutrinos, electrons or muons. Four low mass events remain after the selections in the charged leptonic channels, that are likely to be due to background, especially four fermion processes. These results restrict the mass of the Standard Model Higgs boson to be larger than 55.7 GeV/c2 at the 95% confidence level. © 1994.
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Search for pair-produced heavy scalars in Z0 decays

Zeitschrift für Physik C Particles and Fields 64:2 (1994) 183-193

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, A Andreazza, P Antilogus, WD Apel, RJ Apsimon, 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, KH Becks, M Begalli, P Beilliere, P Beltran, AC Benvenuti, M Berggren, D Bertrand, F Bianchi, M Bigi, MS Bilenky, P Billoir, J Bjarne, D Bloch, J Blocki, S Blyth, V Bocci, PN Bogolubov, T Bolognese, M Bonesini, W Bonivento, PSL Booth, G Borisov, C Bosio, B Bostjancic, S Bosworth, O Botner, B Bouquet, C Bourdarios, TJV Bowcock, M Bozzo, S Braibant, P Branchini, KD Brand, RA Brenner, H Briand, C Bricman, L Brillault, RCA Brown, P Bruckman, JM Brunet, L Bugge, T Buran, A Buys, JAMA Buytaert, M Caccia, M Calvi, AJ Camacho Rozas, R Campion, T Camporesi, V Canale, K Cankocak, F Cao, F Carena, P Carrilho, L Carroll, R Cases, C Caso, E Castelli, MVC Gimenez, A Cattai, FR Cavallo, L Cerrito, V Chabaud, A Chan, M Chapkin, P Charpentier, J Chauveau

Abstract:

A search for charged Higgs bosons decaying into quarks is described, based on statistics of around 1.7 million hadronic Zo decays detected in DELPHI. Despite the very high background from standard hadronic decays of the Zo, masses in the range up to 43.5 GeV/c2 are excluded at the 95% confidence level. After combination with a search for leptonic decays, this mass limit is extended to cover all branching ratios. A similar analysis sets new limits on the possible production of any pair-produced heavy scalar decaying into a pair of jets, such as neutral Higgs bosons in a two doublet scheme and diquarks. © 1994 Springer-Verlag.
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Measurement of the e+e- → γγ(γ) cross section at LEP energies

Physics Letters B 327:3-4 (1994) 386-396

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, A Andreazza, P Antilogus, WD Apel, RJ Apsimon, 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, KH Becks, M Begalli, P Beilliere, P Beltran, AC Benvenuti, M Berggren, D Bertrand, F Bianchi, M Bigi, MS Bilenky, P Billoir, J Bjarne, D Bloch, J Blocki, S Blyth, V Bocci, PN Bogolubov, T Bolognese, M Bonesini, W Bonivento, PSL Booth, G Borisov, C Bosio, B Bostjancic, S Bosworth, O Botner, B Bouquet, C Bourdarios, TJV Bowcock, M Bozzo, S Braibant, P Branchini, KD Brand, RA Brenner, H Briand, C Bricman, L Brillault, RCA Brown, JM Brunet, L Bugge, T Buran, A Buys, JAMA Buytaert, M Caccia, M Calvi, AJ Camacho Rozas, R Campion, T Camporesi, V Canale, K Cankocak, F Cao, F Carena, P Carrilho, L Carroll, R Cases, C Caso, MV Castillo Gimenez, A Cattai, FR Cavallo, L Cerrito, V Chabaud, A Chan, M Chapkin, P Charpentier, J Chauveau, P Checchia

Abstract:

The total and the differential cross sections for the reaction e+e- → γγ(γ) have been measured with the DELPHI detector at LEP using an integrated luminosity of 36.9 pb-1. The results agree with the QED predictions and consequently there is no evidence for non-standard channels with the same experimental signature. The lower limits obtained on the QED cutoff parameters are Λ+ > 143 GeV and Λ- > 120 GeV, and the lower bound on the mass of an excited electron with an effective coupling constant λγ = 1 is 132 GeV/c2. Upper limits on the branching ratios for the decays Z0 → γγ, Z0 → π0γ, Z0 → ηγ and Z0 → γγγ have been determined to be 5.5 × 10-5, 5.5 × 10-5, 8.0 × 10-5, and 1.7 × 10-5 respectively. All the limits are at the 95% confidence level. © 1994.
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Improved measurements of cross sections and asymmetries at the Z0 resonance

Nuclear Physics, Section B 418:3 (1994) 403-427

Authors:

P Abreu, W Adam, T Adye, E Agasi, I Ajinenko, R Aleksan, GD Alekseev, P Allport, S Almehed, FMLA Junior, SJ Alvsvaag, U Amaldi, A Andreazza, P Antilogus, WD Apel, RJ Apsimon, 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, KH Becks, M Begalli, P Beilliere, K Belous, P Beltran, AC Benvenuti, M Berggren, D Bertrand, F Bianchi, M Bigi, MS Bilenky, P Billoir, J Bjarne, D Bloch, J Blocki, S Blyth, V Bocci, PN Bogolubov, T Bolognese, M Bonesini, W Bonivento, PSL Booth, G Borisov, C Bosio, B Bostjancic, S Bosworth, O Botner, B Bouquet, C Bourdarios, TJV Bowcock, M Bozzo, S Braibant, P Branchini, KD Brand, RA Brenner, H Briand, C Bricman, L Brillault, RCA Brown, JM Brunet, L Bugge, T Buran, A Buys, JAMA Buytaert, M Caccia, M Calvi, AJC Rozas, R Campion, T Camporesi, V Canale, K Cankocak, F Cao, F Carena, P Carrilho, L Carroll, R Cases, C Caso, MVC Gimenez, A Cattai, FR Cavallo, L Cerrito, V Chabaud, A Chan, P Charpentier, J Chauveau, P Checchia

Abstract:

During the 1992 running period of the LEP e+e- collider, the DELPHI experiment accumulated approximately 24 pb- of data at the Z0 peak. The decays into hadrons and charged leptons have been analysed to give values for the cross sections and leptonic forward-backward asymmetries which are significantly improved with respect to those previously published by the DELPHI collaboration. Incorporating these new data, more precise values for the Z0 resonance parameters are obtained from model-independent fits. The results are interpreted within the framework of the Standard Model, yielding for the top quark mass mt = 157-48+36(expt.)-20+19(Higgs ) GeV, and for the effective mixing angle sin2 θefflept = 0.2328 ± 0.0013 (expt.)-0.0003+0.0001(Higgs), where (Higgs) represents the variation due to Higgs boson mass in the range 60 to 1000 GeV, with central value 300 GeV. © 1994.
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