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Gerard Smadja

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I have been involved in Particle Physics from my PHD (1969) till 2004, with a permanent position first at CEN Saclay (1965-1989), then as a professor at the University of Lyon. After two years in LBL as a Postdoc (Miller Fellow from 1969 to 1972) I participated into experiments at CERN. In 2004, I started a collaboration with the team of Saul Perlmutter on the Nearby Supernova Factory, using the SNIFS Integral Field soectrograph, built in Lyon. I am now involved in the European EUCLID project for Cosmology, a satellite to be launched by ESA.

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Papers by Gerard Smadja

Determination of Afb at the Z pole using inclusive charge reconstruction and lifetime tagging

A novel method measures the b quark forward-backward asymmetry at the Z pole on a sample of 3,560... more A novel method measures the b quark forward-backward asymmetry at the Z pole on a sample of 3,560,890 hadronic events collected with the DELPHI detector in 1992 to 2000. An enhanced impact parameter tag provides a high purity b sample. For event hemispheres with a reconstructed secondary vertex the charge of the corresponding quark or anti-quark is determined using a neural network tag which combines in an optimal way the full available charge information from the vertex charge, the jet charge and from identified leptons and hadrons. The probability of correctly identifying b quarks and anti-quarks is measured on the data themselves comparing the rates of double hemisphere tagged like-sign and unlike-sign events. The b quark forward-backward asymmetry is determined from the differential asymmetry, taking small corrections due to hemisphere correlations and background contributions into account. The results for different centre-of-mass energies are: A b F B (89.449 GeV) = 0.0637 ± 0.0143(stat.) ± 0.0017(syst.) A b F B (91.231 GeV) = 0.0958 ± 0.0032(stat.) ± 0.0014(syst.) A b F B (92.990 GeV) = 0.1041 ± 0.0115(stat.) ± 0.0024(syst.) Combining these results yields the b quark pole asymmetry A b,0 F B = 0.0978 ± 0.0030(stat.) ± 0.0014(syst.

Study of rare b decays with the DELPHI detector at LEP

Zeitschrift Fur Physik C-Particles and Fields, 1996

A study of the reaction e(+)e(-)->mu(+)mu(-)gamma(ISR) at LEP and search for new physics at annihilation energies near 80 GeV

Zeitschrift Fur Physik C-Particles and Fields, 1997

A study of the channel e + e ! + ISR , where ISR is an initial state radiation photon, is present... more A study of the channel e + e ! + ISR , where ISR is an initial state radiation photon, is presented using data collected by the DELPHI experiment from 1991 to 1994. The total cross-section at eective annihilation energies ( p s 0 ) below the Z 0 peak is obtained by using the events with relatively hard initial state radiative photon(s) (E > 1 GeV). The dierential cross-section as a function of the muon polar production angle is also determined in order to extract the forward-backward asymmetries for the reaction e + e ! + at energies p s 0 between 20 and 87 GeV. The ratio of the helicity cross-sections LL + RR RL + LR , where the two subscripts stand for the helicities of the incoming e and outgoing respectively, is extracted from the dierential cross-sections in order to test the Standard Model and to look for new physics near 80 GeV. No deviations from the Standard Model were found.

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

Physics Letters B, 1996

A search for fully reconstructed 0 b beauty baryons is performed using about 3 million Z decays c... more A search for fully reconstructed 0 b beauty baryons is performed using about 3 million Z decays collected with the DELPHI detector at LEP. The analysis relies on the combined use of the accurate tracking and of the hadron identication capabilities of DELPHI. A total of four events has been found, three in the + c channel and one in the + c a 1 channel over a small background. The 0 b beauty baryon mass is measured to be ( 5668 16 (stat:) 8 (syst:) ) MeV/c 2 .

Λb polarization in Z0 decays at LEP

Physics Letters B, 2000

The longitudinal polarization of the b baryon is measured at the LEP e + e collider by DELPHI. It... more The longitudinal polarization of the b baryon is measured at the LEP e + e collider by DELPHI. It is determined from the charged lepton and neutrino energy spectra in 24919 b semileptonic decays reconstructed in 3.5 million hadronic Z 0 decays using 0 -lepton correlations. The measured polarization is:

Measurement of inclusive f1(1285) and f1(1420) production in Z decays with the DELPHI detector

Physics Letters B, 2003

DELPHI results are presented on the inclusive production of two (K Kπ) 0 states in the mass regio... more DELPHI results are presented on the inclusive production of two (K Kπ) 0 states in the mass region 1.2-1.6 GeV/c 2 in hadronic Z decays at LEP I. The measured masses (widths) are 1274±6 MeV /c 2 (29±12 MeV/c 2 ) and 1426±6 MeV /c 2 (51±14 MeV/c 2 ) respectively. A partial-wave analysis of the (K Kπ) 0 system shows that the first peak is consistent with the I G (J P C ) = 0 + (1 ++ )/(0 -+ ) a 0 (980)π and the second with the I G (J P C ) = 0 + (1 ++ ) K * (892) K + c.c. assignments. The total hadronic production rates per hadronic Z decay are (0.165 ± 0.051) and (0.056 ± 0.012) respectively. These measurements are consistent with the two states being the f 1 (1285) and f 1 (1420) mesons.

Measurements of the trilinear gauge boson couplings WWV (V≡γ,Z) in e+e− collisions at 183 GeV

Physics Letters B, 1999

Measurements of the trilinear gauge boson couplings W W γ and W W Z are presented from data taken... more Measurements of the trilinear gauge boson couplings W W γ and W W Z are presented from data taken by DELPHI in 1997 at an energy of 183 GeV. From a study of the reactions e + e -→ W + W -, e + e -→ W eν and e + e -→ ννγ, values are obtained for ∆g Z 1 and ∆κ γ , the differences of the W W Z charge coupling and of the W W γ dipole couplings from their Standard Model values, and for λ γ , the W W γ quadrupole coupling. The observations are consistent with the predictions of the Standard Model.

Measurement of trilinear gauge boson couplings fromWW+WZ→lνjjevents inpp¯collisions ats=1.96 TeV

Physical Review D, 2009

We present a direct measurement of trilinear gauge boson couplings at WW and ZWW vertices in WW a... more We present a direct measurement of trilinear gauge boson couplings at WW and ZWW vertices in WW and WZ events produced in p " p collisions at ffiffi ffi s p ¼ 1:96 TeV. We consider events with one electron or muon, missing transverse energy, and at least two jets. The data were collected using the D0 detector and correspond to 1:1 fb À1 of integrated luminosity. Considering two different relations between the couplings at the WW and ZWW vertices, we measure these couplings at 68% C.L. to be ¼ 1:07 þ0:26 À0:29 , ¼ 0:00 þ0:06 À0:06 , and g Z 1 ¼ 1:04 þ0:09 À0:09 in a scenario respecting SUð2Þ L Uð1Þ Y gauge symmetry and ¼ 1:04 þ0:11 À0:11 and ¼ 0:00 þ0:06 À0:06 in an ''equal couplings'' scenario.

Determination of Z0 resonance parameters and couplings from its hadronic and leptonic decays

Nuclear Physics B, 1991

Performance of the DELPHI detector

Nuclear Instruments and Methods in Physics Research Section A: Accelerators, Spectrometers, Detectors and Associated Equipment, 1996

DELPHI (DEtector with Lepton, Photon and Hadron Identification) is a detector for e+e-physics, de... more DELPHI (DEtector with Lepton, Photon and Hadron Identification) is a detector for e+e-physics, designed to provide high granularity over a 47r solid angle, allowing an effective particle identification. It has been operating at the LEP (Large Electron-Positron) collider at CERN since 1989. This article reviews its performance.

Determination of A FB b at the Z pole using inclusive charge reconstruction and lifetime tagging

The European Physical Journal C, 2005

A novel high precision method measures the b-quark forward-backward asymmetry at the Z pole on a ... more A novel high precision method measures the b-quark forward-backward asymmetry at the Z pole on a sample of 3,560,890 hadronic events collected with the DELPHI detector in 1992 to 2000. An enhanced impact parameter tag provides a high purity b sample. For event hemispheres with a reconstructed secondary vertex the charge of the corresponding quark or anti-quark is determined using a neural network which combines in an optimal way the full available charge information from the vertex charge, the jet charge and from identified leptons and hadrons. The probability of correctly identifying b-quarks and anti-quarks is measured on the data themselves comparing the rates of double hemisphere tagged like-sign and unlike-sign events. The b-quark forward-backward asymmetry is determined from the differential asymmetry, taking small corrections due to hemisphere correlations and background contributions into account. The results for different centre-of-mass energies are: A b F B (89.449 GeV) = 0.0637 ± 0.0143(stat.) ± 0.0017(syst.) A b F B (91.231 GeV) = 0.0958 ± 0.0032(stat.) ± 0.0014(syst.) A b F B (92.990 GeV) = 0.1041 ± 0.0115(stat.) ± 0.0024(syst.) Combining these results yields the b-quark pole asymmetry A b,0 F B = 0.0972 ± 0.0030(stat.) ± 0.0014(syst.

Study of dimuon production in photon-photon collisions and measurement of QED photon structure functions at LEP

The European Physical Journal C, 2001

Muon pair production in the process e + e , ! e + e , + , is studied using the data taken at LEP1... more Muon pair production in the process e + e , ! e + e , + , is studied using the data taken at LEP1 p s ' m Z with the DELPHI detector during the years 1992-1995. The corresponding integrated luminosity is 138.5 pb ,1 . The QED predictions have been tested over the whole Q 2 range accessible at LEP1 from several GeV 2 =c 4 to several hundred GeV 2 =c 4 b y comparing experimental distributions with distributions resulting from Monte Carlo simulations using various generators. Selected events are used to extract the leptonic photon structure function F 2 . Azimuthal correlations are used to obtain information on additional structure functions, F A and F B , which originate from interference terms of the scattering amplitudes. The measured ratios F A =F 2 and F B =F 2 are signi cantly di erent from zero and consistent with QED predictions.

Measurement and interpretation of the W-pair cross-section in e+e− interactions at 161 GeV

Physics Letters B, 1997

In 1996 LEP ran at a centre-of-mass energy of 161 GeV, just above the threshold of W-pair product... more In 1996 LEP ran at a centre-of-mass energy of 161 GeV, just above the threshold of W-pair production. DELPHI accumulated data corresponding to an integrated luminosity o f 9 : 93 pb 1 , and observed 29 events that are considered as candidates for W-pair production. From these, a cross-section for the doubly resonant e + e ! WW process of 3:67 +0:97 0:85 0:19 pb has been measured. Within the Standard Model, this cross-section corresponds to a mass of the Wboson of 80:40 0:44 (stat:) 0:09 (syst:) 0:03 (LEP) GeV=c 2 . Alternatively, i f m W is held xed at its current v alue determined by other experiments, the observed cross-section is used to obtain limits on trilinear WWV(V ;Z) couplings.

Search for doubly-charged Higgs bosons at LEP

Phys.Lett., 2003

Doubly-charged Higgs bosons are searched for in e + e -collision data collected with the L3 detec... more Doubly-charged Higgs bosons are searched for in e + e -collision data collected with the L3 detector at LEP at centre-of-mass energies up to 209 GeV. Final states with four leptons are analysed to tag the pair-production of doubly-charged Higgs bosons. No significant excess is found and lower limits at 95% confidence level on the doubly charged Higgs boson mass are derived. They vary from 95.5 GeV to 100.2 GeV, depending on the decay mode. Doubly-charged Higgs bosons which couple to electrons would modify the cross section and forward-backward asymmetry of the e + e -→ e + e -process. The measurements of these quantities do not deviate from the Standard Model expectations and doubly-charged Higgs bosons with masses up to the order of a TeV are excluded.

Study of inclusive J/ψ production in two-photon collisions at LEP II with the DELPHI detector

Physics Letters B, 2003

Inclusive J/ψ production in photon-photon collisions has been observed at LEP II beam energies. A... more Inclusive J/ψ production in photon-photon collisions has been observed at LEP II beam energies. A clear signal from the reaction γγ → J/ψ + X is seen. The number of observed N(J/ψ → µ + µ -) events is 36 ± 7 for an integrated luminosity of 617 pb -1 , yielding a cross-section of σ(J/ψ + X) = 45 ± 9(stat) ± 17(syst) pb. Based on a study of the event shapes of different types of γγ processes in the PYTHIA program, we conclude that (74 ± 22)% of the observed J/ψ events are due to 'resolved' photons, the dominant contribution of which is most probably due to the gluon content of the photon.

Kaon interference in the hadronic decays of the Z0

Physics Letters B, 1996

The rst measurement of like-sign charged kaon correlations in hadronic decays of the Z 0 is prese... more The rst measurement of like-sign charged kaon correlations in hadronic decays of the Z 0 is presented, based on data collected by the DELPHI detector. The charged kaons are identied by means of ring imaging Cherenkov detectors. A signicant enhancement at small values of the four-momentum dierence is observed in the ratio of like-sign to unlike-sign KK pairs and in the ratio of likesign pairs to a simulated reference sample. An update of the measurement o f K 0 S K 0 S interference is also presented. An enhancement is found in the production of pairs of K 0 S of similar momenta, as compared with a simulated reference sample. The measured Bose-Einstein correlation parameters and r are similar for charged and neutral kaon pairs. The value of the Bose-Einstein correlation strength is consistent with unity.

Limits on the production of scalar leptoquarks from Z0 decays at LEP

Physics Letters B, 1993

A search has been made for pairs and for single production of scalar leptoquarks of the rst and s... more A search has been made for pairs and for single production of scalar leptoquarks of the rst and second generations using a data sample of 392000 Z o decays from the DELPHI detector at LEP 1. No signal was found and limits on the leptoquark mass, production cross section and branching ratio were set. A mass limit at 95 % condence level of 45.5 GeV/c 2 was obtained for leptoquark pair production. The search for the production of a single leptoquark probed the mass region above this limit and its results exclude rst and second generation leptoquarks D o with masses below 65 GeV/c 2 and 73 GeV/c 2 respectively, at 95% condence level, assuming that the D o lq Yukawa coupling is equal to the electromagnetic one. An upper limit is also given on the coupling as a function of the leptoquark mass m Do .

Identified particles in quark and gluon jets

Physics Letters B, 1997

A sample of about 1.4 million hadronic Z decays, selected among the data recorded by the DELPHI d... more A sample of about 1.4 million hadronic Z decays, selected among the data recorded by the DELPHI detector at LEP during 1994, was used to measure for the rst time the momentum spectra of K + , K 0 , p, and their antiparticles in gluon and quark jets. As observed for inclusive c harged particles, the production spectra of identied particles were found to be softer in gluon jets than in quark jets, with a higher total multiplicity.

Hadronization properties of b quarks compared to light quarks in from 183 to 200 GeV

Physics Letters B, 2000

The DELPHI detector at LEP has collected 54 pb -1 of data at a centre-of-mass energy around 183 G... more The DELPHI detector at LEP has collected 54 pb -1 of data at a centre-of-mass energy around 183 GeV during 1997, 158 pb -1 around 189 GeV during 1998, and 187 pb -1 between 192 and 200 GeV during 1999. These data were used to measure the average charged particle multiplicity in e + e -→ b b events, n b b, and the difference δ bl between n b b and the multiplicity, n l l, in generic light quark (u,d,s) events: δ bl (183 GeV) = 4.55 ± 1.31(stat) ± 0.73(syst) δ bl (189 GeV) = 4.43 ± 0.85(stat) ± 0.61(syst) δ bl (200 GeV) = 3.39 ± 0.89(stat) ± 1.01(syst) . This result is consistent with QCD predictions, while it is inconsistent with calculations assuming that the multiplicity accompanying the decay of a heavy quark is independent of the mass of the quark itself.

Search for the Fermiophobic Higgs at LEP

Nuclear Physics B - Proceedings Supplements, 2002

Higgs bosons predicted by the fermiophobic scenario within Two Higgs Doublets Models were searche... more Higgs bosons predicted by the fermiophobic scenario within Two Higgs Doublets Models were searched for in the data collected by the DELPHI detector at centre-of-mass energies between 189 GeV and 202 GeV, corresponding to a total integrated luminosity of 380 pb -1 . No signal was found and confidence limits were derived in the framework of possible extensions of the Standard Model Higgs sector.