The design and construction of the ZEUS central tracking detector

Abt²,

et al. 2014

J. High Energ. Phys.

Self Cite

The production of beauty and charm quarks in ep interactions has been studied with the ZEUS detector at HERA for exchanged four-momentum squared 5 < Q 2 < 1000 GeV 2 using an integrated luminosity of 354 pb −1 . The beauty and charm content in events with at least one jet have been extracted using the invariant mass of charged tracks associated with secondary vertices and the decay-length significance of these vertices. Differential cross sections as a function of Q 2 , Bjorken x, jet transverse energy and pseudorapidity were measured and compared with next-to-leading-order QCD calculations. The beauty and charm contributions to the proton structure functions were extracted from the double-differential cross section as a function of x and Q 2 . The running beauty-quark mass, m b at the scale m b , was determined from a QCD fit at next-to-leading order to HERA data for the first time and found to be m b (m b ) = 4.07 ± 0.14 (fit) +0.01 −0.07 (mod.) +0.05 −0.00 (param.) +0.08 −0.05 (theo.) GeV.Keywords: Lepton-Nucleon Scattering, QCD, Jets, B physics The ZEUS collaboration 53 IntroductionThe measurement of beauty and charm production in ep collisions at HERA is an important testing ground for perturbative Quantum Chromodynamics (pQCD), since the heavy-quark masses provide a hard scale that allows perturbative calculations to be made. At leading order, the dominant process for heavy-quark production at HERA is boson-gluon fusion (BGF). In this process, a virtual photon emitted by the incoming electron interacts with a gluon from the proton forming a heavy quark-antiquark pair. When the negative squared four-momentum of the virtual photon, Q 2 , is large compared to the proton mass, the interaction is referred to as deep inelastic scattering (DIS). For heavy-quark transverse momenta comparable to the quark mass, next-to-leading-order (NLO) QCD calculations based on the dynamical generation of the massive quarks [1][2][3][4] are expected to provide reliable predictions. Beauty and charm production in DIS has been measured using several methods by the H1 [5][6][7][8][9][10][11][12][13][14][15][16] and ZEUS [17][18][19][20][21][22][23][24][25][26][27][28][29][30][31] Inclusive jet cross sections in beauty and charm events are used in the analysis presented here to extract the heavy-quark contribution to the proton structure function F 2 with high precision, and to measure the b-quark mass. For this purpose, the long lifetimes of the weakly decaying b and c hadrons, which make the reconstruction of their decay vertices possible, as well as their large masses were exploited. Two discriminating variables, the significance of the reconstructed decay length and the invariant mass of the charged tracks associated with the decay vertex (secondary vertex), were used. This inclusive tagging method leads to a substantial increase in statistics with respect to previous ZEUS measurements.Differential cross sections as a function of Q 2 , the Bjorken scaling variable, x, jet transverse energy, E jet T , and pseudorapidit...

Section: Experimental Set-upmentioning

confidence: 99%

Measurement of beauty and charm production in deep inelastic scattering at HERA and measurement of the beauty-quark mass

Abt²,

et al. 2014

J. High Energ. Phys.

Self Cite

“…In the kinematic range of the analysis, charged particles were tracked in the central tracking detector (CTD) [19][20][21] and the microvertex detector (MVD) [22]. These components operated in a magnetic field of 1.43 T provided by a thin superconducting solenoid.…”

Section: Jhep09(2013)058mentioning

confidence: 99%

Measurement of charm fragmentation fractions in photoproduction at HERA

Abt²,

et al. 2013

J. High Energ. Phys.

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The production of D 0 , D * + , D + , D + s and Λ + c charm hadrons and their antiparticles in ep scattering at HERA has been studied with the ZEUS detector, using a total integrated luminosity of 372 pb −1 . The fractions of charm quarks hadronising into a particular charm hadron were derived. In addition, the ratio of neutral to charged D-meson production rates, the fraction of charged D mesons produced in a vector state, and the stangenesssuppression factor have been determined. The measurements have been performed in the photoproduction regime. The charm hadrons were reconstructed in the range of transverse momentum p T > 3.8 GeV and pseudorapidity |η| < 1.6. The charm fragmentation fractions are compared to previous results from HERA and from e + e − experiments. The data support the hypothesis that fragmentation is independent of the production process. 6 Charm-hadron production cross sections 11 The ZEUS collaboration 24 IntroductionThe fragmentation fractions of charm quarks into specific charm hadrons cannot be predicted by Quantum Chromodynamics (QCD) and have to be measured. It is usually assumed that they are universal, i.e. the same for charm quarks produced in e + e − annihilation, in ep collisions and also in pp or other hadronic collisions, even though the charm production mechanisms are not the same: in e + e − collisions, cc pairs are produced dominantly by QED pair production, whereas in ep collisions, the main production mechanism is the QCD boson-gluon fusion process γg → cc. The fragmentation universality can be tested by measuring the fragmentation fractions at HERA and comparing the results with those obtained with e + e − collisions. Additionally, the values of the fragmentation fractions are crucial parameters used in comparisons of perturbative QCD (pQCD) calculations with measurements of charm production at HERA and elsewhere.-1 - JHEP09(2013)058In this paper, measurements of the photoproduction of charm hadrons in ep collisions at HERA are presented. The relative production rates of the most copiously produced charm ground states, the D In addition, the ratio of neutral to charged D-meson production rates, the fraction of charged D mesons produced in a vector state, and the strangeness-suppression factor were determined.The analysis presented here is based on an independent data set with an integrated luminosity over 4.5 times larger than the previous ZEUS measurement [1]. The new measurement benefits also from the ZEUS microvertex detector (MVD), which made it possible to identify the secondary decay vertices of the charm ground states and thereby to suppress background significantly. The new results are compared to the previous ZEUS measurement [1] in photoproduction, other HERA results from H1 [2] and ZEUS [3,4] in deep inelastic scattering, and to results from experiments at the e + e − storage rings CLEO [5,6], ARGUS [7][8][9] and the LEP experiments [10][11][12][13][14][15]. A summary is given in [16], with an update to 2010 branching ratios [17].

“…In the kinematic range of the analysis, charged particles were tracked in the central tracking detector (CTD) [5][6][7], which operated in a magnetic field of 1.43 T provided by a thin superconducting solenoid. The CTD consisted of 72 cylindrical drift-chamber layers, organised in nine superlayers covering the polar-angle 2 region 15 • < θ < 164 • .…”

Section: Experimental Set-upmentioning

confidence: 99%

Measurement of the cross-section ratio sigma(psi(2S))/sigma(J/psi(1S)) in deep inelastic exclusive ep scattering at HERA

Abt²,

Proceedings of XXIV International Workshop on Deep-Inelastic Scattering and Related Subjects — PoS(DIS2016)

et al. 2016

The exclusive deep inelastic electroproduction of ψ(2S) and J/ψ(1S) at an ep centre-of-mass energy of 317 GeV has been studied with the ZEUS detector at HERA in the kinematic range 2 < Q 2 < 80 GeV 2 , * ZEUS Collaboration / Nuclear Physics B 909 (2016) 934-953 937 30 < W < 210 GeV and |t| < 1 GeV 2 , where Q 2 is the photon virtuality, W is the photon-proton centre-of-mass energy and t is the squared four-momentum transfer at the proton vertex. The data for 2 < Q 2 < 5 GeV 2 were taken in the HERA I running period and correspond to an integrated luminosity of 114 pb −1 . The data for 5 < Q 2 < 80 GeV 2 are from both HERA I and HERA II periods and correspond to an integrated luminosity of 468 pb −1 . The decay modes analysed were μ + μ − and J/ψ(1S) π + π − for the ψ(2S) and μ + μ − for the J/ψ(1S). The cross-section ratio σ ψ(2S) /σ J/ψ(1S) has been measured as a function of Q 2 , W and t. The results are compared to predictions of QCD-inspired models of exclusive vector-meson production.