2,536 research outputs found
LHCspin: A polarized internal target for the LHC
No full textThe LHCspin project aims to bring both unpolarized and polarized physics at the LHC through the installation of a gaseous fixed target at the upstream end of the LHCb detector. The forward geometry of the LHCb spectrometer (2 < η < 5) is perfectly suited for the reconstruction of particles produced in fixed-target collisions. The fixed-target configuration, with center-of-mass energies ranging from √sNN = 72 GeV in collisions with Pb beams to √s = 115 GeV in pp interactions, allows to cover a wide backward center-of-mass rapidity region, corresponding to the poorly explored high x-Bjorken and high x-Feynman regimes. The use of transversely polarized H and D targets will allow to study the quarks TMDs in p-p collisions at unique kinematic conditions. Furthermore, being LHCb specifically designed for heavy-flavor physics, final states with c- or b-quarks (e.g. inclusive quarkonia production) will be efficiently reconstructed, thus providing, among other fundamental measurememnts, access to the so-far unknown gluons TMDs. The contribution focuses on the design considerations of the polarized internal target and on a discussion of possible critical machine issues
Pre-equilibrium α-particle emission as a probe to study α-clustering in nuclei
No full textA theoretical approach was developed to describe secondary particle emission in heavy ion collisions, with special regards to pre-equilibrium α-particle production. The probabilities of neutron, proton and α-particle emission have been evaluated for both the equilibrium and pre-equilibrium stages of the process. Effects due the possible cluster structure of the projectile which has been excited during the collisions have been experimentally evidenced studying the double differential cross sections of p and α-particles emitted in the E=250MeV 16O + 116Sn reaction. Calculations within the present model with different clusterization probabilities have been compared to the experimental data. © Owned by the authors, published by EDP Sciences, 2014
Design Consideration on a Polarized Gas Target for the LHC
No full textSince 2017, the LHCSpin study group is investigating the installation of a HERMES-type polarized gas target (PGT) in front of the LHCb detector in order to perform Single-Spin Transverse Asymmetry (SSTA) measurements. In cooperation with LHC experts, the conditions for applying a PGT are being studied. As a viable option, a cold openable storage cell is considered. A key role for avoiding instabilities of the 7 TeV proton beam is the choice of a proper coating and the suppression of wake fields. A first warm (≈ 300 K) test storage cell is planned for installation in 2019 inside the VELO vessel, subject to final approval. It will improve the ongoing SMOG program of LHCb fixed target measurements, and will provide valuable experience of running a storage cell in the harsh LHC environment. The status of the design considerations on a PGT in the LHC beam and of the discussion of critical machine issues is presented
Observation of the suppressed decay with and measurement of its asymmetry
No full textA study of baryon decays to the final state is
presented based on a proton-proton collision data sample corresponding to an
integrated luminosity of 9 fb collected with the LHCb detector. Two
decays are considered, with and , where represents a superposition of
and states. The latter process is expected to be suppressed
relative to the former, and is observed for the first time. The ratio of
branching fractions of the two decays is measured, and the asymmetry of
the suppressed mode, which is sensitive to the CKM angle , is also
reported
Amplitude analysis of B0? D0Ds+p - and B plus ? D -Ds plus p plus decays
No full textResonant contributions in B0→D ̄D0s+π- and B+→D-Ds+π+ decays are determined with an amplitude analysis, which is performed both separately and simultaneously, where in the latter case isospin symmetry between the decays is assumed. The analysis is based on data collected by the LHCb detector in proton-proton collisions at center-of-mass energies of 7, 8, and 13 TeV. The full data sample corresponds to an integrated luminosity of 9 fb-1. A doubly charged spin-0 open-charm tetraquark candidate together with a neutral partner, both with masses near 2.9 GeV, are observed in the Dsπ decay channel
Observation of Lambda b(0) -> D(+)p pi(-)pi(-) and Lambda b(0) -> D-*+p pi(-)pi(-) decays
No full textThe multihadron decays Lambda(0)(b) -> D(+)p pi(-)pi(-) and Lambda(0 )(b)-> D-*+p pi(-)pi(-) are observed in data corresponding to an integrated luminosity of 3fb(-1), collected in proton-proton collisions at centre-of-mass energies of 7 and 8 TeV by the LHCb detector. Using the decay Lambda(0)(b) -> Lambda(+)(c)pi(+)pi(-)pi(-) as a normalisation channel, the ratio of branching fractions is measured to beB(Lambda(0)(b) -> D(+)p pi(-)pi(-))/B(Lambda(0)(b) -> Lambda(+)(c)pi(+)pi(-)pi(-)) x B(D+ -> K-pi(+)pi(+))/B(Lambda(+)(c)-> pK(-)pi(+)) = (5.35 +/- 0.21 +/- 0.16) %,where the first uncertainty is statistical and the second systematic. The ratio of branching fractions for the Lambda(0)(b)-> D-*+p pi(-)pi(-) and Lambda(0)(b) -> D(+)p pi(-)pi(-) decays is found to beB(Lambda(0)(b)-> D-*+p pi(-)pi(-))/B(Lambda(0)(b) -> D(+)p pi(-)pi(-)) x (B(D-*+-> D+pi(0)) + B(D (*)+-> D- (+)gamma)) = (61.3 +/- 4.3 +/- 4.0) %.LPH
The LHCSpin project
No full textThe LHCspin project aims to bring both unpolarized and polarized physics at the LHC through the installation of a gaseous fixed target at the upstream end of the LHCb detector. The forward geometry of the LHCb spectrometer (2 < η < 5) is perfectly suited for the reconstruction of particles produced in fixed-target collisions. The fixed-target configuration, with center-of-mass energies ranging from √sNN = 72 GeV in collisions with Pb beams to √s = 115 GeV in pp interactions, allows to cover a wide backward center-of-mass rapidity region, corresponding to the poorly explored high x-Bjorken and high x-Feynman regimes. The project has several ambitious goals regarding heavy-ion physics and new-era quantitative searches in QCD through the study of the nucleon's internal dynamics in terms of both quarks and gluons degrees of freedom. In particular, the use of transversely polarized H and D targets will allow to study the quarks TMDs in pp collisions at unique kinematic conditions. Furthermore, being LHCb specifically designed for heavy-flavor physics, final states with c- or b-quarks (e.g. inclusive quarkonia production) will be efficiently reconstructed, thus providing, among other fundamental measurememnts, access to the so-far unknown gluons TMDs. The status of the project is presented along with a selection of physics opportunities
Measurement of prompt D -meson production in p-Pb collisions at sNN =5.02TeV
No full textThe p(T)-differential production cross sections of the prompt charmed mesons D-0, D+, D*(-), and D-s(+) and their charge conjugate in the rapidity interval -0.96 < y(cms) < 0.04 were measured in p-Pb collisions at a center-of-mass energy root s(NN) = 5.02 TeV with the ALICE detector at the LHC. The nuclear modification factor R-pPb, quantifying the D-meson yield in p-Pb collisions relative to the yield in pp collisions scaled by the number of binary nucleon-nucleon collisions, is compatible within the 15%-20% uncertainties with unity in the transverse momentum interval 1 < p(T) < 24 GeV/c. No significant difference among the R-pPb of the four D-meson species is observed. The results are described within uncertainties by theoretical calculations that include initial-state effects. The measurement adds experimental evidence that the modification of the momentum spectrum of D mesons observed in Pb-Pb collisions with respect to pp collisions is due to strong final-state effects induced by hot partonic matter
Measurement of the time-integrated asymmetry in decays
No full textThe time-integrated asymmetry in the Cabibbo-suppressed decay is measured using proton-proton collision data, corresponding to an integrated luminosity of 5.7 fb collected at a center-of-mass energy of 13 TeV with the LHCb detector. The mesons are required to originate from promptly produced decays and the charge of the companion pion is used to determine the flavor of the charm meson at production. The time-integrated asymmetry is measured to be \begin{align*} \mathcal{A}_{C\!P}(K^-K^+) = \left[6.8 \pm 5.4 \text{ (stat)} \pm 1.6 \text{ (syst)} \right]\times 10^{-4}. \end{align*} The direct asymmetries in and decays, and , are derived by combining with the time-integrated asymmetry difference, , giving \begin{alignat*}{2} a_{K^-K^+}^{d} &= (\phantom{2}7.7 \pm 5.7) \times 10^{-4}, \end{alignat*} \begin{alignat*}{2} a_{\pi^-\pi^+}^{d} &= (23.2 \pm 6.1) \times 10^{-4}, \end{alignat*} with a correlation coefficient corresponding to . The compatibility of these results with symmetry is 1.4 and 3.8 standard deviations for and decays, respectively. This is the first evidence for direct violation in a specific decay.The time-integrated CP asymmetry in the Cabibbo-suppressed decay D0→K-K+ is measured using proton-proton collision data, corresponding to an integrated luminosity of 5.7 fb-1 collected at a center-of-mass energy of 13 TeV with the LHCb detector. The D0 mesons are required to originate from promptly produced D*+→D0π+ decays, and the charge of the companion pion is used to determine the flavor of the charm meson at production. The time-integrated CP asymmetry is measured to be ACP(K-K+)=[6.8±5.4±1.6]×10-4 where the first uncertainty is statistical and the second systematic. The direct CP asymmetries in D0→K-K+ and D0→π-π+ decays, aK-K+d and aπ-π+d, are derived by combining ACP(K-K+) with the time-integrated CP asymmetry difference, ΔACP=ACP(K-K+)-ACP(π-π+), and other inputs, giving aK-K+d=(7.7±5.7)×10-4,aπ-π+d=(23.2±6.1)×10-4,with a correlation coefficient corresponding to ρ=0.88. The compatibility of these results with CP symmetry is 1.4 and 3.8 standard deviations for D0→K-K+ and D0→π-π+ decays, respectively. This is the first evidence for direct CP violation in a specific D0 decay.The time-integrated asymmetry in the Cabibbo-suppressed decay is measured using proton-proton collision data, corresponding to an integrated luminosity of 5.7 fb collected at a center-of-mass energy of 13 TeV with the LHCb detector. The mesons are required to originate from promptly produced decays and the charge of the companion pion is used to determine the flavor of the charm meson at production. The time-integrated asymmetry is measured to be \begin{align*} \mathcal{A}_{C\!P}(K^-K^+) = \left[6.8 \pm 5.4 \text{ (stat)} \pm 1.6 \text{ (syst)} \right]\times 10^{-4}. \end{align*} The direct asymmetries in and decays, and , are derived by combining with the time-integrated asymmetry difference, , giving \begin{alignat*}{2} a_{K^-K^+}^{d} &= (\phantom{2}7.7 \pm 5.7) \times 10^{-4}, \end{alignat*}\begin{alignat*}{2} a_{\pi^-\pi^+}^{d} &= (23.2 \pm 6.1) \times 10^{-4}, \end{alignat*} with a correlation coefficient corresponding to . The compatibility of these results with symmetry is 1.4 and 3.8 standard deviations for and decays, respectively. This is the first evidence for direct violation in a specific decay
Measurement of Prompt D-Meson Production in p-Pb Collisions at root s(NN)=5.02 TeV
No full textThe p(T)-differential production cross sections of the prompt charmed mesons D-0, D+, D*(-), and D-s(+) and their charge conjugate in the rapidity interval -0.96 < y(cms) < 0.04 were measured in p-Pb collisions at a center-of-mass energy root s(NN) = 5.02 TeV with the ALICE detector at the LHC. The nuclear modification factor R-pPb, quantifying the D-meson yield in p-Pb collisions relative to the yield in pp collisions scaled by the number of binary nucleon-nucleon collisions, is compatible within the 15%-20% uncertainties with unity in the transverse momentum interval 1 < p(T) < 24 GeV/c. No significant difference among the R-pPb of the four D-meson species is observed. The results are described within uncertainties by theoretical calculations that include initial-state effects. The measurement adds experimental evidence that the modification of the momentum spectrum of D mesons observed in Pb-Pb collisions with respect to pp collisions is due to strong final-state effects induced by hot partonic matter
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