Charm physics at BESIII Weidenkaff, P
Journal of physics. Conference series,
01/2019, Letnik:
1137, Številka:
1
Journal Article
Recenzirano
Odprti dostop
The study of mesons and baryons which contain at least one charm quark is referred to as open charm physics. It offers the possibility to study up-type quark transitions. Since the quark can not be ...treated in any mass limit, theoretical predictions are difficult and experimental input is crucial. BESIII collected large data samples of e+e− collisions at several charm thresholds. The at-threshold decay topology offers special opportunities to study open charm decays. We present a selection of recent BESIII results: The measurement of the branching fraction D s + → p n ¯ , the form factor of neutral D decays to K−µ+νµ as well as the search for rare decays D → h(h′)e+e−. Recent results on Λ c + decays are presented in 1.
Charm physics at BESIII Weidenkaff, P
Journal of physics. Conference series,
11/2016, Letnik:
770, Številka:
1
Journal Article
Recenzirano
Odprti dostop
The study of mesons and baryons which contain at least one charm quark is referred to as open charm physics. It offers the possibility to study up-type quark transitions. Since the c quark can not be ...treated in any mass limit, theoretical predictions are difficult and experimental input is crucial. BESIII collected large data samples of e+e- collisions at several charm thresholds. The at-threshold decay topology offers special opportunities to study open charm decays. We present a selection of recent BESIII results. The D+s decay constant is measured using the leptonic decays to μ+ν and τ+ ν. Using the semi-leptonic decays of D0 and D± to Ke+νe and πe+νe, a measurement of the form factors f+K (q2) and f+π (q2) is performed and furthermore, we show preliminary results of a model independent measurement of the strong phase difference between D0 and D0 in the channel D0 → Ks0π+π- which is an experimental input to the measurement of the CKM angle γ/φ3.
The CBM (Compressed Baryonic Matter) experiment constructed at FAIR (Facility for Anti-proton and Ion Research) at GSI, Darmstadt, Germany, will provide unique research opportunities to explore the ...phase diagram of nuclear matter. As one of the core detectors in the CBM experiment, the Time-of-Flight (TOF) system applies the MRPC (Multi-gap Resistive Plate Chamber) for a precise particle identification for all the incident charged hadrons. The CBM-TOF will be operated at an ion beam intensity up to 109/s, which means the particle fluxes on the TOF wall can reach an unprecedentedly high rate of 30 kHz/cm2. Almost half of the MRPC counters are from the inner region of the TOF wall, and they will be assembled with the low-resistive glass which enables them to work under such high rate. This is the first time of the large scale application of the low-resistive glass MRPCs into the nuclear and high-energy physics experiments. It is especially important to study on the production and test procedure to keep the good performance of all these counters. For this mass production, we have developed a set of specified manufacturing procedure and quality control method to guarantee the performance of all the counters. A newly developed method to check the uniformity of the gas gap with help of the projection imaging technique has been first applied. Until now, 73 MRPCs have been produced for the eTOF project in the BESII detector upgrade at STAR and the TOF system of mini-CBM. Tested by cosmic ray in a system based on TRB, all the produced counters show a stable performance of above 95% efficiency and below 90 ps time resolution. The study on the mass production of the low-resistive plate chamber will provide experience for wide application of MRPC into the high rate experiments in the future. In this paper, the counter design, manufacturing procedures, quality control methods and test results for this MRPC counter are described in a detailed way.
We report precision measurements of hypernuclei $^3_ΛH$ and $^4_ΛH$ lifetimes obtained from Au + Au collisions at $\sqrt{sNN}$ = 3.0 GeV and 7.2 GeV collected by the STAR experiment at the ...Relativistic Heavy Ion Collider, and the first measurement of $^3_ΛH$ and $^4_ΛH$ midrapidity yields in Au + Au collisions at $\sqrt{sNN}$ = 3.0 GeV. $^3_ΛH$ and $^4_ΛH$, being the two simplest bound states composed of hyperons and nucleons, are cornerstones in the field of hypernuclear physics. Their lifetimes are measured to be 221 ± 15 (stat) ± 19 (syst) ps for $^3_ΛH$ and 218 ± 6 (stat) ± 13 (syst) ps for $^4_ΛH$. The pT-integrated yields of $^3_ΛH$ and $^4_ΛH$ are presented in different centrality and rapidity intervals. It is observed that the shape of the rapidity distribution of $4_ΛH$ is different for 0%–10% and 10%–50% centrality collisions. Thermal model calculations, using the canonical ensemble for strangeness, describes the $^3_ΛH$ yield well, while underestimating the $^4_ΛH$ yield. Transport models, combining baryonic mean-field and coalescence (jam) or utilizing dynamical cluster formation via baryonic interactions (phqmd) for light nuclei and hypernuclei production, approximately describe the measured $^3_ΛH$ and $^4_ΛH$ yields. Our measurements provide means to precisely assess our understanding of the fundamental baryonic interactions with strange quarks, which can impact our understanding of more complicated systems involving hyperons, such as the interior of neutron stars or exotic hypernuclei.
We report the beam energy and collision centrality dependence of fifth and sixth order cumulants (C_{5}, C_{6}) and factorial cumulants (κ_{5}, κ_{6}) of net-proton and proton number distributions, ...from center-of-mass energy (sqrts_{NN}) 3 GeV to 200 GeV Au+Au collisions at RHIC. Cumulant ratios of net-proton (taken as proxy for net-baryon) distributions generally follow the hierarchy expected from QCD thermodynamics, except for the case of collisions at 3 GeV. The measured values of C_{6}/C_{2} for 0%-40% centrality collisions show progressively negative trend with decreasing energy, while it is positive for the lowest energy studied. These observed negative signs are consistent with QCD calculations (for baryon chemical potential, μ_{B}≤110 MeV) which contains the crossover transition range. In addition, for energies above 7.7 GeV, the measured proton κ_{n}, within uncertainties, does not support the two-component (Poisson+binomial) shape of proton number distributions that would be expected from a first-order phase transition. Taken in combination, the hyperorder proton number fluctuations suggest that the structure of QCD matter at high baryon density, μ_{B}∼750 MeV at sqrts_{NN}=3 GeV is starkly different from those at vanishing μ_{B}∼24 MeV at sqrts_{NN}=200 GeV and higher collision energies.
The chiral magnetic effect (CME) refers to charge separation along a strong magnetic field due to imbalanced chirality of quarks in local parity and charge-parity violating domains in quantum ...chromodynamics. The experimental measurement of the charge separation is made difficult by the presence of a major background from elliptic azimuthal anisotropy. This background and the CME signal have different sensitivities to the spectator and participant planes, and could thus be determined by measurements with respect to these planes. We report such measurements in Au+Au collisions at a nucleon-nucleon center-of-mass energy of 200 GeV at the Relativistic Heavy-Ion Collider. It is found that the charge separation, with the flow background removed, is consistent with zero in peripheral (large impact parameter) collisions. Some indication of finite CME signals is seen with a significance of 1–3 standard deviations in mid-central (intermediate impact parameter) collisions. Furthermore, significant residual background effects may, however, still be present.
The STAR Collaboration reports measurements of back-to-back azimuthal correlations of di-π0s produced at forward pseudorapidities (2.6<η<4.0) in p+p, p+Al, and p+Au collisions at a center-of-mass ...energy of 200 GeV. We observe a clear suppression of the correlated yields of back-to-back π0 pairs in p+Al and p+Au collisions compared to the p+p data. The observed suppression of back-to-back pairs as a function of transverse momentum suggests nonlinear gluon dynamics arising at high parton densities. Furthermore, the larger suppression found in p+Au relative to p+Al collisions exhibits a dependence of the saturation scale $Q^{2}_{s}$ on the mass number A . A linear scaling of the suppression with A1/3 is observed with a slope of -0.09±0.01.
Elliptic flow measurements from two-, four-, and six-particle correlations are used to investigate flow fluctuations in collisions of U+U at sqrts_{NN}=193 GeV, Cu+Au at sqrts_{NN}=200 GeV and ...Au+Au spanning the range sqrts_{NN}=11.5-200 GeV. The measurements show a strong dependence of the flow fluctuations on collision centrality, a modest dependence on system size, and very little if any, dependence on particle species and beam energy. The results, when compared to similar LHC measurements, viscous hydrodynamic calculations, and trento model eccentricities, indicate that initial-state-driven fluctuations predominate the flow fluctuations generated in the collisions studied.
The deconfined quark-gluon plasma (QGP) created in relativistic heavy-ion collisions enables the exploration of the fundamental properties of matter under extreme conditions. Noncentral collisions ...can produce strong magnetic fields on the order of 1018 G, which offers a probe into the electrical conductivity of the QGP. In particular, quarks and antiquarks carry opposite charges and receive contrary electromagnetic forces that alter their momenta. This phenomenon can be manifested in the collective motion of final-state particles, specifically in the rapidity-odd directed flow, denoted as v1(y). Here, we present the charge-dependent measurements of dv1/dy near midrapidities for π±, K±, and $p(\bar{p})$ in Au+Au and isobar $(^{96}_{44}Ru+^{96}_{44}Ru$ and $^{96}_{40}Zr+^{96}_{40}Zr)$ collisions at $\sqrt{s_{NN}}=200$ GeV, and in Au+Au collisions at 27 GeV, recorded by the STAR detector at the Relativistic Heavy Ion Collider. The combined dependence of the v1 signal on collision system, particle species, and collision centrality can be qualitatively and semi-quantitatively understood as several effects on constituent quarks. While the results in central events can be explained by the u and d quarks transported from initial-state nuclei, those in peripheral events reveal the impacts of the electromagnetic field on the QGP. Our data put valuable constraints on the electrical conductivity of the QGP in theoretical calculations.
The STAR collaboration reports a measurement of the transverse single-spin asymmetries, AN , for neutral pions produced in polarized proton collisions with protons ( pp ), with aluminum nuclei ( pAl ...) and with gold nuclei ( pAu ) at a nucleon-nucleon center-of-mass energy of 200 GeV. Neutral pions are observed in the forward direction relative to the transversely polarized proton beam, in the pseudorapidity region 2.7<η<3.8 . Results are presented for π0 s observed in the STAR forward meson spectrometer electromagnetic calorimeter in narrow Feynman x ( xF ) and transverse momentum ( pT ) bins, spanning the range 0.17<xF<0.81 and 1.7<pT<6.0 GeV/c . For fixed xF<0.47 , the asymmetries are found to rise with increasing transverse momentum. For larger xF , the asymmetry flattens or falls as pT increases. Parametrizing the ratio r ( A ) ≡AN ( pA ) / AN ( pp ) =AP over the kinematic range, the ratio r ( A ) is found to depend only weakly on A , with ( P ) =-0.027±0.005 . No significant difference in P is observed between the low- pT region, pT<2.5 GeV/c , where gluon saturation effects may play a role, and the high- pT region, pT>2.5 GeV/c . It is further observed that the value of AN is significantly larger for events with a large- pT isolated π0 than for events with a nonisolated π0 accompanied by additional jetlike fragments. The nuclear dependence r ( A ) is similar for isolated and nonisolated π0 events.
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