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1.
The measurement of the charmonium (J/ψ, ψ′) and bottomonium (γ, γ′, γ″) resonances and Z 0 boson in nucleus-nucleus collisions provides crucial information on high density QCD matter. The observation of anomalous suppression of J/ψ at the CERN-SPS and RHIC is well established but the clarification of some important questions requires equivalent studies of the γ family, only possible at LHC energies. The Z 0 boson will be produced for the first time in heavy-ion collisions at the LHC and, since its dominant production channel is through q-q fusion, it is an excellent probe of the nuclear modification of quark distribution functions. This paper reports the capabilities of the CMS detector to study quarkonium and Z 0 production in Pb-Pb collisions at 5.5 TeV, through the dimuon decay channel.  相似文献   

2.
The PHENIX experiment has measured, J/ψ, ψ′ and γ productions for different collision systems in the forward rapidities 1.2 < | η | < 2.2 at ?{SNN }\sqrt {S_{NN} } = 200 GeV. We have observed significant suppressions of J/ψ production in both Cu+Cu and Au+Au collisions relative to the yield in p+p system. The measurements of higher mass heavy quarkonia states (ψ′ and γ) will help us to constrain various quarkonium suppression models in heavy ion collisions. A first hint of ψ′ and γ productions in 200GeV p+p collisions has been observed at forward and backward rapidities at PHENIX.  相似文献   

3.
R. Arnaldi  K. Banicz  K. Borer  J. Castor  B. Chaurand  W. Chen  C. Cicalò  A. Colla  P. Cortese  S. Damjanovic  A. David  A. de Falco  A. Devaux  L. Ducroux  H. En’yo  J. Fargeix  A. Ferretti  M. Floris  A. F?rster  P. Force  N. Guettet  A. Guichard  H. Gulkanian  J. M. Heuser  M. Keil  L. Kluberg  Z. Li  C. Louren?o  J. Lozano  F. Manso  P. Martins  A. Masoni  A. Neves  H. Ohnishi  C. Oppedisano  P. Parracho  P. Pillot  T. Poghosyan  G. Puddu  E. Radermacher  P. Ramalhete  P. Rosinsky  E. Scomparin  J. Seixas  S. Serci  R. Shahoyan  P. Sonderegger  H. J. Specht  R. Tieulent  G. Usai  R. Veenhof  H. K. W?hri 《The European Physical Journal C - Particles and Fields》2009,59(3):607-623
The yield of muon pairs in the invariant mass region 1<M<2.5 GeV/c 2 produced in heavy-ion collisions significantly exceeds the sum of the two expected contributions, Drell-Yan dimuons and muon pairs from the decays of D meson pairs. These sources properly account for the dimuons produced in proton-nucleus collisions. In this paper, we show that dimuons are also produced in excess in 158 A GeV In-In collisions. We furthermore observe, by tagging the dimuon vertices, that this excess is not due to enhanced D meson production, but made of prompt muon pairs, as expected from a source of thermal dimuons specific to high-energy nucleus-nucleus collisions. The yield of this excess increases significantly from peripheral to central collisions, both with respect to the Drell-Yan yield and to the number of nucleons participating in the collisions. Furthermore, the transverse mass distributions of the excess dimuons are well described by an exponential function, with inverse slope values around 190 MeV. The values are independent of mass and significantly lower than those found at masses below 1 GeV/c 2, rising there up to 250 MeV due to radial flow. This suggests the emission source of thermal dimuons above 1 GeV/c 2 to be of largely partonic origin, when radial flow has not yet built up.  相似文献   

4.
The forward spectrometer upgrade of the PHENIX detector aims to add capabilities at forward rapidities to: probe nucleon structure through W production and promptphotons in polarized p + p, study nucleon structure in nuclei at high parton densities in p + A collisions through the measurement of γ and π0 in the forward region, greatly extend the acceptance for high p T γ-jet measurements (jet tomography) in A + A, and increase our capabilities to measure the production quarkonium states by giving sensitivity to the χ c through the J/ψ + γ channel. for the PHENIX Forward Upgrade Collaboration Presented in the Poster Session “Future Experiments and Facilities” at the 18th International Conference “Quark Matter 2005”, Budapest, Hungary, 4–9 August 2005.  相似文献   

5.
ALICE (A Large Ion Collider Experiment) is the LHC detector designed to measure nucleus-nucleus (AA) collisions where the formation of the Quark Gluon Plasma is expected. The experiment will also study proton-proton (pp) collisions at 14 TeV. Amongst the relevant observables to be investigated in pp collisions, the B-hadron cross-section is particularly interesting since it provides benchmarks for theoretical models and it is mandatory for understanding heavy flavour production in AA collisions. The performances of the ALICE muon spectrometer to measure B-hadron cross-section in pp collisions at 14 TeV via single muons are presented.  相似文献   

6.
The production of heavy quarks in heavy-ion collisions is important because it is expected to give information about high-density QCD matter. One interesting channel of heavy quark measurements at LHC is the decay of B to J/ψ. The J/ψ mesons from this channel can be separated from the primary J/ψ (produced at collision vertex) by using the secondary vertex which is efficiently reconstructed with the CMS tracker. In this work, the generator level results for the primary and secondary J/ψ obtained through dimuon pairs are presented for pp and PbPb collisions at $ \sqrt {s_{NN} } $ \sqrt {s_{NN} } = 5.5 TeV.  相似文献   

7.
The study of formation and interaction of heavy quarkonia in relativistic heavy ion collisions provides important insight into the properties of the produced medium. Lattice QCD studies show sequential suppression of quarkonia states with increasing temperature; which affirms that a full spectroscopy, including bottomonium, can provide us a thermometer for the matter produced under extreme conditions in relativistic heavy ion collisions and the most direct probe of deconfinement. With the completion of the STAR Electromagnetic Calorimeter and with the increased luminosity provided by RHIC in Runs 6 and 7, the study of ϒ production via the di-electron channel becomes possible. We present preliminary results on ϒ measurements in pp collisions (from Run 6) along with preliminary results from Au+Au collisions (in Run 7) at  GeV from the STAR experiment.  相似文献   

8.
《Pramana》2004,62(3):627-630
The NA50 experiment deals with Pb-Pb collisions at 158 GeV/nucleon at the CERN SPS accelerator. TheJ/ψ production is studied through the muon decay channel, using the Drell-Yan dimuons as a reference. New results based on recent analyses, from data taken with improved experimental conditions and using different centrality estimators, are presented and compared to an update of those already obtained from previous data samples. The stepwise pattern of the anomalousJ/ψ suppression as a function of centrality, already present in these previous results, is confirmed. This observation could be a fingerprint of the theoretically predicted melting of charmonia resonances in a deconfined quark-gluon plasma. On leave of absence from York College, CUNY, New York USA On leave of absence from YerPhI, Yerevan, Armenia  相似文献   

9.
At the Paul Scherrer Institute (PSI, Villigen, Switzerland) a new high-intensity muon beam line with momentum p < 40 MeV/c is currently being commissioned. The beam line is especially designed to serve the needs of the low-energy, polarized positive muon source (LE-μ+) and LE-μ SR spectrometer at PSI. The beam line replaces the existing μ E4 muon decay channel. A large acceptance is accomplished by installing two solenoidal magnetic lenses close to the muon production target E that is hit by the 590-MeV PSI proton beam. The muons are then transported by standard large aperture quadrupoles and bending magnets to the experiment. Several slit systems and an electrostatic separator allow the control of beam shape, momentum spread, and to reduce the background due to beam positrons or electrons. Particle intensities of up to 3.5 × 108 μ+/s and 107 μ/s are expected at 28 MeV/c beam momentum and 1.8 mA proton beam current. This will translate into a LE-μ+ rate of 7,000/s being available at the LE-μ SR spectrometer, thus achieving μ+ fluxes, that are comparable to standard μ SR facilities.  相似文献   

10.
We study the prospects for observing double parton scattering through four-muon final states, forming two opposite-sign muon pairs, in the LHCb experiment in pp collisions at 14 TeV centre of mass energy. We consider two special cases, namely double Drell–Yan and J/ψ-pair production. The kinematic properties and prospects for observing these processes are discussed. We find that the production rate depends strongly on the origin of the four muons, while many kinematic properties can be used to help identify the presence of double parton scattering events.  相似文献   

11.
In the framework of the k t-factorization approach, the production of γ mesons at the Fermilab Tevatron and CERN LHC is considered, and the predictions on the spin alignment parameter a are presented. We argue that measuring the polarization of quarkonium states can serve as a crucial test discriminating two competing theoretical approaches to parton dynamics in QCD. The text was submitted by the authors in English.  相似文献   

12.
In this work we present the J/ψ measurement in p+p collisions within the STAR collaboration Quarkonium program. This measurements aim to be the baseline measurement of a more comprehensive systematic study of quarkonium states production in order to understand their in medium modification. Here we report the total cross section and p T distribution, and find them to be consistent with pQCD CEM predictions as well as to previous measurements at the same center-of-mass energy.  相似文献   

13.
We report on the measurements of D0 meson production via direct reconstruction through the hadronic decay channel D0→Kπ in minimum bias d+Au and Au+Au collisions at with pT up to ∼3 GeV/c. We derive the charm production total cross-section per nucleon–nucleon collision from a combination of three measurements: the D0 meson spectra, the non-photonic electron spectra from charm semi-leptonic decays obtained in p+p, d+Au, and Au+Au collisions, and the charm-decayed single muon (prompt muon) spectra at low pT in Au+Au collisions. The cross-section is found to follow binary scaling, which is a signature of charm production exclusively at the initial impact. The implications of charm quark energy-loss and thermalization in the strongly interacting matter are discussed. PACS 25.75.Dw; 13.20.Fc; 13.25.Ft; 24.85.+p  相似文献   

14.
Muon bremsstrahlung photons converted in front of the DELPHI main tracker (TPC) in dimuon events at LEP1 were studied in two photon kinematic ranges: 0.2<E γ ≤1 GeV and transverse momentum with respect to the parent muon p T <40 MeV/c, and 1<E γ ≤10 GeV and p T <80 MeV/c. A good agreement of the observed photon rate with predictions from QED for the muon inner bremsstrahlung was found, contrary to the anomalous soft photon excess that has been observed recently in hadronic Z 0 decays. The obtained ratios of the observed signal to the predicted level of the muon bremsstrahlung are 1.06±0.12±0.07 in the photon energy range 0.2<E γ ≤1 GeV and 1.04±0.09±0.12 in the photon energy range 1<E γ ≤10 GeV. The bremsstrahlung dead cone is observed for the first time in the direct photon production at LEP. Deceased.  相似文献   

15.
The spin dynamics of the positive muon undergoing cyclic charge exchange (μ+⇌Mu) while it is slowing down is compared with that in the case of repeated muonium spin exchange after thermalization. The expectation value of the spin polarization at timet aftern spin exchange collisions (att 1,t 2, ...,t n ) are calculated explicitly from time dependent wave functions, and the quantity is averaged over the statistical distribution of the times of collisions and over all possible numbers of collisions betweent=0 and the observation timet. This result is complementary and equivalent to the conventional density matrix formalism, but offers an insight into the roles of spin flip and spin non-flip processes. The neutral fraction during slowing down is also discussed.  相似文献   

16.
In this paper the charged Higgs signal through the decay to a pair of muon and neutrino (H ±μν) is analyzed. The analysis attempts to estimate the amount of muonic signal of the charged Higgs at LHC at a center of mass energy of 14 TeV. The signal process is the top quark pair production with one of the top quarks decaying to a charged Higgs (non SM anomalous top decay) and the other decaying to a W boson which is assumed to decay hadronically to two light jets. Due to the small branching ratio of charged Higgs decay to muon, results are quoted for data corresponding to an integrated luminosity of 300 fb−1 which is expected to be collected at the LHC high luminosity regime. It is shown that a signal significance close to 5σ down to below 1σ is achievable for a charged Higgs mass in the range 80 GeV<m(H ±)<150 GeV taking the top quark pair production with both top quarks decaying to W bosons as the main irreducible background.  相似文献   

17.
R. Arnaldi  K. Banicz  K. Borer  J. Castor  B. Chaurand  W. Chen  C. Cicalò  A. Colla  P. Cortese  S. Damjanovic  A. David  A. de Falco  A. Devaux  L. Ducroux  H. En’yo  J. Fargeix  A. Ferretti  M. Floris  A. F?rster  P. Force  N. Guettet  A. Guichard  H. Gulkanyan  J. Heuser  M. Keil  L. Kluberg  Z. Li  C. Louren?o  J. Lozano  F. Manso  P. Martins  A. Masoni  A. Neves  H. Ohnishi  C. Oppedisano  P. Parracho  P. Pillot  T. Poghosyan  G. Puddu  E. Radermacher  P. Ramalhete  P. Rosinsky  E. Scomparin  J. Seixas  S. Serci  R. Shahoyan  P. Sonderegger  H. J. Specht  R. Tieulent  A. Uras  G. Usai  R. Veenhof  H. K. W?hri 《The European Physical Journal C - Particles and Fields》2009,64(1):1-18
The NA60 experiment has measured muon pair production in In–In collisions at 158 AGeV at the CERN SPS. This paper presents a high statistics measurement of φμ μ meson production. Differential spectra, yields, mass and width are measured as a function of centrality and compared to previous measurements in other colliding systems at the same energy. The width of the rapidity distribution is found to be constant as a function of centrality, compatible with previous results. The decay muon polar angle distribution is measured in several reference frames. No evidence of polarization is found as a function of transverse momentum and centrality. The analysis of the p T spectra shows that the φ has a small radial flow, implying a weak coupling to the medium. The T eff parameter measured in In–In collisions suggests that the high value observed in Pb–Pb in the kaon channel is difficult to reconcile with radial flow alone. The absolute yield is compared to results in Pb–Pb collisions: though significantly smaller than measured by NA50 in the muon channel, it is found to exceed the NA49 and CERES data in the kaon channel at any centrality. The mass and width are found to be compatible with the PDG values at any centrality and at any p T : no evidence for in-medium modifications is observed.  相似文献   

18.
We study in detail the influence of the nuclear form factor both on the Born cross section and on the Coulomb corrections to the photo-production of muon pairs off heavy nuclei (γ Zμ + μ Z) and in heavy-ion collisions (ZZZZ μ + μ ). Our findings indicate a number of issues which have not been sufficiently described as yet in the literature: (i) the use of a realistic form factor, based on the Fermi charge distribution for the nucleus, is absolutely indispensable for reliable theoretical predictions; (ii) we checked quantitatively that the equivalent photon approximation has a very good accuracy for the discussed processes; and (iii) we present a leading logarithmic calculation of the Coulomb corrections which correspond to multi-photon exchange of the produced μ ± with the nuclei. These corrections are found to be small (on the percent level). Our result justifies using the Born approximation for numerical simulations of the discussed process at the RHIC and LHC colliders. Finally, we calculate the total cross section for muon pair production at RHIC and LHC.  相似文献   

19.
Results for the one-loop calculation of the decay width Γ(HggZ) in the standard model with Higgs boson masses in the range 115 GeV<m H <2m W are presented. We find that among all the helicity amplitudes contributing to the width only those for which the gluons have the same polarization and the Z is longitudinally polarized contribute in any significant way. The calculation includes all contributions from the second and third generations, and kinematic cuts to enhance the HggZ signal. Compared to the width of Hgg, we find Γ(HggZ)/Γ(Hgg)≲10−4.  相似文献   

20.
We report results on quarkonium production from the STAR experiment at the Relativistic Heavy-Ion Collider (RHIC). J/ψ spectra in p+p and Cu+Cu collisions at  GeV with transverse momenta in the range of 0.5–14 GeV/c and 5–8 GeV/c, respectively, are presented. We find that for p T >5 GeV/c yields in p+p collisions are consistent with those in minimum-bias Cu+Cu collisions scaled with the respective number of binary nucleon-nucleon collisions. In this range the nuclear modification factor, R AA , is measured to be 0.9±0.2 (stat). For the first time at RHIC, high-p T J/ψ-hadron correlations were studied in p+p collisions. Implications from our measurements on J/ψ production mechanisms, constraints on open bottom yields, and J/ψ dissociation mechanisms at high-p T are discussed. In addition, we give a brief status of measurements of ϒ production in p+p and Au+Au collisions and present projections of future quarkonia measurements based on an upgrades to the STAR detector and increased luminosity achieved through stochastic cooling of RHIC.  相似文献   

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