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Panel a): Comparison of the pseudorapidity distribution of charged particles for d + Au collisions at √ s N N = 200 GeV for centrality bin 50-70% with compilation of world data on p + Em collisions at five energies. The η measured in center-of-mass system has been shifted to η + y target in order to study the fragmentation regions in the gold/Emulsion direction. Panel b): similar to panel a) but shifted to η − y beam in order to study the fragmentation regions in the deuteron/proton direction. Panels c) and d): the same as panels a) and b) but for more central d + Au collisions and compared to p + Pb collisions at three energies (for more details see text).
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The measured pseudorapidity distributions of primary charged particles are presented for d+Au and p+p collisions at over a wide pseudorapidity range of |η|≤ 5.4. The results for d+Au collisions are presented for minimum-bias events and as a function of collision centrality. The measurements for p+p collisions are shown for minimum-bias events. The...
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Citations
... A natural suggestion to explain the rapidity spectra of produced particles in asymmetric collisions like d+Au [7] is that each participant source preferably showers particles along its direction of motion [2,8]. Such a picture is also well motivated by the parton model [9] as well as saturation models of QCD [10]. ...
Thermalized matter created in non-central relativistic heavy-ion collisions is expected to be tilted in the reaction plane with respect to the beam axis. The most notable consequence of this forward-backward symmetry breaking is the observation of rapidity-odd directed flow for charged particles. On the other hand, the production points for heavy quarks are forward-backward symmetric and shifted in the transverse plane with respect to the fireball. The drag of heavy quarks from the asymmetrically distributed thermalized matter generates a large directed flow for heavy flavor mesons. We predict a very large rapidity odd directed flow of D mesons in non-central Au-Au collisions at GeV, several times larger than for charged particles. A possible experimental observation of a large directed flow for heavy flavor mesons would represent an almost direct probe of the 3-dimensional distribution of matter in heavy-ion collisions.
... A natural suggestion to explain the rapidity spectra of produced particles in asymmetric collisions like d+Au [5] is that each participant source preferably showers particles along its direction of motion [2,6]. Such a picture is also well motivated by the parton model [7] as well as saturation models of QCD [8]. ...
Thermalized matter created in non-central relativistic heavy-ion collisions is expected to be tilted in the reaction plane with respect to the beam axis. The most notable consequence of this forward-backward symmetry breaking is the observation of rapidity-odd directed flow for charged particles. On the other hand, the production points for heavy quarks are forward-backward symmetric and shifted in the transverse plane with respect to the fireball. The drag of heavy quarks from the asymmetrically distributed thermalized matter generates a large directed flow for heavy flavor mesons. We predict a very large rapidity odd directed flow of D mesons in non-central Au-Au collisions at GeV, several times larger than for charged particles. A possible experimental observation of a large directed flow for heavy flavor mesons would represent an almost direct probe of the 3-dimensional distribution of matter in heavy-ion collisions.
... These results focused on the pseudorapidity density [9] and the p T dependence of the nuclear modification factor [10][11][12]; the latter was found to be consistent with unity for p T 2 GeV/c. The nuclear modification factor of charged hadrons was also studied by the BRAHMS and PHOBOS Collaborations in d-Au collisions at the nucleon-nucleon centre- of-mass energy √ s NN = 200 GeV at RHIC [13,14], as a function of pseudorapidity, where values smaller than unity were found for η 1, corresponding to the d-going direction. ...
... 1 < p T < 7 GeV/c p T range, fits well into the trend defined by the two series of points in the backward and forward rapidity re- gions. This observation complements the previous measurements of light-flavour particle production (charged unidentified particles) reported in p-Pb by ALICE at the LHC at mid-rapidity [9], and in d-Au by PHOBOS at RHIC ranging from mid to forward rapid- ity [14]. The comparison between the data and the predictions by HIJING and DPMJET, illustrated in Fig. 4, clearly shows how the models -which successfully described charged particle production at mid-rapidity in the same collision system [9] -fail to prop- erly reproduce the shape and the normalisation of the observed rapidity dependence of the φ cross section. ...
The first study of ϕ-meson production in p–Pb collisions at forward and backward rapidity, at a nucleon–nucleon centre-of-mass energy sNN=5.02 TeV, has been performed with the ALICE apparatus at the LHC. The ϕ-mesons have been identified in the dimuon decay channel in the transverse momentum (pT) range 1<pT<7 GeV/c, both in the p-going (2.03<y<3.53) and the Pb-going (−4.46<y<−2.96) directions — where y stands for the rapidity in the nucleon–nucleon centre-of-mass — the integrated luminosity amounting to 5.01±0.19 nb⁻¹ and 5.81±0.20 nb⁻¹, respectively, for the two data samples. Differential cross sections as a function of transverse momentum and rapidity are presented. The forward–backward ratio for ϕ-meson production is measured for 2.96<|y|<3.53, resulting in a ratio ∼0.5 with no significant pT dependence within the uncertainties. The pT dependence of the ϕ nuclear modification factor RpPb exhibits an enhancement up to a factor 1.6 at pT=3–4 GeV/c in the Pb-going direction. The pT dependence of the ϕ-meson cross section in pp collisions at s=2.76 TeV, which is used to determine a reference for the p–Pb results, is also presented here for 1<pT<5 GeV/c and 2.5<y<4, for a 78±3 nb⁻¹ integrated luminosity sample.
... A lot of experimental data on nuclear collisions at high energies has been published in literature. The relativistic heavy ion collider (RHIC) has performed gold-gold (Au-Au), copper-copper (Cu-Cu), deuteron-gold ( -Au), and other collisions at various GeV energies [22][23][24][25]. Also, the large hadron collider (LHC) has performed lead-lead (Pb-Pb), proton-lead ( -Pb), and other collisions at TeV energies [26]. ...
... The pseudorapidity distributions of charged particles produced in -Au collisions for minimum-bias sample and different centralities at √ NN = 0.2 TeV are shown in Figures 9(a) and 9(b)-9(f), respectively. The circles represent the experimental data quoted in [23,24] (Figure 9(a)) and [25] (Figures 9(b)-9(f)), and the curves are the results calculated by us. The values of peak positions ( , , and ), contribution ratios ( and ), width , and 2 /dof obtained in the fitting are given in Table 4. ...
... According to the widths of rapidity distributions, the extracted values of square speed of sound parameter for different interacting systems, centrality percentages, and energies are listed in the last two columns in Tables 1-6. To see clearly the dependencies of 2 (for the target (or projectile) and central sources) on or √ NN , we plot the values listed in the last two columns in Tables 1-6 [23,24] (Figure 9(a)) and [25] (Figures 9(b)-9(f)). Table 4: Values of peak positions ( , , and ), contribution ratios ( and ), width , and 2 /dof for the curves in Figure 9 which shows -Au collisions at 0.2 TeV for minimum-bias sample (Figure 9(a)) or with different centralities (Figures 9(b)-9(f)). ...
We propose a new revised Landau hydrodynamic model to study systematically
the pseudorapidity distributions of charged particles produced in heavy ion
collisions over an energy range from a few GeV to a few TeV per nucleon pair.
The interacting system is divided into three sources namely the central,
target, and projectile sources respectively. The large central source is
described by the Landau hydrodynamic model and further revised by the
contributions of the small target/projectile sources. In the calculation, to
avoid the errors caused by an unapt conversion or non-division, the rapidity
and pseudorapidity distributions are obtained respectively. The modeling
results are in agreement with the available experimental data at relativistic
heavy ion collider (RHIC), large hadron collider (LHC), and other energies for
different centralities. The value of square speed of sound parameter in
different collisions has been extracted by us from the widths of rapidity
distributions. Our results show that, in heavy ion collisions at RHIC and LHC
energies, the central source undergoes through a phase transition from hadronic
gas to quark-gluon plasma (QGP) liquid phase; meanwhile, the target/projectile
sources remain in the state of hadronic gas. The present work confirms that the
QGP is of liquid type rather than that of a gas. The whole region of
participants undergoes through a mixed phase consisting of a large quantity of
(>90%) QGP liquid and a small quantity of (<10%) hadronic gas.
... These results focused on the pseudorapidity density [9] and the p T dependence of the nuclear modification factor [10][11][12]; the latter was found to be consistent with unity for p T 2 GeV/c. The nuclear modification factor of charged hadrons was also studied by the BRAHMS and PHOBOS Collaborations in d-Au collisions at the nucleon-nucleon centre- of-mass energy √ s NN = 200 GeV at RHIC [13,14], as a function of pseudorapidity, where values smaller than unity were found for η 1, corresponding to the d-going direction. ...
... 1 < p T < 7 GeV/c p T range, fits well into the trend defined by the two series of points in the backward and forward rapidity re- gions. This observation complements the previous measurements of light-flavour particle production (charged unidentified particles) reported in p-Pb by ALICE at the LHC at mid-rapidity [9], and in d-Au by PHOBOS at RHIC ranging from mid to forward rapid- ity [14]. The comparison between the data and the predictions by HIJING and DPMJET, illustrated in Fig. 4, clearly shows how the models -which successfully described charged particle production at mid-rapidity in the same collision system [9] -fail to prop- erly reproduce the shape and the normalisation of the observed rapidity dependence of the φ cross section. ...
23 pages, 6 captioned figures, 7 tables, authors from page 18, submitted to PLB, figures at http://aliceinfo.cern.ch/ArtSubmission/node/1699 ; see paper for full list of authors
... However, it was observed that the ratio of spectra in peripheral Au+Au to those in central d+Au starts above one at low-p T and trends to a constant value of ∼ 0.65 for all identified particles at high p T . One explanation for the low-p T rise is a relative deficit of midrapidity soft particle yield in d+Au collisions compared to Au+Au, which could be due to the participant asymmetry in the d+Au collisions producing a rapidity shift in the peak of particle production [22]. Consequently, measuring identified particles in different regions of rapidity provides a more complete picture of d+Au collisions and sheds light on the relationship between p+p, d+Au and Au+Au. ...
The PHENIX experiment has measured meson production in d+Au
collisions at GeV using the dimuon and dielectron decay
channels. The meson is measured in the forward (backward) d-going
(Au-going) direction, () in the transverse-momentum
() range from 1--7 GeV/c, and at midrapidity in the
range below 7 GeV/c. The meson invariant yields and
nuclear-modification factors as a function of , rapidity, and centrality
are reported. An enhancement of meson production is observed in the
Au-going direction, while suppression is seen in the d-going direction, and
no modification is observed at midrapidity relative to the yield in p+p
collisions scaled by the number of binary collisions. Similar behavior was
previously observed for inclusive charged hadrons and open heavy flavor
indicating similar cold-nuclear-matter effects.
... In our work we use the Glauber model [26-28, 32, 42, 43], where the source is created in an individual NN collision, located in the transverse plane and extending along the spatial rapidity direc- Fig. 2). A particular model of the distribution in η , coming Ref. [44] and used here, is described in Appendix A. It is motivated with the success of Ref. [45] in describing the deuterongold collisions [46], followed with the extension to NN collisions [47][48][49]. We note that other descriptions of the early production could be used as well, for instance the Kharzeev-Levin-Nardi framework [29,50,51]. ...
Analysis of correlation of multiplicities between various rapidity bins is
carried out in the framework of a superposition approach consisting of three
phases of the ultra-relativistic nuclear collision: early partonic phase,
intermediate collective evolution, and statistical hadronization. Simple
relations between the moments of produced hadrons and the moments of the
sources produced in the initial partonic phase are presented. They involve only
a few effective parameters describing the of microscopic dynamics of the
system. We illustrate the practicality of the approach with the Glauber model
simulations. Our study carries direct relevance for the interpretation of the
upcoming results for the multibin multiplicity correlations from the LHC, which
will help in an assessment of the correlation features of the state formed in
the earliest stage of the reaction.
... The increase of (28.4 ± 1.4 ± 2.6)% from 0.9 to 2.36 TeV is significantly larger than the 18.5% (14.5%) increase predicted by the pythia (phojet) model tunes used in this analysis. The collision energy dependence of the measured dN ch /dη| η≈0 is shown in figure 7b, which includes data from the NAL Bubble Chamber [25], the ISR [26], and UA1 [22], UA5 [24], CDF [27], STAR [28], PHOBOS [29] and ALICE [23]. The dN ch /dη measurement reported here is consistent with the previously observed trend. ...
... (b) Charged-hadron pseudorapidity density in the central region as a function of centre-of-mass energy in pp and pp collisions including lower energy data from refs. [22][23][24][25][26][27][28][29], together with various empirical parameterizations fit to the data corresponding to the inelastic (solid and dotted curves with open symbols) and to the NSD (dashed curve with solid symbols) event selection. The error bars indicate systematic uncertainties, when available. ...
Measurements of inclusive charged-hadron transverse-momentum and pseudorapidity distributions are presented for proton-proton collisions at s√=0.9 and 2.36 TeV. The data were collected with the CMS detector during the LHC commissioning in December 2009. For non-single-diffractive interactions, the average charged-hadron transverse momentum is measured to be 0.46 ± 0.01 (stat.) ± 0.01 (syst.) GeV/c at 0.9 TeV and 0.50 ± 0.01 (stat.) ± 0.01 (syst.) GeV/c at 2.36 TeV, for pseudorapidities between --2.4 and +2.4. At these energies, the measured pseudorapidity densities in the central region, dN [subscript ch]/dη|[subscript |η|]<0.5, are 3:48 ± 0:02 (stat.) ± 0.13 (syst.) and 4:47 ± 0:04 (stat.) ± 0.16 (syst.), respectively. The results at 0.9 TeV are in agreement with previous measurements and confirm the expectation of near equal hadron production in p−p and pp collisions. The results at 2.36 TeV represent the highest-energy measurements at a particle collider to date.
... The pseudorapidity distribution is given as a sum of contributions from the emission of forward and backward going wounded nucleons. Within such a scheme Bia las and Czyż successfully described [4] the distribution of charged particles in pseudorapidity in the deuteron-gold collisions [19]. The independent emission from the forward and backward going nucleons determines specific FB multiplicity correlations [6,7]. ...
... For this purpose we take into account primordial particles (those created at the freeze-out hypersurface) only, thus disregarding resonance decays. The result, shown in Fig. 12 with squares, shows a nice agreement between the cumulant measures (18,19) and the functions cos(2∆ F B ) and cos(4∆ F B ), shown with lines, evaluated directly from the fireball torque angle shown in Fig. 10 (we take here the case of the evolution time equal of 6 fm/c). For comparison, the triangles indicate the result of the calculation without the torque, ∆ F B = 0. ...
... In a complete simulation, an average should be taken of the observables over the torque angle distribution. With our calculation, taking the torque angle corresponding to the rms width of the angle distribution, we get a correct estimate for the averages of quantities of the order of the square of ∆ F B (Eqs. 18,19), which is sufficient. ...
We show that the fluctuations in the wounded-nucleon model of the initial
stage of relativistic heavy-ion collisions, together with the natural
assumption that the forward (backward) moving wounded nucleons emit particles
preferably in the forward (backward) direction, lead to an event-by-event
torqued fireball. The principal axes associated with the transverse shape are
rotated in the forward region in the opposite direction than in the backward
region. On the average, the standard deviation of the relative torque angle
between the forward and backward rapidity regions is about 20deg for the
central and 10deg for the mid-peripheral collisions. The hydrodynamic expansion
of a torqued fireball leads to a torqued collective flow, yielding, in turn,
torqued principal axes of the transverse-momentum distributions at different
rapidities. We propose experimental measures, based on cumulants involving
particles in different rapidity regions, which should allow for a quantitative
determination of the effect from the data. To estimate the non-flow
contributions from resonance decays we run Monte Carlo simulations with
THERMINATOR. If the event-by-event torque effect is found in the data, it will
support the assumptions concerning the fluctuations in the early stage of the
fireball formation, as well as the hypothesis of the asymmetric rapidity shape
of the emission functions of the moving sources in the nucleus-nucleus
collisions.
... The increase of (28.4 ± 1.4 ± 2.6)% from 0.9 to 2.36 TeV is significantly larger than the 18.5% (14.5%) increase predicted by the pythia (phojet) model tunes used in this analysis. The collision energy dependence of the measured dN ch /dη| η≈0 is shown in figure 7b, which includes data from the NAL Bubble Chamber [25], the ISR [26], and UA1 [22], UA5 [24], CDF [27], STAR [28], PHOBOS [29] and ALICE [23]. The dN ch /dη measurement reported here is consistent with the previously observed trend. ...
... (b) Charged-hadron pseudorapidity density in the central region as a function of centre-of-mass energy in pp and pp collisions including lower energy data from refs. [22][23][24][25][26][27][28][29], together with various empirical parameterizations fit to the data corresponding to the inelastic (solid and dotted curves with open symbols) and to the NSD (dashed curve with solid symbols) event selection. The error bars indicate systematic uncertainties, when available. ...
Measurements of inclusive charged-hadron transverse-momentum and pseudorapidity distributions are presented for proton-proton collisions at sqrt(s) = 0.9 and 2.36 TeV. The data were collected with the CMS detector during the LHC commissioning in December 2009. For non-single-diffractive interactions, the average charged-hadron transverse momentum is measured to be 0.46 +/- 0.01 (stat.) +/- 0.01 (syst.) GeV/c at 0.9 TeV and 0.50 +/- 0.01 (stat.) +/- 0.01 (syst.) GeV/c at 2.36 TeV, for pseudorapidities between -2.4 and +2.4. At these energies, the measured pseudorapidity densities in the central region, dN(charged)/d(eta) for |eta| < 0.5, are 3.48 +/- 0.02 (stat.) +/- 0.13 (syst.) and 4.47 +/- 0.04 (stat.) +/- 0.16 (syst.), respectively. The results at 0.9 TeV are in agreement with previous measurements and confirm the expectation of near equal hadron production in p-pbar and pp collisions. The results at 2.36 TeV represent the highest-energy measurements at a particle collider to date.
