Charged-particle multiplicities in proton–proton collisions at $\sqrt{s} = 0.9$ to 8 TeV

The ALICE collaboration Adam, Jaroslav ; Adamova, Dagmar ; Aggarwal, Madan Mohan ; et al.
Eur.Phys.J. C77 (2017) 33, 2017.
Inspire Record 1394854 DOI 10.17182/hepdata.77011

A detailed study of pseudorapidity densities and multiplicity distributions of primary charged particles produced in proton-proton collisions, at $\sqrt{s} =$ 0.9, 2.36, 2.76, 7 and 8 TeV, in the pseudorapidity range $|\eta|<2$, was carried out using the ALICE detector. Measurements were obtained for three event classes: inelastic, non-single diffractive and events with at least one charged particle in the pseudorapidity interval $|\eta|<1$. The use of an improved track-counting algorithm combined with ALICE's measurements of diffractive processes allows a higher precision compared to our previous publications. A KNO scaling study was performed in the pseudorapidity intervals $|\eta|<$ 0.5, 1.0 and 1.5. The data are compared to other experimental results and to models as implemented in Monte Carlo event generators PHOJET and recent tunes of PYTHIA6, PYTHIA8 and EPOS.

75 data tables

Measured pseudorapidity dependence of $dN/d\eta$ for INEL collisions at a centre-of-mass energy of 900 GeV.

Measured pseudorapidity dependence of $dN/d\eta$ for NSD collisions at a centre-of-mass energy of 900 GeV.

Measured pseudorapidity dependence of $dN/d\eta$ for INEL>0 collisions at a centre-of-mass energy of 900 GeV.

More…

Forward-backward multiplicity correlations in pp collisions at $ \sqrt{s} $ = 0.9, 2.76 and 7 TeV

The ALICE collaboration Adam, Jaroslav ; Adamova, Dagmar ; Aggarwal, Madan Mohan ; et al.
JHEP 1505 (2015) 097, 2015.
Inspire Record 1342496 DOI 10.17182/hepdata.68880

The strength of forward-backward (FB) multiplicity correlations is measured by the ALICE detector in proton-proton (pp) collisions at $ \sqrt{s} $ = 0.9, 2.76 and 7 TeV. The measurement is performed in the central pseudorapidity region (|η| < 0.8) for the transverse momentum p$_{T}$ > 0.3 GeV/c. Two separate pseudorapidity windows of width (δη) ranging from 0.2 to 0.8 are chosen symmetrically around η = 0. The multiplicity correlation strength (b$_{corr}$) is studied as a function of the pseudorapidity gap (η$_{gap}$) between the two windows as well as the width of these windows. The correlation strength is found to decrease with increasing η$_{gap}$ and shows a non-linear increase with δη. A sizable increase of the correlation strength with the collision energy, which cannot be explained exclusively by the increase of the mean multiplicity inside the windows, is observed. The correlation coefficient is also measured for multiplicities in different configurations of two azimuthal sectors selected within the symmetric FB η-windows. Two different contributions, the short-range (SR) and the long-range (LR), are observed. The energy dependence of b$_{corr}$ is found to be weak for the SR component while it is strong for the LR component. Moreover, the correlation coefficient is studied for particles belonging to various transverse momentum intervals chosen to have the same mean multiplicity. Both SR and LR contributions to b$_{corr}$ are found to increase with p$_{T}$ in this case. Results are compared to PYTHIA and PHOJET event generators and to a string-based phenomenological model. The observed dependencies of b$_{corr}$ add new constraints on phenomenological models.

11 data tables

Correlation strength $b_{\rm corr}$ for $\eta$-windows in $p_{\rm T}$ range $0.3-1.5$ (GeV/c) at $\sqrt{s}=0.9$ TeV.

Correlation strength $b_{\rm corr}$ for $\eta$-windows in $p_{\rm T}$ range $0.3-1.5$ (GeV/c) at $\sqrt{s}=2.76$ TeV.

Correlation strength $b_{\rm corr}$ for $\eta$-windows in $p_{\rm T}$ range $0.3-1.5$ (GeV/c) at $\sqrt{s}=7$ TeV.

More…

Inclusive photon production at forward rapidities in proton-proton collisions at $\sqrt{s}$ = 0.9, 2.76 and 7 TeV

The ALICE collaboration Abelev, Betty Bezverkhny ; Adam, Jaroslav ; Adamova, Dagmar ; et al.
Eur.Phys.J. C75 (2015) 146, 2015.
Inspire Record 1328669 DOI 10.17182/hepdata.69495

The multiplicity and pseudorapidity distributions of inclusive photons have been measured at forward rapidities ( $2.3 < \eta < 3.9$ ) in proton–proton collisions at three center-of-mass energies, $\sqrt{s}$   $=$ 0.9, 2.76 and 7 TeV using the ALICE detector. It is observed that the increase in the average photon multiplicity as a function of beam energy is compatible with both a logarithmic and a power-law dependence. The relative increase in average photon multiplicity produced in inelastic pp collisions at 2.76 and 7 TeV center-of-mass energies with respect to 0.9 TeV are 37.2 $\pm $ 0.3 % (stat) $\pm $ 8.8 % (sys) and 61.2 $\pm $ 0.3 % (stat) $\pm $ 7.6 % (sys), respectively. The photon multiplicity distributions for all center-of-mass energies are well described by negative binomial distributions. The multiplicity distributions are also presented in terms of KNO variables. The results are compared to model predictions, which are found in general to underestimate the data at large photon multiplicities, in particular at the highest center-of-mass energy. Limiting fragmentation behavior of photons has been explored with the data, but is not observed in the measured pseudorapidity range.

8 data tables

Photon multiplicity distribution for INEL proton-proton collisions at sqrt(s)=0.9 TeV.

Photon multiplicity distribution for INEL proton-proton collisions at sqrt(s)=2.76 TeV.

Photon multiplicity distribution for INEL proton-proton collisions at sqrt(s)=7 TeV.

More…

Event-by-event mean ${p}_{\mathbf {T}}$ fluctuations in pp and Pb-Pb collisions at the LHC

The ALICE collaboration Abelev, Betty Bezverkhny ; Adam, Jaroslav ; Adamova, Dagmar ; et al.
Eur.Phys.J. C74 (2014) 3077, 2014.
Inspire Record 1307102 DOI 10.17182/hepdata.66332

Event-by-event fluctuations of the mean transverse momentum of charged particles produced in pp collisions at $\sqrt{s}$ = 0.9, 2.76 and 7 TeV, and Pb–Pb collisions at $\sqrt{s_\mathrm{NN}}$   = 2.76 TeV are studied as a function of the charged-particle multiplicity using the ALICE detector at the LHC. Dynamical fluctuations indicative of correlated particle emission are observed in all systems. The results in pp collisions show little dependence on collision energy. The Monte Carlo event generators PYTHIA and PHOJET are in qualitative agreement with the data. Peripheral Pb–Pb data exhibit a similar multiplicity dependence as that observed in pp. In central Pb–Pb, the results deviate from this trend, featuring a significant reduction of the fluctuation strength. The results in Pb–Pb are in qualitative agreement with previous measurements in Au–Au at lower collision energies and with expectations from models that incorporate collective phenomena.

8 data tables

Relative fluctuation $\sqrt{C_m}/M(p_{\rm T})_m$ as a function of $\langle {\rm d}N_{\rm ch}/{\rm d}\eta \rangle$ in pp collisions at $\sqrt{s}$ = 0.9 TeV.

Relative fluctuation $\sqrt{C_m}/M(p_{\rm T})_m$ as a function of $\langle {\rm d}N_{\rm ch}/{\rm d}\eta \rangle$ in pp collisions at $\sqrt{s}$ = 2.76 TeV.

Relative fluctuation $\sqrt{C_m}/M(p_{\rm T})_m$ as a function of $\langle {\rm d}N_{\rm ch}/{\rm d}\eta \rangle$ in pp collisions at $\sqrt{s}$ = 7 TeV.

More…

Charged-particle multiplicity measurement with Reconstructed Tracks in pp Collisions at $\sqrt{s}$ = 0.9 and 7 TeV with ALICE at the LHC

The ALICE collaboration
No Journal Information, 2013.
Inspire Record 1387699 DOI 10.17182/hepdata.62030

This note describes the details of the analysis of charged-particle pseudorapidity densities and multiplicity distributions measured by the ALICE detector in pp collisions at $\sqrt{s}$ = 0.9 and 7 TeV in specific phase space regions. The primary goal of the analysis is to provide reference measurements for Monte Carlo tuning. The pseudorapidity range |h| < 0.8 is considered and a lower $p_T$ cut is applied, at 0.15, 0.5 GeV/c and at 1 GeV/c. The choice of such phase space regions to measure the charged-particle multiplicity allows a direct comparison with the analogous results obtained by other LHC collaborations, namely ATLAS and CMS. The class of events considered are those having at least one charged particle in the kinematical ranges just described. In the note, the analysis procedure is presented, together with the corrections applied to the data, and the systematic uncertainty evaluation. The comparison of the results with different Monte Carlo generators is also shown.

9 data tables

dNch/deta versus eta obtained at sqrt(s) = 0.9 and 7 TeV with pT > 0.15 GeV.

dNch/deta versus eta obtained at sqrt(s) = 0.9 and 7 TeV with pT > 0.50 GeV.

dNch/deta versus eta obtained at sqrt(s) = 0.9 and 7 TeV with pT > 1.00 GeV.

More…

Energy Dependence of the Transverse Momentum Distributions of Charged Particles in pp Collisions Measured by ALICE

The ALICE collaboration Abelev, Betty Bezverkhny ; Adam, Jaroslav ; Adamova, Dagmar ; et al.
Eur.Phys.J. C73 (2013) 2662, 2013.
Inspire Record 1241422 DOI 10.17182/hepdata.61787
3 data tables

The normalized differential primary charged particle cross sections measured at 0.9, 2.76 and 7 TeV centre-of- mass energies. Additional systematic error for 0.9 TeV data: +5.1% -4.0%. Additional systematic error for 2.76 TeV data: +1.9% -1.9%. Additional systematic error for 7.0 TeV data: +3.6% -3.6%.

The ratios of differential cross sections of charged particles at different collisions energies.

The constructed reference P-P spectra for comparison with PB-PB and p-PB spectra.


Multiplicity dependence of the average transverse momentum in pp, p-Pb, and Pb-Pb collisions at the LHC

The ALICE collaboration Abelev, Betty Bezverkhny ; Adam, Jaroslav ; Adamova, Dagmar ; et al.
Phys.Lett. B727 (2013) 371-380, 2013.
Inspire Record 1241423 DOI 10.17182/hepdata.61692
5 data tables

The average transverse momentum as a function of multiplicity of charged particles having transverse momentum in the range 0.15-10 GeV/c and |eta| < 0.3 produced from P-P collisions at a centre-of mass energy/nucleon of 0.9 TeV.

The average transverse momentum as a function of multiplicity of charged particles having transverse momentum in the range 0.15-10 GeV/c and |eta| < 0.3 produced from P-P collisions at a centre-of mass energy/nucleon of 2.76 TeV.

The average transverse momentum as a function of multiplicity of charged particles having transverse momentum in the range 0.15-10 GeV/c and |eta| < 0.3 produced from P-P collisions at a centre-of mass energy/nucleon of 7 TeV.

More…

Mid-rapidity anti-baryon to baryon ratios in pp collisions at $\sqrt{s}$ = 0.9, 2.76 and 7 TeV measured by ALICE

The ALICE collaboration Abbas, E. ; Abelev, B. ; Adam, J. ; et al.
Eur.Phys.J. C73 (2013) 2496, 2013.
Inspire Record 1232209 DOI 10.17182/hepdata.61965

The ratios of yields of anti-baryons to baryons probes the mechanisms of baryon-number transport. Results for , , and in pp collisions at , measured with the ALICE detector at the LHC, are reported. Within the experimental uncertainties and ranges covered by our measurement, these ratios are independent of rapidity, transverse momentum and multiplicity for all measured energies. The results are compared to expectations from event generators, such as PYTHIA and HIJING/B, that are used to model the particle production in pp collisions. The energy dependence of , , and , reaching values compatible with unity for , complement the earlier measurement of ALICE. These dependencies can be described by exchanges with the Regge-trajectory intercept of , which are suppressed with increasing rapidity interval Δy. Any significant contribution of an exchange not suppressed at large Δy (reached at LHC energies) is disfavoured.

20 data tables

The pbar/p ratio at sqrt(s) = 2.76 TeV as a function of pT.

The pbar/p ratio at sqrt(s) = 2.76 TeV as a function of rapidity.

The LambdaBar/Lambda ratio at sqrt(s) = 0.9 TeV as a function of pT.

More…

Transverse sphericity of primary charged particles in minimum bias proton-proton collisions at $\sqrt{s}=0.9$, 2.76 and 7 TeV

The ALICE collaboration Abelev, Betty ; Adam, Jaroslav ; Adamova, Dagmar ; et al.
Eur.Phys.J. C72 (2012) 2124, 2012.
Inspire Record 1115186 DOI 10.17182/hepdata.58857

Measurements of the sphericity of primary charged particles in minimum bias proton--proton collisions at sqrt(s)=0.9, 2.76 and 7 TeV with the ALICE detector at the LHC are presented. The observable is linearized to be collinear safe and is measured in the plane perpendicular to the beam direction using primary charged tracks with $p_{\rm T}\geq0.5$ GeV/c in $|\eta|\leq0.8$. The mean sphericity as a function of the charged particle multiplicity at mid-rapidity ($N_{\rm ch}$) is reported for events with different $p_{\rm T}$ scales ("soft" and "hard") defined by the transverse momentum of the leading particle. In addition, the mean charged particle transverse momentum versus multiplicity is presented for the different event classes, and the sphericity distributions in bins of multiplicity are presented. The data are compared with calculations of standard Monte Carlo event generators. The transverse sphericity is found to grow with multiplicity at all collision energies, with a steeper rise at low $N_{\rm ch}$, whereas the event generators show the opposite tendency. The combined study of the sphericity and the mean $p_{\rm T}$ with multiplicity indicates that most of the tested event generators produce events with higher multiplicity by generating more back-to-back jets resulting in decreased sphericity (and isotropy). The PYTHIA6 generator with tune PERUGIA-2011 exhibits a noticeable improvement in describing the data, compared to the other tested generators.

7 data tables

pp @ 900 GeV, Mean Transverse Sphericity (y) vs Multiplicity.

pp @ 7000 GeV, Mean Transverse Sphericity (y) vs Multiplicity.

pp @ 2760 GeV, Mean Transverse Sphericity (y) vs Multiplicity.

More…

Underlying Event measurements in $pp$ collisions at $\sqrt{s}=0.9$ and 7 TeV with the ALICE experiment at the LHC

The ALICE collaboration Abelev, Betty ; Abrahantes Quintana, Arian ; Adamova, Dagmar ; et al.
JHEP 1207 (2012) 116, 2012.
Inspire Record 1080735 DOI 10.17182/hepdata.58863

We present measurements of Underlying Event observables in pp collisions at sqrt(s) = 0.9 and 7 TeV. The analysis is performed as a function of the highest charged-particle transverse momentum pT,LT in the event. Different regions are defined with respect to the azimuthal direction of the leading (highest transverse momentum) track: Toward, Transverse and Away. The Toward and Away regions collect the fragmentation products of the hardest partonic interaction. The Transverse region is expected to be most sensitive to the Underlying Event activity. The study is performed with charged particles above three different pT thresholds: 0.15, 0.5 and 1.0 GeV/c. In the Transverse region we observe an increase in the multiplicity of a factor 2-3 between the lower and higher collision energies, depending on the track pT threshold considered. Data are compared to Pythia 6.4, Pythia 8.1 and Phojet. On average, all models considered underestimate the multiplicity and summed pT in the Transverse region by about 10-30%.

23 data tables

Number density as a function of the leading charged-particle PT at a centre-mass-energy of 900 GeV for events having charged-particle PT > 0.15 GeV. The data is shown for the three azimuthal regions.

Number density as a function of the leading charged-particle PT at a centre-mass-energy of 7000 GeV for events having charged-particle PT > 0.15 GeV. The data is shown for the three azimuthal regions.

Number density as a function of the leading charged-particle PT at a centre-mass-energy of 900 GeV for events having charged-particle PT > 0.5 GeV. The data is shown for the three azimuthal regions.

More…

Femtoscopy of $pp$ collisions at $\sqrt{s}=0.9$ and 7 TeV at the LHC with two-pion Bose-Einstein correlations

The ALICE collaboration Aamodt, K. ; Abrahantes Quintana, A. ; Adamova, D. ; et al.
Phys.Rev. D84 (2011) 112004, 2011.
Inspire Record 884741 DOI 10.17182/hepdata.74220

We report on the high statistics two-pion correlation functions from pp collisions at sqrt{s}=0.9 TeV and sqrt{s}=7 TeV, measured by the ALICE experiment at the Large Hadron Collider. The correlation functions as well as the extracted source radii scale with event multiplicity and pair momentum. When analyzed in the same multiplicity and pair transverse momentum range, the correlation is similar at the two collision energies. A three-dimensional femtoscopic analysis shows an increase of the emission zone with increasing event multiplicity as well as decreasing homogeneity lengths with increasing transverse momentum. The latter trend gets more pronounced as multiplicity increases. This suggests the development of space-momentum correlations, at least for collisions producing a high multiplicity of particles. We consider these trends in the context of previous femtoscopic studies in high-energy hadron and heavy-ion collisions, and discuss possible underlying physics mechanisms. Detailed analysis of the correlation reveals an exponential shape in the outward and longitudinal directions, while the sideward remains a Gaussian. This is interpreted as a result of a significant contribution of strongly decaying resonances to the emission region shape. Significant non-femtoscopic correlations are observed, and are argued to be the consequence of "mini-jet"-like structures extending to low p_T. They are well reproduced by the Monte-Carlo generators and seen also in pi^+ pi^- correlations.

14 data tables

Parameters of the three-dimensional Gaussian fits to the complete set of the correlation functions in 8 ranges in multiplicity and 6 in $k_{\rm T}$ for pp collisions at $\sqrt{s}$=7 TeV and 4 ranges in multiplicity and 6 in kT for pp collisions at $\sqrt{s}$=0.9 TeV.

Parameters of the three-dimensional Gaussian fits to the complete set of the correlation functions in 8 ranges in multiplicity and 6 in $k_{\rm T}$ for pp collisions at $\sqrt{s}$=7 TeV and 4 ranges in multiplicity and 6 in kT for pp collisions at $\sqrt{s}$=0.9 TeV.

Parameters of the three-dimensional Gaussian fits to the complete set of the correlation functions in 8 ranges in multiplicity and 6 in $k_{\rm T}$ for pp collisions at $\sqrt{s}$=7 TeV and 4 ranges in multiplicity and 6 in kT for pp collisions at $\sqrt{s}$=0.9 TeV.

More…

Two-pion Bose-Einstein correlations in $pp$ collisions at $\sqrt{s}=900$ GeV

The ALICE collaboration Aamodt, K ; Abel, N ; Abeysekara, U ; et al.
Phys.Rev. D82 (2010) 052001, 2010.
Inspire Record 860477 DOI 10.17182/hepdata.55128

We report on the measurement of two-pion correlation functions from pp collisions at sqrt(s)=900 GeV performed by the ALICE experiment at the Large Hadron Collider. Our analysis shows an increase of the HBT radius with increasing event multiplicity, in line with other measurements done in particle- and nuclear collisions. Conversely, the strong decrease of the radius with increasing transverse momentum, as observed at RHIC and at Tevatron, is not manifest in our data.

36 data tables

Two-particle correlation functions for like-sign and unlike sign pion pairs.

Two-particle correlation functions for like-sign and unlike sign pion pairs.

Two-particle correlation functions for like-sign and unlike sign pion pairs.

More…

Midrapidity antiproton-to-proton ratio in pp collisions at $\sqrt{s} = 0.9$ and $7$~TeV measured by the ALICE experiment

The ALICE collaboration Aamodt, K. ; Abel, N. ; Abeysekara, U. ; et al.
Phys.Rev.Lett. 105 (2010) 072002, 2010.
Inspire Record 859610 DOI 10.17182/hepdata.55557

The ratio of the yields of antiprotons to protons in pp collisions has been measured by the ALICE experiment at $\sqrt{s} = 0.9$ and $7$~TeV during the initial running periods of the Large Hadron Collider(LHC). The measurement covers the transverse momentum interval $0.45 &lt; p_{\rm{t}} &lt; 1.05$~GeV/$c$ and rapidity $|y| &lt; 0.5$. The ratio is measured to be $R_{|y| &lt; 0.5} = 0.957 \pm 0.006 (stat.) \pm 0.014 (syst.)$ at $0.9$~TeV and $R_{|y| &lt; 0.5} = 0.991 \pm 0.005 (stat.) \pm 0.014 (syst.)$ at $7$~TeV and it is independent of both rapidity and transverse momentum. The results are consistent with the conventional model of baryon-number transport and set stringent limits on any additional contributions to baryon-number transfer over very large rapidity intervals in pp collisions.

2 data tables

The PT dependence of the pbar/p ratio for the central rapidity region ABS(YRAP)<0.5.

The central rapidity pbar/p ratio as a function of the rapidity interval Ybeam-Ybaryon and centre-of-mass energy. As well as the present ALICE measurements this table also lists the values from other experiments (see the text of the paper for details).


First proton-proton collisions at the LHC as observed with the ALICE detector: Measurement of the charged particle pseudorapidity density at s**(1/2) = 900-GeV

The ALICE collaboration Aamodt, K ; Abel, N ; Abeysekara, U ; et al.
Eur.Phys.J. C65 (2010) 111-125, 2010.
Inspire Record 838352 DOI 10.17182/hepdata.53751

On 23rd November 2009, during the early commissioning of the CERN Large Hadron Collider (LHC), two counter-rotating proton bunches were circulated for the first time concurrently in the machine, at the LHC injection energy of 450 GeV per beam. Although the proton intensity was very low, with only one pilot bunch per beam, and no systematic attempt was made to optimize the collision optics, all LHC experiments reported a number of collision candidates. In the ALICE experiment, the collision region was centred very well in both the longitudinal and transverse directions and 284 events were recorded in coincidence with the two passing proton bunches. The events were immediately reconstructed and analyzed both online and offline. We have used these events to measure the pseudorapidity density of charged primary particles in the central region. In the range |eta| < 0.5, we obtain dNch/deta = 3.10 +- 0.13 (stat.) +- 0.22 (syst.) for all inelastic interactions, and dNch/deta = 3.51 +- 0.15 (stat.) +- 0.25 (syst.) for non-single diffractive interactions. These results are consistent with previous measurements in proton--antiproton interactions at the same centre-of-mass energy at the CERN SppS collider. They also illustrate the excellent functioning and rapid progress of the LHC accelerator, and of both the hardware and software of the ALICE experiment, in this early start-up phase.

2 data tables

Pseudorapidity dependence of DN/DETARAP in Inelastic (INEL) and Non-Single-Diffractive (NSD) collisions. Note that the plot in the paper shows only statistical errors.

Pseudorapidity density for |ETARAP|<0.5 for Inelastic (INEL) and Non-Single-Diffractive (NSD) collisions.