A few-body proton image, expected to be derivable from QCD in the renormalization group procedure for effective particles, is used within the Monte Carlo Glauber model to calculate the anisotropy coefficients in the initial collision-state of matter in high-energy high-multiplicity proton-proton interaction events. We estimate the ridge-like correlations in the final hadronic state by assuming their proportionality to the initial collision-state anisotropy. In our estimates, some distinct few-body proton structures appear capable of accounting for the magnitude of p-p ridge effect, with potentially discernible differences in dependence on multiplicity.
Secondary charged hadrons multiplicity distributions in proton-proton and proton-antiproton collisions differ on principle. There are three types of inelastic processes in proton-antiproton scattering. The first type is production of secondary hadrons shower at gluon string decay. The second type is shower produced from two quark strings decay, the third type is shower produced from three quark strings decay. At the same time there are only two types of inelastic processes for proton-proton scattering - gluon string shower and two quark strings shower. Theoretical description of multiplicity d…
We compute the proton-proton multiplicity distributions at LHC energies in the framework of a multiple scattering model assuming a Poisson distribution for each inelastic collision. Multiple scattering is essential to broaden the multiplicity distribution. We obtain approximate KNO scaling for small pseudo-rapidity intervals ($|η| < 0.5$) and sizable KNO scaling violations for larger ones, in agreement with experiment.
The forward-backward long-range multiplicity correlations in proton-proton collisions are investigated in the model with two independent sources of particles: one left- and one right-moving wounded nucleon. A good agreement with the UA5 collaboration proton-antiproton data at the c.m. energy of 200 GeV is observed. For comparison the model with only one source of particles is also discussed.
A new approach to phenomenological description of the charged particle multiplicity distributions in proton-(anti)proton and electron-positron collisions is presented. The observed features of the data are interpreted on the basis of stochastic-physical ideas of multiple production. Besides the processes of parton immigration and absorption, two and three patron incremental and decremental recombinations are considered. The complex behaviour of the multiplicity distributions at different energies is described by four parametric generalized hypergeometric distribution (GHD). Application of the …
Measured multiplicity distributions of primary charged particles produced in the forward rapidity region of the $proton-proton$ ($pp$) collisions at the centre-of-mass energy, $\sqrt {s}$ = 7 TeV at the Large Hadron Collider (LHC) have been analyzed in terms of the Negative Binomial Distribution (NBD) function. Like the multiplicity distributions in the mid-rapidity region for the $pp$ collisions at $\sqrt {s}$ = 7 TeV, the distributions for the minimum bias events in the forward region also are better described with the superposition of two-NBDs, as proposed by a two-component model of partic…
In this paper, transverse momentum spectra of pi+, K+ and p measured at fix event-multiplicities and \sqrt s = 0.9, 2.76 and 7 TeV collision energies by the CMS Collabotaion are shown to fit the Tsallis-distribution. It is found that the power of the distribution shows a double-logarithmic dependence on the event-multiplicity N, while the T parameter depends linearly on N. A similar double-logarithmic dependence of the q parameter of pi0 spectra on the collision energy \sqrt{s} is found too. It is also shown that event-by-event fluctuations of the multiplicity N and the total E_T energy going …
Multiple Reflection Expansion (MRE) formalism has been applied to hadron resonance gas (HRG) model to study the finite-size effect on thermodynamics of small systems of hadron gas at the chemical freeze-out temperature in high-multiplicity events of proton-proton (pp) colisions at the LHC. Comparison with larger systems of heavy-ion (AA) collisions helps in undersanding the usefulness of the effect on small systems. Thermodynamic properties of these systems at the chemical freeze-out, with and without system-size effect, are contrasted with those for infinite hadronic phase of strongly interac…
At LHC extreme values of energy density will be reached even for proton-proton collisions. Such values of energy density may be large enough to generate a collective motion in the products of the collision, therefore generating effects such as elliptic flow. Using ideal 3+1D hydrodynamical simulations, we show that elliptic flow can occur at least for top multiplicities p-p events at LHC and that the intensity of such effect is strongly related to quantum fluctuations in the initial proton energy distribution.
The CMS collaboration at the LHC has reported a remarkable and unexpected phenomenon in very high-multiplicity high energy proton-proton collisions: a positive correlation between two particles produced at similar azimuthal angles, spanning a large range in rapidity. We suggest that this "ridge"-like correlation may be a reflection of the rare events generated by the collision of aligned flux tubes connecting the valence quarks in the wave functions of the colliding protons. The "spray" of particles resulting from the approximate line source produced in such inelastic collisions then gives ris…
We consider QCD based model of hadrons interaction in which gluons density in wave function of initial state is low in rapidity space and real hadrons are produced by decay of color field strings. Hadrons production processes in pp and p antip interactions differ on principle. There are three types of inelastic processes in p antip collision. The first type is production of secondary hadrons shower from decay of gluon string. The second type is shower produced from decay of two quark strings and the third one -- from decay of three quark strings. At the same time there are only two types of in…
An unexpected result at the RHIC and the LHC is the observation that high-multiplicity hadronic events in heavy-ion and proton-proton collisions are distributed as two "ridges", approximately flat in rapidity and opposite in azimuthal angle. We propose that the origin of these events is due to the inelastic collisions of aligned gluonic flux tubes that underly the color confinement of the quarks in each proton. We predict that high-multiplicity hadronic ridges will also be produced in the high energy photon-photon collisions accessible at the LHC in ultra-peripheral proton-proton collisions or…
We present the dependence of $D$ production on the charged particle multiplicity in proton-proton collisions at LHC energies. We show that, in a framework of source coherence, the open charm production exhibits a growth with the multiplicity which is stronger than linear in the high density domain. This departure from linearity was previously observed in the $J/ψ$ inclusive data from proton-proton collisions at 7 TeV and was successfully described in our approach. Our assumption, the existence of coherence effects present in proton-proton collisions at high energy, applies for high multiplicit…
The final state hadronic composition of proton-proton collisions at 7 TeV as a function of charged particle multiplicity density is studied. The thermal model is adjusted to match the experimental conditions in order to understand the effect of the experimental cuts on rapidity and multiplicity. This study indicates that the measured hadronic composition under a simultaneous cut on rapidity and multiplicity does not coincide with the fireball hadronic composition. Excluding proton to pion ratio, the adjusted model can explain the measured particle ratios. Therefore, the observed strangeness en…
Multiplicity distributions of charged particles measured by the ATLAS Collaboration in proton-proton collisions at $\sqrt{s}=8$ and 13 TeV are analyzed in the framework of a weighted superposition of three negative binomial distribution functions. The examination of the experimental data confirms the existence of a narrow peak at low multiplicities found earlier at $\sqrt{s}=0.9$ and 7 TeV. The peak is described by the third separate component of the total distribution. The energy dependence of the multiplicity characteristics of the three-component scenario is studied. It is demonstrated that…
Gluons at small x in high-energy nuclei overlap in the longitudinal direction, so the nucleus acts as a single source of gluons, like higher Fock components in a single nucleon, which contribute to inelastic collisions with a high multiplicity of produced hadrons. This similarity helps to make a link between nuclear effects in pA and high-multiplicity pp collisions. Such a relation is well confirmed by data for the J/Psi production rate in high-multiplicity pp events measured recently in the ALICE experiment. Broadening of J/Psi transverse momentum is predicted for high-multiplicity pp collisi…
Analytical formula for multiplicity distribution is derived in the QO approach, where chaotic and coherent fields are contained. Observed charged multiplicity distributions in Au+Au collisions at $\sqrt{s}=200$ AGeV and in pp collisions at $\sqrt{s}=900$ GeV are analyzed by the formula. Chaoticity parameters in the inclusive events estimated from the analysis of multiplicity distributions are compared with those estimated from the analysis of observed two-particle inclusive identical particle correlations.
The two parameters Weibull function is used to describe the charged particle multiplicity distribution in $e^{+}e^{-}$ collisions at the highest available energy measured by TASSO and ALEPH experiments. The Weibull distribution has wide applications in naturally evolving processes based on fragmentation and sequential branching. The Weibull model describes the multiplicity distribution very well, as particle production processes involve QCD parton fragmentation. The effective energy model of particle production was verified using Weibull parameters and the same was used to predict the multipli…
We study the multiplicity dependence of jet structures in pp collisions using Monte Carlo event generators. We give predictions for multiplicity-differential jet structures and present evidence for a non-trivial jet shape dependence on charged hadron event multiplicity, that can be used as a sensitive tool to experimentally differentiate between equally well-preforming simulation tunes. We also propose a way to validate the presence and extent of effects such as multiple parton interactions (MPI) or color reconnection (CR), based on the detection of non-trivial jet shape modification in high-m…
We discuss the recently measured event-by-event multiplicity fluctuations in relativistic heavy-ion collisions. It is shown that the observed non-monotonic behaviour of the scaled variance of multiplicity distribution as a function of collision centrality (such effect is not observed in a widely used string-hadronic models of nuclear collisions) can be fully explained by the correlations between produced particles promoting cluster formation. We define a cluster as a quasi-neutral gas of charged and neutral particles which exhibits collective behaviour. The characteristic space scale of this s…
We analyze high multiplicity proton-proton ($pp$) collision data at the energies $\sqrt{s}=900$ GeV, $2.76$ TeV and $7$ TeV in the framework of the String Percolation Model (SPM) in terms of the ratio of shear viscosity and entropy density ($η/s$) showing that the model allows the formation of strongly interacting collective medium in the high energy and high multiplicity events in p-p collisions.
It is argued that the multiplicity distribution in proton-proton ($pp$) collisions, which is often parameterized by the negative binomial distribution, may result from the multiplicity distribution measured in electron-positron ($e^{+}e^{-}$) collisions, once the fluctuating energy carried by two leading protons in $pp$ is taken into account.
We study $J/Ψ$ absorption in high multiplicity proton-proton (pp) collisions at $\sqrt {s_{NN}}=7\,$TeV. We predict a modification of the $J/Ψ$-yield within the UrQMD transport approach, where explicit interactions of the $J/Ψ$ with the surrounding comovers and a prehadronic phase with adjusted cross sections and $J/Ψ$ melting is included. We present the analog of the nuclear modification factor in pp collisions at various charged particle multiplicities. It turns out that $J/Ψ$-Mesons may be suppressed towards higher particle multiplicities in pp collisions at LHC energies.
We present the results for the evolution of transverse momentum spectra for the jetty and underlying parts of events as a function of multiplicity in pp collisions at 13 TeV measured at midrapidity ($\left|η\right|<0.8$) using PYTHIA8 event generator. The main characteristic of the approach is that it reaches to extreme multiplicities not yet explored by the experiments. We demonstrate that the behavior of both the underlying and hard components are affected by the multiplicity of the events i.e. the energy density. The behavior of the spectra at very high multiplicities suggests that the part…
The study and understanding of the details of proton-proton collisions is important since they are the benchmark for the comparison with heavy ion results. In the present work we have studied the $ΔηΔϕ$ correlations as a function of the event multiplicity and transverse sphericity in pp collisions at $\sqrt{s}$ = 7 TeV using PYTHIA 8.180. The results show large variation in the shape of the correlation as a function of the sphericity and multiplicity indicating the importance of slicing the data in bins of both observables to better understand the complexity of the interactions. Motivated by t…
We discuss the dependence of J/ψ production on the charged particle multiplicity in proton-proton collisions at LHC energies. We show that, in the framework of parton saturation or string interaction models, the hard J/ψ production exhibits a significant growth with the multiplicity, which is stronger than linear in the high density domain. This departure from linearity, that should affect any hard observable, applies for high multiplicity proton-proton collisions in the central rapidity region and is a consequence of the parton saturation or the strong interaction among colour ropes that take…
We study modification of the photon-tagged and inclusive jets in $pp$ collisions at $\sqrt{s}=7$ TeV due to mini-quark-gluon plasma which can be produced in high multiplicity events. We show that for underlying events with $dN_{ch}/dη\sim 20-60$ the medium effects lead to a considerable modification of the photon-tagged and inclusive jet fragmentation functions. For inclusive jets the magnitude of the effect is surprisingly large. The effect is quite strong even for typical underlying events. We find that at $\sqrt{s}=7$ TeV the spectrum of charged hadrons is suppressed by $\sim 35-40$ % at $p…
We analyze high multiplicity proton-proton ($pp$) collision data in the framework of the String Percolation Model (SPM) that has been successful in describing several phenomena of multiparticle production, including the signatures of recent discovery of strongly interacting partonic matter, the Quark Gluon Plasma (QGP), in relativistic heavy-ion collisions. Our study in terms of the ratio of shear viscosity and entropy density ($η/s$) and the (LQCD) predicted signature of QCD change of phase, in terms of effective number of degrees of freedom ($ε/T^4$), reiterates the possibility of strongly i…
Using a fluid dynamical scenario for $pp$ scattering at 7 TeV, we compute correlation functions for $π^+π^+$ pairs. Femtoscopic radii are extracted based on three-dimensional parametrizations of the correlation functions. We study the radii as a function of the transverse momenta of the pairs, for different multiplicity classes, corresponding to recent experimental results from ALICE. We find the same decrease of the radii with $k_T$, more and more pronounced with increasing multiplicity, but absent for the lowest multiplicities. In the model we understand this as transition from string expans…
The CMS experiment at the Large Hadron Collider has recently presented data on the average transverse momentum of protons, kaons and pions as a function of particle multiplicity. We relate the particle multiplicity to saturation momentum using recently published computations of the interaction radius determined from the theory of the Color Glass Condensate. We show that the pp and the pA experimental data scale in terms of these saturation momenta. Computing transverse momentum spectra for identified particles using Boltzmann-type distributions and relating different associated multiplicities …
We present an evidence of strong radial flow in high-multiplicity pp collisions. We analyze the CMS data on the inclusive spectra of the charged pions, kaons and protons in the LHC $\sqrt{s}=7$ TeV collisions. For $<N_{\mathrm{tracks}} >\gtrsim 75$ we demonstrate the consistency of the hydrodynamic description with the (idealized) Gubser's flow. Using a one parameter fit of the model to experimental data, we obtain the initial fireball size to be of the order of 1 fm. At smaller multiplicities, the fit cannot be performed which shows a limitation of the hydrodynamic approach and provides us wi…
Forward-backward multiplicity correlations have been studied in electron-positron, proton-proton and more recently in lead-lead collisions. For the proton-proton case, comparison of experimental results to different models reveals an incomplete understanding of the physical phenomenon associated with these correlations. In this work, we present a study of forward-backward multiplicity correlations in proton-proton collisions using the PYTHIA event generator, at LHC energies. A detailed analysis is presented with and without weak decays, splitting data samples into soft and hard QCD processes, …
Experiments at the Large Hadron Collider (LHC) have measured multiplicity distributions in proton-proton collisions at a new domain of center-of-mass energy ($\sqrt {s}$) in limited pseudorapidity intervals. We analyze multiplicity distribution data of proton-proton collisions at LHC energies as measured by the Compact Muon Solenoid (CMS) experiment in terms of characteristic parameters of the Negative Binomial Distribution (NBD) function that has played a significant role in describing multiplicity distribution data of particle production in high energy physics experiments, in the pre-LHC ene…
We analyze the measured spectra of $π^\pm$, $K^\pm$, $p$($\bar p$) in $pp$ collisions at $\sqrt {s}$ = 0.9, 2.76 and 7 TeV, in the light of blast-wave model to extract the transverse radial flow velocity and kinetic temperature at freeze-out for the system formed in $pp$ collisions. The dependency of the blast-wave parameters on average charged particle multiplicity of event sample or the `centrality' of collisions has been studied and compared with results of similar analysis in nucleus-nucleus ($AA$) and proton-nucleus ($pA$) collisions. We analyze the spectra of $K_{s}^0$, $Λ$($\bar Λ$) and…
Proton-proton collisions at new high energies ($\sqrt {s}=$2.36 and 7 TeV) at LHC resulted into a greater mean multiplicities ($<e n >$) of charged particles in the mid-rapidity region than estimated $< n >$s by different models and event generators. Another significant observation in multiplicity data is a change in slope in the distribution of primary charged hadrons in pseudorapidity intervals $|η|<2.4$ at $\sqrt{s} = 7$ TeV. These new observations merit further studies. We consider a two-component model of particle production to analyze the multiplicity distributions of charged hadrons fro…
We demonstrate that the recent measurement of azimuthally collimated, long range rapidity ("ridge") correlations in $\sqrt{s}=13$ TeV proton-proton (p+p) collisions by the ATLAS collaboration at the LHC are in agreement with expectations from the color glass condensate effective theory of high energy QCD. The observation that the integrated near side yield as a function of multiplicity is independent of collision energy is a natural consequence of the fact that multiparticle production is driven by a single semi-hard saturation scale in the color glass condensate framework. We argue further th…
