High Multiplicity Proton-proton Research Articles

Thermalization of the world's smallest fluids: Recent developments

The late Gerry Brown was not shy to tackle complex scientific problems that took time to play out but yielded in the end a deeper understanding of many-body phenomena. In this note, prepared for a memorial volume in his honor, we provide a perspective on a couple of outstanding scientific puzzles that have their origin in our understanding of the thermalization of matter in ultrarelativistic heavy ion collisions, and possibly, in high multiplicity proton-proton and proton-nucleus collisions.

Medium Modification of Photon-Tagged and Inclusive Jets in High-Multiplicity Proton-Proton Collisions

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∼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 the spectrum of charged hadrons is suppressed by ∼35%-40% at p(T)∼5-10 GeV.

From initial-state fluctuations to final-state observables

Abstract This talk begins with the interpretation of the azimuthally collimated di-hadron correlation with large rapidity separations observed in heavy-ion and high multiplicity proton-proton collisions known as the “ridge”. The physics of the ridge is intimately related to quantum fluctuations responsible for the decoherence of the strongly occupied initial classical fields generated in heavyion collisions. Progress made in the implementation of a program to resum these instabilities and the connection with the final-state observables is discussed.

Charm quark energy loss in proton-proton collisions at LHC energies

Heavy quarks, i.e. charm and bottom quarks are one of the crucial probes in the high energy nuclear collision program at current day accelerators. It has been shown at the Relativistic Heavy Ion Collider (RHIC) that heavy quarks show a remarkable medium suppression despite their high mass. In these proceedings we report on a study of heavy quark energy loss in high multiplicity proton-proton collisions at energies accessible to the Large Hadron Collider (LHC). Recent experimental results from the LHC collaborations have shown that the notion of creating an interacting system is not completely off limits. The higher energies in LHC proton-proton collisions lead to multiplicities comparable to Cu+Cu collisions at RHIC. Within this environment high-momentum heavy quarks experience a non-negligible energy loss.

Evidence for BFKL and saturation dynamics from dihadron spectra at the LHC

We demonstrate that rapidity separated di-hadron spectra in high multiplicity proton-proton collisions at the LHC can be quantitatively described by a combination of BFKL and saturation dynamics. Based on these results, we predict the systematics of di-hadron spectra in proton-nucleus collisions at the LHC.

Possibility forJ/ψsuppression in high-multiplicity proton-proton collisions atsNN=7TeV

We study $J/\Psi$ absorption in high multiplicity proton-proton (pp) collisions at $\sqrt {s_{NN}}=7\,$TeV. We predict a modification of the $J/\Psi$-yield within the UrQMD transport approach, where explicit interactions of the $J/\Psi$ with the surrounding comovers and a prehadronic phase with adjusted cross sections and $J/\Psi$ melting is included. We present the analog of the nuclear modification factor in pp collisions at various charged particle multiplicities. It turns out that $J/\Psi$-Mesons may be suppressed towards higher particle multiplicities in pp collisions at LHC energies.

High multiplicityppevents andJ/ψproduction at energies available at the CERN Large Hadron Collider

We discuss the dependence of $J/\ensuremath{\psi}$ production on the charged particle multiplicity in proton-proton collisions at CERN Large Hadron Collider (LHC) energies. We show that, in the framework of parton saturation or string interaction models, the hard $J/\ensuremath{\psi}$ 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 color ropes that take place at LHC energies. Our assumption, the existence of coherence effects present in proton-proton collisions at high energy, can also be checked by studying the particular shape of the probability distribution associated to the $J/\ensuremath{\psi}$ production. Predictions for the forthcoming $p$Pb collisions at LHC energies are presented.

Heavy Quark Energy Loss in High Multiplicity Proton-Proton Collisions at the LHC

One of the most promising probes to study deconfined matter created in high energy nuclear collisions is the energy loss of (heavy) quarks. It has been shown in experiments at the Relativistic Heavy Ion Collider that even charm and bottom quarks, despite their high mass, experience a remarkable medium suppression in the quark gluon plasma. In this exploratory investigation we study the energy loss of heavy quarks in high multiplicity proton-proton collisions at LHC energies. Although the colliding systems are smaller than compared to those at the Relativistic Heavy Ion Collider (p+p vs Au+Au), the higher energy might lead to multiplicities comparable to Cu+Cu collisions at the Relativistic Heavy Ion Collider. The interaction of charm quarks with this environment gives rise to a non-negligible suppression of high momentum heavy quarks in elementary collisions.

Resonance production in exclusive high multiplicity proton-proton reactions at 12 and 24 GeV/ c

Δ ++ and ρ 0 production has been investigated in the reactions (1) pp → pp2 π +2 π − and (2) pp → pp3 π +3 π − and ω production in the reaction (3) pp → pp2 π +2 π − π 0 at 12 and 24 GeV/ c. Integrated and differential cross sections have been studied. Similar production characteristics are observed for the vector mesons ρ 0 and ω.

Study of correlation effects in high-multiplicity proton-proton reactions at 12 and 24 GeV/c

In this paper we study correlations in multiparticle final states from pp interactions at 12 and 24 GeV/ c. In an attempt to distinguish true dynamical correlations from the consequences of kinematics together with P T damping and the leading-particle effect, we compare the data with an independent-emission model which reproduces the single-particle spectra and also with a model that simulates a fragmentation mechanism. We investigate the forward-backward particle configurations and in particular the multiplicity imbalance and charge transfer, defining forward-backward by the largest rapidity gap as well as simply by c.m.s. hemispheres. We also study clustering by looking at distributions of the dispersions in longitudinal rapidity. From the comparison of the data with the models we find clear evidence for dynamical correlations of a sort one would expect from fragmentation-type mechanisms. We also find indications of non-fragmentation formation of neutral meson clusters.

Experimental results on proton-proton interactions at 10 GeV/c with six charged particles in the final state

High-multiplicity proton-proton reactions at 10 GeV/c have been studied. In the analysis of 1937 events the following results were obtained: reaction 1) pp→ppπ+π+π−π−, σ=(0.46±0.04) mb, 2) pp→ppπ+π+π−π−π0 σ=(0.69±0.05) mb, 3) pp→ppπ+π+π−π−, σ=(0.54±0.04) mb, 4) pp→>1 neutral particle, σ=(0.76±0.05) mb. The fraction of Δ++ is 0.64±0.16 in channel 1), 0.60±0.12 in 2) and 0.48±0.09 in 3). There is evidence for production of Δ++(1920)→pπ+ in reaction 3) and Δ+(1920)→pπ0 in reaction 2). No significant evidence for other baryon resonances, meson resonances or double isobar production was found.