اشترك بالحزمة الذهبية واحصل على وصول غير محدود شمرا أكاديميا
تسجيل مستخدم جديدComments on the observation of high multiplicity events at the LHC
121
0
0.0
(
0
)
تأليف
Mark Strikman
اسأل ChatGPT حول البحث
ﻻ يوجد ملخص باللغة العربية
We analyze the structure of the high multiplicity events observed by the CMS collaboration at the LHC. We argue that the bulk of the observed correlations is due to the production of a pair of jets with p_t > 15 GeV/c. We also suggest that high multiplicity events are due to a combination of three effects: high underlying multiplicity for collisions at small impact parameters, upward fluctuations of the gluon density in the colliding protons, and production of hadrons in the fragmentation of dijets. The data analysis is suggested which may clarify the underlying dynamics of the high multiplicity events and probe fluctuations of the gluon field as a function of x.
قيم البحث
اقرأ أيضاً
New strategy for resonance search in dijet events at the LHC is discussed. The main distribution used for a bump search is the dijet invariant mass distribution with appropriated cuts. The crucial cut, which is applied to maximize signal significance
, is on (pseudo)rapidity difference between the two jets. This is due to the exponential growing of the QCD background contribution with this variable. Usually it is assumed that signal from almost all exotic models populates the central dijet rapidity region y_{1,2} ~ 0 and |y_1-y_2| ~ 0. By contrast, the excited bosons do not contribute into this region, but produce an excess of dijet events over the almost flat QCD background in chi = exp|y_1-y_2| away from this region. Therefore, different sets of cuts should be applied for new physics search depending on the searched resonance properties. In order to confirm the bump and reveal the resonance nature various angular distributions should be used in addition. In particular, for the excited bosons the special choice of parameters could lead to a dip in the centrality ratio distribution over the dijet invariant mass instead of a bump, expected in the most exotic models.
Recently, the CMS Collaboration has published identified particle transverse momentum spectra in high multiplicity events at LHC energies $sqrt s $ = 0.9-13 TeV. In the present work the transverse momentum spectra have been analyzed in the framework
of the color fields inside the clusters of overlapping strings, which are produced in high energy hadronic collisions. The non-Abelian nature is reflected in the coherence sum of the color fields which as a consequence gives rise to an enhancement of the transverse momentum and a suppression of the multiplicities relative to the non overlapping strings. The initial temperature and shear viscosity to entropy density ratio $eta/s$ are obtained. For the higher multiplicity events at $sqrt s $ =7 and 13 TeV the initial temperature is above the universal hadronization temperature and is consistent with the creation of de-confined matter. In these small systems it can be argued that the thermalization is a consequence of the quantum tunneling through the event horizon introduced by the confining color fields, in analogy to the Hawking-Unruh effect. The small shear viscosity to entropy density ratio $eta/s$ near the critical temperature suggests that the matter is a strongly coupled Quark Gluon Plasma.
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 interacting matter at ideal thermodynamic limit, as provided by LQCD calculations. On introduction of finite size effect, the small hadronic systems produced in high-multiplicity pp events, unlike those in AA collisions, remain away from ideal thermodynamic limit. Knudsen number estimations validate the findings.
Centrality selection has been observed to have a large effect on jet observables in pPb collisions at the Large Hadron Collider, stronger than that predicted by the nuclear modification of parton densities. We study to which extent simple considerati
ons of energy-momentum conservation between the hard process and the underlying event affect jets observables in such collisions. We develop a simplistic approach that considers first the production of jets in a pp collision as described by PYTHIA. From each pp collision, the value of the energy of the parton from the proton participating in the hard scattering is extracted. Then, the underlying event is generated simulating a pPb collision through HIJING, but with the energy of the proton decreased according to the value extracted in the previous step, and both collisions are superimposed. This model is able to capture the bulk of the centrality effect for central to semicentral collisions, for the two available sets of data: dijets from the CMS Collaboration and single jets from the ATLAS Collaboration. As expected, the model fails for peripheral collisions where very few nucleons from Pb participate.
This article introduces a new class of searches for physics beyond the Standard Model that improves the sensitivity to signals with high jet multiplicity. The proposed searches gain access to high multiplicity signals by reclustering events into larg
e-radius, or fat, jets and by requiring that each event has multiple massive jets. This technique is applied to supersymmetric scenarios in which gluinos are pair-produced and then subsequently decay to final states with either moderate quantities of missing energy or final states without missing energy. In each of these scenarios, the use of jet mass improves the estimated reach in gluino mass by 20 % to 50 % over current LHC searches.
سجل دخول لتتمكن من نشر تعليقات
التعليقات
جاري جلب التعليقات
سجل دخول لتتمكن من متابعة معايير البحث التي قمت باختيارها
