Pis’ma v ZhETF, vol. 111, iss. 1, pp. 10 - 11
© 2020
January 10
The onset of jet quenching phenomenon
M. T. AlFiky+1), O. Elsherif+1), A. M. Hamed+∗×1)
+Department of Physics, The American University in Cairo, 11835 New Cairo, Egypt
∗Department of Physics & Astronomy, Texas A&M University, College Station, 77843 TX, USA
×Department of Physics & Astronomy, University of Mississippi, Oxford, 38677 MS, USA
Submitted 2 November 2019
Resubmitted 16 November 2019
Accepted 17
November 2019
DOI: 10.31857/S0370274X20010026
The small size systems formed in proton-proton
associated yield per trigger particle has been extracted
(p-p) collisions were simulated in order to study the on-
for the high and low multiplicity events in p-p colli-
set of jet quenching measurements of the Quark Gluon
sions at both energies of RHIC and LHC. The associ-
1
dN
Plasma (QGP) formed in large size systems (nucleus-
ated particles yield, D(z
)=
, has been com-
T
Ntrg d(Δφ)
nucleus) at top central collisions. The formation of
pared between the low and high multiplicity events as
QGP medium has been indicated via different obser-
a function of the hadron fractional energy z
where
T
vations such as the suppression of hadron spectra [1-5],
zT
= passoc/ptrig. In order to quantify the multiplicity
T
T
while the electromagnetically interacting particles (di-
effects, if any, the ratio between the near-side yields at
rect photon) and weakly interacting particles (Z0 and
high and low multiplicities (IN ), and away-side yields
HL
W±) spectra in central nucleus-nucleus collisions com-
at high and low multiplicities (IA
), where:
HL
pared to p-p collisions at Relativistic Heavy Ion Col-
lider (RHIC) and Large Hadron Collider (LHC) [6-9],
N
Dhigh-mult(z
)
near-side
T
were unity. In addition to the suppression of the away-
I
(zT ) =
;
HL
Dlow-mult(z
)
near-side
T
side yield per trigger particle in central A-A collisions
(1)
compared to the peripheral A-A and p-p collisions [1].
Dhigh-mult(z
)
away-side
T
IA
(zT ) =
However, due to the absence of different level of sup-
HL
Dlow-mult
(z
)
away-side
T
pressions for light quarks vs heavy quarks [10, 11], and
for quarks vs gluon jets [12], in contrast to the Quan-
have been calculated and plotted for both energies, as a
tum Chromodynamics (QCD) predictions, indicate the
function of zT , as shown in Fig. 1.
needs for more sensitive observables in order to better
At both energies, the values of IN
and IA were
HL
HL
quantify and constrain the medium parameters. More-
less than unity, and of trivial dependence on z
. The
T
over, observations such as long-range ridge-like struc-
values of IA
are always less than these of IN at the
HL
HL
ture [13, 14] and strangeness enhancement [15] in high
same multiplicity and energy, and both quantities show
multiplicity events in p-p collisions have stimulated the
a pattern of systematic decreases with the multiplic-
search for similar phenomena, e.g., jet quenching in the
ity. Such multiplicity dependence cannot be used nei-
high multiplicity events regardless of the size of the col-
ther to exclude the jet quenching nor to prove it in
liding systems. Previous simulated data using PYTHIA
the high multiplicity events in p-p collisions, as the
[13, 16] have shown similar patterns for some of the ob-
suppressions have been found at both sides, near and
servables as in the central heavy ion collisions, which
away of the high-pT particle. The fact that the near-
might indicate a nontrivial contributions for the com-
side shows a suppression in the high multiplicity events
monly adopted measured observables from the underly-
in p-p collisions is not consistent with the surface bias
ing particle production mechanisms in QCD.
emission as reported by various experiments, and ac-
In order to search for the onset of the jet quench-
cordingly such suppression at both sides shown in this
ing in the high multiplicity events, the two-particle az-
analysis could be due to 1) the evolution of the par-
imuthal correlation functions are constructed and the
ton distribution functions on the trigger particle mo-
mentum, 2) parton energy loss in the high multiplic-
1)e-mail: alfiky@aucegypt.edu; omartare@buffalo.edu;
ity events, or 3) a combination of both effects 1) and
ahamed@comp.tamu.edu
2). More future studies at higher transverse momenta
10
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2020
The onset of jet quenching phenomenon
11
Fig. 1. (Color online) The zT dependence of (a) IN
and (b) IA
for different multiplicity at
√sNN = 200 GeV and
HL
HL
√sNN = 13 TeV
could be used to either rule out or to confirm the mul-
8. S. Chatrchyan, V. Khachatryan, A. Sirunyan et al.
tiplicities dependence for the jet quenching commonly
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