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Antonio Ortiz VelasquezAntonio Ortiz Velasquez
Hungarian Academy of SciencesHungarian Academy of SciencesWigner Research Centre for PhysicsWigner Research Centre for PhysicsHEP SeminarHEP SeminarMay 30, 2014.May 30, 2014.
Instituto de Ciencias NuclearesUniversidad Nacional Autónoma de México.
Isolating the genuine Isolating the genuine radial flow effects in pp radial flow effects in pp
collisionscollisions(separation soft-hard)(separation soft-hard)
May 30, 2014 A. Ortiz Velasquez (ICN-UNAM) 2
Outline
1. Motivation.
2. Event shapes
3. Separation soft and hard using the spherocity approach, simulations for pp @ 7 TeV.
4. Predictions for pp @ 13 TeV.
5. Summary.
May 30, 2014 A. Ortiz Velasquez (ICN-UNAM) 3
In pp and p-Pb collisions at the LHC energies, collective phenomena have been discovered: ridge structure, radial and anisotropic flow. But, so far, there are not signatures of jet quenching. Hence, it is important to understand the origin of the collectivity in small systems.
Motivation
May 30, 2014 A. Ortiz Velasquez (ICN-UNAM) 4Slide shown at QM2014 by C.Andrei
May 30, 2014 A. Ortiz Velasquez (ICN-UNAM) 5
Slide shown at QM2014 by C.Andrei
May 30, 2014 A. Ortiz Velasquez (ICN-UNAM) 6
Slide shown at QM2014 by C.Andrei
Larger push of the p/π for pp?
May 30, 2014 A. Ortiz Velasquez (ICN-UNAM) 7
Increase of multiplicity or centrality
May 30, 2014 A. Ortiz Velasquez (ICN-UNAM) 8
Increase of multiplicity or centrality
The Nch reach is smaller in pp than in p-Pb. However, pp gives a larger <β
T>.
May 30, 2014 A. Ortiz Velasquez (ICN-UNAM) 9
A fragmentation bias affects the high multiplicity events
ALICE Collaboration: JHEP 09, 049, 2013 and Eur. Phys. J. C72, 2124, 2012.
How does this effect affect the observables which we measure
at high multiplicity, e.g. pT spectra of id hadrons?
Is the event multiplicity a good reference to compare results
from different systems?
The same Nch value corresponds to a very different collision regime in the three systems (ALICE Collaboration, PLB 727,2013, 371-380).
ALICE Collaboration, Phys. Lett. B 727 (2013) 371-380.
May 30, 2014 A. Ortiz Velasquez (ICN-UNAM) 10
➢ Compare similar event classes in pp and p-Pb collisions.
➢ Study how well theory describes enhanced soft and hard event samples.
➢ Remove jet contributions and study genuine radial flow effects in pp collisions.
Having a tool to separate soft and hard events would allow:
May 30, 2014 A. Ortiz Velasquez (ICN-UNAM) 11
The frameworkPythia 8 was used since it reproduces QUALITATIVELY WELL many features of data, e.g., radial flow
AO et. al., Phys. Rev. Lett. 111, 042001 (2013)
May 30, 2014 A. Ortiz Velasquez (ICN-UNAM) 12
May 30, 2014 A. Ortiz Velasquez (ICN-UNAM) 13
Event Shapes characterize the distribution of the outgoing particle energy from a high energy collision.
IsotropicJetty-like
The tool
Nch=42 Nch=44
E. Cuautle, R. Jiménez, I. Maldonado, AO, G. Paic and E. Perez, arXiv:1404.2372
May 30, 2014 A. Ortiz Velasquez (ICN-UNAM) 14
Sphericity and spherocity● Sphericity.
The following matrix is diagonalized:
Transverse sphericity is defined as follows:
● SpherocityTransverse spherocity is defined as follows:
Where λ1>=λ
2.
Case λ1=λ
2.
x
y
x
yv2
v1
v2
v1
Case λ1>λ
2.
STpherocity
=π2
4min
n⃗=(nx ,n y , 0)
(∑∣p⃗T i
× n⃗∣
∑ pT i
)
2
Sphe
roci
ty A
xis
Andrea Banfi et al., “Phenomenology of the event shapes at hadron colliders”, arXiv:1001.4082
May 30, 2014 A. Ortiz Velasquez (ICN-UNAM) 15
Features at partonic level of low and high S
O events
Event by event, the transverse momentum, , in the rest frame of all the 2 → 2 process, is calculated.
Low SO events: in average low number of MPIs
(<3) are involved, they are hard to semi hard.High S
O events: in average 12 MPI occur, the
partonic interactions are softer. ISOTROPIC(soft)
PENCIL-LIKE(hard)
p̂T
May 30, 2014 A. Ortiz Velasquez (ICN-UNAM) 16
pT spectrum for
inclusive charged particles
Low sphero(i)city, SO<0.1
High sphero(i)city, SO>0.9
Spherical events:Larger low p
T
production w.r.t. Inelastic events.
➢ Using spheri(o)city is possible to split the sample of pp data into enriched soft and hard events sub-samples.
➢ Jetty-like events (low S
T or S
O) have a harder
pT spectrum than the
one obtained for MB. Isotropic events (high S
T or S
O) have a soft p
T
spectrum.
May 30, 2014 A. Ortiz Velasquez (ICN-UNAM) 17
CR effects on the pT spectra
Full markers, are simulations with CR.
Empty points, are simulations without CR. ISOTROPIC
(soft)PENCIL-LIKE
(hard)
Flow patterns are clearly visible in soft events
May 30, 2014 A. Ortiz Velasquez (ICN-UNAM) 18
ISOTROPIC(soft)
PENCIL-LIKE(hard)
May 30, 2014 A. Ortiz Velasquez (ICN-UNAM) 19
Particle ratios
MB + 30 GeV jets This kind of measurement could be done in ALICE.But to see these effects we simulated 3X109 events!RUN II is a good chance to do it.
Flow signature in K/π
ISOTROPICISOTROPIC(soft)(soft)
PENCIL-LIKEPENCIL-LIKE(hard)(hard)
May 30, 2014 A. Ortiz Velasquez (ICN-UNAM) 20
Actually, this is only a modification of the spectral spahes
May 30, 2014 A. Ortiz Velasquez (ICN-UNAM) 21
The effect is not seen if one just cuts on multiplicity
LM, z<2HM, z>7
Selection on multiplicity is a selection on harder processes
High multiplicity starts to be dominated by fragmentation.
Within uncertainties the same trend in seen in ALICE pp data (see slide 6).
May 30, 2014 A. Ortiz Velasquez (ICN-UNAM) 22
ISOTROPIC(soft)
PENCIL-LIKE(hard)
Results for pp @ 7 TeV are shown with solid lines (Pythia 8.180 tune 4C), the amount of reconnection is the same. But remember that flow effects grows with Nmpi.
Predictions for pp @ 13 TeV
Will we be able to see the increase (large nMPI) of flow using only the MB sample?
May 30, 2014 A. Ortiz Velasquez (ICN-UNAM) 23
φ/π p/π
Inel
astic
pp
colli
sion
s The curves cross here.
May 30, 2014 A. Ortiz Velasquez (ICN-UNAM) 24
φ/π p/π
Sof
t pp
colli
sion
s Flow + production of φ
Larger flow effect
The curves cross here.
ISOTROPIC(soft)
May 30, 2014 A. Ortiz Velasquez (ICN-UNAM) 25
φ/π p/π
Har
d pp
col
lisio
ns There is not a crossing point.
PENCIL-LIKE(hard)
May 30, 2014 A. Ortiz Velasquez (ICN-UNAM) 26
Combining event shapes and event multiplicity
jets
Low Q2 processes
May 30, 2014 A. Ortiz Velasquez (ICN-UNAM) 27
Average pT vs Nch
May 30, 2014 A. Ortiz Velasquez (ICN-UNAM) 28
Combining dN/dη and SO
(dN/dη ~ 35)
ISOTROPIC(soft)
PENCIL-LIKE(hard)
May 30, 2014 A. Ortiz Velasquez (ICN-UNAM) 29
ISOTROPIC(soft)
PENCIL-LIKE(hard)
Combining dN/dη and SO
(dN/dη ~ 41)
May 30, 2014 A. Ortiz Velasquez (ICN-UNAM) 30
ISOTROPIC(soft)
PENCIL-LIKE(hard)
Combining dN/dη and SO
(dN/dη ~ 46)
May 30, 2014 A. Ortiz Velasquez (ICN-UNAM) 31
ISOTROPIC(soft)
PENCIL-LIKE(hard)
Combining dN/dη and SO
(dN/dη ~ 53)
May 30, 2014 A. Ortiz Velasquez (ICN-UNAM) 32
Tkin vs <βT>
(Lines are drawn just to guide the eye)
ISOTROPICISOTROPIC(soft)(soft)
PENCIL-LIKEPENCIL-LIKE(hard)(hard)
May 30, 2014 A. Ortiz Velasquez (ICN-UNAM) 33
Tkin vs <βT>(ALICE data)
Plot shown by C. Andrei at QM2014Pythia 8 results are in better agreement with data when high Q2 events are removed.
May 30, 2014 A. Ortiz Velasquez (ICN-UNAM) 34
SummaryThe event multiplicity is not the best reference to compare results which come from different colliding systems. For Pythia 8 events the high multiplicity is produced by means of hard partonic interactions.
Using spherocity I showed that it is possible to have enriched high Q2 and low Q2 event samples.
The pT spectra of identified hadrons which come from two
extreme event classes, high So and low So, were analyzed. The results from the Blast-wave analysis, Tkin vs <βT>, show that jets may increase the average transverse velocity and reduce the temperature. While for soft processes the agreement with LHC data is much better.
E. Cuautle, R. Jiménez, I. Maldonado, AO, G. Paic and E. Perez, arXiv:1404.2372
May 30, 2014 A. Ortiz Velasquez (ICN-UNAM) 35
Backup
May 30, 2014 A. Ortiz Velasquez (ICN-UNAM) 36
➢ The effect is nicely illustrated in the two particle correlation analysis as a function of the event multiplicity: the per-trigger near side pair-yield increases with Nch.
Motivation
ALICE Collaboration, JHEP09(2013)049
Multiplicity is not a good variable to compare the results from different systems.