underlying event (ue) study as a function of rt in pp ... · aditya nath mishra (december 02, 2019)...

Underlying Event (UE) study as a function of RT in pp collisions

at 13 TeV Aditya Nath Mishra (ICN- UNAM, Mexico)December 02, 2019

Motivation

Aditya Nath Mishra (December 02, 2019)ZIMÁNYI SCHOOL’19, Budapest

1

q Understand in more details the dependence of the underlying event on multiplicity presented in the previous talk.

q Understand the development of the Transverse Side spectra.

q We use Relative Transverse activity classifier (RT) observable to observe the leakage of high multiplicity events from Near side to Transverse Side.

Motivation

q study of the leading-hadron correlationsfor isotropic events also show an excessof particles in Transverse Side and peakeliminates at Near and Away side.

S0 = 0 “pencil-like” limit (hard events)1 “isotropic” limit (soft events).{

Spherocity:


2

ALI-PERF-8868

ALI-PERF-8876

A. Ortiz MPI@LHC 2019, Prague

Underlying Event (UE)

Antonio Ortiz (26/10/2018)ALICE Physics Week

(CERN, October 2018)

Traditional analysis

!4

Definition of 3 distinct regions based on the leading particle transverse momentum

Transverse (sensitive to UE)Toward and Away (sensitive to jet fragmentation)

Xiaowen Ren (CCNU)

Lea

ding

par

ticle

Tow

ards

Aw

ay

Tran

sver

se

Tran

sver

se

Δ"<$ 3

Δ">2 3$

$ 3<

Δ"<2 3$

$ 3<

Δ"<2 3$

Δ"

−Δ"

q Traditional UE measurement: according to theazimuthal direction of leading charged particle,three distinct topological regions are defined:

Ø Near Side (NS): |∆Ф| < π/3

Ø Away Side (AS): |∆Ф| > 2π/3

Ø Transverse Side (TS): π/3 < |∆Ф| < 2π/3 (sensitive to UE )

(sensitive to Jetfragmentation )

In parton-parton scattering, the UE is usually defined to be everything except thetwo outgoing hard scattered partons:• Beam-beam remnants.• Additional parton-parton interactions.• Initial and final state radiations

etc.…..

2

Oldrich Kepka

PRAGUE

Underlying event in hadron collision● Underlying event (UE) – particle production not associated with the leading hardest

parton-parton process. Attempts to exclude initial and final state radiation if it is hard

● Convincing evidence that UE is due to secondary interactions of other constituent

partons in the hadron – Multiple Parton-parton Interaction (MPI)

● Impact-parameter dependence of the matter distribution → pedestal effect in UE

distributions

● MPI interactions are not independent

- Color interaction between products of MPI collisions creates correlation


3

Underlying Event (UE): PYTHIA 8 has GOOD AGREEMENTUnderlying events in pp collisions atp

s = 13 TeV ALICE Collaboration

)c (GeV/leading

Tp

5 10 15 20 25 30 35 40

chN)

ϕ∆

η∆

ev

N1/(

0

1

2

3

c > 0.15 GeV/track

Tp

c > 0.5 GeV/track

Tp

c > 1.0 GeV/track

Tp

PYTHIA 8

PYTHIA 8

PYTHIA 8

EPOS LHC

EPOS LHC

EPOS LHC

= 13TeVspp,

| < 0.8ηtrack: |Transverse region

ALICE

)c (GeV/leading

Tp

5 10 15 20 25 30 35 40

(G

eV

/c)

Tp

Σ)ϕ

∆η

∆ev

N1/(

0

1

2

3 c > 0.15 GeV/track

Tp

c > 0.5 GeV/track

Tp

c > 1.0 GeV/track

Tp

PYTHIA 8

PYTHIA 8

PYTHIA 8

EPOS LHC

EPOS LHC

EPOS LHC

= 13TeVspp,


ALICE

Figure 5: Number density Nch (left) and Â pT (right) distributions as a function of pleadingT along with the MC

predictions in Transverse region for three transverse momentum thresholds of ptrackT > 0.15, 0.5, and 1.0 GeV/c.

The shaded areas represent the systematic uncertainties and vertical error bars indicate statistical uncertainties.

ps. Larger fitting ranges were also considered and consistent results were obtained. The shapes of the

particle densities as a function of pleadingT are then compared after dividing the densities by the height of

the jet pedestal. The results are shown in Fig. 6 (right). For the two higher energies the coverage extendsbeyond the fitting range, i.e. to pT > 10 GeV/c. In this range the densities agree within the statistical andsystematic uncertainties. In the region of the rise (pT < 5 GeV/c) one observes a clear ordering amongthe three collision energies, the lowest energy having the highest density relative to the plateau. At lowerp

s the jet pedestal starts at a slightly lower pleadingT .

)c (GeV/leading

Tp

0 5 10 15 20 25 30 35 40

chN)

ϕ∆

η∆

ev

N1/(

0

0.5

1

1.5

2

2.5

3

pp collisions

= 13TeVs

= 7TeV, JHEP 2012 (07):116s

= 0.9TeV, JHEP 2012 (07):116s

Constant fitting

| < 0.8η, |c > 0.15 GeV/track

TpTransverse region

ALICE

0 5 10 15 20 25 30 35 40

chN)

ϕ∆

η∆

ev

N1/(

0.5

1

pp collisions

= 13TeVs (1./2.23), ×

= 7TeVs (1./1.77), ×

= 0.9TeVs (1./1.00), ×| < 0.8η, |c > 0.15 GeV/track

Tp

Transverse region

ALICE

)c (GeV/leading

Tp

0 5 10 15 20 25 30 35 40

Ratio

0.5

1

1.5 0.9TeV/13TeV

7TeV/13TeV

Figure 6: Left: Number density Nch in the Transverse region as a function of pleadingT (p

trackT > 0.15 GeV/c thresh-

old) forp

s = 0.9, 7 and 13 TeV. A constant function is used to fit the data in the range 5 < pleadingT < 10 GeV/c

and the results are shown as solid lines. Right: Number densities Nch scaled by the pedestal values obtained fromthe fit in order to compare the shapes. The open boxes represent the systematic uncertainties and vertical error barsindicate statistical uncertainties.

Figure 7 shows thep

s-dependence of the number density of the jet pedestal in the Transverse region forp

trackT > 0.5 GeV/c, from a fitting of a constant function in the p

leadingT range 5 < p

leadingT < 10 GeV/c.

The lower energy data are taken from ALICE [12] and CDF [5] measurements. It is compared with

14

arXiv:1910.14400 (ALICE collaboration)

q Number density for charged particlesfor three different pT cuts

q A Steep rise in observed at low pTleading

(pTleading < 5 GeV/c).

q At pTleading > 5 GeV/c, Number density

in Transverse Side becomes almostindependent of pT

leading

q PYTHIA8 Monash 2013 explains thisbehaviour very well.


4

PYTHIA 8 (Monash 2013 )


5

q pT > 0.15 GeV

q |𝜂| < 0.8

q pTleading > 5.0 GeV/c

Keep environment similar to the ALICE at LHC.

Relative Transverse activity classifier (RT)

Above a lower threshold corresponding to the onset of the UE plateau in the transverse region (roughly, pTleading > 5 GeV/c), particle production can be studied as a function of event activity using the Relative Transverse activity classifier defined as follows:

<NInc> is the event-averaged multiplicity of the inclusive set of particles. Ninc is total numbers of the inclusive charged particles in the event.

RT =NInc.

< NInc. ><latexit sha1_base64="Bo1NvT5EU0F3IDfuw5Ycp+MsnPE=">AAACF3icbZDLSgMxFIYzXmu9VV26CRbB1TBTBV2oFN3oRqr0Bp0yZNJMG5rJDElGKGHewo2v4saFIm5159uYXgRt/SHw8Z9zODl/kDAqleN8WXPzC4tLy7mV/Ora+sZmYWu7LuNUYFLDMYtFM0CSMMpJTVHFSDMRBEUBI42gfzmsN+6JkDTmVTVISDtCXU5DipEyll+wtReE0KNK32W+rmbwDHqhQFjf+PqaYzvL9OkPnmeZXyg6tjMSnAV3AkUwUcUvfHqdGKcR4QozJGXLdRLV1kgoihnJ8l4qSYJwH3VJyyBHEZFtPborg/vG6cAwFuZxBUfu7wmNIikHUWA6I6R6cro2NP+rtVIVnrQ15UmqCMfjRWHKoIrhMCTYoYJgxQYGEBbU/BXiHjKxKBNl3oTgTp88C/WS7R7apdujYvliEkcO7II9cABccAzK4ApUQA1g8ACewAt4tR6tZ+vNeh+3zlmTmR3wR9bHN6tsn54=</latexit>

T. Martin, P. Skands, S. Farrington, Eur. Phys. J. C (2016) 76:299


6

Underlying events in pp collisions atp

s = 13 TeV ALICE Collaboration

)c (GeV/leading

Tp

5 10 15 20 25 30 35 40ch

N)ϕ∆η∆ev

N1/

(0

1

2

3

c > 0.15 GeV/track

Tp

c > 0.5 GeV/track

Tp

c > 1.0 GeV/track

Tp

PYTHIA 8

PYTHIA 8

PYTHIA 8

EPOS LHC

EPOS LHC

EPOS LHC

= 13TeVspp,


ALICE

)c (GeV/leading

Tp

5 10 15 20 25 30 35 40

(GeV

/c)

TpΣ)ϕ∆η∆ev

N1/

(

0

1

2

3 c > 0.15 GeV/track

Tp

c > 0.5 GeV/track

Tp

c > 1.0 GeV/track

Tp

PYTHIA 8

PYTHIA 8

PYTHIA 8

EPOS LHC

EPOS LHC

EPOS LHC

= 13TeVspp,


ALICE

Figure 5: Number density Nch (left) and Â pT (right) distributions as a function of pleadingT along with the MC

predictions in Transverse region for three transverse momentum thresholds of ptrackT > 0.15, 0.5, and 1.0 GeV/c.

The shaded areas represent the systematic uncertainties and vertical error bars indicate statistical uncertainties.

ps. Larger fitting ranges were also considered and consistent results were obtained. The shapes of the

particle densities as a function of pleadingT are then compared after dividing the densities by the height of

the jet pedestal. The results are shown in Fig. 6 (right). For the two higher energies the coverage extendsbeyond the fitting range, i.e. to pT > 10 GeV/c. In this range the densities agree within the statistical andsystematic uncertainties. In the region of the rise (pT < 5 GeV/c) one observes a clear ordering amongthe three collision energies, the lowest energy having the highest density relative to the plateau. At lowerp

s the jet pedestal starts at a slightly lower pleadingT .

)c (GeV/leading

Tp

0 5 10 15 20 25 30 35 40

chN)ϕ∆η∆

evN

1/(

0

0.5

1

1.5

2

2.5

3

pp collisions

= 13TeVs

= 7TeV, JHEP 2012 (07):116s

= 0.9TeV, JHEP 2012 (07):116s

Constant fitting

| < 0.8η, |c > 0.15 GeV/track

TpTransverse region

ALICE

0 5 10 15 20 25 30 35 40

chN)ϕ∆η∆

evN

1/(

0.5

1

pp collisions

= 13TeVs (1./2.23), ×

= 7TeVs (1./1.77), ×

= 0.9TeVs (1./1.00), ×| < 0.8η, |c > 0.15 GeV/track

Tp

Transverse region

ALICE

)c (GeV/leading

Tp

0 5 10 15 20 25 30 35 40

Rat

io

0.5

1

1.5 0.9TeV/13TeV

7TeV/13TeV

Figure 6: Left: Number density Nch in the Transverse region as a function of pleadingT (p

trackT > 0.15 GeV/c thresh-

old) forp

s = 0.9, 7 and 13 TeV. A constant function is used to fit the data in the range 5 < pleadingT < 10 GeV/c

and the results are shown as solid lines. Right: Number densities Nch scaled by the pedestal values obtained fromthe fit in order to compare the shapes. The open boxes represent the systematic uncertainties and vertical error barsindicate statistical uncertainties.

Figure 7 shows thep

s-dependence of the number density of the jet pedestal in the Transverse region forp

trackT > 0.5 GeV/c, from a fitting of a constant function in the p

leadingT range 5 < p

leadingT < 10 GeV/c.

The lower energy data are taken from ALICE [12] and CDF [5] measurements. It is compared with

14

Multiplicity bin covers a wide range of RT


7

0 10 20 30 40 50 60 70TSchN

0

50

100

150

200

> 0

.15 G

eV

/c)

T|

< 0

.8 &

ph

(|

ch

N

1

10

210

310

410

510

610

710

810

10£ Mult. £6

60£ Mult. £51

100£ Mult. £91

3£ T R£2 5£ T R£4 8£ T R£7

0 2 4 6 8 10 12 14TR

10 20 30 40 50 60 70TSchN

1-10

1

10

210

310

410

510

610

710

810

910

co

un

t

Mult Bins 0³

6 - 1051 - 6091 - 100

Spectra for different RT bins for the particular Multiplicity class.


8

1 10 210 (GeV/c)

Tp

17-10

15-10

13-10

11-10

9-10

7-10

5-10

3-10

1-10

1) T dph/d chN2 (d Tpp

1/2 ev1/N

Near Side

10)£ Mult. £(6 BinsTR

2 - 3

4 - 57 - 8

> 8

1 10 210 (GeV/c)

Tp

17-10

15-10

13-10

11-10

9-10

7-10

5-10

3-10

1-10

1) T dph/d

chN2 (d Tpp 1/2

ev1/N

Near Side

60)£ Mult. £(51

1 10 210 (GeV/c)

Tp

17-10

15-10

13-10

11-10

9-10

7-10

5-10

3-10

1-10

1) T dph/d

chN2 (d Tpp 1/2

ev1/N

Near Side

100)£ Mult. £(91

1 10 210 (GeV/c)

Tp

15-10

14-10

13-10

12-10

11-10

10-10

9-10

8-10

7-10

6-10

5-10

4-10

3-10

2-10

1-10


1/2 ev1/N

Transverse Side

10)£ Mult. £ (6 BinsTR

2 - 3

4 - 57 - 8

> 8

1 10 210 (GeV/c)

Tp

15-10

14-10

13-10

12-10

11-10

10-10

9-10

8-10

7-10

6-10

5-10

4-10

3-10

2-10

1-10

1) T dph/d

chN2 (d Tpp 1/2

ev1/N

Transverse Side

60)£ Mult. £(51

1 10 210 (GeV/c)

Tp

15-10

14-10

13-10

12-10

11-10

10-10

9-10

8-10

7-10

6-10

5-10

4-10

3-10

2-10

1-10

1) T dph/d

chN2 (d Tpp 1/2

ev1/N

Transverse Side

100)£ Mult. £(91

Particle leakages from Near Side to Transverse Side!

Particle leakages from Near Side to Transverse Side!

Spectra for different RT bins for the particular Multiplicity class.


9

1 10 210 (GeV/c)

Tp

17-10

15-10

13-10

11-10

9-10

7-10

5-10

3-10

1-10


1/2 ev1/N

Near Side

10)£ Mult. £(6 BinsTR

2 - 3

4 - 57 - 8

> 8

1 10 210 (GeV/c)

Tp

17-10

15-10

13-10

11-10

9-10

7-10

5-10

3-10

1-10

1) T dph/d

chN2 (d Tpp 1/2

ev1/N

Near Side

60)£ Mult. £(51

1 10 210 (GeV/c)

Tp

17-10

15-10

13-10

11-10

9-10

7-10

5-10

3-10

1-10

1) T dph/d

chN2 (d Tpp 1/2

ev1/N

Near Side

100)£ Mult. £(91

1 10 210 (GeV/c)

Tp

15-10

14-10

13-10

12-10

11-10

10-10

9-10

8-10

7-10

6-10

5-10

4-10

3-10

2-10

1-10


1/2 ev1/N

Transverse Side

10)£ Mult. £ (6 BinsTR

2 - 3

4 - 57 - 8

> 8

1 10 210 (GeV/c)

Tp

15-10

14-10

13-10

12-10

11-10

10-10

9-10

8-10

7-10

6-10

5-10

4-10

3-10

2-10

1-10

1) T dph/d

chN2 (d Tpp 1/2

ev1/N

Transverse Side

60)£ Mult. £(51

1 10 210 (GeV/c)

Tp

15-10

14-10

13-10

12-10

11-10

10-10

9-10

8-10

7-10

6-10

5-10

4-10

3-10

2-10

1-10

1) T dph/d

chN2 (d Tpp 1/2

ev1/N

Transverse Side

100)£ Mult. £(91

Conclusions:


10

q The "leaking" of hadrons from the Near Side into the Transverse Side is not a suddenoccurrence. It happens even at moderate multiplicities for a part of the events.

q We observe a gradual evolution of the transverse spectra for rising RT values.

q We believe that the origin of the hedgehog events should be sought in high RT eventswhere the jetty events do not exist.

Antonio Ortiz (November 18, 2019)11th International Workshop on Multiple Partonic Interactions at the LHC, Prague

Transverse spherocity

3

Transverse spherocity ( ) is an event shape which measures the particle production which is perpendicular to the plane formed by the beam axis and that of the main partonic scattering (~spherocity axis, )

S0

n̂

For the calculation of spherocity we consider at least three primary charged particles, GeV/c,

Several works have been reported:Adv. Ser. Direct. High Energy Phys. 29 (2018) 343-357Nucl. Phys. A941 (2015) 78-86arXiv:1404.2372

pT > 0.15 |η | < 0.8

Spherocity (So close to 0)

Spherocity (So close to 1)

S0 = min π2

4 (∑i | ⃗p T,i × n̂ |

∑i pT.i )2

underlying event (ue) study as a function of rt in pp ... · aditya nath mishra (december 02, 2019)...

Documents