universality of particle production and energy balance in

Universality of particle production and energy balance

in hadronic and nuclear collisions

Aditya Nath MishraIndian Institute of Technology Indore, INDIA

ISMD2015 (Munich, October 5-‐9, 2015)

E.K.G. Sarkisyan, A.N. Mishra, R. Sahoo, A.S. Sakharov arXiv:1405.2819

03/10/15 ISMD2015 1

MOTIVATIONv  Bulk observables - mean multiplicity and rapidity densities - control

parameters of the formation and evolution of the collision initial state

v  Extensively studied in heavy-ion collisions at RHIC

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v  Similarities with e+e- and pp data: universality in multihadron production

30% of a spectator energy?

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v  pp multiplicity data to be scaled

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v  pp multiplicity data to be scaled

v  pp midrapidity density does not obey a similar scaling

Not the same scaling for both variables and for different types of Interactions

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Energy Scaling vs. Types of Collisionsv  e+e- (structureless particles) annihilation - the total interaction energy

is deposited in the initial state

v  pp (superposition of three pairs of constituents) collision - only the energy of the interacting single quark pair is deposited in the initial state

v  Both multiplicity and midrapidity density should be similar in pp at c.m. energy √spp and e+e- at c.m. energy √see≈ √spp/3

v  Head-on heavy ion collisions: all three quarks participate nearly simultaneously and deposit their energy coherently into initial state

v  Both multiplicity and midrapidity density should be similar in pp at c.m. energy √spp and head-on AA at c.m. energy √sNN ≈ √spp/3

E. Sarkisyan & A. Sakharov (2004) : dissipaFng energy parFcipants

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Hydrodynamics of CollisionsØ  Two head-on colliding Lorentz-contracted particles stop within

the overlapped zone v Formation of fully thermalized initial state at the collision momentv  The decay (expansion) of the initial state is governed by relativistic hydrodynamics - Landau model (1953)

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Steinberg, nucl-‐ex/0405022

BRAHMS, nucl-‐ex/0410003

2Nch

Npart

exp(�y

2/2L)p2⇡L

, L = ln

ps

2m


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Steinberg, nucl-‐ex/0405022


2Nch

Npart

exp(�y

2/2L)p2⇡L

, L = ln

ps

2m


The production of secondaries is defined by the energy deposited into the initial state

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Hydrodynamics & Effective Energy

From Landau Hydrodynamics

L = ln

ps

2m

Landau Hydrodynamics + Constituent Quark approach:

2Nch

Npart= Npp

ch

⇢(0)

⇢pp(0)

sLNN

Lpp,

2Nch

Npart= Npp

ch

⇢(0)

⇢pp(0)

s

1� 2ln3

ln(4.5psNN/mp)

,psNN =

pspp/3.

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Hydrodynamics & Effective Energy

From Landau Hydrodynamics

L = ln

ps

2m

Landau Hydrodynamics + Constituent Quark approach:

2Nch

Npart= Npp

ch

⇢(0)

⇢pp(0)

sLNN

Lpp,

2Nch

Npart= Npp

ch

⇢(0)

⇢pp(0)

s

1� 2ln3

ln(4.5psNN/mp)

,psNN =

pspp/3.

Effective Energy:Effective energy can be calculated as following:

Here α is centrality percentile. e.g. For 0-5% central collision α = 0.025

✏NN =psNN(1 � ↵)

2Nch

Npart= Npp

ch

⇢(0)

⇢pp(0)

s

1� 2ln3

ln(4.5psNN/mp)

,psNN =

pspp/3

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Pseudorapidity and ET Midrapidity Densities

2

4

6

8

10

12

0 100 200 300 400Npart

ρ(0)

= 2

dNch

/dη|

η=0 / N

part

CMS 2.76 TeVPHOBOS 200 GeV × 2.12PHOBOS 200 GeVPHOBOS 130 GeVPHOBOS 62.4 GeVPHOBOS 19.6 GeVCQM + Landau, pp-basedEffective energy dissip. model

Effective energy dissip. modelprediction for √s−NN = 5.52 TeVCMS 2.76 TeV × 1.43

2

4

6

8

10

12

14

1 10 10 2 10 3

√s−

NN , εNN [GeV]

ρ(0)

= 2

dNch

/dη|

η=0 / N

part

AA central collisionsLHC data

ALICEATLASCMS

RHIC AuAu dataBRAHMSPHENIX

PHOBOS STAR

SPS dataNA45NA49

AGS dataE802/917

GSI dataFOPI

hybrid fit: log(s) + power-lawpower-law fitlog(s) fit up to RHIC data

Energy dissipation model calculationfor AA centrality data at εNN

CMSPHOBOSSTAR

Fits to weighted LHC and RHIC dataLHC: ALICE, ATLAS, CMSRHIC: PHENIX, PHOBOS, STAR

hybrid fit: log(s) + power-lawpower-law fit

Prediction for AA at √s−NN = 5.52 TeV

2

4

6

8

10

12

14

16

0 100 200 300 400Npart

ρ T(0) =

2 dE

T /dη|

η=0 /N

part [

GeV]

CMS 2.76 TeVPHENIX 200 GeV × 3.07PHENIX 200 GeVPHENIX 130 GeVPHENIX 62.4 GeVPHENIX 19.6 GeVEffective energy dissip. model

Effective energy dissip. modelprediction for √s−NN = 5.52 TeVCMS 2.76 TeV × 1.59

0

2

4

6

8

10

12

14

16

1 10 10 2 10 3

√s−

NN , εNN [GeV]

ρ T(0) =

2 dE

T /dη|

η=0 / N

part [

GeV] AA central collisions

LHC dataCMS

RHIC dataPHENIXSTAR

SPS dataNA49WA98

AGS dataE802/917

GSI dataFOPI

hybrid fit: log(s) + power-lawpower-law fitlog(s) fit up to RHIC data (PHENIX)

Energy dissipation model calculationfor AA centrality data at εNN

CMSPHENIX

Fits to weighted CMS, PHENIX, STAR datahybrid fit: log(s) + power-lawpower-law fit

Prediction for AA at √s−NN = 5.52 TeV

v  CQM+Landau calculations have a very good agreement with data

v  Effective energy dissipation well explains the centrality behaviour

v  Similarity in the data from peripheral to the most central collisions: all the data follow the same (effective) energy behavior

v  The combined data indicate possible transition to a new regime at √sNN=0.5-1.0 TeV

Effective energy approach provides a good description of both the pseudorapidity and transverse energy densities at midrapidity in heavy-ion collisions

ANM, R Sahoo, EKG Sarkisyan, AS Sakharov, Eur.Phys.J. C 74 (2014) 11, 3147

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v  Hybrid and power-law functions provide good fits for all available AA data and are almost indistinguishable up to LHC energy

v  LHC data departs from log2-polynomial fit at √sNN about 1 TeV, indicates a possible transition to a new regime in heavy-ion collisions

Mean Multiplicity Energy Dependence

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v  Hybrid and power-law functions provide good fits for all available AA data and are almost indistinguishable up to LHC energy

v  LHC data departs from log2-polynomial fit at √sNN about 1 TeV, indicates a possible transition to a new regime in heavy-ion collisions

v  Charged particles mean multiplicities calculated from the dissipation energy approach for AA data, using the pp/ppbar measurements, well describe the heavy-ion measurements


v  The dotted l ines represent the calculations from the effective-energy approach

v  The calculations, driven by the centrality-defined effective c.m. energy εNN, well reproduce the LHC data

v  RHIC da ta show a s ign i fican t difference with the calculations for peripheral collisions

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Mean Multiplicity Centrality Dependence

η6− 4− 2− 0 2 4 6

part

/ Nη /d ch

) = 2 d

Nη (ρ

2

4

6

8

10

= 2.76 TeV, 10-20% (ALICE)NNsPbPb at = 7 TeV (CMS) ppspp at = 7 TeV (LHCb)ppspp at = 7 TeV (TOTEM) ppspp at

Energy dissipation, pp-based

η4− 2− 0 2 4

part

/ Nη /d ch

) = 2 d

Nη (ρ

0

0.5

1

1.5

2

2.5 = 19.6 GeV, 6-10% (PHOBOS)NNsAuAu at

= 53 GeV (UA5)ppsp at pEnergy dissipation, pp-based

η4− 2− 0 2 4

part

/ Nη /d ch

) = 2 d

Nη (ρ

0

0.5

1

1.5

2

2.5

3

3.5 = 62.4 GeV, 0-3% (PHOBOS)NNsAuAu at

= 200 GeV (UA5) ppsp at pEnergy dissipation, pp-based

η4− 2− 0 2 4

part

/ Nη /d ch

) = 2 d

Nη (ρ

0

1

2

3

4

5

= 200 GeV, 0-3% (PHOBOS)NNsAuAu at = 630 GeV (CDF)ppsp at p = 630 GeV (P238) ppsp at p

Energy dissipation, pp-based

v  Calculations for high-central collisions, are in very good agreement with the measurements.

v  At LHC energy, pp measurements from the three different experiments are used and shown to reproduce AA data

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Pseudorapidity Distributions: Most Central Collisions

v  Calculations for non-central collisions, agree well with the measurements in the central η region while fall below the data outside this region

v  Within the effective-energy approach, one expects the limiting fragmentation scaling of ρ(η) (fragmentation area of ρ(η) independence of collision energy in the beam/target rest frame) measured at √sNN to be similar to that of the calculated distribution but taken at the effective energy εNN , i.e. η → η − yeff , where yeff = ln(εNN /mp)

03/10/15 ISMD2015 16

Pseudorapidity Distributions: Non-central Collision

v  The measured distribution ρ(η) is shifted by the beam rapidity, ybeam, while the calculated distribution is shifted by yeff = ln(εNN /mp) and becomes a function of η′ = η − yeff. Then the distributions coincide as expected.

- yη = ’η5− 4− 3− 2− 1− 0

part

/ Nη /d

ch) =

2 dN

η (ρ

0

0.5

1

1.5

2

2.5

3

3.5

4 = 130 GeVNNsAuAu at

beam45-50% (PHOBOS), y = y

beam = 200 GeV (UA5), y = yppsp at p

effEffective-energy dissipation, pp-based, y = y

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Energy Balanced Limiting Fragmentation

v  The measured distribution ρ(η) is shifted by the beam rapidity, ybeam, while the calculated distribution is shifted by yeff = ln(εNN /mp) and becomes a function of η′ = η − yeff. Then the distributions coincide as expected.

v  The newly calculated distribution ρ(η) needs to be shifted by the difference (yeff − ybeam) in the fragmentation region: η → η − (yeff − ybeam ) = η − ln(1 − α).

v  These represent the energy balanced limiting fragmentation scaling phenomena

- yη = ’η5− 4− 3− 2− 1− 0

part

/ Nη /d

ch) =

2 dN

η (ρ

0

0.5

1

1.5

2

2.5

3

3.5

4 = 130 GeVNNsAuAu at

beam45-50% (PHOBOS), y = y

beam = 200 GeV (UA5), y = yppsp at p

effEffective-energy dissipation, pp-based, y = y

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Energy Balanced Limiting Fragmentation

η4− 2− 0 2 4

part

/ Nη /d

ch) =

2 dN

η (ρ

0

0.5

1

1.5

2

2.5

3

3.5

4 = 130 GeV, 45-50% (PHOBOS)NNsAuAu at

= 200 GeV (UA5) ppsp at pEffective-energy dissipation with energy balanced limiting fragmentation, pp-basedEffective-energy dissipation, pp-based

20

40

60

80

100

120

100 200 300 400

Npart

2 Nch

/ N pa

rt

ALICE 2.76 TeV x 1.4ALICE 2.76 TeVPHOBOS 200 GeV x 2.87PHOBOS 200 GeVPHOBOS 130 GeVPHOBOS 62.4 GeV

Effective-energy dissipationwith energy balancedlimiting fragmentationEffective-energy dissipationEnergy dissipation, pp-based

Effective-energy dissipationprediction for √s

−

NN = 5.13 TeV

v  The dotted l ines represent the calculations from the effective-energy approach

v  The calculations, driven by the centrality-defined effective c.m. energy εNN, well reproduce the LHC data

v  RHIC da ta show a s ign i fican t difference with the calculations for peripheral collisions

v  The difference between RHIC data and calculations is explained by including the Energy Balanced Limiting Fragmentation Scaling

03/10/15 ISMD2015 14

Mean Multiplicity Centrality Dependence:Energy Balanced Limiting Fragmentation

03/10/15 ISMD2015 12

0

20

40

60

80

100

120

10 10 2 10 3

√s−

NN , √s−

pp/3 , εNN [GeV]

2 N ch

/ N pa

rt

AA central collisionsALICEPHOBOSNA49

E895hybrid fit: log2(s) + power-lawpower-law fitlog2(s) fit up to RHIC dataHADES

Effective-energy calculationsfor AA centrality data at εNN

ALICEPHOBOS (with energy balancedlimiting fragmentation scaling)hybrid fit: log2(s) + power-lawpower-law fit

AA energy dissipation calculationswith pp/p

–p data

LHC (using hybrid fit, this work)E735UA5ISRbubble chamber

Predictions for LHCAA at √s

−

NN = 5.13 TeVAA from energy dissipation for pp at √s

−

pp = 13 TeV

v  Hybrid and power-law fits show a good agreement with AA data and are almost indistinguishable

v  LHC data departs from log2 polynomial fit at √sNN about 1 TeV, indicates a possible transition to a new regime in heavy-ion collisions

v  Charged particles mean multiplicities calculated from the dissipation energy approach for AA data, using the pp/ppbar measurements, well describe the heavy-ion measurements

v  The centrality data show the energy dependence similar to head-on data as soon as the centrality data are considered in terms of the effective energy. The RHIC data are recalculated by using the Energy Balanced Limiting Fragmentation Scaling

Prediction for heavy-ion collisions at √sNN = 5.13 TeV and the expectation at √spp = 13 TeV are shown.


10

20

30

40

50

60

70

80

10 10 2 10 3 10 4

√s−

pp [GeV]

Nchpp

pp/p–p interactionsE735 n.s.d.UA5 n.s.d.ISR n.s.d.bubble chamberhybrid fit: log2(s) + power-lawpower-law fitlog2(s) fit

Energy dissipation predictions

v  The power-law and hybrid fit functions fit well the data in the entire c.m. energy region and are seen to overlap up to √spp= 10 TeV

v  Log2-polynomial fit function is also very close to the power-law fit even for √spp > 2 TeV

v  No change in the multihadron production in pp interactions up to the top LHC energy in contrast to a new regime possibly occurred at √sNN ≈ 1 TeV in heavy-ion collisions

v  pp participant dissipating energy approach predictions are given

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Mean Multiplicity Energy Dependencesin pp Interactions

v  The AA multiplicity measurements are well reproduced under the assumption of the effective energy deriving the multiparticle production process and pointing to the same energy behaviour for all types of heavy-ion collisions, from peripheral to the most central collisions

v  A new scaling, called the energy balanced limiting fragmentation scaling, which takes into account the balance between the collision energy and the energy shared by the participants, is introduced

v  Energy balanced limiting fragmentation scaling provides a solution of the RHIC “puzzle” of the difference between the centrality independence of the mean multiplicity vs. the monotonic decrease of the midrapidity pseudorapidity density with the increase of centrality

v  Under the concept of the effective energy and using the energy balanced limiting fragmentation scaling, the centrality data are found to follow the head-on collisions √sNN dependence

v  A possible transition to a new regime at √sNN ~1 TeV is indicated

v  Predictions are made for heavy-ion and pp collisions for upcoming energies at the LHC

03/10/15 ISMD2015 20

Summary and Conclusions

universality of particle production and energy balance in

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