Rivet for heavy-ions: current status & future developments

Rivet for heavy-ions: current status & futuredevelopments

Przemek Karczmarczyk

Rivet dev & user workshop, Lunga, 28.05.2019

Przemek Karczmarczyk Rivet for HI 28.05.2019 1 / 20

Overview

1 Currently available HI implementations

2 Planned HI implementationsEvent mixingEvent type determination

3 Rivet for HI: impactHI paperMCPLOTS for heavy-ions


Currently available HI implementations

Overview






Implemented HI features: centrality framework

� Centrality framework: allows an analysis to cut on percentiles ofsingle event quantities preloaded to that analysis

� Consist of:I Set of calibration analysesI Preloading calibration files as an input to the next runI Options for centrality to select the type of calibration to useI Centrality projection that allows to access centrality value

� ’Options’ parameter to allow selection of centrality calibrationI REF (default): get calibration histogram from reference dataI GEN: get generated calibration histogramI IMP: get impact parameter calibration histogramI USR: get user-defined calibration histogramI RAW: get generated centrality (available only with HepMC3)



Implemented HI features: reentrant finalize

� Postprocessing implemented in a form of ’reentrant finalize’ method

I Analyses produce ’RAW’ histograms - saved in the output file beforecalling finalize() method

I rivet-merge to call finalize with preloaded files from previous runs andget final plots

I ’Reentrant’ flag to mark analyses using reentrant finalize method



Implemented HI features: event mixing

� Event mixing procedure projects out an event mixed of several events

I Based on a mixing observable provided as an input to define whatshould qualify as a mixable event

I Mixing observable: number of final state particles, centrality, eventplane angle, etc.

I Consist of a buffer that is filled with events on the runtimeI This buffer can be returned and used in the analysis to perform

required operations

� Partial support for event mixing already available since Rivet 2.7.0



HI analyses

� Analyses, that are using at least one HI feature:1 ALICE 2010 I880049: dNch/dη analysis2 ALICE 2012 I930312: IAA analysis3 ALICE 2012 I1127497: RAA analysis4 ALICE 2012 I1126966: pi, K, p spectra5 ALICE 2013 I1225979: Charged multiplicity6 ALICE 2014 I1243865: Multi-strange baryons7 ALICE 2014 I1244523: Multi-strange baryons8 ALICE 2016 I1394676: Charged multiplicity9 ALICE 2016 I1419244: Multiparticle correlations (flow)10 ALICE 2016 I1471838: Multi-strange baryons11 ALICE 2016 I1507090: Charged multiplicity12 ALICE 2016 I1507157: Angular correlations13 ATLAS 2015 I1360290: Charged multiplicity14 ATLAS 2015 I1386475: Charged multiplicity + spectra15 BRAHMS 2004 I647076: pi, K, p spectra as function of rapidity16 STAR 2016 I1414638: Di-hadron correlations17 CMS 2017 I1471287: Multiparticle correlations (flow)18 + few calibration analyses (without data)


Planned HI implementations

Overview





Planned HI implementations Event mixing

Event mixing

� Reason to use it: measurements sensitive to detector acceptance� 1st example: gaps in ϕ distributions cause peak stuctures in

two-particle ∆ϕ distributions - only experimental effect

� 2nd example: limited η acceptance causes a tent-like structure in twoparticle ∆η distribution - can be visible in Rivet analysis


Planned HI implementations Event mixing

Event mixing

� What is supported?

I Simple event mixing that assumes unitary event weights and that isusing just 1 observable simultaneously for binning

I By default it uses multiplicity as an observable

� What is not supported?

I Non-unitary event weightsI Using other observables like centrality, event plange angle, etc. - some

recent developments allow that alreadyI Using 2 observables simultaneously to create a 2-dimensional map of

events for event mixing


Planned HI implementations Event type determination

Event type determination

� Use-case: an analysis using >1 beam (for example for calculatingratios of PbPb/pp)

1 const HepMC:: HeavyIon* hi = event.genEvent ()->heavy_ion ();

2 if (hi && hi ->is_valid ()) {

3 // Fill PbPb plots

4 [...]

5 }

6 else {

7 // Fill pp plots

8 [...]

9 }

� Ideal case:

I Well-defined beam and correct heavy-ion line in HepMC file

� Realistic case:

I Inconsistency in MC generators: errors/bugs or conceptual differencesI Current solution not reliable: does not work in all cases



Examples

1 Pythia pp: normal behaviour, no HepMC heavy-ion line

2 Pythia pPb: normal behaviour, heavy-ion line exists and it’s notempty (works well with bugfix)

3 Jewel pp and PbPb: exception, we always end up with pp beam andnot empty HI line in .hepmc file → we need to see what exactly is inthe heavy-ion line to check what kind of events we are dealing with

4 Epos-LHC pp: exception, heavy-ion line always exists and may be notempty even for non-heavy-ion events

5 Epos-LHC PbPb: normal behaviour, heavy-ion line exists and it’s notempty (works well with bugfix)

Bug in HepMC

HepMC does not pass heavy-ion properties from the file in case number ofhard collisions is equal to 0

Bug fix in ALICE HepMC branch: https://github.com/alisw/hepmc/commit/d921ebd87634b09f55c8a18669bec56c020ad000


https://github.com/alisw/hepmc/commit/d921ebd87634b09f55c8a18669bec56c020ad000


Event type determination: solution 1

� Generic method to call inside analysis

1 bool Event:: is_heavy_ion () const {

2 // Generic check for the existence of the HepMC heavy -ion line.

3 // If it does not exist , this can’t be a heavy -ion event

4 const HepMC:: HeavyIon* hi = genEvent ()->heavy_ion ();

5 if (!hi) return false;

6 // Generic check for invalid heavy -ion line according to HepMC ,

7 // which means this event contain heavy -ion line , but it is empty

8 // (everything equal to 0). The following code works properly

9 // only for HepMC version >= 2.07.00

10 #if HEPMC_VERSION_CODE >= 2007000

11 if (!hi->is_valid ())

12 return false;

13 // All known exceptions for all inconsistent generators

14 [...]

15 // In all other cases , this must be a heavy -ion event

16 return true;

17 #else

18 // For older HepMC versions , there is no reliable method

19 // to check for the event type

20 MSG_ERROR("Not possible to check for the event type using HepMC < 2.07.00!");

21 exit (1);

22 #endif

23 }

� Can be split to have a method per generator




� A flag to tell Rivet what kind of events are provided

� Could look something like this:

I rivet --heavyion input PbPb.hepmcI rivet --pp input pp.hepmc

� This will force Rivet to fill heavy-ion plots inside analyses, no matterwhat kind of events are in the HepMC file

� Possible use-case:

1 if (event.is_heavy_ion ()) { // value set depending on a flag

2 // Fill PbPb plots

3 [...]

4 }

5 else {

6 // Fill pp plots

7 [...]

8 }



Method comparison

Solution 1: analysis’ method

Pros

� Fully automatic - nothing to dofrom user’s point of view

� No additional flag required

Cons

� May not account for all existingexceptions

� Difficult to predict behaviour offuture generator versions

� Problematic to extend to checkfor a particular beam type

Solution 2: user’s flag

Pros

� User has full control

� All exceptions can beaccounted for

Cons

� Additional flag required

� Requires user to do some workand relies on his correctness

� Problematic to extend to checkfor a particular beam type



Event type determination: other solutions

� Can we combine these 2 solutions?

� Are there other solutions to that problem?

� Can we assume that future versions of MC generators will be reliable?


Rivet for HI: impact

Overview





Rivet for HI: impact HI paper

HI paper

� Paper started during the last workshop

� Overleaf link: https://www.overleaf.com/18807575kvqryczhhyjr

� It will include:

I Description of implemented heavy-ion featuresI Description of what measurements are possible in Rivet using these

features:

Centrality inclusive measurementsCentrality differential measurementsFlow measurementsetc.

I Results from implemented HI analyses using different MC generators


https://www.overleaf.com/18807575kvqryczhhyjr

Rivet for HI: impact MCPLOTS for heavy-ions

MCPLOTS for heavy-ions

� MCPLOTS adapted to HI version of Rivet� What was taken into account:

I Production of calibration filesI Handling of centrality optionsI Merging output .yoda files using reentrant finalizeI New HI analyses

� ALICE production webpage: http://mcplots-alice.cern.ch/ - for AAonly, results to be included in the official website


http://mcplots-alice.cern.ch/


Thank you!



Backup




1 // Exception for JEWEL: it always produces a valid (non -empty) heavy -ion

2 // line for all types of events (according to HepMC) and it always uses

3 // pp events as beam particles. We need to check if all properties in

4 // heavy -ion line are equal to 0, except the impact parameter value ,

5 // which will be -1 for non -heavy -ion events

6 if (genEvent ()->beam_particles ().first ->pdg_id () == 2212 &&

7 genEvent ()->beam_particles ().second ->pdg_id () == 2212 &&

8 hi->Ncoll_hard () == 0 &&

9 hi->Npart_proj () == 0 &&

10 hi->Npart_targ () == 0 &&

11 hi->Ncoll () == 0 &&

12 hi->spectator_neutrons () == 0 &&

13 hi->spectator_protons () == 0 &&

14 hi->N_Nwounded_collisions () == 0 &&

15 hi->Nwounded_N_collisions () == 0 &&

16 hi->Nwounded_Nwounded_collisions () == 0 &&

17 hi->event_plane_angle () < 1.0e-3 &&

18 hi->eccentricity () < 1.0e-3 &&

19 hi->sigma_inel_NN () < 1.0e-3) {

20 if (hi->impact_parameter () + 1. < 1.0e-3)

21 return false;

22 else

23 return true;

24 }

25 // Exception for EPOS -LHC: we can have some non -heavy -ion events

26 // with a valid (non -empty) HepMC heavy -ion line , so we need to

27 // check beam particles IDs explicitly

28 if (genEvent ()->beam_particles ().first ->pdg_id () < 1e+9 &&

29 genEvent ()->beam_particles ().second ->pdg_id () < 1e+9) {

30 return false;

31 }



Results from EPOS

b

b

b

b

b

b

bb

b

b DataRivet

0

200

400

600

800

1.0 ·103

1.2 ·103

1.4 ·103

1.6 ·103

1.8 ·103Nch vs. centrality, Pb–Pb

√sNN = 2.76 TeV

dN

ch/

dη

b b b b b b b b b

0 10 20 30 40 50 60 70 800.50.60.70.80.9

11.11.21.31.4

Centrality [%]

MC

/Dat

a

(a) ALICE 2010 I880049analysis

b b b b b b b b b b b b b b b b b b b b b b b b b b bbbbbbbbbbbb

bbbbbbbbbbbbbbbbbbbbbbb bbbb

b Dataoutput

10−3

10−2

10−1

1

10 1

10 2

10 3

Nch vs. p⊥, Centr = 0 − 20 %,√

sNN = 2.76 TeV

1/N

evt1

/(2

πp ⊥

)(d

2 Nch)/

(dη

dp ⊥

)[(

GeV

/c)

−2 ]

b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b

1 10 10.50.60.70.80.9

11.11.21.31.4

p⊥ [GeV / c]

MC

/Dat

a

(b) ALICE 2012 I1127497analysis

b

b bb

b DataEPOS-LHC

0

0.5

1

1.5

2

2.5

ICP (0-5% / 60-90%) near-side

I CP

(0-5

%/

60-9

0%)

b b b b

3 4 5 6 7 8 9 100.50.60.70.80.9

11.11.21.31.4

pt,assoc [GeV/c]

MC

/Dat

a

(c) ALICE 2012 I930312analysis

� Multiplicity distribution used for calibration



Results: calibration plots

b (fm)

Eve

nts

1

10

210

310

410 Epos (LHC)

2760 GeV PbPb Heavy Ion

mcp

lots

-alic

e-de

v2.c

ern.

ch 1

0k e

vent

s≥

Riv

et 2

.7.0

,

Epos 1.99.crmc.1.7.0-hi

Impact parameter distribution (alice2015)

b (fm)0 5 10 15 20

Rat

io to

Epo

s (L

HC

)

1

2

0.5

+20%

-20%

+10%

-10%

2×

-50%

+50%

V0M

Eve

nts

7−10

6−10

5−10

4−10

3−10

2−10

1−10

1

10

210

310

ALICEEpos (LHC)

2760 GeV PbPb Centrality calibration

mcp

lots

-alic

e-de

v2.c

ern.

ch 1

0k e

vent

s≥

Riv

et 2

.7.0

,


ALICE_2015_PBPBCentrality

ALICE V0M distribution (alice2015)

V0M0 10000 20000 30000

Rat

io to

ALI

CE

1

2

0.5

+20%

-20%

+10%

-10%

2×

-50%

+50%



Results (1)

Centrality [%]

η /

dch

dN

210

310

410ALICEEpos (LHC)


mcp

lots

-alic

e-de

v2.c

ern.

ch 1

0k e

vent

s≥

Riv

et 2

.7.0

,


ALICE_2010_I880049

vs centrality (alice2010-1)chN

Centrality [%]0 20 40 60 80

Rat

io to

ALI

CE

1

2

0.5

+20%

-20%

+10%

-10%

2×

-50%

+50%

400

600

800

1000

1200

1400

1600

1800

2000

2200

2400

ALICEEpos (LHC)


mcp

lots

-alic

e-de

v2.c

ern.

ch 1

0k e

vent

s≥

Riv

et 2

.7.0

,


ALICE_2013_I1225979

(alice2013,centr=00-05)ηdN/d

5− 0 5

Rat

io to

ALI

CE

1

2

0.5

+20%

-20%

+10%

-10%

2×

-50%

+50%



Results (2)

,[GeV / c]T

p

]2 )

, [(G

eG/c

)T

dp

η)

/ (d

chN2

) (d

T pπ

1(2

evt

1 / N

14−10

12−10

10−10

8−10

6−10

4−10

2−101

210

410

610

810

10101110

ALICEEpos (LHC)Jewel-Simple (default)

2760 GeV PbPb Soft QCD

mcp

lots

-alic

e-de

v2.c

ern.

ch 5

k ev

ents

≥R

ivet

2.7

.0,

Epos 1.99.crmc.1.7.0-hi, JEWEL(simple) 2.0.2

ALICE_2012_I1127497

(alice2012,centr=00-05)t

vs pchN

,[GeV / c]T

p1 10

Rat

io to

ALI

CE

1

2

0.5

+20%

-20%

+10%

-10%

2×

-50%

+50%

,[GeV / c]T

p

RA

A

1−10

1

ALICEJewel-Simple/Jewel-Vac (default,default)

2760 GeV PbPb_pp Soft QCD

mcp

lots

-alic

e-de

v2.c

ern.

chR

ivet

2.6

.0-p

reH

I

JEWEL(simple/vac) 2.0.2;2.0.2

ALICE_2012_I1127497

(alice2,centr:00-20)AAR

,[GeV / c]T

p1 10

Rat

io to

ALI

CE

1

2

0.5

+20%

-20%

+10%

-10%

2×

-50%

+50%


Documents

Rivet for heavy-ions: current status & future developments