muon simulation : status & plan partha pratim bhaduri subhasis chattopadhyay vecc, kolkata

Muon simulation : status & planMuon simulation : status & plan

Partha Pratim BhaduriSubhasis Chattopadhyay

VECC, Kolkata

2

CBM Physics – keywords

• physics program complementary to RHIC, LHC

• rare probes

What does theory expect? → mainly predictions from lattice QCD:

• crossover transition from partonic to hadronic matter at small B and high T

• critical endpoint in intermediate range of the phase diagram

• first order deconfinement phase transition at high B but moderate T

However ...

• deconfinement = chiral phase transition ?

• hadrons and quarks at high ?

• signatures (measurable!) for these structures/ phases?

• how to characterize the medium?

3

Physics of CBM : Observablesphysics topics

Deconfinement at high B ?

Equation of State at highB ?

order of phase transition ?

Critical point ?

in-medium properties of hadrons

onset of chiral symmetry restoration at high B

observables

strangeness production: K,

charm production: J/, D

flow excitation function

event-by-event fluctuations

l+l-

open charm

CBM: rare probes → high interaction rates!

CBM: detailed measurement over precise energy bins (pp, pA, AA) FAIR beam energy range 10-40 AGeV (protons 90 GeV)

4

Charm production at threshold

[W. Cassing et al., Nucl. Phys. A 691 (2001) 753]

HSD simulations

• CBM will measure charm production at threshold

→ after primordial production, the survival and momentum of the charm quarks depends on the interactions with the dense and hot medium!

→ direct probe of the medium!

• charmonium in hot and dense matter?

• relation to deconfinement?

• relation to open charm?

5

• screening of pairs in partonic phase

• anomalous J/ suppression observed at top-SPS and RHIC energies

• Sequential suppression - signal of deconfinement?

OR

• Co-mover absorption?

Deconfinement : charmonium suppression

no J/ψ, ψ' → e+e- (μ+μ-) data below 158 AGeV

Measure excitation functions of J/ψ and ψ' in p+p, p+A and A+A collisions

Still an open issue

cc

6[Rapp, Wambach, Adv. Nucl. Phys. 25 (2000) 1, hep-ph/9909229]

• -meson couples strongly to the medium

• vacuum lifetime 0 = 1.3 fm/c

• dileptons = penetrating probe

• -meson spectral function particular sensitive to baryon density

• connection to chiral symmetry restoration?

pn

++

p

e+, μ+

e-, μ-

In medium effects: -meson

7

In-medium modifications : mesons (II)

no ρ,ω,φ → e+e- (μ+μ-) data between 2 and 40 AGeV

Data: In+In 158 AGeV, NA60Calculations: H.v. Hees, R. Rapp

Low mass excess well established by CERES (dielectrons). Clear discrimination between different theoritical explanations is still missing.

Latest NA60 data shows a clear evidence for broadening of width- no mass shift

Data: CERESCalculations: R. Rapp

broadening

mass shift

8

Detector requirements

Systematic investigations:A+A collisions from 10 to 45 (35) AGeV, Z/A=0.5 (0.4) (up to 8 AGeV: HADES)p+A and p+p collisions from 8 to 90 GeV

observables detector requirements & challenges

strangeness production: K,

charm production: J/, D

flow excitation function

event-by-event fluctuations

e+e-

open charm

tracking in high track density environment (~ 1000)

hadron ID

lepton ID

myons, photons

secondary vertex reconstruction

(resolution 50 m)

large statistics: large integrated luminosity:

high beam intensity (109 ions/sec.) and duty cycle

beam available for several months per year

high interaction rates (10 MHz)

fast, radiation hard detector

efficient trigger

rare signals!

9

Dipolemagnet

The Compressed Baryonic Matter Experiment

Ring ImagingCherenkovDetector

Transition Radiation Detectors Resistive

Plate Chambers(TOF)

ECAL

SiliconTrackingStation

Tracking Detector

Muondetection System

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Di-muon measurement : •De-confinement transition (charmonia)

•Medium modification ( LMVM)

Major Indian participation

Building of Muon chambers :Detector simulation for feasibility measurement

R & D with Chambers

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Standard Muon Chambers

low-mass vector mesonmeasurements

(compact setup)

125 cm. Fe≡ 7.5 λI

225 Cm. Fe≡ 13.5 λI

Fe20 20 2

0 30

35 1

00 cm

W-shielding

J/

12

Challenges in muon measurement

Dimuons from vector meson decays are notoriously difficult to measure :

Low multiplicity at FAIR energies

Very small branching ratios in di-muon channel (Yield per event = multiplicity

×branching ratio)

Large combinatorial background in heavy-ion collisions due to

Weak decays , decays into

Hadron punch through

Secondary electrons ( electrons)

compact layout to minimize K,p decays → use excellent tracking to reject p,K decays in the STS by kink detection → absorber-detector sandwich for continous tracking → use TOF information to reject punch through K,p → Increase Air gap between detector-absorber to reduce delta electrons → Incerase number of stations after each absorber

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Simulation Framework: CbmRoot

Input : Pluto event generator for signal

UrQMD event generator for background

HSD for multiplicity

GEANT3 for transportation of the particles through detector materials Cellular Automata (CA) for track finding Kalman Filter (KF) for track fitting

Super Event Analysis (SE) technique for estimation of signal to background ratio

Much working group at different countries

GSI, Germany India Russia

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15

Muon simulations @ GSI

Time measurements for the muon identification LMVM trigger J/ψ pT reconstruction

Muon simulations with reduced detector acceptance

16

Background rejection via mass determination

(L, t) → β

simple design of MuCh

Muon ToF

TOF gives velocity

Measure mass of incoming particle

17

Full reconstructionω→μ+μ- + central Au+Au collisions at 25 AGeV

time

informationwithout with

time

resolution30 psec 50 psec 80 psec

S/B ratio 0.099 0.201 0.175 0.155

ε, % 1.85 1.57 1.56 1.56

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Invariant mass spectra

time information:— without with time resolution: — 80 psec— 50 psec— 30 psec

ω→μ+μ- + central Au+Au collisions at 25 AGeV

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Trigger strategy

zz target

target

xtarget,ytarget

∆x,∆y1. Find events with min. 12

hits in 6 detector layers, which might correspond to two tracks (hit selection in muon ToF: velocity value)

2. Straight line fit

3. Track selection: fit criteria

Remark: if track passes cuts, its hits will not used for second track searching

Muon ToF

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Trigger

1000 central events (Au+Au collisions at 25 AGeV)

min. 12 hits in 6 detector layers +

β [0.96; 1.02]

(β cut)

β cut

+

χ2, XZ=0, YZ=0 cuts

β cut

+

χ2, XZ=0, YZ=0 cuts

+

ZX=Y=0 cut

676 211 114

ω→μ+μ- + central Au+Au collisions at 25 AGeV

εall trigger cuts/εwithout trigger cuts

40%

background suppression factor ~35

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Pt [0.0, 0.2] GeV/c Pt [0.2, 0.4] GeV/c Pt [0.4, 0.6] GeV/c Pt [0.6, 0.8] GeV/c



Invariant mass spectra for different Pt

J/ψ

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Spectra of extracted J/ψ for different Pt

J/ψPt [0.0, 0.2] GeV/c Pt [0.2, 0.4] GeV/c Pt [0.4, 0.6] GeV/c Pt [0.6, 0.8] GeV/c



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Reconstruction results

STS acceptance full reduced

S/B ratio 3.4 4.5

εJ/ψ (%) 17.5 18.4

Cuts• STS:

2prim.vertex

– N of STS hits

• MuCh:– N of MuCh hits

• TRD: – N of TRD hits

• TOF:– hit in ToF cut

STS acceptance:

full

reduced

J/ψμ+μ- + Au+Au collisions at 25 AGeV

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Muon simulations @ India

• Optimization of muon detection system

•Detector in-efficiency study

• Development of charmonium trigger

• J/Psi pT reconstruction

We have to decide upon :– Total number of stations (layers)– Total absorber thickness, total no. of absorbers & the

absorber material– Number of layers (2/3) in between two absorbers– Distance between stations & absorber to station distance

Present constraints :– Absorber material (Fe, Pb, W )– Layer to layer distance >= 10 cm.– Layer to absorer distance >= 5cm.

Much Geometry optimization

Much Geometry optimization

Comparative study between two extreme cases:

SIS100 geometry: 9 detector layers; (proposed by us @BHU collaboration meeting)

SIS 300 geometry: 18 detector layers; (existing in SVN)

Total absorber thickness in both the cases is same (225 cm. of Fe)

• Optimization should be done with low mass vector mesons (lmvms) rather than J/ψ and at the lowest available energy.

• J/ψ measurements due to low background after more than 2 m of Fe are not so sensitive to the muon setup as the measurements of muons from LMVM.

• Issue is to reconstruct the soft muons ( eg: ω→μμ )

• Use the same set-up for in simulation for J/ψ & LMVM. For LMVM use information from stations just before the last thick absorber.

• Run full simulation & obtain signal reconstruction efficiency & S/B ratio.

• Simulate both lowest (minimum boost) & highest energy (maximum multiplicity).

Few facts to remember …

Much Geometries: specifications

Standard Geometry# of stations : 6# of layers : 3*6 =18Total absorber thickness : 225 Cm (20+20+20+30+35+100)Distance between layers : 10 cm.Detector to absorber distance : 10 cm.

Reduced Geometry:# of stations: 3# of layers : 3*3 = 9Total absorber thickness: 225 cm.(30+70+125)Distance between layers : 10 cm.Detector to absorber distance: 10 cm.

Simulation : Transport : Central Au+Au @ 10 AGeV, 25 AGeV & 35 AGeV

Signal : Pluto (ω→μμ) Background : UrQMD

Reconstruction : Segmentation scheme : Manual segmentation

Segmentation 1: minimum pad size: 4mm. ; maximum pad size : 3.2 cm. Segmentation 2: minimum pad size: 5mm. ; maximum pad size : 5 cm.

Simple Much hit producer w/o cluster & avalanche

Ideal (STS) & Lit (Much) tracking

Implementation of detector in-efficiency

5% in-efficiency w/o in-efficiency

~ 5% change in average number of hits

Implementation of detector in-efficiency

No loss5 % hit loss

No hit loss

No hit loss

5% hit loss

5% hit loss

Effect of hit loss on reconstructed tracks

Global tracks

Much tracks

Invariant mass spectrum (ω→μμ )

Cuts :1. No. of Muchhits>=42. No. of STS Hits >=43. chi2primary < 3

Super event (SE) analysis for bkg (combine all the positive tracks with all the negative tracks over all the events excluding only tracks from same event). Gaussian fit to signalPolynomial fit to bkg.

10k central embedded events for Au + Au @ 10GeV/n

Reduced Geometry

Results for various pad sizes (ω→μμ )

Pad size ( station #1 )

Total Pads Reconstruction efficiency (%)

S/B

2 mm. 1092456 1.9 0.0013

3 mm. 523332 1.74 0.0027

4 mm. 309384 1.77 0.0027

5 mm. 227556 1.64 0.0029

6 mm. 167904 1.64 0.003

10k central embedded events for Au + Au @ 10GeV/n

Invariant mass spectra (ω→μμ)


Super event (SE) analysis for bkg (combine all the positive tracks with all the negative tracks over all the events excluding only tracks from same event). Gaussian fit to signalPolynomial fit to bkg.

Standard Geometry

Central embedded events for Au + Au @ 25GeV/n

Invariant mass spectrum Standard Geometry

Central embedded events for Au + Au @ 25GeV/n

Super event (SE) analysis for bkg (combine only urqmd the positive tracks with urqmd negative tracks over all the events excluding only tracks from same event). Gaussian fit to signalPolynomial fit to bkg.


Results of full reconstruction

Energy (GeV/n)

Segmentation

Total pads Reconstruction efficiency (%)

S/B S/B (UrQMD)

8 1 0.45 0.03 0.954

8 2 0.4 0.027 0.943

25 1 1.2 0.015 0.31

25 2 1.3 0.015 0.34

35 1 1.9 0.017 0.25

35 2 1.85 0.018 0.28

Segmentation 1: Minm. Pad size: 4 mm. Maxm. Pad size: 3.2 cm.Segmentation 2: Minm. Pad size: 5 mm. Maxm. Pad size : 5 c,m.

Standard geometry

38

Development of charmonium trigger

Charmonia (J/, ’ are rare probes i.e. they have very low multiplicity(~10-5 or 10-6). For example for central Au+Au collisions @25 AGeV beam energy multiplicity of J/ is 1.5*10-5 and that of ’ is 5*10-6.

They have very low branching ratio (~5-6%) to decay into dimuon channel.

Their detection requires an extreme interaction rate. For example to detect one J/through its decay into di-muons it requires around 107 collisions.

Online event selection based on charmonium trigger signature is thus mandatory, in order to reduce the data volume to the recordable amount.

Wednesday, April 15, 2009

CbmRoot Version: Trunk version

Much geometry : Standard Geometry

• 2 layers in 5 stations

• Distance between layers 10 cm.

• Gap between absorbers 20 cm

• 3 layers at the last trigger station

• Total 13 layers

• Total length of Much 350 cm

Signal : J/ decayed muons from Pluto

Background : minimum bias UrQMD events for Au+ Au at 25 GeV/n

Much Hit producer w/o cluster & avalanche

L1(STS) & Lit (Much) tracking with branching

Input : reconstructed Much hits

Simulation

Absorber thickness (cm):20 20 20 30 35 100


Trigger algorithm• Take 3 hits from the trigger station with

one from each of the 3 layers & fit with st. line both in X-Z & Y-Z plane passing through the origin (0. 0) i.e.

X = m0*Z ; Y=m1*Z

Make all possible combinations

• Find 2 & apply cut on both 2X &2

y

• Hit combination satisfying the cuts is called a triplet.

• Hits once used for formation of a triplet is not used further.

• Find m0 & m1 of the fitted st. lines

• Define a parameter α=√(m02+m1

2)

• Apply cut on α

Magnetic field

(0,0,0)(0,0.0)

11 12 13

Trigger station


Specification of cuts

Cut 1: at least 1 triplet/event

Cut 2 : at least 2 triplets/event

Cut 3 : at least one of the selected triplets satisfy alpha cut

Cut 4 : at least two of the selected triplets satisfy alpha cut

Events analyzed: 80k minimum bias UrQMD event for background suppression factor & 1k embedded minimum bias events for J/ reconstruction efficiency


Background suppression factor (B. S. F)

Cut Events survived

Statistical Error

B. S. F

1 2624 1.95 % ~ 30

2 255 6.26 % ~314

3 91 10.4 % ~879

4 56 13.36 % ~1430

B. S. F = Input events (80,000) / events survived


Reconstructed J/

Trigger cut Reconstruction efficiency (%)

no cut 29.3 %

Cut 1 29.2 %

Cut 2 24.5 %

Cut 3 24.2 %

Cut 4 15.3 %

1k embedded minimum bias events

Motivation:

Physics performance analysis for SIS-100.

Developed a “close-to-standard” version of Much for SIS-100.

pT & Y dependent J/ reconstruction efficiency

First step towards physics case study.

J/Psi pT reconstruction

MethodologyIn cbmroot framework J/Psi’s are generated and decayed into di-leptons employing the event generator PLUTO.

Pluto generates J/Psi’s following gausian rapidity & thermal pT distribution.

Generated J/Psi’s are decayed into di-leptons isotropically in the rest frame of mother (J/Psi) & the decayed leptons are lorentz boosted in lab frame.

J/Psi yield is low at high pT (exponential pT spectra); not suitable for studying pT dependent efficiencies.

Either huge increase in statistics (exponential distribution) or use flat distribution with moderate statistics.

Modify the Box generator to generate J/Psi’s with specified rapidity (2.0<Y<4.0) & pT (up to 4 GeV with steps of 100 MeV).distribution.

Generated J/Psi’s are decayed following isotropic angular distribution into two muons .

Simulation : Transport : Central Au+Au @ 8A GeV

Signal : Box generator • J/ with given kinematic range : • rapidiy (y) =2-4;

• pT : up to 4 GeV with steps of 100 MeV

• 1k embedded events for each step

Background : UrQMD Au+Au @ 8 GeV/n

Reconstruction : Segmentation scheme : Manual segmentation

Station 1 (layers 1, 2, 3) : 2 regions (pad size in the central region : 0.4 cm.)

Station 2 (layers 4, 5, 6) : one region with pad size 3.2 cm * 3.2 cm.

Station 3 (layers 7, 8, 9) : one region with pad size 5 cm.*5 cm.

Implementation of detector in-efficiency at hit producer level. Simple Hit producer w/o clustering

pT dependent reconstruction efficiency

Small bin size (100 MeV) ; Low statistics (1k in each bin)Large statistical fluctuation

Cuts : No. of Muchhit>=7 No. of STS Hits >=4 Track MCId <2 Track pdgcode 13

pT dependent reconstruction efficiency

Rebin the previous plot to reduce statistical fluctuation

Discussion pT dependent reconstruction efficiency does not show any monotonic

variation.

Higher be the pT of J/Psi, easier should be the reconstruction.

Reconstruction efficiency should monotonically increase with pT.

Results do not show such increasing trend; instead a large fluctuation (even

though 1k input J/Psi’s per pT bin).

Re-binned results decrease the fluctuation but does not show the increasing

nature with pT.

Generate J/Psi’s in the entire pT range & look at the reconstructed J/Psi pT.

Distribution for J/Psi

Pair pT distribution does not show any trend Pair Y distribution show a dip in the middle Look at the distribution of single muons

Distribution for single muons

Input muons Reco. muons

Discussion

Significant loss in the single muon level

Input muons are distributed over a large rapidity

interval.

Some input muons are even at negative rapidity in the

lab frame (backward scattering??)

Input muons are even lost at mid-rapidity & high pT.

Recheck the decay kinematics employed in the box

generator.

Summary

For SIS-100 we have a ‘close to standard’ geometry for muon

detection system.

Full simulation with different segmentation (varying pad size)

shows we can use 4mm. /5mm. Pads in the first station. Issues

with occupancy & rate needs to be fixed.

Use the ‘reduced’ geometry for J/Psi simulation for 30 GeV p +Au

collisions.

Detector in-efficiency has been implemented in the hit producer

level.

J/Psi pT reconstruction needs to be completed

Future plans

To complete the comparative study with more statistics & with other particles.

Repeat the same simulations with an intermediate geometry with number of

layers 12/15.

Gap study & absorber study (change the air gap between layers; change the

absorber material /thickness).

Physics performance simulation : J/Psi pT & rapidity distribution. J/Psi flow study.

Physics simulation of different observables (following Peter Senger’s list)

Thank you

56

Quarkonium dissociation temperatures: (Digal, Karsch, Satz)

Measure excitation functions of J/ψ and ψ' in p+p, p+A and A+A collisions !

rescaled to 158 GeV

Probing the quark-pluon plasma with charmonium

J/ψ ψ'

sequential dissociation?

57

Dipolemagnet

The Compressed Baryonic Matter Experiment

Ring ImagingCherenkovDetector

Transition Radiation Detectors Resistive

Plate Chambers(TOF)

ECAL

SiliconTrackingStation

Tracking Detector

Muondetection System

Signal TracksBackground tracks

Distribution of chi2vertex

59

Summary: CBM physics topics and observables

Onset of chiral symmetry restoration at high B

in-medium modifications of hadrons (,, e+e-(μ+μ-), D)

Deconfinement phase transition at high B

excitation function and flow of strangeness (K, , , , ) excitation function and flow of charm (J/ψ, ψ', D0, D, c) (e.g. melting of J/ψ and ψ') exitation function of low-mass lepton pairs

The equation-of-state at high B

collective flow of hadrons particle production at threshold energies (open charm?)

QCD critical endpoint excitation function of event-by-event fluctuations (K/π,...)

CBM Physics Book (available online)

60

Observables:Penetrating probes: , , , J/ (vector mesons)Strangeness: K, , , , , Open charm: Do, D

Hadrons ( p, π)

Experimental program of CBM:

Systematic investigations:A+A collisions from 10 to 45 (35) AGeV, Z/A=0.5 (0.4) p+A collisions from 10 to 90 GeVp+p collisions from 10 to 90 GeVBeam energies up to 2 to 8 AGeV: HADES

Large integrated luminosity:High beam intensity and duty cycle,Available for several month per year

Detector requirementsLarge geometrical acceptance good particle identificationexcellent vertex resolutionhigh rate capability of detectors, FEE and DAQ

61

CBM setup with muon detector

Muonsystem

TRD

ToF

STS track, vertex and momentum reconstruction

Muon system muon identification

TRD global tracking

RPC-ToF time-of-flight measurement

STS

62

Tracks of one central Tracks of one central collision (GEANT3)collision (GEANT3)

Central Au+Au collision at 25 AGeV: 160 p, 400 -, 400 +, 44 K+, 13 K-,....

muon simulation : status & plan partha pratim bhaduri subhasis chattopadhyay vecc, kolkata

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