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Muon simulation : status & plan. Partha Pratim Bhaduri Subhasis Chattopadhyay VECC, Kolkata. CBM Physics – keywords. What does theory expect? → mainly predictions from lattice QCD: crossover transition from partonic to hadronic matter at small m B and high T

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Muon simulation : status & plan

Partha Pratim Bhaduri

Subhasis Chattopadhyay

VECC, Kolkata


Cbm physics keywords
CBM Physics – keywords

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

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

  • critical endpoint in intermediate range of the phase diagram

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

  • However ...

  • deconfinement = chiral phase transition ?

  • hadrons and quarks at high m?

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

  • how to characterize the medium?

  • physics program complementary to RHIC, LHC

  • rare probes


Physics of cbm observables

observables

strangeness production: K, L, S, X, W

charm production: J/y, D

flow excitation function

r, w, f l+l-

open charm

event-by-event fluctuations

Physics of CBM : Observables

physics topics

Deconfinement at high rB ?

Equation of State at high rB?

order of phase transition ?

in-medium properties of hadrons

 onset of chiral symmetry restoration at high rB

Critical point ?

CBM: rare probes → high interaction rates!

CBM: detailed measurement over precise energy bins (pp, pA, AA)

FAIR beamenergy range 10-40 AGeV (protons 90 GeV)


Charm production at threshold
Charm production at threshold

  • 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!

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

  • charmonium in hot and dense matter?

  • relation to deconfinement?

  • relation to open charm?

HSD simulations


Deconfinement : charmonium suppression

  • screening of pairs in partonic phase

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

  • Sequential suppression - signal of deconfinement?

  • OR

  • Co-mover absorption?

Still an open issue

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


In medium effects r meson

r

e+, μ+

e-, μ-

In medium effects: r-meson

  • r-meson couples strongly to the medium

  • vacuum lifetime t0 = 1.3 fm/c

  • dileptons = penetrating probe

  • r-meson spectral function particular sensitive to baryon density

  • connection to chiral symmetry restoration?

n

p

p

++

[Rapp, Wambach, Adv. Nucl. Phys. 25 (2000) 1,

hep-ph/9909229]


In-medium modifications : r mesons (II)

Data: In+In 158 AGeV, NA60

Calculations: H.v. Hees, R. Rapp

Data: CERES

Calculations: R. Rapp

 broadening

 mass shift

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

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


Detector requirements

tracking in high track density environment (~ 1000)

hadron ID

lepton ID

myons, photons

secondary vertex reconstruction

(resolution  50 mm)

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

strangeness production: K, L, S, X, W

charm production: J/y, D

flow excitation function

rare signals!

r, w, f e+e-

open charm

event-by-event fluctuations

Detector requirements

detector requirements & challenges

observables

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


The Compressed Baryonic Matter Experiment

Transition

Radiation

Detectors

Tracking

Detector

ECAL

Muon

detection

System

Resistive

Plate

Chambers

(TOF)

Ring Imaging

Cherenkov

Detector

Silicon

Tracking

Station

Dipole

magnet


  • 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


Standard mu on ch ambers
Standard Muon Chambers

mJ/y

20 20 20 30 35 100 cm

Fe

W-shielding

mr

low-mass vector meson

measurements

(compact setup)

125 cm. Fe≡ 7.5 λI

225 Cm. Fe≡ 13.5 λI


Challenges in muon measurement
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 p,K decays into mn

    • Hadron punch through

    • Secondary electrons (d 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


Simulation
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



Muon simulations @ gsi
Muon simulations @ GSI

  • Time measurements for the muon identification

  • LMVM trigger

  • J/ψ pT reconstruction

  • Muon simulations with reduced detector acceptance


Background rejection via mass determination
Background rejection via mass determination

(L, t) → β

TOF gives velocity

Measure mass of incoming particle

Muon ToF

simple design of MuCh


Full reconstruction
Full reconstruction

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


Invariant mass spectra
Invariant mass spectra

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

time information:

— without

with time resolution:

— 80 psec

— 50 psec

— 30 psec


Trigger strategy
Trigger strategy

∆x,∆y

  • Find events with min. 12 hits in 6 detector layers, which might correspond to two tracks (hit selection in muonToF: velocity value)

  • Straight line fit

  • Track selection: fit criteria

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

Muon ToF

xtarget,ytarget

ztarget


Trigger
Trigger

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

background suppression factor ~35


Invariant mass spectra for different p t j
Invariant mass spectra for different PtJ/ψ

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

Pt [0.8, 1.0] GeV/c

Pt [1.0, 1.2] GeV/c

Pt [1.2, 1.4] GeV/c

Pt [1.4, 1.6] GeV/c

Pt [1.6, 1.8] GeV/c

Pt [1.8, 2.0] GeV/c

Pt [2.0, 2.2] GeV/c

Pt [2.2, 2.4] GeV/c


Spectra of extracted j for different p t j
Spectra of extracted J/ψ for different PtJ/ψ

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

Pt [0.8, 1.0] GeV/c

Pt [1.0, 1.2] GeV/c

Pt [1.2, 1.4] GeV/c

Pt [1.4, 1.6] GeV/c

Pt [1.6, 1.8] GeV/c

Pt [1.8, 2.0] GeV/c

Pt [2.0, 2.2] GeV/c

Pt [2.2, 2.4] GeV/c


Reconstruction results
Reconstruction results

J/ψμ+μ- + Au+Au collisions at 25 AGeV

STS acceptance:

 full

reduced

  • Cuts

  • STS:

    • 2prim.vertex

    • N of STS hits

  • MuCh:

    • N of MuCh hits

  • TRD:

    • N of TRD hits

  • TOF:

    • hit in ToF

    •  cut


Muon simulations @ India

  • Optimization of muon detection system

  • Detector in-efficiency study

  • Development of charmonium trigger

  • J/Psi pTreconstruction


Much Geometry optimization

  • 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)


Few facts to remember …

  • 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).


Much Geometries: specifications

Standard Geometry

# of stations : 6

# of layers : 3*6 =18

Total 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 = 9

Total 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



Effect of hit loss on reconstructed tracks

5% hit loss

No hit loss

Global tracks

No hit loss

5% hit loss

Much tracks


Invariant mass spectrum

Cuts :

No. of Muchhits>=4

No. of STS Hits >=4

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 signal

Polynomial fit to bkg.

Invariant mass spectrum (ω→μμ )

Reduced Geometry

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


Results for various pad sizes
Results for various pad sizes (ω→μμ )

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


Invariant mass spectra1

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 signal

Polynomial fit to bkg.

Invariant mass spectra(ω→μμ)

Standard Geometry

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

Cuts :

No. of Muchhits>=15

No. of STS Hits >=4

chi2primary < 3


Invariant mass spectrum1

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 signal

Polynomial fit to bkg.

Invariant mass spectrum

Standard Geometry

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

Cuts :

No. of Muchhits>=15

No. of STS Hits >=4

chi2primary < 3


Results of full reconstruction
Results of full reconstruction

Standard geometry

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.


Development of charmonium trigger
Development of charmonium trigger

  • Charmonia (J/y, y’ 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/y is 1.5*10-5 and that of y’ 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/y 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.


Simulation1
Simulation

  • 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/y 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

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 c2 & apply cut on both c2X & c2y

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+m12)

Apply cut on α

Trigger algorithm

Trigger station

(0,0,0)

(0,0.0)

Magnetic field

11 12 13


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

  • 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
Background suppression factor (B. S. F) the 3 layers & fit with st. line both in X-Z & Y-Z plane passing through the origin (0. 0) i.e.

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


Reconstructed j
Reconstructed J/ the 3 layers & fit with st. line both in X-Z & Y-Z plane passing through the origin (0. 0) i.e.

1k embedded minimum bias events


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

Physics performance analysis for SIS-100.

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

pT& Y dependent J/y reconstruction efficiency

First step towards physics case study.

J/Psi pT reconstruction


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

  • In 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 : the 3 layers & fit with st. line both in X-Z & Y-Z plane passing through the origin (0. 0) i.e.

  • Transport :

  • Central Au+Au @ 8A GeV

  • Signal : Box generator

  • J/y 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


P t dependent reconstruction efficiency
p the 3 layers & fit with st. line both in X-Z & Y-Z plane passing through the origin (0. 0) i.e.T dependent reconstruction efficiency

Cuts :

No. of Muchhit>=7

No. of STS Hits >=4

Track MCId <2

Track pdgcode 13

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

Large statistical fluctuation


P t dependent reconstruction efficiency1
p the 3 layers & fit with st. line both in X-Z & Y-Z plane passing through the origin (0. 0) i.e.T dependent reconstruction efficiency

Rebin the previous plot to reduce statistical fluctuation


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

  • pT dependent reconstruction efficiency does not show any monotonic variation.

  • Higher be the pTof 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 pTrange & look at the reconstructed J/Psi pT.


Distribution for j psi
Distribution for J/Psi the 3 layers & fit with st. line both in X-Z & Y-Z plane passing through the origin (0. 0) i.e.

  • 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
Distribution for single the 3 layers & fit with st. line both in X-Z & Y-Z plane passing through the origin (0. 0) i.e.muons

Input muons

Reco. muons


Discussion1
Discussion the 3 layers & fit with st. line both in X-Z & Y-Z plane passing through the origin (0. 0) i.e.

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

  • 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
Future plans the 3 layers & fit with st. line both in X-Z & Y-Z plane passing through the origin (0. 0) i.e.

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


Probing the quark-pluon plasma with charmonium the 3 layers & fit with st. line both in X-Z & Y-Z plane passing through the origin (0. 0) i.e.

rescaled to 158 GeV

J/ψ

ψ'

Quarkonium dissociation temperatures:

(Digal, Karsch, Satz)

sequential dissociation?

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


The Compressed Baryonic Matter Experiment the 3 layers & fit with st. line both in X-Z & Y-Z plane passing through the origin (0. 0) i.e.

Transition

Radiation

Detectors

Tracking

Detector

ECAL

Muon

detection

System

Resistive

Plate

Chambers

(TOF)

Ring Imaging

Cherenkov

Detector

Silicon

Tracking

Station

Dipole

magnet


Distribution of chi2vertex the 3 layers & fit with st. line both in X-Z & Y-Z plane passing through the origin (0. 0) i.e.

Signal Tracks

Background tracks


Summary: CBM physics topics and observables the 3 layers & fit with st. line both in X-Z & Y-Z plane passing through the origin (0. 0) i.e.

The equation-of-state at high B

 collective flow of hadrons

 particle production at threshold energies (open charm?)

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

QCD critical endpoint

 excitation function of event-by-event fluctuations (K/π,...)

Onset of chiral symmetry restoration at high B

in-medium modifications of hadrons (,, e+e-(μ+μ-), D)

CBM Physics Book (available online)


Experimental program of CBM: the 3 layers & fit with st. line both in X-Z & Y-Z plane passing through the origin (0. 0) i.e.

Observables:

Penetrating probes: , , , J/ (vector mesons)

Strangeness: K, , , , ,

Open charm: Do, D

Hadrons ( p, π)

Detector requirements

Large geometrical acceptance

good particle identification

excellent vertex resolution

high rate capability of detectors, FEE and DAQ

Systematic investigations:

A+A collisions from 10 to 45 (35) AGeV, Z/A=0.5 (0.4)

p+A collisions from 10 to 90 GeV

p+p collisions from 10 to 90 GeV

Beam energies up to 2 to 8 AGeV: HADES

Large integrated luminosity:

High beam intensity and duty cycle,

Available for several month per year


Cbm setup with muon detector
CBM setup with muon detector the 3 layers & fit with st. line both in X-Z & Y-Z plane passing through the origin (0. 0) i.e.

STS track, vertex and momentum reconstruction

Muon systemmuon identification

TRD global tracking

RPC-ToF time-of-flight measurement

ToF

TRD

Muon

system

STS


Tracks of one central collision (GEANT3) the 3 layers & fit with st. line both in X-Z & Y-Z plane passing through the origin (0. 0) i.e.

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


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