Muon simulation : status & plan Partha Pratim Bhaduri Subhasis Chattopadhyay VECC, Kolkata.
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Transcript of 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
10
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
11
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
13
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
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
18
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
19
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
20
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
21
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
Invariant mass spectra for different Pt
J/ψ
22
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
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
23
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
24
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
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)
Cuts :1. No. of Muchhits>=152. 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.
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.
Cuts :1. No. of Muchhits>=152. No. of STS Hits >=43. chi2primary < 3
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
Wednesday, April 15, 2009
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
Wednesday, April 15, 2009
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
Wednesday, April 15, 2009
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
Wednesday, April 15, 2009
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
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
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)
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
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