Muon simulation : status & plan

1. Muon simulation : status & plan Partha Pratim Bhaduri Subhasis Chattopadhyay VECC, Kolkata

2. 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

3. 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)

4. 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

5. 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

6.  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]

7. 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

8. 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

9. 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

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 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

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 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

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

14. Much working group at different countries • GSI, Germany • India • Russia

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 TOF gives velocity Measure mass of incoming particle Muon ToF simple design of MuCh

17. Full reconstruction ω→μ+μ- + central Au+Au collisions at 25 AGeV

18. 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

19. 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

20. Trigger 1000 central events (Au+Au collisions at 25 AGeV) background suppression factor ~35

21. 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

22. 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

23. 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

24. Muon simulations @ India • Optimization of muon detection system • Detector in-efficiency study • Development of charmonium trigger • J/Psi pTreconstruction

25. 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.

26. 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)

27. 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).

28. 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.

29. 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

30. Implementation of detector in-efficiency 5% in-efficiency w/o in-efficiency ~ 5% change in average number of hits

31. Implementation of detector in-efficiency No loss 5 % hit loss

32. Effect of hit loss on reconstructed tracks 5% hit loss No hit loss Global tracks No hit loss 5% hit loss Much tracks

33. 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

34. Results for various pad sizes (ω→μμ ) 10k central embedded events for Au + Au @ 10GeV/n

35. 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

36. 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

37. 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.

38. 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.

39. 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

40. 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

41. 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

42. Background suppression factor (B. S. F) B. S. F = Input events (80,000) / events survived

43. Reconstructed J/ 1k embedded minimum bias events

44. Motivation: 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

45. Methodology • 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 .

46. Simulation : • 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

47. pT 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

48. pT dependent reconstruction efficiency Rebin the previous plot to reduce statistical fluctuation

49. Discussion • 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.

50. 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