Muon Simulation activities at VECC, India

1. Muon Simulation activities at VECC, India Partha Pratim Bhaduri, VECC Subhasis Chattopadhyay, VECC Bipasha Bhowmick, Calcutta Univ. Presented by Y. P. Viyogi IOP-Bhubaneswar, India

2. Topics • Update on the development of a Muon Trigger • Muon simulation with addition of extra hits • Dynamic Range simulation • Optimization of Muon Chamber design

3. Development of muon Trigger

4. Motivation • Low cross section for rare probes • High interaction rate (10 MHz) • Online event selection • Required background suppression : 400 (from foreseen DAQ BW)

5. Geometry Used Much Standard Geometry

6. Development of trigger Algorithm J/y multiplicity (@25 GeV/n Au+Au) : 5*10-5 B.R (J/y : m+m-) : 5% Event rate :10 MHz Recording rate : 25 kHz (,f) 1.Choice of a hit-triplet 2. Two hit-triplets/event 3.Extrapolation up to vertex (x3,y3,z3) (x2,y2,z2) (x1,y1 , z1) Z-axis Magnetic field 16 17 For a st. line passing through points 1, 2, 3 : 12 = 13 ; f12 = f13 :Triplet 18

7. Trigger Simulation: Algorithm 1) Look for the hits in the last three detector stations i.e. station # 16, 17, 18. 2) Measure the space co-ordinates (x & y) of the hits in all the three stations. For a particular station z is fixed. 3) Calculate del X1(=x16-x17) , delX2(x16-x18) , delY1(=y16-y17) & delY2 (=y16-y18) and make hit-triplet by taking the hits (one from each of the three stations) which are in close proximity in space (x & y). Members of a triplet are chosen by applying cut values on delX & delY. 4) Accept only those events which have at least two such triplets. 5) Calculate the transverse co-ordinate r(=sqrt(x2+y2)) of the hits of each triplet plot r as a function of the horizontal co-ordinate z i.e. r = f(z). 6) Make straight line fitting such that r=ao+a1z & extrapolate it up to z=0.

8. Contd.. 7) Look for the hits in the stations 13, 14 & 15 and calculate transverse co-ordinate using r(=sqrt(x2+y2)) from projected positions. 9)Take the difference rpro-rcal and plot delr for each station and apply the transverse cut. 10) Finally look for the value of r at z=0 (r (z=0)=a0) and apply the final(4th cut). (a) delX, delY cut (b) two triplet cut (c ) projection on penultimate stations (c ) Projection cut on z=0

9. Preliminary results Aim: To optimize the algorithm

10. Results ( Event selection) Bkg. Suppression Factor: Central : 60 Minm. Bias : 375

11. Calculation of Reconstruction Efficiency Sample : 1k embedded (central) events Input: Reconstructed Much tracks satisfying: NMuchHits =18 (Hard tracks) Fraction of true sts hits (truehits/(true hits+ wrong hits+fake hits) >= 0.7 Associated STSHits >=4 c2primary <=2.0 No. of missed stations =0

12. Result (# of Reconstructed J/y)

13. Observation • Overall background suppression : ~375 • Most effective cut : 2 hit-triplets/event • Around factor of 2 reduction in reco. efficiency • More optimization under progress

14. Developing new software : Muon simulation with addition of extra hits

15. Method The addition is at the MC-Point level. • Take a MC point produced by GEANT. • Get its co-ordinates (x, y). • Apply Gaussian smearing both in x & y with a given resolution to get a new point with a different (x, y). This is our added point. - Added point has all other properties same as that of the previous (eg. : mc_pdg, track-Id, motherID, momentum etc.). • Go through the digitization and add as hit. Repeat above steps to add as many more hits as one wants. We can vary the amount of the added hits for a track and amount of tracks for which hits are added independently.

16. Hits used for track reconstruction in L1 Original 90% extra added

17. (Hit addition contd.) Track reconstruction efficiency with different added-hit fraction

18. Dynamic Range simulation for n-XYTER in MUCH • Dynamic range is a quantity essential for design of the read-out chips. • Determination of the energy deposition at each cell of the muon chambers ( in terms of MIP as muons give MIP signal). • Take different cell sizes (2mm. – 4cm.) & find out the fraction of multiple-hit cells & singly-hit cells for particles generated by UrQMD. • Optimize the cell size based on multi-hit fraction. • For the optimal cell size find cell by cell energy deposition (E_dep) both for single muons (MIP spectra) & UrQMD particles. • Apply different MIP cuts & calculate the loss due to saturation.

19. Optimise the cell size Fraction of multiple-hit cells= (total # of cells having >1 hit)/ (total # of cells hit) Optimal cell-size : 4mm. for inner stations, 4cm. For outer stations (stn 12 onwards)

20. Station# 1 Cell size : 4mm. Station# 12 Cell size: 4cm. E_dep by UrQMD particles

21. Single muon energy deposition spectra : Fitted with Landau distribution MIP value : 0.197 KeV (MPV of the Landau)

22. Saturation loss : part of the energy spectra above the selected energy deposition cut (in terms of MIP) value MIP cut: E_dep cut (keV)/MIP value(= 0.197 keV)

23. Summary: Trigger study: Suppression factor upto 375 for minb Hit addition: needs to optimise with new tracking algorithm. details need discussion Digitization:Waiting for Dipanwita’s results Dynamic range simulation: need to see the effect on tracking

24. Motivation • One of the major experimental tasks of the CBM experiment is to identify hidden charms or charmonia (J/y, y’). • They 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.

25. Focus • The main focus is to develop an algorithm to suppress the background as much as possible but simultaneously to preserve the reconstruction efficiency as much as possible. • For feasibility study of the trigger algorithm for J/y we took 103 central and minimum bias events Au+Au events @ 25 AGeV. • Reconstructed much-hits are used as input to our trigger study. • The idea is to look for high momentum muon tracks which reach up to the last detector station & which propagate approximately in straight line (no magnetic field in Much system).

26. Observation • With the application of trigger cuts (applied in sequential order) reconstruction efficiency (normalized w.r.t 1000 events) decreases. • Application of 1st trigger cut (minimum 1 hit-triplet per event) does not change the no. of reconstructed J/y compared to that in absence of trigger. • Application of 2nd trigger cut (2 hit-triplet /event) reduces the no. of reconstructed J/y. • Application of 3rd trigger cut (transverse cut in the penultimate detector triplet i.e. station no. 13, 14 & 15) does no reduce the reconstructed J/y further. • Application of 4th & final trigger cut ( Extrapolation cut at the target) further reduces the no. of reconstructed J/y.