1 G4MICE studies of PID transverse acceptance MICE video conference Rikard Sandström

2 Outline Background Setup –Field map and iron shields –Two beam settings –Good muon criteria Radial position of good muons at TOF2 –Conclusion Radial position of good muons at calorimeter –Comparison split/non split design –Conclusion Radial position of good muons at 1 st and 2 nd iron shields –Conclusion Summary

3 A bit of background Graphs shown at Osaka in spring ‘06 by Rikard suggested TOF2 is too small. –Or that the calorimeter is too large compared to TOF2… It raised the question; should we modify the size of TOF2?

4 Iron shields and field map TOF2’s PMTs are sitting in high B-field. –Iron shielding! A double shield configuration is an effective solution. (Osaka ‘06) With no CKOV2, the calorimeter is closer to TOF2 and hence suffer from the same effect as TOF2. –Could multiple iron shields help? One suggestion is to split the 0 th layer (lead & fiber) from the following in order to fit a 3 rd iron shield between layer 0 and 1. Putting calorimeter layer 0 in the same space as TOF2 (between shield 1 & 2) reduces the effective shielding of TOF2 and was ruled out.

5 MICE – Magnetic Shields Dimensions –1 st shield: ID=500mm, OD=1500mm, t=100mm –2 nd shield: 120 mm downstream from 1 st shield, ID=600mm, OD=1800mm, t=20mm –3 rd shield: 100mm downstream from 2 nd shield, ID = 660mm, OD=1800mm, t=10mm Inner radius of shields –John Cobb’s estimate End Coil 2 From Holger Witte

6 Two beams studied The problem can be approached from two different viewpoints: 1.A certain number of good muons should be detected (efficiency 99.9%, 3 sigma etc). Only meaningful if input distribution is realistic. 2.All muons which are not scraped and are good for tracking should be detected. Useful criterion for scraping studies. Option 1 is examined by a diffused Aug’05 beam, inserted at TOF1 exit. Option 2 uses a beam which covers all phase space. –See next slide.

7 A handmade, full phase space, beam If we require any muon which is good in the trackers to be within downstream detector volumes, we should scan all phase space. –I made a hand written beam with all combinations of x 0 & y 0 = {-5,0,5} mm x 0 ’ & y 0 ’ = {-0.35,… 0.0, 0.1, 0.2, …, 0.35} p tot = {100, 110, …, 350} MeV/c –This is a highly scraping beam, only ~14% pass tracker criteria and survive to TOF2.

8 Good muon criteria Time of flight corresponding to 0.5 < β z < 1. In trackers: –50 < p z < 400 MeV/c. –  max = p t /(0.3*4) + √((-p y /(0.3*4)+x) 2 + (p x /(0.3*4)+y) 2 ) < 15 cm Ensures particles stay inside active region of tracker. For upstream b field or negative particles, flip signs of p.

9 TOF2, full phase space beam

10 TOF2, Aug’05

11 TOF2, Aug’05

12 …but we are square Probability a particle between the circles is also inside gray area: –p= r 1 2 (4-  )/(  r 1 2 )  27% –This is average effect, p depends on dr. This means number of lost muons is 73 % between r 1 and r 1 √2 if square shape compared to circular shape. –On the previous slides, this covers up to 425 mm for a 300 mm half length. Beware of systematic errors if beam not cylindrically symmetrical! r1r1 dr

13 Material effect at end of tracker It could be that we are partially scraping the beam at the end of the tracker module. End Coil 2 Estimated positions OK Cables etc Cryostat wall

14 Material effect, continued Reminder: This simulation uses field map for iron shields, but shields not physically present. –Could look different with other ID of first shield. –A hard cut on particles hitting material would have impact downstream detector sizes -> Smaller!

15 TOF2 conclusions Muons are often well outside the base line 48x48 cm 2. –This introduces dangerous bias to emittance measurement and scraping studies. Before a final size of TOF2 can be fixed, we need to –Cut/deal with particles hitting passive material between tracker and TOF2. –A field map with adjusted inner diameter of iron shields.

16 Calorimeter Assuming TOF2 and iron shields have ideal sizes (all muons hit TOF2, no muons hit shields), the size of the calorimeter can be studied. Again, the same beams are used, and in all cases the 3 iron shield field map is used.

17 Entrance of layer 0

18 Entrance of layer 1 Ouch!

19 Full phase space beam 51 k events

20 Aug’05, 7.6 mm diffused 74 k events

21 Full phase space beam, non split 63 k events

22 z=7m, non split calorimeter

23 Calorimeter conclusions The calorimeter can be smaller with a non-split design than a split design. –Long tails towards large rho for split calorimeter. Layer 0 (lead & fiber): –80 x 80 cm 2 is a suitable size. –90 x 90 cm 2 is fail safe size. Non split calorimeter, layer 1-10: – 100 x 100 cm 2 is recommended. –First layers could be smaller (~90 x 90 cm 2 ). –Last layers could be smaller due to low rates. Depends on highest momentum in run plan.

24 1 st iron shield Present size

25 2 nd iron shield Present size

26 Iron shield conclusions Present design of iron shields has too small inner diameter. –Still true if muons hitting passive tracker module material are removed from analysis? Larger hole = less effective shielding. …but, larger TOF2 = less B field at PMTs.

27 Summary Two problems: 1.Partial scraping at end of tracker worrying. –That material was not present in these simulations. 2.TOF2 and iron shields too small. –Solving 1 could help 2. A non split calorimeter allows for smaller transversal size of plastic layers than a split design.