1 / 19

An experiment for the FLAIR ring at GSI

An experiment for the FLAIR ring at GSI. There are extensive data from Crystal Barrel at LEAR on pp in flight to17 neutral final states: pp -> R -> A + B

kerem
Download Presentation

An experiment for the FLAIR ring at GSI

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. An experiment for the FLAIR ring at GSI There are extensive data from Crystal Barrel at LEAR on pp in flight to17 neutral final states: pp -> R -> A + B The experiment looks for resonances in formation, as in pN. For neutral final states, C is a good quantum number. For C=+1,I =0, a unique set of partial wave amplitudes is found from 6 CBAR final states + ds/dW and polarisation data for pp ->p+p- from PS172 at LEAR and an earlier PS expt of Eisenhandler et al. The new experiment would measure transverse polarisation in enough all neutral channels to obtain a complete partial wave analysis for all remaining quantum numbers: C = +1, I=0, and C = -1, I = 0 and 1. This appears feasible and straightforward. The detector and polarised target exist and are understood; makes a fairly cheap expt.

  2. In practice, the reactions to be studied are: I=1, C = +1: pp -> hp0, hhp0and 3p0 I=1, C = -1: pp -> wp0and whp0 (w -> p0g) I=0, C = -1: pp -> wh and wp0p0 I=0, C = +1: pp -> p0p0, hh and hp0p0(as a check on the present solution) It is essential to extend the momentum range of present data down to ~360 MeV/c, (a mass of 1910 MeV). 12 momenta are required to scan two towers of resonances near 2000 and 2270 MeV. At LEAR, CBAR had very little data below 900 MeV/c. That gap needs to be closed to cover the lower tower.

  3. Separation of h and w from backgrounds data at 1800 MeV/c h->3p in hp w->pg in wp h’ in h’p h in wh

  4. Why are polarisation vital for other channels? Quarks and nucleons have spin 1/2, so qq and pp have total spin s=0 or 1 (singlet S or triplet T); we need P data to separate S and T; • Triplet states can have L=J or J+1 Polarisation separates 3P2 and 3F2 because Clebsch-Gordan coefficients are orthogonal and very different; this is thecrucial missinginformation; for C=-1 states, P separates 3S1 and 3D1;and 3D3 from 3G3. • ds/dW = Tr(A*A) = |T|2 + |S|2 and measure Re(interferences); PNds/dW = Tr(A*sYA) -> Im (interferences), notably Im(T*S). Wherever you are on the Argand diagram, either P or differential cross sections are phase sensitive.

  5. Earlier polarisation data for pp -> p+p-

  6. The Crystal Barrel (as used at LEAR) Magnet not needed at FLAIR; without it, dimensions over the Barrel ~1.6m. System for polarising it needs further space.

  7. I=0 C=+1 resonances F states typically 60 MeV above P states; D states midway

  8. 3F4 -> a2p 3F4 -> f2h 3H4 -> f2h Equally clear in p0p0, hh and hh’; 3F4 acts as an interferometer for all triplet states. Similar interferometers exist for other I and C.

  9. Singlet partial waves JP = 0- f2h’ -> (pp)h’ JP=2- f0(1500)h in 3h At 2030 MeV, there is further clear 2- in [a2p]L=2; a 0- state at 2010 MeV has sizable errors in M and G.

  10. I=1, C=-1: Amplitudes nearly unique because of P(p+p-). BUT • data on both ds/dW and P are needed for other channels from 360 to 750 MeV/c; (ii) 3S1 partial waves are poorly determined because they are isotropic in ds/dW and easily confused with backgrounds; (iii) Nothing seen in 3G3; P needed to separate it from 3D3 (which happens to be large); I=1, C = +1: The solution looks similar to I=0, C=+1. BUT (i) there is a twofold ambiguity in hp which P data would resolve; (ii) there is almost no separation between 3P2 and 3F2, and between 3F4 and 3H4; polarisation would separate them and improve precision of M and G by a factor 3; If `mock’ polarisation data are added to the present data set, there always appears to be a unique solution.

  11. I=0, C=-1 is the most difficult, therefore used for planning: • (i) Present wh statistics are only 7.5K events; 50K are needed. (ii) the wp0p0 channel is the most difficult of all channels; it is dominated by wf2(1270), but the nominal threshold for this is at 2050 MeV; there are clear but small pb1(1235) signals; but there is a large interfering ws amplitude across the whole Dalitz plot; it hinders the amplitude analysis. • The possible upper tower near 2270 MeV is a mess because of confusion between 3S1 and 3D1, 3D3 and 3G3. P needed ! • 2) The good news is that there is a pair of well established 1P1(1965 and 2265) and 1F3(2025 and 2275); they will serve as interferometers in P data for sorting out triplet states.

  12. Present ds/dW data Stat BG e(%) ph -> 4g 52K 2% 32 3p 322K <1% 29 I=1,C=+1 hhp->6g 6.3K 5% 15 wp ->5g 22K 19% 24 whp->7g 9.4K 16% 15 I=1,C=-1 Have P(p+p-) wh ->5g 7.5K 9% 25 wpp->7g 39.4K 13% 10 I=0,C=-1 pp 133K 0.3% 39 hh ->4g 11K 0.7% 26 I=0,C=+1 hpp->6g 85K 3.5% 23 At FLAIR, statistics would increase by roughly a factor 7.

  13. The Polarised Target Frozen-spin target: a dilution refrigerator operating at ~0.06K using solid NH3 Lifetime of polarisation ~4 to 5 days; Pmax~98%,Pmean~65%. Target length 4cm Estimation of background Background from nitrogen: 14/(3x141/3)~2 at trigger level; events on both neutrons and protons contribute to pile-up. Events on neutrons nearly all trigger the vertex detector and do not need to be written out. Events on protons in nuclei roughly double backgrounds compared with liquid hydrogen. Kinematics Fermi momentum along each axis ~115 MeV/c; simulated by folding it into Monte Carlo events and making fits and cuts.

  14. Separation of signal and BG in earlier expts.

  15. Event Rates The data taken at LEAR with Crystal Barrel suffered from dead-times in the data-acquisition which limited the rate to 60 Hz. The read-out of the charged particle detector was 100 times slower than the CsI crystals. This is not needed for the new experiment at FLAIR, so the event rate rises potentially to ~8KHz. From the polarised target (NH3), there will be triggers from events in nitrogen. Relative triggers from H and N are in the ratio 3 : 5.8. This reduces the rate of H events to 2.7KHz which is adequate. Pile-up with new electronics is ~7%, and can be identified and bad events can be rejected.

  16. Data taking The aim is to get statistics of 50K events for the weakest channels: hhp, wh and whp. With a beam intensity of 6 x 104 p/s, this can be achieved at 12 momenta in ~100 days of data taking – a factor 2 more than at LEAR; there would be some dead-time in addition for flipping target polarisation. Also need to check that ds/dW can be determined from the polarised target.

  17. Summary It would be a relatively cheap experiment, since the detector and polarised target exist, though there is the cost of moving the detector and polarised target to GSI. There would be some small costs of modifications to electronics. This experiment should complete the determination of a complete set of unique partial wave amplitudes for I=0 and 1, C=+1 and -1 from 1910 to 2410 MeV. Hopefully this would determine all the light meson resonances for radial excitations n=1 to 5: enough for understanding systematics.[That is unlikely to be achieved by production experiments, because of the difficulty of disentangling the spin of exchanged particles.] This full set of resonances will act as a backdrop for exotic glueballs and hybrids (BESIII). Anyone interested in the expt should talk to me.

  18. Physics At low masses, chiral symmetry is broken. It disappears to some extent at higher masses. Glozman proposes that chiral symmetry may be fully restored in this mass range. His idea is that parity doublets appear: e.g. 2- and 2+ masses are degenerate. From present data, pairs of states are definitely present, but they may not be strictly of equal mass: 2-+ is 1D2 and there are two 2++ states for 3P2 and 3F2. Experimentally, these two 2++ definitely differ in mass by ~60 MeV. So it appears that L plays some role. It may, for example appear from the orbital angular momentum of a rotating flux-tube between q and q. It also looks as if G states are absent at 2000 MeV; they appear only at 2270 MeV. These further data are crucial information for understanding how confinement really works.

  19. Status of Regge trajectories

More Related