CERN/LHCC 93-33

LHCC 6

19 May, 1993

LARGE HADRON COLLIDER COMMITTEE

Minutes of the sixth meeting held on Tuesday and Wednesday, 11-12 May 1993

Present: J.V. Allaby, J.J. Aubert (Chairman), G. Brianti*, R.J. Cashmore, L. Di Lella, P.J. Dornan, F. Eisele, J. Ellis, E. Fernandez, L. Foa, W. Hoogland*, P.G. Innocenti, K. Kajantie, V. Khovansky, C. Llewellyn Smith, G.W. London, L. Maiani*, G. Mikenberg, T. Osborne (replacing D.O. Williams)*, K. Potter, K. Pretzl, K. Schubert, D.M. Sendall (Secretary), D.O. Williams*

*) Part time

Apologies: P. Duinker, K. Einsweiler, E. Iarocci, C. Rubbia, S. Yamada

SPECIAL CLOSED SESSION (B PHYSICS WORKSHOP):

Present by invitation to the collaborations:

L. Camilleri, G. Carboni, M. Danilov, D. Denegri, P. Eerola, N. Ellis, S. Erhan, F. Ferroni, G. Fidecaro, D. Froidevaux, S. Gadomski, J. Gareyte, P. F. Harrison, J. Hassard, D. Hitlin, W. Hofmann, P. Jenni, M. Konecki, Y. Lemoigne, M. Medinnis, T. Nakada, N. Neumeister, J. P. Perroud, W. Ruckstuhl, P. Schlein, W. Schmidt-Parzefall, V. Shoutko, J. Spalding, T. Virdee, R. Waldi, D. Websdale, T. Ypsilantis, J. Zweizig

1. INTRODUCTION

L. Maiani gave an introduction to CP violation in B decays. Observation of this phenomenon, up to now seen only in K decays, would be an important achievement. It could show whether CP violation is due to the weak interaction, and also provide a clean test of the Standard Model with three generations.

He reviewed the parametrisation of the CKM matrix and the unitarity constraints on the angles alpha beta and gamma. The current best estimates of the parameters and the prospects for future measurements were presented. Lattice calculations of fB suggest that the asymmetry in the J/psi Ks channel may be large: this offers the hope of easily observable effects, and also a possible test of the lattice predictions. Bounds on the asymmetry in semileptonic channels would offer an interesting test of the Standard Model.

2. B PHYSICS WITH GENERAL-PURPOSE DETECTORS

Prospects for B physics were presented by P. Eerola (ATLAS), N. Neumeister (CMS), and V. Shoutko (L3P). This physics could be investigated at the lower luminosities of LHC startup, and therefore would use the first stage of the detectors. It would be possible to extend these measurements to higher luminosities.

Such experiments would essentially measure sin2beta using the asymmetries of the J/psi Ks channel. Estimates of the precision of this measurement were given, and other possible channels of interest were mentioned. Problems of triggering, tagging, dilution and background were described: systematic uncertainties could be estimated by the use of control channels.

3. B PHYSICS WITH DEDICATED DETECTORS

P. Schlein presented COBEX, which would use b bbar production in pp collider mode, with an open geometry forward detector. The experiment would run at a luminosity of 10**32cm-2s-1.

F. Ferroni presented LHB, a fixed target experiment with beam extraction based on channeling by a bent crystal in the halo of the circulating beam, a technique which has been tested at the SPS. The intention would be to run parasitically during normal LHC operation: the machine might also be used in dedicated mode, especially at startup.

L. Camilleri presented GAJET, an experiment with a gas jet target. A gas jet design similar to UA6 could be used, with some modifications.

All three speakers gave estimates of the achievable accuracy of a sin2beta measurement using the J/psi Ks channel, and of sin2alpha using the pi+pi- channel. Other channels were also discussed.

4. B PHYSICS AT OTHER FACILITIES

D. Hitlin reported on the prospects for B physics at the asymmetric e+e- colliders under discussion in the USA, Japan and Russia. Theoretical considerations were discussed, including implications for possible physics beyond the standard model. A collider of this type operating at the Upsilon(4S) energy could offer good conditions for B decay studies. The potential contribution of various decay modes was summarised. Tests of experimental systematic uncertainties could be made, as well as tests for penguin contributions. Many channels could be used to measure sin2alpha and sin2beta, providing additional tests of Standard Model assumptions. For sin2gamma the channel Bs -> rho Ks would require running at the Upsilon(5S), with increased energy asymmetry to compensate for the larger value of xs.

W. Hofmann presented the HERA B experiment, for which a Letter of Intent has been submitted. This would use an internal thin wire target in the HERA proton beam. The primary goal is to detect CP violation in B -> J/psi Ks using a dedicated detector with a J/psi trigger. Initial tests of the thin wire technique were encouraging. The detector would need to reconstruct multiple events per bunch crossing, and would have some features in common with LHC detectors: several DRDC projects were of interest in this connection.

5. IMPLICATIONS FOR THE MACHINE AND EXPERIMENTAL AREAS

J. Gareyte introduced a likely scenario for LHC startup and the evolution of luminosity. He summarised the implications for the LHC machine of the three dedicated experiments. COBEX with head-on collisions would contribute to head-on beam-beam effects like a main experiment. During the startup period normal insertion could be used; at full luminosity a special high b insertion would have to be envisaged. GAJET would need a small beam, and a jet close to a waist would require a special asymmetric insertion. For both COBEX and GAJET, electromagnetic beam-chamber interactions would need to be studied.

For LHB, tests of crystal extraction had shown good efficiency and control. However, at the LHC some new problems would occur. The crystal would need to be considered as the primary collimator of the cascaded collimation system. It is not yet known if this is feasible, or what would be the implications for extraction. Dedicated operation would be easier than parasitic running from the point of view of control of the halo.

K. Potter summarised the prospects for the experimental areas. Both COBEX and GAJET could be installed in existing LEP intersections with some additional civil engineering work. For LHB, the crystal extraction would probably have to be installed at an even intersection, where extraction would be in the vertical plane. Due to the small extraction angle, the experimental area would be about 600m away from the crossing point, which would mean that an entirely new pit and surface buildings would be needed.

6. SUMMARY AND DISCUSSION

K. Schubert gave a brief summary, with a comparative table of sensitivities for the different experiments. In addition to the primary concerns, it would be interesting to consider measurement of xs, since measurements of this quantity in other experiments may be difficult. Observation of rare decays would also be of interest. In the discussion which followed, a number of points were raised. Given the reach of the general-purpose experiments, it would be important to understand the potential of the dedicated experiments for CP violation measurements in channels other than J/psi Ks.

CLOSED SESSION :

7. The committee had a preliminary discussion of the B physics workshop, the appropriate timescale for submitting Letters of Intent, and a number of questions that should be addressed in the Letters of Intent. The Chairman will discuss these points with the spokesmen and the CERN management. It was agreed that a single team of referees should be appointed for all the Letters of Intent.

8. The minutes of the fifth LHCC meeting (LHCC 93-27 / LHCC 4) and recommendations (LHCC 93-31 / LHCC M1) were approved with the following amendment to the minutes. Item 11, page 3 (Cost Review Group): after the sentence "F. Brasse also presented the reaction of CORE to the staging scenarios." add the sentence "As in the case of the Letters of Intent, CORE has corrected some costs to be on the safer side." The Chairman reported on the 15 and 23 April meeting of the Research Board. This was followed by a brief discussion.

9. TIMETABLE AND FUTURE MEETINGS

It was agreed that a report on experimental areas should be presented at the 8-9 June meeting, to allow the committee to understand infrastructure issues before making recommendations to proceed to technical proposals.

10. DATES FOR 1993 MEETINGS

8-9 June

31 August - 1 September

16-17 November

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MS, 21 July 1993