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Experimental prospects in CP violation in K meson decay
Nuclear Physics A478 (1988) 259c-260c North-Holland, Amsterdam
259c
EXPERIMENTAL PROSPECTS IN CP VIOLATION IN K MESON DECAY GEORGE D. GOLLIN Princeton University, Princeton, New Jersey 08544, USA Abstract: Several experiments which are performing precision measurements of CP parameters in hopes of shedding new light on the origins of CP violation are discussed . Two are measuring the ratio the phase difference between atm I%o/+1+_1, one is measuring +l+ _o , two experiments will+ measure and n+_, and one will search for the decay ICL ~ tru e e -,
All experimental studies of CP violation are consistent with the existence ®f a single source for CP violation, the AS = 2 interaction which mixes Ko and Ko. This CP violation is caused by a time asymmetry in the two transitions W-), and Ko -> 140. Several new experiments which will produce results within the next few years may shed more light on the origins of CP violation. Two experiments are meast,ring 7100/,q+-, one is measuring 9+ _o, two will measure the phase difference between ,10o and t1+-, and one experiment will search for li.L -> w'e'e-. Standard model calculations predict the existence of a AS= 1 source for CP violation in addition to the (larger) AS = 2 source. A ®S ==1 CP violating amplitude is expected to split the magnitudes of alvo and 71+- by a few percent. A ChicagoElmhurst-Fermilab-Princeton-Saclay group (13731) is measuring 71 ./rl+- using a novel double-beam technique. Two KL beams enter the 13731 detector simultaneously; a boron-carbide regenerator in onet.ekm produces Ks. To good approximation, the ratio of ara decays in the two beams is proportional to (al/p1 2, where p is the KL-> Ks regeneration amplitude. By recording a+a- decays during one set of data-taking, ar°a° decays during another set, then dividing the ratios of KL to Ks from each mode, this group determines ah/al+- . Systematic effects due to detector efficiency and beam flux uncertainties cancel in the double ratio. The parameters e' and e are defined through the expression a oo /al+ _= 1-3e'/s. 13731 has measured e'/e=0.0035±0.0030 (statistical)±0.0020 (systematic) from test run data accumulated in 1985 ; the experiment's main run will take place during the summer o¬ 1987. Atotal data sample of 105 KL -> aoaro, and more of the otherdecay modes, is expected . Anticipated precision is ±0.001 in e'/s. A CERN-DortmundEdinburgh-Mainz-Orsay-Pisa-Siegen group (NA31) is measuring 1700/al+_ using a single beam containing amoveable target. By adjusting the target location, the group +a_ and aro ° can change the ratio of Ks to KL decays recorded . NA31 runs ar a modes simultaneously, and changes target positions frequently . They have finished
260c
G.D. Gollin / CP violation in K decay
taking data and mayhave results sometime in 1987. The NA31 data sample contains more than 105 KL -> a°1r°; a precision of 10.001 in e'je is expected . A Michigan-Minnesota-Rutgers group (13621) is measuring r1+-o, the CP violating amplitude ratio for K -> or +w-a° decays. il+_o is expected to be similar in magnitude to q+-; different models of the weak interactions predict different splittings between the values of q+-o and q+-. The 13621 apparatus at Fermilab uses two kaon beams, one produced far from the detector, the other produced close to the detector. The proper time distribution for a+rr- decays in the "far" beam should fall exponentially with the KL lifetime . Interference between Ks and KL -r lr +w in the "near" beam should produce a more steeply falling proper time spectrum . The expected interference is small: a 0.3% enhancement should be seen at small proper times if q+-o=71+-" Eased on 8.6x 10° decays, 13621 finds 71+-o= 0.022+0.026. An event sample of 3.2x106 decays is currently being analyzed ; a final accuracy of +0.003 is expected. Note that v1+-=0.0023. The phase difference, uo=Arg (9.)-Arg (71+-), should be less than one degree if CPT is conserved in K decays. The current value for ®O is (9 .4+5.1) degrees. The 13731 and NA31 groups have both proposed to measure ®O to an accuracy of +1 degree . The 13731 group will take data in 1989 ; the NA31 group in 1988 . 11äs measurement will demand great care to guard against systematic problems. A UCLA-LANL-Penn-Stanford-Temple-William and Mary group will search for K L -> iroe+e- during the course of a lepton-number violation experiment at Brookhaven looking for KL -*,ce decays . A sensitivity to ar"e't- decay at the level of 2.3 x 10 -" is claitnt d in the group's proposal. This is a difficult experiment, and cuts required to reduce backgrounds may eliminate a lai ge fraction of a possible 7roe+e- ,,.fnal. Since the amplitude for KL -> v"e + e- might be dominated by a C? violating term, discoveryof a 7r°e+e decay mode might herald a new signal for CP violation . The,qoo/ q+_experiments hold thegreatest promise for providing newinformation about CP violation in K decay. The q+-O, phase, and -.r°e+ e- experiments may produce striking results if CP violation comesfrom a non-standard weak interaction . All experiments will publish results during the next few years.
v
e
259c
EXPERIMENTAL PROSPECTS IN CP VIOLATION IN K MESON DECAY GEORGE D. GOLLIN Princeton University, Princeton, New Jersey 08544, USA Abstract: Several experiments which are performing precision measurements of CP parameters in hopes of shedding new light on the origins of CP violation are discussed . Two are measuring the ratio the phase difference between atm I%o/+1+_1, one is measuring +l+ _o , two experiments will+ measure and n+_, and one will search for the decay ICL ~ tru e e -,
All experimental studies of CP violation are consistent with the existence ®f a single source for CP violation, the AS = 2 interaction which mixes Ko and Ko. This CP violation is caused by a time asymmetry in the two transitions W-), and Ko -> 140. Several new experiments which will produce results within the next few years may shed more light on the origins of CP violation. Two experiments are meast,ring 7100/,q+-, one is measuring 9+ _o, two will measure the phase difference between ,10o and t1+-, and one experiment will search for li.L -> w'e'e-. Standard model calculations predict the existence of a AS= 1 source for CP violation in addition to the (larger) AS = 2 source. A ®S ==1 CP violating amplitude is expected to split the magnitudes of alvo and 71+- by a few percent. A ChicagoElmhurst-Fermilab-Princeton-Saclay group (13731) is measuring 71 ./rl+- using a novel double-beam technique. Two KL beams enter the 13731 detector simultaneously; a boron-carbide regenerator in onet.ekm produces Ks. To good approximation, the ratio of ara decays in the two beams is proportional to (al/p1 2, where p is the KL-> Ks regeneration amplitude. By recording a+a- decays during one set of data-taking, ar°a° decays during another set, then dividing the ratios of KL to Ks from each mode, this group determines ah/al+- . Systematic effects due to detector efficiency and beam flux uncertainties cancel in the double ratio. The parameters e' and e are defined through the expression a oo /al+ _= 1-3e'/s. 13731 has measured e'/e=0.0035±0.0030 (statistical)±0.0020 (systematic) from test run data accumulated in 1985 ; the experiment's main run will take place during the summer o¬ 1987. Atotal data sample of 105 KL -> aoaro, and more of the otherdecay modes, is expected . Anticipated precision is ±0.001 in e'/s. A CERN-DortmundEdinburgh-Mainz-Orsay-Pisa-Siegen group (NA31) is measuring 1700/al+_ using a single beam containing amoveable target. By adjusting the target location, the group +a_ and aro ° can change the ratio of Ks to KL decays recorded . NA31 runs ar a modes simultaneously, and changes target positions frequently . They have finished
260c
G.D. Gollin / CP violation in K decay
taking data and mayhave results sometime in 1987. The NA31 data sample contains more than 105 KL -> a°1r°; a precision of 10.001 in e'je is expected . A Michigan-Minnesota-Rutgers group (13621) is measuring r1+-o, the CP violating amplitude ratio for K -> or +w-a° decays. il+_o is expected to be similar in magnitude to q+-; different models of the weak interactions predict different splittings between the values of q+-o and q+-. The 13621 apparatus at Fermilab uses two kaon beams, one produced far from the detector, the other produced close to the detector. The proper time distribution for a+rr- decays in the "far" beam should fall exponentially with the KL lifetime . Interference between Ks and KL -r lr +w in the "near" beam should produce a more steeply falling proper time spectrum . The expected interference is small: a 0.3% enhancement should be seen at small proper times if q+-o=71+-" Eased on 8.6x 10° decays, 13621 finds 71+-o= 0.022+0.026. An event sample of 3.2x106 decays is currently being analyzed ; a final accuracy of +0.003 is expected. Note that v1+-=0.0023. The phase difference, uo=Arg (9.)-Arg (71+-), should be less than one degree if CPT is conserved in K decays. The current value for ®O is (9 .4+5.1) degrees. The 13731 and NA31 groups have both proposed to measure ®O to an accuracy of +1 degree . The 13731 group will take data in 1989 ; the NA31 group in 1988 . 11äs measurement will demand great care to guard against systematic problems. A UCLA-LANL-Penn-Stanford-Temple-William and Mary group will search for K L -> iroe+e- during the course of a lepton-number violation experiment at Brookhaven looking for KL -*,ce decays . A sensitivity to ar"e't- decay at the level of 2.3 x 10 -" is claitnt d in the group's proposal. This is a difficult experiment, and cuts required to reduce backgrounds may eliminate a lai ge fraction of a possible 7roe+e- ,,.fnal. Since the amplitude for KL -> v"e + e- might be dominated by a C? violating term, discoveryof a 7r°e+e decay mode might herald a new signal for CP violation . The,qoo/ q+_experiments hold thegreatest promise for providing newinformation about CP violation in K decay. The q+-O, phase, and -.r°e+ e- experiments may produce striking results if CP violation comesfrom a non-standard weak interaction . All experiments will publish results during the next few years.
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