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A search for narrow lines in the gamma spectra from P D annihilation at rest
5,t
Nuclear Physics B (Proc Suppl ) 8 (1989) 51 56 North-llolland, Amst,'rdam
A SEARCH FOR NARROW LINES IN THE GAMMA SPECTRA FROM PD ANNINILATION AT REST Athens-lrvine-Karlsruhe-New
Mex~co-Pennsylvanla
State
A. ANGELOPOULOS a, A. APOSTOLAKIS a, T.A. ARMSTRONG b. B. BASSALLECK c' G. BUECHE d, M. FERO e, M. GEE e, N.A. GRAF e, H. KOCH d, R.A. LEWIS b, M. MANDELKERN e, H. POTH d, H. ROZAKI a, L. SAKELLIOU a, J. SCHULTZ e, J. SCHWERTEL d, G.A. SMITH b, M.J. SOULLIERE b, T. U~HER e, and D.M. WOLFE c (Presented by N.A. Graf) aNuclear Physics Laboratory, University of Athens, Athens 144, Greece bLaboratory for Elementary Particle Science, Department of Physics, Pennsylvania State University, University Park, PA 16802, USA CDepartment of Physics, University of New Mexico, Albuquerque, NM 87131, dKernforschungszentrum Karlsruhe, Institut fur KernphysLk and Universitat Karlsruhe, Institut fur Experimentelle,KernphysLk, Karlsruhe, FRG. eDepartment of Physics, University of California, Irvine, CA 92717, USA ABSTRACT The y ray spectr~n from pd annhilatlons at rest was studied by stopping antiprotons in liquid deuterium and analyzing the gamma rays using a magnetic pair spectrometer. No clear evidence is found for monochromatic y rays and the u~per limit for the br@nching ratio pp + yX with II00 MeV/c 2 < m E < 1770 MeV/c is less than 5 x I0 J at the 95% confidence level. The search for narrow lines in the ga~mna ray spectrum produced in antiproton-proton annihilations at rest has been intense. Despite the predictions if various models and earlier experimental evidence for their existence, exotic four quark stat~s (qqqq), known as baryonium, have not been confirmed by recent experiments. Evidence for bound pN states has also been claimed in the pionic and gamma ray spectra resulting fro~ the annihilatLon of antiprotons in deuterlt~. Prompted by such claims, we conducted an experiment to measure the inclusive gamma ray spectrum from the annihilation of antiprotons at rest in liquid deuterium. In this report we present the results of a high-resolution, high-statistics measurement of the gamma spectrum from the annihilation of antiprotons at rest in liquid deuterium, using the well-understood PS183 magnetic pair spectrometer. The 350 MeV/c antiproton beam entered a 7 cm diameter, 70 cm long liquid deuterium target and the antiprotons annihilated at rest after ranging through approximately 17 cm of deuterium. A cylindrical multiwire proportional chamber surroundlng the target was used to measure the charged multipllclty of each event and planar drift chambers were used to determine the stopping vertex. The gamma rays from the annihilation were converted into electronpositron pairs in a thin lead foil (10% of a radiation length) which was situated at the front of the magnet aperture and subtended 1.5% of 4~ solid angle. Depending upon the momentum of the particle, the magnetic field of 7.SkG either reflected the particle back out of the magnet (R track), trapped it wlthin the magnet aperture (T track), or allowed it to penetrate (P track). The gamma ray events analysed in this report fall into one of three different types; RR, RT, or TT. The acceptance for penetrating tracks was too low at
0920 5632/89/$03.50 © Elsevier Science Publishers B.V (North-Holland Physics Publishing Division)
N.A. Graf et al./Search for narrow lines
this magnetic field ..10 3 setting to accumulate sufficient statistics. Details of the detector c~n be found elsewhere. The moment tun of a particle was reconstructed using the radius of a circle ~ 1 6 fit to the multiwire proportional chamber hits times a correction factor to correct for the ~ 0 8 inhomogeneities in the field. Hit patterns in the 04chambers and tlme-offlight between various scintillators o 2oo ~oo soo 800 ensured a highFi~rel vEner~(MeV) quality sample of events from annihilations at rest. Of 2.8 million gamma-triggered events written to tape, 750000 survived all the cuts and made their way into the spectra presented in Figure I. The acceptance and resolution functions of the spectr~neter were obtained from a Monte Carlo simulation of the detector using the GEANT3 code developed at CERN.
L
i
The spectra were fit with low-order polynomials and the search for narrow states was carried out by stepping through the spectra bin-by-bin and fitting with the global polynomial plus a gaussian constrained to have a width consistent with the spectrometer resolution at the energy of the bin. No clear evidence for narrow structures is seen in the spectra. Figure 2 shows the 95% confidence level upper limits on the yield of narrow structure. •,.~ 1 0
--
3
B
7 °,=~
6
2 1 0
0
200
4-00
600
Figure 2
800
"7 Energy (MeV)
55
N.A
56
Graf et a l . / S e a r c h for narrow line~
REFERENCES 1)
R.L. Jaffe, Phys. Rev. D 17 (1978 1445; C.H. Mo and H. Hogaasen, Nucl. Phys. B 136 (1978) 401; W.W. Buck, C.B. Dover and J.M. Richard, Ann Phys. 121 (1979) 48; C.B. Dover and J.M. Richard, Ann Phys. 121 (1979) 70.
2)
B. Richter et al., Phys. Lett. B 126 (1983) 284; P. Pavlopoulos et al. Phys. Lett. B72 (1978) 415.
3)
A. Angelopoulos et al. Phys. Lett. B 178 (1986 441; L. Adiels et al. Phys. Lett. B 182 (1986) 405; M. Chiba et al. Phys. Rev. D 36 (1987) 3321.
4)
L. Gray et al. Phys. Rev. Lett. 26 (1971) 1491; D. Brldges et al. Phys. Rev. Lett. 56 (1986) 211.
5)
T. E. Kalogeropoulos et al. Phy. Rev. Lett. 33 (1974) 1635.
6)
A. Angelopoulos et al. Phys. Lett. B 178 (1986) 441.
Questioner's name: N.W. Tanner Questioner's institution: Oxford Question: Are there now any sharp y ray lines still surviving, e.g. pHe? Answer: To my knowledge there is no experimental evidence for narrow gamma lines remaining. The lines seen in helium by Adiels et al. were used to confirm their lines in hydrogen. These hydrogen lines have since disappeared, so although the search for lines in heliun has not been repeated I would guess that they were due to the same, perhaps systematic, effect. Questioner's name: l.S. Shapiro Questioner's institution: Lebedev Phys. Inst., Moscow Quest,on: Are your limits for existing narrow y lines in the pd annihilation at rest inside two or three standard deviations? Answer: The 95% confidence levels which we quote correspond to two standard deviations.
Nuclear Physics B (Proc Suppl ) 8 (1989) 51 56 North-llolland, Amst,'rdam
A SEARCH FOR NARROW LINES IN THE GAMMA SPECTRA FROM PD ANNINILATION AT REST Athens-lrvine-Karlsruhe-New
Mex~co-Pennsylvanla
State
A. ANGELOPOULOS a, A. APOSTOLAKIS a, T.A. ARMSTRONG b. B. BASSALLECK c' G. BUECHE d, M. FERO e, M. GEE e, N.A. GRAF e, H. KOCH d, R.A. LEWIS b, M. MANDELKERN e, H. POTH d, H. ROZAKI a, L. SAKELLIOU a, J. SCHULTZ e, J. SCHWERTEL d, G.A. SMITH b, M.J. SOULLIERE b, T. U~HER e, and D.M. WOLFE c (Presented by N.A. Graf) aNuclear Physics Laboratory, University of Athens, Athens 144, Greece bLaboratory for Elementary Particle Science, Department of Physics, Pennsylvania State University, University Park, PA 16802, USA CDepartment of Physics, University of New Mexico, Albuquerque, NM 87131, dKernforschungszentrum Karlsruhe, Institut fur KernphysLk and Universitat Karlsruhe, Institut fur Experimentelle,KernphysLk, Karlsruhe, FRG. eDepartment of Physics, University of California, Irvine, CA 92717, USA ABSTRACT The y ray spectr~n from pd annhilatlons at rest was studied by stopping antiprotons in liquid deuterium and analyzing the gamma rays using a magnetic pair spectrometer. No clear evidence is found for monochromatic y rays and the u~per limit for the br@nching ratio pp + yX with II00 MeV/c 2 < m E < 1770 MeV/c is less than 5 x I0 J at the 95% confidence level. The search for narrow lines in the ga~mna ray spectrum produced in antiproton-proton annihilations at rest has been intense. Despite the predictions if various models and earlier experimental evidence for their existence, exotic four quark stat~s (qqqq), known as baryonium, have not been confirmed by recent experiments. Evidence for bound pN states has also been claimed in the pionic and gamma ray spectra resulting fro~ the annihilatLon of antiprotons in deuterlt~. Prompted by such claims, we conducted an experiment to measure the inclusive gamma ray spectrum from the annihilation of antiprotons at rest in liquid deuterium. In this report we present the results of a high-resolution, high-statistics measurement of the gamma spectrum from the annihilation of antiprotons at rest in liquid deuterium, using the well-understood PS183 magnetic pair spectrometer. The 350 MeV/c antiproton beam entered a 7 cm diameter, 70 cm long liquid deuterium target and the antiprotons annihilated at rest after ranging through approximately 17 cm of deuterium. A cylindrical multiwire proportional chamber surroundlng the target was used to measure the charged multipllclty of each event and planar drift chambers were used to determine the stopping vertex. The gamma rays from the annihilation were converted into electronpositron pairs in a thin lead foil (10% of a radiation length) which was situated at the front of the magnet aperture and subtended 1.5% of 4~ solid angle. Depending upon the momentum of the particle, the magnetic field of 7.SkG either reflected the particle back out of the magnet (R track), trapped it wlthin the magnet aperture (T track), or allowed it to penetrate (P track). The gamma ray events analysed in this report fall into one of three different types; RR, RT, or TT. The acceptance for penetrating tracks was too low at
0920 5632/89/$03.50 © Elsevier Science Publishers B.V (North-Holland Physics Publishing Division)
N.A. Graf et al./Search for narrow lines
this magnetic field ..10 3 setting to accumulate sufficient statistics. Details of the detector c~n be found elsewhere. The moment tun of a particle was reconstructed using the radius of a circle ~ 1 6 fit to the multiwire proportional chamber hits times a correction factor to correct for the ~ 0 8 inhomogeneities in the field. Hit patterns in the 04chambers and tlme-offlight between various scintillators o 2oo ~oo soo 800 ensured a highFi~rel vEner~(MeV) quality sample of events from annihilations at rest. Of 2.8 million gamma-triggered events written to tape, 750000 survived all the cuts and made their way into the spectra presented in Figure I. The acceptance and resolution functions of the spectr~neter were obtained from a Monte Carlo simulation of the detector using the GEANT3 code developed at CERN.
L
i
The spectra were fit with low-order polynomials and the search for narrow states was carried out by stepping through the spectra bin-by-bin and fitting with the global polynomial plus a gaussian constrained to have a width consistent with the spectrometer resolution at the energy of the bin. No clear evidence for narrow structures is seen in the spectra. Figure 2 shows the 95% confidence level upper limits on the yield of narrow structure. •,.~ 1 0
--
3
B
7 °,=~
6
2 1 0
0
200
4-00
600
Figure 2
800
"7 Energy (MeV)
55
N.A
56
Graf et a l . / S e a r c h for narrow line~
REFERENCES 1)
R.L. Jaffe, Phys. Rev. D 17 (1978 1445; C.H. Mo and H. Hogaasen, Nucl. Phys. B 136 (1978) 401; W.W. Buck, C.B. Dover and J.M. Richard, Ann Phys. 121 (1979) 48; C.B. Dover and J.M. Richard, Ann Phys. 121 (1979) 70.
2)
B. Richter et al., Phys. Lett. B 126 (1983) 284; P. Pavlopoulos et al. Phys. Lett. B72 (1978) 415.
3)
A. Angelopoulos et al. Phys. Lett. B 178 (1986 441; L. Adiels et al. Phys. Lett. B 182 (1986) 405; M. Chiba et al. Phys. Rev. D 36 (1987) 3321.
4)
L. Gray et al. Phys. Rev. Lett. 26 (1971) 1491; D. Brldges et al. Phys. Rev. Lett. 56 (1986) 211.
5)
T. E. Kalogeropoulos et al. Phy. Rev. Lett. 33 (1974) 1635.
6)
A. Angelopoulos et al. Phys. Lett. B 178 (1986) 441.
Questioner's name: N.W. Tanner Questioner's institution: Oxford Question: Are there now any sharp y ray lines still surviving, e.g. pHe? Answer: To my knowledge there is no experimental evidence for narrow gamma lines remaining. The lines seen in helium by Adiels et al. were used to confirm their lines in hydrogen. These hydrogen lines have since disappeared, so although the search for lines in heliun has not been repeated I would guess that they were due to the same, perhaps systematic, effect. Questioner's name: l.S. Shapiro Questioner's institution: Lebedev Phys. Inst., Moscow Quest,on: Are your limits for existing narrow y lines in the pd annihilation at rest inside two or three standard deviations? Answer: The 95% confidence levels which we quote correspond to two standard deviations.