Electron Capture and Ionization of Pb Ions at 33 TeV

Abstract

We have measured the total cross sections for electron capture by bare Pb 821 ions and ionization of hydrogenlike Pb 811 ions at 33 TeV (160 GeV͞A, g 168) in solid targets of Be, C, Al, Cu, Sn, and Au. The total capture cross sections are dominated by electron capture from pair production and are compared with theoretical calculations. The 1s ionization cross sections obtained are significantly smaller than those predicted by Anholt and Becker [Phys. Rev. A 36, 4628 (1987)]. The Pb radiative lifetimes extended by g 168 have a strong effect on the survival probability of excited states against ionization in high-Z solid targets. [S0031-9007(97) PACS numbers: 34.50. Fa, 34.80.Lx Interactions involving high-Z ions in the ultrarelativistic regime ͑.10 GeV͞amu͒, where the relevant physics is best described in terms of the Lorentz factor g, are currently a frontier in high-energy atomic collision physics [1]. A theoretical description of electron capture and ionization processes has been challenging in this regime because the interaction of high-Z projectile and target species (where Za ϳ 0.5) is strong enough at small impact parameters and large g to potentially invalidate perturbation treatments. Numerous methods for treating these processes using quantum electrodynamics (QED) in the ultrarelativistic regime now exist [1][2][3][4][5][6][7][8][9][10].An ultrarelativistic ion can capture an electron via three mechanisms: (i) radiative electron capture (REC), (ii) nonradiative capture (NRC), and (iii) electron capture via e 1 e 2 pair production (ECPP), in which the e 1 e 2 pair is produced by the intense electromagnetic pulse that arises when the projectile ion passes near a target nucleus. Capture cross sections s REC , s NRC , and s ECPP scale roughly as ϳZ t ͞g, ϳZ 5 t ͞g, and ϳZ 2 t ln g, respectively, where Z t is the target atomic number [2]. Each process has approximately the same dependence on the projectile atomic number, i.e., Z 5 p . The REC and NRC mechanisms, which dominate below the ultrarelativistic regime [11][12][13], become insignificant compared to ECPP when g . 100 even for high Z t . We report the first highenergy measurements ͑g 168͒ where s ECPP dominates the capture cross sections of competing mechanisms. Ionization cross sections are several orders of magnitude larger than capture, and our measurements test theory at the highest energy reported to date [2,10].The development of new relativistic ion colliders such as the Relativistic Heavy-Ion Collider at Brookhaven National Laboratory or the Large Hadron Collider at CERN [2,8,14] requires knowledge of the capture cross sections at high enough g so that beam lifetimes can be accurately predicted. The cross section for the ECPP process is of practical interest to collider designers because the lower charge-state projectiles produced are lost from the beam circulating in a ring. A significant loss rate of these ions by ECPP and also by nuclear loss processes decreases the ion storage time. These machines will operate at an effective g of 2.3 ...

Observations of Beam Losses Due to Bound-Free Pair Production in a Heavy-Ion Collider

“…It is therefore vital to test our quantitative understanding of the features of the BFPP process in order to ensure safe operation of the LHC, uninterrupted by lengthy quenchrecovery procedures. BFPP has been measured in fixed target experiments [9][10][11] at lower energy but not, until now, in a collider. An opportunity arose during 63 Cu 29 operation of RHIC at Brookhaven National Laboratory.…”

Peripheral Collisions of Relativistic Heavy Ions

“…The probability to eject a K-electron is much larger than for other atomic orbitals. Recent experiments have reported ionization cross sections for P b 81+ (33 TeV) beams on several targets [7]. In this case, the role of projectile and target are exchanged in the previous equation.…”

“…A nice book on this subject has been written by Eichler and Meyerhof (see also the review by Anholt and Gould) [6]. Figure 3: Pair production with capture for P b 82+ (33 TeV) beams on several targets [7].…”

“…This dependence was used in the analysis of the experiment in ref. [7]. In recent calculations, attention was given to the correct treatment of the distortion effects in the positron wavefunction [20].…”

Measurement of electromagnetic cross sections in heavy ion interactions and its consequences for luminosity lifetimes in ion colliders

“…The data of Figure 1 can be used to determine both the capture cross section (σ c ) and the cross section for electron loss (σ i ) by fitting the data using a two-state model [6]: As mentioned in the introduction three different reaction mechanisms contribute to the total capture cross section. Each of the processes has a different scaling behaviour relative to the target atomic number (Z T ) and the relativistic Lorentz factor of the incoming ion (γ).…”