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論文

Measurement of jet-medium interactions via direct photon-hadron correlations in Au+Au and $$d$$+Au collisions at $$sqrt{s_{_{NN}}}=200$$ GeV

Acharya, U.*; 長谷川 勝一; 今井 憲一*; 永宮 正治*; 佐甲 博之; 佐藤 進; 谷田 聖; PHENIX Collaboration*; 他572名*

Physical Review C, 102(5), p.054910_1 - 054910_11, 2020/11

 被引用回数:1 パーセンタイル:36.99(Physics, Nuclear)

We present direct photon-hadron correlations in 200 GeV/A Au$$+$$Au, $$d$$$$+$$Au and $$p$$$$+$$$$p$$ collisions, for direct photon $$p_T$$ from 5 - 12 GeV/$$c$$, collected by the PHENIX Collaboration in the years from 2006 to 2011. We observe no significant modification of jet fragmentation in $$d$$$$+$$Au collisions, indicating that cold nuclear matter effects are small or absent. Hadrons carrying a large fraction of the quark's momentum are suppressed in Au$$+$$Au compared to $$p$$$$+$$$$p$$ and $$d$$$$+$$Au. As the momentum fraction decreases, the yield of hadrons in Au$$+$$Au increases to an excess over the yield in $$p$$$$+$$$$p$$ collisions. The excess is at large angles and at low hadron $$p_T$$ and is most pronounced for hadrons associated with lower momentum direct photons. Comparison to theoretical calculations suggests that the hadron excess arises from medium response to energy deposited by jets.

論文

Change in structure between the $$I$$=1/2 states in $$^{181}$$Tl and $$^{177,179}$$Au

Cubiss, J. G.*; Barzakh, A. E.*; Andreyev, A. N.; 他57名*

Physics Letters B, 786, p.355 - 363, 2018/11

 被引用回数:19 パーセンタイル:83.92(Astronomy & Astrophysics)

The first accurate measurements of the $$alpha$$-decay branching ratio and half-life of the I$$^pi$$=1/2$$^{+}$$ ground state in $$^{181}$$Tl have been made, along with the first determination of the magnetic moments and I=1/2 spin assignments of the ground states in $$^{177,179}$$Au. The results are discussed within the complementary systematics of the reduced $$alpha$$-decay widths and nuclear g factors of low-lying, I$$^pi$$=1/2$$^{+}$$states in the neutron-deficient lead region. The findings shed light on the unexpected hindrance of the 1/2$$^{+}$$ $$rightarrow$$ 1/2$$^{+}$$, $$^{181}$$Tl$$^{g}$$ $$rightarrow$$ $$^{177}$$Au$$^{g}$$ $$alpha$$decay, which is explained by a mixing of $$pi$$3s$$_{1/2}$$and $$pi$$2d$$_{3/2}$$ configurations in $$^{177}$$Au$$^{g}$$, whilst $$^{181}$$Tl$$^{g}$$ remains a near-pure $$pi$$3s$$^{1/2}$$. This conclusion is inferred from the g factor of $$^{177}$$Au$$^{g}$$ which has an intermediate value between those of $$pi$$3s$$_{1/2}$$ and $$pi$$2d$$_{3/2}$$ states. A similar mixed configuration is proposed for the I$$^pi$$=1/2$$^{+}$$ ground state of $$^{179}$$Au. This mixing may provide evidence for triaxial shapes in the ground states in these nuclei.

論文

Search for dark photons from neutral meson decays in $$p+p$$ and $$d$$+Au collisions at $$sqrt{s_{NN}} = 200$$ GeV

Adare, A.*; 長谷川 勝一; 今井 憲一; 佐甲 博之; 佐藤 進; 谷田 聖; PHENIX Collaboration*; 他574名*

Physical Review C, 91(3), p.031091_1 - 031091_8, 2015/03

AA2015-0710.pdf:1.35MB

 被引用回数:41 パーセンタイル:93.63(Physics, Nuclear)

The standard model (SM) of particle physics is spectacularly successful, yet the measured value of the muon anomalous magnetic moment $$(g-2)_{mu}$$ deviates from SM calculations by $$3.6sigma$$. Several theoretical models attribute this to the existence of a "dark photon", an additional $$U(1)$$ gauge boson, which is weakly coupled to ordinary photons. The PHENIX experiment at the Relativistic Heavy Ion Collider has searched for a dark photon, $$U$$, in $$pi^0,;eta to gamma e^+e^-$$ decays and obtained upper limits of O(2$$times 10^{-6})$$ on $$U$$-$$gamma$$ mixing at 90% C.L. for the mass range $$30 < m_U < 90 {rm MeV}/c^2$$. Combined with other experimental limits, the remaining region in the $$U$$-$$gamma$$ mixing parameter space that can explain the $$(g-2)_{mu}$$ deviation from its SM value is nearly completely excluded at the 90% confidence level, with only a small region of $$29 < m_U < 32 {rm MeV}/c^2$$ remaining.

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