1. Heavy Quarkonium production in p-Pb collisions at LHCb
清华大学高能物理研究中心
Center for High Energy Physics, Tsinghua University
Heavy Quarkonium production in p-Pb collisions at LHCb
Physics motivation
LHCb detector and 𝒑𝐏𝐛 data-taking
Asymmetric beam energy
𝑠 𝑁𝑁 =5 TeV
rapidity shift Δ𝑦=±0.465
Rapidity coverage (in 𝑁𝑁 c.m.s.)
Forward direction (pPb) 1.5<𝑦<4.0
Backward direction (Pbp) −5.0<𝑦<−2.5
Common coverage
2.5< 𝑦 <4.0
pA collisions are important to study cold nuclear matter (CNM) effects
Heavy quarkonia production sensitive to CNM effects, which are usually characterized by
Forward
𝑝Pb
𝑬 𝒑 =𝟒 𝐓𝐞𝐕
20 Jan Feb.
𝑬 𝒑/𝒏 =𝟏.𝟓𝟖 𝐓𝐞𝐕
JHEP 03 (2013) 122
5 TeV 𝒚
𝑹 𝒑𝐏𝐛 (𝒚) 𝚼
𝑱/𝝍
Nuclear modification factor: 𝑅 𝑝A 𝑦, 𝑠 𝑁𝑁 = 1 𝐴 ⋅ d 𝜎 𝑝A d𝑦 𝑦, 𝑠 𝑁𝑁 d 𝜎 𝑝𝑝 d𝑦 𝑦, 𝑠 𝑁𝑁
Forward-backward production ratio: 𝑅 FB 𝑦, 𝑠 𝑁𝑁 = 𝜎 𝑝A + 𝑦 , 𝑠 𝑁𝑁 𝜎 𝑝A − 𝑦 , 𝑠 𝑁𝑁
Backward
Low pile-up
Integrated ℒ :
Forward (pPb) : 1.1 n b −1
Backward (Pbp): 0.4 n b −1
Higher multiplicity in Pbp case as expected
Pb𝑝
Pb𝑝
𝑝Pb
𝝍 (′) production and cold nuclear matter effects in 𝒑𝐏𝐛 collisions at 𝒔 𝑵𝑵 = 5 TeV
JHEP 02 (2014) 072
JHEP 03 (2016) 033
𝑱/𝝍 cross-sections
Forward (𝑝Pb)
𝑝 T [GeV/𝑐]
Backward (Pb𝑝)
𝑝 T [GeV/𝑐]
Forward (𝑝Pb) 𝑦
Backward (Pb𝑝) −𝑦
Nuclear modification factor 𝑹 𝒑𝐏𝐛
Strong dependence on rapidity
𝐽/𝜓 from 𝑏 less suppressed in forward region than prompt 𝐽/𝜓 ⇒ 𝑏 hadrons less affected by cold nuclear matter effects
Prompt 𝜓 2𝑆 more suppressed than prompt 𝐽/𝜓
Theoretical calculations underestimate prompt 𝜓 2𝑆 suppression
𝐽/𝜓 from 𝑏 ( 𝑝 T < 14 GeV) :
Prompt 𝜓 (′)
Prompt 𝐽/𝜓 ( 𝑝 T < 14 GeV) :
𝝍(𝟐𝐒) cross-sections
𝜓 (′) from 𝑏
Forward (𝑝Pb)
Backward (Pb𝑝)
Forward (𝑝Pb)
Backward (Pb𝑝)
Forward-backward production ratio 𝑹 𝐅𝐁
Independent of 𝑝𝑝 cross-sections
Part of experimental and theoretical uncertainties cancel
Clear difference between prompt 𝐽/𝜓 and 𝐽/𝜓 from 𝑏
Consistent with theoretical calculations
𝜓(2S) from 𝑏 ( 𝑝 T < 14 GeV) :
𝑝 T [GeV/𝑐]
𝑝 T [GeV/𝑐] 𝑦 −𝑦
Prompt 𝜓(2S) ( 𝑝 T < 14 GeV) :
Relative suppression of 𝝍(𝟐𝑺) to 𝑱/𝝍
Suppression of prompt 𝜓(2𝑆) stronger than that of prompt 𝐽/𝜓
Same suppression expected for 𝜓(2𝑆) from 𝑏 and 𝐽/𝜓 from 𝑏
𝒃 𝒃 cross-sections
𝚼 production and cold nuclear matter effects in 𝒑𝐏𝐛 collisions at 𝒔 𝑵𝑵 = 5 TeV
JHEP 07 (2014) 094
𝑹 𝐅𝐁 for 𝚼(𝟏𝐒)
𝚼 production
𝑹 𝒑𝐏𝐛 for 𝚼(𝟏𝐒)
Part of experimental and theoretical uncertainties cancel
Agreement with different theoretical models, but statistical uncertainty large
Reconstructed using Υ 𝑛𝑆 → 𝜇 + 𝜇 −
Forward region: suppression smaller than prompt 𝐽/𝜓, and compatible with 𝑏 hadrons
Backward region: indication of antishadowing effect
𝑚 𝜇 + 𝜇 − [MeV/ 𝑐 2 ]
Forward
𝑚 𝜇 + 𝜇 − [MeV/ 𝑐 2 ]
Backward
Systematic uncertainty dominated by mass fit model, data-MC discrepancy and trigger
Production ratios 𝑅 𝑛𝑆/1𝑆 ≡ 𝜎 Υ 𝑛𝑆 ×ℬ𝑟(Υ 𝑛𝑆 → 𝜇 + 𝜇 − ) 𝜎 Υ 1𝑆 ×ℬ𝑟(Υ 1𝑆 → 𝜇 + 𝜇 − )
清华大学高能物理研究中心