Recent results of double parton scattering studies at LHCb Liupan - - PowerPoint PPT Presentation
Recent results of double parton scattering studies at LHCb Liupan An On behalfof the LHCb collaboration Tsinghua University 1 /15 Outline Introduction The LHCb detector LHCb measurements / + open charm & 2open charm
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Recent results of double parton scattering studies at LHCb
On behalfof the LHCb collaboration
Tsinghua University
Liupan An
1
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Outline
ØIntroduction ØThe LHCb detector ØLHCb measurements
ü𝐾/𝜔 + open charm & 2×open charm @ 7 TeV
[JHEP 06 (2012) 141]
ü𝛷 + open charm @ 7 & 8 TeV
[JHEP 07 (2016) 052]
ü2×𝐾/𝜔 @ 13 TeV
[LHCb-PAPER-2016-057]
ØSummary and prospects
[JHEP 1403 (2014) 108]
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Introduction
Ø DPS studies in various experiments ü 𝑞𝑞: W+2-jets, 𝐾/𝜔+W, 𝐾/𝜔+Z, 2×𝐾/𝜔, 2×𝛷 etc. ü 𝑞𝑞̅: 4-jets, 𝛿+3-jets, 𝐾/𝜔 + 𝛷 etc. ü 𝑞 − 𝑄𝑐: 𝑋±𝑋± (proposed) ü 𝑄𝑐 − 𝑄𝑐: 2×𝐾/𝜔 (proposed) Ø LHCb: 𝑞𝑞 collisions, smaller 𝑦 Ø Pocket formula 𝜏DEDF = 1 1 + 𝜀DEDF 𝜏DE𝜏DF 𝜏IJJ
ü 𝜏IJJ thought to be universal, i.e. independent of process and energy
Ø General purpose of DPS measurements
ü Measure 𝜏IJJ : validate its universality or probe the dependence on process and energy ü Test the pocket formula for differential cross-sections
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Effective cross-section
[PLB 751 (2015) 479]
14.5 mb
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The LHCb detector
ØA single-arm forward region spectrometer covering 2 < 𝜃 < 5
ØRunI (2011-2012): ℒRST = 3 fbVW @ 7 & 8 TeV ; 𝜏 𝑐𝑐 X ≈ 250 µbVW @ 7 TeV ØRunII (2015-2018): ℒRST = 5 fbVW @ 13 & 14 TeV ; 𝜏 𝑐𝑐 X ≈ 500 µbVW @ 13 TeV
ü Vertex Locator: 𝜏\],_/`~10 µm , 𝜏\],b~60 µm ü Tracking (TT, T1-T3):Δ𝑞/𝑞 = 0.5 − 0.6% for 5 < 𝑞 < 100 GeV/𝑑 ü RICHs: 𝜁 𝐿 → 𝐿 ~95%@ misIDrate 𝜌 → 𝐿 ~5% ü Muon system (M1-M5): 𝜁 𝜈 → 𝜈 ~97% @ misIDrate 𝜌 → 𝜈 ~1 − 3% ü ECAL: 𝜏n/𝐹~10% / 𝐹 ⊗ 1% (𝐹 in GeV) ü HCAL: 𝜏n/𝐹~70% / 𝐹 ⊗ 10% (𝐹 in GeV)
𝑞𝑞 interaction point
[JINST 3 (2008) S08005] [JHEP 10 (2015) 172] [EPJC 71 (2011) 1645]
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Ø Using 350 pbVW data at 𝑡 = 7 TeV Ø Production cross-sections ü Significantly larger than SPS predictions ü SPS fraction 1 − 5%
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𝐾/𝜔 + open charm & 2×open charm
Ø ℛvEvF ≡ 𝛽y z{E×z{F
z{E{F
ü Interpreted as 𝜏IJJ in DPS ü 𝐾/𝜔 + open charm: in good agreement with CDF measurement in multi-jet production 𝜏IJJ = 14.5 ± 1.7V|.}
~W.• mb
ü 2×open charm: closer to 20 mb
LHCb LHCb SPS
[PRD 87 (2013) 074039] [EPJC 60:693-703, 2009] [PRD 57 (1998) 4385] [PRD73 (2006) 074021] [JHEP 06 (2012) 141] [PRD 56 (1997) 3811]
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𝛷 + open charm
ØUsing 3 fbVW data at 𝑡 = 7 TeV & 8 TeV ØFiducial region: 𝛷 ∈ 2.0 < 𝑧 < 4.5, 𝑞‚ < 15 GeV/𝑑
> 5𝜏
Ø Results: Ø DPS predictions:
ü With 𝜏IJJ = 14.5 mb
Ø Consistent!
[JHEP 07 (2016) 052] [PRD 56 (1997) 3811]
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More comparisons
ü Consistent with DPS prediction 2.41 ± 0.18 ü Consistent with DPS prediction ~10% ü Exceeds SPS expectation 0.1 − 0.6 % ü Compatible with DPS prediction 0.249 ± 0.033 Neglecting SPS contribution: 𝜏IJJ = 18.0 ± 1.3 stat ± 1.2 syst mb ü Consistent with previous measurements ü Kinematic distributions of 𝛷 + open charm also show good agreement with DPS
[JHEP 07 (2016) 052]
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2×𝐾/𝜔 @ 7 TeV
ØUsing 37.5 pbVW data at 𝑡 = 7 TeV ØFiducial region: 2 < 𝑧‡/ˆ < 4.5, 𝑞‚
‡/ˆ < 10 GeV/𝑑
ØObserved with significance > 6𝜏 Ø𝜏 ‡/ˆ‡/ˆ = 5.1 ± 1.0 ± 1.1 nb
ü𝜏‰\‰ = 4.0 ± 1.2 nb; LO NRQCD CS ü𝜏Š\‰ ≈ 3.8 ± 1.3 nb; 𝜏IJJ = 14.5 mb
ØNot enough events to disentangle SPS and DPS contributions
Raw yield 141 ± 19 SPS, [PRD 84 (2011) 094023]
[PLB 707 (2012) 52-59]
Efficiency-corrected yield 672 ± 129
[PRD 56 (1997) 3811]
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2×𝐾/𝜔 @ 13 TeV
ØUsing ~279 pbVW data at 𝑡 = 13 TeV ØFiducial region: 2 < 𝑧‡/ˆ < 4.5, 𝑞‚
‡/ˆ < 10 GeV/𝑑
ØCut-based selection ØEfficiency estimated using simulation & data ØSignal yield obtained from simultaneous fit to the efficiency-corrected 2D 𝑁 𝜈W
~𝜈W V ,𝑁 𝜈| ~𝜈| V
distribution Ø𝜏 𝐾/𝜔𝐾/𝜔 = 13.5 ± 0.9 stat ± 0.8 syst nb
LHCb preliminary LHCb preliminary
New!
[LHCb-PAPER-2016-057]
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Comparison to theory
SPS
[PRD 94 (2016) 054017] [PRD 94 (2016) 054017] [PRD 84 (2011) 054012] [CPC 198 (2016) 238] [CPC 198 (2016) 238]
DPS: assuming 𝜏IJJ = 14.5 ± 1.7V|.}
~W.• mb
[PRD 56 (1997) 3811]
ØLO CO : contribution very small ØLO CS/ NLO* CS’ : need DPS contribution ØLO 𝑙‚ and NLO* CS’’ : uncertainty quite large; consistent with measurement within uncertainty
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Differential cross-sections
LHCb preliminary LHCb preliminary LHCb preliminary LHCb preliminary
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Differential cross-sections (cont.)
LHCb preliminary LHCb preliminary LHCb preliminary LHCb preliminary
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DPS contribution
LHCb preliminary
Ø DPS contribution essential for the region Δ𝑧 > 1.5 Ø Compatible with expectations for 𝜏IJJ = 14.5 ± 1.7V|.}
~W.• mb
Ø Much smaller 𝜏IJJ values are disfavoured Ø Comparisons with 𝑞‚ 𝐾/𝜔𝐾/𝜔 > 1 GeV/𝑑 or 3 GeV/𝑑 give same conclusions
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Summary & prospects
ØDPS is explored at LHCb through several processes ØRelevant DPS contribution is observed in
ü 𝐾/𝜔 + open charm & 2×open charm ü𝛷 + open charm
ØIndication for DPS contribution in 2×𝐾/𝜔 @ 13 TeV
ØProspects
üStill a lot to be analyzed with RunI data
üRunII is in progress
Th Thank you
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DPS formula
Generalized double parton PDF SPS parton-level cross-section
Ø Assumption 1: factorization of transverse & longitudinal components ΓŽ• 𝑦W,𝑦|,𝒄W,𝒄| = 𝐸Ž• 𝑦W,𝑦| 𝑈Ž•(𝒄W,𝒄|) Ø Assumption 2: no correlation 𝐸Ž• 𝑦W,𝑦| = 𝑔
Ž 𝑦W 𝑔
𝑈Ž• 𝒄W,𝒄| = 𝑈Ž 𝒄W 𝑈
⇒ Pocket formula 𝜏DEDF = 1 1 + 𝜀DEDF 𝜏DE𝜏DF 𝜏IJJ ü Also valid for differential cross-sections
𝑅W 𝑅|