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 Ø Introduction Ø The LHCb detector Ø LHCb measurements ü 𝐾/𝜔 + open charm & 2×open charm @ 7 TeV [JHEP 06 (2012) 141] [JHEP 1403 (2014) 108] ü 𝛷 + open charm @ 7 & 8 TeV [JHEP 07 (2016) 052] ü 2×𝐾/𝜔 @ 13 TeV [LHCb-PAPER-2016-057] Ø Summary and prospects 11/29/16 Liupan An 2 /15

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 𝜏 D E 𝜏 D F 1 𝜏 D E D F = 1 + 𝜀 D E D F 𝜏 IJJ ü 𝜏 IJJ thought to be universal, i.e. independent of process and energy Ø General purpose of DPS measurements ü Measure 𝜏 IJJ : validate its universality or probe the dependence on process and energy ü Test the pocket formula for differential cross-sections 11/29/16 Liupan An 3 /15

Effective cross-section 14.5 mb [PLB 751 (2015) 479] 11/29/16 Liupan An 4 /15

The LHCb detector Ø A single-arm forward region spectrometer covering 2 < 𝜃 < 5 X ≈ 250 µb VW @ 7 TeV Ø RunI (2011-2012): ℒ RST = 3 fb VW @ 7 & 8 TeV ; 𝜏 𝑐𝑐 [EPJC 71 (2011) 1645] X ≈ 500 µb VW @ 13 TeV Ø RunII (2015-2018): ℒ RST = 5 fb VW @ 13 & 14 TeV ; 𝜏 𝑐𝑐 [JHEP 10 (2015) 172] 𝑞𝑞 interaction point [JINST 3 (2008) S08005] 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: 𝜏 n /𝐹~10% / 𝐹 ⊗ 1% (𝐹 in GeV) ü HCAL: 𝜏 n /𝐹~70% / 𝐹 ⊗ 10% (𝐹 in GeV) 11/29/16 Liupan An 5 /15

𝐾/𝜔 + open charm & 2×open charm [JHEP 06 (2012) 141] Ø ℛ v E v F ≡ 𝛽 y z {E ×z {F Ø Using 350 pb VW data at 𝑡 = 7 TeV z {E{F LHCb Ø Production cross-sections LHCb SPS [PRD 87 (2013) 074039] [EPJC 60:693-703, 2009] [PRD 57 (1998) 4385] [PRD73 (2006) 074021] ü Interpreted as 𝜏 IJJ in DPS [PRD 56 (1997) 3811] ü 𝐾/𝜔 + open charm : in good agreement with CDF measurement in multi-jet ü Significantly larger than SPS predictions ~W.• mb production 𝜏 IJJ = 14.5 ± 1.7 V|.} ü SPS fraction 1 − 5% ü 2×open charm : closer to 20 mb 11/29/16 Liupan An 6 /15

𝛷 + open charm Ø Using 3 fb VW data at 𝑡 = 7 TeV & 8 TeV Ø Fiducial region: 𝛷 ∈ 2.0 < 𝑧 < 4.5 , 𝑞 ‚ < 15 GeV/𝑑 open charm ∈ 2.0 < 𝑧 < 4.5 , 1 < 𝑞 ‚ < 20 GeV/𝑑 [JHEP 07 (2016) 052] Ø Results: Ø DPS predictions: [PRD 56 (1997) 3811] With 𝜏 IJJ = 14.5 mb ü Ø Consistent! > 5𝜏 11/29/16 Liupan An 7 /15

More comparisons ü Consistent with DPS prediction 2.41 ± 0.18 ü Consistent with DPS prediction ~10% Exceeds SPS expectation 0.1 − 0.6 % ü ü Compatible with DPS prediction 0.249 ± 0.033 ü Kinematic distributions of 𝛷 + open charm also show good agreement with DPS Neglecting SPS contribution: 𝜏 IJJ = 18.0 ± 1.3 stat ± 1.2 syst mb ü Consistent with previous measurements [JHEP 07 (2016) 052] 11/29/16 Liupan An 8 /15

2×𝐾/𝜔 @ 7 TeV Ø Using 37.5 pb VW data at 𝑡 = 7 TeV ‡/ˆ < 10 GeV/𝑑 Ø Fiducial region: 2 < 𝑧 ‡/ˆ < 4.5 , 𝑞 ‚ Ø Observed with significance > 6𝜏 [PLB 707 (2012) 52-59] Raw yield Efficiency-corrected yield 141 ± 19 672 ± 129 Ø 𝜏 ‡/ˆ‡/ˆ = 5.1 ± 1.0 ± 1.1 nb ü 𝜏 ‰\‰ = 4.0 ± 1.2 nb ; LO NRQCD CS ü 𝜏 Š\‰ ≈ 3.8 ± 1.3 nb ; 𝜏 IJJ = 14.5 mb SPS, [PRD 84 (2011) 094023] [PRD 56 (1997) 3811] Ø Not enough events to disentangle SPS and DPS contributions 11/29/16 Liupan An 9 /15

2×𝐾/𝜔 @ 13 TeV New! Ø Using ~279 pb VW data at 𝑡 = 13 TeV ‡/ˆ < 10 GeV/𝑑 Ø Fiducial region: 2 < 𝑧 ‡/ˆ < 4.5 , 𝑞 ‚ Ø Cut-based selection Ø Efficiency estimated using simulation & data Ø Signal yield obtained from simultaneous fit to the efficiency-corrected 2D V ,𝑁 𝜈 | ~ 𝜈 W ~ 𝜈 | V 𝑁 𝜈 W distribution LHCb preliminary LHCb preliminary [LHCb-PAPER-2016-057] Ø 𝜏 𝐾/𝜔𝐾/𝜔 = 13.5 ± 0.9 stat ± 0.8 syst nb 11/29/16 Liupan An 10 /15

Comparison to theory [PRD 94 (2016) 054017] [CPC 198 (2016) 238] [PRD 84 (2011) 054012] SPS [PRD 94 (2016) 054017] [CPC 198 (2016) 238] ~W.• mb DPS: assuming 𝜏 IJJ = 14.5 ± 1.7 V|.} [PRD 56 (1997) 3811] Ø LO CO : contribution very small Ø LO CS/ NLO* CS’ : need DPS contribution Ø LO 𝑙 ‚ and NLO* CS’’ : uncertainty quite large; consistent with measurement within uncertainty 11/29/16 Liupan An 11 /15

Differential cross-sections LHCb preliminary LHCb preliminary LHCb preliminary LHCb preliminary 11/29/16 Liupan An 12 /15

Differential cross-sections (cont.) LHCb preliminary LHCb preliminary LHCb preliminary LHCb preliminary 11/29/16 Liupan An 13 /15

DPS contribution LHCb preliminary Ø DPS contribution essential for the region Δ𝑧 > 1.5 ~W.• mb Ø Compatible with expectations for 𝜏 IJJ = 14.5 ± 1.7 V|.} Ø Much smaller 𝜏 IJJ values are disfavoured Ø Comparisons with 𝑞 ‚ 𝐾/𝜔𝐾/𝜔 > 1 GeV/𝑑 or 3 GeV/𝑑 give same conclusions 11/29/16 Liupan An 14 /15

Summary & prospects Ø DPS is explored at LHCb through several processes Ø Relevant DPS contribution is observed in ü 𝐾/𝜔 + open charm & 2×open charm ü 𝛷 + open charm Ø Indication for DPS contribution in 2×𝐾/𝜔 @ 13 TeV Ø Prospects ü Still a lot to be analyzed with RunI data • Update existing measurements with more data • New channels to look into: 𝛷 + 𝐾/𝜔 , 2×𝛷 etc. ü RunII is in progress • New energy scale: 𝑡 = 13 TeV • More statistics expected: ℒ RST = 5 fb VW • Possibility for triple-parton scattering? Thank you Th ou! 11/29/16 Liupan An 15 /15

Back up 11/29/16 Liupan An 16 /15

DPS formula 𝑅 W 𝑅 | Generalized double parton PDF SPS parton-level cross-section Ø Assumption 1: factorization of transverse & longitudinal components Γ Ž• 𝑦 W ,𝑦 | ,𝒄 W ,𝒄 | = 𝐸 Ž• 𝑦 W ,𝑦 | 𝑈 Ž• (𝒄 W ,𝒄 | ) Ø Assumption 2: no correlation 𝐸 Ž• 𝑦 W ,𝑦 | = 𝑔 Ž 𝑦 W 𝑔 • 𝑦 | , 𝑈 Ž• 𝒄 W ,𝒄 | = 𝑈 Ž 𝒄 W 𝑈 • (𝒄 | ) ⇒ Pocket formula 1 𝜏 D E 𝜏 D F 𝜏 D E D F = 1 + 𝜀 D E D F 𝜏 IJJ ü Also valid for differential cross-sections 11/29/16 Liupan An 17 /15