Heavy Flavor and Jet Production at LHCb Mike Williams on behalf of the LHCb Collaboration Department of Physics & Laboratory for Nuclear Science Massachusetts Institute of Technology January 12, 2016
The Large Hadron Collider Outline { LHCb overview open beauty & charm jets (V+j,b-jets,c-jets,...) quarkonia fixed-target running
LHCb Detector LHCb is a forward Spectrometer (2 < η < 5) DLL 1 JINST 3 (2008) S08005 ε RICH 0.8 Int.J.Mod.Phys. A 30(2015) 1530022 DLL muDLL 0.6 1.4 Efficiency LogL(K - ) > 0 � � LHCb Data 0.4 � � 1.2 LogL(K - ) > 5 � � � � (a) 0.2 1 LHCb 0.8 0 K K � � 0.005 0.01 ( ) ℘ π → µ 0.6 DLL 0.4 MUON 0.2 � � K � � 0 stuff 20 40 60 80 100 Momentum (GeV/c) VELO CALO 100 m] LHCb 90 µ resolution [ 80 70 60 50 x IP 40 Tracking 30 Magnet 20 2012 data 10 Simulation 0 0 0.5 1 1.5 2 2.5 3 -1 1/ p [GeV c ] 3 T
LHCb Trigger LHCb 2015 Trigger Diagram 40 MHz bunch crossing rate Precision measurements benefit greatly from using the final (best) reconstruction L0 Hardware Trigger : 1 MHz in the online event selection -- need real- readout, high E T /P T signatures time calibration! 450 kHz 400 kHz 150 kHz h ± µ/µµ e/ γ JINST 8 (2013) P04022 Heavy use of machine Software High Level Trigger learning algorithms Partial event reconstruction, select all tracks p T > 0.5 GeV throughout the Run 1 displaced tracks/vertices and dimuons (no IP requirements) and Run 2 trigger. same calibration Buffer events to disk, perform online V.Gligorov, MW, JINST detector calibration and alignment constants used online & offline 8 (2012) P02013. Full offline-like event selection, mixture full reconstruction, offline-like of inclusive and exclusive triggers particle ID, track quality, etc. 12.5 kHz Rate to storage Plan to move to a triggerless-readout system in Run 3! 4
LHCb Detector pixel silicon strip ECAL Cherenkov drift tube HCAL muon CMS LHCb Complimentary kinematical coverage to CMS & ATLAS. 5
LHCb Physics Core physics program involves searching for BSM physics in the decays of heavy-flavor hadrons -- but their production is also of great interest! 7 10 LHCb 6 10 ATLAS/CMS Tevatron 5 10 HERA fixed target ] 2 4 [GeV 10 Q 2 ( x ) = e ± 2 y x 2 s 3 2 10 Q 2 10 10 1 − 6 − 5 − 3 − 4 − 2 − 1 10 10 10 10 10 10 1 x LHCb probes unique regions of (x,Q) so there are many measurements we can (potentially) make that are sensitive to (largely unknown) PDFs*. *PDFs means “parton distribution functions” throughout this talk. 6
Open Charm σ (cc)[13TeV] shown @ EPS (2015) within a week of recording the data; it was measured using online-reconstructed data. Excellent probe of the small-x gluon PDF. <x 1 > ~ 0.05, <x 2 > ~ 2e-5 × 10 3 ( d 2 σ ) / ( d y d p T ) · 10 − m [ µ b / ( GeV c − 1 )] D 0 data Candidates / ( 1 MeV / c 2 ) LHCb D 0 POWHEG+NNPDF3.0L LHCb 10 3 150 Fit √ s = 13TeV √ s = 13 TeV FONLL 10 2 Sig. + Sec. GMVFNS Comb. bkg. 10 1 2 . 0 < y < 2 . 5 , m = 0 100 10 0 10 − 1 2 . 5 < y < 3 . 0 , m = 2 10 − 2 50 10 − 3 3 . 0 < y < 3 . 5 , m = 4 10 − 4 10 − 5 0 3 . 5 < y < 4 . 0 , m = 6 1800 1850 1900 10 − 6 m ( K − π + ) [ MeV / c 2 ] 10 − 7 10 − 8 4 . 0 < y < 4 . 5 , m = 8 LHCb-PAPER-2015-041 Results also published for D + , 10 − 9 D s , D* at both 7 and 13 TeV. 0 2 4 6 8 10 12 14 p T [ GeV / c ] POWHEG+NNPDF [1506.08025], FONLL [1507.06197], )] GMVFNS [1202.0439] 7
Open Beauty σ (bb)[13TeV] also shown at EPS, and previously measured at lower energies. LHCb-PAPER-2015-037: JHEP 10 (2015) 172 )] Candidates per 0.2 ps c Data LHCb 5 LHCb 10 ) [nb/(GeV/ Total fit -1 s = 13 TeV, L =3.05 pb -1 int s = 13 TeV, L =3.05 pb J/ ψ -from- b 3 < y < 3.5 int 2 4 Prompt J/ 10 ψ 10 2 < p < 3 GeV/ c Wrong PV T Background 3 10 T 2 10 10 p d 2.0< y <2.5 y 2.5< y <3.0 10 /(d 3.0< y <3.5 σ 3.5< y <4.0 1 2 1 d 4.0< y <4.5 -10 -8 -6 -4 -2 0 2 4 6 8 10 0 5 10 t [ps] � � z z J/ ψ − z PV × M J/ ψ p ( J/ ) [GeV/ c ] ψ t z = , T p z The pseudo-lifetime distribution of J/ ψ ’s is fitted to determine both the prompt and “from b” content. LHCb has also measured production of many open- beauty meson and baryon species separately. See http://lhcbproject.web.cern.ch/lhcbproject/Publications/LHCbProjectPublic/Summary_all.html for all LHCb publications. 8
Example Impact Impact of 7 TeV prompt-charm* results on the low-x gluon PDF: Gauld, Rojo, Rittoli, Talbert [1506.0825] NNPDF3.0 NLO =0.118 2 2 2 α ( g(x,Q ) ) for Q =4 GeV , NNPDF3.0 NLO Δ s 16 200 0 +- no LHCb D ,D data 0 +- no LHCb D ,D data 180 14 0 +- with LHCb D ,D data (wgt) Percentage PDF uncertainty 0 +- with LHCb D ,D data 0 +- 160 with LHCb D ,D data (unw) 12 ) 140 2 = 4 GeV 10 120 8 100 2 6 g ( x, Q 80 60 4 40 2 20 0 0 − 6 − 5 4 − 3 2 1 − 6 − 5 4 − 3 2 1 − − − − − − 10 10 10 10 10 10 10 10 10 10 10 10 x x See also Gauld et al [1511.06346] for updated prompt atmospheric neutrino flux predictions for IceCube constrained by LHCb prompt-charm data. *LHCb-PAPER-2012-041: Nucl. Phys. B871 (2013) 1 9
Vector Boson + Jet Jets @ LHCb: anti-k T , R=0.5, particle flow. First LHCb jet paper provides differential measurements of Z+jet production: LHCb-PAPER-2013-058: JHEP 01 (2014) 33 [1/GeV] -1 Z 10 σ dy 1.4 Data (stat.) d Data (stat.) LHCb LHCb Data (tot.) 1 σ Data (tot.) jet 1.2 p > 20 GeV jet POWHEG + PYTHIA: p > 10 GeV T POWHEG + PYTHIA: T s = 7 TeV Data O MSTW08, ( α ) jet -2 s = 7 TeV Data s 10 σ T 1.0 MSTW08, O ( ) α MSTW08, O ( 2 ) α s p s d O 2 MSTW08, ( α ) 2 d CTEQ10, O ( α ) s s 2 CTEQ10, O ( ) NNPDF 2.3, O ( 2 ) α α 1 σ 0.8 s s 2 NNPDF 2.3, O ( ) α s 0.6 -3 10 0.4 0.2 -4 10 0.0 20 40 60 80 100 120 140 2.0 2.5 3.0 3.5 4.0 4.5 jet p [GeV] y Z T σ (W + j)/ σ (Zj) and σ (W - j)/ σ (Zj) also measured integrated over LHCb acceptance for p T (j) > 20 GeV; these also agree with NLO SM predictions. LHCb-PAPER-2015-021 PRD 92 (2015) 052001 Run 1 differential W+jet measurements are in preparation. Such measurements in Runs 2 & 3 will enable strongly constraining d/u at large-x. Farry, Gauld [1505.01399] 10 1.2
Jet Tagging Jet Tagging Use a SV-based algorithm to identify b and c jets (leveraging LHCb VELO): JINST 10 (2015) P06013 LHCb-PAPER-2015-016 example SV feature: “corrected mass” 1 ) candidates c | LHCb data b 1000 LHCb BDT( 10000 data 0.5 beauty 800 b SV features used c 600 0 light parton in 2 BDTs udsg charm 5000 400 -0.5 200 Initial (no-tagging) sample: D +jet 70% light parton, 22% charm, 8% beauty. 0 0 -1 -1 -0.5 0 0.5 1 0 2 4 6 8 10 SV M [GeV] BDT( bc | udsg ) cor candidates Performance validated & calibrated using large heavy-flavor-enriched jet data samples. Two-D BDT distributions fitted to extract SV-tagged jet flavor content; c-jet and b-jet yields each precisely determined simultaneously. 11
W+b & W+c W+charm production probes the strange content of the proton. In the forward region, this includes large-x s vs s-bar. W + c -jet PRD 92 (2015) 052001 s W LHCb-PAPER-2015-021 8TeV LHCb g c MCFM (NLO) W+c W+b W + b -jet q i W 7TeV b 0 5 -0.25 0 0.25 0.5 (Wq)/ (Wj) [%] Charge Asymmetry σ σ q j b Expect ~10x larger stats in Run 2; will be able to probe s vs s-bar PDFs using differential measurements of W+c. 12
Top Top production in the forward region probes the large-x gluon PDF and may be more sensitive to BSM. Kagan, Kamenik, Perez, Stone [1103.3747] LHCb made the first observation of forward top production in Run 1: <x 1 > ~ 0.2, <x 2 > ~ 0.02 PRL 115 (2015) 112001, LHCb-PAPER-2015-022 8TeV Results for σ (tt+t+t-bar): LHCb MCFM (NLO) σ (top)[7 TeV] = 239 ± 53 (stat) ± 33 (syst) ± 24 (theory) fb , 7TeV σ (top)[8 TeV] = 289 ± 43 (stat) ± 40 (syst) ± 29 (theory) fb . 100 200 300 400 (top) [fb] σ Expect ~20x more stats in Run 2; will explore separating pair and single-top production, and differential measurements. Should reduce the large-x gluon PDF uncertainty by ~20% [Gauld, 1311.1810]. 13
Z+c Whether there exists “intrinsic” (non-perturbative) charm content in the proton has long been debated. LHCb can say a lot here in Runs 2 and 3. c Z Boettcher, Ilten, MW [arxiv:1512.06666] ) Zj s = 14 TeV ( ∫ -1 σ Ldt = 15 fb )/ 0.08 Zc ( σ 0.06 g c c Z 0.04 CT14NNLO BHPS1 BHPS2 SEA1 SEA2 CT14NNLO 4.5 3 2 2.5 3 3.5 4 4.5 2 IC 1 g c 4.5 2 2.5 3 3.5 4 4.5 ) y ( Z ) Also effects Higgs production by ~2% (more for H+c), direct dark matter detection (assuming H exchange), and prompt atmospheric neutrino rates. 14
PDFs Summary small-x gluon large-x gluon intrinsic charm c Z large-x d/u s vs s-bar et s W W g c g g c 15
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