Antiproton production in p-He collisions, and more, at LHCb LHCb on a Space Mission He at 6.5 TeV rest proton antiproton Giacomo Graziani (INFN Firenze) on behalf of the LHCb Collaboration ICRC 2017, Busan, Korea July 15, 2017
The LHCb Experiment LHCb is the experiment devoted to heavy flavours at the LHC Focused on CP violation and rare signatures in b and c decays Exploiting LHC as the biggest b and c fac- tory on earth Detector requirements: Forward geometry optimize acceptance for bb pairs Tracking : best possible proper time and momentum resolution Particle ID : excellent capabilities to select exclusive decays Trigger : high flexibility and bandwidth (up to 15 kHz to disk) ➨ allowed to widen our physics program to include hadron spectroscopy, EW physics, kaon physics, heavy ion physics (pPb and PbPb collisions) ... ICRC 2017 G. Graziani slide 2
SMOG: the LHCb internal gas target LHCb is the LHC experiment with “fixed-target like” geometry very well suited for...fixed target physics! JINST 3, (2008) S08005 Int.J.Mod.Phys.A30 (2015) 1530022 The System for Measuring Overlap with Gas (SMOG) allows to inject small amount of noble gas (He, Ne, Ar, ...) inside the LHC beam around ( ∼ ± 20 m) the LHCb collision region Expected pressure ∼ 2 × 10 − 7 mbar Originally conceived for the luminosity determination with beam gas imaging JINST 9, (2014) P12005 Became the LHCb internal gas target for a rich and var- ied fixed target physics program ICRC 2017 G. Graziani slide 3
Soft QCD for Cosmic Rays Physics Fixed target collisions allow to study exclusive particle production at the energy scale of ∼ 100 GeV , with access to large x in the target; can provide valuable inputs for modeling cosmic ray showers in the atmosphere and in the cosmos, in particular for antimatter production AMS02 results provide unprecedented accuracy for measurement of p / p ratio in cosmic rays at high energies PRL 117, 091103 (2016) hint for a possible excess, and milder en- ergy dependence than expected prediction for p / p ratio from spallation of primary cosmic rays on intestellar medium (H and He) is presently limited by uncertainties on p production cross- sections, particularly for p -He no previous measurement of p production in p -He, current predictions vary within a factor 2 the LHC energy scale and LHCb +SMOG are very well suited to perform this mea- surement Giesen et al., JCAP 1509, 023 (2015) ICRC 2017 G. Graziani slide 4
Detector and Acceptance JINST 3, (2008) S08005 Int.J.Mod.Phys.A30 (2015) 1530022 4 [GeV/c] 0.8 3.5 0.7 3 T 0.6 5 p . η 4 = 2.5 0.5 2 0.4 Total acceptance × reconstruction η =5 1.5 0.3 efficiency for antiprotons 1 0.2 0.5 0.1 Tracking efficiency estimated from LHCb Preliminary 0 0 simulation, validated on (pp) data 20 40 60 80 100 p [GeV/c] LHCb-CONF-2017-002 ICRC 2017 G. Graziani slide 5
The p -He run LHCb-CONF-2017-002 Data p 21.4 - 24.4 pt 1.2- 1.5 200 ) π DLL (p - Data collected in May 2016, with proton en- LHCb Preliminary 150 ergy 6.5 TeV, √ s NN = 110 GeV 100 Most data from a single LHC fill (5 hours) 50 Minimum bias trigger, fully efficient on can- 0 didate events -50 Exploit excellent particle identification (PID) -100 capabilities in LHCb to count antiprotons in -150 ( p , p T ) bins within the kinematic range -200 -200 -100 0 100 200 12 < p < 110 GeV /c, p T > 0 . 4 GeV /c DLL (p -K) 200 200 Exploit excellent vertexing capabilities to 900 π 140 Template for p Template for 150 150 800 120 100 100 700 separate prompt and detached 100 600 50 50 500 80 0 0 components . 400 60 -50 -50 300 40 -100 -100 Only the prompt component included in this 200 20 -150 -150 100 -200 0 -200 0 preliminary result (analysis of component -200 -100 0 100 200 -200 -100 0 100 200 from hyperon decays ongoing). 200 200 60 Template for ghost Template for K 250 150 150 50 Residual detached component estimated to be 100 100 200 40 50 50 150 (2 . 6 ± 0 . 6)% and subtracted 0 0 30 -50 -50 100 20 -100 -100 Background from gas contamination 50 10 -150 -150 -200 0 -200 0 measured to be 0 . 6 ± 0 . 2% -200 -100 0 100 200 -200 -100 0 100 200 ICRC 2017 G. Graziani slide 6
Normalization Gas target density not precisely known, using p-e − elastic scattering Pro : LHCb sees the purely elastic regime: θ > 10 mrad ➨ ϑ s < 29 mrad, Q 2 < 0 . 01 GeV 2 ➨ cross-section very well known distinct signature with single low-p and very low p T electron track, and nothing else scattered electron candidates 9000 LHCb Preliminary 8000 background events mostly expected from very 7000 soft collisions, where candidate comes from γ - Simulation of single e 6000 - 5000 e candidates conversion or pion from central exclusive pro- 4000 + e candidates duction event ➨ background expected to be 3000 2000 charge symmetric , can use “single positrons” 1000 to model it in data 5 10 15 20 SPD hits LHCb-CONF-2017-002 Cons: cross-section is small (order 100 µ b, 3 orders of magnitude below hadronic cross section) electron has very low momentum and showers through beam pipe/detectors ➨ low acceptance and reconstruction efficiency ICRC 2017 G. Graziani slide 7
Event display of a candidate scattered electron ICRC 2017 G. Graziani slide 8
Electron spectra LHCb-CONF-2017-002 Candidates per 260 MeV/c Candidates per 2.4 MeV/c 5000 LHCb Preliminary LHCb Preliminary 2500 4000 2000 - e candidates 3000 1500 + e candidates 2000 1000 1000 500 Very good agreement with 5000 10000 15000 0 50 100 p [MeV/c] p [MeV/c] simulation of single scat- T Candidates per 2.4 MeV/c 1800 Candidates per 260 MeV/c tered electrons LHCb Preliminary LHCb Preliminary 1600 3000 1400 Data confirm charge sym- 2500 - e candidates (Bkg Sub.) 1200 2000 metry of background 1000 800 1500 Simulation (normalized) 600 1000 400 500 200 0 50 100 5000 10000 15000 p [MeV/c] p [MeV/c] T L = 0 . 443 ± 0 . 011 ± 0 . 027 nb − 1 Systematic from variation of selection cuts, largest dependence is on azimuthal angle equivalent gas pressure is 2 . 4 × 10 − 7 mbar, in agreement with the expected level in SMOG ICRC 2017 G. Graziani slide 9
Total relative uncertainty per bin, in per cent LHCb-CONF-2017-002 [GeV/c] 25.8 24.9 24.4 20.9 20.6 20.1 19.6 20.4 22.2 28.6 25 20.6 17.0 16.9 14.5 13.0 12.0 15.8 11.1 10.8 10.8 10.8 11.3 11.2 10.5 12.2 12.3 12.5 25.1 20 T p 17.5 11.6 12.9 10.7 9.1 12.5 10.3 9.4 10.1 9.4 9.4 9.4 9.5 9.5 10.2 14.0 20.0 25.7 15 12.4 11.0 10.1 8.7 8.5 10.3 9.8 15.8 9.8 9.2 9.2 9.2 9.5 12.8 11.6 10.7 12.6 17.2 17.3 13.7 10.8 11.7 11.4 9.8 9.9 9.2 11.4 11.1 9.6 9.6 10.4 9.7 13.4 12.1 1 14.7 9.6 9.8 8.2 8.5 7.9 8.0 8.1 15.1 21.0 10.4 9.4 11.1 9.7 10.6 10 10.7 8.1 9.3 7.9 8.5 8.6 8.0 13.6 23.3 10.7 9.5 9.8 13.9 12.2 8.5 9.4 9.5 15.0 9.7 9.4 10.2 10.4 15.7 10.2 10.9 10.8 9.5 9.6 17.5 8.2 8.8 7.9 19.9 17.0 9.8 22.2 12.4 5 LHCb Preliminary 13.3 27.6 19.1 24.7 0 η 5 5 = . η 4 = 2 10 p [GeV/c] dominated by systematics largest correlated uncertainty is the 6% from normalization largest uncorrelated uncertainty from PID analysis ICRC 2017 G. Graziani slide 10
Result for cross section, compared with EPOS LHC LHCb-CONF-2017-002 ] 2 -0 10 x (12.0 < p < 14.0 GeV/c) 2 /GeV 10 LHCb Preliminary -1 10 x (14.0 < p < 16.2 GeV/c) 10 -2 10 x (16.2 < p < 18.7 GeV/c) 2 Result for prompt production − 1 b c 10 -3 10 x (18.7 < p < 21.4 GeV/c) (excluding weak decays of hy- µ -4 10 x (21.4 < p < 24.4 GeV/c) − 3 [ 10 perons) T -5 10 x (24.4 < p < 27.7 GeV/c) X)/dpdp − 5 -6 10 10 x (27.7 < p < 31.4 GeV/c) -7 10 x (31.4 < p < 35.5 GeV/c) − The total inelastic cross section 7 10 -8 10 x (35.5 < p < 40.0 GeV/c) is also measured to be p -9 ( 10 x (40.0 < p < 45.0 GeV/c) − 9 10 σ 2 -10 10 x (45.0 < p < 50.5 GeV/c) d σ LHCb − 11 -11 10 10 x (50.5 < p < 56.7 GeV/c) = (140 ± 10) mb inel -12 10 x (56.7 < p < 63.5 GeV/c) − 13 10 -13 10 x (63.5 < p < 71.0 GeV/c) The EPOS LHC prediction -14 − 10 x (71.0 < p < 79.3 GeV/c) 15 10 [T. Pierog at al, Phys. Rev. C92 (2015), 034906] -15 10 x (79.3 < p < 88.5 GeV/c) is 118 mb, ratio is 1 . 19 ± 0 . 08 . − 17 10 -16 10 x (88.5 < p < 98.7 GeV/c) -17 10 x (98.7 < p < 110.0 GeV/c) − 19 10 0 1 2 3 4 p [GeV/c] T ICRC 2017 G. Graziani slide 11
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