Antiproton production in p-he collisions, and more, at LHCb LHCb on a Space Mission 6.5 ev proton He at rest antiproton Giacomo Graziani (INFN Firenze) on behalf of the LHCb Collaboration ICRC 7, Busan, Korea July 5, 7
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 factory on earth he LHCb Experiment Detector requirements: Forward geometry optimize acceptance for bb pairs racking : best possible proper time and momentum resolution Particle ID : excellent capabilities to select exclusive decays rigger : high flexibility and bandwidth (up to 5 khz to disk) allowed to widen our physics program to include hadron spectroscopy, EW physics, kaon physics, heavy ion physics (ppb and PbPb collisions)... G. Graziani slide ICRC 7
SMOG: the LHCb internal gas target LHCb is the LHC experiment with fixed-target like geometry very well suited for... fixed target physics! JINS 3, (8) S85 Int.J.Mod.Phys.A3 (5) 53 he System for Measuring Overlap with Gas (SMOG) allows to inject small amount of noble gas (He, Ne, Ar,... ) inside the LHC beam around ( ± m) the LHCb collision region Expected pressure 7 mbar Originally conceived for the luminosity determination with beam gas imaging JINS 9, (4) P5 Became the LHCb internal gas target for a rich and varied fixed target physics program G. Graziani slide 3 ICRC 7
Soft QCD for Cosmic Rays Physics Fixed target collisions allow to study exclusive particle production at the energy scale of 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 AMS results provide unprecedented accuracy for measurement of p/p ratio in cosmic rays at high energies PRL 7, 93 (6) hint for a possible excess, and milder energy 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 crosssections, particularly for p-he no previous measurement of p production in p-he, current predictions vary within a factor the LHC energy scale and LHCb +SMOG are very well suited to perform this measurement Giesen et al., JCAP 59, 3 (5) the olderdata. he curve labelled fiducial assumes nties: best fit proton and helium alue G. Graziani for the Fisk potential. slide 4 ICRC 7
Detector and Acceptance JINS 3, (8) S85 Int.J.Mod.Phys.A3 (5) 53 [GeV/c] p 4 3.5 3.5.5.5 LHCb-CONF-7-4 6 8 η=4.5 η=5.8.7.6.5.4.3.. otal acceptance reconstruction efficiency for antiprotons racking efficiency estimated from simulation, validated on (pp) data G. Graziani slide 5 ICRC 7
he p-he run Data collected in May 6, with proton energy 6.5 ev, s NN = GeV Most data from a single LHC fill (5 hours) Minimum bias trigger, fully efficient on candidate events Exploit excellent particle identification (PID) capabilities in LHCb to count antiprotons in (p, p ) bins within the kinematic range < p < GeV/c, p >.4 GeV/c Exploit excellent vertexing capabilities to separate prompt 5 and LHCb detached Preliminary components. Only the prompt 5component included in this preliminary result (analysis of component from hyperon decays -5 ongoing). Residual detached - component estimated to be (.6 ±.6)% and -5 subtracted Background from - gas contamination measured to be.6 ±.% DLL (p - π) Data p.4-4.4 pt.-.5 DLL (p - π) - - DLL (p -K) 5 5-5 - -5 LHCb-CONF-7- Data p.4-4.4 pt.-.5 - - - DLL (p -K) 5 5-5 - -5 - - - 5 5-5 - -5 emplate for p emplate for K - - - 4 5 5 8 6-5 4 - -5 - - - 5 5 5 5 5-5 - -5 emplate for π emplate for ghost - - - 9 8 7 6 5 4 3 6 5 4 3 5 5-5 - -5 empla - - - 5 5-5 - -5 emplat - - - G. Graziani slide 6 ICRC 7
Normalization Gas target density not precisely known, using p-e elastic scattering Pro: LHCb sees the purely elastic regime: θ > mrad ϑ s < 9 mrad, Q <. GeV cross-section very well known distinct signature with single low-p and very low p electron track, and nothing else background events mostly expected from very soft collisions, where candidate comes from γ conversion or pion from central exclusive production event background expected to be charge symmetric, can use single positrons to model it in data scattered electron candidates 9 8 7 6 5 4 3 LHCb-CONF-7- - Simulation of single e - e e + candidates candidates 5 5 Cons: cross-section is small (order µb, 3 orders of magnitude below hadronic cross section) electron has very low momentum and showers through beam pipe/detectors low acceptance and reconstruction efficiency SPD hits G. Graziani slide 7 ICRC 7
Event display of a candidate scattered electron G. Graziani slide 8 ICRC 7
LHCb-CONF-7- Candidates per 6 MeV/c Candidates per 6 MeV/c 5 4 3 3 5 5 5 - e e + candidates candidates 5 5 p [MeV/c] - e candidates (Bkg Sub.) Simulation (normalized) Candidates per.4 MeV/c Candidates per.4 MeV/c 5 5 5 8 6 4 8 6 4 5 [MeV/c] p Electron spectra Very good agreement with simulation of single scattered electrons Data confirm charge symmetry of background 5 5 p [MeV/c] 5 [MeV/c] p L =.443 ±. ±.7 nb Systematic from variation of selection cuts, largest dependence is on azimuthal angle equivalent gas pressure is.4 7 mbar, in agreement with the expected level in SMOG G. Graziani slide 9 ICRC 7
otal relative uncertainty per bin, in per cent LHCb-CONF-7- [GeV/c] p 5.8 4.9 4.4.9.6. 9.6.4. 8.6.6 7. 6.9 4.5 3.. 5.8..8.8.8.3..5..3.5 5. 7.5.6.9.7 9..5.3 9.4. 9.4 9.4 9.4 9.5 9.5. 4.. 5.7 5.4.. 8.7 8.5.3 9.8 5.8 9.8 9. 9. 9. 9.5.8.6.7.6 7. 7.3 3.7.8.7.4 9.8 9.9 9..4.. 9.6 9.6.4 9.7 3.4 4.7 9.6 9.8 8. 8.5 7.9 8. 8. 5...4 9.4. 9.7.6.7 8. 9.3 7.9 8.5 8.6 8. 3.6 3.3.7. 9.5 9.8 3.9 8.5 9.4 9.5 5. 9.7 9.4..4 5.7..9.8 5 9.5 9.6 7.5 8. 8.8 7.9 9.9. 7..4 9.8 4.7 3.3 7.6 9. η=4.5 η=5 5 dominated by systematics largest correlated uncertainty is the 6% from normalization largest uncorrelated uncertainty from PID analysis G. Graziani slide ICRC 7
Result for cross section, compared with EPOS LHC LHCb-CONF-7- [µb c /GeV ] 3 - x (. < p < 4. GeV/c) - x (4. < p < 6. GeV/c) - x (6. < p < 8.7 GeV/c) -3 x (8.7 < p <.4 GeV/c) -4 x (.4 < p < 4.4 GeV/c) -5 x (4.4 < p < 7.7 GeV/c) Result for prompt production (excluding weak decays of hyperons) d σ(px)/dpdp 5 7 9 3 5 7-6 x (7.7 < p < 3.4 GeV/c) -7 x (3.4 < p < 35.5 GeV/c) -8 x (35.5 < p < 4. GeV/c) -9 x (4. < p < 45. GeV/c) - x (45. < p < 5.5 GeV/c) - x (5.5 < p < 56.7 GeV/c) - x (56.7 < p < 63.5 GeV/c) -3 x (63.5 < p < 7. GeV/c) -4 x (7. < p < 79.3 GeV/c) -5 x (79.3 < p < 88.5 GeV/c) -6 x (88.5 < p < 98.7 GeV/c) he total inelastic cross section is also measured to be σ LHCb inel = (4 ± ) mb he EPOS LHC prediction [. Pierog at al, Phys. Rev. C9 (5), 3496] is 8 mb, ratio is.9 ±.8. 9 3 4-7 x (98.7 < p <. GeV/c) G. Graziani slide ICRC 7
DAA / PREDICION.5.5.5.5.5.5 Result for cross section, ratio with models LHCb-CONF-7-3. < p < 4. GeV/c.5.5.5 3 8.7 < p <.4 GeV/c.5.5.5 4. < p < 6. GeV/c 3.4 < p < 4.4 GeV/c.5 6. < p < 8.7 GeV/c 3 4 3 4.5.5 3 7.7 < p < 3.4 GeV/c.5.5 3 3.4 < p < 35.5 GeV/c.5.5 3 4.4 < p < 7.7 GeV/c 3 4 3 4 3 4.5.5.5.5.5 3 4. < p < 45. GeV/c.5.5 3 45. < p < 5.5 GeV/c.5.5 3 35.5 < p < 4. GeV/c 3 4 3 4 3 4.5.5.5.5.5 3 56.7 < p < 63.5 GeV/c 3 79.3 < p < 88.5 GeV/c.5.5 3 63.5 < p < 7. GeV/c.5.5.5.5 3 5.5 < p < 56.7 GeV/c 3 7. < p < 79.3 GeV/c 3 4 3 4 3 4.5.5.5.5.5.5.5.5.5 3 88.5 < p < 98.7 GeV/c p 3 4 3 [GeV/c] p 4 3 4 [GeV/c] rasverse Momentum (GeV/c) 3 98.7 < p <. GeV/c EPOS LHC EPOS.99 QGSJEII-4 HIJING.38 Cross section is larger by factor.5 wrt EPOS LHC (mostly from larger p rate per collision). Better agreement with EPOS.99, HIJING.38 and QGSJE-IIm (low energy extension of QGSJE-II-4, not shown) Many thanks to. Pierog for his advice with EPOS/CRMC! G. Graziani slide ICRC 7
Prospects for antimatter production We plan to extend the study to p produced by hyperon decays (accounting for -3% of the production). LHCb can cleanly select decays of Λ Candidates /.6 MeV/c 3 µ = 5.75 ±.3 MeV/c σ =.3 ±.33 MeV/c N = 77 ± 36 LHCb s =.9 ev Λ pπ +.5 < p <.5 GeV/c.5 < y < 3. 3 pπ + Invariant Mass [MeV/c ] JHEP 8 () 34 Another p-he run was performed in november 6 with a 4 ev beam ( s NN =87 GeV) scaling violation can be constrained production of pions and kaons is also being measured positron production. Ratios of particle species, not affected by uncertainty on luminosity, can provide precise constraints to soft QCD models investigating our potential for antinuclei d, t and 3 He RICH can actively identify d from p 36 GeV/c and t, 3 He from 54 GeV/c. de/dx and time-of-flight information from tracking detectors at low momentum G. Graziani slide 3 ICRC 7
And charm, of course Exclusive production of charm states is a specialty of LHCb Candidates / (5 MeV/ c ) 7 6 5 4 3 D K π + LHCb preliminary s NN = 87 GeV phe Candidates / ( MeV/ c ) 8 6 4 J/ψ µ + µ LHCb preliminary s NN = 87 GeV phe 8 8 84 86 88 9 9 94 - m(k π + ) [MeV/c ] 95 3 35 3 35-3 m(µ + µ ) [MeV/c ] 4 In fixed target mode, access the large-x (target fragmentation) region, where charm PDF is affected -7 by antishadow- ing and possibly intrinsic charm (IC) effects. -8 Important for high-energy neutrino astrophysics: background for the ICECUBE experiment -9 is dominated dotted grey: Conv. Atm. e by solid grey: Conv. Atm. e + BERSS charm production in atmospheric showers E [GeV cm - s - sr - ] -6 - Intrinsic Charm IceCube atmospheric e solid black: Conv. Atm. e + Intrinsic Charm (H3A) + BERSS IceCube astrophysical flux 3 4 5 6 E e [GeV] E [GeV cm - s - sr - ] -6-7 -8-9 - solid black: Conv. Atm. µ + Intrinsic Charm (H3A) + BERSS Intrinsic Charm IceCube µ IceCube astrophysical flux dotted grey: Conv. Atm. µ solid grey: Conv. Atm. µ + BERSS 3 4 5 6 E µ [GeV] Laha and Brodsky, arxiv:67.84 G. Graziani slide 4 ICRC 7 FIG.. Left: Comparison of the total atmospheric ν e + ν e data (IceCube-86 for 33 days) with calculations. he contribution to the ν e + ν e flux from intrinsic charm for Case (A) for various cosmic ray spectra is shown by the dashed lines (H3A =
Charm in p-ar collisions @ GeV LHCb-CONF-7- x-feynman distribution for D and J/ψ, compared to Pythia8 prediction /dx F D dn.5..5..5 6 LHCb preliminary = GeV par s NN x F = M D s NN sinh(y*).5..5..5 Feynman-x x F /dx F J/ψ dn.8.6.4..8.6.4. 3 LHCb preliminary = GeV par s NN sinh(y*).45.4.35.3.5..5..5 Obtained from the first small (few nb ) p-ar data sample acquired in 5 65 D and 5 J/ψ Result limited by statistics, but demonstrates the potential for unique measurements Differential shapes can already constrain models with IC x F = M J/ψ s NN Feynman-x x F G. Graziani slide 5 ICRC 7
Conclusions LHCb started its fixed target program becoming an unexpected contributor to cosmic ray physics! he p production measurement in p-he collisions is expected to narrow down significantly the uncertainty on the p/p prediction for cosmic rays Nice interplay with the cosmic rays community thanks to O. Adriani, L. Bonechi, F. Donato and A. ricomi for proposing this measurement the LHCb space mission just started! G. Graziani slide 6 ICRC 7
Additional Material G. Graziani slide 7 ICRC 7
RICH Performance Eur. Phys. J. C 73 (3) 43 Particle separation in RICH K/p separation vs momentum G. Graziani slide 8 ICRC 7
Selection of prompt component: the Vertex Detector Current analysis limited to prompt component (direct production and p from strong resonance decays) Can be distinguished from p produced by weak decays of hyperons and secondary interactions using the excellent LHCb vertexing capabilities JINS 9 (4) P97 G. Graziani slide 9 ICRC 7
Background from weak hyperon decays detached component from weak decays of hyperons is treated as a background suppressed by requiring small impact parameter (IP) resolution [µm] IP x 9 8 7 6 5 4 3 LHCb VELO data, σ =.6 + 3.4/p Simulation, σ =.6 +.6/p.5.5 /p.5 [GeV c - ] 3 JINS 9 (4) P97 Residual detached component estimated to be (.6 ±.6)% and subtracted Systematic uncertainty estimated from data/mc comparison of IP tails G. Graziani slide ICRC 7
Background from Residual Vacuum Residual vacuum in LHC is not so small ( 9 mbar ) compared to SMOG pressure Can be a concern, especially for heavy contaminants (larger cross section than He), and beam-induced local outgassing Direct measurement in data: about 5% of delivered protons on target acquired before He injection (but with identical vacuum pumping configuraton) fraction of candidates.8.7.6.5.4.3.. p on He gas p on Residual Vacuum 5 5 5 3 35 4 PV rack Multiplicity Gas impurity found to be small:.6 ±.% PV multiplicity in residual vacuum events is lower than in He events, but has longer tails confirm findings from Rest Gas Analysis that residual vacuum is mostly H, with small heavy contaminants LHCb-CONF-7- G. Graziani slide ICRC 7
Result for cross section: final uncertainties (relative) LHCb-CONF-7- Statistical: Yields in data/pid calibration.7.8% (< 3% for most bins) Normalization.5% Correlated Systematic: Normalization 6.% GEC and PV cut.3% PV reco.8% racking.% Residual Vacuum Background.% Non-prompt background.3.7% PID. 5.% Uncorrelated Systematic: racking 3.% IP cut efficiency.% PID 6% (< % for most bins) MC statistics.8 5% (< 4% for p < GeV/c) G. Graziani slide ICRC 7
Comparison with EPOS LHC, vs x-feynman ] /GeV [µb c σ/dpdp d <p<4 GeV/c 4<p<6. GeV/c 6.<p<8.7 GeV/c 8.7<p<.4 GeV/c.4<p<4.4 GeV/c 4.4<p<7.7 GeV/c 7.7<p<3.4 GeV/c 3.4<p<35.5 GeV/c 35.5<p<4 GeV/c 4<p<45 GeV/c 45<p<5.5 GeV/c 5.5<p<56.7 GeV/c 56.7<p<63.5 GeV/c 63.5<p<7 GeV/c 7<p<79.3 GeV/c 79.3<p<88.5 GeV/c 88.5<p<98.7 GeV/c 98.7<p< GeV/c EPOSLHC.. x F G. Graziani slide 3 ICRC 7
Comparison with models [GeV/c] 4 3.5 EPOS LHC PRC9, 3496 (5) σ LHCb / σ EPOS.99.8.6 [GeV/c] HIJING.38 Comp. Phys. Comm. 83, 37 (994) 4 3.5 σ LHCb / σ HIJING.8.6 p 3.4 p 3.4.5..5..5.8.5.8.6.6.5.4.5.4 4 6 8. 4 6 8. [GeV/c] 4 3.5 QGSJE-II-4 PRD83, 48 () σ LHCb / σ QGSJEII.8.6 [GeV/c] 4 3.5 QGSJE-IIm Astr. J. 83:54 (5) σ LHCb / σ QGSJEIIm.8.6 p 3.4 p 3.4.5..5..5.8.5.8.6.6.5.4.5.4. 4 6 8 4 6 8 G. Graziani slide 4 ICRC 7.