Fixed Target Physics at LHCb

Transcription

1 Fixed arget Physics at LHCb LHCb on a Space Mission Giacomo Graziani (INFN Firenze) on behalf of the LHCb Collaboration 5nd Rencontres de Moriond on Electroweak Interactions and Unified heories La huile, Italy Mar, 7

2 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 Moriond EW 7

3 Fixed target LHCb Many things to learn from studying hadronic collisions in fixed target mode at the relatively unexplored scale of s NN GeV: Nuclear effects, by changing the target atoms: study Cold Nuclear Matter effects in Heavy Flavour production, to distinguish from QGP effects occurring at higher scales Access the large-x (target -6 IceCube fragmentation) atmospheric e region, to better constrain (n)pdfs -7 solid black: Conv. Atm. e + Intrinsic Charm (H3A) + BERSS possible contributions of intrinsic charm important for LHC: can -8 affect high-q processes, e.g. Higgs production very important for high-energy -9 dotted grey: Conv. Atm. neutrino e astrophysics: background for the ICECUBE exper- - solid grey: Conv. Atm. e + BERSS iment is dominated by charm 3 production 4 5 E e [GeV] in atmospheric 6 showers E [GeV cm - s - sr - ] Intrinsic Charm IceCube astrophysical flux E [GeV cm - s - sr - ] 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 E µ [GeV] 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 Laha ray and spectra Brodsky, is shown arxiv:67.84 by the dashed lines (H3A = magenta, H3P = green, H4A = brown, and H4B = magenta. H4A and H4B are on top of each other). he conventional ν e + ν e flux [3], conventional ν e + ν e + BERSS (H3A), and conventional ν e + ν e + BERSS + intrinsic charm contribution for H3A are shown. Right: Same as the left panel, but for ν µ + ν µ [6] (IceCube-79/ 86 for years). his measurement also G. Graziani slide 3 includes the astrophysical neutrino flux. he astrophysical flux shown in these panels is from Refs. [4]. Moriond EW 7 4

4 Charm in p-ar GeV LHCb-CONF-7- J/ψ/ D ratio vs transverse momentum and pseudorapidity ) σ(j/ψ) / σ(d LHCb preliminary s NN = GeV par ) σ(j/ψ) / σ(d LHCb preliminary s NN = GeV par ransverse momentum p [MeV/c] Rapidity y Figure First 8: result J/ψ from µ µ + thetolhcb D fixed K π + target cross-section program, ratios as a function of left: p and r y. See presented Fig 5 forat uncertainty the Quarkgraphical Matter conference conventions. last month Obtained from the first small (few nb ) p-ar data sample Result limited by statistics, but demonstrates the physics potential Differential shapes can already test differences among models G. Graziani slide 4 Moriond EW 7

5 Soft QCD for Cosmic Rays Physics Fixed target data at the GeV scale can also provide valuable inputs to MC models describing underlying event Very important 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 5 Moriond EW 7

6 he p-he run Data collected in May 6, with proton energy 6.5 ev, s NN = GeV Using fill for Van der Meer scan (parasitic data taking) Most data from a single fill (5 hours) Minimum bias trigger, fully efficient on candidate events Exploit excellent particle Data p identification (PID) capabilities 5 pt.-.5 in LHCb to count antiprotons in (p, p ) bins 5 within the kinematic range DLL (p - π) -5 < - p < GeV/c -5 p - >.4 GeV/c DLL (p - π) - - DLL (p -K) LHCb-CONF-7- Data p pt DLL (p -K) emplate for p emplate for K emplate for π emplate for ghost empla emplat G. Graziani slide 6 Moriond EW 7

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 p on He gas p on Residual Vacuum 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 7 Moriond EW 7

8 Normalization 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 form very soft collisions, where candidate comes from γ conversion or pion from CEP event background expected to be charge symmetric, can use single positrons to model it in data scattered electron candidates 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 8 Moriond EW 7

9 Event display of a candidate scattered electron G. Graziani slide 9 Moriond EW 7

10 LHCb-CONF-7- Candidates per 6 MeV/c Candidates per 6 MeV/c 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 [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 Moriond EW 7

11 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 Moriond EW 7

12 otal relative uncertainty per bin, in per cent LHCb-CONF-7- [GeV/c] p η=4.5 η=5 G. Graziani slide Moriond EW 7

13 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 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 ± x (98.7 < p <. GeV/c) G. Graziani slide 3 Moriond EW 7

14 Result for cross section, ratio with models LHCb-CONF-7- DAA / PREDICION < p < 4. GeV/c < p <.4 GeV/c < p < 6. GeV/c 3.4 < p < 4.4 GeV/c.5 6. < p < 8.7 GeV/c < p < 3.4 GeV/c < p < 35.5 GeV/c < p < 7.7 GeV/c < p < 45. GeV/c < p < 5.5 GeV/c < p < 4. GeV/c < p < 63.5 GeV/c < p < 88.5 GeV/c < p < 7. GeV/c < p < 56.7 GeV/c 3 7. < p < 79.3 GeV/c < p < 98.7 GeV/c p [GeV/c] p [GeV/c] rasverse Momentum (GeV/c) < 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 and HIJING.38 Many thanks to. Pierog for his advice with EPOS/CRMC! G. Graziani slide 4 Moriond EW 7

15 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 Many thanks to our colleaugues in cosmic rays community, O. Adriani, L. Bonechi, F. Donato and A. ricomi for proposing this measurement More to come on p production: dataset with beam energy of 4 ev also collected will also measure the detached (Λ decays) component and much more to harvest from the SMOG samples: charged particle yields, particle/antiparticle ratios, positrons, gamma, charm... the LHCb space mission just started! G. Graziani slide 5 Moriond EW 7

16 Additional Material G. Graziani slide 6 Moriond EW 7

17 Detector and Acceptance [GeV/c] p η=4.5 η= LHCb-CONF otal acceptance reconstruction efficiency for antiprotons G. Graziani slide 7 Moriond EW 7