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Multiplicity-dependent enhancement of strange and multi-strange hadron production in proton-proton collisions at $\sqrt{s} = 7$ TeV

The ALICE collaboration
No Journal Information, 2016

Abstract (data abstract)
CERN-LHC. The yields of strange (${\rm K}^{0}_{S}$, $\Lambda$, $\bar{\Lambda}$) and multi-strange ($\Xi^{-}$, $\bar{\Xi}^{+}$, $\Omega^{-}$, $\bar{\Omega}^{+}$) hadrons are measured at midrapidity in proton-proton (pp) collisions at $\sqrt{s}$ = 7 TeV as a function of the charged-particle multiplicity density (${\rm d}N_{\rm ch}/{\rm d}\eta$).The production rate of strange particles increases faster than that of non-strange hadrons, leading to an enhancement of strange particles relative to pions, similar to that found in nucleus-nucleus collisions as well as in proton-nucleus collisions at the LHC. This is the first observation of an enhanced production of strange particles in high-multiplicity pp collisions. The magnitude of this strangeness enhancement increases with the event activity, quantified by ${\rm d}N_{\rm ch}/{\rm d}\eta$, and with hadron strangeness. It reaches almost a factor of two for the $\Omega$ at the highest multiplicity presented. No enhancement is observed for particles with no strange quark content, demonstrating that the observed effect is strangeness rather than mass related. The results are not reproduced by any of the Monte Carlo models commonly used at the LHC, suggesting that further developments are needed for a complete microscopic understanding of strangeness production and indicating the presence of a phenomenon novel in high-multiplicity pp collisions.

  • Table 1

    Data from Figure 1

    10.17182/hepdata.77284.v1/t1

    $K^{0}_{S}$ transverse momentum spectrum: V0M Class I (pp at $\sqrt{s}=7$ TeV).

  • Table 2

    Data from Figure 1

    10.17182/hepdata.77284.v1/t2

    $K^{0}_{S}$ transverse momentum spectrum: V0M Class II (pp at $\sqrt{s}=7$ TeV).

  • Table 3

    Data from Figure 1

    10.17182/hepdata.77284.v1/t3

    $K^{0}_{S}$ transverse momentum spectrum: V0M Class III (pp at $\sqrt{s}=7$ TeV).

  • Table 4

    Data from Figure 1

    10.17182/hepdata.77284.v1/t4

    $K^{0}_{S}$ transverse momentum spectrum: V0M Class IV (pp at $\sqrt{s}=7$ TeV).

  • Table 5

    Data from Figure 1

    10.17182/hepdata.77284.v1/t5

    $K^{0}_{S}$ transverse momentum spectrum: V0M Class V (pp at $\sqrt{s}=7$ TeV).

  • Table 6

    Data from Figure 1

    10.17182/hepdata.77284.v1/t6

    $K^{0}_{S}$ transverse momentum spectrum: V0M Class VI (pp at $\sqrt{s}=7$ TeV).

  • Table 7

    Data from Figure 1

    10.17182/hepdata.77284.v1/t7

    $K^{0}_{S}$ transverse momentum spectrum: V0M Class VII (pp at $\sqrt{s}=7$ TeV).

  • Table 8

    Data from Figure 1

    10.17182/hepdata.77284.v1/t8

    $K^{0}_{S}$ transverse momentum spectrum: V0M Class VIII (pp at $\sqrt{s}=7$ TeV).

  • Table 9

    Data from Figure 1

    10.17182/hepdata.77284.v1/t9

    $K^{0}_{S}$ transverse momentum spectrum: V0M Class IX (pp at $\sqrt{s}=7$ TeV).

  • Table 10

    Data from Figure 1

    10.17182/hepdata.77284.v1/t10

    $K^{0}_{S}$ transverse momentum spectrum: V0M Class X (pp at $\sqrt{s}=7$ TeV).

  • Table 11

    Data from Figure 1

    10.17182/hepdata.77284.v1/t11

    $\Lambda+\bar{\Lambda}$ transverse momentum spectrum: V0M Class I (pp at $\sqrt{s}=7$ TeV).

  • Table 12

    Data from Figure 1

    10.17182/hepdata.77284.v1/t12

    $\Lambda+\bar{\Lambda}$ transverse momentum spectrum: V0M Class II (pp at $\sqrt{s}=7$ TeV).

  • Table 13

    Data from Figure 1

    10.17182/hepdata.77284.v1/t13

    $\Lambda+\bar{\Lambda}$ transverse momentum spectrum: V0M Class III (pp at $\sqrt{s}=7$ TeV).

  • Table 14

    Data from Figure 1

    10.17182/hepdata.77284.v1/t14

    $\Lambda+\bar{\Lambda}$ transverse momentum spectrum: V0M Class IV (pp at $\sqrt{s}=7$ TeV).

  • Table 15

    Data from Figure 1

    10.17182/hepdata.77284.v1/t15

    $\Lambda+\bar{\Lambda}$ transverse momentum spectrum: V0M Class V (pp at $\sqrt{s}=7$ TeV).

  • Table 16

    Data from Figure 1

    10.17182/hepdata.77284.v1/t16

    $\Lambda+\bar{\Lambda}$ transverse momentum spectrum: V0M Class VI (pp at $\sqrt{s}=7$ TeV).

  • Table 17

    Data from Figure 1

    10.17182/hepdata.77284.v1/t17

    $\Lambda+\bar{\Lambda}$ transverse momentum spectrum: V0M Class VII (pp at $\sqrt{s}=7$ TeV).

  • Table 18

    Data from Figure 1

    10.17182/hepdata.77284.v1/t18

    $\Lambda+\bar{\Lambda}$ transverse momentum spectrum: V0M Class VIII (pp at $\sqrt{s}=7$ TeV).

  • Table 19

    Data from Figure 1

    10.17182/hepdata.77284.v1/t19

    $\Lambda+\bar{\Lambda}$ transverse momentum spectrum: V0M Class IX (pp at $\sqrt{s}=7$ TeV).

  • Table 20

    Data from Figure 1

    10.17182/hepdata.77284.v1/t20

    $\Lambda+\bar{\Lambda}$ transverse momentum spectrum: V0M Class X (pp at $\sqrt{s}=7$ TeV).

  • Table 21

    Data from Figure 1

    10.17182/hepdata.77284.v1/t21

    $\Xi^{-}+\bar{\Xi}^{+}$ transverse momentum spectrum: V0M Class I (pp at $\sqrt{s}=7$ TeV).

  • Table 22

    Data from Figure 1

    10.17182/hepdata.77284.v1/t22

    $\Xi^{-}+\bar{\Xi}^{+}$ transverse momentum spectrum: V0M Class II (pp at $\sqrt{s}=7$ TeV).

  • Table 23

    Data from Figure 1

    10.17182/hepdata.77284.v1/t23

    $\Xi^{-}+\bar{\Xi}^{+}$ transverse momentum spectrum: V0M Class III (pp at $\sqrt{s}=7$ TeV).

  • Table 24

    Data from Figure 1

    10.17182/hepdata.77284.v1/t24

    $\Xi^{-}+\bar{\Xi}^{+}$ transverse momentum spectrum: V0M Class IV (pp at $\sqrt{s}=7$ TeV).

  • Table 25

    Data from Figure 1

    10.17182/hepdata.77284.v1/t25

    $\Xi^{-}+\bar{\Xi}^{+}$ transverse momentum spectrum: V0M Class V (pp at $\sqrt{s}=7$ TeV).

  • Table 26

    Data from Figure 1

    10.17182/hepdata.77284.v1/t26

    $\Xi^{-}+\bar{\Xi}^{+}$ transverse momentum spectrum: V0M Class VI (pp at $\sqrt{s}=7$ TeV).

  • Table 27

    Data from Figure 1

    10.17182/hepdata.77284.v1/t27

    $\Xi^{-}+\bar{\Xi}^{+}$ transverse momentum spectrum: V0M Class VII (pp at $\sqrt{s}=7$ TeV).

  • Table 28

    Data from Figure 1

    10.17182/hepdata.77284.v1/t28

    $\Xi^{-}+\bar{\Xi}^{+}$ transverse momentum spectrum: V0M Class VIII (pp at $\sqrt{s}=7$ TeV).

  • Table 29

    Data from Figure 1

    10.17182/hepdata.77284.v1/t29

    $\Xi^{-}+\bar{\Xi}^{+}$ transverse momentum spectrum: V0M Class IX (pp at $\sqrt{s}=7$ TeV).

  • Table 30

    Data from Figure 1

    10.17182/hepdata.77284.v1/t30

    $\Xi^{-}+\bar{\Xi}^{+}$ transverse momentum spectrum: V0M Class X (pp at $\sqrt{s}=7$ TeV).

  • Table 31

    Data from Figure 1

    10.17182/hepdata.77284.v1/t31

    $\Omega^{-}+\bar{\Omega}^{+}$ transverse momentum spectrum: V0M Class I+II (pp at $\sqrt{s}=7$ TeV).

  • Table 32

    Data from Figure 1

    10.17182/hepdata.77284.v1/t32

    $\Omega^{-}+\bar{\Omega}^{+}$ transverse momentum spectrum: V0M Class III+IV (pp at $\sqrt{s}=7$ TeV).

  • Table 33

    Data from Figure 1

    10.17182/hepdata.77284.v1/t33

    $\Omega^{-}+\bar{\Omega}^{+}$ transverse momentum spectrum: V0M Class V+VI (pp at $\sqrt{s}=7$ TeV).

  • Table 34

    Data from Figure 1

    10.17182/hepdata.77284.v1/t34

    $\Omega^{-}+\bar{\Omega}^{+}$ transverse momentum spectrum: V0M Class VII+VIII (pp at $\sqrt{s}=7$ TeV).

  • Table 35

    Data from Figure 1

    10.17182/hepdata.77284.v1/t35

    $\Omega^{-}+\bar{\Omega}^{+}$ transverse momentum spectrum: V0M Class IX+X (pp at $\sqrt{s}=7$ TeV).

  • Table 36

    Data from Figure 2

    10.17182/hepdata.77284.v1/t36

    $2K^{0}_{S}/(\pi^{+}+\pi^{-})$ ratio for pp collisions at $\sqrt{s}=7$ TeV as a function of the average charged particle multiplicity density at midrapidity.

  • Table 37

    Data from Figure 2

    10.17182/hepdata.77284.v1/t37

    $(\Lambda+\bar{\Lambda})/(\pi^{+}+\pi^{-})$ ratio for pp collisions at $\sqrt{s}=7$ TeV as a function of the average charged particle multiplicity density at midrapidity.

  • Table 38

    Data from Figure 2

    10.17182/hepdata.77284.v1/t38

    $(\Xi^{-}+\bar{\Xi}^{+})/(\pi^{+}+\pi^{-})$ ratio for pp collisions at $\sqrt{s}=7$ TeV as a function of the average charged particle multiplicity density at midrapidity.

  • Table 39

    Data from Figure 2

    10.17182/hepdata.77284.v1/t39

    $(\Omega^{-}+\bar{\Omega}^{+})/(\pi^{+}+\pi^{-})$ ratio for pp collisions at $\sqrt{s}=7$ TeV as a function of the average charged particle multiplicity density at midrapidity.

  • Table 40

    Data from Figure 2

    10.17182/hepdata.77284.v1/t40

    $\pi^{+}+\pi^{-}$ integrated yields, pp at $\sqrt{s}=7$ TeV (V0M Multiplicity Classes).

  • Table 41

    Data from Figure 2

    10.17182/hepdata.77284.v1/t41

    $p+\bar{p}$ integrated yields, pp at $\sqrt{s}=7$ TeV (V0M Multiplicity Classes).

  • Table 42

    Data from Figure 2

    10.17182/hepdata.77284.v1/t42

    $K^{0}_{S}$ integrated yields, pp at $\sqrt{s}=7$ TeV (V0M Multiplicity Classes).

  • Table 43

    Data from Figure 2

    10.17182/hepdata.77284.v1/t43

    $\Lambda+\bar{\Lambda}$ integrated yields, pp at $\sqrt{s}=7$ TeV (V0M Multiplicity Classes).

  • Table 44

    Data from Figure 2

    10.17182/hepdata.77284.v1/t44

    $\Xi^{-}+\bar{\Xi}^{+}$ integrated yields, pp at $\sqrt{s}=7$ TeV (V0M Multiplicity Classes).

  • Table 45

    Data from Figure 2

    10.17182/hepdata.77284.v1/t45

    $\Omega^{-}+\bar{\Omega}^{+}$ integrated yields, pp at $\sqrt{s}=7$ TeV (V0M Multiplicity Classes).

  • Table 46

    Data from Figure 3

    10.17182/hepdata.77284.v1/t46

    $(\Lambda+\bar{\Lambda})/2K^{0}_{S}$ ratio for pp collisions at $\sqrt{s}=7$ TeV as a function of charged particle multiplicity density at midrapidity.

  • Table 47

    Data from Figure 3

    10.17182/hepdata.77284.v1/t47

    $(p+\bar{p})/(\pi^{+}+\pi^{-})$ ratio for pp collisions at $\sqrt{s}=7$ TeV as a function of charged particle multiplicity density at midrapidity.

  • Table 48

    Data from Figure 4

    10.17182/hepdata.77284.v1/t48

    $(2K^{0}_{S})/(\pi^{+}+\pi^{-})$ double-ratio vs multiplicity for pp collisions at $\sqrt{s}=7$ TeV.

  • Table 49

    Data from Figure 4

    10.17182/hepdata.77284.v1/t49

    $(\Lambda+\bar{\Lambda})/(\pi^{+}+\pi^{-})$ double-ratio vs multiplicity for pp collisions at $\sqrt{s}=7$ TeV.

  • Table 50

    Data from Figure 4

    10.17182/hepdata.77284.v1/t50

    $(\Xi^{-}+\bar{\Xi}^{+})/(\pi^{+}+\pi^{-})$ double-ratio vs multiplicity for pp collisions at $\sqrt{s}=7$ TeV.

  • Table 51

    Data from Figure 4

    10.17182/hepdata.77284.v1/t51

    $(\Omega^{-}+\bar{\Omega}^{+})/(\pi^{+}+\pi^{-})$ double-ratio vs multiplicity for pp collisions at $\sqrt{s}=7$ TeV.

  • Table 52

    Data from Table 1

    10.17182/hepdata.77284.v1/t52

    Event multiplicity classes, their corresponding fraction of the INEL>0 cross-section and their corresponding average charged particle density at midrapidity ($|\eta|<0.5$)....

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