A bstract The first measurement of the Z boson production cross-section at centre-of-mass energy $$ \sqrt{s} $$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:msqrt> <mml:mi>s</mml:mi> </mml:msqrt> </mml:math> = 5 . 02 TeV in the forward region is reported, using pp collision data collected by the LHCb experiment in year 2017, corresponding to an integrated luminosity of 100 ± 2 pb − 1 . The production cross-section is measured for final-state muons in the pseudorapidity range 2 . 0 < η < 4 . 5 with transverse momentum p T > 20 GeV/ c . The integrated cross-section is determined to be $$ {\sigma}_{Z\to \mu +\mu -}=39.6\pm 0.7\left(\textrm{stat}\right)\pm 0.6\left(\textrm{syst}\right)\pm 0.8\left(\textrm{lumi}\right)\textrm{pb} $$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:msub> <mml:mi>σ</mml:mi> <mml:mrow> <mml:mi>Z</mml:mi> <mml:mo>→</mml:mo> <mml:mi>μ</mml:mi> <mml:mo>+</mml:mo> <mml:mi>μ</mml:mi> <mml:mo>−</mml:mo> </mml:mrow> </mml:msub> <mml:mo>=</mml:mo> <mml:mn>39.6</mml:mn> <mml:mo>±</mml:mo> <mml:mn>0.7</mml:mn> <mml:mfenced> <mml:mtext>stat</mml:mtext> </mml:mfenced> <mml:mo>±</mml:mo> <mml:mn>0.6</mml:mn> <mml:mfenced> <mml:mtext>syst</mml:mtext> </mml:mfenced> <mml:mo>±</mml:mo> <mml:mn>0.8</mml:mn> <mml:mfenced> <mml:mtext>lumi</mml:mtext> </mml:mfenced> <mml:mi>pb</mml:mi> </mml:math> for the di-muon invariant mass in the range 60 < M μμ < 120 GeV/ c 2 . This result and the differential cross-section results are in good agreement with theoretical predictions at next-to-next-to-leading order in the strong coupling constant. Based on a previous LHCb measurement of the Z boson production cross-section in p Pb collisions at $$ \sqrt{s_{NN}} $$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:msqrt> <mml:msub> <mml:mi>s</mml:mi> <mml:mi>NN</mml:mi> </mml:msub> </mml:msqrt> </mml:math> = 5 . 02 TeV, the nuclear modification factor R p Pb is measured for the first time at this energy. The measured values are $$ {1.2}_{-0.3}^{+0.5} $$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:msubsup> <mml:mn>1.2</mml:mn> <mml:mrow> <mml:mo>−</mml:mo> <mml:mn>0.3</mml:mn> </mml:mrow> <mml:mrow> <mml:mo>+</mml:mo> <mml:mn>0.5</mml:mn> </mml:mrow> </mml:msubsup> </mml:math> (stat) ± 0 . 1(syst) in the forward region (1.53 < $$ {y}_{\mu}^{\ast } $$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:msubsup> <mml:mi>y</mml:mi> <mml:mi>μ</mml:mi> <mml:mo>∗</mml:mo> </mml:msubsup> </mml:math> < 4 . 03) and $$ {3.6}_{-0.9}^{+1.6} $$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:msubsup> <mml:mn>3.6</mml:mn> <mml:mrow> <mml:mo>−</mml:mo> <mml:mn>0.9</mml:mn> </mml:mrow> <mml:mrow> <mml:mo>+</mml:mo> <mml:mn>1.6</mml:mn> </mml:mrow> </mml:msubsup> </mml:math> (stat) ± 0 . 2(syst) in the backward region ( − 4 . 97 < $$ {y}_{\mu}^{\ast } $$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:msubsup> <mml:mi>y</mml:mi> <mml:mi>μ</mml:mi> <mml:mo>∗</mml:mo> </mml:msubsup> </mml:math> < − 2 . 47), where $$ {y}_{\mu}^{\ast } $$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:msubsup> <mml:mi>y</mml:mi> <mml:mi>μ</mml:mi> <mml:mo>∗</mml:mo> </mml:msubsup> </mml:math> represents the muon rapidity in the centre-of-mass frame.
Tópico:
Particle physics theoretical and experimental studies
