Measurement of Charged Particle Transverse Momentum Spectra in Deep Inelastic Scattering

TL;DR

The paper measures charged-particle transverse momentum spectra in deep-inelastic scattering at HERA as a function of Bjorken-$x$ and photon virtuality $Q^2$ using the H1 detector. It compares the data to QCD-based event generators implementing different parton-evolution schemes, including DGLAP-based MEPS (LEPTO) and HERWIG, and the color-dipole model ARIADNE with unordered radiation. The results show that at small $x$ the observed $p_T$ distributions are harder than predicted by suppressed-radiation models, while ARIADNE provides a good description across the kinematic range, highlighting the need for enhanced parton radiation than offered by conventional leading-log DGLAP showers. These findings point toward $BFKL$-type dynamics and motivate further theoretical and Monte Carlo development to explicitly include such terms in DIS final-state descriptions.

Abstract

Transverse momentum spectra of charged particles produced in deep inelastic scattering are measured as a function of the kinematic variables x_B and Q2 using the H1 detector at the ep collider HERA. The data are compared to different parton emission models, either with or without ordering of the emissions in transverse momentum. The data provide evidence for a relatively large amount of parton radiation between the current and the remnant systems.

Figures (7)

• Figure 1: Generic diagram for parton evolution.
• Figure 2: The transverse momentum spectra of charged particles, measured in the CMS in the pseudorapidity interval $1.5 < \eta < 2.5$. Data are shown for nine different kinematic bins (see Table 1) and the combined sample (bin 0). For comparison, the models ARIADNE (full line), LEPTO (dashed) and HERWIG (dotted) are overlayed. The mean values of $x~$ and $Q^2~$ are indicated. The inner error bars represent the statistical errors, the outer error bars the quadratic sum of statistical and systematic errors.
• Figure 3: a) Comparison of the $p_T~$ spectra at high $x~$ (bin 6) and at low $x~$ (bin 3) for fixed (intermediate) $Q^2~$. b) Comparison of the $p_T~$ spectra at two different $Q^2~$ values (bins 2 and 7) for fixed (large) $W$. c) Comparison of the $p_T~$ spectra at two different $Q^2~$ values (bins 6 and 8) for fixed (large) $x$. d) Comparison of the $p_T~$ spectra in two different $\eta$ intervals in the kinematic bin 3 (low $x$, intermediate $Q^2$). The mean values of $x~$ and $Q^2~$ are indicated in the figures. The error bars represent the quadratic sum of the statistical and systematic errors.
• Figure 4: The transverse momentum spectra of charged particles, measured in the CMS in the pseudorapidity interval $0.5 < \eta < 1.5$. Data are shown for seven different kinematic bins (see Table 1) plus the combined sample (bin 0). For comparison, the models ARIADNE (full line), LEPTO (dashed) and HERWIG (dotted) are overlayed. The mean values of $x~$ and $Q^2~$ are indicated. The inner error bars represent the statistical errors, the outer error bars the quadratic sum of statistical and systematic errors.
• Figure 5: The CMS pseudorapidity spectra for charged particles with $p_T>1$ GeV. The proton remnant direction is to the left. Data are shown for nine different kinematic bins (see Table 1) plus the combined kinematic region (bin 0). For comparison, the models ARIADNE (full line), LEPTO (dashed) and HERWIG (dotted) are overlayed. The mean values of $x~$ and $Q^2~$ are indicated. The inner error bars represent the statistical errors, the outer error bars the quadratic sum of statistical and systematic errors.