# Measurement of charged particle multiplicities and densities in $pp$ collisions at $\sqrt{s}$ = 7 TeV in the forward region

[to restricted-access page]

## Abstract

Charged particle multiplicities are studied in proton-proton collisions in the forward region at a centre-of-mass energy of $\sqrt{s} = 7\;$TeV with data collected by the LHCb detector. The forward spectrometer allows access to a kinematic range of $2.0<\eta<4.8$ in pseudorapidity, momenta down to $2\;$GeV/$c$ and transverse momenta down to $0.2\;$GeV/$c$. The measurements are performed using minimum-bias events with at least one charged particle in the kinematic acceptance. The results are presented as functions of pseudorapidity and transverse momentum and are compared to predictions from several Monte Carlo event generators.

## Figures and captions

 Charged particle density as a function of $\eta$. The LHCb data are shown as points with statistical error bars (smaller than the marker size) and combined systematic and statistical uncertainties as the grey band. The measurement is compared to several Monte Carlo generator predictions, (a) Pythia 6 and Phojet , (b) Pythia 8 and Herwig++ . Both plots show predictions of the LHCb tune of Pythia 6, which is used in the analysis. Fig_1a.pdf [16 KiB] HiDef png [204 KiB] Thumbnail [175 KiB] *.C file Fig_1b.pdf [18 KiB] HiDef png [243 KiB] Thumbnail [188 KiB] *.C file Charged particle density as a function of $p_{\rm T}$ . The LHCb data are shown as points with statistical error bars (smaller than the marker size) and combined systematic and statistical uncertainties as the grey band. The measurement is compared to several Monte Carlo generator predictions, (a) Pythia 6 and Phojet , (b) Pythia 8 and Herwig++ . Both plots show predictions of the LHCb tune of Pythia 6, which is used in the analysis. Fig_2a.pdf [18 KiB] HiDef png [225 KiB] Thumbnail [185 KiB] *.C file Fig_2b.pdf [18 KiB] HiDef png [268 KiB] Thumbnail [206 KiB] *.C file Observed charged particle multiplicity distribution in the full kinematic range of the analysis. The error bars represent the statistical uncertainty, the error band shows the combined statistical and systematic uncertainties. The data are compared to several Monte Carlo predictions, (a) Pythia 6 and Phojet , (b) Pythia 8 and Herwig++ . Both plots show predictions of the LHCb tune of Pythia 6, which is used in the analysis. Fig_3a.pdf [19 KiB] HiDef png [271 KiB] Thumbnail [220 KiB] *.C file Fig_3b.pdf [19 KiB] HiDef png [255 KiB] Thumbnail [189 KiB] *.C file Observed charged particle multiplicity distribution in different $\eta$ bins. Error bars represent the statistical uncertainty, the error bands show the combined statistical and systematic uncertainties. The data are compared to Monte Carlo predictions, (a,b) Pythia 6 and Phojet , (c,d) Pythia 8 and Herwig++ . All plots show predictions of the LHCb tune of Pythia 6, which is used in the analysis. Fig_4a.pdf [16 KiB] HiDef png [251 KiB] Thumbnail [213 KiB] *.C file Fig_4c.pdf [16 KiB] HiDef png [264 KiB] Thumbnail [224 KiB] *.C file Fig_4b.pdf [16 KiB] HiDef png [255 KiB] Thumbnail [213 KiB] *.C file Fig_4d.pdf [16 KiB] HiDef png [280 KiB] Thumbnail [220 KiB] *.C file Observed charged particle multiplicity distribution in different $\eta$ bins. Error bars represent the statistical uncertainty, the error bands show the combined statistical and systematic uncertainties. The data are compared to Monte Carlo predictions, (a-c) Pythia 6 and Phojet , (d-f) Pythia 8 and Herwig++ . All plots show predictions of the LHCb tune of Pythia 6, which is used in the analysis. Fig_5a.pdf [16 KiB] HiDef png [253 KiB] Thumbnail [208 KiB] *.C file Fig_5d.pdf [16 KiB] HiDef png [284 KiB] Thumbnail [218 KiB] *.C file Fig_5b.pdf [16 KiB] HiDef png [250 KiB] Thumbnail [211 KiB] *.C file Fig_5e.pdf [16 KiB] HiDef png [286 KiB] Thumbnail [221 KiB] *.C file Fig_5c.pdf [16 KiB] HiDef png [268 KiB] Thumbnail [226 KiB] *.C file Fig_5f.pdf [16 KiB] HiDef png [295 KiB] Thumbnail [229 KiB] *.C file Observed charged particle multiplicity distribution in different $p_{\rm T}$ bins. Error bars represent the statistical uncertainty, the error bands show the combined statistical and systematic uncertainties. The data are compared to Monte Carlo predictions, (a,b) Pythia 6 and Phojet , (c,d) Pythia 8 and Herwig++ . All plots show predictions of the LHCb tune of Pythia 6, which is used in the analysis. Fig_6a.pdf [16 KiB] HiDef png [265 KiB] Thumbnail [231 KiB] *.C file Fig_6c.pdf [16 KiB] HiDef png [274 KiB] Thumbnail [236 KiB] *.C file Fig_6b.pdf [16 KiB] HiDef png [282 KiB] Thumbnail [233 KiB] *.C file Fig_6d.pdf [16 KiB] HiDef png [292 KiB] Thumbnail [242 KiB] *.C file Observed charged particle multiplicity distribution in different $p_{\rm T}$ bins. Error bars represent the statistical uncertainty, the error bands show the combined statistical and systematic uncertainties. The data are compared to Monte Carlo predictions, (a-c) Pythia 6 and Phojet , (d-f) Pythia 8 and Herwig++ . All plots show predictions of the LHCb tune of Pythia 6, which is used in the analysis. Fig_7a.pdf [16 KiB] HiDef png [278 KiB] Thumbnail [222 KiB] *.C file Fig_7d.pdf [16 KiB] HiDef png [278 KiB] Thumbnail [217 KiB] *.C file Fig_7b.pdf [16 KiB] HiDef png [267 KiB] Thumbnail [223 KiB] *.C file Fig_7e.pdf [16 KiB] HiDef png [267 KiB] Thumbnail [219 KiB] *.C file Fig_7c.pdf [16 KiB] HiDef png [260 KiB] Thumbnail [230 KiB] *.C file Fig_7f.pdf [16 KiB] HiDef png [280 KiB] Thumbnail [234 KiB] *.C file Example of the parametrized detector response matrix in the full kinematic range. The matrix is obtained from fully simulated events showing the relation between the true charged particle multiplicity and the reconstructed and background subtracted track multiplicity. Fig_8.pdf [35 KiB] HiDef png [314 KiB] Thumbnail [323 KiB] *.C file Animated gif made out of all figures. PAPER-2013-070.gif Thumbnail ## Tables and captions

 Charged particle density as a function of pseudorapidity. The first quoted uncertainty is statistical and the second systematic. Table_1.pdf [30 KiB] HiDef png [251 KiB] Thumbnail [125 KiB] tex code Charged particle density as a function of transverse momentum. The first quoted uncertainty is statistical and the second systematic. Table_2.pdf [45 KiB] HiDef png [208 KiB] Thumbnail [75 KiB] tex code Truncated mean value and root-mean-square deviation for charged particle multiplicities in different $\eta$-bins. The range is from 0 to 20 particles. The first quoted uncertainty is statistical and the second systematic. Table_3.pdf [31 KiB] HiDef png [83 KiB] Thumbnail [43 KiB] tex code Truncated mean value and root-mean-square deviation for charged particle multiplicities in different $p_{\rm T}$ -bins. The range is from 0 to 20 particles. The first quoted uncertainty is statistical and the second systematic. Table_4.pdf [38 KiB] HiDef png [66 KiB] Thumbnail [32 KiB] tex code Created on 17 August 2019.Citation count from INSPIRE on 23 August 2019.
{"ft_lang_label":"__label__en","ft_lang_prob":0.7091252,"math_prob":0.8787315,"size":6861,"snap":"2019-35-2019-39","text_gpt3_token_len":1969,"char_repetition_ratio":0.20285839,"word_repetition_ratio":0.48813868,"special_character_ratio":0.28873342,"punctuation_ratio":0.11171875,"nsfw_num_words":0,"has_unicode_error":false,"math_prob_llama3":0.95994383,"pos_list":[0,1,2,3,4,5,6,7,8,9,10,11,12,13,14,15,16,17,18,19,20,21,22,23,24,25,26,27,28,29,30,31,32,33,34,35,36,37,38,39,40,41,42,43,44,45,46,47,48,49,50,51,52,53,54,55,56,57,58,59,60,61,62,63,64],"im_url_duplicate_count":[null,2,null,2,null,2,null,2,null,2,null,2,null,2,null,2,null,2,null,2,null,2,null,2,null,2,null,2,null,2,null,2,null,2,null,2,null,2,null,2,null,2,null,2,null,2,null,2,null,2,null,2,null,2,null,2,null,2,null,2,null,2,null,2,null],"WARC_HEADER":"{\"WARC-Type\":\"response\",\"WARC-Date\":\"2019-08-23T18:19:04Z\",\"WARC-Record-ID\":\"<urn:uuid:b624782c-1923-4bcc-89ed-3e664cad3a93>\",\"Content-Length\":\"28517\",\"Content-Type\":\"application/http; msgtype=response\",\"WARC-Warcinfo-ID\":\"<urn:uuid:6ea61742-36cf-40d1-a634-b39cf875b786>\",\"WARC-Concurrent-To\":\"<urn:uuid:9a65e355-f218-4ac2-9f18-28276af690c2>\",\"WARC-IP-Address\":\"137.138.150.3\",\"WARC-Target-URI\":\"http://lhcbproject.web.cern.ch/lhcbproject/Publications/LHCbProjectPublic/LHCb-PAPER-2013-070.html\",\"WARC-Payload-Digest\":\"sha1:DYTI5D6IK2O2DK6VZVAWX43RNKJYACL7\",\"WARC-Block-Digest\":\"sha1:LGUIP7HZIIIKQUYMNI4MSPBQ6K6WSCP2\",\"WARC-Identified-Payload-Type\":\"application/xhtml+xml\",\"warc_filename\":\"/cc_download/warc_2019/CC-MAIN-2019-35/CC-MAIN-2019-35_segments_1566027318952.90_warc_CC-MAIN-20190823172507-20190823194507-00100.warc.gz\"}"}